Damage Behaviour of Ti/GFRP Laminates under Low-Velocity Impact Loading

Abstract

In the present paper, the impact responses and overall damages of Fibre-Metal Laminates based on titanium alloys and glass fibre-reinforced polymers (Ti/GFRP) as Ti/FRP laminate system were evaluated. Low-velocity impact tests using a drop-weight tower were conducted for the cross-plied GFRP laminates and the Ti/GFRP laminates, and the impact responses during impact loading were obtained. Impact damages such as cracks in titanium layer and delamination of titanium-GFRP interface or matrix cracks and interlaminar delamination in GFRP layer were observed from the impact direction. From the experimental evidence, it was found that the Ti/GFRP laminates showed same impact damage modes as of other types of Fibre-Metal Laminates. Internal damages in the Ti/GFRP laminates were restrained by the reinforcing effect of titanium and adhesive layer compared to the cross-plied GFRP laminates. The Ti/GFRP laminates showed two patterns of the impact responses and damages with the threshold impact energy of about 4.8J. With higher impact energy than this threshold, single crack was presented in titanium layer at non-impacted side. The interlaminar delamination area in GFRP layer increased sharply due to the occurrence of this crack. Numerical analysis model that represent the impact behaviour of the Ti/GFRP laminates using finite element method was suggested based on the damage observations. The impact responses obtained by the dynamic analyses agreed well with the experimental results. The calculated area of interlaminar delamination in GFRP layer as a function of impact energy showed same behaviour as seen in the experiments. As a consequence, it was shown by the analysis as well that the drastic increase in the internal damage area of the Ti/GFRP laminates was induced by the fracture in outer titanium layer under the out-of-plane impact loading.