Abstract
This study was investigated the nondestructive characteristics of the damage caused by low-velocity impact on symmetric cross-ply laminates. These laminates were $[0^{\circ}/90^{\circ}]{_{16s,}}\;{_{24s,}}\;{_{32s,}}\;{_{48s}}$, that is, the thickness was 2, 3, 4 and 6 mm. The impact machine, model 8250 Dynatup Instron, was used a drop-weight type with gravity. The impact velocities used in experiment were 0.75, 0.90, 1.05, 1.20 and 1.35 m/sec. The load and deformation were increased as impact velocity increase. Even if the load increased with laminates thickness in same impact velocity, the deformation decreased. The extensional velocity was a quick as laminate thickness increase in same impact velocity and as impact velocity increase in same laminate thickness. In ultrasonic scans, damaged area was represented an dimmed zone. This is due to the fact that the wave, after having been partially reflected by the defects, has not enough energy to tough the oposite side or to come back from it. The damaged laminate areas were different according to the laminate thickness and the impact velocity. The extensional velocities became lower in if direction and higher in $0^{\circ}$ direction when the size of the defects increases. But, it was difficult to draw any conclusion for the extensional velocities in $45^{\circ}$ direction.