复合材料板结构损伤监测的兰姆波谱元法研究

The principal goal of this research is to advance the technology of structural health management for composite plate using Lamb wave methods. A new composite structural health management framework is proposed to provide a baseline free damage quantification methodology. The methodology utilizes the First Order Shear Deformation Theory (FSDT) to formulate a new Wavelet Spectral Finite Element (WSFE) for Lamb wave propagation modeling, which can reduce the 3-D wave propagation computation to an equivalent 2-D computation. The novel WSFE It has several advantages over the current Spectral Finite Element method for wave propagation computation. In particular, the high frequency feature of the Lamb wave propagation can be captured and the "wraparound" effect can be minimized. In addition, the proposed method can greatly reduce the wave propagation computational demand due to model reduction. Experimental testing is used to validate the effectiveness and efficiency of FSDT-based WSFE. To quantify damage without using baseline signals, the FSDT-based WSFE model for Lamb wave propagation is constructed to obtain the dynamic stiffness matrix. Using the dynamic stiffness matrix and the measured Lamb wave signal, a Damage Force Indicator (DFI) for the structure can be computed. The element corresponds to the largest DFI value is regarded as the damaged location. To further quantify the damage in composite plates, signal damage features are extracted from the Lamb wave signal to formulate a damage prognosis model. Experimental validation is performed to validate the overall methodology. The study provides an viable solution for actual engineering problems where baseline signals are required but are difficult to be acquired accurately.

本研究的目的是提供一种对于复合材料板结构采用兰姆波实现实时健康监控的方法。研究以复合材料板结构为研究对象，针对现有谱元法兰姆波损伤监控计算方法无法准确建模兰姆波高频部分，存在“残响波干扰”，计算量过大等缺陷，重点探讨对于复合材料板结构的基于小波分析的兰姆波建模，提出一种结合一阶剪切形变理论的兰姆波有限元模型，并且通过和现有方法的比较（以经典层合理论为基础的谱元法模型和常规有限元方法），验证此模型在精确性及高效性方面的优势。最后针对复合材料层合板结构中常见的分层和筋条脱粘两种失效模式，研究不需要提前测量参考信号的兰姆波损伤监控方法，该方法通过以上小波谱元法建模获得的动刚度矩阵及实际测量的兰姆波信号计算损伤力因子，实现损伤检测及评价。最后通过实验的方式对提出的损伤监控方法进行验证。此研究能够解决工程实际中因参考信号测量所带的不确定因素大，实际可操作性差，无法实现实时结构健康监控等缺点。

在对于金属和复合材料平板类结构的损伤监测研究中，基于Lamb波的结构健康监测技术具有对微小损伤和初始损伤敏感、易于组成传感器网络、扫查面积大等多种优势，能够完成对板壳结构的裂纹损伤、腐蚀损伤、冲击损伤、焊点损伤、复合材料分层损伤等多种损伤的监测，被认为是目前最热门和最有发展前景的平板类结构实时健康监测方法。项目主要建立了基于一阶剪切变形理论的小波谱元法模型，模拟Lamb波在健康结构和含损伤结构中的传播，研究金属平板和复合材料平板中Lamb波的传播机理、Lamb波与损伤耦合作用机制，提出具有物理含义且能够表征损伤信息的特征值提取方法。提出基于小波谱元法的概率成像方法，实现对不同位置复合材料层合板分层损伤的监测。建立基于贝叶斯理论的金属裂纹定量监测方法，提高监测模型对外场复杂结构的适应性。（1）考虑平板结构横向剪切变形与转动惯量对Lamb波力学建模的影响，建立基于一阶剪切变形理论的小波谱元法模型；（2）建立了含横向裂纹损伤的小波谱元法模型，研究在脉冲回波和一发一收两种传感器布局形式下Lamb波与裂纹损伤耦合作用规律；（3）建立了基于小波谱元法的损伤概率成像方法；（4）建立基于贝叶斯理论的监测模型更新方法。本项目开展基于一阶剪切变形理论的小波谱元法Lamb波结构健康监测研究，研究Lamb波在铝合金板结构、复合材料层合板结构中的传播机理，提出铝合金裂纹损伤、复合材料层合板分层损伤的有效监测方法，为实际复杂结构基于Lamb波的健康监测应用提供技术支撑。