Absolute and Relative Measurements of Ultrasonic Nonlinearity and Application to Quantitative Evaluation of Material Degradation

Abstract

Abstract Absolute and Relative Measurements of Ultrasonic Nonlinearity and Application to Quantitative Evaluation of Material Degradation

Jongbeom Kim Directed by Prof. Kyung-Young Jhang Dept. of Mechanical Convergence Engineering Graduate School, Hanyang University

The ultrasonic nonlinear technique has been regarded as a powerful nondestructive method for evaluating material degradation. This method is based on the ultrasonic nonlinear effect to evaluate the changes in the elastic properties of a material and measures the ultrasonic nonlinearity parameter, 𝛽𝛽, which is defined as the ratio of the amplitude of the second-order harmonic component to the square of the amplitude of the fundamental frequency component. There are two definitions for this parameter: the absolute parameter defined by the displacement amplitude and the relative parameter defined by the detected signal amplitude. Many researchers have measured the relative parameter, so that conventional piezoelectric transducers can be used, which is much easier and more practical than the absolute parameter measurement. However, the relative parameter can be used only for the relative comparison between before and after damage in a material. Therefore, the absolute nonlinearity parameter is still required to evaluate the material degradation quantitatively. In this study, the relationship between the relative and absolute parameters is identified and a novel method for estimating the absolute nonlinearity parameter from the relative nonlinearity parameters was proposed. The estimated absolute parameters were in good agreement with the measured absolute parameter. Furthermore, ultrasonic nondestructive evaluation methods have been limited to showing the correlation between the nonlinearity parameter and the material degradation. Thus, in this study, a method for directly evaluating the material degradation by estimating the strength variation was proposed. The estimated yield strength using the linear and nonlinear ultrasonic characteristics is similar with that obtained from the tensile test as a function of the aging time.