Development of a small punch testing method to evaluate the creep property of high Cr ferritic steel: Part II - Stress analysis of small punch test specimen by finite element method

From the creep rupture data for the reduced activation ferritic/martensitic steel F82H, the ratio between the load in the small punch (SP) creep test and the stress in the standard creep test is estimated to be 2.1 in an argon atmosphere and 2.3 in a vacuum. However, the reasons for the difference between the values of stress conversion coefficients and the physical meaning of these values have not been clarified. In this study, stress analyses of SP creep specimens were carried out for F82H by using finite element analysis to clarify the physical meaning of the stress conversion coefficient. The friction coefficient between the ball and specimen affected the SP creep properties, and an increase in the friction coefficient resulted in an increase in the rupture time. The applied load (F) and the averaged equivalent stress in the steady state (σs) correlated linearly, and the increasing friction coefficient tended to decrease σs. It was possible to replicate the test results obtained in the argon atmosphere with a friction coefficient of 0.39 and the results obtained in the vacuum with a friction coefficient of 1.3. It was also found that the SP creep test results, which were determined by σs, agree well with the standard creep test results.