Three-dimensional phase-field modeling of the fracture constraint effects in Ti6Al4V alloy fabricated by laser powder bed fusion

The effect of constraint on fracture toughness is a critical issue in assessing the integrity of engineering structures. The brittle phase-field model (PFM) for fracture has been extended to the elastic–plastic solids. This study aims to enhance the understanding of constraint effects on the fracture behavior of an additively manufactured Ti6Al4V alloy. The fracture behavior of three-dimensional (3D) compact tension (CT) specimens with varying crack lengths and thicknesses is investigated experimentally and numerically. The results demonstrate that phase-field modeling is an effective tool for evaluating the fracture constraint effects of 3D cracked metalic material under mode I loading. With a single set of parameters, the elastic–plastic PFM accurately captures both the peak load and the post-peak softening behavior of specimens subjected to different constraint levels. While the elastic PFM can adequately assess peak loads in elastic–plastic materials, it lacks the capability to replicate the softening curve of the material. Loading affects in-plane constraints more than out-of-plane constraints, and the smaller the in-plane constraints, the higher the specimen fracture toughness and the longer the crack extension under the same loading conditions. In addition, the PFM can capture the necking effect at the crack tip and the crack propagation profiles, in particular, crack nucleation, propagation and even branching on the specimen surface can be accurately and effectively predicted by the elastic–plastic PFM. This work is beneficial in determining the fracture toughness of 3D elastic–plastic materials under different levels of constraint and demonstrates the feasibility of using PFM to study the fracture behavior of complex structures in the future.