Masafumi Yamauchi

Thermal Fatigue Behavior of a SUS304 Pipe Under Longitudinal Cyclic Movement of Axial Temperature Distribution

In a structural thermal fatigue test which imposed an oscillating axial temperature distribution on a SUS 304 pipe specimen, different crack initiation lives were observed between the inner and the outer surfaces, although the values of the von-Mises equivalent strain range calculated by FEM inelastic analysis were almost the same for both surfaces. The outer surface condition was an in-phase thermal cycle and an almost uniaxial cyclic stress (low hydrostatic stress). The inner surface condition was an out-of-phase thermal cycle and an almost equibiaxial cyclic stress (high hydrostatic stress). A uniaxial thermal fatigue test was performed under the simulated conditions of the outer and inner surfaces of the pipe specimen. The in-phase uniaxial thermal fatigue test result was in good agreement with the test result of the pipe specimen for the outer surface. The out-of-phase uniaxial thermal fatigue test which simulated the inner surface condition, showed a longer life than the in-phase uniaxial test, and thus contradicted the result of the structural model test. However, the structural model test life for the inner surface agreed well with the uniaxial experimental measurement when the strain range of the inner surface was corrected by a triaxiality factor.

Evaluation of creep-fatigue design methods by structural failure tests under thermal loads

Abstract Creep-fatigue tests were conducted under cyclic thermal stresses using two types of simple structural models, the free surface model and ring cylinder model. All models were made of SUS304 stainless steel and some of the specimens had longitudinal welds. Failure lives were defined as the cycle at which small visible cracks were detected. Three kinds of life evaluations were made. Two of these were based on elastic analysis and one of these was based on inelastic analysis. The estimated lives were compared with the experimental results and the results can be summarized as follows. 1. (1) Life estimation based on inelastic analysis was adequate and the estimated lives agreed well with the experimental results. 2. (2) Life estimation by the Monju Design Guide based on elastic analysis gave conservative results. However, the accuracy of life estimation could be improved by using the elastic follow-up factor ( q value) obtained from inelastic analysis.

Comparison of creep-fatigue Life prediction by Life Fraction Rule and Strainrange Partitioning methods

A comparison of two kinds of creep-fatigue life prediction methods, Life Fraction Rule and Strainrange Partitioning, was performed for the cases of creep-fatigue tests under uniaxial strain-controlled conditions at 500 to600°C in air, using a normalized and tempered 2 1/4 Cr-1Mo steel. The main focus was on the influence of stress-strain behavior on life prediction. Two kinds of stress-strain values (i.e., experimental values and calculated values by inelastic analysis) were used for the life prediction of creep-fatigue tests. The results show that life prediction by the Life Fraction Rule was very sensitive to the stress-strain values, indicating a large discrepancy between predicted and observed lives in some cases, and that life prediction by the Strainrange Partitioning method was not so sensitive to the stress-strain values, indicating a good agreement between predicted and observed lives in all cases.

Cyclic stress-strain behavior and creep-fatigue life prediction of perforated plates

ABSTRACT Prediction methods of macroscopic and local stress-strain behavior of perforated plates in plastic and creep regime are proposed in this paper. Predicted results for macroscopic behavior are compared with the experimental results for cyclic stress-strain behavior and relaxation behavior. Creep-fatigue lives at around a hole of perforated plates are predicted by using the local stress-strain behavior and are compared with experimentally observed lives.