Creep-behavior-based material selection for a clamping spring of ceramic-matrix composite inner-shroud in utility and industrial gas-turbine engines:

This paper addresses the problem of materials selection for springs used to clamp an inner shroud segment to the outer shroud block in utility and industrial gas turbine engines. Clamping is achieved through the application of an initial compressive load to the spring. However, since the spring is subjected to high temperature and oxidizing conditions, it experiences creep and surface oxidation. Both of these processes result in the loss of the compressive load within the spring with time. A material selection procedure is developed, which identifies optimum materials (design variables), with respect to the minimum loss in the clamping-spring load (objective function) for a given set of geometrical constraints (i.e. maximum size of the spring is constrained by the outer-shroud cavity which houses the spring) and functional constraints (force retention should persist over the expected life of the inner-shroud segment). Two material selection procedures are devised: (a) one, fairly rigorous and computationa...