Optimal fiber orientation in locally transversely isotropic creeping structures

An approximate method is developed for comparing various fiber configuratio ns in a composite structure with the objective of achieving optimal resista nce to creep failure. The class of composite structures addressed has a sin gle family of long or continuous strong fibers embedded in a creeping matri x material, e.g., a polymer; metal. etc. Thus, the structure is locally tra nsversely isotropic with the fiber orientation generally varying throughout the structure. The proposed method, intended as an early design tool, is b ased on an upper bound on creep rupture time and an associated representati ve failure stress. The latter is evaluated and compared for different fiber configurations, thereby identifying that with optimal creep rupture resist ance. This approach allows a substantial saving in computational time by av oiding a detailed analysis of the actual failure process. Application is ma de to a fiber -reinforced thick-walled cylindrical pressure vessel.