Wan Xiang, Tse Peter W, Chen Jingming, Xu Guanghua, Zhang Qing
School of Mechanical Engineering, Xi'an University of Science and Technology, Xi'an 710054, China; School of Mechanical Engineering, Xi'an Jiaotong University, Xi'an 710049, China; Department of Systems Engineering and Engineering Management, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, China.
Department of Systems Engineering and Engineering Management, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, China.
Ultrasonics. 2018 Jan;82:57-71. doi: 10.1016/j.ultras.2017.07.005. Epub 2017 Jul 10.
Second harmonic generation has been widely used in characterizing microstructural changes which are evenly distributed in a whole structure. However, few attention has been paid to evaluating localized micro-scale damages. In this paper, second harmonic reflection and transmission from the primary S0 mode Lamb wave interacting with a localized microstructural damage is numerically discussed. Schematic diagram for deriving fundamental temporal waveform and reconstructing the second harmonic temporal waveform based on Morlet wavelet transform is presented. Second harmonic reflection and transmission from an interface between the zones of linear elastic and nonlinear materials is firstly studied to verify the existence of interfacial nonlinearity. Compositions contributing to second harmonic components in the reflected and transmitted waves are analyzed. Amplitudes of the reflected and transmitted second harmonic components generated at an interface due to the interfacial nonlinearity are quantitatively evaluated. Then, second harmonic reflection and transmission from a localized microscale damage is investigated. The effects of the length and width of a microscale damage on WCPA (wavelet coefficient profile area) of the reflected and transmitted second harmonic components are studied respectively. It is found that the second harmonic component in the reflected waves mainly reflects the interfacial nonlinearity while second harmonic in the transmitted waves reflects the material nonlinearity. These findings provide some basis on using second harmonic generation for characterization and detection of localized microstructural changes.
二次谐波产生已被广泛用于表征在整个结构中均匀分布的微观结构变化。然而，很少有人关注评估局部微观尺度的损伤。本文对与局部微观结构损伤相互作用的基模S0兰姆波的二次谐波反射和透射进行了数值讨论。给出了基于莫雷特小波变换推导基波时间波形和重构二次谐波时间波形的示意图。首先研究了线性弹性材料区和非线性材料区界面的二次谐波反射和透射，以验证界面非线性的存在。分析了反射波和透射波中二次谐波分量的组成。定量评估了由于界面非线性在界面处产生的反射和透射二次谐波分量的幅度。然后，研究了局部微观尺度损伤的二次谐波反射和透射。分别研究了微观尺度损伤的长度和宽度对反射和透射二次谐波分量的小波系数轮廓面积（WCPA）的影响。发现反射波中的二次谐波分量主要反映界面非线性，而透射波中的二次谐波反映材料非线性。这些发现为利用二次谐波产生来表征和检测局部微观结构变化提供了一些依据。
