Two Dimensional (2D) Damage Percolation with Stress State

Abstract

Butcher and Chen (2009a, b, c) extended the 2-D damage percolation model used by Chen (2004) to directly incorporate the stress state, material softening and a coalescence model linking the void geometry with the stress state via the plastic limit-load criterion. Unlike the prior percolation model, the stress state is directly determined from the GT yield surface by performing a dynamic homogenization at each time step to calculate the equivalent void in the material to account for softening. In the previous damage percolation models (Worswick et al. 2001; Chen 2004; Chen et al. 2005), void nucleation and coalescence were modeled using only geometric considerations and the effect of stress state was not considered. Void growth and shape evolution are strain-controlled and were reasonably well represented in the percolation model for well-defined stress states but a simplified coalescence rule was employed that did not account for the stress state. In addition, the fracture predictions of the percolation model are extremely sensitive to the void nucleation rule. In continuum modeling, void nucleation is often represented using a bulk averaged criterion. Obviously, this averaged criterion is unsuitable for percolation modeling since nucleation occurs at the individual particle scale.