Cyclic plasticity analysis of welded joint with welding residual stress using the direct method

To meet the growing energy demands, the power sector continuously strives at enhancing the efficiency of its power plants by increasing the operating temperature. Under cyclic loading conditions, this leads to creep-cyclic plasticity driven damage mechanisms such as cyclically enhanced creep, creep enhanced plasticity and creep ratcheting. A detailed understanding of creep and related damages is therefore essential for predicting any potential failure mechanisms and ensuring confidence in the safe-working of the components. This becomes particularly difficult and challenging in the presence of welds due to two main reason; a) presence of different material zones, namely parent metal, weld metal and heat affected zone; b) introduction of residual stress during welding. An extended Direct Steady Cycle Analysis within the Linear Matching Method (LMM) framework has been previously developed to consider the full interaction between creep and cyclic plasticity. This paper presents the basic theory and an overview behind the LMM framework along with a new application of a welded flange, considering for the first time the effect of residual stress due to welding. A 3D finite element model is adopted for the flange, and it is subjected to a constant pressure and cyclic thermal load of varying dwell. The effects of welding residual stress on the creep-cyclic plastic response of the welded flange are investigated. Additional parametric studies considering different levels of the applied load and dwell period are performed. The results reflect the ease of using LMM over conventional inelastic analysis.