Abstract: To construct composite fatigue life models of three-dimensional stress state, a solution of using rigidity element and spring element to simulate the interaction between layers was proposed.Then three-dimensional finite element models were constructed by combining the interlamination models and two-dimensional plate element. A fatigue life analysis method of any stress ratio was developed with the aid of the fatigue test results and damage models of typical stress ratio, as well as the transformation theory of equilife curves. Fatigue life models of multiaxial cyclic stress were constructed by introducing compound cumulative damage. With the aid of stress analysis, failure analysis of static strength and fatigue cumulative damage and degradation models of material property, the processes of damage, the emergence and expansion of damage and the general destruction, in-plane and between layers, can be simulated.Then the fatigue life can be attained. By the contrast of the predicted values with the test results of fatigue life of laminates, the validity of the constructed models is verified. Considering the space complexity of the design variables, the two-level optimizations—system-level layout optimization and subsystem-level dimension optimization—was adopted. Adopting the self-adaption genetic algorithm, regarding the minimum mass as the objective function, the fatigue life requirement as the constraint condition, the composite cabin is optimized. The optimization framework of composite structure is built based on multiaxial stress fatigue life, which can provide references for the optimization design of composite structure. 

Key words: Fatigue life; Three-dimensional model; Multiaxial stress; Graded optimization; In-plane damage; Interlaminar damage

摘要： 为构建三维应力状态复材结构疲劳寿命模型,提出由刚性元和弹簧元来模拟层间作用,结合二维板元构建三维有限元模型。借助典型应力比下的疲劳试验结果和损伤模型,结合等寿命曲线转化理论,发展一种任意应力比下的疲劳寿命分析方法。引入复合累积损伤建立多轴循环应力下的疲劳寿命模型。借助应力分析、静强度和疲劳累积损伤失效分析及材料性能退化模型,模拟面内和层间损伤产生、发展直至整体破坏过程,得到疲劳寿命。通过层合板疲劳寿命预测值和试验结果对比,验证所建模型的正确性。考虑设计变量空间复杂性,采用二级优化方法:系统级布局优化和子系统级尺寸优化。采用自适应遗传算法,以质量最小为目标函数,以疲劳寿命要求为约束条件,对复材舱体进行优化。建立基于多轴应力疲劳寿命的复材结构优化框架,为复材结构优化设计提供参考。 

关键词: 疲劳寿命;三维模型;多轴应力;分级优化;面内损伤;层间损伤 