Effects of voids on residual tensile strength after impact of hygrothermal conditioned CFRP laminates

This paper presents a study on the effect of porosity, the environmental factors and impact energies on the impact resistance and damage tolerance properties of carbon/epoxy laminates. Impact tests on the carbon/epoxy laminates with three porosity levels were conducted at five impact energy levels of 3 J, 6 J, 9 J, 12 J and 15 J at the room temperature. The damage area and the dent depth were assessed combined effects of different impact energy and porosity levels. The damage area was evaluated by visual inspections and ultrasonic C-scan measurement. The thermal deply technique was used to evaluate the damage evolution behavior. Non-impacted and impacted laminates were exposed to the room temperature, the hygrothermal, and the drying environments, followed by tensile test performed at the room temperature. The curves of the impact resistance and damage tolerance of the tested laminates mutated at the impact energy of 9 J. The thermal deply technique reveals the failure mechanism of the impact damage mutation of the tested laminates when the impact energy exceeds the threshold 9 J.