Fracture behaviour of laser powder bed fusion AlSi10Mg microlattice structures under uniaxial compression

Abstract

Microlattice structures produced by laser powder bed fusion (LPBF) have been tested in compression extensively. Yet, their failure modes remain unexplained. This study bridges this research gap by accurately predicting the crack initiation process in LPBF body centred cubic (BCC) microlattices and their failure mode. In this study, LPBF AlSi10Mg BCC microlattice structures were tested in uniaxial compression and their detailed response modelled using a finite element (FE) modelling methodology on microlattices with idealised struts which was validated experimentally. Crack initiation in BCC microlattices with 2 × 1 × 2 unit cells loaded in compression was observed in situ via a scanning electron microscope (SEM). The force–displacement response of the microlattice was studied with respect to crack initiation and propagation. It was found that the locations of crack initiation could be predicted by considering the equivalent plastic strain and stress triaxiality fields obtained by an FE analysis and assuming a monotonically decreasing fracture locus. Subsequently, microlattices with 4 × 4 × 4.5 unit cells were similarly subjected to compression. Using a monotonically decreasing fracture locus extrapolated from uniaxial tension testing of the bulk LPBF AlSi10Mg, an FE simulation successfully predicted the commonly reported diagonal shear band failure mode of the microlattice on a model with idealised struts.