Examining the effect of crack initiation angle on fracture behavior of orthotropic materials under mixed-mode I/II loading

Abstract

In this research, the maximum strain energy release rate concept is adapted for predicting the fracture response of orthotropic materials under mixed-mode I / II loading with an arbitrary precrack-fiber angle. Adaptive maximum strain energy release rate criterion (AMSER) is derived using the crack tip stress field of orthotropic materials with a precise look on the crack initiation direction. In precrack along the fibers, the crack initiation angle is assumed to be in the direction of maximum strain energy release rate (SER). Several experimental observations on a macroscopic scale prove that in the arbitrary angle between the precrack and fiber case, precrack kinks and propagates along the fibers; thus in the derivation of AMSER, crack initiation angle is considered as a superposition of the angle between precrack and fibers and the predicted angle based on the SER criterion (θC). The main purpose of this paper is to investigate the effect of crack initiation angle on the predicted fracture behavior. Due to the arbitrary angle between precrack and fibers, it is impossible to establish pure mode I conditions and derive pure mode I stress intensity factor. Thus, the equivalent fracture toughness concept in pure mode I is presented. AMSER criterion is validated by comparing fracture envelope curves with available experimental data in mixed-mode I / II loading. It can be concluded that accurate prediction of the crack initiation angle based on SER criterion causes the fracture behavior of orthotropic materials to be extracted with high accuracy. The results prove that the hypothesis of precisely predicting crack initiation angle based on the superposition of kink and θC angles complies with the nature of fracture of orthotropic materials.