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ANTONIO STROZZI
Professore emerito
Dipartimento di Ingegneria "Enzo Ferrari"
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Pubblicazioni
2023
- Advancing contact of a 2D elastic curved beam indented by a rigid pin with clearance
[Articolo su rivista]
Radi, E.; Strozzi, A.
abstract
A two-dimensional analytical solution is presented for stresses and displacements in an elastic curved beam forming an incomplete ring in frictionless and unbonded contact with a rigid pin loaded by a point force and in the presence of clearance. The circular beam is modelled as an incomplete elastic thick ring, constrained at both ends and in a plane stress state. The stress and displacement fields within the beam are derived from a biharmonic Airy stress function, according to the Michell solution in polar coordinates. The mixed boundary value problem is reduced to a set of dual series equations and then to a non-homogeneous linear system of infinite equations, which is then solved by truncation. The non-linear relations between the applied load and the contact angle
or the pressure distribution are obtained by using an inverse method. The analytical results are compared with finite element predictions for a pin-lug connection and a reasonable agreement is
observed for several typical geometries. The peaks of contact pressure and von Mises equivalent stress and their location within the curved beam are evidenced.
2023
- Analytical tool assisting the designer of pin-lug connections
[Articolo su rivista]
Strozzi, Antonio; Radi, Enrico
abstract
A theoretical model of a pin-lug fitting in the presence of a pin-lug gap is developed that accounts for the nonlinear link between the load and the pin-lug angular width in this progressive contact, which is assumed frictionless. This model adopts a simplified lug geometry, described by a purely flexural partial ring whose extremities are fixed to a base, solved with the virtual work principle. Based on an already available load factor regrouping the effect on the contact angular extent of the applied load, of the Young’s modulus, and of the gap, but not of the lug geometry, an enhanced load factor is developed that includes, although approximately, the influence of the lug geometry on the contact angle. This approach is useful in selecting a suitable clearance between the lug and the pin, which keeps the contact pressure to a minimum for an imposed load.
2023
- Two analytical structural models of the connecting rod cap
[Articolo su rivista]
Strozzi, Antonio; Mantovani, Sara; Barbieri, SAVERIO GIULIO; Baldini, Andrea
abstract
The mathematical models available in the pertinent literature for designing the cap of
a connecting rod are critically examined, and it is shown that some currently adopted
assumptions are inaccurate. Spurred by these critical remarks, two more realistic
mathematical models are developed of the contact between the crankpin and the cap.
In both these models, the crankpin is modelled as rigid, and the cap is idealized as a
purely flexural, curved beam of constant cross-section, in progressive contact with the
crankpin. In the first model, the cap is mimicked as a twice twice-statically redundant
structure solved with the Castigliano theorem. The cap structural response is
mechanically examined starting from the central part of the cap-crankpin contact. In
the second model, the cap is mimicked as a statically determined structure. Particular
attention is paid to the cap change of curvature when moving along the cap axis. The
beginning of the cap-crankpin contact is determined by requiring that the curvature of
the deformed cap equal the curved border of the crankpin. A result common to the two
approaches is the definition of a combined factor summarizing the mechanical effect
of several variables, namely the total load, the initial clearance, Young’s modulus, and
the cap geometry; the last factor is recapped by the radius defining the centre of mass,
and by the moment of inertia. To evidence the merits and limits of the two approaches,
the extent of the cap-crankpin angular contact, and the value of representative cap
stresses, are determined and compared to Finite Element (FE) forecasts. Furthermore,
the effect of the ratio between the moment of inertia of the abutment and the cap central
cross-section is investigated. This ratio influences the prediction of the contact angle,
when the ratio is higher than 4, the numerical FE results significantly differ from the
analytical calculations.
2022
- Shafts with U-shaped circumferential grooves: design charts for stress concentration factors, radial displacement and Poisson’s ratio influence
[Articolo su rivista]
Mantovani, Sara; Chiari, Alessandro; Giacalone, Mauro; Strozzi, Antonio
abstract
Shafts with U-shaped circumferential grooves subjected to internal normal force and bending moment
are investigated on the basis of finite element analysis. The classical problem of the Stress
Concentration Factors (SCFs) identification is addressed. SCF charts are provided, adopting the
maximum equivalent von Mises stress in the SCF definition. The discrepancy between the uniaxial
SCFs extracted from the standard reference books and the multiaxial SCF obtained by finite element
increases from 5% up to 20%. The intersections between the SCF curves are studied, which reveal a
non-monotonic profile of the SCFs with respect to the outer and inner diameter ratio of the notched
shaft. The radial displacement at the notch root is examined and design charts of ample validity and
prompt access are compiled. It is found that the radial displacement sign and magnitude are largely
dependent on the geometry of the notch. Furthermore, the strain and stress state of extremely shallow
grooves are analysed and a critical discussion on their SCFs using the von Mises criterion is presented.
The influence of the Poisson’s ratio is considered. A simplified method for the evaluation of a
multiaxial SCF is proposed to account for the Poisson’s ratio effect. Thanks to the employment of
few dedicated diagrams, the present method allows an accurate evaluation of the SCF for U-grooved
shafts, when the Poisson’s ratio differs from the common 0.3 value.
2022
- Towards an analytical model of a pin-lug connection
[Articolo su rivista]
Strozzi, A.; Giacopini, M.; Bertocchi, E.; Mantovani, S.; Baldini, A.
abstract
A preliminary analytical model of a pinned connection is carried out. The lug is idealized in terms of a curved beam, and the presence of an initial clearance between the pin and the lug is accounted for. This model rationalizes the nonlinear and linear mechanical responses of the structure; a coefficient summarizing the effect of the load, Young’s modulus, and initial clearance, is derived; this coefficient is kindred to that computed according to the theory of elasticity. An enhanced load factor that accounts for the lug geometry is proposed. Two loci of local maximum stress occur. One point is the stress at the centre of the pin-lug contact, whereas the other point falls laterally along the lug bore border. While the central stress is forecast by the analytical model with reasonable accuracy, the analytical stress computed laterally is too approximate to be employed in engineering applications. Despite this drawback, a better understanding of the load transfer mechanism within the pinned connection is achieved, by particularly rationalizing the nonlinear, progressive character of the pin-lug contact, and the usefulness of the load factor.
2021
- Stresses in the cap of a connecting rod
[Articolo su rivista]
Baldini, A.; Strozzi, A.; Bertocchi, E.; Mantovani, S.
abstract
In this practically oriented paper, representative examples of cap failures in a connecting rod are discussed, and deeply dissimilar geometries of the cap cross section are presented. An analytical model of the stresses within a connecting rod cap is developed and satisfactorily validated versus FE (Finite Elements). This model accounts for the effect of the initial clearance between the crankpin surface and the cap intrados, and it realistically mimics the crankpin-cap progressive contact. A load parameter that accounts for the combined effects of several leading variables is analytically derived, on which the following variables depend: a) the contact angular extent between the crankpin and the cap; b) the ratio between the normal and bending stress. This model indicates that the cap bending stress depends on the initial gap between the crankpin and the cap, and not on the applied load. The normal stress within the cap is found to be considerably higher than its bending counterpart. The mechanical response of cap rectangular and ribbed cross sections is compared, and it is found that ribbed sections undesirably increase the cap bending stress. Consequently, the employment of ribs appears to be unjustified from a purely stress related viewpoint.
2019
- A paradox in curved beams
[Articolo su rivista]
Strozzi, Antonio; Bertocchi, Enrico; Mantovani, Sara
abstract
It is sometimes possible to relieve the stresses in a mechanical component by removing material, where relief grooves are the commonest expedient approach. Within the rectilinear beam realm, rare situations are known in which, by removing material in the cross-sectional zones that are farthest from the neutral axis, a bending stress diminution is achieved. With regard to curved beams, selected examples are presented in which a bending stress diminution is achieved by laterally removing material from the zones close to the neutral axis. An approximate mathematical approach based on Gateaux linearization is developed that delimits the lateral zones of the beam cross-section in which material removal is accompanied by bending stress reduction. While the achievable stress diminution is generally marginal, the reduction of the beam’s cross-section is technically interesting.
2019
- On the strength weakening effect of stiffening ribs in the design of machine components
[Capitolo/Saggio]
Strozzi, A.; Bertocchi, E.; Mangeruga, V.
abstract
The bending stress in beams may often be reduced by adding material to the cross section. In some paradoxical cases, however, the bending stress increases by adding material from zones far away, or close to, the neutral axis. Similarly, the bending stress of rectilinear or curved beams may often be reduced by adding ribs to the initial beam section. However, such ribs may sometimes cause a both undesired and unexpected stress increase, although they still produce a beneficial stiffening effect. The aim of this paper is twofold: A) to examine this unexpected result within the context of the paradoxical behaviour of some known beam sections, and especially of a recently noted paradox; b) to provide a preliminary rule of thumb for the mechanical design of ribs sometimes added to the outer surface of an eye, with particular regard to the small end of a connecting rod.
2019
- Two extensions towards practical applications of a paradox in curved beams
[Relazione in Atti di Convegno]
Leopardi, L.; Strozzi, A.
abstract
For particular sections of a rectilinear beam subjected to bending it is possible to simultaneously lower the bending stress and reduce the beam mass, by wisely removing material from zones far from the neutral axis. It has recently been shown that an analogous paradoxical behaviour occurs in a curved beam subjected to bending, by laterally removing material from section zones close to the neutral axis. The bending stress diminution is often of the order of a few %, whereas the mass diminution may reach 10 %. To get practically more interesting results, in this paper the demanding achievement of a concurrent stress and mass reduction is relaxed in favour of two weaker requests: a) for a general section, the intrados stress is assumed as the reference stress, and the maximum mass reduction achieved by laterally removing material is sought under the condition that the intrados stress equals such reference stress; b) the intrados stress of a particular section is assumed as the reference stress, and material is laterally removed from the adjacent sections until their intrados stress equals the above reference value. Analytical applications of the two above approaches to a crane hook are carried out and compared to FE forecasts.
2018
- A repertoire of failures in gudgeon pins for internal combustion engines, and a critical assessment of the design formulae
[Articolo su rivista]
Strozzi, A.; Baldini, A.; Giacopini, M.; Bertocchi, E.; Mantovani, S.
abstract
The geometries commonly employed in gudgeon pins for internal combustion engines are examined. In particular, various methods for reducing the pin weight are considered. The selection of the appropriate clearance is addressed. The most typical failure modes are classified and interpreted in the light of stress analysis. The available approximate design formulae are assessed versus selected Finite Element forecasts. The fatigue cycles of stress and displacement related parameters are examined. The effect of the initial clearance on the contact pressure and on the pin ovalization is explored for selected clearance values. A typical Y-shaped fatigue crack is interpreted with the aid of Mohr circle. An error in a classical design approach based upon the containment of the pin ovalization is hypothesized.
2018
- Analysis of a segmented locking ring for shell-bottom connection in pressure vessels
[Articolo su rivista]
Strozzi, A.; Bertocchi, E.; Mantovani, S.
abstract
A simplified mechanical analysis is carried out for a specific closure system of a pressure vessel, consisting of a segmented locking ring, partially inserted into an annular slot; the ring portion protruding from the slot supports the vessel bottom; sealing is achieved by placing a copper gasket between the ring and the bottom. An approximate contact reaction is assumed, that is formed by a distributed constant linear force and by concentrated forces at the extremities of the ring-slot contact. Analytical expressions of the ring internal forces are provided. A numerical example is presented.
2018
- Appreciable cross section reduction upon moderate intrados bending stress increase in curved beams
[Relazione in Atti di Convegno]
Strozzi, A.; Bertocchi, E.; Mantovani, S.
abstract
2018
- Shaft-hub press fit subjected to couples and radial forces: analytical evaluation of the shaft-hub detachment loading
[Articolo su rivista]
Bertocchi, Enrico; Lanzoni, Luca; Mantovani, Sara; Radi, Enrico; Strozzi, Antonio
abstract
A shaft-hub press fit subjected to two non-axisymmetric loading conditions is examined and the situation
of incipient detachment between the shaft and the hub is determined. The first condition consists of a
central radial load P applied to the hub, balanced by two lateral forces P=2 applied to the shaft at a
distance d from the hub lateral walls. In the second condition, a central couple C is applied to the hub,
and it is balanced by two lateral opposite loads withstood by the shaft at a distance d from the hub
lateral walls. The shaft-hub contact is modelled in terms of two elastic Timoshenko beams connected by
distributed elastic springs (Winkler foundation), whose constant is analytically evaluated. Based upon
this enhanced beam-like modelling, the loading inducing an undesired shaft-hub incipient detachment
is theoretically determined in terms of the shaft-hub geometry, of the initial shaft-hub interference, and
of the elastic constants. Finite element forecasts are presented to quantify the error of this beam-like
approximate analytical approach.
2017
- ANALYSIS OF A SEGMENTED LOCKING RING FOR SHELL - BOTTOM CONNECTION IN PRESSURE VESSELS
[Poster]
Strozzi, Antonio; Bertocchi, Enrico; Mantovani, Sara
abstract
An approximate structural analysis is presented
of a shell-bottom connection in which a locking
ring, partially protruding from an annular slot
machined in the vessel wall, supports the bottom
loaded by the internal pressure. The ring is
segmented into four parts, to permit assembling.
The contact pressure between the ring and the slot
lower face may be conveniently approximated.
Simplified expressions of the internal forces within
the ring are obtained.
