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Dipartimento di Ingegneria "Enzo Ferrari"

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2023 - Fatigue and failure analysis of aluminium and composite automotive wheel rims: Experimental and numerical investigation [Articolo su rivista]
Zanchini, Michele; Longhi, Daniel; Mantovani, Sara; Puglisi, Francesco; Giacalone, Mauro

This paper deals with the adoption of composites in the design of the wheel rims of a sports car. With particular reference to cornering structural performance, the design of a composite wheel rim, produced via Resin Transfer Moulding (RTM) led to a reduction in mass and to an increase in bending stiffness. The adoption of alternatives to aluminium alloys allows the unsprung masses, as well as the total mass of vehicle to be contained. This paper provides a comprehensive view of the fatigue tests used for the wheel rim type-approval, followed by a rundown of wheel rims designed by Ferrari S.p.A from 2009 to present. These wheel rims have been classified in terms of mass and stiffness, and manufacturing process like casting, forging, or RTM. The failure modes of the reference Ferrari 488 GTB wheel rim were compared to those of the new composite wheel. In addition, the interpretation of the failures is supported by the results of Finite Element analyses. Though some initial defects led to a loss of stiffness of the wheel throughout the cornering fatigue test, the experimental results show that composite wheel rims are considered safe and they comply with the homologation targets and the Ferrari S.p.A. regulations.

2022 - Effective Mechanical Properties of AlSi7Mg Additively Manufactured Cubic Lattice Structures [Articolo su rivista]
Mantovani, Sara; Giacalone, Mauro; Merulla, Andrea; Bassoli, Elena; Defanti, Silvio

Lattice structures, whose manufacturing has been enabled by additive technologies, are gaining growing popularity in all the fields where lightweighting is imperative. Since the complexity of the lattice geometries stretches the technological boundaries even of additive processes, the manufactured structures can be significantly different from the nominal ones, in terms of expected dimensions but also of defects. Therefore, the successful use of lattices needs the combined optimization of their design, structural modeling, build orientation, and setup. The article reports the results of quasi-static compression tests performed on BCCxyz lattices manufactured in a AlSi7Mg alloy using additive manufacturing. The results are compared with numerical simulations using two different approaches. The findings show the influence of the relative density on stiffness, strength, and on the energy absorption properties of the lattice. The correlation with the technological feasibility points out credible improvements in the choice of a unit cell with fewer manufacturing issues, lower density, and possibly equal mechanical properties.

Mantovani, Sara; Ceruti, Alessandro

2022 - On the Numerical Modelling of Conductive CNT-Polymers: The Electro-mechanical Response [Relazione in Atti di Convegno]
Goldoni, G.; Mantovani, S.; Grasso, M.; Strano, S.; Terzo, M.; Tordela, C.

In the automotive field, piezo-resistive strain sensors have been increasingly integrated into “intelligent tyres”, to monitor the operating parameters, and to transmit them in real-time to the ECU. This work deals with polymer based piezo-resistive strain sensors with Carbon NanoTubes (CNT) embedded. CNTs slightly increase the mechanical strength of the sensor while improve the conductive and piezo-resistive behaviour of the polymer. A numerical methodology based on the Representative Volume Element (RVE) is proposed to predict the mechanical and electrical response of CNT-polymer. Finite Element method has been applied to obtain equivalent properties, which have been compared to experimental data available in the literature. Good estimate of the mechanical (i.e. Young’s Modulus) and electrical (i.e., resistivity) parameters has been achieved. The proposed methodology is thus suitable to identify electrical and mechanical properties of polymers with dispersed nanofibres

2022 - On the Ride Comfort Effect of Unsprung Mass Reduction Using a Composite Wheel Rim [Relazione in Atti di Convegno]
Zanchini, M.; Longhi, D.; Mantovani, S.; Puglisi, F.

