Geometry effects on fracture behaviour of polymethyl methacrylate

The mixed mode I/II fracture resistance of polymethylmethacrylate (PMMA) is studied using four different test samples namely the Brazilian disc (BD), semi-circular bend (SCB), four-point bend (FPB) and diagonally loaded square plate (DLSP) specimens. The noticeable discrepancy observed between the different sets of fracture toughness data reveals the influence of specimen geometry and loading condition on the crack growth behaviour. It is shown that the upper and lower bound mixed mode fracture toughness data obtained from the BD and SCB specimens, respectively are mainly due to the effects of negative T-stress in the BD and positive T-stress in the SCB samples. The FPB and DLSP test data are also close to each other and lie between the BD and SCB test results because the T-stress is nearly zero in both FPB and DLSP specimens.