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Nondestructive Evaluation using Nonlinear Characteristics of Surface Acoustic Wave

Title
Nondestructive Evaluation using Nonlinear Characteristics of Surface Acoustic Wave
Author
전지현
Alternative Author(s)
전지현
Advisor(s)
장경영
Issue Date
2021. 2
Publisher
한양대학교
Degree
Doctor
Abstract
The potential of the nonlinear ultrasonic technique as a technique that can diagnose material damage in early-stage has been verified by many researchers in the nondestructive evaluation field. There are various techniques using the nonlinear characteristics of ultrasound, and this thesis focused on the acoustoelastic effect and acoustic nonlinearity parameters. The nonlinear characteristics occur in all types of ultrasonic waves and this is the same for surface acoustic waves. The surface acoustic wave is optimized for surface area inspection. Surface area contact with the external environment, so it is directly exposed to external environmental effect. Therefore, the evaluation of the integrity of the surface area is important to diagnose the integrity of the entire material. In this thesis, researches for material integrity evaluation using the nonlinear characteristic of surface acoustic waves were performed. The nonlinear ultrasonic technique of the surface acoustic wave meets the need for a surface inspection technology and the nonlinear ultrasonic technology. Research on nondestructive testing techniques using nonlinear characteristics of surface acoustic waves has been conducted by many researchers. However, areas that need to be supplemented for the practical application of the nonlinear ultrasonic technique still remains. In this thesis, studies were conducted for increase the utility of the surface acoustic wave nonlinear ultrasound technology, which has been proven that excellence in material evaluation. This thesis composed of two parts, one is stress estimation using acoustoelastic effect and the other is acoustic nonlinearity parameter measurement for material evaluation. In the part of stress estimation, the stress estimation method using the acoustoelastic effect applicable to weakly anisotropic materials was proposed. The proposed stress estimation method is simple and can estimate not only magnitude of stress but also direction of stress. The effectiveness of the proposed method in anisotropic materials has been numerically and experimentally verified. The effectiveness of the proposed method was verified by stress estimation error is very small in anisotropic materials. As another nonlinear ultrasonic technique, researches about acoustic nonlinearity parameters were performed. Both relative acoustic nonlinearity parameters for evaluating the relative damage and the absolute acoustic nonlinearity parameter for quantitative evaluation were discussed. First, the fully non-contact method using the laser is introduced for the measurement of relative acoustic nonlinearity parameter via surface acoustic wave. In order to improve the utilization of nondestructive evaluation technology using acoustic nonlinearity parameters, it is necessary to introduce a fully non-contact technology that is advantageous for field application. Heat-treated specimens were used to confirm the feasibility of material evaluation of the relative acoustic nonlinearity parameters of surface acoustic waves measured by a fully non-contact technique. The possibility was verified by confirming that the relative nonlinear parameter measurement results correlate with the fracture test results. Next, a method of estimating absolute parameter values using relative acoustic nonlinearity parameter of SAWs was proposed and experimentally verified. As an indirect method applicable to dissimilar materials, a fully non-contact measurement method has been introduced. The absolute acoustic nonlinearity parameters were estimated by the proposed technique using the ratio of relative acoustic nonlinearity parameters and a compensation factor involving the wavenumber. The proposed method was verified through the results that the estimated values for the three materials showed almost the same values as those measured by the conventional method. In this paper, studies were conducted to increase the field applicability of the nonlinear ultrasonic technology of surface acoustic waves. A stress estimation method applicable to anisotropic materials was developed by using the acoustoelastic effect of surface acoustic waves, and a method of measuring relative and absolute acoustic nonlinearity parameters using fully non-contact surface acoustic waves was developed. All techniques have been verified for their effectiveness through experimental verification. These research results show that the non-destructive testing technology utilizing the nonlinear characteristics of surface waves will be applied and utilized in various fields requiring soundness evaluation.
URI
https://repository.hanyang.ac.kr/handle/20.500.11754/159120http://hanyang.dcollection.net/common/orgView/200000485638
Appears in Collections:
GRADUATE SCHOOL[S](대학원) > MECHANICAL CONVERGENCE ENGINEERING(융합기계공학과) > Theses (Ph.D.)
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