Shell and Solid Type Finite Element Analysis of Creep in Thin-Walled Structures

Abstract

In many applications thin-walled structures (beams, plates, pipes, pipe bends, etc.) operate at elevated temperatures. Under such conditions the behavior of metals and alloys is primarily determined by irreversible time-dependent creep and material deterioration processes. In order to estimate the long-term behavior it is important to understand the mechanisms of the time-dependent stress redistribution and damage growth, particularly in the zones of nozzles, pipe connections and welds. The widely used approach in modelling the creep-damage behavior is the continuum damage mechanics, which proposes constitutive equations for the creep strain rate tensor, evolution equations for damage variables, and states nonlinear initial-boundary value problems in order to perform a structural analysis, e.g. [7]. With the progress in the material science and continuum mechanics, many new constitutive models have been developed which include physically motivated state variables and are able to consider different effects in material behavior such as the damage induced anisotropy, stress state dependence of damage evolution, etc. These models can be incorporated into a commercial finite-element code in order to analyze time-dependent deformations and stresses in a thin-walled structure under a specific mechanical loading. As usual, an important step is to select a structural mechanics model or to specify the type of finite elements. One way is a “three-dimensional approach” which is based on balance equations of three-dimensional continuum.