The fatigue life of CMCs must be well characterized for the safe and reliable use of these materials as integrated TPS components. Existing fatigue life prediction models for composite materials may be classified into three different categories: a) fatigue life model (S-N curves), b) residual strength or residual stiffness model, and c) progressive damage model. Recently, a damage index and accumulation model has been developed by Liu and Mahadevan based on Tsai-Hill static strength failure criterion. Using this approach as a framework, MR&D is proposing to develop and verify a relatively simple and computationally manageable approach to the fatigue life prediction of fabric reinforced C/SiC composites for hypersonic vehicle load bearing thermal protection system designs. A combined experimental and analytical program is proposed to achieve the objective of the proposed Phase I effort. At the conclusion of Phase I, a TRL of 2 will have been achieved and progress towards achieving a TRL of 3 will have been made.