Is it possible to feel the difference in terms of comfort and handling between wheel rims having the same size but different weight in a sports vehicle? It is well known that reducing the unsprung mass has a positive effect both on vertical accelerations and forces transferred from the ground to the body of the vehicle. In the present study, a simplified quarter car model is exploited to quantify the real advantage of using composite wheel rim instead of aluminium one for a sports vehicle. Despite the common belief, a reduction of more than 12 kg of the unsprung mass leads to a reduction of less than 1% of the vertical force oscillation; unfortunately, this positive effect is not perceived by the occupants. The influence of the damping parameter on the dynamic response is critically discussed. © 2022, The Author(s), under exclusive license to Springer Nature Switzerland AG.

2022 - On the Technological Feasibility of additively manufactured self-supporting AlSi10Mg lattice structures [Articolo su rivista]
Bassoli, Elena; Mantovani, Sara; Giacalone, Mauro; Merulla, Andrea; Defanti, Silvio

The capability to design and manufacture metal lattice structures is today one of the most promising targets of Powder Bed Fusion technologies. Not only additively manufactured lattices offer great lightweighting possibilities, but they open the way to tailored and graded mechanical response. To best capitalize on this opportunity, research effort is first needed to assess the feasibility of reticular structures and to quantify the expected deviations from the nominal geometry, as a function of the cell topology and dimensions. Notwithstanding the inherent suitability of additive processes to complex shapes, this paper proposes a more exact definition of the technological boundaries for body-centred cubic lattices, showing to what extent specific dimensional ratios, as well as a self-supporting cell structure, can be favourable to minimize thedeviation from the nominal reticulum in terms of dimensions, density and presence of defects.

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

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 - Structural Analysis of the Forming Process for Hairpin Windings for Electric Motor Applications: Torsional-Flexural Instability Issues [Relazione in Atti di Convegno]
Barbieri, S. G.; Mangeruga, V.; Giacopini, M.; Mantovani, S.

Electric motor manufacturing technology is evolving due to automotive transport development. Besides, environmental issues and the need of CO2 emission reduction have led to an increasing demand for electric drives efficiency. Permanent magnet synchronous machines are widely employed for traction systems and distributed windings produced by using insert techniques are growing in popularity. These methods require preformed wires such as the well-known hairpin shape. The advantages of hairpins are discussed in the pertinent literature. In the present paper, the manufacturing process of a hairpin is investigated by analysing its mechanical behaviour via Finite Element simulations. In fact, many problems might occur during the forming of a hairpin, depending on the shape required. In particular, this study aims at describing the influence of the geometry of the wire cross-section on the resulting final shape of the formed hairpin. Suitable ranges of geometrical and manufacturing parameters are identified to avoid torsionalflexural instabilities.

Strozzi, Antonio; Mantovani, Sara; Barbieri, SAVERIO GIULIO; Baldini, Andrea

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 - Towards an analytical model of a pin-lug connection [Articolo su rivista]
Strozzi, A.; Giacopini, M.; Bertocchi, E.; Mantovani, S.; Baldini, A.

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 - Additive manufacturing and topology optimization: A design strategy for a steering column mounting bracket considering overhang constraints [Articolo su rivista]
Mantovani, Sara; Campo, GIUSEPPE ALESSIO; Ferrari, Andrea

In the present paper, the use of the topology optimization in a metal Additive Manufacturing application is discussed and applied to an automotive Body-in-White component called dash. The dash is in the front area of the Body-in-White, between the left-hand-side shock-tower and the Cross Car Beam, and its task is to support the steering column. The dash under investigation is an asymmetric rib-web aluminium casting part. The influence of Additive Manufacturing constraints together with modal and stiffness targets is investigated in view of mass reduction. The constraints drive the topology result towards a feasible and fully self-supporting Additive Manufacturing solution. A simplified finite element model of the steering column and of the Body-in-White front area is presented, and the limiting assumption of isotropic material for Additive Manufacturing is discussed. The optimization problem is solved with a gradient-based method relying on the Solid Isotropic Material with Penalization and on the RAtional Material with Penalization algorithms, considering the overhang angle constraint with given build directions. Three metals are tested: steel, aluminium and magnesium alloys. Topology optimization results with and without overhang angle constraints are discussed and compared. The aluminium solution, preferred for its lesser weight, has been preliminarily redesigned following the optimization results. The new dash concept has been validated by finite element considering stiffness, modal responses, and buckling resistance targets. The proposed dash design weighs 721 g compared to the 1537 g of the reference dash, with a weight reduction of 53%, for the same structural targets.

