APPLICATION OF SHAKEDOWN ANALYSIS TO EVALUATION OF CREEP-FATIGUE LIMITS

Shakedown analysis may be used to provide a conservative estimate of local rupture and hence cyclic creep damage for use in a creep-fatigue assessment. The shakedown analysis is based on an elastic-perfectly plastic material with a temperature-dependent pseudo yield stress defined to guarantee that a shakedown solution exists, which does not exceed rupture stress and temperature for a defined life. The ratio of design life to the estimated cyclic life is the shakedown creep damage. Fatigue damage may be calculated from the local strain values in the shakedown analysis using the existing procedures in Appendix T of Subsection NH for equivalent strain range. The methodology does not require stress classification and is also applicable to cycles over the full range of temperature above and below the creep regime.