CONTACT OF MULTI-LEVEL PERIODIC SYSTEM OF INDENTERS WITH COATED ELASTIC HALF-SPACE

The contact of a periodic system of spherical indenters of different heights and radii of curvature with two-layered elastic half-space is considered. Numerical-analytical method is developed to determine contact pressure distribution and internal stresses taking into account mutual effect of contact spots. The results for relatively hard and soft coatings are analyzed for different values of input parameters: nominal pressure, contact density, coating thickness

Effect of Surface Layers in Sliding Contact of Viscoelastic Solids (3-D Model of Material)

Sliding contact of a smooth indenter and a two-layered half-space is considered to take rheological properties of materials into account. A viscoelastic layer bonded with a rigid half-space is analyzed as well as the opposite viscoelastic half-space covered by a rigid layer. The problem is formulated as quasi-static. A numerical-analytical method of solution is based on a boundary element method and an iteration procedure. A new analytical solution is used to calculate the influence of coefficients for the computation procedure. Contact pressure, energy dissipation and internal stresses are analyzed depending on sliding velocity, layer thickness and Poisson's ratio

Damage of functionalized self-assembly monomolecular layers applied to silicon microgear MEMS

Tooth surfaces of silicon-based MEMS microgears are described as smooth surfaces covered by adhesive asperities (nanoblocks). To reduce adhesive effects, the tooth surfaces are functionalized by OTS-SAM (Octadecyltrichlorosilane self-assembly monomolecular) carbon-based functionalized coatings. The wear of the coating is modelled using the modified Goryacheva-Torskaya model of damage accumulation. The amount of energy dissipated by different physical and chemical mechanisms along with energy dissipated by mechanical deformation of the counterparts is used to evaluate the frictional force. The main scenarios of wear process within the coating are described and discussed. The damage evolution is described for several levels of external load

Secondary structures on the friction surface of diamond-like coating

Peculiarities of the formation of secondary structures on the surface of a diamond-like coating are studied on the example of a friction contact between a steel ball and a diamond-like coating. The friction surface was examined in various areas; the zone of wear products (the boundary of the friction track) and the original surface outside the friction area. It is shown that secondary structures with a high content of iron, nickel, manganese, chromium, and oxygen are characteristic of areas with the highest wear resistance. Such secondary structures are formed because of the intense interaction of the diamond-like coating with the steel of the ball during dry friction

Friction Reduction Due to Heating in the Sliding Contact of Smart Coating: Modeling of Mutual Effect

In smart coatings designed for friction units operating in wide temperature ranges, the material reacts to heating by changing its frictional properties. Appropriate experimental studies are available. In this paper, a model is proposed for studying the mutual effect of frictional heating, which is inhomogeneous in the contact area, and shear stresses. The distribution of the latter differs from the Amonton–Coulomb law according to local temperatures, from which the local friction coefficient depends. Two problems are independently solved in the model: the problem of elastic contact between a smooth slider and a two-layer elastic half-space, and the thermal problem. The solution methods are numerical–analytical and are based on Hankel integral transforms and iterative procedures. The problem has been solved for two types of sliders simulating pin-on-disk and ball-on-disk test schemes. For the selected dependences of the local friction coefficient on temperature, an analysis was made to study the influence of sliding velocity and coating thickness on the distribution of temperatures, tangential stresses in the contact zone, as well as integral friction force. Relatively rigid and relatively compliant coatings were considered. It was found that for such smart coatings, which implement the mechanism of self-lubrication during frictional heating, there is a decrease in the friction force with increasing velocity, especially for relatively thick coatings with low thermal conductivity

PARAMETER DETERMINATION OF THE CONTACT INTERACTION AND PARTICULAR FEATURES OF THE SURFACE DESTRUCTION FOR BODIES WITH HETEROGENEOUS MECHANICAL AND TRIBOTECHNICAL CHARACTERISTICS