2021 - Damage modelling strategies for unidirectional laminates subjected to impact using CZM and orthotropic plasticity law [Articolo su rivista]
Goldoni, G.; Mantovani, S.

In the present paper, the crashworthiness of a thick unidirectional carbon fibre reinforced polymer is investigated. This material is manufactured via compression moulding process. A Low-Velocity Impact (LVI) test is implemented on a quasi-isotropic laminate for the experimental evaluation of the energy absorption due to impact, while the internal failure mechanism is detected using Computerized Tomography (CT). Two different Finite Element (FE) models are applied to model the damage onset and propagation: firstly, a shell-based model and, secondly, a solid-based model using Cohesive Zone Method (CZM). In the CZM, the analytical modelling of the cohesive element properties is adopted, and the critical force evaluated experimentally is related to the energy release rate of mode II, and to the equivalent elastic properties of the laminate. The strength and weakness of the proposed approach in mimicking the impact behaviour and the actual failure mechanism, are discussed, and validated versus numerical simulation. The models are in good agreement with the experimental results; in fact, the relative error of the maximum force is about 4 per cent, and it occurs in the shell-based model.

2021 - Stresses in the cap of a connecting rod [Articolo su rivista]
Baldini, A.; Strozzi, A.; Bertocchi, E.; Mantovani, S.

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.

2021 - Synergy between topology optimization and additive manufacturing in the automotive field [Articolo su rivista]
Mantovani, Sara; Barbieri, SAVERIO GIULIO; Giacopini, Matteo; Croce, Alessandro; Sola, Antonella; Bassoli, Elena

This article purposes on developing and on re-interpreting the numerical results of a topology optimization for a structural component built via additive manufacturing. A critical appraisal of the optimization results is presented by modeling the feasible component with a holistic approach that merges structural and manufacturing requirements. The procedure is expected to provide a design guideline for similar applications of practical relevance, toward an increase of the right-first-time parts that is required to bring additive manufacturing to its full competitiveness. Topology optimization of a steering upright for a Formula SAE racing car was performed by targeting weight minimization while complying with severe structural constraints, like global and local stiffness performance. Cornering, bumping and braking vehicle conditions were considered. The optimization constraints were evaluated via finite element analysis on a reference component, where the loading conditions were retrieved from telemetry data. The reference part was manufactured by computer numerical control machining from a solid aluminum block. Spurred by the interpretation of the topology optimization predictions, a new upright geometry was designed and validated by calculating its stress field and the possible occurrence of Euler buckling. The new upright was 9% lighter than the reference component. The new geometry was analyzed according to Design for Additive Manufacturing principles to choose the orientation on the build platform and the supports’ location and geometry. The part was successfully manufactured and proved consistent with the application.

2020 - Feasibility analysis of a double-acting composite cylinder in high-pressure loading conditions for fluid power applications [Articolo su rivista]
Mantovani, S.

