EVALUATION OF SURFACE DAMAGE,DEGRADATION AND STRESS WITH BROADBAND SURFACE ELASTIC WAVES

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(1) A digital ultrasonic measurement system of the surface waves has been established to measure their velocities of the leaky Rayleigh, creeping and surface SV waves as well as attenuation of the leaky Rayleigh wave with line-focused broadband PVDF ultrasonic transducers of 10-50MHz. The relative precision of their velocities measured on fused quartz and 2017 aluminum alloy with a 10MHz transducer are 0.015,0.03 and 0.018%, respectively.(2) The densities of the surface layr of fused quartz and 2017 aluminum alloy were measure nondestructively by using the velocities of those surface waves and attenuation of the leaky Rayleigh wave. The measured values are agreed with those measured by Archimedes'method within 10%.(3) The acoustoelastic coefficients of Rayleigh wave on 2017 aluminum alloy are found to be-2.3 and 0.9x10^<-5>/MP_a for the loading and transverse direction.(4) Young's modulus of TiN coating of 4mum thickness on WC-Co substrate is estimated to be 400GP_a by using the dispersion of the leaky Rayleigh wave and a wave equations of layred structures. The value is consistent with the reported so far.Wave propagation excited by a line-focused transducer has been analyzed by FEM for an aluminum plate which is immersed in water. The calculated and measured velocities of the leaky Rayleigh and creeping waves agree within 2%. The attenuation of the leaky Rayleigh wave due to energy leak into water also agree well with the measured.The minute cracks generated in fatigue tests on stainless steel have been detected as a drop of amplitude spectra of the leaky Rayleigh wave in high frequency range.