中文摘要：

在管道导波检测中损伤反射回波包含了丰富的损伤相关信息，对回波信号的全面分析有助于识别损伤的几何特征。纵向模态导波与损伤相互作用会发生双模态转换，即L（0，2）导波与L（0，1）导波之间的相互转换。由L（0，21导波转换而来的L（0，1）导波也反映了管道的损伤特征信息。利用数值模拟和实验方法，研究了损伤沿管道径向和周向扩展时L（0，1）和L（0，2）导波的反射特征。结果表明：L（0，2）导波与非贯穿型损伤相互作用会发生双模态转换现象，而与贯穿型损伤作用时，不发生双模态转换；对于周向长度一定的损伤，L（0，1）导波反射系数随损伤径向扩展呈先增大后减小的趋势，且损伤深度小于管道半壁厚时，L（0，1）导波与L（0，2）导波反射系数相当。研究结果为管道检测过程中评估损伤的径向深度提供了参考。

英文摘要：

A comprehensive analysis of a defect＇s reflection in guided wave-based pipeline inspection usually provides sufficient information about the defect. The interaction of the longitudinal mode waveguide with the defect results in a double mode conversion： the L（0,2） mode and L（0,1） mode. The L（0,1） mode, which is converted from the L（0,2） mode after the interaction with defects, provides significant information about the defect. The reflection coefficients of L（0,1） and L（0,2） mode from defects with different depths and circumferential extent has been investigated using finite element analysis and laboratory experiments. The results show that the double mode conversion only occurs when the L（0,2） mode interacts with non-through-thickness defects; For a defect of a given circumferential length, increasing the depth of the defect at first increases the reflection coefficient of L（0,1） mode and then starts to decrease it; The reflection of the L（0,1） is as strong as that of the L（0,2） mode when the defect depth is less than half of the wall thickness. Results from this research provide a reference for the assessment of defect depth in pipeline inspection.