A. P. Sychev

Triboinduced Adsorption of Liquid-Crystal Nanomaterials under Frictional Interaction of Solids

269 Nowadays, ever increasing attention of experts in the field of the triboengineering and physics of condensed state is focused on the problem of realization of boundary layers structured at the nanolevel in contact with solids. It is actual under conditions of both static and dynamic contact with solids, when the presence of boundary layers with a special structure in the microgap between them defines the degree of friction-energy dissipation [1‐4]. The cholesteric liquid-crystal substances, which quite justifiably can be referred to the class of nanoobjects due to the size of their molecules and the structural features, occupy a special place in these events. Some authors cited them as an example of compounds that are widely involved in the production of unique nanoconstructions, for example, nucleinic acids, etc., in nature [5]. However, despite the very large number of experimental data revealing the mechanism of lubricant action of such liquid-crystal compounds, the regularities of their adsorption on friction surfaces between solids remain unclear. The theoretical and experimental data concerning the interaction of such nanomaterials with a solid surface, in particular, the adsorption of their molecules, describe the behavior of individual mesogenic substances and mainly consider the sphere of their electrooptical application [6, 7]. At the same time, the data on the interaction of solutions of nanocompositions having liquid-crystal properties with friction surfaces represent the clear interest in the tribologic aspect.

Association of evaluation methods of the effective permittivity of heterogeneous media on the basis of a generalized singular approximation

Various methods for evaluation of the effective permittivity of heterogeneous media, namely, the effective medium approximation (Bruggeman’s approximation), the Maxwell-Garnett approximation, Wiener’s bounds, and the Hashin-Shtrikman variational bounds (for effective static characteristics) are combined on the basis of a generalized singular approximation.

Studying thermal state of friction pairs of multidisc brake

A dimensionless heat problem for a friction pair of a multidisc brake was formulated under conditions of a linear decrease in the friction power of discs with time. Thermal state of friction pairs of the multidisc brake under load and velocity conditions of the friction of the discs that simulate service brakings of a wheel tractor was experimentally and theoretically studied. The validity of a mathematical model of the temperature field in the discs of the brake has been experimentally confirmed and functional dependences of the maximum temperature of friction surfaces of the discs on values of the main performance parameters have been obtained.

Predicting the Limiting Strength of Nontextured Matrix Composites

The limiting strength in the compression of composites based on an epoxy-resin matrix with disperse inclusions (graphite, E-glass, copper, and iron) is simulated on the basis of the generalized singular approximation of random-field theory, using the stress-concentration operator and data regarding the strength of the epoxy matrix.

Bulk strain energy density in randomly reinforced polymer composites with antifriction dispersed additives

Bulk strain energy density was numerically simulated for epoxy-phenol-based composites randomly reinforced with short polyimide fibers, with antifriction dispersed polytetrafluoroethylene (PTFE) additives. A mathematical model was constructed using the notion of a stress concentration operator (fourth-rank tensor) that relates volume averaged, or external, stresses within a heterogeneous material with their local values within an individual heterogeneity. The simulation was based on a generalized singular approximation of random field theory used to solve a stochastic differential equation of equilibrium of an elastic medium. This approximation yields an explicit expression for stress concentration in a composite material. The explicit expression allows one to analyze the distribution of bulk strain energy density depending on the composition, structure, volume and mass fraction of heterogeneities, and on the type and value of applied load. We studied how the considered energy characteristic depends on the type of external mechanical loading and concentration of isotropic components in the model composites. It is shown that with the increasing concentration of polyimide fibers at a fixed concentration of PTFE inclusions, the bulk strain energy density values of all components decrease and approach each other independently of the type of external loading. The form of these dependences is nonlinear. A change in the mass fraction of dispersed PTFE inclusions in the model composites exerts little effect on local energy values of all components under any of the considered applied external loads.

A method of analysis of distributions of local electric fields in composites

A method of prediction of distributions of local electric fields in composite media based on analysis of the tensor operators of the concentration of intensity and induction is proposed. Both general expressions and the relations for calculating these operators are obtained in various approximations. The analytical expressions are presented for the operators of the concentration of electric fields in various types of inhomogeneous structures obtained in the generalized singular approximation.

Thermoinduced effect of reversible lubricating ability of cholesteric liquid-crystalline nanomaterials in friction of solids

123 Currently, the efficient operation of transport and other industries necessitates reducing the energy con� sumption of machinery, which is associated with fric� tional interaction at friction units. Active control of the frictional interaction of solids is one of the chal� lenges of modern tribology [1–5]. Once friction is actively controlled, the response of the elements of tri� bological units to the energy input is reversible and can be done automatically with the help of modern control systems and the use of feedback. Research in this area is constantly evolving and focuses on several issues.

Lubricants with ceramic nanoadditives and wear-resistant surface structures of heavy-duty frictional joints

The addition of β-Sialon nanoparticles to lubricants in heavy-duty frictional joints is shown to be effective.

A generalized effective-field approximation for an inhomogeneous medium with coated inclusions

An approach developed on the basis of a model of a composite with heterogeneous inclusions—the effective-field approximation—is proposed. With the help of this approximation, an expression is obtained for the tensor of effective dielectric characteristics of a heterogeneous medium consisting of inclusions representing a core inside a coating, the outer and inner boundaries of which are ellipsoids. The proposed approach has a large degree of generality and can be used both for multicomponent composites and for polycrystals. It was shown that this approach gives the same result as the generalized singular approximation in the case of the uncoated inclusions.

Deformational energy density in antifrictional fabric composites

The bulk deformational energy density is simulated in antifrictional fabric composites with an epoxy base reinforced by polytetrafluoroethylene and glass fibers in two mutually perpendicular directions. The fibers in different directions consist of different materials. The influence of the external mechanical action and the content of fibers in the composite on the bulk deformational energy density is investigated.