中文摘要：

利用非线性导波检测早期损伤的潜在优势，在于其对微裂纹或以微结构变化的形式表现出来的材料性能退化的敏感性．而长距离传播能力使得振幅具有累积效应的非线性二阶谐纵向导波成为检测管道的理想方法．论文提出了在均匀各向同性的应力自由弹性固体管道中，产生轴对称二阶谐纵向导波的方案，该方案使用同频零阶纵向导波作为激励波．根据相速度匹配条件得到与此方案相对应的可能的谐导波生成点后，利用另一条件即非零功率流对生成点进行了数值验证，最终确定了在管道中产生二阶谐纵向导波的生成点．

英文摘要：

The potential advantage of using nonlinear guided waves to detect early damage is their sensitivity to micro-cracks or degradation in the form of micro-structural changes. The ability to long-distance communication makes the nonlinear second-order harmonic longitudinal guided wave with the cumulative effect of amplitude to become the ideal method of testing pipe. A scheme is presented to generating axisymmetric second-harmonic longitudinal guided waves in a homogeneous, isotropic, stress-free elastic solid pipe with the same frequency of the zero-order longitudinal guided wave as the excitation wave. After the possible harmonic guided wave generation point is obtained according to the phase velocity matching conditions, the numerical validation for the generation point is conducted with using another condition of non-zero power flux. Finally, the operating points to generate second-harmonic longitudinal guided waves in pipes are determined.