CRACK-DEFECT INTERACTIONS IN ADDITIVELY MANUFACTURED TI-6AL-4V: DUAL SCALE POROSITY MODELLING USING WARP3D

Localized microstructural defects that often lead to unpredictable fracture have limited the wider adoption of additively manufactured (AM) alloys in critical components. In addition to the background porosity responsible for ductile failure in conventional alloys, defects resulting from the AM process can include large pre-existing voids (~30 μm) resulting in a dual-scale porosity failure process in AM alloys. In the present work, we undertook a numerical approach to explore the dual-scale void and crack interaction processes in both two and three dimensions in AM Direct Metal Laser Melted (DMLM) Ti-6Al-4V. A small-scale yielding modified boundary layer model with monotonically increasing applied displacement was used. The Gurson ductile damage model was implemented to model typical background pores, while the larger AM defects were explicitly represented in a finite element mesh. Fracture resistance curves were numerically generated for random instantiations of AM void distributions with increasing levels of AM defects. Individual outliers of fracture resistance, both over and under perfroming, were analyzed in more detail. It was seen that AM defects may activate a larger fracture process zone ahead of the crack tip, promote crack tortuosity, and on occassion lead to increased local material toughness over the conventional alloy.
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