Lyashenko I. Statistical representation of boundary friction and fragmentation of metals

The purpose of the dissertation is the study of phenomenological models which describe the processes of boundary friction and severe plastic deformation (SPD) based on the systems of self-consistent differential equations. Boundary friction is investigated within the framework of the rheological model which takes into account thermodynamic and shear melting. Description of these processes, occurring as a result of self-organization of the fields of shear stress and strain, as well as temperature of lubricant film is carried out. Different temperature dependences of viscosity, additive uncorrelated fluctuations of basic parameters, correlated fluctuations of temperature are taken into account. Influence of deformation defect of shear modulus of lubricant on melting is investigated. The process of SPD is studied on the basis of model that is based on the Landau theory of phase transitions. It is shown that the deformation defect of the shear modulus of lubricant results in a hysteresis behavior at melting. Parameters are found at which the periodic stick-slip mode of friction is realized. At consideration of noise the phase diagrams are built with different friction modes. The self-similar mode is described. The changes of the friction modes are observed using the time dependences of stresses. The fragmentation of metals during the process of SPD is investigated, and the phase diagram with different modes of fragmentation is built. It is found out that with the growth of elastic strain the size of grains decreases in samples formed by SPD. The principle possibility of quasi-fractal grain structures formation is shown.