Interaction of lamb waves with the edges of a delamination in CFRP composites

Delamination is one of the most common types of damages in carbon fiber reinforced polymer composites. This paper analyzes the interaction of fundamental symmetric (S0) and anti-symmetric (A0) mode Lamb waves with the start and end of a delamination using finite element simulations. Propagations of Lamb waves in a 4-layer [0/90]s laminate are compared with propagations obtained in a 1-layer [0] and a 3-layer [90/90/0] sub-laminates, which are the two sub-laminates separated by the delamination. Results show that the Lamb waves travel at different velocities in the delaminated region and in the healthy region. The signals obtained in the delaminated region were also compared with the excitation. It was found that mode conversion happened at the start of a delamination. After passing the start of a delamination, a new mode other than the excitation mode can be identified. And at the end of a delamination, mode conversion only happened when S0 waves arrived. A new A0 wave can be found after S0 waves passing the end of a delamination. However, after A0 waves passing the end of a delamination, they continued to travel and only generate a very small S0 wave which can be neglected.