Numerical Analysis of Crack Initiation Direction in Quasi-brittle Materials: Effect of T-Stress

A two-dimensional finite element analysis was adopted to assess the effect of T-stress on predicting crack initiation angle in a quasi-brittle material. Asymmetric semicircular PMMA specimen containing a vertical edge crack subjected to three-point bending was employed. The specimen was assumed as an isotropic and homogeneous material. Relative crack length ratios of 0.3, 0.4, 0.5, 0.6 and 0.7 were examined. Several relative bottom span ratios were included to develop a wide range of mixed-mode I/II loading conditions. The conventional maximum tangential stress (MTS) criterion could not precisely predict the crack initiation angle through the total range of pure mode I to pure mode II. The generalized maximum tangential stress (GMTS) criterion showed a significant effect of T-stress on the numerical prediction of the crack initiation angles in PMMA specimens. In the present study, neglecting the T-stress in the MTS criterion overestimates the crack initiation angle. The numerical predictions using the GMTS criterion showed a good agreement with the relevant experimental data found in the literature. The ability of GMTS in predicting the crack initiation angle is improved by considering the T-stress.