Stationary Creep

Abstract

AbstractAn introduction to creep and its main characterstics are given. Stationary creep has been studied extensively in the literature. Stationary creep is a result of a balance between work hardening and recovery processes, which allows for a continues plastic deformation without raising the stress. The starting point for the basic modeling of creep is a differential equation for the dislocation density that describes how it varies with strain or time. The model explains how the dislocation density is influenced by work hardening and recovery. From the dislocation model, a basic equation for the creep rate is derived that is in many respects similar to the classical Bird, Mukherjee and Dorn (BMD) formula but with the values of the parameters given. By taking the role of strain induced vacancies into account, the applicability of the BMD equation is widely expanded because the basic model can also handle low temperatures and high stresses that is usually referred to as the power-law break down regime. It is illustrated that the creep model can represent the creep rate for pure metals such as Al and Ni.