THE USE OF X-RAY DIFFRACTION MEASUREMENTS TO DETERMINE THE EFFECT OF AGING ON RESIDUAL STRESSES IN UNIDIRECTIONAL AND WOVEN GRAPHITE/POLYIMIDE COMPOSITES

The purpose of this study is to evaluate the effect of aging in either air or nitrogen on the residual interlaminar strains and stresses in unidirectional and woven graphite/polyimide composites. In order to accomplish this goal, XRD measurements have been made on embedded aluminum inclusions placed between the first and second plies of both unidirectional and fabric graphite /PMR-15 composite specimens subjected to aging in either air or nitrogen at 315°C for up to 1024 hours. The interlaminar residual stresses in the composites were subsequently numerically extracted from the XRD strains in the embedded inclusions using an approach based on the Eshelby/Mori-Tanaka model. It has been shown in this work that the aging of the composites in air affects the strains and stresses in the inclusions as well as the residual stresses in the composites. The effect of aging in nitrogen on the strains in the inclusions was found to be significantly less pronounced.