The paper considers methods of accelerated determination of endurance limits of metals and alloys based on the analysis of regularities in their inelastic deformation, strain and energy criteria of fatigue fracture, and methods for life prediction with the use of those criteria.Keywords: endurance limit, accelerated method, strain and energy criteria, life prediction.Introduction. Strain and energy criteria of fatigue fracture of metals and alloys are based on the analysis of either inelastic strains and inelastic strain energy or total strains and strain energy of which inelastic strains and energy are a part. This gives grounds to conclude that the regularities in the nonlocalized fatigue damage form the basis of these criteria.The purpose of the development of the fatigue fracture strain and energy criteria is to establish the relationship between these criteria and the number of cycles to fracture with allowance for the mean stress in a cycle, multiaxial proportional and nonproportional loading, stress concentration, loading conditions, etc. using the characteristics obtained under uniaxial steady-state loading.The criteria, which allow determining the endurance limit without performing a complete cycle of testing in order to plot a fatigue curve, are of special importance when considering the strain and energy criteria of the fatigue fracture. Methods that make it possible to determine the fatigue limit without full-scale tests have come to be known as accelerated methods. Figure 1 shows a fatigue curve for metals and alloys plotted with allowance for the results of recent investigations [1][2][3][4][5] in the coordinates stress-number of cycles to fracture in a wide range of numbers of cycles to fracture, where stage I corresponds to the fatigue fracture in which the main role belongs to the processes on the surface, stage III -to fracture in which the main role belongs to the internal defects (inclusions, pores, etc.), stage II corresponds to the endurance limit when the fatigue fracture is governed by the surface processes, and stage IV to the endurance limit when the fatigue fracture is related to the internal defects.From Fig. 1 it follows that, firstly, the limiting stress amplitude decreases even when the number of the load cycles exceeds 10 7 cycles; secondly, the transition of the fatigue curve from stage I to stage III is accompanied by the appearance of a discontinuity on the fatigue curve, which cannot always be well determined, specifically, when a small number of specimens is tested; thirdly, at stage IV the endurance limit is not always observed, which was noted in [3][4]. Discontinuities on the fatigue curves of aluminum alloys and steels were also observed in the region of stresses corresponding to 10 5 -10 6 cycles to fracture [6][7][8].Results of the experimental investigation into fatigue and inelasticity of metals and alloys known from the literature were obtained for the number of cycles to fracture below 10 8 cycles and, according to the scheme presented in Fig. 1, pertain to fatigue d...
