COMPUTATIONAL METHODOLOGY TO PREDICT DAMAGE GROWTH IN UNIDIRECTIONAL COMPOSITES .1. THEORETICAL FORMULATION AND NUMERICAL IMPLEMENTATION

The theoretical formulation and numerical implementation of a computat ional methodology for predicting both the initiation and growth of dam age in a unidirectional composite monolayer is presented. The methodol ogy has been implemented into a finite element program to form the Mic romechanics Analysis and Damage Growth In Composites (MADGIC) code. A node splitting and nodal force relaxation algorithm that is capable of generating new crack surfaces has been incorporated to simulate damag e initiation and growth. One of the unique features of this code is th at the instantaneous direction of damage progression is dictated by th e local mechanics and failure criteria. Thus, the crack path need not be preselected. Common modes of damage that take place in composites, including fiber breakage, matrix cracking and fiber-matrix debonding, are simulated using the node splitting mechanisms in conjunction with mechanistic failure criteria. An incremental elastic-plastic algorithm with J(2) flow theory and isotropic hardening has also been incorpora ted to account for matrix plastic deformation when analyzing damage gr owth in metal matrix composites. In order to efficiently model standar d laboratory size composite specimens, a hybrid micromechanical-anisot ropic continuum model has been used consisting of a heterogeneous regi on enclosing the micromechanical damage processing zone, and an outer homogeneous region to which the far-field load is applied.