A Differential CDM Model for Fatigue of Unidirectional Metal Matrix Composites

A multiaxial, isothermal, continuum damage mechanics model for fatigue of a unidirectional metal matrix composite volume element is presented The model is phenomenological, stress based, and assumes a single scalar internal damage variable, the evolution of which is anisotropic. The development of the fatigue damage model (i.e., evo lutionary law) is based on the definition of an initially transversely isotropic fatigue limit surface, a static fracture surface, and a normalized stress amplitude function. The anisot ropy of these surfaces and function, and therefore the model, is defined through physically meaningful invariants reflecting the local stress and material orientation. This transversely isotropic model is shown, when taken to its isotropic limit, to directly simplify to a previ ously developed and validated isotropic fatigue continuum damage model.