2008 Volume 79 Issue 4 Pages 289-297
Over the past few decades nonlinear ultrasonic has been researched actively for the purpose of inspection technology for closed clacks or estimation of bonding quality of dissimilar materials. Nonlinear ultrasonic is a harmonic signal generated by a material’s nonlinear stress-strain relation or nonlinear reflection phenomena at a closed crack. Considering the practical application of the signal, it is indispensable to establish a calibration method. Reference reflectors, such as flat bottom holes or back wall, are used in the application of conventional pulse echo ultrasonic inspection. However, calibration methods of the nonlinear ultrasonic signal have not been established yet. This paper is intended to investigate calibration method of nonlinear ultrasonic signal. A convex Newton lens was utilized for the purpose of understanding acoustic signal response around a narrow gap. A new calibration test block made of stainless steel was designed to generate a harmonic signal. As a result, effectiveness of calibration of nonlinear ultrasound signal using the block was confirmed.
