Wave mixing offers several practical benefits relative to harmonic generation for detecting both distributed and localised damage. An analytical model is proposed for predicting the frequency, mode and direction of propagation of the mixed modes arising from the nonlinear mixing of two incident guided-wave modes at an interface exhibiting contact acoustic nonlinearity. These predictions are validated by a finite-element (FE) analysis involving a unilateral contact law that models both clapping and frictional sliding at the interface. This analysis also provides quantitative insights regarding the optimal interaction angle between the incident waves in the case of shear-horizontal SH0 modes, and the dependence of the mixed-wave amplitude on the load ratio (i.e. ratio of contact stress to normal stress across the interface due to both incident waves). The non-collinear mixing of guided waves is also investigated experimentally for various values of contact stress and incident stress amplitude, demonstrating the existence of mixed waves, as well as showing that interface mixing leads to a higher amplitude mixed wave than that due to the background material nonlinearity. This higher amplitude combined with great flexibility in the choice of incident wave parameters (frequency, mode and direction) makes wave mixing an attractive practical approach for detecting contact acoustic nonlinearity at crack-like defects and interfaces. Experimentally, the maximum value of mixed-wave amplitude is obtained at the same value of contact stress for the various incident stress amplitudes, whereas the FE model shows a maximum at a unique value of the load ratio. This difference may be a consequence of surface roughness, which is not included in the FE model.

中文翻译：

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接触界面处非共线导波的非线性混合

与谐波生成相比，混波提供了多种实际优势，可用于检测分布式和局部损坏。提出了一种分析模型，用于预测混合模式的频率、模式和传播方向，该混合模式是由两个入射导波模式在呈现接触声非线性的界面处非线性混合引起的。这些预测得到了有限元 (FE) 分析的验证，该分析涉及对界面处的拍手和摩擦滑动进行建模的单边接触定律。该分析还提供了关于在横切水平 SH0 模式下入射波之间的最佳相互作用角以及混合波振幅对载荷比（即 由于两种入射波而产生的接触应力与跨界面法向应力的比率）。还通过实验研究了导波的非共线混合接触应力和入射应力幅度的各种值，证明了混合波的存在，并表明界面混合导致比背景混合波幅度更高的混合波材料非线性。这种更高的振幅与入射波参数（频率、模式和方向）选择的极大灵活性相结合，使混波成为一种有吸引力的实用方法，用于检测裂纹状缺陷和界面处的接触声学非线性。实验上，混合波振幅的最大值是在不同入射应力振幅的相同接触应力值下获得的，而有限元模型在负载比的唯一值处显示最大值。这种差异可能是表面粗糙度的结果，不包括在有限元模型中。