Experimental Evaluation of Nonlinear Wave/Damage Interaction for Delamination Detection in Laminated Composites

Structural health monitoring (SHM) deals with the early detection of structural damages to prevent catastrophic failures and is expected to provide major improvements with respect to safety and maintenance costs. With the increasing development of aeronautic industry, composite materials are being more and more widely used. In this case, the SHM of composite structure is crucial, especially the monitoring of local delamination of plies in composite materials. This paper presents an investigation on the detection of delamination type damage in carbon fiber reinforced polymer (CFRP) composite plates based on nonlinear acoustic effects. The LASER shock wave technique is used to generate realistic delamination in the composite plates. A damage index (DI) is proposed in this paper based on total harmonic distortion (THD) to evaluate the nonlinear acoustic effects induced by delamination. Experiments are conducted on four plates containing different sizes of delamination, including one undamaged plate for reference. Results show that acoustic nonlinearities are generated due to the presence of a realistic delamination damage, and the proposed DI is appropriate to evaluate the influence of the delamination size on the nonlinear acoustic effects under different excitation amplitudes.