2017
- On the contact stresses at the indenting edge of a shaft-hub interference fit subject to bending and shear forces
[Relazione in Atti di Convegno]
Bertocchi, Enrico; Mantovani, Sara; Strozzi, Antonio
abstract
The contact stress field is addressed that is developed at the indenting edge of a keyless shaft-hub interference fit, in the case that both bending and shear forces are applied, and in the absence of friction. The combined effect of a set of elementary load cases is assessed for the sharp notch case in terms of a generalized stress intensity factor, with the aid of Finite Elements and for a class of shaft-hub geometries. In fact, linearity is preserved in the case of a sharp edged bore up to the incipient detachment condition; such event, which may occur as a result of e.g. excessive bending loads, may be forecast based on the proposed framework. Contact stresses in the case of rounded edge may be subsequently predicted by scaling an appropriate local solution; fatigue analysis may then be performed in the case of rotating or fluctuating loads. An exhaustive design table is finally compiled to assist the designer in dimensioning an interference fit in the presence of an arbitrary combination of time varying bending and shear forces.
2017
- On the evaluation of the peak contact stresses in a press-fitted shaft-hub coupling subject to bending
[Relazione in Atti di Convegno]
Bertocchi, Enrico; Mantovani, Sara; Baldini, Andrea; Strozzi, Antonio
abstract
The peak contact stresses are addressed that are developed from the frictionless press fit of a shaft subjected to bending into an elastically similar hub with bore rounded edges. The non-linear behavior of this progressive contact is addressed by scaling a local solution available from the literature, with the aid of intermediate, auxiliary problems extracted from the fracture mechanics realm. The title problem being linear on the global domain with both the bending couple and the interference, this problem is solved by combining the FE forecasts obtained for
two separate load cases, i.e. a) the interference alone and, b) the bending couple alone. Such results are expressed in terms of a) stress intensity factors for the auxiliary FM problems, and b) hoop strain component, as sampled in the proximity of the indenting edge for both the mating members. Design formulae for the contact stresses are proposed, that account for various normalized geometrical parameters, such as the outer to inner hub radii ratio, the radius of the hub bore fillet, and the contact length. Comprehensive coefficient tables are provided as well. Finally, an error analysis for the proposed method is presented.
2017
- Shaft-hub press fit subjected to bending couples: Analytical evaluation of the shaft-hub detachment couple
[Articolo su rivista]
Radi, Enrico; Lanzoni, Luca; Strozzi, Antonio; Bertocchi, Enrico
abstract
A mathematical modelling of a shaft-hub press-fit subjected to bending couples applied to the shaft extremities is developed, and the value of the bending couple inducing an un- desired shaft-hub incipient detachment is analytically determined. The shaft-hub contact is modelled in terms of two elastic Timoshenko beams connected by a distributed elastic spring, whose stiffness is analytically evaluated. Two models of the distributed spring are considered. The first model expresses the combined deformability of both the shaft and the hub cross sections. The second model accounts for the stiffening effect exerted by the shaft portion protruding from the hub on the adjacent shaft part that is in contact with the hub, and, consequently, it assumes only a rigid body motion of the shaft cross section, thus neglecting its deformability. Based upon this beam-like model, the bending couple producing the incipient detach- ment between the shaft and the hub is theoretically determined in term of the shaft-hub geometry, of the initial shaft-hub interference, and of the elastic constants. Comparisons with selected Finite Element (FE) forecasts indicate that the first modelling produces an incipient detachment couple that appreciably overrates the FE forecasts, whereas the sec- ond modelling lowers the error down to technically acceptable predictions.
2016
- A complete 3-D description of the elastic behavior of a piston ring and its influence on the tribological behavior of the piston ring-cylinder liner interface
[Relazione in Atti di Convegno]
Mastrandrea, LUCA NICOLO'; Giacopini, Matteo; Bertocchi, Enrico; Strozzi, Antonio; Dini, D.
abstract
Advances in modern engine development are becoming more and more challenging. The intense increase of thermal and mechanical loads as a result of higher power density requires perfecting the function of all engine components especially with regard to emission and friction reduction.
In particular, piston rings pack represent one of the most important cause of mechanical friction loss in internal combustion engine [1], and inadequate ring-liner lubrication leads to high fuel/oil consumption and increased engine emissions with dramatic impact over the entire system efficiency.
A desirable piston ring-pack set has to provide efficient sealing performance with both the cylinder wall in a radial direction and the top or bottom sides of the piston ring housing in an axial direction, leading to minimal gas blow-by, oil consumption and friction loss. Moreover piston ring other requirement are low friction, low wear and good resistance against mechanical/thermal fatigue. This is a challenging task due to the nature of the phenomena and interactions associated with piston rings. For example, increasing the installed ring tension, which is a method to control oil consumption, also tends to increase ring friction. Hence, any attempt to optimize ring-pack performance output parameters requires a good understanding of the dynamics of all the involved components.
Different key elements have to be considered: the ring shape in its free state (namely free shape), the ring crossing-section geometry and the contact surface profile, which play important roles in determining the ring behavior.
In order to achieve sealing, the piston rings are first held against the cylinder liner in its front face by their tension after being installed into the cylinder bore. The contact pressure on the cylinder wall is achieved by the inherent spring force of the ring in conjunction with the gas pressure behind the ring. During different engine operating conditions, the piston rings experience dynamically changing forces and axial as well as radial movements of the rings can occur. The contact on the side of the piston housing is achieved by the axial forces acting on the ring. The axial forces are composed of the gas pressure above and under the ring, the mass forces (inertia), and the friction forces. These forces change their direction during the cycle, and, as a result, the piston ring moves from one side of the groove to the other during the engine cycle. This is known as ring fluttering when the axial movement becomes excessive. This behavior open an additional gas flow path: gas can flow around the inner diameter of the ring which results in very high engine blow-by loss. In addition the ring pack design should also consider other factors, including gas blowback and, as said before, ring pack friction. The blowback is the reverse process of blowby and is highly related to engine emission and oil consumption while ring friction can cause severe ring and cylinder wall wear, which results in the ring losing its sealing capability. These factors are related to the ring circumferential pressure distribution, which is defined by the ring free shape and the ring cross section geometry.
The understanding of the piston ring behavior is an hard challenge for automotive engineer. Firstly, in 1936 Castleman [2] investigated and proposed the concept of hydrodynamic lubrication for the piston ring. Thereafter, more and more research has been done in this field. Dowson et al. [3] predicted the behavior of a piston ring using the EHL theory. Sun [4] conducted his study for ring-bore conformability, in which the ring was modeled as a curved beam under in-plane loads. Liu and Tian [5, 6] developed an FEA tool for piston ring design. Ejakov et al. [7] modeled ring twist behavior predicting ring axial, radial displacements, bending and twisting angles along the ring periphery over an engine cycle.
In this contributions a complete 3D model of the piston ring is propose
2016
- A repertoire of failures in connecting rods for internal combustion engines, and indications on traditional and advanced design methods
[Articolo su rivista]
Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Bertocchi, Enrico; Mantovani, Sara
abstract
Several typical and uncommon failure modes in con-rods for internal combustion engines are commented from the stress level viewpoint. The interpretation of the fractures is supported with traditional calculations, with more advanced analytical models, and with Finite Element (FE) predictions. The repertoire of failures in a con-rod is presented by separately addressing the parts composing the con-rod itself, namely the shank, and the small and big ends.
2016
- Analytical evaluation of the peak contact pressure in a rectangular elastomeric seal with rounded edges
[Articolo su rivista]
Strozzi, Antonio; Bertocchi, Enrico; Mantovani, Sara; Giacopini, Matteo; Baldini, Andrea
abstract
The contact pressure is considered for an elastomeric rectangular seal with rounded edges. An asymptotic matching is performed between an available analytical expression of the contact pressure that neglects the finiteness of the seal dimensions and a fracture mechanics solution describing a periodically laterally cracked strip of finite width. This matching provides a corrected formula for the peak contact pressure that accounts for the finiteness of the seal dimensions. The analytical expression for the peak contact pressure is validated versus finite element predictions for a large family of seal geometries and, in particular, for a seal reference shape extracted from the pertinent literature. An appraisal of the finite deformation effect has been carried out numerically.
2016
- Normalization of the stress concentrations at the rounded edges of an interference fit between a solid shaft subjected to bending and a hub
[Articolo su rivista]
Strozzi, Antonio; Bertocchi, Enrico; Baldini, Andrea; Mantovani, Sara
abstract
The elastic stress concentrations are addressed that are developed from the keyless frictionless press fit of a shaft subjected to bending into a hub with rounded bore edges. Derived from a formal modeling of the title problem in terms of an integral equation, a set of normalized parameters is proposed that accounts for the combined effects on the hub stress concentration of the fillet radius, the shaft radius, the hub outer radius, the hub axial length, the interference, the Young's modulus, and the bending couple. A numerical validation of the normalized parameters is presented. With the aid of Finite Elements, various design charts are compiled that (a) forecast the bending couple initiating the detachment between the shaft and the hub, and (b) report the elastic stress concentrations within the hub versus the proposed normalized parameters in the absence of shaft–hub detachment. Such charts assist the designer in dimensioning an interference fit in the presence of a bending couple.
2015
- A Note on the Legendre Series Solution of the Laplace Equation for Cylindrical Problems
[Articolo su rivista]
Strozzi, Antonio; Bertocchi, Enrico
abstract
The mechanical modelling of cylindrical problems is addressed. A series solution is considered of the Laplace equation, in which the series terms of the stress function Φ are expressions based upon Legendre polynomials and logarithmically singular functions. An explicit form of a polynomial supplementing each logarithmically singular part of the series solution is obtained.
2015
- Analytical evaluation of the peak contact pressure in a rectangular elastomeric seal with rounded edges
[Abstract in Atti di Convegno]
Baldini, Andrea; Bertocchi, Enrico; Giacopini, Matteo; Mantovani, Sara; Strozzi, Antonio
abstract
Rectangular seals constitute an alternative design to O-rings. Rectangular seals are employed in demanding applications such as aircraft actuators, e.g. ref. [1]. The seal edges are generally rounded, ref. [2]. As a consequence of the presence of filleted edges, the contact pressure exhibits Hertzian-type local bumps in its lateral zones; it remains almost flat in the central zone of the contact. The lateral bumps and the central flattish zone confer to the contact pressure distribution a camel-backed profile, see ref. [2], and ref. [3] for a similar axisymmetric problem. It is difficult to derive a rigorous, analytical expression of the contact pressure curve for the title problem. In fact, the analytical solution available for a rectangular punch with rounded edges indenting a half plane, e.g. ref. [4] and related bibliography, is exact only in the situation of a rigid punch indenting a deformable half plane, ref. [5], whereas in the title problem the punch (i.e., the seal) is flexible and the half plane (i.e., the counterface) is rigid. It has recently been shown in refs [5-7] that the unrealities of the above analytical solution may be corrected by combining the analytical solution with Fracture Mechanics (FM) results dealing with the stress singularities at the tip of a transverse crack in a strip of finite width. In this paper, an extension of formula (20) of ref. [5] is developed, that accounts for the combined effects of a) the presence of a filleted edge, and b) a finite seal width and height.
2015
- On the applicability of the Boussinesq influence function in modelling the frictionless elastic contact between a rectangular indenter with rounded edges and a half-plane
[Articolo su rivista]
Strozzi, Antonio; Bertocchi, Enrico; Baldini, Andrea; Giacopini, Matteo
abstract
The applicability of the Boussinesq influence function in modelling the frictionless elastic contact between a rectangular indenter with rounded edges and a half-plane is numerically explored. The potential of the asymptotic matching method combined with classical fracture mechanics results is investigated. Manageable design formulae for evaluating the maximum equivalent stress are analytically derived with the aid of the asymptotic matching method.
2015
- Preliminary investigation of the cavitation damage in the conrod big end bearing of a high performance engine via a mass-conserving complementarity algorithm
[Abstract in Atti di Convegno]
Giacopini, Matteo; Bertocchi, Enrico; Baldini, Andrea; Strozzi, Antonio
abstract
The conrod big end bearing is one of the most critical components of internal combustion engines; it is usually subjected to high dynamic loads and high sliding velocities between contacting surfaces are often involved. Therefore, the tribological behaviour of the conrod big end bearing is often one of the key elements to engine reliability, and it has been investigated both theoretically and experimentally in several contributions in the pertinent literature [1]. With the ever-increasing quest to improve engine performance, and the consequent increase of the rotational speed and combustion/inertial loads, the cavitation of the lubricant used in conrod big end bearings may play a crucial role in the assessment of bearing durability. To overcome problems related to film cavitation, palliatives such as the reduction of the clearance between the components, the increase of the oil supply pressure and/or the use of harder coating materials have been commonly adopted. However, such simple adjustments do not always represent a valid solution; further investigations are required in order to avoid cavitation damage occurrence. The cavitation damage has been studied for more than a century both theoretically [2-5] and experimentally [6,7], and many attempts have been made to predict or measure the pressure spikes developing in the cavitated areas due to bubble collapse. Although a universally accepted theory seems not to exist, it is clear that the cavitation damage occurs due to the rapid and violent collapse of the vapour bubbles in the proximity of a solid boundary. The aim of the present work is the preliminary evaluation of the damaging effect of the cavitation in a conrod big end bearing via elasto-hydrodinamic numerical analyses.
