Maslo O. Damage and limiting condition of metallic materials under conditions of plastic deformation under different types of mechanical loading

The object of the study is the kinetics of accumulation of scattered microdamages in the structural material under the influence of external temperature and force factors. The purpose of the dissertation is to experimentally study the patterns of accumulation of scattered damage during elastic-plastic deformation and destruction of a wide range of structural materials under different loading conditions and to determine phenomenological approaches to finding yield strength and failure using non-destructive testing methods based on generalized strength criteria. Research methods - experimental methods for studying the kinetics of damage accumulation in materials under static, re-static, long-term static and cyclic loads. Theoretical and practical results - the kinetics of damage accumulation of a wide range of structural materials using the non-destructive method of LM-hardness, under static, re-static, long-term static, low-cycle and multi-cycle loads, has been experimentally studied. For the researched materials, the values of the Weibull homogeneity coefficient characterizing the limit state of the beginning of their fluidity and fracture were determined and experimental limit curves corresponding to fracture and state of plasticity at flat stress state were obtained, taking into account the structural inhomogeneity of the material. The scientific novelty of the obtained results is to establish the patterns of accumulation of damage by assessing the structural heterogeneity of structural materials of different classes with a wide range of operating loads, as well as to determine the values of structural heterogeneity parameters corresponding to yield strength and fracture. The results of the dissertation were used in solving problems related to the assessment of the resource and strength of elements of the equipment of South-Ukrainian NPP and Rivne NPP. The practical significance of the obtained results lies in the possibility of applying the proposed method for determining the yield strength and fracture of the material to assess the residual service life of materials of structural elements by non-destructive method.