Cell model for nonlinear fracture analysis - I. Micromechanics calibration

A computational approach based on a cell model of material offers real promise as a predictive tool for nonlinear fracture analysis. A key feature of the computational model is the modeling of the material in front of the crack by a layer of similarly-sized cubic cells. Each cell of size D contains a spherical void of initial volume fraction f(o). The microseparation characteristics of the material in a cell, a result of void growth and coalescence, is described by the Gurson-Tvergaard constitutive relation; the material outside the layer of cells can be modelled as an elastic-plastic continuum. The success of this computational model hinges on developing a robust calibration scheme of the model parameters. Such a scheme is proposed in this study. The material-specific parameters are calibrated by a two-step micromechanics/fracture-process scheme. This article describes the micromechanics calibration of void growth taking into account both the strain hardening and the strength of the material. The fracture-process calibration is addressed in a companion paper.