Non-local stress approach in conjunction with reinforcement isotropic solid model (NLS-RIS): an efficient orthotropic mixed mode I/II fracture criterion.

Providing any accurate fracture criteria for composite materials requires consideration of energy dissipation effects at the crack tip due to its quasi-brittle nature. In this paper, a non-local damage model is incorporated into the reinforced isotropic solid (RIS) model for mixed mode I/II fracture assessment of orthotropic materials. In contrast with the local stress, in the non-local stress approach the effects of the fracture process zone (FPZ) can be included into the criterion with defined coefficients. After choosing an appropriate criterion to investigate the growth of micro-cracks, the concept of non-local stress (NLS) is used for developing the mentioned criterion. Due to the formation of the fracture process zone in the matrix of the damaged material, the RIS concept is used as a superior material model to simulate the fracture behavior of orthotropic materials. In RIS model, fibers take part as matrix reinforcements, and their effects are considered as stress reduction coefficients in theoretical investigation. Initial cracks are considered along and perpendicular to the fibers. The concept of crack kinking and growth along the fibers is utilized to develop fracture criterion for cracks perpendicular to the fibers. In comparison with available criteria, this criterion can consider different crack–fiber angles. Combination of the RIS theory with this defined damage coefficient presents a new model for prediction of the properties of damage zone for the cracked orthotropic materials. Fracture envelop curves in comparison with the available experimental results show the capability of the presented criterion in predicting the moment of failure of orthotropic materials. [ABSTRACT FROM AUTHOR]