Mixed mode brittle fracture in PMMA - An experimental study using SCB specimens

A series of mixed mode I/II fracture tests is conducted on polymethylmethacrylate (PNMA) in the full range from pure mode I to pure mode H using a semi-circular bend (SCB) specimen containing an edge crack. The fracture load and the path of crack growth are obtained from experiments for various crack angles. It is shown that the conventional mixed mode L/H fracture criteria such as the maximum tangential stress (NITS) criterion overestimate the fracture strength of PMMA when the SCB specimen is used for fracture tests, particularly for mode II dominant loading conditions. However, improved predictions of fracture load are achieved when a generalized NITS criterion is employed. While the path of crack growth is straight for pure mode 1, it deviates significantly from the angle of fracture initiation for pure mode II and mode II dominant loading conditions. It is shown that the path of crack growth predicted by the generalized NITS criterion is also in a good agreement with the observed fracture path in the fractured SCB samples. (c) 2005 Elsevier B.V. All rights reserved.