Kissing Bond Damage Detection Based on the Non-Reciprocity of Nonlinear Guided Waves in CFRP-Reinforced Steel Plates

Kissing bond damage, as an early stage of debonding in CFRP-reinforced structures, severely threatens the integrity and performance of structures. However, conventional ultrasonic guided wave methods are not sensitive to this sort of damage due to the micro scale of the damage and the complexity of the wave at the interface. To address this problem, the reciprocity of nonlinear guided waves is proposed to identify this damage and a novel reciprocity index based on the correlation coefficient of kissing bond damage-induced second harmonic waves is developed. A finite element model is established and kissing bond in CFRP-reinforced steel plate is simulated with a novel method, which is close to the actual condition of the kissing bond and can help reveal the interaction between guided waves and the interface. Experimental tests are also carried out to verify the proposed method. In addition, to prove the high efficiency of the proposed method, correlation coefficients of directly received signals are calculated to compare with the proposed reciprocity index. Both simulation and experiment results illustrate that the reciprocity index rises as the length of kissing bond increases, while correlation coefficients of directly received signals did not show a monotonic trend as the damage length changes, reflecting the validity and high sensitivity of the proposed method in identifying and quantitatively evaluating kissing bond damage in CFRP bonded steel structures.