Damage Assessment of Similar Martensitic Welds Under Creep, Fatigue, and Creep-Fatigue Loading

For the assessment of welds under high-temperature conditions in the creep or creep-fatigue regimes, the knowledge of the damage location and its temporal evolution is of high importance. The local failure behavior of weld joints is not reflected in design guidelines using weld reduction factors or in typical assessment approaches. The evaluation of local strains and stresses in the heat affected zone (HAZ) is essential for a more detailed consideration of weld behavior and has a high potential for improvement of design and inspection guidelines. In this paper, an overview of current developments in the assessment of weld joints is given. Uni-axial creep, component tests, low cycle fatigue (LCF), and creep-fatigue experiments with base material, weld joints and microstructure simulated HAZ material are presented. The use of test results of microstructure simulated HAZ material allows the parameter identification of numerical material models for the HAZ and improves the simulation of the local stress and strain behavior of weld joints. Two assessment methods, one for creep and one for fatigue/creep-fatigue were presented, based on the local behavior determined by the numerical simulations. The assessment approach for pure creep loads was validated using several uni-axial creep tests and two component tests. The approach for the fatigue/creep-fatigue loads is still in the developmental stage but the first results were presented and further areas for improvement were identified.