Abstract
In the present paper, compressive behavior and failure mechanism of quasi-isotropic CFRP laminates with impact damage are studied numerically by a finite element method. The impact damage is modeled as a double-spiral-shape damage consisting of pairs of fan-shape delaminations and transverse cracks which links the delaminations above and below the lamina. The results of the geometrically nonlinear analysis show that the post-buckling behavior comprises three stages; buckling of thin damaged portions near the surfaces, buckling of the whole damaged area (through-thickness buckling) and global bucking. Stress concentration in 0 layer was caused at the transverse direction against the load. The energy release rate distribution was calculated by the virtual crack closure technique (VCCT) along the whole delamination tips. The energy release rate of the every transverse direction rapidly increased after through-thickness buckling of the damage portion. The increasing curves of maximum energy release rate with increasing compressive load well correlated with the relationship between the compression-after-impact (CAI) strength and the mode II interlaminar fracture toughness of various laminates. The final failure of the impact damaged laminates is probably caused by simultaneous growth of the all delaminations to the transverse direction when the interface of laminates is not very brittle.
