Damage development in composites with large stress gradients

Implementation of a meso-scale damage model into the commercial finite elem ent code ABAQUS via user-defined FORTRAN subroutines is described, and the results of investigations on damage development in structural configuration s 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 d amage growth in finite-width angle-ply coupons and a composite panel with a terminated stiffener. The definition and evolution of state-dependent vari ables for layer damage is accomplished by means of a user-defined subroutin e and the damageable interface is accomplished by using a user-defined elem ent. It is demonstrated that as the fiber orientation progresses from 10 to 45 degrees, the mode of damage changes from interlaminar damage, (i.e. del amination) to intralaminar damage, consistent with experimental observation s. Analysis of damage development in the composite panel subjected to unifo rm 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. (C) 2001 E lsevier Science Ltd. All rights reserved.