Pulse inversion technique for nonlinear ultrasonic harmonic measurements and its applications

摘要

For measurement of second harmonic amplitude to determine the nonlinear ultrasonic parameter β, pulse inversion technique that works on superimposition of two 180° out of phase transmitted signals has been implemented. The superimposed signal obtained after pulse inversion is found to be free from the fundamental component and the second harmonic amplitude is found doubled. It is observed that the accuracy in determination of β parameter is significantly enhanced by adopting the pulse inversion technique. The experimental error in determining the β parameter is reduced to 4.5% as compared to 18.9% resulted by the traditional Fast Fourier Transform (FFT) technique. The pulse inversion technique has been successfully applied to determine optimal ageing duration with desired mechanical properties in age hardened M250 grade Maraging steel and to study the influence of cold work on β parameter in AISI type 304 stainless steel. The observed changes in β parameter during ageing of Maraging steel has been explained based on the variations in hardness measurements. Optical microscopy and XRD based estimation of volume percentage of martensite have been used to explain the changes in β parameter during cold working of AISI type 304 SS.