Nonlinear wave mixing provides a potential method to evaluate localized micro-damage in structures. The wave mixing technique has some unique advantages over the nonlinear ultrasonic technique based on the higher harmonic generation, such as frequency selectivity, which can separate harmonic components generated due to instrumentation. In this paper, we numerically studied the frequency mixing response induced by the nonlinear interaction of two primary Rayleigh waves in a concrete material. The nonlinearity considered in the present study is due to crack-wave interaction, which is often called contact acoustic nonlinearity (CAN). A limited number of experimental studies were conducted on concrete prisms to evaluate surface cracks. Both numerical and experimental results illustrate the generation of the second- and third-order combined harmonics, which can be utilized to detect and localize subsurface cracks in concrete structures. The newly discovered third-order combined harmonics, which result from the mutual interaction between the primary Rayleigh waves and their induced second-harmonic waves, can be exploited to characterize micro-damage in various applications.

中文翻译：

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基于混合谐波生成的损伤混凝土非线性超声评价

非线性波混合提供了一种潜在的方法来评估结构中的局部微损伤。与基于高次谐波产生的非线性超声技术相比，混波技术具有一些独特的优势，例如频率选择性，可以分离由于仪器产生的谐波分量。在本文中，我们数值研究了混凝土材料中两个初级瑞利波的非线性相互作用引起的混频响应。本研究中考虑的非线性是由裂波相互作用引起的，通常称为接触声学非线性 (CAN)。对混凝土棱柱进行了有限数量的实验研究以评估表面裂缝。数值和实验结果都说明了二阶和三阶组合谐波的产生，可用于检测和定位混凝土结构中的地下裂缝。新发现的三阶组合谐波是由初级瑞利波与其诱发的二次谐波之间的相互作用产生的，可用于表征各种应用中的微损伤。