The Effect of Load Frequency on the Temperature Dependence of Fracture Life of Notched Specimens for 9-12Cr Steel Under Creep-Fatigue Conditions

In order to operate a thermal power plant safely, it is necessary to establish the prediction methods of fracture life for heat-resistant steels which is used in thermal power plant. For the establishment of prediction methods, it is necessary to consider the effects of creep damage and creep-fatigue interaction on the fracture life. Therefore, in this paper, creep-fatigue tests were conducted on notched specimens of W-added 9-12Cr steels for various temperatures and load frequencies. From these results, the influence of load frequency on temperature dependence of crack growth life for 9-12Cr steels was determined.

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Verification of the Prediction Methods of Strain Range in Notched Specimens Made of Mod.9Cr-1Mo

ASME 2010 Pressure Vessels and Piping Conference: Volume 1 ◽

10.1115/pvp2010-25489 ◽

2010 ◽

Cited By ~ 1

Author(s):

Masanori Ando ◽

Yuichi Hirose ◽

Shingo Date ◽

Sota Watanabe ◽

Yasuhiro Enuma ◽

...

Keyword(s):

Fatigue Life ◽

Elevated Temperature ◽

Low Cycle Fatigue ◽

Strain Range ◽

Fatigue Tests ◽

Estimation Methods ◽

Prediction Methods ◽

Test Machine ◽

Notched Specimens ◽

Creep Fatigue

Several innovative prediction methods of strain range have been developed in order to apply to the Generation IV plants. In a component design at elevated temperature, ‘strain range’ is used to calculate the fatigue and creep-fatigue damage. Therefore, prediction of ‘strain range’ is one of the most important issues to evaluate the components’ integrity during these lifetimes. To verify the strain prediction method of discontinues structures at evaluated temperature, low cycle fatigue tests were carried out with notched specimens. All the specimens were made of Mod.9Cr-1Mo, because it is a candidate material for a primary and secondary heat transports system components of JSFR (Japanese Sodium Fast Reactor). Deformation control fatigue tests and thermal fatigue tests were performed by ordinary uni-axial push-pull test machine and equipment generating the thermal gradient in the notched plate by induction heating. Stress concentration level was changed by varying the notch radius in the both kind of tests. Crack initiation and propagation process during the fatigue test were observed by the digital micro-scope and replica method. Elastic and inelastic FEAs were also carried out to estimate the ‘strain range’ for the prediction of fatigue life. Then the ranges of several strain predictions and estimations were compared with the test results. These predictions were based on the sophisticated technique to estimate the ‘strain range’ from elastic FEA. Stress reduction locus (SRL) method, simple elastic follow-up method, Neuber’s rule method and the methods supplied by elevated temperature design standards were applied. Through these results, the applicability and conservativeness of these strain prediction and estimation methods, which is the basis of the creep-fatigue life prediction, is discussed.

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