Micromechanical modelling of damage behaviour of multiphase steels

Abstract Multiphase steels offer very attractive combinations between strength and formability, due to the coexistence of different microstructural components and their interactions. The advantages of multiphase steels can be utilised by adjusting the type, the amount and the spatial distribution of the different phases, which are ferrite, martensite, bainite, and retained austenite. Understanding damage initiation and evolution are important to successfully process the material with only small scatter band of the formability properties. In the investigations two failure modes were simultaneously observed on a micro-scale, cleavage and dimple fractures. The model presented here attempts to describe the influence of the multiphase microstructure on the complex failure mechanism as well as mechanical properties by approaching the problem using representative volume elements (RVE) within the framework of continuum damage mechanics. Simulations for the dimple failure of TRIP steels, using the Gurson–Tvergaard–Needleman (GTN) model with two void nucleation mechanisms, will be presented. The cohesive zone model, based on the traction-separation law, is applied to the cleavage failure modelling.