Stress based fracture criteria for mixed-mode I/II delamination of unidirectional composite laminates

Mixed mode delamination is prone to occur in composite laminates subjected to complicated loading. In current study, the modified maximum principal stress (M-MPS) criterion and the modified maximum shear stress (MMSS) criterion considering the effect of mode ratio on the critical distance are developed to predict the mixed mode delamination of unidirectional laminates. The accuracy of the proposed fracture criteria is validated by the comparison of the predicted fracture locus curve with extensive experimental data available in the literatures, a higher correlation is observed between the predicted results and the experimental data. Finally, comprehensive discussion on the capability of the proposed M-MPS and M-MSS criteria is conducted, a dimensionless parameter named fracture index composed of the difference of elastic properties and the difference of pure mode fracture toughness is proposed to reveal the fracture mechanisms of the unidirectional composites.