2014
- ANALISI PRELIMINARE DELL’INFLUENZA DI SUPERFICI TEXTURIZZATE SUL COMPORTAMENTO DEL FILM FLUIDO IN PROTESI D’ANCA ATTRAVERSO UN ALGORITMO COMPLEMENTARE CON CONSERVAZIONE DELLA MASSA
[Relazione in Atti di Convegno]
Mulas, Giuseppe Antonio; Giacopini, Matteo; Strozzi, Antonio; Baldini, Andrea; Bertocchi, Enrico
abstract
Il comportamento tribologico e in particolare l’usura gioca un ruolo cruciale nel fallimento di una protesi d’anca. La lubrificazione dell’accoppiamento tra testa protesica e coppa acetabolare può influenzare sia la dinamica del contatto sia l’usura della protesi. Il regime di lubrificazione che governa l’accoppiamento testa-acetabolo è elastoidrodinamico. Nei diversi studi presenti nella bibliografia pertinente, raramente le analisi sono effettuate considerando la possibile cavitazione del fluido nella zona di contatto, o al più applicando una modellistica di cavitazione che si è dimostrata imperfetta in termini di conservazione della massa. Al fine di incrementare le prestazioni tribologiche di protesi d’anca, recenti studi hanno proposto l’impiego di superfici texturizzate. Attraverso l’utilizzo di un preliminare modello semplificato, viene studiata l’influenza, sul comportamento dell’accoppiamento, dei parametri geometrici che descrivono le texture. Si è utilizzato un recente algoritmo di complementarietà lineare capace di simulare il fenomeno della cavitazione conservando la massa di fluido.
2014
- Formulation of the tangential velocity slip problem in terms of variational inequalities
[Articolo su rivista]
Strozzi, Antonio; Giacopini, Matteo; Bertocchi, Enrico; Dini, D.
abstract
This contribution deals with a modelling of the tangential velocity slip problem in terms of variational inequalities. In particular, various technical situations for which the slippage problem appears to play an important role are first reviewed. Then, a mathematical formulation in terms of variational inequalities is developed where the critical shear stress criterion is considered. The theoretical conditions under which a unique solution exists are also discussed and an algebraic description based upon a complementarity approach is presented. Preliminary numerical results end the paper and a validation versus an analytical solution is proposed.
2014
- On the Effect of Electrodischarge Drilling on the Fatigue Life of Inconel 718
[Relazione in Atti di Convegno]
Bassoli, Elena; Baldini, Andrea; Gatto, Andrea; Strozzi, Antonio; Denti, Lucia
abstract
Difficult-to cut-materials are associated with premature tool failure, most likely in the case of complex geometries and this shapes. However, Nickel-based alloys are commonly used in high-temperature and aerospace applications, where thin deep holes are often required. Then, the only viable manufacturing solution relies on non-contact processes, like electrodischarge (ED) drilling. Morphology of ED machined surfaces is significantly different than obtained by metal-cutting operation and is known to jeopardize fatigue strength, but the extent needs to be gauged and related to the process parameters. Aim of the paper is to study the effect of holes (0.8 mm diameter, aspect ratio 10) produced by ED drilling on the fatigue life of Inconel 718. Rotating bending fatigue tests are carried out on specimens drilled under two ED setups, as well as with a traditional cutting tool. Specimens free from holes are fatigued under the same conditions for comparison. Based on previous studies, extremal ED parameters are selected, giving best surface finish versus highest productivity. S-N curves show that the ED process causes a decrease of the fatigue resistance with respect to traditional drilling, whereas the effect of different ED setups is negligible. Maximum productivity can thus be pursued with no threat to fatigue performance. The fatigue limit variation is quantified by using the superposition effect principle: ED drilling causes an increase of the stress concentration factor around 25% if compared to traditional drilling. The macroscopic fatigue behavior is integrated with a study of the effects of the different drilling processes in the micro-scale, by means of a microstructural and fractographic analysis.
2013
- A Complementarity Formulation of the Tangential Velocity Slip Problem in
Lubricant Films
[Relazione in Atti di Convegno]
Strozzi, Antonio; Giacopini, Matteo; Bertocchi, Enrico; Daniele, Dini
abstract
This contribution deals with a modelling of the
tangential velocity slip problem in terms of variational
inequalities. In particular, the critical shear stress
criterion is considered. The theoretical conditions under
which a unique solution exists are discussed and an
algebraic description based upon a complementarity
approach is presented, similar to the one adopted in [7].
Finally, preliminary numerical results are presented and
discussed.
2013
- A complementarity formulation to study lubricated contact problems in the presence of cavitation
[Relazione in Atti di Convegno]
Bertocchi, Luca; Giacopini, Matteo; Strozzi, Antonio
abstract
A mass-conserving formulation of the Reynolds equation has been recently developed using the concept of complementarity [1]. The mathematical derivation of the Linear Complementarity Problem (LCP) implemented in the solver favoured in [1] overcomes the drawbacks previously associated with the use of such complementarity formulations for the solution of cavitation problems in which reformation of the liquid film occurs. In the present paper, the proposed methodology, already successfully applied to solve textured bearing and squeeze problems in the presence of cavitation in a one dimensional domain and for incompressible fluids [1], has been extend to a two dimensional domain and the fluid compressibility has been included in the formulation. The evolution of the cavitated region and the contact pressure distribution are studied for a number of different configurations. Some of the results obtained with the proposed scheme are critically analysed and compared with the predictions obtained using alternative formulations (including full CFD calculations). The stability of the proposed algorithm and its flexibility in terms of the implementation of different compressibility laws is highlighted.
2013
- Achievement of a uniform contact pressure in a shaft–hub press-fit
[Articolo su rivista]
Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Bertocchi, Enrico; Bertocchi, Luca
abstract
In this article, the achievement of a uniform elastic contact pressure in a frictionless, keyless, shaft-hub interference fit obtained by properly shaping the mating profiles is examined. The peculiarity of the hub mechanical response according to which, under the effect of a uniform pressure applied to the hub bore, the bore axial profile moves radially without any distortion, is exploited to simplify the determination of the mating profiles that return a uniform pressure. In particular, the hub radial deflection may be computed with a simple plane model, whereas only the shaft radial deflection requires a more complex analysis in cylindrical coordinates. Explicit approximate expressions are reported for the shapes to be conferred to the mating profiles to achieve a uniform pressure. Selected examples are presented to clarify the proposed design procedure and to preliminarily explore the effect on the pressure profile of simple shape errors.
2013
- OPTIMIZATION METHODOLOGY FOR INNOVATIVE AUTOMOTIVE CRASH ABSORBERS
[Relazione in Atti di Convegno]
D'Agostino, Luca; Bertocchi, Luca; Splendi, Luca; Strozzi, Antonio; Moruzzi, P.
abstract
The simulation of vehicle crash impacts requires accurate and computationally expensive Finite Element analysis. An effective procedure consists in considering and establishing which improvement can be made on an equivalent sub-model of the full vehicle. In this way, all the analysis can be performed on smaller models, thus saving computational time. A full vehicle simulation is required only at the end of the design process to validate the results of the sub-model analysis.A software based on a genetic optimization algorithm has been developed in order to optimize the geometrical parameters of a variable-thickness crash absorber. A numerical study on the folding of thin-walled aluminum tubes with variable-thickness has been performed in order to achieve the maximum energy absorption-to-mass ratio. Moreover, the performance in terms of folding length and crush load peaks have been considered.Different optimization strategies have been implemented to find out which solution guarantees the achievement of the optimization target with the lowest computational cost.The results show how the approach proposed by the authors allows an efficient variable-thickness crash absorber to be obtained. In fact it performs better in term of crash behavior and energy dissipation-to-mass ratio, with respect to the original constant_thickness model.
2013
- SEM Analysis of Sandblasted Double Acid Etched Titanium Implant.
[Abstract in Rivista]
Bortolini, Sergio; Martinolli, Matteo; Natali, Alfredo; Berzaghi, Andrea; Strozzi, Antonio; Baldini, Andrea; Consolo, Ugo
abstract
Objective:
The purpose of this work is to determine the surface morphology obtained by sandblasting and double treatment with acids of titanium implants (BioActive Treatment, B&B Dental Implant Company S.r.l., Bologna, Italy).
Method:
Implant surfaces are sandblasted with alumina oxide (Al₂0₃) by using a dedicated appliance. The surface is treated with a double etching by using mineral acids (phosphoric acid). Implant surfaces are cleaned with Argon plasma in a class 10.000 clean room, to guarantee the absence of environmental contamination. As an efficacy test, surfaces undergo x-ray photoelectron spectroscopy (XPS or ESCA). The surface topography of the implants was evaluated by Scanning Electron Microscope (SEM). Roughness was evaluated quantitatively using dedicated software to convert conventional SEM images into three-dimensional data (Mex 4.2, Alicona Imaging GmbH, Graz, Austria). EDX (Energy Dispersive X-ray spectroscopy) analysis was performed.
Result:
The SEM observation shows, in a low magnification (200x), a nice machining work, together with a homogeneous surface finish without particles or blasting residuals. Increasing the magnification, (2500-5000x) show the typical structure of micro-roughness surfaces treated with double acid attack. Values emerged from stereo SEM analysis:Ra 3.19 ± 1.06, Rq 4.78±1.15, Rt 11.41±1.06. EDX analysis confirms that the only elements detected are Ti, Al and V.
Conclusion:
As known and reported in the scientific literature, this micro-topography enables the surface to act as a “sponge”, interacting strongly with the clot and stimulating bone regeneration. The initial roughness level favours osteoblast cells anchor and the integration with the bone tissue, reducing the osseointegration time. With the limits of this study, this treatment seem to obtain by subtraction an implant surface with a controlled micro-roughness and absence of contaminants or foreign deposits.
2012
- A Mass-Conserving Complementarity Formulation to Study Fluid Film Lubrication in the Presence of Cavitation for Non-Newtonian and Compressible Fluids
[Relazione in Atti di Convegno]
Daniele, Dini; Mark T., Fowell; Strozzi, Antonio; Giacopini, Matteo; Luca, Bertocchi
abstract
A mass-conserving formulation of the Reynolds equation has been recently developed using the concept of complementarity [1]. The mathematical derivation of the Linear Complementarity Problem (LCP) implemented in the solver favoured in [1] overcomes the drawbacks previously associated with the use of such complementarity formulations for the solution of cavitation problems in which reformation of the liquid film occurs. In the present paper, the proposed methodology, already successfully applied to solve textured bearing and squeeze problems in the presence of cavitation in a one dimensional domain and for incompressible fluids [1], has been extend to a two dimensional domain and the fluid compressibility has been included in the formulation. The evolution of the cavitated region and the contact pressure distribution are studied for a number of different configurations. Some of the results obtained with the proposed scheme are critically analysed and compared with the predictions obtained using alternative formulations (including full CFD calculations). The stability of the proposed algorithm and its flexibility in terms of the implementation of different compressibility laws is highlighted.
2012
- A contribution to the Legendre series solution of the mechanical analysis of cylindrical problems
[Relazione in Atti di Convegno]
Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Bertocchi, Enrico; Campioni, Eleonora; Mantovani, Sara
abstract
A series solution in terms of Legendre polynomials of the stress function suitable for modelling the mechanical response of a cylindrical component is revisited, and some contributions to the definition of the series terms are given. In particular, the correction to be imparted to a logarithmically singular series solution is considered, and a recursive approach for its determination is developed. A preliminary example dealing with an elastic, deformable cylindrical hub forced onto a rigid shaft is presented.
2012
- A note on the Legendre series solution of the biharmonic equation for cylindrical problems
[Articolo su rivista]
Strozzi, Antonio
abstract
The solution of cylindrical problems is addressed. A series solution is considered of the biharmonic equation, in which the series terms of the stress function Φ are expressions based upon Legendre polynomials and logarithmically singular functions. An explicit form of a polynomial supplementing each logarithmically singular part of the series solution is obtained.
2012
- On the loosening mechanism of a bush press-fitted in the small end of a connecting rod
[Articolo su rivista]
L., Marmorini; Baldini, Andrea; Bertocchi, Enrico; Giacopini, Matteo; Rosi, Roberto; Strozzi, Antonio
abstract
The loosening mechanism is explored of a bush press-fitted into the small end bore of a con-rod. A modelling of the bush loosening mechanism is proposed. Numerical and analytical forecasts of the tensile inertial force responsible for the bush loosening are presented for a purely elastic model. Proper design charts are compiled that allow (a) the initial interference precluding any bush loosening to be determined within the respect of an imposed safety factor and (b) the maximum elastic stress within the small end to be computed for a general inertial load.
2012
- Stress Concentrations at the Rounded Edges of a Shaft-Hub Interference Fit Expressed in Terms of a Coefficient Normalizing the Coupling Geometry and the Young’s Modulus Effects
[Relazione in Atti di Convegno]
Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Bertocchi, Enrico; Bertocchi, Luca
abstract
The elastic stress concentrations developed from the keyless, frictionless, static press-fit of a solid shaft into a hub with bore rounded edges are addressed. Derived from an analytical approach, a normalising parameter Φ is employed that accounts for the combined effects on the hub stress concentration of the fillet radius of the hub bore, the shaft radius, the interference, and the Young’s modulus. Compiled with the aid of Finite Elements, several design charts are presented that report the elastic stress concentrations within the hub versus the normalising parameter Φ. Each curve is valid for prescribed ratios of a) the hub inner radius to the outer radius, and b) the fillet radius to the shaft radius. An approximating expression of ample validity is also presented for a prompt evaluation of the hub stress concentration factor.
