In addition to structural loads such as internal pressure nuclear power plant components are generally also subjected to thermal cyclic loading conditions. The transient cyclic nature of these events causes stress-strain hysteresis loops which are considered to be fatigue relevant events. To consider the impact of such events for the fatigue assessment a short crack approach using a J integral based damage parameter is utilized. The local stresses and strains are computed from a two step FE Analysis. All calculations are based on the component example of a thick walled tube. In a transient thermal analysis the temperature solution is obtained using temperature dependant material parameters. The mechanical temperature dependent material behavior is implemented using a Chaboche type elastic plastic material model for a typical stabilized austenitic stainless steel. Appropriate material parameter identification relies on systematic experiments. The loading conditions are taken from sample low cycle temperature transients comparable to those arising during the operation of nuclear power plants. To calculate the solution for a cracked configuration a short crack in axial direction is introduced into the wall of the tube. The algorithm uses a node release technique as well as contact elements along the crack flanks to describe different states of a short crack configuration as well as opening and closure effects. The results are interpreted for fatigue assessment using a damage parameter based on the cyclic effective J integral. The values are calculated based on the results of the FE Analysis.
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