Fracture behavior of GPPS brittle polymer under mixed mode I/III loading

Cracks in engineering structures are sometimes subjected to out-of-plane shear deformation (mode III) in addition to the other modes. In this paper, with the aim of evaluating the mixed mode fracture behavior of a brittle polymer called Crystal (or GPPS), first, a recently developed loading configuration which provides pure modes I and III as well as some mixed mode I/III loading cases, has been redesigned and improved. Then, utilizing the improved configuration, mixed mode I/III fracture tests have been conducted on edge cracked rectangular samples made from Crystal polymer. The out-of-plane angles of fracture initiation have been measured by two methods of photography and optical CMM (Coordinate Measuring Machine). Also, crack growth path and fracture surface of the test specimens have been simulated by using the extended finite element method (XFEM). It is shown that the experimental results obtained for the fracture resistance of GPPS using the improved test configuration are in good agreement with the theoretical results estimated by the well-known MTS (maximum tangential stress) criterion.