Mixed-mode cohesive laws and the use of linear-elastic fracture mechanics

Small-scale cohesive-zone models based on potential functions are expected to be consistent with the important features of linear-elastic fracture mechanics (LEFM). These include an inverse-square-root K-field ahead a crack, normal and shear stresses being proportional mode-I mode-II stress-intensity factors, KI KII, work done against crack-tip tractions equal KI2+KII2?E?, where E? is appropriate modulus, failure controlled by toughness. The use LEFM model also implicitly implies that partition into components given phase angle defined as ?K=tan?1KII?KI. In this paper, we show in if deformations across interface uncoupled. However, not case for coupled cohesive laws, even these derived from function. For cannot used predict at crack tip when small-scale requirements conditions met; furthermore, may depend loading path. This mixed-mode interfaces described have phase-angle-dependent