2011
- Maximum equivalent stress in a pin-loaded lug in the presence of initial clearance
[Articolo su rivista]
Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Bertocchi, Enrico; Bertocchi, Luca
abstract
Various design charts of ample validity and prompt access are presented, which permit the contact stresses within the lug of a pinned connection to be forecast in the presence of an initial clearance between the pin periphery and the lug bore. To cover the range of the practically encountered geometries and loadings, round-ended lugs of various widths and with a variously tapered shank are considered, and several inclinations of the applied load are addressed. The charts are compiled with the aid of finite elements. The employment of the recently proposed load factor Φ allows the combined effects on the peak contact stresses of the load intensity and of the initial clearance to be predicted.
2011
- Normalization of the stress concentrations at the rounded edges of a shaft–hub interference fit
[Articolo su rivista]
Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Bertocchi, Enrico; Bertocchi, Luca
abstract
The elastic stress concentrations developed from the keyless frictionless static press-fit of a shaft into a hub are addressed. Two configurations are examined, namely (a) an infinitely long solid shaft press-fitted into a hollow hub with bore rounded edges, and (b) a shaft with filleted extremity, partially inserted into a hub. Derived from an analytical approach, a normalizing parameter is proposed that accounts for the combined effects on the stress concentrations of the fillet radius, the shaft radius, the interference, and Young’s modulus. With the aid of finite elements, various design charts are compiled that report the elastic stress concentrations within the hub versus the proposed normalizing parameter. Each curve is valid for a fixed ratio of inner to outer hub radii.
2011
- Torque Transmission by Friction in a Keyed Shaft-Hub Press-Fits
[Relazione in Atti di Convegno]
Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Bertocchi, Enrico; Bertocchi, Luca; Campioni, Eleonora; Mantovani, Sara; O., Quareshi
abstract
Interference fits are widely employed to semi-permanently connect gears, pulleys, flanges, wheels, disks, rotors, and similar mechanical components, to a shaft. The stress state along the hub central portion may be thoroughly predicted by modelling the press-fit problem as plane and by employing the Lamé equations for thick-walled cylinders, and the transmissible torque may be confidently estimated by relying on the Lamé predictions, since they are valid along most of the contact axial length.
Often a key is added to the press-fit, to secure the torque transmission and to prevent any relative rotation between the shaft and the hub. Both parallel and tapered keys are employed in practical applications. With respect to their tapered counterparts, parallel keys possess the advantage that they do not cause any eccentricity. This study considers parallel keys only.
The presence of the keyseat increases the compliance of the hub and the shaft, thus producing a diminution of the contact pressure between the hub and the shaft, which results in a similar diminution of the transmissible torque. In this paper, a preliminary Finite Element analysis is carried out to quantify the above diminution of the contact pressure in the assumption of frictionless contact. The analysis is carried out for a solid shaft and for a practically relevant selection of ratios between the hub inner and outer radii.
A preliminary development is presented of an analytical approach based upon the classical Michell polar solution, which is particularly suitable to mimic rings.
The diminution of the transmissible torque with respect to a keyless shaft-hub press-fit is quantified, and the results are presented in a design diagram.
2011
- Validation of a combined CFD/FEM methodology for the evaluation of thermal load acting on aluminum alloy pistons through hardness measurements in internal combustion engines
[Articolo su rivista]
Cantore, Giuseppe; Giacopini, Matteo; Rosi, Roberto; Strozzi, Antonio; P., Pelloni; C., Forte; M., Achiluzzi; G. M., Bianchi; L., Ceschini; A., Morri
abstract
This work presents the results of a multidisciplinary research project, carried out in close collaboration with Ducati Motor Holding S.p.A., for the development of an integrated methodology to design engine components in aluminum alloy under high thermal loads. The results refer to the study of an AA2618 (Al-Cu-Mg) alloy piston for high performance motorcycle engines. The piston has been selected as the pilot component for the development and validation of an advanced Fluid Dynamics (CFD) and Finite Element (FE) simulation methodology for the prediction of the inner thermal diffusion. The subsequent validation has been achieved through both the mechanical and microstructural characterization of the component. The methodology here presented consists of close interaction between fluiddynamics (CFD) simulations of the combustion process and Finite Element (FEM) simulations of the thermal diffusion inside the components. Combustion is the main engine heat source and is simulated by means of a threedimensional CFD code for reactive flows (FIRE v2008-AVL), with the use of advanced combustion (ECFM) and wall interaction models. The temperature map on the surfaces is based on the results of the iteration with FEM simulation of thermal diffusion. The FEM model used for the diffusion analysis receives the results of combustion analysis as input. Two different methods have been tested for the transfer of the CFD thermal load to the FEM models: a) imposition on the piston crown of a spatial distribution of heat flux averaged over the mean engine cycle; b) imposition on the piston crown of both heat flux coefficients and temperatures. The latter option allows the reduction of the number of iterations for the convergence of the thermal map inside the piston. The dissipation of the thermal load is accomplished by applying heat coefficients and temperatures, on the remaining parts of the piston surface. The validation of the CFD/FEM methodology is carried out through hardness measurements in different piston locations after bench tests. The identification of the hardness curves, as a function of temperature and time, for the T6 heat-treated AA2618 allowed the assessment of the local temperature reached by the component from the knowledge of the operating time of the engine and local hardness.
2010
- A Mass-Conserving Complementarity Formulation to Study Lubricant Films in the Presence of Cavitation
[Articolo su rivista]
Giacopini, Matteo; M. T., Fowell; D., Dini; Strozzi, Antonio
abstract
A new mass-conserving formulation of the Reynolds equation is developed using the concept of complementarity. This new method overcomes the drawbacks previously associated with the use of such complementarity formulations for the solution of cavitation problems in which reformation of the liquid film occurs. Validation against a number of analytical and semi-analytical formulations, for a variety of problems including textured bearings and squeeze film dampers, is performed. The current formulation is shown to be in very good agreement with existing analytical and numerical mass-conserving solutions.
2010
- Advanced high performance vehicle frame design by means of topology optimization
[Relazione in Atti di Convegno]
Cavazzuti, Marco; A., Merulla; Bertocchi, Enrico; Strozzi, Antonio; M., Pettazzoni
abstract
Automotive chassis design, often based on the company know-how and the designer experience, usually leads to consolidated solutions that are poorly innovative and not necessarily altogether efficient. Optimization techniques are powerful means for systematic design that can make it possible to avoid this drawback.
The present study proposes a methodology for automotive chassis design based on topology, topometry and size optimizations coupled with fem analyses. In particular, the methodology is applied to the design of a chassis
suitable for a rear-central engine high performance car. A massive 3d fem model is conceived, in order to respect the geometrical requirements yet leaving maximum freedom to the topology optimization algorithm. Shell mod-
els are employed for the subsequent topometry and size optimizations. The objective is the minimization of the chassis mass in fulfillment of a given set of structural performance constraints. The results demonstrate the
general applicability of the method proposed.
2010
- Analisi Termo-Meccanica a Fatica di un Motore Diesel Automobilistico
[Relazione in Atti di Convegno]
Cantore, Giuseppe; Fontanesi, Stefano; Cicalese, Giuseppe; Strozzi, Antonio; Giacopini, Matteo
abstract
L’articolo presenta alcuni risultati relativi all’analisi termo-meccanica di un motore Diesel automobilistico. Lo studio è condotto utilizzando simulazioni disaccoppiate CFD e FEM allo scopo di valutare la resistenza a fatica del motore. Una metodologia semplificata per stimare la caratteristica termo-meccanica di testate motore soggette alle reali condizioni operative è stata proposta dagli autori in precedenti pubblicazioni [1,2], ed è ora affinata apportando rilevanti miglioramenti su entrambi i fronti di simulazione.Dal lato CFD, l’analisi CHT (conjugate heat transfer) include nel dominio di calcolo anche il metallo del basamento, dei componenti forzati della testa, nonché della guarnizione. Particolare cura è rivolta alla rappresentazione dello strato limite e all’applicazione delle condizioni al contorno termiche, in particolare alla distribuzione dei flussi termici tra i vari componenti motore. Al fine di massimizzare l’accuratezza delle previsioni CFD, sono valutati criticamente gli effetti dell’ebollizione del refrigerante sulla previsione dello scambio termico.L’accuratezza della previsione numerica viene valutata mediante confronto con misure sperimentali di temperatura in alcuni punti della testa per condizioni stazionarie di funzionamento del motore. I risultati delle simulazioni CFD, ed in particolare la distribuzione puntuale del flusso di calore all’interfaccia fluido/solido, sono trasferiti come condizione al contorno all’analisi termo-strutturale tramite una routine appositamente realizzata. Dal lato termo-meccanico, la principale novità introdotta è l’implementazione di un criterio di tipo energetico per la stima della resistenza a fatica a basso numero di cicli; tale criterio, utilizzato congiuntamente ai più classici criteri tensionali o deformativi, consente di disporre di uno strumento di progettazione capace di predire la resistenza delle singole parti del motore soggette ai differenti carichi agenti. Sono infatti analizzati carichi affaticanti sia ad alto sia a basso numero di cicli, e la metodologia proposta è applicata con successo per predire i possibili punti di innesco di fratture sulla testa e migliorare le caratteristiche del circuito di raffreddamento.
2010
- Automazione e Verifica del Processo di Incollaggio in Linee Produttive di Telai per Vetture d’Alta Gamma
[Abstract in Atti di Convegno]
Andrisano, Angelo Oreste; Baldini, Andrea; Bertocchi, Enrico; Giacopini, Matteo; Leali, Francesco; Mantovani, Sara; Pellicciari, Marcello; Pini, Fabio; Strozzi, Antonio; Vergnano, Alberto
abstract
Sommario. La produzione industriale dei telai auto ha registrato, nel tempo, una grande evoluzione progettuale e tecnologica, spinta dalla necessità di garantire alte prestazioni e comfort elevato, nel rispetto della sicurezza dei passeggeri e della sostenibilità ambientale. Le linee produttive di assemblaggio sono, soprattutto in segmenti di fascia alta, progettate per l‟esecuzione, su telai diversi, di articolati processi ibridi di giunzione, basati, cioè, sull‟adozione di tecnologie di saldatura, rivettatura ed incollaggio. I sistemi che ne derivano sono, dunque, caratterizzati da elevata complessità e richiedono lo sviluppo di dispositivi automatici dedicati e l‟impiego simultaneo di robot industriali e risorse umane. La soluzione di tali problematiche richiede l‟intervento sinergico di vari settori dell‟Ingegneria Meccanica poiché coinvolge competenze metallurgiche, progettuali e tecnologiche. A queste si aggiungono le competenze necessarie alla progettazione di sistemi produttivi ad alta flessibilità che, secondo la visione proposta dagli autori, siano caratterizzati da elevata modularità strutturale ed operativa, parametricità e standardizzazione delle soluzioni progettuali e dei componenti, autonomia esecutiva, e che assicurino una rapida ed efficace riconfigurazione, garantendo, parallelamente, l‟alto livello qualitativo dei prodotti ed il completo controllo dei processi realizzati. Il presente articolo tratta lo sviluppo e la progettazione integrata del modulo robotizzato di incollaggio per linee di assemblaggio ibride di telai in alluminio, svolta in collaborazione con il gruppo ALCOA e con SIR SpA. Successivamente vengono presentati i risultati sperimentali ottenuti dalla verifica strutturale a lap shear e peeling di alcuni provini ricavati da assemblati del tunnel, effettuata secondo normative interne Ferrari SpA.
Abstract. In the last years, industrial production of automotive chassis has gained a great evolution in design and technology, spurred by the need to achieve high performance and comfort, while ensuring both the safety of passengers and the environmental sustainability. State-of-the-art assembly lines, especially in top class segments, are designed to employ hybrid junctions on different chassis. Such complex process is based on the simultaneous adoption of welding, riveting and adhesive bonding technologies. The production systems design engages the development of specific automated devices and the cooperation of industrial robots and human resources. The solution of these issues involves the synergic action of various sectors of mechanical engineering, as metallurgy, design, and mechanical technology. Design of high flexibility production systems is another important issue: according to the viewpoint proposed by the authors, such systems are characterized by high structural and operational modularity, by parametric and standard design of solutions and components, by executive autonomy and rapid reconfiguration capability, thus simultaneously ensuring high quality of products and the complete control of processes. The present paper deals with the development and integrated design of the robotic adhesive bonding module in hybrid assembly lines for aluminum chassis, carried out in collaboration with the ALCOA group and SIR SpA. Experimental results are also presented, that refer to lap shear and peeling tests, carried out on specimens extracted from the chassis tunnel, according to Ferrari SpA internal standards.
2010
- On the integral equation formulations of some 2D contact problems
[Articolo su rivista]
P., Junghanns; G., Monegato; Strozzi, Antonio
abstract
Two integral equations, representing the mechanical response of a 2D infinite plate supported along a line and subject to a transverse concentrated force, are examined. The kernels of the integral operators are of the type (x - y)ln|x - y| and (x - y)^2ln|x - y|.In spite of the fact that these are only weakly singular, the two equations are studied in a more general framework, which allows us to consider also solutions having non-integrable endpoint singularities. The existence and uniqueness of solutions of the equations are discussed and their endpoint singularities detected.Since the two equations are of interest in their own right, some properties of the associated integral operators are examined in a scale of weighted Sobolev type spaces.Then, new results on the existence and uniqueness of integrable solutions of the equations that in some sense are complementary to those previously obtained are derived.
