Life Prediction of Long-Term Creep-Fatigue

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The objective of this project is to develop a life prediction method of long term creep-fatigue.The test material used here was a SUS 304 austenitic stainless steel and the push-pull creep-fatigue test was carried out at K. the main conclusions obtained are as follows:(1)We developed a life prediction method of long term creep-fatigue based on the static creep and the no-hold-time low cycle fatigue data. The strain controlled fatigue tests with various hold-times ranging from 5 min and 24 hr were carried out and the fatigue data were generated.The life prediction was made based on the linear summation damage rule with the critical creep/fatigue damage defined in the ASME Code Case for the short and long term creep-fatigue life.The predicted results closely agreed with the experimental creep-fatigue life with the hold-times between 5min and 24hr.(2)The life prediction method developed in the smooth specimen was extended to the notched specimen in the second year of this project.The cyclic elastic-plasticcreep FEM analysis was made for the made for the three types of the circumferential notched specimens whose elastic stress concentration factors were 2.6,4.2 and 6.0. The stress waves analyzed were the triangular stress wave with frequency of 0.1 Hz,the trapezoidal stress wave with 166-min tensile hold-time and slow-slow wave with frequency of 0.0001 Hz. The analysis was made up to 1(1/4)cycle. The creep-fatigue life was predicted based on the calculated local stress/strain at the notched root from linear summation damage rule and the strain range partitioning method. The predicted life agreed with the experimental creep-fatigue life and we concluded that the FEM method was applicable to estimating the long term hold-time and slow-slow fatigue life.