Bond quality assessment of CFRP lap joints using shear guided waves cutoff frequency.

Ensuring the integrity of carbon fiber reinforced polymer (CFRP) bonded structures is critical due to their widespread use in aerospace and other high-performance industries. However, inspecting the bondline in these structures remains a significant challenge due to the anisotropic nature of CFRP and the complexity of its bonding interfaces. Conventional guided waves-based inspection techniques, typically developed for isotropic materials, often fail to reliably indicate bond quality. To address this limitation, we propose a novel nondestructive assessment method based on the cutoff frequency of first-order shear guided waves, which are highly sensitive to variations in interfacial bonding. Our analysis confirms that, in anisotropic material, the cutoff frequency is independent of propagation direction, making it a stable and reliable detection parameter. A finite element model is developed to simulate wave propagation in bonded structures and to examine the relationship between bond quality and cutoff frequency. Experimental validation demonstrates that as bond quality deteriorates, the cutoff frequency decreases, highlighting its potential as a quantitative and robust metric for bond evaluation.