A preliminary study on a double-acting hydraulic cylinder subject to high-pressure loading conditions (pressure = 350 bar) and with a bore diameter of 300 mm is presented. The substitution of the reference steel cylinder tube with a multi-material tube is investigated. In detail, a solution providing a steel thin inner liner wrapped by carbon composite materials is analytically and numerically tested in terms of weight reduction. The composite lay-up design and the component geometry are built to comply with manufacturing constraints for a relatively high-volume production. The alternative multi-material cylinder is designed to ensure the same expected performance as its steel counterpart. Firstly, the non-conventional hydraulic cylinder was designed by extending Lame's solution to composite materials, by adopting the micro-mechanics theory of composites in order to bear the maximum operating pressure by monitoring its radial and axial deformation. The selection of the most appropriate carbon reinforcement was investigated. The influence of the stiffness-to-weight and the strength-to-weight ratio of the reinforcement on the design is discussed. Secondly, finite element analyses were performed to evaluate the occurrence of buckling and the modal response of the actuator considering the fluid and of the cylinder own weight influence. The results confirm the validity of the new cylinder tube design compared to the reference steel component. The proposed barrel weights 80 kg compared to the 407 kg of the reference cylinder, with a weight reduction of ~80%. Furthermore, it has a compact design with a decrease of the barrel outer diameter of ~5.3%.

2020 - Steering column support topology optimization including lattice structure for metal additive manufacturing [Articolo su rivista]
Mantovani, S.; Campo, G. A.; Giacalone, M.

Structural engineering in the automotive industry has moved towards weight reduction and passive safety whilst maintaining a good structural performance. The development of Additive Manufacturing (AM) technologies has boosted design freedom, leading to a wide range of geometries and integrating functionally-graded lattice structures. This paper presents three AM-oriented numerical optimization methods, aimed at optimizing components made of: i) bulk material, ii) a combination of bulk material and graded lattice structures; iii) an integration of solid, lattice and thin-walled structures. The optimization methods were validated by considering the steering column support of a mid-rear engine sports car, involving complex loading conditions and shape. The results of the three methods are compared, and the advantages and disadvantages of the solutions are discussed. The integration between solid, lattice thin-walled structures produced the best results, with a mass reduction of 49.7% with respect to the existing component.

2020 - Technological Feasibility of Lattice Materials by Laser-Based Powder Bed Fusion of A357.0 [Articolo su rivista]
Sola, A.; Defanti, S.; Mantovani, S.; Merulla, A.; Denti, L.

Lattice materials represent one of the utmost applications of additive manufacturing. The promising synergy between additive processes and topology optimization finds full development in achieving components that comprise bulky and hollow areas, as well as intermediate zones. Yet, the potential to design innovative shapes can be hindered by technological limits. The article tackles the manufacturability by laser-based powder bed fusion (L-PBF) of aluminum-based lattice materials by varying the beam diameter and thus the relative density. The printing accuracy is evaluated against the distinctive building phenomena in L-PBF of metals. The main finding consists in identification of a feasibility window that can be used for development of lightweight industrial components. A relative density of 20% compared with fully solid material (aluminum alloy A357.0) is found as the lowest boundary for a 3-mm cell dimension for a body-centered cubic structure with struts along the cube edges (BCCXYZ) and built with the vertical edges parallel to the growth direction to account for the worst-case scenario. Lighter structures of this kind, even if theoretically compliant with technical specifications of the machine, result in unstable frameworks.

2019 - A paradox in curved beams [Articolo su rivista]
Strozzi, Antonio; Bertocchi, Enrico; Mantovani, Sara

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.

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.

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 - A simple method of analysis of partial slip in shrink-fitted shafts under torsion [Articolo su rivista]
Bertocchi, E.; Mantovani, S.; Ciavarella, Michele

A solution method is proposed for the partial slip problem of a shrink-fitted shaft under torsion, that relies on the superposition of axisymmetric, elastically uncoupled problems all solved with FE. First, a problem is solved for the contact pressure induced by the interference coupling alone. In the presence of remotely applied torque, antiplane slip occurs at the indenting edge contact extremity; shear actions at the slip portion of the contact interface may merely be derived by scaling the pressure profile through the friction coefficient. A semi-inverse solution approach is derived, based on the assumed extent for the near-edge slip zone; two linear elastic solutions are parametrically mated to cancel stress singularities at the stick-slip transition point, the first solution concerning the remote torque alone, and the second one addressing the interface slip actions alone. We finally discuss the results for a selection of geometrical ratios, and the viability of simplified approaches based on beam theory.

