Low Cycle Fatigue Strength Reduction Factor for a Mild Steel

Abstract

This paper deals with the results of the low cycle fatigue tests on hour-glass type and round notched specimens of SM 41 A. Strain-controlled and load-controlled low cycle fatigue tests at ambient temperature were carried out to investigate the notch effect on the fatigue strength reduction factor.The following conclusions were obtained :1) A visible crack of 0.2 to 0. 5 mm in length will be initiated on the notch root of a notched specimen with any shape factor at an approximately same number of cycles, if the same equivalent strain at the root of a notch is used as the measure of evaluating strain amplitude.2) A concept was proposed on low cycle fatigue strength reduction factor. The fatigue strength reduction factor Kf, _??_ which is calculated from the results of strain-controlled low cycle fatigue tests on smooth and notched specimens, would be equal to the dynamic strain concentration factor. In case that no low cycle fatigue tests would be carried out, the fatigue strength reduction factor may be obtained from the result of dynamic strain analysis.3) “A” factor for a carbon steel, which is given in the Fig. D-201 in the Nuclear Piping Code (USAS B 31. 7 1969), is found to give lower and higher value than the Kf, _??_ value depending on an applied stress amplitude. It is also revealed that “A” factor in the Nuclear Power Piping Code is much lower than that obtained by the Method proposed by S. W. Tagart for the material used in the present test.