Validation and background of crack opening and closing relation for use in high temperature assessment

摘要

Crack opening and closure behaviour is well documented for positive stress ratio R conditions at room temperature. The present paper reports on fatigue and creep-fatigue tests at elevated temperatures for a variety of steels and for negative values of R. The results indicate that compression-tension loading increases fatigue crack growth rates above those for R = 0 tests because of differences in opening/closure effects. However the full tension-compression range need not be applied when calculating the effective stress intensity range. The results also show that the R5 procedures for high temperature assessment of structures provide a reliable upper bound limit for use by designers.