Carbon Fiber Reinforced Plastic (CFRP) composite were studied for low-velocity impact damage. Quasi-isotropic laminates of size 150 x 150 mm were subjected to impact simulating tool drop and runway debris using drop-weight and gas-gun impact testing machines respectively. Impact energies were chosen based on the practical conditions a typical aircraft structure encounters. Ultrasonic pulse-echo immersion scanning was carried out using a 3 axes automated system. The system has a provision for depth gate setting facilitating the layerwise scanning of the laminates. Thus, the layerwise distribution of damage was obtained. Conventionally damage is assumed to be elliptical and the area is calculated by measuring major and minor axes. However, this is a very crude way of representing the area and it often overestimates the size of damage. Therefore, a software was developed using image processing technique wherein the scanned points showing the damage below a certain threshold attenuation level were cumulated and the percentage area of damage was calculated by dividing this count with the total number of scanned points. This gives an accurate measure of the size of damage.

The results of the study indicate that threshold energy for damage initiation could be quantified below which specimen show no sign of damage due to impact. All the energy upto this level is absorbed in elastic deformation. The damage induced is nearly elliptical in shape and the damage distribution through thickness shows a near conical distribution. Total damage is effected by complex interaction of contact, interlaminar, flexural and membrane stresses. Layerwise scanning of specimens show that damage increases with depth with maximum damage occurring at about 2/3 thickness. It was observed in many cases that the maximum damage occurs between layers with major difference in fiber orientation such as 0/90 and ±45.