Stress intensity factors in novel specimens for crack propagation under loading conditions II+III in polymers

Since numerous service failures are reportedly occurring due to the cracks exposed to mixed-mode loading conditions, this topic started to attract more attention recently. Therefore, a special device was designed to study mixed mode loading conditions of polymer materials. CRB (cracked round bar) specimen was not loaded conventionally in tension or torsion, as they are in most cases and thanks to special loading device, combination of loading modes II and III was reached in the central section of the specimen. To use such loading device experimentally, it is necessary to numerically estimate stress intensity factors on the crack fronts. Stress intensity factors were determined for all combinations of modes II and III along the circumferential crack front that was introduced by razor blade in the specimen. Additionally, stress intensity factors in modes I, II and III were determined for a re-initiated deflected crack by several angles of deflection. It was found that the most probable crack deflection from mode II to local mode I is by angle between 50° and 60°. The results are important for further experimental investigation of mixed-mode crack behavior using this experimental device.