Recent advances in finite element modelling of ductile fracture at mesoscale

Abstract

This work addresses ductile fracture at the meso-scale by accounting for the influence of particles on nucleation, growth and coalescence mechanisms for complex loading paths. A finite element approach was developed to model and study 3D heterogeneous microstructures with interfaces defined by level-set functions and the use of a body fitted mesh adaption technique. Specific developments were also carried out in order to model failure mechanisms occurring both during the nucleation and the coalescence stages. Initial 3D microstructures of nodular graphite cast iron are obtained from X-ray laminography pictures. In-situ tensile tests with varying stress states are carried out and nucleation, growth and coalescence mechanisms are observed. Digital volume correlation is used to access to 3D displacement (and strain) field in the bulk. These data are also used to prescribe exact boundary conditions on the faces of the finite element domain. The finite element approach therefore enables to study strain and stress states in critical areas and aims at improving the understanding of coalescence mechanisms (internal necking of the intervoid ligament or void-sheet mechanism) by comparing finite element simulations with experimental observations and digital volume correlation results. This finite element approach is used to conduct a parametric study on the relative position of three voids on void growth and coalescence modes. It is shown that 2D views of coalescence mechanisms may sometimes be misleading.