Generation mechanism of nonlinear ultrasonic Lamb waves in thin plates with randomly distributed micro-cracks

Youxuan Zhao; Feilong Li; Peng Cao; Yaolu Liu; Jianyu Zhang; Shaoyun Fu; Jun Zhang; Ning Hu

doi:10.1016/j.ultras.2017.04.004

Generation mechanism of nonlinear ultrasonic Lamb waves in thin plates with randomly distributed micro-cracks

Ultrasonics. 2017 Aug:79:60-67. doi: 10.1016/j.ultras.2017.04.004. Epub 2017 Apr 12.

Authors

Youxuan Zhao¹, Feilong Li¹, Peng Cao², Yaolu Liu¹, Jianyu Zhang¹, Shaoyun Fu¹, Jun Zhang¹, Ning Hu³

Affiliations

¹ College of Aerospace Engineering, Chongqing University, Chongqing 400044, China.
² Department of Hydraulic Engineering, Tsinghua University, Beijing 100084, China.
³ College of Aerospace Engineering, Chongqing University, Chongqing 400044, China; Key Laboratory of Optoelectronic Technology and Systems of the Education Ministry of China, Chongqing University, Chongqing 400044, China. Electronic address: ninghu@cqu.edu.cn.

PMID: 28433810
DOI: 10.1016/j.ultras.2017.04.004

Abstract

Since the identification of micro-cracks in engineering materials is very valuable in understanding the initial and slight changes in mechanical properties of materials under complex working environments, numerical simulations on the propagation of the low frequency S₀ Lamb wave in thin plates with randomly distributed micro-cracks were performed to study the behavior of nonlinear Lamb waves. The results showed that while the influence of the randomly distributed micro-cracks on the phase velocity of the low frequency S₀ fundamental waves could be neglected, significant ultrasonic nonlinear effects caused by the randomly distributed micro-cracks was discovered, which mainly presented as a second harmonic generation. By using a Monte Carlo simulation method, we found that the acoustic nonlinear parameter increased linearly with the micro-crack density and the size of micro-crack zone, and it was also related to the excitation frequency and friction coefficient of the micro-crack surfaces. In addition, it was found that the nonlinear effect of waves reflected by the micro-cracks was more noticeable than that of the transmitted waves. This study theoretically reveals that the low frequency S₀ mode of Lamb waves can be used as the fundamental waves to quantitatively identify micro-cracks in thin plates.

Keywords: Lamb waves; Micro-cracks; Numerical simulation; S(0) mode; Ultrasonic nonlinearity.

Publication types

Research Support, Non-U.S. Gov't