Augmented Strain Energy Release Rate (ASER): A novel approach for investigation of mixed-mode I/II fracture of composite materials

In the present research, a comprehensive mixed-mode I/II criterion for fracture investigation of orthotropic materials with arbitrary crack-fibre angle is proposed. The strain energy release rate concept is extended for orthotropic materials based on a Reinforced Isotropic Solid Model (RISM). RISM assumes that the crack growth occurs in isotropic matrix of a composite material. Fibres are defined as reinforcement of the matrix and have appeared in analytical relations as stress reduction coefficients. Since in arbitrary crack-fibre angle case, fracture toughness of the orthotropic material is not measurable, a new material property called 'Equivalent Fracture Toughness' (EFT) is introduced. The ETF is defined in such a manner that it is easy to measure and is not dependent on fracture properties of composite material such as mode II fracture toughness (KIIc) which needs large number of tests. The accuracy of the proposed criterion as well as the coincidence with the nature of fracture of orthotropic materials will be approved by comparing the extracted fracture limit curves for various crack-fibre angles with available experimental data.