ELASTIC RESPONSE AND EFFECT OF TRANSVERSE CRACKING IN WOVEN FABRIC BRITTLE-MATRIX COMPOSITES

This paper examines the linear elastic tensile and fracture behavior o f biaxial plain weave SiC/SiC ceramic woven fabric composites, Iso-pha se mode and random-phase made have been adopted to simulate multilayer stacking and to predict the initial linear elastic constants, It has been found that both modes predict very close results, Porosities in t he composite affect the stiffness significantly, while fiber undulatio n shows only minimal effect, The nonlinear stress-strain relation of t he composite is due to transverse cracks, which initiate mainly from i nteryarn pores, In the second part of this paper, two methods, classic al fracture mechanics and energy balance approach, have been used to e xamine the crack initiation and growth, A finite element method and a modified shear-lag method have been developed to evaluate the stress d istribution in the yarn with transverse cracks, The composite stiffnes s reduction due to transverse cracking has been obtained by both the f inite element and shear-lag methods, Strain energy release rates of th e growth of transverse cracks have been studied by the crack-closure p rocedure, using finite element methods. Effects of the yarn size and c rack position on the strain energy release rate have been quantified, It is concluded that thinner yarns lead to higher critical strains for transverse cracking.