Effects of randomly distributed defects on Mode-I interlaminar fracture of composite materials

•The Interlaminar Tensile (ILT) strength and the mode-I delamination fracture energy of composite materials are sensitive to the distributed interlaminar defects.•Both the ILT strength and the mode-I delamination fracture energy scale linearly with the defect area fraction on a critical fracture plane.•For a fixed area fraction of the defects, the ILT strength is not sensitive to the defect size.•The mode-I fracture propagation behavior is sensitive to the defect size especially when the defect size is greater than the fracture process-zone size of the delamination crack. Effects of defects on the mode-I interlaminar fracture behavior of composite materials are studied using computational fracture mechanics. Cohesive-zone Finite Element (FE) models of both the Interlaminar Tension (ILT) and Double Cantilever Beam (DCB) test configurations are simulated where randomly distributed defects are explicitly modeled on a critical fracture plane. The effective interlaminar tensile strength and the effective mode-I fracture energy are derived by matching the simulation results with appropriate homogenized models that do not consider the defects explicitly. The results from the computational parametric studies show that both the effective ILT strength and the effective mode-I fracture energy are quite sensitive to defects, scaling linearly with the defect area fraction on the critical fracture plane. The effects of defect size on the mode-I fracture behavior are also studied. It is shown that, for a fixed area fraction of the defects, the ILT strength is not sensitive to the defect size. On the other hand, the mode-I fracture propagation behavior is sensitive to the defect size especially when the defect size is greater than the fracture process-zone size of the delamination crack.