2010
- Preliminary plane mechanical modeling of hexagonal contact
[Relazione in Atti di Convegno]
Strozzi, Antonio; Radi, Enrico; Baldini, Andrea; Giacopini, Matteo; Campioni, Eleonora
abstract
A hexagonal joint is mechanically analysed. A cross section of the contact between male and female components is modelled as a plane strain problem, and the contact and detachment zones are investigated with two approaches, a) an analytical study
formulated in terms of an integral equation; b) a FE analysis. Preliminary results refer to the situation of null initial clearance and coefficient of friction. For each side of the hexagonal contact, the contact zone constitutes a small portion of the length of the
hexagonal side, since separation occurs along a sizeable side length.
2010
- Sviluppo di una metodologia CFD e FEM per l’analisi a fatica di componenti motoristici
[Relazione in Atti di Convegno]
Cantore, Giuseppe; Fontanesi, Stefano; Cicalese, Giuseppe; Strozzi, Antonio; Giacopini, Matteo
abstract
L’articolo presenta alcuni risultati relativi all’analisi termo-meccanica di un motore Diesel automobilistico 6 cilindri a V di cilindrata complessiva 2900cc. Lo studio è condotto utilizzando simulazioni disaccoppiate CFD e FEM allo scopo di valutare la resistenza a fatica dei componenti. La distribuzione di fluido nel circuito di raffreddamento è stata in precedenza oggetto di approfondite analisi e ottimizzazioni al fine di migliorare le caratteristiche dei passaggi del refrigerante. Una metodologia semplificata al fine di stimare la caratteristica termo-meccanica di testate motore soggette alle reali condizioni operative è stata proposta dagli autori in precedenti pubblicazioni. Come conseguenza dell’elevata complessità dei vari fenomeni coinvolti, in questo articolo si introducono alcune importanti migliorie, che consentono un’analisi più accurata della resistenza a fatica del motore, soggetto a carichi affaticanti ad alta frequenza e a bassa frequenza. La metodologia oggetto del presente articolo si basa ancora una volta sull’analisi disaccoppiata CFD e FEM, con rilevanti miglioramenti apportati su entrambi i fronti di simulazione. Dal lato CFD, si utilizza una nuova tipologia di griglia poliedrica, che riesce a combinare l’elevata risoluzione spaziale della mesh con una richiesta computazionale accettabile e un’elevata stabilità numerica della simulazione; particolare attenzione viene dedicata alla rappresentazione del flusso in parete. Mediante l’analisi CFD – CHT (conjugate heat transfer) è valutata la distribuzione puntuale del flusso di calore al refrigerante, includendo nel dominio di calcolo anche il metallo del basamento, della testa completa dei componenti forzati, nonché della guarnizione. Al fine di valutare e incrementare l’accuratezza della previsione numerica, sono stati effettuati e vengono mostrati alcuni confronti con misure sperimentali di temperatura in alcuni punti della testa per condizioni stazionarie di funzionamento del motore. Particolare cura è rivolta alla rappresentazione dello strato limite, fluidodinamico e termico. Allo stesso tempo, grande attenzione è data all’applicazione delle condizioni al contorno termiche, in particolare alla distribuzione dei flussi termici tra i vari componenti affacciati alla camera di combustione. Al fine di massimizzare l’accuratezza delle previsioni CFD, sono valutati criticamente gli effetti dell’ebollizione del refrigerante sulla previsione dello scambio termico tra refrigerante e metallo. I risultati delle simulazioni CFD, ed in particolare la distribuzione puntuale del flusso di calore sulla superficie di contatto fluido/solido, sono successivamente trasferiti come condizione al contorno all’analisi termo-strutturale per la valutazione della resistenza a fatica del componente. A tal fine, si utilizza una routine appositamente realizzata, in grado di mappare la distribuzione puntuale dei flussi termici calcolata tramite le simulazioni CFD su una griglia di calcolo ottimizzata per le analisi FEM. Dal lato termo-meccanico, la principale novità introdotta è l’implementazione di un criterio di tipo energetico per la stima della resistenza a fatica a basso numero di cicli; tale criterio, utilizzato in congiunzione con i più classici criteri tensionali o deformativi, consente di disporre di uno strumento di progettazione capace di predire la resistenza delle singole parti del motore soggette ai differenti carichi agenti. Sono infatti analizzati carichi affaticanti sia ad alto sia a basso numero di cicli, e la metodologia proposta è applicata con successo al fine di predire i possibili punti di innesco di fratture sulla testa e di migliorare le caratteristiche del circuito di raffreddamento.
2009
- Contact stresses within a split ring inserted into acircular housing
[Articolo su rivista]
Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Rosi, Roberto; Bertocchi, Enrico
abstract
The contact problem between a split ring and a circular housing is mechanicallyexamined. This contact is revisited in terms of receding contact, the zones along which the ringbeds over the housing are investigated, and normalizing design parameters are evidenced. Thesplit ring is modelled in terms of a straight, purely flexural beam as well as of a curved, shearelasticbeam; for both models, analytical solutions are obtained. Various easy accessible designdiagrams, useful for estimating the maximum elastic stresses within the split ring and the axialinsertion force, have been prepared with the aid of these two beam models and using finiteelements. The mechanical response of the split ring when its angular width is appreciably lowerthan p is clarified.
2009
- Influence of the initial clearance on the peak stress in connecting-rod small ends
[Articolo su rivista]
A., Pioli; Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Rosi, Roberto
abstract
The stress increase that is caused by the presence of an initial clearance within thesmall end of connecting rods for motorbike and car engines is investigated. Plane analyticaland numerical modellings of the dry contact between the small-end and piston pin areadopted. Based upon a recent analytical result, a normalizing parameter is introduced, whichallows the stress concentration factor at the small-end bore sides to be expressed as a functionof a proper combination of the initial clearance between the small end and gudgeon pin, theapplied load, and Young’s modulus, for prescribed aspect ratios of the small end and hollowpin. Design diagrams summarizing the consequences of an initial clearance between the smallendbore and gudgeon pin on the eye peak stress are reported, which cover a wide range ofgeometries, clearances, and loadings. Selected comparisons between two-dimensional andthree-dimensional models are carried out.
2009
- Jeffery solution for an elastic disk containing a sliding eccentric circular inclusion assembled by interference fit
[Articolo su rivista]
Radi, Enrico; Strozzi, Antonio
abstract
An analytic solution is presented for stresses induced in an elastic and isotropic disk by an eccentric press-fitted circular inclusion. The disk is also subject to uniform normal stress applied at its outer border. The inclusion is assumed to be of the same material as the annular disk and both elements are in a plane stress or plane strain state. A frictionless contact condition is assumed between the two members. The solution is obtained by using the general expression for a biharmonic stress function in bipolar coordinates. The results show that the maximum of the von Mises effective stress due to the inclusion interference occurs in the ligament for large eccentricity, but it deviates from the symmetry axis for small eccentricity. Moreover, along the border of the circular inclusion the hoop stress locally coincides with the contact pressure, in agreement with a similar classical result valid for a half plane.
2009
- Solid Circular Plate Clamped along Two Antipodal Edge Arcs and Deflected by a Central Transverse Concentrated Force
[Articolo su rivista]
Strozzi, Antonio; G., Monegato
abstract
A static, purely flexural mechanical analysis is presented for a Kirchhoff solidcircular plate, deflected by a transverse central force, and clamped along two antipodal arcs,the remaining part of the boundary being free. By adopting an integral formulation, the contactreaction is assumed to be formed by four equal concentrated forces acting at the supportextremities, accompanied by two distributed moments with radial and circumferential axis,respectively. This plate problem is rephrased in terms of a complex-valued Hilbert singularintegral equation of the second kind, whose solution is obtained in analytical, integralform. A design chart is presented that reports the plate central deflection as a function of theangular width of the plate supports.
2009
- Three examples of inadequacy of the Williams asymptotic method in predicting the singularity strength in elastic problems
[Relazione in Atti di Convegno]
Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Rosi, Roberto
abstract
Three examples are presented for which the Williams asymptotic method
appears to be inadequate in forecasting the strengh of the singularity encountered in elastic
problems. The first case addresses a Kirchhoff plate resting on an irregular linear support;
the second example revisits a classical plane elasticity contact problem; the third case
considers an infinite sheet with a square hole. The reasons of the inadequacy of the Williams
asymptotic method in treating the above situations are discussed.
2008
- Biomechanical aspects in dental replacements
[Capitolo/Saggio]
Baldini, Andrea; Bruzzesi, G.; Zaffe, Davide; Giacopini, Matteo; Strozzi, Antonio; DE POL, Anto
abstract
This chapter deals with biomechanical aspects in dental replacements. The state of the art is critically reviewed taking into account the body of the literature results. The initial section is devoted to the mechanical properties of bone and to a description of the jaw geometry and of its loading and constraining. The following section presents a classifi cation of the various tooth replacement confi gurations and of the various materials adopted, where single and multiple replacements are considered. A specifi c section is devoted to the solid modelling of the jaw as input to numerical analyses, where the aid offered by reverse engineering and tomography
is underlined. The fi nite element method as well as alternative numerical and experimental approaches are reviewed in a dedicated section. The stress analysis forecasts and measurements are biomechanically interpreted in the light of the current literature results. The chapter ends with a section devoted to biological aspects.
2008
- Integral Equations and Contact Problemsin Kirchhoff Plates Resting on Irregular Linear Supports
[Articolo su rivista]
G., Monegato; Strozzi, Antonio
abstract
The construction of (boundary) singular integral equation formulations of contact problems for Kirchhoff (thin) plates is addressed. In particular, the need to forecast the singularity strength of the contact reaction is evidenced. It is shown that, when employing the integral formulation to describe contact problems between Kirchhoff plates and irregular linear supports, the equivalent shear force concept may be incopatible with the integral equation approach. In such circumstances the equivalent shear force concept has to be abandoned in favour of, or coupled with, an equivalent twisting moment approach. These concepts are described and applied to two particular contact problems.
2008
- ON THE INCOMPATIBILITY BETWEEN THE EQUIVALENT SHEAR FORCE CONCEPT AND THE INTEGRAL FORMULATION OF CONTACT PROBLEMS BETWEEN KIRCHHOFF PLATES AND IRREGULAR LINEAR SUPPORTS
[Articolo su rivista]
Strozzi, Antonio; G., Monegato
abstract
It is shownthat, when employing the integral formulation to describe contact problemsbetween Kirchhoff plates and irregular linear supports, the equivalent shear force concept maybe incompatible with the integral approach. In such circumstances the equivalent shear forceconcept has to be abandoned in favour of an equivalent twisting moment approach. A classicalexample of an infinite plate resting on a linear central segment is revisited in the light of theequivalent twisting moment concept, where all the computations are carried out in exact form.An additional example is developed to show that the usefulness of an integral approach basedupon the equivalent twisting moment concept remains valid even when the equivalent twistingmoment is applied at a plate border along which the twisting moment must be null, as it occursin a partially clamped border. The reaction singularity at the endpoints of a linear support isexamined with theWilliams asymptotic method. Finally, a physical interpretation is proposed forthe adoption of a distributed twisting moment among the contact reactions
2008
- ON TORSIONAL VIBRATIONS IN CONROD ASSEMBLIES FOR HIGH
PERFORMANCE ENGINES
[Relazione in Atti di Convegno]
Baldini, Andrea; Bertocchi, Enrico; Giacopini, Matteo; Margini, Stefano; Rivasi, Stefano; Rosi, Roberto; Strozzi, Antonio
abstract
In the paper, the authors discuss possible causes of conrod torsional vibrations. Several simplified
models are laid out for prediction, evaluation and future research. Some critical remarks about these
prospective models are presented. Comparisons with a limited number of experimental cases is
finally provided.
2008
- The numerical evaluation of two integral transforms
[Articolo su rivista]
G., Monegato; Strozzi, Antonio
abstract
We derive recurrence relationships for the evaluation of two integral transforms which are of interest for the numerical solutionof some integral equations and for the construction of certain quadrature rules.
2007
- Adult human dental pulp stem cells (DPSC): preliminary observations for selecting and conditioning DPSC according osteogenic aims.
[Abstract in Rivista]
Palumbo, Carla; Riccio, Massimo; Resca, Elisa; Bertoni, Laura; Baldini, Andrea; Strozzi, Antonio; G., Bruzzesi; DE POL, Anto
abstract
The previlinary observations have shown the possibility to obtain in vitro bone formation to apply in regenerative medicine.
2007
- Maximum Stresses in a Taper-shanked Round-ended Lug Loaded by an Oblique Concentrated Force
[Articolo su rivista]
Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Rivasi, Stefano; Rosi, Roberto
abstract
In this study, the stress state in a round-ended, taper-shanked lug loaded by an oblique point force is investigated. Numerical, analytical and, partially, photoelastic studies were carried out. In the analytical model, the lug is modelled as a plane problem, and it is partially likened to a ring examined with a Michell-type series solution; the differences in shape between lug and ring are overcome by endowing the series solution with degrees of freedom suitable for adapting the ring solution to the lug actual geometry. Three prompt access design charts are presented, which report the normalised stress concentration for three lug shank taper angles, for selection of five aspect ratios between bore radius and radius of the rounded extremity, and for load inclinations ranging from longitudinal to transverse directions
2007
- NORMALIZATION OF LOAD AND CLEARANCE EFFECTS IN BALL-IN-SOCKET-LIKE REPLACEMENTS
[Articolo su rivista]
M., Ciavarella; Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo
abstract
A normalizing loading parameter useful in summarising the mechanical response ofplane pin-in-plate-like contacts is extended to axisymmetric ball-in-socket-like contacts. Anexample addressing a compliant layered artificial hip joint is presented, and the usefulness ofthe normalizing loading parameter is evidenced.
