Two-parameter fracture mechanics analysis of mixed-mode specimens under static and fatigue loading

The T-stress is a constant stress that acts parallel to the crack-front. In two-parameter fracture mechanics, the T-stress in conjunction with the stress intensity factor (SIF) is an important parameter for characterizing the stress state in the vicinity of a crack-tip. Due to its importance in characterizing the crack-tip stress field, T-stress values were calculated using finite element analysis (FEA) for a center cracked plate (CCP) and single-edge cracked plate (SECP) specimen. The T-stress values for both the CCP and SECP specimens were determined for cracks with relative sizes varying from 0.1 to 0.8 with respect to the specimen width and oriented at various angles between 0° and 90° with respect to the horizontal.;The crack-tip stress field is defined in terms of both the SIF and the T-stress using the William's series expansion [Williams, 1957]. The crack-tip stress field is incorporated into the Von Mises yield formula to develop an expression that models the crack-tip plastic zone under static mixed-mode loading conditions influenced by T-stress. Using the static plastic zone expression, the plastic zone is mapped and analyzed for various combinations of mode II to mode I SIF ratios and T-stress. The static plastic zone expression enables the characterization of constraint and fracture resistance under mixed-mode conditions.;The static plastic zone expression is adapted for cyclic loading conditions and used to develop a fatigue crack propagation model that takes into account the effect of both mixed-mode loading and T-stress. Finally, the cyclic plastic zone expression is used to demonstrate the significance of T-stress when predicting fatigue crack growth.