Introduction. At the present time, the problem of determining current values of strains and stresses in the case of plastic deformation of metal is very topical since it is rather difficult to calculate these characteristics by the plasticity theory methods. Such data are required for the determination of stresses in the body surface layers, optimization of the manufacturing process, improvement of quality and for the design of products of optimal weight.To determine stresses in an elastoplastic deformed material in different stages of manufacture of products and to control their mechanical properties during operation, the static and dynamic hardness method is widely employed [1,2]. The hardness method appears to be most suitable in terms of the ease of realization, convenience, low cost, availability of instrumentation and the possibility to carry out research without loss of product integrity.The aim of this work is to further develop nondestructive testing methods, in order to improve the reliability of determination of current stresses in plastically deformed metal from hardness values.Procedure and Test Results. It is known that hardness characterizes such properties of materials as strength and ability to resist plastic deformation or brittle fracture or brittle fracture on local contact interactions with a harder body, indenter [1]. If one has a calibration curve of hardness against stress level, it is proposed to determine stresses in the plastic domain from hardness distribution [3].However, in spite of obvious advantages, the classical version of the hardness method is insufficiently informative since hardness is in most cases only slightly sensitive to many types of structure transformation [4], and the correlation of hardness values with other mechanical characteristics is not always stable and unambiguous [5].Analysis of the results of the research carried out for technical applications using the hardness method shows that it is very difficult to improve reliability of correlation between hardness values and other mechanical characteristics, such as the ultimate and yield strength of material [3,6,7]. Note that the more plastic the material, the less exact will be the derived relationships between hardness and strength.The ambiguity of variation of metal hardness as a function of the strain level reached has been established experimentally from the test results for specimens of steels of different classes: St. 3, 20KhN3, 17G1SA, 40Kh, stainless steels, titanium alloys and V95 aluminum alloy under short-time static, sustained and cyclic loading conditions. The hardness of metals changes only slightly under the above loading conditions; moreover, it may both increase and decrease [8][9][10]. Similar results were obtained when investigating metalworks of lifting machines in the case of high-cycle fatigue [11].It may be noted that hardness as the most common characteristic of material, which determines its quality and the possibility to use it in constructions under different operation conditions, is amb...