Mechanical response of a woven graphite/polyimide composite to in-plane shear dominated loads at room and elevated temperatures

Abstract

In this work, the effect of two types of in-plane shear dominated loads on the initiation of intralaminar damage has been evaluated in an 8-harness satin (8HS) T650-35/PMR-15 (graphite/polyimide) composite tested at room and elevated temperatures. The composite was subjected to either pure in-plane shear or combined biaxial tension and shear, which represented the stress conditions in the gage sections of the Iosipescu shear and ±45° tensile tests, respectively. The stress distributions in the composite were determined as a function of load and temperature by performing non-linear stress computations on the micro-, meso- and macro-levels. Both the concept of representative micro- and meso-unit-cells and the viscoelastic Eshelby/Mori–Tanaka approach were used in the analyses. The macro-response of the composite to the in-plane shear and biaxial loads was predicted at both temperatures and then validated by comparing it with the available experimental data. The micro-stress calculations have shown that on the micro-scale noticeably higher maximum principal stresses in the polyimide matrix in the vicinity of the graphite fibers were determined for the biaxial load case than in pure shear, both at room and high temperatures. It was shown that by using the numerical stress predictions, the experimentally observed differences can be explained in the initiation of tow micro-cracking in the woven composite subjected to the Iosipescu and ±45° tests at room and elevated temperatures.