Some regularities in the variation of heat-resistant nickel alloy fatigue resistance under the combined action of alternating and static loading

Abstract

1. Static tensile loading, characteristic for the operation of gas turbine rotor blades, leads to a reduction in fatigue resistance and endurance of heat-resistant EI867 and VZhL12U nickel alloys. The magnitude and intensity of the reduction in fatigue resistance under the influence of static tensile load depends on the temperature range (above and below 0.6TM) at which the load is applied. 2. The nature of the limiting condition for heat-resistant alloys under asymmetric loading conditions is expressed in the form of an ultimate stress diagramσ a −σm, and is also defined by the temperature level. A linear relationship between values ofσ a andσm is appropriate for the moderate-temperature range (below 0.6TM). In the high-temperature range (above 0.6TM) ultimate stress diagrams satisfactorily approximate two straight lines, characterizing the different intensity of the reduction in alternating failure stress amplitude with increasing mean stress. 3. Two basic forms of failure, fatigue and quasistatic, are possible during tests on heat-resistant alloys in the high-temperature range with different ratios of alternating and static loading and a smooth loading schedule. The level of material ductility realized, determined as the ratio of accumulated unilateral plastic strain ɛ∑(t) during cyclic loading to long-term ductility ɛf(t), can serve as a criterion of the failure type.