Session: Virtual Presentations in Acoustics, Vibration, and Phononics

Paper Number: 95409

95409 - Local Stress Measurement in Thin Aluminum Plates Based on Zero-Group-Velocity Lamb Mode 

The stress state of engineering structures is the key information for the reliability evaluation. Residual stress is usually generated during the production of structural parts and it is easy to be affected by the change of environment. Excessive residual stress will bring down the stability of the structure, leading to eventual structure failure. Compared to other stress measurement methods, the ultrasonic method has been widely studied and applied, due to theirs unique characteristics, such as nondestructive, deep penetration, and convenient for on-site inspection. Lamb wave technology is widely applied for testing and monitoring of large-scale plate-like structures. However, the Lamb wave acoustoelastic effect is not well studied, especially for the higher-order Lamb wave modes, which has higher stress sensitivity. Moreover, current ultrasonic stress measurement requires suitable length to measure the difference of time-of-flight. It brings difficulties in the local stress measurement. In this study, zero-group-velocity (ZGV) Lamb mode is proposed to measure the local stress in the aluminum plates. Firstly, Floquet-Bloch theory and Murnaghan hyperelastic material model were utilized to investigate the influence of applied stress on the dispersive characteristics of Lamb wave. By comparing the dispersion curves under different stress, it is found that the frequency of Lamb wave S1-ZGV mode is linearly changing with the stress level. As the S1-ZGV mode occurs near the cut-off frequency of S1, it implies that the stress in the plates can be evaluated by the variation of the frequency of S1-ZGV mode with a high sensitivity. Then, a series of numerical experiments were conducted to illustrate the feasibility and accuracy of local stress measurement in an aluminum plate based on ZGV mode. Both single localized stress and multiple localized stresses with Gaussian distribution were investigated. The reconstructed results based on S1-ZGV method agree well with the applied stress profile, proving that S1-ZGV method is a precise method to measure complex stress field. At last, a contact ultrasonic system was built for experimental validation. The wedges were tailored made by the Snell’s law to efficiently excite and receive the signal of S1-ZGV mode. The received signal was processed by time-frequency analysis and the S1-ZGV is confirmed by comparing to the dispersion curves. The frequency of S1-ZGV was obtained by spectra analysis after filtering out the direct wave part. Tensile experiments were carried out on a uniform plate to obtain the relation between S1-ZGV frequency and stress level. Then a step-wise plate was designed to generate different stress at different positions on a tensile test machine. The stresses were then evaluated by the calibrated frequency-stress relation. The measured stresses agreed well with the calculated stress, proving that S1-ZGV method is very effective for local stress measurement in plates.

Presenting Author: HE Pancong GuangDong University of Technology

Presenting Author Biography: Pancong He , born in 1999, a master candidate at Guangdong University of Technology, China. He received his bachelor degree from NanJing Tech University, China.His research interests include Lamb wave, Lcr wave and stress measurement. <br/>E-mail: 2316789031@qq.com<br/><br/>Maodan Yuan, born in 1988, is currently an assistant professor at Guangdong University of Technology, China. He received his PhD degree from Sungkyunkwan University, Korea. His research interests include nonlinear ultrasonic technology, guided wave and residual <br/>stress measurement. <br/>E-mail: mdyuan@gdut.edu.cn<br/><br/>Xuanrong Ji, is currently a Professor at Guangdong University of Technology, China. His current research focus is mainly placed on the novel design and fabrication of piezoelectric transducer, high-frequency ultrasonic array microscopy, phased array ultrasonic, guided wave detection, and large-scale ultrasonic wireless monitoring system. <br/>E-mail: xr.ji@gdut.edu.cn<br/><br/>Weiming Xuan, born in 1995, is currently a master candidate at Guangdong University of Technology, China. He received his bachelor degree from Guangdong Polytechnic Normal University, China, in 2018. His research interests include Lamb wave and stress measurement.<br/>E-mail: 772446573@qq.com

Authors:

HE Pancong GuangDong University of Technology
Yuan Maodan Guangdong University of Technology
Ji Xuanrong Guangdong University of Technology
Xuan Weiming Guangdong University Of Technology