Failure analysis of center notched CFRP laminates under multi-axial loading

There exists extensive literatures on damage and failure mechanisms of notched fiber reinforced composite laminates under uniaxial tension or uniaxial compression, however, equivalent works of notched laminates under combined tension-shear loading are limited. In this paper, failure mechanisms of center notched quasi-isotropic composite laminates under a series of in-plane loading (including uniaxial tension, uniaxial compression and mixed tension-shear) were studied numerically. An energy based continuum damage mechanics model in conjunction with the 3D Hashin failure criterion was employed to predict matrix cracking and fiber failure in each ply. For the intra-ply longitudinal splitting and inter-ply delamination prediction, surfaced-based cohesive contacts instead of the traditionally used cohesive elements were inserted along the potential damage zones. This allows different mesh configurations for different plies and the structured mesh can be aligned with the fiber direction for each ply to accurately model the matrix crack propagation. In addition, the proper boundary conditions in finite element models were investigated in this paper for laminates loaded by 'modified Arcan rig', which uses friction gripping to transfer loading to specimens. It is found that the small rotation of the Arcan rig has a significant effect on the failure mechanisms of the laminates. By modeling the Arcan rig in the finite element analyses, the simulation results compared very well with experimental results for both failure modes and failure loads of the center notched laminates.