2018 - Analysis of a segmented locking ring for shell-bottom connection in pressure vessels [Articolo su rivista]
Strozzi, A.; Bertocchi, E.; Mantovani, S.

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.

2018 - Design methodology for gear design of a formula one racing car: A modelling procedure based on finite element [Relazione in Atti di Convegno]
Mantovani, Sara; Calacci, Fabio; Fanelli, Sergio; Parlamento, Matteo

FIA regulations for the 2015 Formula One World Championship introduced an upper limit to the number of transmission assemblies employed during the season; a new approach to reliability has been forced on the designers, along with a reconsideration of the calculation procedures. Whereas mechanical transmission reliability calculations are well coded within the commercial transportations field, the peculiar aspects of the motorsport branch - namely a) the quest for an extreme lightweight design, b) the harsh dynamic transitions in speed and torque at gear shifts with a seamless shift transmission and wheel-road chattering, c) the circumscribed consequences of a breakage due to the controlled nature of the racing track environment, and d) the frenzied design procedures pace - urged for the development of specific validation procedures, that have to be rapidly redefined with the 2015 regulation adjustment. The present contribution rethinks those reliability assessment procedures - mostly based on nonlinear, dynamic Finite Element (FE) calculations - for a Formula One gearbox. In particular, the required model complexity is discussed with respect to the inclusion of shafts, bearings and carter compliance, chassis load induced deformation, significant load case selection, misuse robustness. The finalized validation procedure is shown to be predictive with respect to the augmented reliability requirements, while remaining feasible within the motorsport timescale environment.

2018 - Design of an Additive Manufactured Steel Piston for a High Performance Engine: Developing of a Numerical Methodology Based on Topology Optimization Techniques [Articolo su rivista]
Barbieri, SAVERIO GIULIO; Giacopini, Matteo; Mangeruga, Valerio; Mantovani, Sara

Modern high performance engines are usually characterized by high power densities, which lead to high mechanical and thermal loadings acting on engine components. In this scenario, aluminum may not represent the best choice for piston manufacturing and steel may be considered as a valid alternative. In this article, a methodology involving optimization techniques is presented for the design of an internal combustion engine piston. In particular, a design strategy is preliminary investigated aiming at replacing the standard aluminum piston, usually manufactured by forging or casting, with an alternative one made of steel and manufactured via an Additive Manufacturing process. Three different loading conditions are employed for the topology optimizations setup. Optimization results are then interpreted and the various structural features of the steel piston are designed starting from the density distribution contour plots. Different Finite Element thermomechanical models are finally prepared in order to correct and validate the designed geometry.

2018 - Design of an Additive Manufactured Steel Piston for a High Performance Engine: Developing of a Numerical Methodology Based on Topology Optimization Techniques [Articolo su rivista]
Barbieri, S. G.; Giacopini, M.; Mangeruga, V.; Mantovani, S.

Modern high performance engines are usually characterized by high power densities, which lead to high mechanical and thermal loadings acting on engine components. In this scenario, aluminium may not represent the best choice for piston manufacturing and steel may be considered as a valid alternative. In this paper, a methodology involving optimization techniques is presented for the design of an internal combustion engine piston. In particular, a design strategy is preliminary investigated aiming at replacing the standard aluminium piston, usually manufactured by forging or casting, with an alternative one made of steel and manufactured via an Additive Manufacturing process. Three different loading conditions are employed for the topology optimizations set up. Optimization results are then interpreted and the various structural features of the steel piston are designed starting from the density distribution contour plots. Different Finite Element thermo-mechanical models are finally prepared in order to correct and validate the designed geometry.