2007
- Thermo-mechanical analysis of an engine head by means of integrated CFD and FEM
[Relazione in Atti di Convegno]
Fontanesi, Stefano; Carpentiero, Davide; Gagliardi, Vincenzo; Malaguti, Simone; Margini, Stefano; Giacopini, Matteo; Strozzi, Antonio; L., Arnone; M., Bonanni; D., Franceschini
abstract
A 2200 cc engine head for marine applications has been analysed and optimized by means of both fluid-dynamic and thermo-structural simulations. First, the fluid distribution within the cooling jacket has been deeply investigated, in order to point out critical aspects of the current jacket layout and propose modified gaskets aiming at modifying the coolant path and increasing the cooling performance. A new generation polyhedral grid has been employed to combine high resolution surface spacing, computational demand, and numerical stability of the CFD simulations. Different turbulence models and near-wall approaches have been tested in order to accurately predict the boundary layer behaviour, which is fundamental for the subsequent thermal analysis. Comparisons have been carried out between the different gasket layouts in terms of both cylinder to cylinder flow balancing and cooling effectiveness in the critical regions of the engine head.At a second stage, the CFD model has been extended to the whole engine head, i.e. covering both the cooling jacket and the metal cast, and heat flux distribution on the fluid/solid interface has been computed and transferred as a boundary condition to a structural finite elements code for the analysis of the fatigue strength of the component. To this aim, an ad-hoc developed routine has been created to map the computed punctual distribution of the heat transfer coefficient on a FEM-optimized grid. Particular attention has been paid to the thermal boundary conditions, i.e. the distribution of the heat losses among the combustion chamber and pre-chamber components.Along with this coherent approach of thermo-mechanical loading, the mechanical constitutive law of the material, the damage parameters and an energy based fatigue strength criterion have been considered in order to create a design strategy capable of performing predictive calculations of automotive parts subjected to thermo-mechanical loading. The methodology favoured in this study has been successfully applied to predict the site of incipient crack on an actual engine head.
2006
- Maximum equivalent stress in a pin-loaded lug subject to inclined loading
[Articolo su rivista]
Strozzi, Antonio; Baldini, Andrea; M., Nascimbeni
abstract
The elastic maximum equivalent stress in a pin-loaded, straight- or taper-shanked, round-ended lug subject to inclined loading is investigated using the finite element and the boundary element methods, and, partly, photoelasticity. The influence of the load direction, of the ratio between the bore diameter and lug width, and of the shank taper angle are particularly addressed. In addition, the effects of the axial length of the lug trunk and, partially, of the initial clearance between the lug bore and pin are numerically examined in the presence of a loading variously inclined to the lug axis. An interpolating expression for the maximum equivalent stress as a function of the ratio between the bore diameter and lug width, taper angle, and load inclination angle is proposed.
2006
- On the Applicability of the Loading Parameter PHI in Pinned Connections with Relevant Initial Clearance
[Relazione in Atti di Convegno]
Ciavarella, M; Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Rivasi, Stefano; Rosi, Roberto
abstract
In pinned connections, the presence of an initial clearance increases the lug stress concentration with respect to a neat fit configuration. By employing a recently proposed loading parameter Φ valid for plane models, the applied load and initial clearance effects on the stress concentration are normalised for a straight-shanked, round-ended, longitudinally loaded pin-lug connection of fixed outer to inner radius ratio. Results are obtained with a Mitchell-type, Fourier series solution and with commercial Finite Elements. The applicability of the loading parameter Φ to pinned connections with small to relevant initial clearances is explored. Two preliminary design charts are presented, which quantify the lug stress concentration factor versus the loading parameter Φ for two lug geometries defined by inner to outer radii ratios of 0.376 and 0.77.
2006
- Reduced dependence on loading parameters in almost conforming contacts
[Articolo su rivista]
M., Ciavarella; Baldini, Andrea; J. R., Barber; Strozzi, Antonio
abstract
In cases of completely conforming frictionless contact, the contact area generally either decreases or stays the same under load, in which case the extent of the contact area is subsequently independent of load and the stress and displacement fields vary linearly with the loading parameter. Dundurs and Stippes describe such cases as receding contact problems. Here, we demonstrate that similar results apply in the presence of Coulomb friction, in which case the extent of the stick and slip zones and the local direction of sliding are independent of load. We also show that if there is a small initial gap or interference throughout the potential contact area, the extent of the contact area and the stress and displacement fields will approach those of the corresponding receding contact problem as the applied load is increased. If the interface conditions permit adhesion between the contacting surfaces, the extent of the adhesion zone shrinks to zero as the load increases without limit. Progress of the contact configuration towards the limit is governed solely by a dimensionless load factor involving the ratio between the applied load and the initial clearance or interference. This permits results for a variety of initial geometries (due to tolerance variations) to be obtained from a set of finite element results for a single case. Some of these characteristics are demonstrated using a finite element solution of a connecting rod/bushing/gudgeon pin contact. Other interesting applications are those with complex geometries, ranging from biomechanics, as in prostheses, to the design of multiple fasteners. (C) 2006 Elsevier Ltd. All rights reserved.
2005
- Coating photoelasticity applied to a rapid prototyping model of a hub for high performance cars
[Capitolo/Saggio]
Baldini, A.; Cevolini, F.; Giacopini, M.; Piraccini, M.; Ronco, V.; Strozzi, A.
abstract
A photoelastic technique is presented that is based on a photoelastic coating applied along the surface of a model of a mechanical component made with rapid prototyping. The proposed procedure allows more flexible models to be obtained in comparison to metal parts, thus favouring the outset of a higher number of photoelastic fringes. In addition, the proposed approach permits enlarged models to be easily constructed, thus easing the photoelastic readings. The preliminary study here presented addresses a wheel hub for high performance cars, with particular regard to the stress concentrations by the fin fillets.
2005
- Hoop stresses in the con-rod small end
[Articolo su rivista]
Strozzi, Antonio; F., De Bona
abstract
Having in mind con-rods for motorbike and car engines, and spurred by the disagreements evidenced in the pertinent literature, the maximum circumferential stresses within the small end are investigated analytically, photoelastically, and numerically. The analytical models are based upon a plane assumption, and they adopt both beam and theory of elasticity idealizations. The plane photoelastic study concentrates on small ends with outer to inner radii ratios ranging from 1.2 to 1.5. A plane numerical model aimed at thoroughly mimicking the pin ovalization is developed, and a design chart of the peak hoop stress within the small end is provided for a wide spectrum of small end and pin geometries, for zero initial clearance. Such diagrams allow a prompt preliminary dimensioning of the small end to be carried out, which may be refined by effecting a three-dimensional finite element study of the specific conrod geometry. The consequences of an initial clearance between small end bore and gudgeon pin are examined for selected geometries, and three-dimensional aspects are explored for specific con-rod shapes.
2005
- On the analytical solutions of two singular integral equations with Hilbert kernels
[Articolo su rivista]
Monegato, G; Strozzi, Antonio
abstract
The analytical solution of two singular integral equations with Hilbert kernel of thefirst and second kind, respectively, is derived from the known solution of the correspondingsingular integral equations with Cauchy kernel of the first and second kind by introducinga proper change of variables.
2005
- On the contact reaction in a solid circular plate simply supported along an edge arc and deflected by a central transverse concentrated force
[Articolo su rivista]
G., Monegato; Strozzi, Antonio
abstract
A static, purely flexural mechanical analysis is presented for a Kirchhoff solid circular plate, deflected by a transverse central force, and bilaterally supported along a single periphery arc, the remaining part of the boundary being free. The contact reaction is assumed to be formed by a distributed reaction force accompanied by a distributed moment with radial axis. This plate problem is formulated in terms of an integral equation of the Prandtl type, supplemented by a vertical and a rotational equilibrium condition. It is shown that the Prandtl equation coupled to the equilibrium condition possesses a unique solution in a proper scale of weighted Sobolev-type spaces, with certain smoothness properties, and that no solution exists if the distributed moment is absent. Finally, the behaviour of the solution at the endpoints of the support is clarified.
2005
- Optimization of a Cooling Circuit in an Internal Combustion Engine for Marine Applications
[Relazione in Atti di Convegno]
Cantore, G.; Fontanesi, S.; Gagliardi, V.; Malaguti, S.; Baldini, A.; Giacopini, M.; Strozzi, A.; Rosi, R.
abstract
An optimization study involving both fluid-dynamic and thermostructural aspects has been carried out for a 2200 cc turbocharged engine head for marine applications. In this cross-disciplinary problem, the structural and thermodynamic aspects have been decoupled. A preliminary set of CFD numerical analyses of the cooling jacket layout has been performed, in order to investigate critical aspects of the present configuration and improve the cooling performance, by means of local flow patterns and flow distribution analysis. At a second stage, temperature distributions within the metal cast parts have been derived from CFD in order to assess the fatigue strength of the component with structural finite elements. A proper choice of both CFD methodology and boundary conditions is carried out in order to determine a trade-off between computational effort and actual engine behavior representation. The proposed modelling procedure allows a sensitivity study to be carried out of the engine head to variations of the leading geometric parameters, thus devising an optimized component. The methodology favored in this study is finally applied to carry out a comparison between the basic configuration and a fluid-dynamic improved solution, in order to estimate the effectiveness of the design optimization on the fatigue strength of the component.
2003
- On the press fit of a crankpin into a circular web in pressed-up crankshafts
[Articolo su rivista]
Strozzi, Antonio; P., Vaccari
abstract
The contact stresses induced by press-fitting a crankpin into a crankweb bore in pressed-up crankshafts are analysed for crankwebs possessing a circular geometry. The three-dimensional nature of this problem is reduced to a plane model, where the crankweb is described in terms of an eccentrically bored disc of uniform thickness, while the crankpin is idealized as an annular ring. Two different approaches are employed. Firstly, an elastic plane finite element analysis is carried out for this contact problem. Secondly, based upon the results of the numerical study, three variously approximated plane analytical models are developed. The contact pressure and the circumferential stress by the web bore are investigated, as well as the transmissible torque, where normalized diagrams are provided exploring a variety of disc-type crankweb geometries. Finally, selected three-dimensional finite element results are discussed, which highlight the limits of a plane model.
2002
- On the form of the contact reaction in a solid circular plate simply supported along two antipodal edge arcs and deflected by a central transverse concentrated force
[Articolo su rivista]
G., Monegato; Strozzi, Antonio
abstract
A static, purely flexural mechanical analysis is presented for a Kirchhoff solid circular plate, deflected by a transverse central force, and bilaterally supported along two antipodal periphery arcs, the remaining part of the boundary being free. Two kinds of contact reactions are considered, namely the case of distributed reaction force alone, and the situation in which the distributed force is added to a distributed couple of properly selected profile. For both cases this plate problem is formulated in terms of an integral equation of the Prandtl type, coupled with two constraint conditions. The existence of solutions in an appropriate scaled weighted Sobolev space is discussed, and the behaviour of the solution at the endpoints of the support is exhibited.
2001
- Circular solid plate supported along an edge arc and deflected by a central transverse force
[Articolo su rivista]
Strozzi, Antonio; P., Vaccari
abstract
A purely flexural structural analysis is carried out for a thin solid circular plate, deflected by a static central transverse concentrated force, and simply supported along an edge are, the remaining part of its periphery being free. This problem is modelled in terms of a Fredholm integral equation of the first kind, where the kernel is expressed analytically, and where the unknown function is the reaction force along the support. The initial equation is then modified into a new Fredholm integral equation of the first kind, which implicitly respects the condition imposed on the plate edge deflections by the rigidity of the support, but which has still to be coupled with the translational and rotational equilibrium conditions. By showing that a certain operator is a contraction mapping, it is demonstrated that this new integral equation coupled only with the translational equilibrium condition possesses a unique solution expressed in terms of a smooth function with square root singularities at the support ends. It is also shown that this unique solution, when expressed via Chebyshev polynomials, does not fulfil the rotational equilibrium condition, apart from the limit case when the plate is axisymmetrically supported. It is concluded that, in the framework of the purely flexural plate theory, the title problem does not possess any smooth solution with square root singularities at the ends. An approximate solution is nevertheless computed with the collocation method, by accepting limited undulations of the plate periphery.
2001
- Exact deflection expressions for a thin solid circular plate loaded by periphery couples
[Articolo su rivista]
Nobili, Andrea; Strozzi, Antonio; Vaccari, Paolo
abstract
A mechanical analysis is carried out for a thin, solid, circular plate, deflected by a series of periphery-concentrated couples with a radial or circumferential axis. Although such couples need not be of equal intensity or angularly equispaced, they must constitute a self-equilibrated system of couples. This problem is decomposed into a combination of two basic models, the first of which considers a single periphery couple with a radial axis, and the second addresses an edge couple with a circumferential axis. In both models the concentrated border couple is equilibrated by a sinusoidal boundary line load of proper intensity, whose wavelength equals the plate edge. When such basic configurations are combined, respecting the condition that the system of concentrated couples be self-equilibrated, the effects of the sinusoidal loads cancel out, and the title problem is recovered. A classical series solution in terms of purely flexural plate deflections is achieved for the two basic models, where the series coefficients are computed with the aid of an algebraic manipulator. For both models, the series is summed in analytical form over the whole plate region. Closed-form deflection formulae can thus be easily derived from the two basic models for any combination of self-equilibrated edge couples, where some selected relevant situations are developed in detail.