The approximate method for the solution of a contact problem for a system of dies and a two-layer elastic half-space has been suggested. The form modification of local-strenghtened surfaces has been investigated. The forecasting of the type of the coating destruction at the multiply character of the contact interaction in the dependence on coating parameters has been represented. Optimum (from the point of view of the conjugation durability) parameters of heterogeneity have been determinedAvailable from VNTIC / VNTIC - Scientific & Technical Information Centre of RussiaSIGLERURussian Federatio

Friction Reduction Due to Heating in the Sliding Contact of Smart Coating: Modeling of Mutual Effect

In smart coatings designed for friction units operating in wide temperature ranges, the material reacts to heating by changing its frictional properties. Appropriate experimental studies are available. In this paper, a model is proposed for studying the mutual effect of frictional heating, which is inhomogeneous in the contact area, and shear stresses. The distribution of the latter differs from the Amonton–Coulomb law according to local temperatures, from which the local friction coefficient depends. Two problems are independently solved in the model: the problem of elastic contact between a smooth slider and a two-layer elastic half-space, and the thermal problem. The solution methods are numerical–analytical and are based on Hankel integral transforms and iterative procedures. The problem has been solved for two types of sliders simulating pin-on-disk and ball-on-disk test schemes. For the selected dependences of the local friction coefficient on temperature, an analysis was made to study the influence of sliding velocity and coating thickness on the distribution of temperatures, tangential stresses in the contact zone, as well as integral friction force. Relatively rigid and relatively compliant coatings were considered. It was found that for such smart coatings, which implement the mechanism of self-lubrication during frictional heating, there is a decrease in the friction force with increasing velocity, especially for relatively thick coatings with low thermal conductivity

Interfacial fracture of thin elastic layers due to cyclic load

AbstractFracture of thin surface layers, which are harder or softer than the substrate material, is considered for the case of cyclic sliding contact. The study is based on modeling of multiple and single contact of two-layered elastic half-space, identification of elastic properties of the surface layers from indentation results, theoretical and experimental study of relatively hard coatings delamination due to contact fatigue, which arises at the level of asperities. The parameters of damage accumulation law at the coating-substrate interface for two component oxide coating are estimated. The properties of relatively soft coatings, which arises during friction of aluminium alloys because of soft faze extrusion are obtained from indentation data

Effect of Non-Linear Properties of Intermediate Layer on Sliding Contact of Homogeneous and Coated Elastic Solids

Lubrication in the contact area can be considered as a viscoelastic layer, especially in the presence of particles in it, or under conditions of low temperatures. The properties of this layer are often non-linear, in particular, they depend on local pressure. The paper presents a formulation and numerical-analytical method for solving the contact problem in the presence of viscoelastic layers, the compliance of which depends on the applied pressure and is included in the formulation as the corresponding operator. The layer is homogeneous or coated elastic half-space. For the selected type of operator, the influence of parameters, which characterize the nonlinearity of the model, on the distribution of contact pressure and the coefficient of friction due to hysteresis losses was analyzed. It is shown that for the nonlinear model, the maximum contact pressures are higher, and the friction coefficient is lower than for the linear model with constant compliance. The effect of non-linearity for a wide range of sliding velocities is considered. An analysis of principal shear and tensile-compressive stresses for a homogeneous elastic half-space and for a coating, in particular, for a coating-substrate interface, was also carried out

Modeling of Fatigue Wear of Viscoelastic Coatings

A new model for studying the kinetics of fatigue wear of a viscoelastic coating bonded to a rigid substrate is proposed. The fatigue mechanism is due to the cyclic interaction of the coating with a rough counterbody, which is modeled by a periodic system of smooth indenters. The study includes the solution of the problem of sliding contact of the indenter at a constant velocity along the viscoelastic coating, the calculation of stresses taking into account the mutual effect, and study of the process of damage accumulation in the material. The calculation of the damage function of the surface layer was carried out using the reduced stress criterion. Assuming the possibility of summation of accumulated damage, two processes were considered: delamination of surface layers of the coating and continuous fracture of the surface by the fatigue mechanism. The effect of the sliding velocity and viscoelastic properties of the material on the damage accumulation and the coating wear rate was analyzed. Two types of load, constant and stochastically varying, were used in modeling and analysis. It was found that the rate of fatigue wear of the coating increased and then became constant