Phase field fracture model for additively manufactured metallic materials

Abstract

Phase field models have been extensively studied in the analysis of ductile fracture. However, few have been explored to simulate additively manufactured materials and validated by experimental data to date. This study aims to develop a phase field framework for modelling complex mechanical behaviours of laser powder bed fusion printed metallic materials. To consider the laser powder bed fusion induced microstructural orientation, transversely isotropic Hill48 and modified Mohr-Coulomb constitutive models are incorporated here to depict the plastic and fracture behaviours, respectively. Five types of material specimens representing a wide spectrum of stress states are designed to identify the material parameters of plasticity and fracture. Three groups of crack propagation specimens are also tested to demonstrate the capacity of the developed model. The numerical results divulge that, by considering the stress state-dependent crack initiation, the proposed phase field model is able to better reproduce force-displacement responses of all specimens. Remarkably, the complex cracking sequences, including crack initiation, propagation and final rupture, can be properly captured by the proposed phase field model. More importantly, it is necessary to apply a transversely isotropic fracture model to characterise the orientation-dependent fracture behaviour; otherwise, the crack path would be predicted incorrectly, resulting in unacceptable global force-displacement responses. This study offers an effective phase field modelling framework for the sophisticated constitutive characterisation of laser powder bed fusion fabricated metallic materials.