Abstract
The question of failure criteria for textile composites is taken up, with reference to the micormechanics of known failure mechanisms in broad classes of 2D and 3D textile composites. Of primary importance is the definition of the measure of local stress or strain that should be compared against a putative material constant to predict local damage. In most prior work, some combination of strain or stress components evaluated at a single point has been used. Due to the complexity and inevitahle irregularity of textile composites, this approach is not favoured. Instead, micromechanical considreations recommend using strains averaged over gauge volumes whose dimensions are greater than or equal to approximately half the width dimensions of a single tow. Engineering tests that can be used for calibration are suggested but remain to be proven repeatable and consistent.