Evaluation of Mixed-mode Stress Intensity Factor under Crack Close Loading

Abstract

Stress intensity factor (SIF) under mode I and mode II mixed-mode loading is considered. SIFs under various conditions (which are the plus/minus sign of K_I and K_II, the ratio of K_I to K_II and crack width) are evaluated using a circular disk specimen. Fracture toughness determined by the caustic method is compared with the calculated value through the fracture load K_C(Load). As a result, it is revealed that K_C(Load) is extremely overestimated under the minus sign of K_I condition. Moreover, pure mode II tensile test with the crack closing load P_t is carried out. Consequently, tensile fracture load Pfract is increased with the rise of P_t, but fracture toughness measured by the caustics is constant regardless of P_t and P_fract. Finally, attempt for determining the mode I compressive fracture toughness is made with a V - notched specimen.