Fracture of laser powder bed fusion additively manufactured Ti–6Al–4V under multiaxial loading: Calibration and comparison of fracture models

The fracture behavior of laser powder bed fusion (L-PBF) additively manufactured Ti–6Al–4V alloy manufactured in two orientations was investigated using a combined experimental and computational simulation approach. To quantify the effect of stress state on fracture of L-PBF Ti–6Al–4V, mechanical tests subjecting the material to seven distinct stress states were performed. For each test performed, computational simulations were used to determine the evolution of plastic strain and the stress state parameters stress triaxiality and Lode angle parameter up to fracture. Six existing fracture criteria were calibrated, and their ability to capture and/or predict the fracture behavior over a wide range of stress states was evaluated. It was determined that fracture models that explicitly take into account the effects of both the stress triaxiality and Lode angle parameter more accurately captured the multiaxial failure behavior of L-PBF Ti–6Al–4V compared to models that consider no stress state-dependence or only a dependence on stress triaxiality. Additionally, samples loaded in the vertical build direction had a higher ductility than corresponding samples loaded perpendicular to the vertical build direction. The stress state-dependent fracture behavior of L-PBF Ti–6Al–4V quantified in this study highlights the importance of experimentally measuring the fracture behavior of this material under a range of stress states that could be accessed during service, and defining appropriate models to prevent failure in components.