3D microstructure-based modelling of ductile damage at large plastic strains in an aluminum sheet

Abstract

Damage initiation in high-strength aluminum alloys with a precipitate-rich matrix is typically particle-driven. In AA7075-O temper, particle cracking and decohesion are the primary void nucleation mechanisms. However, the impact of particle-induced voiding on subsequent void growth and coalescence remains inadequately understood. Given that void growth and coalescence are inherently three-dimensional (3D) phenomena, conventional two-dimensional microstructure-based numerical models fail to accurately capture these damage evolution processes. The current work investigates void growth and coalescence phenomena in AA7075-O by developing 3D finite element (FE) real microstructure based models, created from plasma focused ion beam-scanning electron (PFIB-SEM) tomography and 3D electron back scattered diffraction (3D-EBSD). The models incorporate three key damage processes: particle cracking, particle decohesion, and matrix damage, to examine their effects on void growth and coalescence behavior in AA7075-O. Additionally, the influence of aluminum matrix grains on damage evolution in AA7075-O is explored. Complementary multi-scale modeling tools, along with in-situ scanning electron microscopy (SEM) and in-situ micro-X-ray computed tomography (μXCT), were employed for validation and supplementary insights. It is shown that 3D RVEs can capture the general 3D experimental trends in plastic heterogeneity and damage development at the microstructural length scale. Also, void growth and coalescence is influenced by the local stress fields, which in turn is dictated by particle morphology, particle cracking and decohesion. Particle cracking can accelerate the final specimen fracture, while particle decohesion promotes void growth but delays final coalescence. Void coalescence is shown to occur through void sheeting mechanism while the influence of grain characteristics on ductile void damage progression is found to be relatively limited.