Calculation of the service life of parts operating in the field of high-cycle fatigue is, as a rule, based on the linear hypothesis of damage accumulation, which is the result of many years of experience in assessing the service life of machines and structures under the action of time-varying loads. At the same time, the linear hypothesis assumes that the fatigue resistance characteristics of materials remain unchanged during the calculation process and therefore does not fully reflect the physical processes of damage accumulation. In this regard, the development of new approaches to calculating fatigue life under operational loads is an urgent task. This paper examines a model for the continuous reduction of the endurance limit: the main characteristic of resistance to fatigue failure under cyclic loading. This model makes it possible to formulate and analytically substantiate the patterns of decrease in static and cyclic properties with operating time, on the basis of which a model is proposed for calculating the resource under irregular (schematized block) loading by iteratively sequentially calculating the current value of the endurance limit and determining the residual durability from the action of the damaging amplitude.
The iterative process involves assessing the durability, determined from the corresponding secondary fatigue curve, that is, it is assumed that at each iteration step there is a continuous decrease in the characteristics of fatigue and static properties.
To experimentally test the methodology, we used the results of fatigue tests of AVT-1 and D16 alloys, as well as natural elements of a helicopter rotor blade spar made of AB alloy under regular and programmed loading conditions, which showed satisfactory agreement between the experimental and calculated values of the characteristics of resistance to fatigue failure.