AN IMPROVED THEORY OF DETERMINING THE PARAMETERS OF PLASTIC FLOW OF MATERIAL UNDER COMPRESSION BY MEASURED MEYER HARDNESS
Background. The research object is a problem of elastoplastic indentation of indenters of various shapes in an elastoplastic coating. It is relevant as it is the theoretical basis for measuring the surface hardness of parts in production. The research subject is the establishment of a relationship between the surface Meyer hardness and yield strength under compression. The aim of the study is to construct improved formulas that bind Meyer hardness and yield strength under compression, taking into account the hardening of the material under compression. Materials and methods. An improved theory of determining the parameters of the plastic flow of a material under compression by the measured Meyer hardness is constructed using a generalized core model of the coating. All types of indenters used both in industry and in scientific research are considered. As an approximation of the elastoplastic behavior of the material, the well-known Prandtl bilinear diagram is used. It was this diagram that found the most widespread use in engineering-oriented software for modeling the elastic-plastic behavior of a structure. Results. For the first time, equations are obtained that determine the relationship between two plasticity parameters under compression (yield strength and the ratio of the plastic modulus to the elastic modulus) with the values of Meyer hardness. The term “plasticity modulus” is a direct borrowing from the manual to the ANSYS finite element calculation program. It determines the angle of inclination of the hardening section to the axis of deformation. Since the results obtained in the article formally do not depend on the thickness of the coating, they can be interpreted as universal, true for any solids. Conclusions. It is established that for the unambiguous determination of two plasticity parameters during compression, it is easiest to use two indenters of different shapes. It can be balls of various diameters, or a ball and a cone with a standard angle at the apex, or a ball and a pyramid (also with a standard angle of inclination of the faces). In this case, at the first step, due to the choice of a relatively large diameter of the ball and low force, the researcher will be able to uniquely determine the yield strength, and the second parameter will be determined by the introduction of the second indenter (a ball of small radius, a cone or a pyramid).