Behaviour of composite materials under impact loading

In this study, low velocity impact tests on the glass/epoxy, carbon/epoxy and glass/carbon hybrid laminated composite plates at 20, 90 and -50 °C temperatures were performed to investigate impact behaviors of the laminates. Impact responses of the composite specimens were characterized in terms of impact parameters such as permanent deflection, maximum contact force, maximum contact time, energy to maximum contact force, and total energy absorption at low, intermediate, and high impact energy levels. Energy profile diagrams and force versus deflection curves were plotted for each temperature and specimen type. Impact tests on the saturated specimens kept in seawater for 7 months were also conducted at the same impact energy levels as that of dry specimens. The initial damage, perforation and propagation energies were obtained for each temperature and specimen type. The impacted specimens were observed by visual inspection. A high-intensity light was used to identify the projected delamination areas in the impacted glass/epoxy composite laminates. The photographs of the cross-sections of the impacted specimens were taken. Delaminated surfaces were observed by an optical microscope. There point bending tests on the impacted specimens were also performed. In addition, mechanical properties of unidirectional glass/epoxy and carbon/epoxy composite plates were determined at 20 and 90 °C temperature. Thermal residual stresses at 20, 90 and -50 °C temperatures were obtained by using ANSYS software and the effects of the residual stresses on matrix cracking damage before impact were analyzed. The results showed that impact behaviors of the laminated composites were affected by the different environmental conditions.