Elastic Response and Effect of Transverse Cracking in Woven Fabric Brittle Matrix Composites

This paper examines the linear elastic tensile and fracture behavior of biaxial plain weave SiC/SiC ceramic woven fabric composites. Iso-phase mode and random-phase mode 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 the composite affect the stiffness significantly, while fiber undulation shows only minimal effect. The nonlinear stress-strain relation of the composite is due to transverse cracks, which initiate mainly from interyarn pores. In the second part of this paper, two methods, classical fracture mechanics and energy balance approach, have been used to examine the crack initiation and growth. A finite element method and a modified shear-lag method have been developed to evaluate the stress distribution in the yarn with transverse cracks. The composite stiffness reduction due to transverse cracking has been obtained by both the finite element and shear-lag methods. Strain energy release rates of the growth of transverse cracks have been studied by the crack-closure procedure, using finite element methods. Effects of the yarn size and crack position on the strain energy release rate have been quantified. It is concluded that thinner yarns lead to higher critical strains for transverse cracking.