An experimental investigation of the compressive failure in quasi-isotropic ultra-thick CFRP laminates

This study investigates the compressive failure of quasi-isotropic ultra-thick carbon fiber composites using highspeed camera and Digital Image Correlation (DIC) technology. Test specimens of four different thicknesses (30, 40, 50, and 60 mm) were subjected to uniaxial compression in a modified test fixture and fractured within the effective gauge section. The experimental results reveal three unique compressive fracture characteristics of ultra-thick laminates: through-thickness shear, wedge splitting, and multistage shear. Although the compressive properties of the specimen did not change significantly with increasing thickness, a correlation between failure strength and fracture aspects was identified. The side-surface strain fields of the specimen effectively characterize shear fracture paths and delamination positions in the post-test specimen. They are utilized to analyze stress drop events, changes in loading states, and damage evolution during compression. High-speed camera images revealed that the fracture initiates with continuous delamination on one side of the surface, and the overall failure is accompanied by internal sublaminar shear kinking. The sequence of fracture events in ultra-thick laminates is comprehensively interpreted by considering the specimen's damage distribution before fracture and identifying the complex post-fracture effects.