2018 - Optimization methodology for automotive chassis design by truss frame: A preliminary investigation using the lattice approach [Relazione in Atti di Convegno]
Mantovani, Sara; Campo, GIUSEPPE ALESSIO; Ferrari, Andrea; Cavazzuti, Marco

The present paper investigates the application of optimization methodologies to vehicle chassis in view of an integrated and transdisciplinary vehicle design. A detailed sizing optimization in cascade to Topology Optimization (TO) for the design of automotive chassis is investigated. This approach is also known as lattice optimization. The TO is employed to find a coarse optimum chassis lay-out under linear elastic conditions. The second stage of the methodology converts into a truss frame the edges of the FE cells, including only the elements that remained above a certain density threshold after TO. The diameter of each truss is then optimized in view of chassis weight reduction while meeting a set of given design requirements, such as maximum stress and minimum size. Various tubular frame architectures for lightweight solutions are considered complying with different sets of constraints over different design spaces. Finally, the balance between the computational cost and the feasibility of the lattice solution is discussed in comparison to TO.

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

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 - A Design Strategy Based on Topology Optimization Techniques for an Additive Manufactured High Performance Engine Piston [Articolo su rivista]
Barbieri, Saverio Giulio; Giacopini, Matteo; Mangeruga, Valerio; Mantovani, Sara

In this paper, a methodology for the design of a motorcycle piston is presented, based on topology optimization techniques. In particular, a design strategy is preliminary investigated aiming at replacing the standard aluminum piston, usually manufactured by forging or casting, with an alternative one made of steel and manufactured via an Additive Manufacturing process. In this methodology, the minimum mass of the component is considered as the objective function and a target stiffness of important parts of the piston is employed as a design constraint. The results demonstrate the general applicability of the methodology presented for obtaining the geometrical layout and thickness distribution of the structure.

Strozzi, Antonio; Bertocchi, Enrico; Mantovani, Sara

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 - Dynamic modal correlation of an automotive rear subframe, with particular reference to the modelling of welded joints [Articolo su rivista]
Rotondella, Vincenzo; Merulla, Andrea; Baldini, Andrea; Mantovani, Sara

This paper presents a comparison between the experimental investigation and the Finite Element (FE) modal analysis of an automotive rear subframe. A modal correlation between the experimental data and the forecasts is performed. The present numerical model constitutes a predictive methodology able to forecast the experimental dynamic behaviour of the structure. The actual structure is excited with impact hammers and the modal response of the subframe is collected and evaluated by the PolyMAX algorithm. Both the FE model and the structural performance of the subframe are defined according to the Ferrari S.p.A. internal regulations. In addition, a novel modelling technique for welded joints is proposed that represents an extension of ACM2 approach, formulated for spot weld joints in dynamic analysis. Therefore, the Modal Assurance Criterion (MAC) is considered the optimal comparison index for the numerical-experimental correlation. In conclusion, a good numerical-experimental agreement from 50 Hz up to 500 Hz has been achieved by monitoring various dynamic parameters such as the natural frequencies, the mode shapes, and frequency response functions (FRFs) of the structure that represent a validation of this FE model for structural dynamic applications.

2017 - Influence of Manufacturing Constraints on the Topology Optimization of an Automotive Dashboard [Articolo su rivista]
Mantovani, Sara; Lo Presti, Ignazio; Cavazzoni, Luca; Baldini, Andrea

Topology Optimization (TO) methods optimize material layout to design light-weight and high-performance products. However, TO methods, applied for components or assembly with high complexity shape or for structures with copious number of parts respectively, do not usually take into account the manufacturability of the optimized geometries, then a heavy further work is required to engineer the product, risking to compromise the mass reduction achieved. Within an Industry 4.0 approach, we propose to evaluate manufacturing constraints since early stages of the conceptual design to perform a TO coherent with the manufacturing technology chosen. Several approaches of TO with different manufacturing constraints such as casting and extrusion are proposed and each solution is compared. The optimum conceptual design is determined in order to minimize the component weight while satisfying both the structural targets and the manufacturing constraints; a case study on a high-performance sport car dashboard is finally presented.

