Low cycle fatigue behaviour of cellular materials: Experimental comparative study of strut-based and gyroid structures made of additively manufactured 316L steel

Cellular materials are an attractive option to improve mechanical properties in lightweight design. Given their complex geometry, cellular materials present small features at the meso-scale that make them highly susceptible to fatigue failures. Fatigue of these materials has been receiving adequate attention only in the last few years, nevertheless, studies of low cycle fatigue (LCF) behaviour are extremely scarce and fragmented. In this study, 316L steel strut-based (FBCCZ) and gyroid cellular specimens were successfully manufactured by laser-powder bed fusion and tested in the LCF regime, considering their post-manufacturing morphological characteristics. The cyclic elastoplastic response revealed a higher stiffness for the strut-based than the gyroid cellular structure. The latter, in contrast, exhibited higher fatigue strength in strain-control mode, thanks to the absence of severe stress and strain raisers when compared to the strut-based counterpart. Overall, strain-life curves of both types of cellular materials are shifted to lower number of cycles to failure with respect to the base material. Detailed fractographic analyses revealed complex and tri-dimensional fracture surfaces for the gyroid specimens, whereas the strut-based lattice displayed planar fracture surfaces.