Mixed mode fracture toughness testing of PMMA with different three-point bend type specimens

•Mixed mode fracture toughness of PMMA was studied by different bend type specimens.•Noticeable effect of specimen geometry and crack type was observed for the tests.•The obtained mixed fracture toughness data were predicted well by the GMTS theory.•The path of mixed mode crack growth was studied experimentally and theoretically.•The crack tip constraint level was affected significantly by the type of specimen.

Mixed mode fracture behavior of PMMA, was studied experimentally and theoretically using four different test configurations and with different crack types. Although all the test samples were subjected to three-point bend loading but completely different mixed mode fracture behaviors were observed for the tested samples. For each test configuration, especial mixed mode fracture toughness curves were obtained for fracture initiation direction and fracture toughness in the whole ranges of mixed mode I/II loading conditions. The level of crack tip constraint in the tested samples (which is related to the stress intensity factors (K) and the T-stress) was used as the main affecting parameter for predicting the mixed mode fracture results based on a two parameter (K-T) fracture theory. It was observed that the loss of crack tip constraint in the tested samples increases the mixed mode fracture resistance and decreases the fracture initiation direction and vice versa.