Propagation path bending of ultrasonic guided waves in composite plates with variable thickness

This paper discovered the propagation path bending phenomenon of ultrasonic guided waves in composite plates with variable thickness (CPVT). After analysing the coupling effects of the structure thickness variation and the material anisotropy on the propagation path of ultrasonic guided waves, a mathematical model for calculating guided wave propagation paths is proposed. CPVT face dual challenges during non-destructive testing. On the one hand, the structural thickness variation induces a gradient in guided wave velocity, causing the propagation path to bend. On the other hand, the material anisotropy leads to the velocity anisotropy and tilt effect, which alters the guided wave propagation direction and further complicates the propagation path. This paper establishes a mathematical model to solve ultrasonic guided wave propagation paths in CPVT to describe the complex propagation characteristics accurately. The slowness diagram is introduced to solve the guided wave propagation paths affected by the tilt effect and velocity anisotropy. The FEM calculation and experimental studies were conducted on carbon fibre reinforced polymer (CFRP) plates with variable thickness to verify the propagation path bending characteristics of the guided wave. This research extends the theoretical framework of the ultrasonic guided wave propagation mechanism in anisotropic composite structures with variable thickness. It provides a theoretical basis for improving the damage detection accuracy in CPVT.