Sun Maoxun, Xiang Yanxun, Shen Wei, Liu Hongye, Xiao Biao, Zhang Yue, Deng Mingxi
School of Mechanical Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China.
School of Mechanical and Power Engineering, East China University of Science and Technology, Shanghai 200237, China.
Materials (Basel). 2023 Mar 1;16(5):2039. doi: 10.3390/ma16052039.
Nonlinear guided elastic waves have attracted extensive attention owing to their high sensitivity to microstructural changes. However, based on the widely used second harmonics, third harmonics and static components, it is still difficult to locate the micro-defects. Perhaps the nonlinear mixing of guided waves can solve these problems since their modes, frequencies and propagation direction can be flexibly selected. Note that the phenomena of phase mismatching usually occur due to the lack of precise acoustic properties for the measured samples, and they may affect the energy transmission from the fundamental waves to second-order harmonics as well as reduce the sensitivity to micro-damage. Therefore, these phenomena are systematically investigated to more accurately assessing the microstructural changes. It is theoretically, numerically, and experimentally found that the cumulative effect of difference- or sum-frequency components will be broken by the phase mismatching, accompanied by the appearance of the beat effect. Meanwhile, their spatial periodicity is inversely proportional to the wavenumber difference between fundamental waves and difference- or sum-frequency components. The sensitivity to micro-damage is compared between two typical mode triplets that approximately and exactly meet the resonance conditions, and the better one is utilized for assessing the accumulated plastic deformations in the thin plates.
非线性导波因其对微观结构变化具有高灵敏度而受到广泛关注。然而，基于广泛使用的二次谐波、三次谐波和静态分量，仍然难以定位微观缺陷。也许导波的非线性混合可以解决这些问题，因为它们的模式、频率和传播方向可以灵活选择。需要注意的是，由于被测样品缺乏精确的声学特性，通常会出现相位失配现象，这可能会影响从基波到二次谐波的能量传输，并降低对微损伤的灵敏度。因此，对这些现象进行系统研究以更准确地评估微观结构变化。从理论、数值和实验上发现，差频或和频分量的累积效应会因相位失配而被打破，并伴随着拍频效应的出现。同时，它们的空间周期性与基波和差频或和频分量之间的波数差成反比。比较了两个近似和精确满足共振条件的典型模式三重态对微损伤的灵敏度，并利用较好的一个来评估薄板中的累积塑性变形。
