碳纤维/环氧复合材料的低温微损伤监测和损伤机理研究

The damage mechanism of advanced materials in complex environment is a research hotspot. Nonlinear guided waves is a new method to study the damage mechanism by monitoring the nonlinear response of ultrasonic guided wave at the damage. The nonlinear response is mainly caused by the distributed material nonlinearity and intermittent opening and closing of crack surfaces. In the cryogenic temperature environment, due to the increase of the strength and modulus of the resin matrix, the strength of interfacial bond between matrix and fiber is increased, and the distributed nonlinearity of composite materials is reduced. On the other hand, due to the large difference in thermal expansion coefficient between fiber and matrix, there is a thermal residual deformation in composite materials at cryogenic temperature. Under the external load, the composite material is liable to be damaged inside, and the nonlinear response caused by the damage is more remarkable. Therefore, it is potential to establish an effective method for micro-damage monitoring based on nonlinear ultrasonic guided wave technique for the damage mechanism study of composite structures at cryogenic temperature. In this project, a combination of theoretical analysis, numerical simulation and experimental study will be used to analyze the cryogenic temperature effects on the transducer piezo-mechanical properties, the transducer-panel interaction, and the panel wave dispersion properties. Then the mechanism of nonlinear response between ultrasonic guided wave and micro-structure of composite materials is studied by a model that accounts the cryogenic temperature effects. Combined with micro-observation method, a relationship between structural micro-damage -material nonlinearity - nonlinear guided wave characteristics will be established, and a reliable monitoring method for composite micro-damage will be developed; thus to reveal the damage mechanism of composites at cryogenic temperature.

先进材料在复杂环境下的损伤机理是个研究热点，通过监测损伤处超声导波非线性响应是研究该问题的新型手段。非线性响应主要由材料非线性和损伤呼吸效应引起。低温环境下，树脂基体强度提高导致基体和纤维界面结合力增强，材料非线性会降低；与之相反，纤维和基体热膨胀系数差异引起的热残余变形导致材料更易萌生损伤，其损伤非线性响应会更显著。因此，基于非线性超声导波技术发展复合材料微损伤监测方法对研究其低温损伤机理具有可行性。本项目将采用理论分析、数值模拟和实验研究相结合的研究手段，分析低温环境对压电传感器性能、传感器与结构的耦合作用、以及超声导波频散特性的影响规律，理解超声导波与复合材料材料微观组织之间的非线性响应机理；结合微观观测方法，建立结构微损伤－材料非线性－非线性导波特征之间的联系，发展可靠的复合材料微损伤监测方法；最后通过实时监测材料真实损伤情况，揭示复合材料在低温下的损伤和失效机理。

本课题通过理论分析、数值模拟和实验研究相结合的方案，对碳纤维/环氧复合材料的低温微损伤监测和损伤机理进行了初步研究。首先测试压电材料、粘接剂、碳纤维和环氧树脂在液氮温度下的主要性能参数，并制备实验所需的高性能低温碳纤维/环氧复合材料试验件，测试了碳纤维/环氧复合材料在低温下的主要性能参数；进而根据性能参数通过热弹理论与半解析有限元法分析温度环境对超声导波激励/接收性能的影响规律，给出不同温度环境下超声导波的频散特性；引入高阶弹性常数计算复合材料结构在施加预应力后的声弹性导波传播，利用半解析有限元计算施加轴向应力下，超声导波的频散曲线，并得到应力灵敏度曲线，选取最适合进行应力监测的模态和激励频率，对导波与应力相关的信号特征提取完成监测；另一方面利用哈密顿体系方法求解了表面载荷作用下 Lamb 波的激励问题，提出了基于压电传感器的 Lamb 波模态控制方法和模态分离方法；最后提出了一种超声导波­机电阻抗（GW­EMI）相结合的损伤诊断技术。本研究为探讨碳纤维/环氧复合材料的损伤监测和损伤机理奠定了坚实的工作基础，同时对于认识超声导波在复杂结构中的传播特性，发展无基准的损伤监测方法提供了新思路。项目资助发表学术论文11篇，其中SCI收录10篇，EI收录1篇。培养博士生3名，其中1名已经取得博士学位，2名在读。项目投入经费30万元，支出29.85万元，各项支出基本与预算相符。