Abstract
1. For 15Kh2NMFA steel at 293°K an increase in the value of R from−1 to 0.5 with the same value of Kmax decreases the fatigue crack growth rate in the medium amplitude area of the fatigue crack growth curve by about an order of magnitude. The use of the Forman equation for describing the results leads to a significant deviation of the data from the calculated relationship. 2. The character of the influence of the compressive portion of the load cycle on the fatigue crack growth rate in the investigated steel depends upon test temperature. At 293°K a symmetric load cycle leads to a substantial increase in fatigue crack growth rate in the medium amplitude area. With a reduction in test temperature to 183–213°K, the influence of the compressive portion of the cycle ondl/dN does not appear. 3. With an increase in cyclic fracture toughness, the fatigue crack growth rate before the jump increases. At a temperature of 183°K the influence of cycle asymmetry coefficient (in the R =−1 to +0.4 range) on this relationship is insignificant. 4. For 15Kh2NMFA steel in the 183–213°K range a change in R from−1 to 0 does not influence the value of Kfc1. In constant sign loading with an increase in the asymmetry coefficient, the value of Kfc1 increases and there is a more substantial increase at 213°K.
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