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超聲波焊接原理

諧振聲譜法表征圓柱形工件彈性性能（二）

研究中使用短脉冲激发声源，以期覆盖包含所有谐振频率在内的较宽频率范围。图9-3是从铝棒反射回来的典型的背散射回波波形，其中第一部分是镜面反射回波，其后的部分则可分别归类于Rayleigh和Whispering Gallery波。

1.材料的諧振聲譜表征法(MCRAS)

谐振声谱表征法(Material Characterization by Resonance Acous-tic Spectroscopy,MCRAS)是指从各向同性弹性体的形状函数测量结果，提取出有关材料弹性性质的信息。在MCRAS中，借助计算机迭代算法，通过使实测和计算所得的形状函数的频率相匹配，從而可以得到固體彈性圓柱體工件的彈性性能。

實踐表明，所有的諧振頻率都對剪切波速度 (因此還有拉密常數λ)的擾動有一定的敏感性，但只有部分諧振頻率對縱波速度(因此還有拉密常數λ)的變化敏感，如圖9-4和圖9-5所示。采用MCRAS，通過叠代算法，利用諧振頻率對變化的高度敏感性，可以計算出相應的值的值也可以采用類似方法加以確定。

采用MCRAS和时间渡越测量法( time-of-flight measurement)分别对铝和钢样品的弹性性能进行了检测，结果见表9-1。表中数据下面的括号中给出了相速度测量的不确定度。所用的铝棒和钢棒尺寸分别为Φ7.67mmx280mm和Φ 8.02mmx300mm。采用與試樣同樣材料制成的樣品，然後通過分別測定它們的質量和體積，計算出鋁和鋼的密度分別爲 =2694kg/m³和 =7828kg/m³。密度測量的不確定度小于0.3%。將時間渡越測量法和MCRAS的測量結果進行比較表明，兩者符合得很好。

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諧振聲譜法表征圓柱形工件彈性性能（三）

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