Study of the properties of materials under complicated conditions of low cycle deformation

Operational integrity of structures under complex combined modes of a loading depends on a significant number of combinations of operational parameters of thermomechanical impacts in part of loads, temperatures, duration, number of cycles, and deformation rates. The main laws governing the deformation of structural materials under complex loading are determined in conditions of combined standard, unified and special tests in laboratories. Using representative substantiations of physical and mechanical models for deformation diagrams in a wide range of loading conditions, taking into account the different scales of models, the structure of materials and the responsibility of structures, a stepwise consideration of the corresponding types of deformation is proposed: elastic, sign-variable flow, progressing accumulation of strains and their combination. At the same time, calculations of the structures can be carried out in the form of a hierarchical system in which each next level specifies the boundaries of permissible impacts towards expansion of the range of acting loadings, temperatures, rates and modes of deformation, which entails an increase in the bulk of the required initial data and complicates the calculations. The proposed methods of schematization of the physicomechanical properties and types of the equations of state for description of the deformation curves take into account the requirements of compactness of the initial data and the need of using both standard and unified methods for determining the characteristics of cyclic inelastic deformation and special methods as well. To describe the kinetics of deformation diagrams under aforementioned conditions both from the theoretical point of view and from the point of view of practical applications, power equations appeared most suitable; to reflect the role of the temperature factor exponential dependences should be used; whereas power dependences are useful to take into account time factors, strain rate, and conditions of two-frequency loading. The refined calculations at the higher and more complicated steps of the considered hierarchy providing the maximum possible use of the deformation and strength reserves of the materials and structures are to be based on the kinetic laws describing processes of low cycle deformation under complex modes of loading.

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