Creep-fatigue life prediction method of 316FR welded joints, 1; Prediction based on macroscopic stress and strain concentration

Asayama, Tai ; Hasebe, Shinichi

Form the viewpoint of cost reduction, it is necessary to avoid using expensive forged rings by adapting weldments in the parts where relatively large creep-fatigue damage is expected such as the part of pressure vessel to which the sodium surface contacts. Therefore the authors have been developing a creep-fatigue life prediction method for weldments. This report presents the newly developed prediction method ('3-element model') which describes the creep-fatigue life as well as the location of failure for 316FR weldments which is a candidate material for large scale FBRs. It was shown that the model satisfactory predicts the location of failure and that the prediction of life is possible within an accuracy of factor of 3 with a tendency of slight unconservatism for the results of mechanical fatigue/creep-fatigue tests with small and large specimens as well as for the thermal fatigue/creep-fatigue tests. Improvement of the accuracy of prediction is considered to be achieved by using more accurate dynamic stress-strain curve of weld metal and HAZ at lower strain range and more accurate fatigue strength of weld metal at lower strain range which are the base of the prediction. Thus fatigue tests of weld metal and HAZ at lower strain ranges are needed.