复合材料冲击损伤的非线性超声导波混叠检测方法研究

Low velocity impact damage is taken as a major concern related to the structural integrity of composite structures. To maintain the safety of long time in-service of composite structures, there are demanding needs to detect and locate the impact damage in composites. Nonlinear ultrasonic guided waves technique has been accepted as a useful tool for detecting the micro-damages in composites. The purpose of this project is to investigate the nonlinear ultrasonic technique based on guided waves mixing to locate and detect the impact damages in composites. Based on nonlinear wave mechanics and combined with the features of guided wave propagation, acoustic nonlinear response of guided waves mixing is firstly studied in this project. It aims to studying the mechanism of the acoustic nonlinear response of guided waves mixing in the composites with impact damages. The correlation between the acoustic nonlinearity by waves mixing and material micro-damages will be obtained in this project. The local impact damage can be located by acoustic nonlinear response, and the composite laminates can be scanned by controlling the guided waves mixing area. To overcome the limitations of current nonlinear guided waves approach based on second harmonic generation, the proposed guided waves mixing method can be used to locate the nonlinearity and to clarify the sources of nonlinearity. The developed technique can be applied for detecting and locating the impact damages of composite structures in this project, which has important theoretical value and engineering applications.

低速冲击损伤对复合材料结构完整性影响严重。为保障复合材料结构的长期服役和安全运行，需要及时检测、定位复合材料冲击损伤。非线性超声导波是检测复合材料微损伤的有效手段。本项目拟开展基于导波波束混叠的非线性超声检测方法研究，对复合材料冲击损伤进行检测与定位：首先基于非线性波动理论，结合导波传播特点，研究波束混叠条件下超声导波非线性响应特征；分析材料冲击损伤诱发超声非线性响应的机理；构建导波波束混叠后声学非线性响应与损伤的对应关系；通过控制导波波束混叠区域对复合材料板进行扫查检测，探索根据声学非线性响应的变化对局部损伤定位的方法，解决目前基于二阶谐波法的非线性超声导波技术无法有效区分非线性源、无法对局部损伤定位的技术难题。开展针对复合材料局部冲击损伤的非线性超声导波混叠检测方法研究，具有重要的理论研究意义和工程应用价值。

复合材料结构已广泛应用于航空航天等飞行器结构，复合材料结构受冲击后，对压缩载荷和层间剪切载荷的阻抗作用会变弱。如果在冲击损伤的初始阶段没有检测出这些损伤并采取相应维修措施，损伤会迅速累积，导致结构不能正常使用，甚至装备彻底损毁，带来灾难性后果。本项目就针对这一研究背景提出开展面向复合材料结构低速、低能冲击微损伤的非线性超声导波混叠检测方法的研究。研究内容涉及复合材料低速、低能冲击损伤诱发超声非线性响应的机理研究；非超声导波混叠非线性效应发生与传播的解析理论研究；超声导波混频非线性效应测量的实验方法研究以及复合材料冲击损伤的非线性超声导波检测与定位研究。研究的手段包括：理论分析、仿真和实验等。本项目通过4年多的研究，理论方面，获得了完整的超声导波混频非线性项的解析解；数值方面方面获得并验证了超声导波混频非线性发生和传播的特点；开发了基于导波混频效应的频谱阈值法（MFPC）并应用于复合材料冲击损伤检测，实现了对复合材料局部微损伤的量化检测，解决了航空复合材料结构完整性评估和寿命预测的难题。