Introduction. To keep automobiles and tractors in operation conditions, it is necessary to restore the inner cylindrical surfaces of the friction pair parts. This is the most laborintensive activity. The method of electroplated contact deposition of composite coatings, based on elastic plastic deformation of formed layers, is used for repairing surfaces. To use this method it is necessary to determine the values of the elasticity modulus, on which the wear resistance of tribocouplings depends. Materials and Methods. For the study, cylindrical samples made of 30 HGSA and 30 HGSNA steels were used. Electrolyte containing 200–250 g/l chromium oxide, 2.0–2.5 g/l sulfuric acid, and distilled water was used for electroplating the coatings. When calculating the stress-strain state, the apparatus of continuum mechanics was used. Results. The dependence of the coating pliability as a function of the parameters of individual elementary layers is determined. When the multilayer coating of three types (orthogonal-reinforced, cross-reinforced and quasi-isotropic) is applied, its structure does not depend on the angles of kinematic tool movement on the inner cylindrical surface of the part. For each type of coatings, the way to determine the constant stiffness coefficients of the layers is specified. The dependences for calculating the elasticity modulus of the applied material are derived from the values of the stiffness coefficients. Discussion and Conclusion. In determining the modulus of elasticity of multilayered composite coatings, the calculation is made for the individual layers by passing to the convective coordinates, which is in complete agreement with the Lagrange point of view on the study of the motion of a continuous medium. The results obtained are of practical significance in the selection of the coating material to be applied for the restoration of internal cylindrical surfaces.

Introduction. The article deals with the problem of calculating the strength of the shaft of the wheel drive of agricultural machinery. The strength conditions of both the maximum torque and the values of relative deformations of the shaft are taken into account. Aim of the Article. Of the research is to determine the limits of external influences on a structural element, caused by the distributed weight of the motor-tractor machinery, at which it is necessary to construct not only the torque and strain diagrams, but also to determine the extreme values at each section, where the strength index of the structure is nonlinear. Materials and Methods. In calculations, the main provisions of continuum mechanics, theory of machines and mechanisms, as well as the basics of design in mechanical engineering are used. Central attention is paid to the influence of external influencing factors on the character of internal force distribution in the shaft. Results. The obtained area of variation of parameters P-q allows us to determine the necessity of more detailed calculation of strength parameters of the considered part. This is due to the emergence of extreme areas outside the boundaries of individual areas of consideration of the shaft work. The results are presented as a two-dimensional graph of the ratio of external influences, at which the specified effect takes place. Discussion and Conclusion. In comparison with typical calculations, regulated by normative documents, the proposed algorithm at the preliminary stage allows to determine the cases when nonlinear regions of bending moment changes require additional investigations. The use of the proposed algorithm allows, without resorting to time-consuming numerical methods of calculating the strength indicators of a wheel drive shaft, such as the finite element method, to obtain a more detailed picture of the nature of distribution of internal forces and deformations in the part under study.

One of the most common reasons for the failure of hydraulic drive systems for agricultural machinery is the working fluid leak in the contact points of the rubbing surfaces of hydraulic blocks. The application of composite coatings based on chromium on the contacting surfaces allows you to restore the defect in the shape of the part caused by wear, as well as reduce the friction coefficient at the contact points, which positively affects the wear resistance of the part. (Research purpose) The research purpose is in developing technologies for restoring parts of agricultural machinery with predetermined operational properties. (Materials and methods) A servo valve, widely used in various hydraulic drive systems, was used as an experimental sample. Its working surface was restored with a composite coating applied by electroplating to increase the wear resistance of the servo valve. (Results and discussion) Authors conducted a series of direct measurements under the same conditions. The article presents the de-pendence of the microhardness on the parameters of the electrolysis mode and the thickness of the applied coating using the method of least squares. The nature of changes in microhardness and residual stresses was evaluated to determine the quality of the coatings. The article presents the dependences of these indicators on various control parameters (current density, temperature, tool pressure). The equations of the regression of the main qualitative and accuracy characteristics of the parts were deter-mined using the apparatus of the theory of experimental planning. (Conclusions) The article presents the method for predicting coatings of a given quality, taking into ac-count the influence of the current density and the temperature of the electrolyte during electrolysis on the nature of the precipitation obtained. The influence of the tool pressure on the depth of deformation of the formed layers was estimated. This approach allows us to evaluate the nature of the stress distribution in the formed coating and the quality of the restored parts.