Dual-scale porosity effects on crack growth in additively manufactured metals: 3D ductile fracture models

• Published in: Journal of the mechanics and physics of solids Vol. 159; p. 104727
• Main Authors: Muro-Barrios, R., Cui, Y., Lambros, J., Chew, H.B.
• Format: Journal Article
• Language: English
• Published: London Elsevier Ltd 01.02.2022; Elsevier BV
• Subjects: Additive manufacturing; Additively manufactured metals; Crack growth; Crack propagation; Crack tips; Defects; Dual-scale voids; Ductile fracture; Failure; Finite element method; Fracture toughness; Metals; Porosity; Porous materials; Three dimensional boundary layer; Three dimensional models; Titanium base alloys; Tortuosity; Void growth and coalescence; Finite element method; Void growth and coalescence; Dual-scale voids; Additively manufactured metals; Crack growth; Fracture toughness
• ISSN: 0022-5096; 1873-4782
• DOI: 10.1016/j.jmps.2021.104727

The presence of microstructural defects resulting in unpredictable failure behavior has limited the use of additively manufactured (AM) metals in structural applications. In addition to the distributed porosity responsible for ductile fracture in conventional metals, larger defects (20–50 μm) can be introduced during additive manufacturing resulting in a dual-scale porosity failure process in AM metals. Here, we subject a three-dimensional, small-scale yielding boundary layer model containing a centerline crack to remote mode I K-field loading to study the effects of such dual-scale porosity on crack-defect interactions in an AM Ti-6Al-4V alloy. We model the background porosity implicitly within the fracture process zone viz. several rows of void-containing computational cell elements governed by the Gurson porous material relation, while the larger AM void defects are discretely represented based on size and porosity distributions of actual AM Ti-6Al-4V specimens characterized using optical and electron microscopy. Results show that AM defects can contribute to an increased apparent toughness of the AM metal over its conventional counterpart by activating isolated and/or clustered damage zones surrounding the crack, which shields and blunts the crack-tip and promotes crack tortuosity. However, the presence of planar clusters of AM defects can also accelerate crack growth and cause premature failure by forming preferential crack paths.