The effect of laminate lay-up on the multi-axial notched strength of CFRP panels: Simulation versus experiment

The effect of laminate lay-up upon the evolution of damage and upon the multi-axial failure locus of notched carbon fibre reinforced polymer (CFRP) panels is investigated experimentally and numerically. The proportion of 0° plies and ±45° plies is varied, and combined tensile and shear loading (and direct compression) is generated by a modified Arcan test rig. The failure surface is measured for panels containing a central hole or sharp notch, and the evolution of sub-critical damage is observed by X-ray CT and sectioning of the specimens. Three distinct damage modes are evident, depending upon the applied stress state, lay-up and geometry of the stress-raiser. The open-hole and open-notch values of tensile and compressive strength increase with the proportion of 0° plies, whereas the shear strengths do not scale with the proportion of ±45° plies. Inter-fibre splitting of the main loading bearing plies reduces the stress concentration, but the degree of splitting varies with loading direction and lay-up. The Finite Element (FE) method is used to predict not only damage development within each ply but also inter-ply delamination by the use of cohesive interfaces using a traction-separation law. The predicted failure envelopes and damage evolution are in good agreement with the observations, provided the mesh aligns with the fibre direction. This supports the adopted ply-by-ply FE strategy as a useful predictive tool for composite failure.