2001
- On the existence of a solution for a solid circular plate bilaterally supported along two antipodal boundary arcs and loaded by a central transverse concentrated force
[Articolo su rivista]
G., Monegato; Strozzi, Antonio
abstract
A purely flexural mechanical analysis is presented for a thin, solid, circular plate, deflected by a central transverse concentrated force, and bilaterally supported along two antipodal periphery arcs, the remaining part of the boundary being free. This problem is modeled in terms of a singular integral equation of the Prandtl type, which possesses a unique solution expressed in terms of a reaction force containing a factor exhibiting square root endpoint singularities. This solution is then shown not to respect the requested boundary constraints. It is therefore concluded that, within the framework of the purely flexural plate theory, the title problem cannot admit the weighted L-2 solution here examined. It, cannot, however, be excluded that a solution to the title problem exists, which possesses stronger endpoint singularities than those examined in this paper or is of a more general form than the one considered here.
2000
- Analytical modelling of the elastomeric layer in soft layer hip replacements.
[Articolo su rivista]
Strozzi, Antonio
abstract
A mechanical analysis is carried out for a flat deformable layer, firmly anchored to a rigidsubstrate, and frictionlessly compressed by a rigid spherical indenter, with reference to the design ofhip replacements whose cup is covered by an elastomeric layer. An available perturbation solutionof differential character, developed for a layer subject to plane strain conditions, indented by acylinder approximated as parabolic in shape and valid for high contact widths, is here extended tothe axisymmetric problem of a layer compressed by a paraboloidal indenter. In addition to theparaboloidal idealization, an accurate mathematical description of the indenter spherical profile isincorporated into the modelling of this contact problem. Perturbed solutions up to the second orderare developed for both compressible and incompressible layers. Selected numerical examples addressingactual joint geometries are included to assess the validity of the proposed analytical modelling,to explore the accuracy in describing the spherical profile and to compare the contact pressure profilesactivated by paraboloidal and spherical indenters.
1996
- Analisi numerica di una guarnizione elastomerica O-R montata in cava a coda di rondine
[Articolo su rivista]
Dragoni, Eugenio; Strozzi, Antonio
abstract
Per il loro corretto funzionamento gli O-ring sono normalmente alloggiati all'interno di cave. Le forme di queste ultime possono essere diverse, ma la più comune è la forma a cosiddetta "coda di rondine". Ma qual è la forma ideale della sezione trapezoidale di tale cava e quali sono i comportamenti della guarnizione all'interno di essa. Ecco i risultati di uno studio condotto dagli autori di questo articolo.
1995
- Axisymmetric Finite Element Analysis of a Hip Replacement with an Elastomeric Layer: the Effects of Clearance and Poisson's Ratio
[Articolo su rivista]
A., Unsworth; Strozzi, Antonio
abstract
A finite element analysis has been performed for a hip replacement incorporating an elastomeric surface layer. The effects of assuming the elastomer as incompressible have been examined for imposed loads, by comparing the incompressible solution to that using accurately measured values for Poisson's ratio, and while deflections were found to be significantly different, the changes in maximum pressure in the contact, maximum shear stress, contact angle and angular position to maximum shear stress were all small (less than 10 per cent). Comparisons have also been made between the finite element results for ABAQUS and an asymptotic solution, and it was found to be important to use the numerical model particularly at small values of clearance
1995
- Mechanical analysis of a thin solid circular plate deflected by transverse periphery forces and by a central load
[Articolo su rivista]
Dragoni, Eugenio; Strozzi, Antonio
abstract
A thin, solid, circular plate deflected by a number of transverse, concentrated, periphery forces, not necessarily angularly equispaced or equally oriented, and sustaining a central, transverse, equilibrating lead, is mechanically anaoysed via a purely flexural model. This problem is interpreted as a angularly dephased combination of a relatively simple model. This fundamental scheme consists of a plate loaded by a single periphery force, by a central load of equal intensity and opposite direction, and by a sinusoidal periphery line loading whose wavelength equals the plate border and whose intensity render the plate loading self-equilibrated. When a sequence of basic schemes, possibly referring to loads is different intensity, is combined, respecting the condition that the resultant of the periphery loads is equilibrated by a central force alone, the sinusoidal load effects vanish and the title problem is recovered. A series solution in terms of plate deflections is obtained for the basic model, whose coefficients are analytically evaluated via a computer algebra package. The series sum is expressed in finite terms involving the dilogarityhmic function, valid over the whole plate region. In particular, the series is summed in analytical form for the whole plate periphery, along which the boundary deflections are expressed in closed form.
1995
- Observations on the Paper by O'Carrol et al.
[Articolo su rivista]
Strozzi, Antonio; A., Unsworth
abstract
Some discrepancies between experimental and numerical results in the compression of a soft layer for biomechanical applications are explored.
1995
- Simply supported annular plates transversely loaded by a concentrated force applied at an arbitrary point
[Articolo su rivista]
Strozzi, Antonio; Dragoni, Eugenio; V., Ciavatti
abstract
An analysis is performed for a thin, annular plate, simply supported at its inner boundary, free at its periphery, and loaded by a concentrated force applied at any plate position. A purely flexural model is adopted, for which a series solution is obtained with the aid of an algebraic manipulator. Experimental tests are carried out for a specific plate geometry and the results obtained are compared to the analytical forecasts. A diagram is presented which summarizes the plate theoretical deflection by the loaded point for a wide range of aspect ratios of the annular plate and of normalized loaded positions.
1994
- Axisymmetric Finite Element Analysis of a Hip Replacement with an Elastomeric Head: the Eeffects of Layer Thickness
[Articolo su rivista]
Strozzi, Antonio; A., Unsworth
abstract
Finite element analysis of compliant layered artificial hip joints has been used to study the mechanical response of four different layer thicknesses from 0.5 to 3 mm.The results have been compared with a classical asymptotic model in terms of maximum contact pressure and contact width, and of maximum shear stress at the layer-backing interface and its location.The surface deformations and load capacities have also been compared.The best thickness was found to be 2 mm; though a marginal reduction in stresses would be found in the 3 mm layer, the penetrations would be greater and these might have implications for the fatigue life of the material.A formula for the thickness of the fluid film has been derived on the basis of the inverse hydrodynamic theory and the results show good correlation with existing theories.
1993
- ON THE BURSTING MECHANISM IN ROTATING RINGS
[Articolo su rivista]
C., Bandera; M., Nicolich; Strozzi, Antonio
abstract
The bursting mechanism in rotating, bored discs is theoretically reviewed in the light of published experimentalinformation. In particular, the segmentation sequence in bursting wheels is analysed according to a curved barmodelling and to a quasi-static loading, where a dynamic correction factor is introduced which reconciles theory withexperiments. Finally, a diagram reporting the number of wheel fragmented pieces in terms of the ratio of ring inner toouter radii is presented, based upon available experimental data and theoretical interpretation.
1992
- Finite element redesign of reciprocating 'PTFE' rod seals
[Capitolo/Saggio]
Botto, P.; Dragoni, E.; Strozzi, A.
abstract
The paper deals with a non-linear Finite Element analysis of the mechanical behaviour of a reciprocating rod seal assembly, composed of a PTFE Edge-seal and of an elastomeric O-ring. As a first step, a widely spread commercial version of this composite seal is numerically analyzed and the predictions are compared with published experimental data. Next, following the indications of an oversimplified model of the seal, several geometric parameters of the Edge-seal section are tentatively adjusted for improved performance and checked by means of refined Finite Element analyses. (from Authors)
1992
- Mechanical analysis of an annular plate transversely loaded at an arbitrary point by a concentrated force
[Articolo su rivista]
V., Ciavatti; Dragoni, Eugenio; Strozzi, Antonio
abstract
An annular plate clamped at the inner rim, free at the outer edge and loaded at an arbitrary point by a concentrated force is mechanically analyzed via a purely flexural model. A series solution is achieved, whose coefficients are analytically evaluated with the aid of an algebraic manipulator. A series acceleration technique is also developed. Experimental data are obtained for a particular plate geometry, and the results retrieved in terms of deflections and stresses are compared to the analytical forecasts. A technically relevant diagram detailing the theoretical deflection of the plate at the loading point for a variety of plate proportions and load locations is also presented.
1991
- Displacements in a Clamped Annular Plate Transversely Loaded at an Arbitrary Point by a Concentrated Force
[Articolo su rivista]
Bandera, C; Strozzi, Antonio
abstract
The displacements in an annular plate partly clamped and loaded by a transverse point force are analytically evaluated with a series solution
1991
- Mechanical analysis of an annular plate subject to a concentrated radial moment
[Articolo su rivista]
Dragoni, Eugenio; Strozzi, Antonio
abstract
An annular plate loaded by a concentrated radial moment applied to one of its contours and simply supported along the other boundary is mechanically analysed via a series solution. The sensitivity of the plate deflections to modifications of the Poisson's ratio is examined numerically. Several useful tables and interpolating expressions are reported which describe the deflections of the plate loaded edge for various geometries. Finally, the case of a uniform radial moment applied to an arc of the plate periphery is also studied.
1990
- A Photoelastic analysis of ceramic heads for total hip replacements
[Articolo su rivista]
Andrisano, Angelo Oreste; V., Ciavatti; Dragoni, Eugenio; Strozzi, Antonio
abstract
The main stress features in a hip joint replacement are studied photoelastically. In particular, the load transfer mechanism and the outcome of pressure peaks are examined and interpreted. An improved solution which permits a reduction of the stress level to be achieved is also investigated photoelastically. Some joint design directives are included.
1990
- Axisymmetric mechanical analysis of ceramic heads for total hip replacement
[Articolo su rivista]
Andrisano, Angelo Oreste; Dragoni, Eugenio; Strozzi, Antonio
abstract
An axisymmetric, mechanical analysis of conical press-fit ceramic heads is performed. The head strength and its fracture modes are assessed experimentally. The stress field is examined by finite element, strain gauge and photoelastic methods. An alternative head design, characterized by a cylindrical engagement with the stem, is analysed with the same techniques and its merits are explored.
1989
- Analisi fotoelastica di una protesi d’anca in ceramica. Parte I: Metodologia
[Relazione in Atti di Convegno]
Andrisano, Angelo Oreste; V., Ciavatti; Dragoni, Eugenio; Strozzi, Antonio
abstract
-
1989
- Analisi fotoelastica di una protesi d’anca in ceramica. Parte II: Risultati
[Relazione in Atti di Convegno]
Andrisano, Angelo Oreste; V., Ciavatti; Dragoni, Eugenio; Strozzi, Antonio
abstract
-
1989
- MECHANICAL ANALYSIS OF AN ANNULAR PLATE SUBJECT TO A TRANSVERSE CONCENTRATED LOAD
[Articolo su rivista]
Strozzi, Antonio
abstract
The periphery deflection in an annular plate clamped along its inner edge and loaded at its outer boundary by a transverse concentrated force are studied via a series solution. The corrected expressions for the series coefficients are presented. The series convergence is accelerated via a simple technique. Approximate methods are proposed to account for the compliant clamp and shear strain effects on the plate deflections, and they are validated against simplified theoretical models.
1989
- Measuring the load eccentricity in helical compression springs
[Articolo su rivista]
Dragoni, Eugenio; Strozzi, Antonio
abstract
An experimental device able to detect the load eccentricity in helical compression springs is described. The theory underlying the resolution of measured bending strains of the apparatus into effective load eccentricity is discussed. Laboratory results are offered for heavy duty springs and compared to theoretical estimates retrieved from the literature.
1989
- Mechanical analysis of a simply supported annular plate loaded by a periphery force
[Articolo su rivista]
Dragoni, Eugenio; Strozzi, Antonio
abstract
An annular plate subject to a concentrated force applied to one of its edges and simply supported along the other contour is mechanically analised. A series solution method is employed, the analytical expressions of the series coefficients are derived and the series convergence is accelerated via a simple, yet effective, technique. An approximate analytical expression for the loaded edge deflection is derived via a Taylor expansion of the series coefficients. The sensitivity of the plate deflection to modifications of the Poisson's ratio is examined numerically. Various practically relevant diagrams are presented which describe the deflections of the plate loaded edge for several geometries. Finally, the case of a uniform linear force applied to an arc of the plate periphery is also examined.
1989
- Mechanisches Verhalten von durch ein konzentriertes Radialmoment belasteten Kreisringplatten
[Articolo su rivista]
Dragoni, Eugenio; Strozzi, Antonio
abstract
In dieser Arbeit wird der Fall einer an einem Rand durch ein konzentriertes Radialmoment belasteten, am anderen Rand eingespannten Ringplatte behandelt. Die Verschiebung der Platte wird durch eine unendliche konvergente Reihe ausgedrückt, deren Koeffizienten ausgerechnet werden. Es wird gezeigt, wie die Reihenkonvergenz verbessert werden kann. Verschiedene Kurvenbilder der Durchbiegung längs des belasteten Plattenrandes und Näherungsausdrücke der Verschiebung am Belastungspunkt werden geliefert. Schließlich werden verschiedene Kurvenbilder auch für den Fall eines längs eines Randbogens gleichförmig verteilten Radialmomentes dargestellt.
