Optimal Fiber Orientation in Locally Transversely Isotropic Creeping Structures

An approximate method is developed for comparing various fiber configurations in a composite structure with the objective of achieving optimal resistance to creep failure. The class of composite structures addressed has a single family of long or continuous strong fibers embedded in a creeping matrix material, e.g., a polymer, metal, etc. Thus, the structure is locally transversely isotropic with the fiber orientation generally varying throughout the structure. The proposed method, intended as an early design tool, is based on an upper bound on creep rupture time and an associated representative failure stress. The latter is evaluated and compared for different fiber configurations, thereby identifying that with optimal creep rupture resistance. This approach allows a substantial saving in computational time by avoiding a detailed analysis of the actual failure process. Application is made to a fiber-reinforced thick-walled cylindrical pressure vessel.