A comprehensive study on the influence of T-stress term on crack initiation angle in orthotropic materials based on the modification of MTS, MSS, SER and SED criteria

Theoretical predictions using conventional fracture criteria indicate that the theoretical approaches are not compatible with the experimental data. The most important reasons for the inconsistency between theoretical criteria and experimental data are lack of attention to accurate prediction of the crack initiation angle in fracture phenomenon and the role of T-stress term in the theoretical analysis. In available theoretical criteria, the fracture behavior of orthotropic materials was studied roughly considering crack initiation angle in the fiber direction. In this way, the accurate prediction of this angle has a significant impact on the extraction of the fracture limit curve consistent with experimental data. In the presented work, a comprehensive study on the role of the T-stress term on the fracture assessment of orthotropic materials based on the maximum strain energy release rate, minimum strain energy density, maximum tangential stress, and maximum shear stress criteria is performed. These criteria can characterize the mechanism of crack initiation under mixed-mode I/II loading and consider the effect of the T-stress term on the crack initiation angle. The formulations of the presented criteria for orthotropic materials are developed using the orthotropic stress field. Based on these criteria, the crack initiation angle is extracted in each mode mixity and the effect of the T-stress term on crack initiation angle is studied. A new approach is used to derive the T-stress term. The results indicate that by crossing pure mode I and approaching pure mode II, the T-stress term has a remarkable influence on the crack initiation angle and fracture assessment of orthotropic materials. Also, based on these criteria, FLC's are extracted for orthotropic materials and the influence of this stress on crack behavior is evaluated. To verify the proposed formulations of these criteria, the fracture behavior based on the presented criteria is compared with the available experimental data and the accuracy of proposed theoretical approaches is discussed. It reveals that the presented criteria reliably estimate crack initiation angle and the crack behavior more accurately than the conventional fracture criteria for orthotropic materials.