Study of long-term cyclic strength under soft asymmetric and rigid loading

Abstract

1. Experimental data obtained in the case of rigid loading on steel Kh18N9T at 600°C with rest periods during constant strain showed that rest periods in the tensile half-cycle are more damaging than during tensioncompression. 2. Rest periods in the compressive half-cycle on steel Kh18N9T increase its long-term ductility. 3. With soft asymmetric loading in the range r=−1.5 to −2.0 and rest periods under constant load conditions in the tensile half-cycle, the magnitude and sign of strain accumulation is determined by the maximum cycle, cycle asymmetry, and rest period duration. The same factors determine the nature of damage; with increasing cycle asymmetry the proportion of fatigue damage increases, and with increasing maximum stress and rest period duration the proportion of long-term static damage increases. 4. The strain-kinetic criterion of long-term cyclic failure satisfactorily describes damage during soft asymmetric (in the range r=−1.5 to−2.0) and rigid loading with rest periods.