Fatigue damage accumulation and failure of high temperature polymeric composite materials

拟议的研究的中心目标是调查新一代的高温聚合物基复合材料在其最高设计温度或接近其最高设计温度下使用的疲劳失效，并提出广义的数学和数值模型来预测损伤累积和最终失败在这种负载环境下。 为了实现这一目标，将开发一个连续损伤力学疲劳模型，考虑到统计因素和非线性粘弹性本构方程的规定，以考虑高温环境。该疲劳模型基于材料性能退化模拟失效，将被实现为有限元解，以便于聚合物基复合材料制成的实际结构的疲劳失效分析。材料性能退化将通过基于微观力学的损伤张量进行建模，该张量将作为整体建模方法的一部分开发，并将考虑各种损伤机制，如基体开裂，分层，纤维-基体脱粘和纤维断裂，以及它们对材料性能的影响。高温复合材料的实验表征将在高温下的静态和疲劳载荷条件下进行，然后通过测试由新一代高温聚合物基体材料（用连续单向碳纤维增强）制成的单向、角向铺层、交叉铺层和准各向同性层压板来验证所提出的失效模型。还将获得另外两种高温聚合物复合材料的测试结果，以获得比较数据。提出的研究的长期目标包括为其他形式的高温聚合物基复合材料的疲劳失效建模铺平道路，例如用编织或编织纤维增强的那些。

The central objective of the proposed research is to investigate the fatigue failure of new generations of high temperature polymer matrix composites utilized at or near their maximum design temperatures and propose generalized mathematical and numerical models to predict damage accumulation and ultimate failure under this loading environment. To meet this objective, a continuum damage mechanics fatigue model will be developed, with statistical considerations and provisions for nonlinear viscoelastic constitutive equations to account for the elevated temperature environment. This fatigue model, simulating failure based on material property degradation, will be implemented into a finite element solution, to facilitate the fatigue failure analysis of practical structures made of polymer matrix composites . The material property degradation will be modeled via a micromechanically-based damage tensor that will be developed as part of the overall modeling approach and will consider the various damage mechanisms, such as matrix cracking, delamination, fiber-matrix debonding and fiber fracture, and their influence on the material properties. Experimental characterization of the high temperature composite will be carried out under static and fatigue loading conditions at high temperature followed by validation of the proposed failure model through testing of unidirectional, angle-plied, cross-plied, and quasi-isotropic laminates made from a new generation of high temperature polymeric matrix materials reinforced with continuous unidirectional carbon fibers. Test results will also be obtained on two other high temperature polymer composites to obtain comparative data. The long term objectives of the proposed research include paving the way for the fatigue failure modeling of other forms of high temperature polymer matrix composites such as those reinforced with woven or braided fibers.