Fatigue damage accumulation and failure of high temperature polymeric composite materials

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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.