Damage and Lifetime Modeling for Structure Computations

Ceramic matrix composites (CMC) are good candidates for structural applications at high temperatures in oxidizing environments. A main question is then to be able to predict, that is, to compute the lifetime of engineering structures. Multiphysic models are needed to reproduce couplings between the mechanical and environmental fields. The chapter is first focused on the central and crucial question of highly anisotropic materials as CMCs: how does one handle mathematically what we call damage, that is, how does one reproduce the microcracking mechanisms? The answer described here is a general anisotropic damage theory that takes into account crack closure effects. The second part deals with the modeling of couplings with the environment characterized by temperature, oxygen partial pressure, and humidity. Fatigue of interface, matrix and fiber oxidation, and self-healing mechanisms are also taken into account. The idea, here, is to develop micro-multiphysic models that provide information for the computational macromodel. This strategy is illustrated on a self-healing CMC material. The last part concerns the use of the computational multiphysic model, which allows one to predict the macrocracks' initiation and their propagation. Classical numerical difficulties are displayed and answers are given. To end, an application to an engineering structure is shown.