Evolution of strains and damages at a cyclic elastoplastic deformation with dwells and superimposition on them additional pulsations of loading

It is noted that the major factor characterizing process of a cyclic elastoplastic loading is the diagram of a deformation in coordinates «stress – strain». The kinds of this diagram generally depends on the level of service stresses and strains, the mode and conditions of a loading, type of constructional material. At the same time one of fundamental problems of mechanics of a deformation and fracture which solution allows to carry out formation of the basic state equations, describing conditions of achievement of limit states on the basis of criteria of accumulation of damages, is the task about establishment of regularities of a kinetics of strains at a cyclic elastoplastic deformation which directly form basic parameters of deformation criteria of low cycle fracture. On the basis of results of the executed experimental researches it is shown that at the presence in cycles of dwells on extrema of loading and superimposition on these dwells of variable stresses in comparison with a regular cyclic loading with equal amplitudes of stresses the evolution of additional strains owing to an propagation of processes of a creep takes place. These strains of a creep substantially cause growth of cyclic plastic strain in each cycle of a loading, and also stimulate increase in an elastoplastic strain from an active cyclic deformation. At the same time existence of dwells on extrema of stresses without superimposition of additional variable stresses most influences on growth of full plastic strain in cycles. Superimposition of additional variable stresses during dwells also increases values of strain of a creep, but this increase is shown more at their impact with smaller frequencies, than at their dynamic application. The factor of increase in cyclic plastic strain at forms of a cycle with dwells and superimposition at their course of additional variable stresses causes decrease in these cases of a low cycle fatigue life in comparison with a regular loading without dwells, equal on amplitudes of stresses, and that more than values of strain from a static and dynamic creep are higher. Growth of cyclic plastic strain due to the additional plastic strain of a creep progressing during dwells according to deformation kinetic criteria increases damageability of material in the course of a cyclic elastoplastic deformation that causes decrease in a cyclic fatigue life.