Damage development in composites with large stress gradients

Implementation of a meso-scale damage model into the commercial finite element code ABAQUS via user-defined FORTRAN subroutines is described, and the results of investigations on damage development in structural configurations with large stress gradients are presented for carbon-fiber/polymer-matrix composites. The implemented model, which involves damage in both the meso-scale layer and an interface between the layers, is applied in a study of damage growth in finite-width angle-ply coupons and a composite panel with a terminated stiffener. The definition and evolution of state-dependent variables for layer damage is accomplished by means of a user-defined subroutine and the damageable interface is accomplished by using a user-defined element. It is demonstrated that as the fiber orientation progresses from 10 to 45°, the mode of damage changes from interlaminar damage, (i.e. delamination) to intralaminar damage, consistent with experimental observations. Analysis of damage development in the composite panel subjected to uniform compression shows that interlaminar shear stresses produce delamination at the skin-stiffener interface before failure of the panel due to tensile fiber rupture,— again consistent with experimental observations.