Numerical Simulation of Contact Acoustic Nonlinearities in Damaged CFRP Laminates Through Laser-Induced Guided Waves

The importance of Carbon Fiber Reinforced Polymer (CFRP) materials in numerous industries demands more accurate and timely damage identification methods. Delamination, a typical damage mechanism, heavily affects laminates' performance and requires prompt detection to ensure the safeness and operability of CFRP structures. This paper explores the use of guided waves to excite contact acoustic nonlinearities (CANs) in a damaged quasi-isotropic CFRP laminate. Delamination-induced CANs are exploited to identify the shape and position of delamination. The Finite Element Method (FEM) is used to model CAN generation and propagation. In the numerical model, a Gaussian laser beam heating the laminate surface induces Ultrasonic Guided Wave (UGW) propagation. The vertical displacement of the damaged laminate is measured by simulating a Scanning Laser Doppler Vibrometer (SLDV). Using 2D Continuous Wavelet Transformation (2D-CWT), the 2D wavefield is converted into the spatiotemporal frequency domain and analyzed to detect resonance frequencies. Two case scenarios are analyzed for a 16 plies CFRP laminate: delamination between the 13th and 14th layer (near the surface) and delamination between the 4th and 5th layer (near the bottom). The ability of this method to detect and assess both shallow and deep delamination in CFRP laminates is confirmed.