Impact Damage Detection in Composite Structures Considering Nonlinear Lamb Wave Propagation

To detect micro-structural damages like fiber/matrix cracks and delaminations in composite materials accurately new methods are developed. Previous works have investigated and shown that the acoustical nonlinearity parameter is a good tool to detect micro-structural damages like plasticity in metal and fatigue damages in metal and composites. In this work, the second harmonic generation is used to analyze composite specimens for impact damages. Therefore, Lamb waves are launched and detected by a piezoelectric actuator and sensor, respectively, at a certain frequency to generate cumulative second harmonic modes. The excitation frequency has to meet special conditions. The signal processing is done by using the wavelet transform to avoid misinterpretations that may occur using the short-time Fourier transform. The Morlet wavelet is used as the mother wavelet. The results of the relative acoustical nonlinearity parameter are compared to the development of the group velocity due to impact damages. It is shown that the relative acoustical nonlinearity parameter is more sensitive to impact damages than the development of the group velocity.