Predicting Crack Growth Direction in Unidirectional Composites

Abstract

The purpose of this study is to gain a better understanding of the parameters affect ing crack growth direction in unidirectional composite materials. To achieve this, the effect of anisotropy and biaxial, far field loading on the direction of crack growth in unidirectional off-axis composite materials is investigated. Specific emphasis is placed on defining the crack tip stress field and finding a consistent criterion for predicting the direction of crack growth. An anisotropic crack tip stress analysis was implemented using three criteria (the normal stress ratio theory, the tensor polynominal failure criterion and the strain energy density theory) to predict the direction of crack extension in unidirectional off- axis graphite-epoxy. The theoretically predicted crack extension directions were then compared with experimental results. After comparison, it was determined that only the normal stress ratio criterion correctly predicts the direction of crack extension.