Bond thickness effect on impact response and damage of adhesively-bonded graphite/epoxy composites

Adhesively-bonded composites are often subjected to impact during manufacturing or service. This impact may result in a reduction in strength and structural integrity of engineering components made of adhesively-bonded composite structures. In this study, an impact test was carried out on adhesively-bonded graphite/epoxy composite panels at different low impact energies, ranging from 5 to 20 J, using a drop-weight impact test equipment. The effect of bond thickness on impact response and the resulting damage was investigated. The resulting internal damage due to impact on the adhesive bondline was interrogated using ultrasonic nondestructive evaluation. The ultrasonic C-scan of the gated ultrasonic wave signal was acquired and the ensuing debond area was determined quantitatively for specimens joined by different thickness adhesive bonds. The results revealed that increasing the thickness of the bond increased the maximum contact force reached during impact. In addition, the shape and size of the debond area in the adhesive layer showed dependence on both bond thickness and impact energy.