Creep Buckling of Cylindrical Shell under Variable Loading

Abstract

The ability for structural alloys to exhibit recovery of state, i.e., return to a softer state following periods of hardening, under varying stress and temperature is known to strongly influence structural response under some important thermomechanical loadings. For example, those involving thermal ratchetting and creep crack growth. Here the influence of dynamic and thermal recovery on the axisymmetric creep buckling response of a circular cylindrical shell under variable uniform axial loading is investigated. The real shell is idealized as a two-membrane sandwich shell while the constitutive model, unlike the commonly employed Odqvist creep law, incorporates a representation of both dynamic and thermal (state) recovery. The material parameters of the constitutive model are chosen to characterize Narloy-Z, a representative copper alloy used in thrust nozzle liners of reusable rocket engines. Variable loading histories investigated include rapid cyclic unloading/reloading sequences and intermittent reductions of load for extended periods of time. The calculated results show that failure to account for state recovery in the constitutive relations can lead to nonconservative predictions of the critical creep buckling time.