Thermal fatigue - Materials modeling

In the framework of the ongoing joint research project "Thermal Fatigue - Basics of the system-, outflow- and material-characteristics of piping under thermal fatigue" funded by the German Federal Ministry of Education and Research (BMBF) fundamental numerical and experimental investigations on the material behavior under transient thermal-mechanical stress conditions (high cycle fatigue - HCF and low cycle fatigue - LCF) are carried out. The primary objective of the research is the further development of simulation methods applied in safety evaluations of nuclear power plant components. In this context the modeling of crack initiation and growth inside the material structure induced by varying thermal loads are of particular interest. Therefore, three scientific working groups organized in three sub-projects of the joint research project are dealing with numerical modeling and simulation at different levels ranging from atomistic to micromechanics and continuum mechanics, and in addition corresponding experimental data for the validation of the numerical results and identification of the parameters of the associated material models are provided. The present contribution is focused on the development and experimental validation of material models and methods to characterize the damage evolution and the life cycle assessment as a result of thermal cyclic loading. The individual purposes of the subprojects are as following: Material characterization, Influence of temperature and surface roughness on fatigue endurances, biaxial thermo-mechanical behavior, experiments on structural behavior of cruciform specimens and scatter band analysis (IfW Darmstadt) Life cycle assessment with micromechanical material models (MPA Stuttgart) Life cycle assessment with atomistic and damage-mechanical material models associated with material tests under thermal fatigue (Fraunhofer IWM, Freiburg) Simulation of fatigue crack growth, opening and closure of a short crack under thermal cyclic loading conditions, developing methods for the damage assessment based on the cyclic J-integral (IFSW Darmstadt, AREVA) Further development of plasticity models (IFSW Darmstadt, AREVA) Within this paper the various investigations and the main results are presented.