Measurement of Frequency-Dependent Shear Wave Attenuation Coefficients Using an Oblique Incidence Pulse-Echo Ultrasonic Method

A pulse-echo oblique incidence technique for determining the frequency-dependent attenuation of ultrasonic shear waves in metallic materials is considered and improved. To measure the attenuation coefficient, the wave signals are measured when the waveform-converted shear waves propagate over different distances. A diffraction correction is introduced to minimize the beam-spreading loss of the wave, and narrowband signals are used to minimize the effects of a downward shift in frequency. The attenuation coefficient is measured at a certain frequency, and experiments are performed over a broad bandwidth range of frequencies; a curve fitting method is then applied to these attenuation values to ensure an accurate estimate of the frequency-dependent shear wave attenuation. Experiments are performed to evaluate the effectiveness of the proposed method, and the frequency-dependent shear attenuation curves for some commonly used metallic materials are obtained. One of the most significant findings from the results is that the shear wave attenuation follows a power law dependence on frequency with exponents between 2 and 3, which lie between the theoretical values of the exponents from the classical stochastic and Rayleigh scattering theories. The effects of grain size on shear wave attenuation are investigated, and a quantitative comparison is drawn between the experimentally observed attenuation and that predicted by the classical theory. The proposed measurement method and the experimental results presented here are expected to provide good references for researchers interested in frequency-dependent shear wave attenuation behavior.