Lamb波理论及层合板冲击损伤的实验研究

从理论上分析了板中Lamb波信号的传播特性,并给出Lamb波在板中传播的频散方程。理论分析及实验均表明,Lamb波的频散特性与复合材料结构损伤有着直接的联系,而且最低阶的对称和反对称Lamb波模态对层合板的损伤比较敏感,但应用Lamb波的频散效应监测结构的损伤在检测技术上还难以实现。根据板中导波形成Lamb波的共振原理,板中应力波的幅频特性很大程度上反映了Lamb波的谐振特征。因此,利用压电元件的压电阻抗谱分析应力波的各阶模态频率及振幅对结构损伤的变化,能够反映材料内部损伤与Lamb波的频散特性。文中针对表面粘贴压电元件的层合板智能结构,建立了包含Lamb波谐振模式的压电阻抗计算模型。冲击损伤试件的实验表明,由于结构损伤的出现压电阻抗谱中的模态频率及其阻抗幅值等特征信息将发生变化。因此,引入应力波损伤因子可以对结构冲击损伤的存在和程度进行初步评价。该方法基于结构的机-电动态阻抗特性,不受结构的几何形状限制,测试用的压电元件成本低,方法简单可行,有望在智能结构的健康诊断方面获得应用。

Lamb Wave Theory and Experimental Study on Impact Damage in Laminated Plate

The propagation characteristics of Lamb waves in the elastic plate are analyzed theoretically and their dispersion equations are presented. It is theoretically and experimentally indicated that the dispersion characteristics of Lamb waves are concerned directly with the damages in the compositive material structures, and the lowest symmetrical or anti-symmetrical Lamb modes are more sensible of the damage in laminated plates. But it is technologically difficult to distinguish the damages in the structures using the dispersion characteristics. Because the frequence spectrums of stress waves that propagate in elastic plates are characterized with the vibration modes of Lamb waves, therefore the changes of mode frequencies and values of the stress waves can reflect the relation between dispersion characteristics of Lamb waves and the damages in the materials. The computational models of piezoelectric dynamic impedance for laminated plate pasted PZT wafer are established. The results of the experiment study on impact damaged pieces show that the emergence of structure damages makes such characteristic information as mode frequencies and values of piezoelectric impedance changed. Hereby, stress wave damage factor (SWDF) is introduced, by which the presence and extent of impact damages in structures may be evaluated. The electro-mechanical impendance method is simple, effective and may be used in the health monitoring of smart structures.