阶梯板兰姆波散射特征模式展开法研究

Scattering Characteristics of Lamb Wave of Step Plate

基于模式展开的方法,求解阶梯板对于不同兰姆波模式入射时的散射声场。分析了具有不同结构特点的阶梯板对于低频a0模和s0模的散射规律。研究发现,阶梯板两侧任意一组模式之间的能量透射系数幅值相等。对于同一模式,透射系数与反射系数与阶梯板厚度差在低频时具有单调线性特征。板厚差越大,同一模式的反射系数越大,透射系数越小。如果板厚变化相对于中心面对称,那么频率增加并不能提高s0模的检测灵敏度。同样厚度差下,板厚变化越接近对称,s0模和a0模的透射系数越高,模式转换越少;如果沿板厚减小方向传播,s0模式在板厚对称时反射最少,a0模式则最多;如果方向相反,结果正好相反。能量散射系数能反映出实际检测时收发不同模式时接收信号的幅度,对于实际检测方案确定具有指导意义。

Based on mode decomposition method, the scattering field of different Lamb waves of step plate was investigated. The characteristics of ao and so modes at low frequency are analyzed. It＇ s found that the amplitudes of the energy transmission coefficients are equal for two modes at both sides of the step plate, regardless of the transmission directions. It＇ s also found that the transmission coefficients decrease linearly and the reflection coefficients increase linearly as the thickness margin increases. If the thickness variation is symmetrical with the central plane, the frequency increase could not improve the sensitivity to the thickness difference. The closer the structure is to symmetry, the more energy is transmitted to opposite side in the same mode and the less energy is converted to other modes. In the direction of thickness decrease, so mode reaches the smallest and ao mode reaches the biggest at the symmetric point of plate thickness, while in opposite direction, the results are contrary for both modes. The energy scattering coefficients can reflect the amplitude of signals, so they are important indexes for inspection plan selection.