湿热环境与疲劳载荷交替作用下飞机复合材料疲劳寿命退化规律及预测模型研究

Carbon fiber reinforced resin composites are widely applied in the airplane structures. However, the composites are very sensitive to hygrothermal environment. The fatigue properties of composites can be obviously deteriorated under the long exposure of hygrothermal environment. In this project, fatigue life degradation of typical airplane carbon fiber reinforced resin composites under alternative hygrothermal-fatigue condition will be deeply studied. Firstly, degradation rule of fatigue life are determined by conducting the alternative hygrothermal-fatigue tests on composites. And the statistical analysis and reliability analysis on the fatigue life are carried out. Secondly, based on the degradation trend of interlaminate properties, evolution of micro-damages (using crack density and delamination area) and micro-observations on the fatigue fracture sections, the mechanisms of fatigue life degradation hygrothermal-fatigue condition are verified. Thirdly, macro-micro constitutive is proposed considering both the hygrothermal damage and fatigue damage. Failure rules are obtained according to micro failure mechanisms and macro failure modes. Then the fatigue life prediction models of composite under alternative hygrothermal-fatigue condition are built. Achievement of this project not only has obvious academic significance to recognize the degradation of composites fatigue life under alternative hygrothermal-fatigue condition, but also can provide theoretical references to the life prediction and scientific measurement of airplane structures.

碳纤维树脂基复合材料广泛应用于飞机结构中，但其对湿热环境异常敏感，湿热环境的长期作用会显著降低其疲劳性能。本项目拟对飞机结构常用碳纤维树脂基复合材料在实际服役过程中经历湿热-疲劳交替作用下的疲劳寿命退化问题进行深入研究。首先，开展复合材料湿热-疲劳交替试验，明确交替作用下疲劳寿命退化规律，并对寿命进行统计分析及可靠性分析；其次，探明湿热-疲劳交替下层间界面性能的衰减趋势，通过裂纹密度、脱粘面积等指标定量掌握细观损伤演化过程，并对疲劳断口形貌进行显微观察，综合确定湿热-疲劳交替作用下复合材料寿命退化机理。最后，提出考虑湿热损伤、疲劳损伤的宏细观统一本构模型，得到基于细观失效机理、宏观失效模式的失效准则，综合建立湿热-疲劳交替作用下复合材料寿命预测模型。该项目成果对认识复合材料在湿热-疲劳交替作用下的寿命退化具有重要学术意义，也可为飞机结构寿命预测及科学管理提供理论参考依据。

项目通过试验探索、理论分析以及数值模拟等方法，系统性研究了湿热环境与疲劳载荷交替作用下飞机复合材料疲劳寿命退化规律、退化机理及预测模型。首先明确了复合材料湿热-疲劳交替作用下寿命退化规律。确定了复合材料的吸湿性能和静强度特性，开展了预湿热条件下疲劳试验并获得了疲劳寿命，确定了相应疲劳寿命分布规律及可靠性寿命，基于不同交替周期确定了疲劳寿命及相应退化规律，并分析了不同周期下寿命分布规律以及可靠性寿命；其次，揭示了复合材料湿热-疲劳交替作用寿命退化机理。确定了静力破坏的失效模式，对比分析了预湿热和湿热-疲劳交替两类条件下的破坏模式，进而确定了湿热-疲劳交模式的影响效应。通过层间剪切性能试验，分析了湿热环境对界面性能的影响，联合显微观察得到的湿热过程中的损伤和疲劳过程中损伤，共同确定了交替条件下的疲劳寿命退化机理；最后，建立了复合材料湿热-疲劳交替的寿命预测模型。基于Miner线性累积损伤理论，建立了包含交替参数信息的修正Miner模型，并基于该模型对疲劳寿命进行了估算，预测值与疲劳寿命试验均值的误差在15%以内，表现出较高精度。