厚梁结构中的超声导波传播与损伤识别

基于导波的结构健康监测技术研究中,结构厚度与不同损伤形式对导波传播特性的影响是该技术在工程应用中对实际结构进行损伤识别的关键。通过导波在厚梁结构中传播时所表现出的特性,分析并试验研究损伤对导波传播的影响。通过在结构中引入切槽损伤,理论分析与试验研究导波在有损结构中的传播特性。以此为基础,重点研究疲劳裂纹损伤。试验得出导波在厚梁结构中的实际传播速度,并由此分析损伤反射波中的波包成分,研究并总结损伤大小对导波幅值、相位和到达时间的影响规律。分别对结构中的对称和非对称损伤进行研究,验证具有非对称损伤结构中模式转换波包的存在,分析模式转换波包的形成与传播机理,研究不同的非对称损伤对模式转换波包形式的影响。此外,还介绍了试验试件和疲劳裂纹的加工过程。总结了切槽损伤与疲劳裂纹损伤对导波传播的不同影响。

Research on Propagation of Guided Waves in Thick Beam and Crack Damage Identification

In guided wave-based structural health monitoring technique,structure thickness and different damage forms impacting upon the propagation of guided wave plays a crucial role in the application of this technique to engineering practice.Propagation characteristics of guided waves in thick steel beam and the interaction between damages(cracks and notches) and guided waves are investigated.Mechanism of guided wave propagation in damaged structures is investigated by introducing cutting damages.Moreover,influence of the typical damage form in steel structures,fatigue crack,to guided wave propagation is further studied to verify the results obtained by using finite element analysis(FEA) method and notch simulation.Actual group velocities of guided waves in thick beam are calculated from experimental wave signals.The damage-reflected wave packages are therefore analyzed.Relations between the damage size and amplitude,phase and arrival time of guided waves are proposed for further applications in damage detection.Difference from the through-the-thickness damage in plate structure,crack/notch in thick beam can be symmetric and asymmetric.Effects of these two damage forms to guided wave propagation are inspected and summarized.Mechanism of guided wave mode conversion is analyzed and verified by using FEA method and experimental results.