Experimental Damage Evolution and Failure Mechanisms in GFRP Composite Laminates with Open Holes

In the present study, effects of the geometric discontinuity, here is a circular hole in a laminate, on the damage progression and failure mechanisms of the glass/epoxy general symmetric composite laminates are investigated. Different damage mechanisms in micro-scale including matrix cracking, delamination and fiber fracture cause the failure of laminates. The stress-strain data for samples with cross-ply and quasi-isotropic layup configurations under quasi static uni-axial tensile displacement control loading condition are obtained. The stacking sequence and thickness effects on the strength of the laminates are investigated. The experimental observations show that by increasing the number of off-axis plies in cross ply laminates and by doubling the number of plies in quasi-isotropic laminates the strength is reduced. For these laminates, at applied strain of about 0.3~0.4%, the stress-strain curve is bended and the stiffness of the laminate is reduced mainly due to the matrix crack evolution and delamination progression in high stress concentration region near the hole. The final failure mechanism for cross ply laminates is fiber fracture while in others the pull out of off-axis plies causes the rupture of the specimens.