Abstract
In the design of high-temperature equipments, the inelastic analysis comes to be frequently used in predicting a creep-fatigue life of the equipments. This paper describes the accuracy of the inelastic analysis and the life prediction.
The material used in the investigation was normalized and tempered 2-1/4Cr-1Mo steel. The constitutive equation in which the total strain is equated as the sum of elastic, plastic and creep strain was used in the inelastic analysis. The accuracy of the inelastic analysis was pre-checked by applying the analysis to the experiments studying the strain rate effect.
Uniaxial strain-controlled creep-fatigue tests were performed at 600°C in air, and the actual creep-fatigue lives were compared with the predicted lives using the inelastic analysis and two kinds of life prediction methods; the life fraction rule of ASME B & PV Code N-47 (LFR) and the strain range partitioning method (SRP).
The comparison showed that LFR was influential to the accuracy of a calculated value of the stress, and that the predicted lives were far shorter because of higher calculated stresses in the prediction. In order to improve the accuracy of the life prediction by LFR, plasticity-creep interaction should be considered in the inelastic analysis.
On the other hand, SRP was not so influential to the accuracy of a calculated value of the stress, and a good agreement was observed between the predicted and actual lives.
