Noncontact inspection of impact damage properties of woven fabric-reinforced composites after low-velocity impact by using air-coupled ultrasonic technique

The impact response to twill weave carbon fabric/epoxy composite laminate structure has been investigated by employing two types of the stacking sequences of composite laminate structure to low-velocity impact loadings by using a Drop-Weight Machine (CEAST 9350 drop tower). An engine hood is the intended application for the composites. The air-coupled ultrasonic C-scan technique (NAUT21) has been selected in order to characterize impact damage size, delamination, flaw detection, and damage in composite laminate structures. The effect of increasing impact energy was illustrated with both types of the stacking sequences of the composite laminate structures until complete perforation of specimens at 25 J due to degradation of mechanical properties of composite laminates. The failure processes of damaged specimens for different three impact energies (5 J, 15 J, and 25 J) were being evaluated comparing load–displacement curves and images of damaged samples were taken from both impacted and nonimpacted sides through C-scan. The performance index and absorbed energy of the tested structures were investigated. The primary damage modes were found to be fiber fracture, delamination, and matrix cracks.