Mixed mode I/II fracture criterion for arbitrary cracks in orthotropic materials considering T-stress effects

General and extended minimum strain energy density criterion for orthotropic materials with unidirectional fibers is employed to anticipate the onset of crack growth. It is postulated that the crack is embedded in the material in an arbitrary orientation with respect to fibers. As crack growth occurs in the isotropic matrix, isotropic stress state is used in the proposed criterion. Crack tip stress state of the isotropic matrix is related to composite one by definition of Reduced Stress (ReSt) coefficients. Since in the case of arbitrary crack-fiber angle, the effect of nonsingular term is significant on crack growth, T-stress term is considered in the calculations. Furthermore, a new concept of critical stress intensity factor is defined and formulated for arbitrary inclination cracks with respect to the fibers. Finally, a test procedure is presented to validate the proposed mixed mode I/II fracture criterion. Test results display excellent consistency with new criterion's fracture limit curve.