考虑温度影响的复合材料夹芯结构疲劳损伤机理与寿命预测

In recent years, sandwich structures have been widely used in Civil Engineering due to the advantages of high strength to weight ratios, anti-corrosion ability and convenient usage. However, the face sheet and core are sensitive to the temperature, which leads to stress concentration in the interface under the conditions of temperature changes. Once the difference between the temperatures is large, the effects of temperature on the structural performance are significant, especial subjected to fatigue loads. Then the interface peeling and fiber fracture can accelerate the failure. In this program, the study of fatigue damage and lifetime prediction of sandwich structures considered the temperature effect will be carried out in this research. The main research contents include three sections: (1) Study of fatigue behavior of sandwich structures. The effects of amplitude, frequency and cyclic number on fatigue damage and deflection will be summarized under the temperature range from -50℃ to 70℃, in the meantime, the fatigue dissipation energy can be obtained based on thermodynamics theory; (2) Study of damage mechanism. Based on the elastic fracture theory, the delamination damage area analytical model will be established. Then the relationship among fatigue dissipation energy, interface fracture toughness and mode mixity can be obtained;（3）Study of lifetime prediction. According to Lemaitre expression and Miner analytical model, the fatigue lifetime prediction of sandwich structures, considered the member stiffness and fatigue dissipation energy, will be proposed by the use of particle swarm optimization algorithm. The above work can generate a theoretical framework to investigate the fatigue damage and lifetime prediction of sandwich structures under coupling effects of temperature and fatigue loads, and aid engineers to design sandwich structures.

复合材料夹芯结构轻质高强、耐腐蚀、可设计性好，在土木交通领域具有良好的应用前景，但其组分多为热膨胀系数不同的温度敏感材料，温度的变化会在界面处产生应力积聚。当温差较大时，温度对结构性能的影响尤为明显，特别是在交变荷载长期作用下，易导致结构出现界面剥离、基体脱粘、纤维断裂等疲劳破坏，影响结构的使用寿命。本项目针对温度影响下复合材料夹层结构的疲劳失效问题，拟开展以下三方面研究：①疲劳性能研究：通过开展疲劳试验和理论建模分析，研究温度在-50℃到70℃范围内构件力学性能随温度、交变荷载等参量的变化规律，基于热力学理论计算疲劳耗散能；②损伤机理分析：建立损伤区分析模型，导出耗散能、断裂韧度与模式混合度之间的关系，建立包含温度参量的复合材料夹芯结构疲劳损伤扩展模型；③寿命预测研究：综合基于刚度的Lemaitre损伤模型和基于耗散能的Miner累积损伤模型，运用粒子群优化算法，预测结构的疲劳寿命。

复合材料夹芯结构因具有轻质高强、耐腐蚀、可设计、易装配等优势，在土木交通和海洋工程领域具有广阔的应用前景。本项目围绕该结构在实际工程应用时的疲劳累积损伤和寿命预测关键问题，考虑服役温度环境影响和循环荷载作用，采用试验研究和理论分析相结合的方法，系统地研究了不同温度条件下复合材料夹芯结构组分玻璃纤维增强复合材料GFRP面板和芯材的力学性能退化特征，以温度、荷载等级和时间为主要控制参数，开展了GFRP面板、轻木芯材的力学性能试验和疲劳性能试验，考虑纤维铺层和芯材木纹的影响，得到两种组分材料的力学性能指标随温度的变化规律，GFRP面板的疲劳失效模式、破坏机理和疲劳寿命，为细观分析整体夹芯结构的疲劳机理提供依据。项目通过开展复合材料夹芯梁四点弯疲劳加载试验研究结果发现，温度影响下（恒湿）传统复合材料夹芯结构极易发生界面剥离破坏，在研究其疲劳性能的基础上，本项目通过优化芯材设计提出界面性能增强的格构增强型夹芯结构形式，并对不同跨高比及格构设置的轻木夹芯复合材料梁进行弯曲疲劳试验，研究其疲劳性能和界面剥离机理。项目通过研究温度环境对疲劳破坏过程、失效模式和疲劳寿命的影响规律，建立含有温度参数的全生命周期疲劳寿命曲线模型，基于等效截面法和多元非线性回归方法，对多参数寿命模型进行参数精细化分析，得到适用范围较广的寿命预测模型。基于累积损伤理论、剪切变形理论和剩余刚度理论，建立基于刚度退化的 “指数型”疲劳累积损伤模型，分析模型中各参数的影响特征，对夹芯结构的疲劳寿命进行预测，解决了复合材料夹芯结构寿命预测和损伤评价问题，为复合材料夹芯结构在不同温度环境的实际应用提供依据。