Multi-scale Modelling for Studying Ductile Damage of Free

Abstract: This paper builds upon previous studies (Farrugia, 2006, 2008) for developing a more physical approach to predict the mechanisms of high temperature ductile damage acting at surface/sub-surface and across the length scale of continuously cast free cutting steel billet feedstock. A methodology combining mechanical testing and modelling has been developed to account for local microstructural heterogeneities such as MnS inclusions and used to refine the science of nucleation, growth and coalescence acting at high temperature for this range of low ductility steels. A 5-step modelling approach from macroscale damage criteria integrated into ABAQUS/Viewer to mesoscale elastoplastic and viscoplastic constitutive material models implemented as VUMAT into the ABAQUS/Explicit software (Lin et al, 2007) combined with microscale FEMs of inclusion behaviour has been developed to deal with aspect of physical length scale. To account for localization and bridging physical length scale, a two-scale transition Cellular Automaton Finite Element (CAFE) model (Shterenlikht, 2003) coupled with the meso-scale viscoplastic approach has also been implemented for refining prediction of damage in key representative volumes of mechanical test specimens. The multi-scale CAFE model is implemented into a VUMAT subroutine to compute the evolution of damage within each active cell within the CA array associated to each FE element. The CA has many advantages compared to other techniques as both physical and probabilistic/statistical knowledge can be implemented and tested via dissociation of material and FEM structure. Using this approach, a better characterisation of the underlying mechanisms of ductile damage can be achieved.