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2020 - Effect of shot peening conditions on the fatigue life of additively manufactured A357.0 parts [Articolo su rivista]
Gatto, A.; Sola, A.; Tognoli, E.

Fatigue performance can be a critical attribute for the production of structural parts or components via additive manufacturing (AM). In comparison to the static tensile behavior of AM components, there is a lack of knowledge regarding the fatigue performance. The growing market demand for AM implies the need for more accurate fatigue investigations to account for dynamically loaded applications. A357.0 parts are processed by laser-based powder bed fusion (L-PBF) in order to evaluate the effect of surface finishing on fatigue behavior. The specimens are surface finished by shot peening using φ = 0.2 and φ = 0.4 mm steel particles and φ = 0.21-0.3 mm zirconia-based ceramic particles. The investigation proves that all the considered post-processing surface treatments increase the fatigue resistance of as-built parts, but the effect of peening with φ = 0.4 mm steel particles or with ceramic particles is more pronounced than that of peening with φ = 0.2 mm steel particles, although this treatment has the same Almen A value as the ceramic one. The surface morphology and the crack surface of the samples are also investigated.

2019 - Effect of Three Different Finishing Processes on the Surface Morphology and Fatigue Life of A357.0 Parts Produced by Laser‐Based Powder Bed Fusion [Articolo su rivista]
Gatto, Andrea; Bassoli, Elena; Denti, Lucia; Sola, Antonella; Tognoli, Emanuele; Comin, Andrea; Porro, Juan Antonio; Cordovilla, Francisco; Angulo, Ignacio; Ocaña, Jose Luis

A357.0 parts are processed by laser-based powder bed fusion and surface finished via plastic media blasting, ceramic sand blasting, and laser shock processing. The morphological analysis proves that plastic media blasting causes the most effective peak removal, the most efficient decrease in valley depth, and the greatest reduction in surface roughness. All the surface finishing processes enhance the fatigue life, however ceramic sand blasting bring about the greatest increase in the value of σmax for an infinite fatigue life limit of 2106 cycles. The experimental results suggest therefore that the infinite fatigue life value is more sensitive to the residual stress state engendered by ceramic sand blasting than to the reduction in surface roughness. Breakthrough cracks start at the interface between crushed or modified surface particles and the underlying macro-surface. However, at a distance of a few hundred microns from the crack initiation point, the fracture surface morphology become cellular for all the specimens.

2018 - Fatigue behavior of as-built L-PBF A357.0 parts [Articolo su rivista]
Bassoli, Elena; Denti, Lucia; Comin, Andrea; Sola, Antonella; Tognoli, Emanuele

Laser-based powder bed fusion (L-PBF) is nowadays the preeminent additive manufacturing (AM) technique to produce metal parts. Nonetheless, relatively few metal powders are currently available for industrial L-PBF, especially if aluminum-based feedstocks are involved. In order to fill the existing gap, A357.0 (also known as A357 or A13570) powders are here processed by L-PBF and, for the first time, the fatigue behavior is investigated in the as-built state to verify the net-shaping potentiality of AM. Both the low-cycle and high-cycle fatigue areas are analyzed to draw the complete Wohler diagram. The infinite lifetime limit is set to 2 × 106stress cycles and the staircase method is applied to calculate a mean fatigue strength of 60 MPa. This value is slightly lower but still comparable to the published data for AlSi10Mg parts manufactured by L-PBF, even if the A357.0 samples considered here have not received any post-processing treatment.