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

(1)建立了表面波的数字超声测量系统，利用10-50MHz的线聚焦宽带PVDF超声换能器测量泄漏瑞利波、爬行波和表面SV波的速度以及泄漏瑞利波的衰减。用10MHz换能器在熔融石英和2017铝合金上测量其速度的相对精度分别为0.015、0.03和0.018%。(2)利用石英和2017铝合金表面波的速度和泄漏瑞利波的衰减，对石英和铝合金表面层的密度进行了无损测量。测量值与阿基米德法测量值在10%以内一致。(3) 2017铝合金在加载和横向上的瑞雷波声弹性系数分别为-2.3和0.9x10^<-5>/MP_a。(4)利用泄漏瑞利波的色散和层状结构的波动方程，估计WC-Co衬底上厚度为4mum的TiN涂层的杨氏模量为400GP_a。与目前报告的值一致。用有限元法分析了线聚焦换能器对浸入水中铝板的波传播特性。泄漏瑞利波和蠕变波的计算速度和测量速度一致在2%以内。由于能量泄漏到水中，泄漏瑞利波的衰减也与实测结果吻合较好。在不锈钢疲劳试验中产生的微小裂纹在高频范围内表现为泄漏瑞利波振幅谱的下降。

(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.