1989
- Theoretical analysis of an unpressurized, elastomeric O-ring seal inserted into a rectangular groove
[Articolo su rivista]
Dragoni, Eugenio; Strozzi, Antonio
abstract
Based on linear elasticity, a theoretical model is developed which is able to describe the mechanical behaviour of an unpressurized, elastomeric O-ring seal inserted into a rectangular groove. First, the analytical tools employed to handle the unilateral contact problem and to improve the pressure profile regularity are discussed in detail. Next, an assessment of the model is performed for a laterally free seal, for which a variety of studies exist in the literature. Finally, the model is applied to the analysis of a seal installed into several grooves of different width, and the results retrieved are compared with the few data available. The model response to a perturbation of Poisson ratio of the elastomer is also critically examined.
1988
- Analisi meccanica di testine in ceramica per protesi d’anca
[Articolo su rivista]
Andrisano, Angelo Oreste; Dragoni, Eugenio; Strozzi, Antonio
abstract
Il lavoro è rivolto all'analisi meccanica di testine di ceramica comunemente impiegate in protesi d'anca ed alla definizione di una nuova geometria della testina. La ricerca si articola in quattro parti. La prima parte riguarda l'analisi geometrica (errori di forma) delle superfici interessate al collegamento testina-stelo. La seconda parte è dedicata alla determinazione sperimentale dei carichi e dei modi di rottura delle testine. Nella terza parte viene svolta l'analisi delle sollecitazioni nelle testine, condotta con metodi sperimentali (fotoelasticità) e numerici (elemento finito). La quarta parte propone un disegno alternativo delle testine per ottenere una resistenza maggiore rispetto a quelle esistenti.
1988
- Analysis of an unpressurized, laterally restrained, elastomeric O-ring seal
[Articolo su rivista]
Dragoni, Eugenio; Strozzi, Antonio
abstract
An unpressurized, elastomeric O-Ring seal inserted into a rectangular groove is analysed numerically and experimentally. The salient parameters characterizing the seal deformed geometry and stress field are investigated. The results gathered are confronted to those holding for a laterally unrestrained toroidal seal. Based on such a comparison, an analytical model is developed which accounts for the lateral restraining effect.
1988
- Mechanical Analisys of Ceramic Total Hip Replacements Heads
[Relazione in Atti di Convegno]
Andrisano, Angelo Oreste; Dragoni, Eugenio; Strozzi, Antonio
abstract
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1987
- AN ASSESSMENT OF THE NUMERICAL SOLUTION OF THEELASTOHYDRODYNAMIC PROBLEM FOR SOFT CONTACTS
[Articolo su rivista]
Strozzi, Antonio
abstract
A method is presented which enables the determination of closed form solutions for the ~lastohydrodyn~ic problem which can be used as test cases. The possible outcome of spurious undulations in the numerical description of the fluid film profile is rationalized. A numerical procedure which can placate the outcome of spurious oscillations in the film curve is illustrated.Such tools are applied to the analysis of cases of practical relevance partially derived from published experimental data.
1987
- Analisi sperimentale di testine in ceramica per protesi d’anca
[Relazione in Atti di Convegno]
Andrisano, Angelo Oreste; V., Ciavatti; Strozzi, Antonio
abstract
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1987
- Design of an end face seal assembly for lubricated rotary joints
[Articolo su rivista]
Dragoni, Eugenio; Strozzi, Antonio
abstract
A novel end face seal assembly composed of a rubber load ring, a metal stiffening ring, and a rubber seal ring serially connected together is presented. The design procedures adopted to achieve good operational effectiveness and long wear life are discussed in detail. Particular attention is focused on obtaining a load ring exhibiting a linear load-deflection relationship, and a seal ring capable of producing a semi-elliptical pressure profile at the sealing lip. These requirements are met by acting on the cross sectional shape of the rings. A comparison between well-correlating theoretical, numerical, and experimental results is given for both the elastomeric components.
1987
- Numerical Solution of the Elastohydrodynamic Problem in Soft Reciprocating Seals
[Articolo su rivista]
Strozzi, Antonio
abstract
A class of exact solutions to the elastohydrodynamic problem to be used as test cases is presented. A numerical solution to the elastohydrodynamic problem according to the Petrov-Galerkin merthod is developed. The appearance of spurious numerical undulations in the film profile is examined. A comaprison between analytial and numericalresults is employed to determine which numerical schemes limit the outcome of numerical oscillations without compromising the solution accuracy.
1987
- Stress Fields in a Compressed Unconstrained Elastomeric 'O' Ring Seal and a Comparison of Computer Predictions with Experimental Results
[Articolo su rivista]
A. F., George; Strozzi, Antonio; J. I., Rich
abstract
Stress-strain fields in an elastomeric unit. comparison between numerical and experimental results.
1986
- Analysis of a split ring inserted into a circular housing
[Articolo su rivista]
Dragoni, Eugenio; Strozzi, Antonio
abstract
The internal forces and contact zones of a split ring inserted into a circular housing are examined analytically, numerically, and experimentally. The mechanical components which can be likened to such a configuration are illustrated. The results obtained show that only one third of the ring periphery is in contact with the housing and that the effects of the shear strain on the contact pressure profile are appreciable.
1986
- Soluzione numerica di problemi di lubrificazione termoelastoidrodinamica
[Relazione in Atti di Convegno]
Andrisano, Angelo Oreste; Strozzi, Antonio
abstract
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1986
- Static Stresses in an Unpressurized, Rounded, Rectangular, Elastomeric Seal
[Articolo su rivista]
Strozzi, Antonio
abstract
The static stress field in an unpressuirized, rounded, rectangular, elastomeric seal is exmained using both experimental and numerical techniques. A particular stress separation method is successfully employed in the photoelastic study. The salient features of the stress field and their relevance in the sela performances are outlined. An approximate theoretical model is proposed which permits the determination of the contact pressure profile.
1986
- Stress-Strain Fields in Compressed Elastomeric Seals and their Extension to Fracture Mechanics
[Articolo su rivista]
G., Medri; Strozzi, Antonio
abstract
Stress and deformation fields in a compressed elastomeric unit, and extension to fracture mechanics
1986
- The Elastohydrodynamic Problem Expressed in Terms of Extended Variational Formulation
[Articolo su rivista]
Strozzi, Antonio
abstract
The elastohydrodynamic problem is revisited in terms of an extended variational formulation, where the corresponding functional exhibits minimum properties in the solution neighborhood. Such features are exploited in the development of a relaxation-type solver. The numerical results indicate the the convergence rate of the proposed relaxation scheme becomes increasingly poor as the solution of the elastohydrodynamic problem is approached. A polyalgorithm based on a combination between relaxation-type and Newton-type schemes is proposed. The numerical experiments referred to various sealing profiles of increasing foundation compliance show that the proposed procedure is particularly advantageous in the case of soft lubricated contacts.
1985
- Extended Variational Formulations and Finite Element Models for the Elastohydrodynamic Lubrication Problem
[Articolo su rivista]
S., Alliney; Strozzi, Antonio; A., Tralli
abstract
A finite element model for the elastohydrodynamic lubrication problem is presented. A coupling between the hydrodynamic equation and the foundation compliance equation is performed, then the resulting functional problem is given an ‘extended’ variational formulation. Some preliminary numerical results are also presented.
1985
- Formulation of Three Lubrication Problems in Terms of Complementarity
[Articolo su rivista]
Strozzi, Antonio
abstract
It is shown that the cavitation, the mixed lubrication and the tangentialvelocity slip problems can be rigorously described in terms of the complementarityformulation. The salient aspects of this formulation are discussed.A numerical example dealing with the tangential velocity slipproblem in a lubricated rigid slider is presented.
1985
- Mechanical behaviour of two elastomeric seals for rlling element bearing units
[Articolo su rivista]
G., Medri; Strozzi, Antonio; J. C., Bras; A., Gabelli
abstract
The mechanical properties of a commercial elastomer in use for axial and radial rolling bearing seals have been experimentally determined by means of biaxial, uniaxial and compresison tests. A finite-element program has been developed for large hyperelastic deformations, and a numerical analysis of the stress-strain field in the seal investigated has been performed. In this program, mechanical properties of the rubber are described by means of an experimentally determined constitutive relationship. The numerical results have been verified in the experiments, but substantial additional work is required before the analytical methods can be used with complete effectiveness.
1984
- A study of the Elastohydrodynamic Problem in Rectangular Elastomeric Seals
[Articolo su rivista]
Prati, E; Strozzi, Antonio
abstract
Analysis of the elastohydrodynamic lubrication problem. Elastomeric Seal, Photoelasticity, Lubricating film, numerical and experimental methods
1984
- MECHANICAL Analysis of Elastomeric Seals by Numerical Methods
[Articolo su rivista]
G., Medri; Strozzi, Antonio
abstract
A procedure which permits the evaluation of the stress-strain field in an elastomeric seal is presented. Such a procedure is based upon a mechanical modeling of the elastomer and on the employ of finite elements which can cope with high strains. Finally, the above-mentioned procedure is checked against experimental results. The problems connected with the material modeling are examined. In aprticular, the monotonicity of the constitutive relation is discussed. The difficulties encountered in the numerical simulation of the elastomeric seal are investigated. In particular, the convergence problems are discussed. The procedure is applied to a rectangular seal with rounded edges, to an O-ring seal, and to a U-ring seal. The numerical isochromatic pattern is drawn automatically and is compared to the photoelastic one. The validity and limits of the proposed procedure are discussed with regard to the three seal configurations examined.
1984
- On the Elastohydrodynamic Lubrication in Soft Seals
[Articolo su rivista]
Strozzi, Antonio
abstract
This communication is concerned with the elastohydrodynamic lubrication(EHL) problem in soft seals under reciprocating motion. The aim is todemonstrate theoretically that, if the Reynolds equation for isoviscous fluidsis coupled with a Winkler foundation [l] describing the seal deformabilityand if it is assumed that the dry contact pressure vanishes at the inlet andoutlet, in the absence of a sealed pressure no fluid film formation can occur.
1984
- THEORETICAL ANALYSIS OF A SEGMENTED LOCKING RING FOR SHELL-BOTTOM CONNECTION IN PRESSURE VESSELS SHELL-BOTTOM CONNECTION
[Articolo su rivista]
Strozzi, Antonio
abstract
The internal forces and deflections of a segmented locking ring inserted in an annular slot in a cylindrical vessel, andsupporting its bottom while the vessel is subjected to high internal pressure, are studied.The behaviour of the ring sectors is described in terms of a curved beam of rectangular cross section resting onelastic foundations.A closed form solution is obtained. The results presented show that the reaction force between the ring sectors andthe cylindrical vessel exhibits peaks at the sector ends, and that the maximum value of the bending moment for thering sectors is noticeably higher than that for a complete ring.
1983
- Elastohydrodynamic Lubrication in Elastomeric Reciprocating Seals
[Articolo su rivista]
Strozzi, Antonio
abstract
The elastohydrodynamic problem is numerically examined in soft contacts. The outcome of spurious oscillations is interpreted.
1983
- L’importanza di alcuni parametri geometrici in guarnizioni elastomeriche di sezione rettangolare: studio numerico
[Articolo su rivista]
Dragoni, Eugenio; G., Medri; Strozzi, Antonio
abstract
Con l'impiego di un programma di calcolo agli elementi finiti, viene esaminata l'influenza di alcuni parametri geometrici sull'andamento della pressione di contatto al bordo interno di una guarnizione dinamica, di sezione circa rettangolare, realizzata in materiale elastomerico. E' evidenziata la possibilità di modificare tale andamento in maniera più agevole di quanto possa avvenire negli anelli di tenuta O-Ring. E' proposta una formula empirica che fornisce l'influenza della curvatura della guarnizione sulla pressione di contatto massima. Essa consente di correggere i risultati ottenibili nell'ipotesi semplificativa che la sezione dell'organo di tenuta si trovi in condizioni di deformazione piana.
1983
- The importance of some geometrical parameters for rectangular section elastomeric seals: numerical study
[Articolo su rivista]
Dragoni, E.; Medri, G.; Strozzi, A.
abstract
The influence of geometrical factors on the variation of contact pressure at the inner edge of an approximately rectangular cross section dynamic sealing ring was studied using finite-element techniques. The possibility of varying the contact pressure distribution between the seal and the moving element was demonstrated and shown to be easier than for O-rings. An empirical formula is proposed which allows the calculation of curvature on maximum contact pressure. This permits the correction of results obtained by assuming conditions of plans deformation of the seal cross-section, and is particularly useful for the study of wear. (C.C.B.)
1978
- NUMERICAL AND EXPERIMENTAL STRESS-STRAIN ANALYSIS ON RUBBER-LIKE SEALS IN LARGE ELASTIC DEFORMATIONS UNDER UNILATERAL CONTACT
[Relazione in Atti di Convegno]
Medri, G.; Molari, P. G.; Strozzi, A.
abstract
A finite-element program taking into account the nonlinearities deriving from the behavior of the material, from large displacements and from unilateral contact, is developed. The photoelastic properties and energy function for a polyurethane rubber being determined, a comparison between numerical and experimental results is presented for simple shapes in a state of plane strain sketching seal cross sections.