Abstract
With the advantages of uniform stress transfer and weight reduction, adhesive joints are widely used in engineering. The propagation of non-linear Lamb waves in an adhesive joint with micro-cracks distributing in a random way is systematically investigated by using the numerical simulation method in this paper. A finite element model of the tri-layer adhesive structure with micro-cracks distributing randomly is established, and the Lamb wave mode pair with a matching condition of the phase velocity is chosen to examine the interaction of the micro-cracks with Lamb waves. The results show that the micro-cracks within the adhesive layer will lead to the generation of second harmonics. We also find that the Acoustic Non-linearity Parameters (ANP) increase with the propagation distance in the micro-crack damage zone and the density of the micro-cracks. However, ANPs are less concerned with the friction coefficients of the surface of micro-cracks. This numerical research reveals that non-linear Lamb waves can be employed to effectively characterize the micro-cracks related damages within an adhesive joint.
Highlights
Adhesively-bonded structures are widely employed in industries because of their inherent nature of providing uniform stress transfer, high fatigue resistance, and the reduction in structural weight [1].Under in-service conditions, defects such as voids, micro-cracks, disbonding and kissing bonds often occur in adhesive joints due to fatigue loading and environmental corrosion
The results showed that the micro-cracks, which lead to the generation of second harmonics, can be applied to simulate the early micro damages in structures
It is clear that the length of the microadhesive harmonics structurewith withthemicro-cracks distributing in a random way within the adhesive layer
Summary
Adhesively-bonded structures are widely employed in industries because of their inherent nature of providing uniform stress transfer, high fatigue resistance, and the reduction in structural weight [1]. As one of the most powerful non-destructive techniques, the ultrasonic detection method has been applied extensively in detecting such defects as voids, cracks and fractures in structural materials It is based on the principle of linear acoustic physics, including transmission, reflection, scattering, and absorption of the acoustic energy. According to different non-linear effects, sub-harmonic technology, acoustoelasticity, harmonic generation, and wave mixing are common methods for measuring the non-linearity in solids Both experimental investigations and theoretical studies show that these techniques can detect and evaluate micro damages effectively, and the sensitivity is much higher than traditional linear ultrasonic techniques [19,20,21,22]. The propagation of non-linear Lamb waves in a tri-layer adhesive structure model with micro-cracks distributing in a random way is systematically investigated using the numerical simulation method. This study is expected to provide a deeper understanding for the characterization of the damage of the adhesive layer with micro-cracks for the adhesive joints by effectively employing the non-linear Lamb waves
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