Influence of the volume fraction of fibre-reinforced orthotropic composite on the mode-I stress intensity factor

In the case of infinite bodies involving self-equilibrating loads, stress intensity factors (SIFs) for isotropic and orthotropic materials are the same. However, when the specimen is bounded, material orthotropy does influence the value of SIFs. Delale and Erdogan evaluated the mode-I SIF by solving singular integral equations numerically and showed that the SIF can be greater than the isotropic material value for certain types of orthotropic materials and can be smaller than the isotropic material value for certain other types of materials. They also observed that the mode-I SIF is not altered when either the crack is parallel or perpendicular to the fibre. These observations are verified by finite element analysis. The contours of isochromatics observable in a photoelasticity experiment are plotted to verify the suitability of finite element (FE) modelling and discretization. Using the FE code developed, the variation of the mode-I SIF for a singleedge notched (SEN) specimen as a function of volume fraction for unidirectional glass fibre-polyester laminate is obtained. The volume fraction is varied from 0.1 to 0.8 and the a/w ratio is varied from 0.1 to 0.8 in steps of 0.1. The contours of isochromatics observable in a photo-orthotropic elasticity experiment are plotted for the case of the a/w ratio of 0.3 as a function of fibre volume fraction.