Vol 38, No 2 (2017)

Using full factorial design in experiment 3², the contents of vanadium and chromium in heattreated V–Cr–Mn–Ni cast irons with spheroidal vanadium carbide have been optimized with regard to the conditions of quartz sand erosion. It has been found that, in the case of bulk quenching from 760°C (or in combination with a subsequent plasma surface hardening), the maximum wear resistance of cast iron is achieved at 5.0% V and 2.0–4.5% Cr and, in the case of bulk quenching from 840°C followed by cryogenic treatment (–196°C), at 5.0% V and 7.0–9.0% Cr. It has been shown that the wear mechanism of the investigated alloys consists of the repeated deformation (indentation) of the matrix accompanied with spalling of spheroidal carbides and with chipping of eutectic carbides. Spheroidal vanadium carbides provide an effective protection of dendrites regions against erosion due to their uniform distribution in the bulk of the alloys.

Today, it is considered that the latest principally new breakthrough in the sphere of tooling materials was the invention of metal-ceramic solid alloys in the 1930s. Moreover, model materials for cutting tools have slowed down the further development of metal-working equipment, which, e.g., may propose higher cutting modes. That is why the main current trends in improving the performance of tooling materials is improving manufacturing technologies and changing their chemical composition and hardening applications. The subject of our study is the wear pattern of a cutting tool made of BK-8 solid alloy subjected to VPLH under production conditions. Furthermore, the aim is not only to determine the most optimum hardening modes (energy and duration of the laser impulse, diameter of the laser beam, distance from the radiation point to the cutting edge), but also to analyze the stability of the BK-8 solid oil from the point of view of the obtained wear pattern.

The study of antifriction properties of different calcium sulfonates has been carried out in a wide temperatures range. It was revealed that the alkalinity increase improves the antifriction properties of these detergents due to the formation of a protective film with higher uniformity on the friction surfaces, and this effect is the most evident at high temperatures. Calcium carbonate, which is contained in the additive, plays the main role in the formation of a protective film.

Effective conditions of friction in units that ensure performance and maximum longevity have been created by flood lubrication under the conditions of elastohydrodynamic (EHD) lubrication. In connection with this, prolonging the service life of friction units by ensuring local requirements to the amount of oil in the contact area and establishing the optimum choice of lubricating material in terms of its viscosity ratings is a topical problem for rolling bearings. Thus, it is suggested to determine the parameter of the lubricating layer (λ) values for the conditions of flood lubrication (λ_o) and progressing (λ_o.s) and catastrophic (λ_c.s) oil starvation for a wide spectrum of lubricating materials of different viscosity, since, in oil starvation mode, the efficiency of EHD conditions is violated, the lubrication mode is disturbed, and the bearing capacity of the EHD lubricating layer is lost.

The axisymmetric contact problem for a spherical indenter and viscoelastic base has been considered within a cycle of increasing and decreasing of load. The loading-unloading cycle has been performed at a constant speed of indenter movment. The quasi-static approximation has been used. The study has been carried out according to linear viscoelasticity theory, while the material model allows one to take into account an arbitrary number of relaxation times. The dependence of load on the indenter on time has been defined. Expressions for determining the unknown boundary of the contact area in the loading–unloading process has been given. The hysteretic loop area at different values of the material relaxation time has been analyzed. The applicability of the offered analytical model of elastomer indentation experiments data processing has been discussed.

The temperature and stress distributions in a disk under single braking have been studied. The finite-element method (FEM) has been used to obtain a numerical solution to the heat-conduction boundary problem for a steadily decelerated rotating disk heated in a local area of the working surface by a frictional heat flow. Given the temperature field, the finite-element method has been used to solve the corresponding quasistatic thermoelasticity boundary problem. The elastostatic boundary problem has been numerically solved separately for a disk loaded with distributed normal and shear stresses in the contact area. The complete field of stresses in the disk has been determined by adding up elastic and thermoelastic components. Numerical analysis has been performed for a cerametallic (FMC-11) pad—cast-iron (ChNMKh) disk friction couple.

The paper presents an experimental facility designed to model a single particle impact at an angle to the rubber surface. It has been established that the dominant failure mechanism of rubbers under an oblique angle was crack formation. The direction of crack propagation is close to that of the angle of attack, i.e., to the force action. The failure bears a cyclic nature of the following pattern: surface tear–crack rip–turn of the crack and the separation of the fragment. The factors that define the length and depth of the initial crack propagation have been described.