2017 - Mechanical analysis of a hexagonal joint [Relazione in Atti di Convegno]
Mantovani, S.

A hexagonal joint is mechanically analysed. A cross section of the receding contact between the male and female components is modelled as a plane strain problem. Particular attention is paid to the effect of the presence of fillets in the hexagonal male. Finite Element (FE) results show that, for each side of the hexagonal contact, the contact zone constitutes a small portion of the length of the hexagonal side, and separation occurs elsewhere. The normalized peak contact pressure and the contact length along the male sides are numerically evaluated.

2017 - Numerical-experimental correlation of composite laminates for automotive applications [Relazione in Atti di Convegno]
Cavazzoni, Luca; Calacci, Fabio; Lo Presti, Ignazio; Mantovani, Sara

Lightweight design, structural performance and safety requirements represent the reference tasks for the development of innovative cars. For these reasons, both composites and Finite Element (FE) modelling have been widely employed in the last years. This study illustrates a numerical-experimental correlation methodology for Carbon Fibre Reinforcement Plastic (CFRP) laminates employed in a front Maserati hood. At first, an elastic-plastic material law is assessed for orthotropic shells using the Crash Survivability (CRASURV) nonlinear formulation, and a card material is compiled. A wide experimental campaign is performed according to the ASTM standards. Therefore, tensile, compression, shear, inter-laminar shear strength tests and drop weight tests are mandatory for the evaluation of the material properties and its failure modes. Finally, nonlinear forecasts of head impact on the hood are examined, and a preliminary numerical-experimental correlation is presented.

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

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

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 - Optimization methodology for an automotive cross-member in composite material [Relazione in Atti di Convegno]
Lo Presti, I; Cavazzoni, L.; Calacci, F.; Mantovani, S.

Optimization methods are useful and effective techniques for the design and development of components from the weight reduction point of view. This paper presents an optimization methodology applied to the front cross-member of a Maserati chassis for metal replacement application with the objective of the minimization of the mass of the structure using composite materials. Firstly, a topological optimization of the front side of the vehicle is performed, and the available design space is considered to determine the optimal load path of the design volume and, consequently, to assess a preliminary geometry of the component under scrutiny. Secondly, free-size optimization of the preliminary cross-member design is developed, initially neglecting and subsequently considering the manufacturing constraints. In addition, a linear analysis of the cross-member, modeled as a rigid component, is carried out to evaluate the maximum contribution of this component on the structural performance of the front side of the vehicle. Finally, size and shuffle optimizations are carried out on the new design concept to determine the number and the thickness of the composite plies, and the optimal stacking sequence, respectively, in order to fulfill the structural requirements. A comparison between the new composite structure and the aluminium Maserati cross-member is presented.

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

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

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

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 - 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

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.

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

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.

2011 - Lightweight crash energy absorber design using composite materials [Relazione in Atti di Convegno]
Mantovani, Sara; Cavazzuti, Marco

In an ongoing effort to increase the effectiveness of crash energy absorbers, thus improving the safety performance of cars, the interest in automotive industry in exploring lightweight alternatives to aluminum is deepening. In view of weight reduction, the research on composite materials has grown quickly because of their higher energy absorption-to-weight ratio. In the present work fiberglass composites with different shapes, types of fiber and stacking sequence are considered and analyzed by means of experiments and numerical simulations. At first, tension, compression, and shear properties of the materials are evaluated. Their dynamic properties are also investigated by drop testing according to ASTM D7136 standard. At a later stage, drop-tests are performed on cylindrical composite specimens in order to simulate the crash absorbers dynamic behaviour. Although the cylindrical specimens are not adhering to the standard, the drop tests allow to correlate the experimental data with the numerical simulations. Finally, in the light of the previous dynamic results, the stacking sequence of the composite crash absorbers is numerically optimized by means of design of experiments and optimization techniques for different geometrical shapes. Those considered are simple regular shapes, namely: circular, hexagonal, and octagonal.

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

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.

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

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.