Appearance Of Friction Research Articles

Molecular dynamics simulation of frictional strengthening behavior of graphene on stainless steel substrate

During the last few years, friction studies of graphene applied to stainless-steel materials have mainly focused on the macroscopic scale, but the friction behavior and friction mechanism of graphene on stainless-steel surfaces at the nanoscale are still unclear. Here, the frictional behavior of graphene on stainless-steel was analyzed by molecular dynamics simulations. The results show that the average adsorption energy between stainless-steel and graphene is large, but the graphene/stainless-steel system exhibits frictional strengthening behavior. The frictional strengthening behavior decreases with the increase of the number of graphene layers. In addition, the frictional strengthening behavior appears only in localized regions of graphene on the stainless-steel surface. We demonstrate that the polycrystalline character of stainless-steel is a key factor in the appearance of frictional strengthening behavior. The presence of stainless-steel grain boundaries causes the change of graphene adsorption state, which leads to the appearance of graphene friction forcing behavior. Moreover, the multi-element characteristics of stainless-steel exacerbate the influence of grain boundaries on the graphene adsorption state. The correlation between stainless-steel grain boundaries and graphene frictional behavior provides insight into the application of graphene on stainless-steel surfaces.

Atomistic mechanisms for frictional energy dissipation during continuous sliding

After more than a century of detailed investigations into sliding friction, we have not arrived yet at a basic understanding of energy dissipation, even for the simple geometry of a rigid slider moving over a perfectly periodic counter surface. In this article, we use a first-principles-based analysis to establish the atomistic mechanisms of frictional energy dissipation for a rigid object that moves continuously in the periodic surface potential landscape of a solid with vibrational degrees of freedom. We identify two mechanisms that can be viewed as (i) the continuous pumping of energy into the resonant modes, if these exist, and (ii) the destructive interference of the force contributions introduced by all excited phonon modes. These mechanisms act already in a purely dynamic system that includes independent, non-interacting phonon modes, and they manifest irreversibility as a kind of “dynamical stochastization”. In contrast to wide-spread views, we show that the transformation of mechanical energy into heat, that always takes place in real systems due to the coupling between phonon modes, can play only a minor role in the appearance of friction, if any. This insight into the microscopic mechanisms of energy dissipation opens a new, direct way towards true control over friction.

ЗАЛЕЖНІСТЬ ОПОРУ ПЕРЕМІЩЕННЯ ГНУЧКОЇ СМУГИ ПО ПОВЕРХНІ ВІД КРИВИНИ ЇЇ ОСІ

During considering the movement of the body on the surface, it is usually replaced by a material particle. It greatly simplifies the analytical description of the movement, which makes it possible with some probability to predict the impact of certain factors on the process. The particles can create a continuous environment, one of which may be a flexible strip. It is deformed during moving on the surface, acquiring its shape. This movement can occur during plowing the soil, permeated with roots. In this case, the slice can be taken as a strip of the rectilinear cross-section, the length of which does not change during deformation, i.e. it is incompressible. The article considers the movement of such a strip on a cylindrical surface with a horizontal arrangement of rectilinear generatrices. The strip can enter the surface perpendicularly to the generatrices and moves farther in this direction. In this case, the trajectory will be a flat curve – in fact, a cross-section of the cylinder. The article considers the variant when the strip enters the surface of the cylinder at a certain angle to the generatrices. In this case, the trajectory of the strip movement will be a spatial curve. Some effort is required to overcome the slip resistance of the strip. It is the sum of certain components: the effort to lift the strip, to overcome the friction, to its deformation in the case of an elastic strip. The article considers the forces, the magnitude of which is influenced by the curvature of the trajectory of the strip, for which its axis is taken. The force is determined by the summation of the elementary forces acting on the elements of the strip along its axis. It is considered that at the deformation of a strip the profile of its cross-section does not change and remains rectangular. On the basis of this rectangle, an elementary parallelepiped of a strip is formed, one of the dimensions of which is the differential of the arc of its axis. Thus, the definition of the force is reduced to the integration of the forces applied to the elementary parallelepiped along the length of the arc of the axis of the strip. One of such forces is the centrifugal force, which depends on the curvature of the trajectory along which the strip moves on the surface. The component of this force causes the pressure of the strip element on the surface, which causes the appearance of friction. If the strip is elastic, then there are deformation forces, which also depend on the curvature of the axis of the strip. Keywords: flexible strip, cylindrical surface, axis curvature, centrifugal force, friction force.

Influence of rotational speed on the dissimilar friction welding of heat-treated aluminum alloys

Union of dissimilar alloys by means of welding processes is often challenging than union of like material or alloys. The trivial distinction in mechanical, metallurgical and formation of alloys lead in major changes in the welded joints. Friction welding can be implemented effectively to unite a much wide variety of dissimilar materials. It efficiently resolves so many complex issues in front of contemporary manufacturing, like recuperating quality, dipping costs and safeguarding the environs. It produces the high strength joints compared to fusion welding process. The properties of the welded joints contingent on the right assortment of the welding parameters. In this investigation, the effect of rotational speed on mechanical properties was assessed by tensile, microhardness tests and weld flash appearance of friction welded joint of aluminium alloy 6063-O and aluminium alloy 6063-T6.

THE TENSE-DEFORMED STATE OF VARIOUS DISC TYPES IN VEHICLE BRAKE DEVICES

The article is devoted to the tense-deformed state of solid and self-ventilated brake discs with cooling elements in the structure of vehicle brakes. The effect of energy loading of different disc types on the appearance and development of microcracks on their working surfaces is shown. The insufficient power consumption of brake discs on the cyclic braking mode of the vehicle affects the braking effectiveness of the working surfaces of discs due to the appearance of microcracks on them. The latter are the result of the influence of energy loading, and as a consequence, of high thermal stresses. The frictional interaction of the friction pairs disk-overlays contributes to the appearance of friction on the treadmill of grinding machines. The latter are a grid of arachnoid or separate arbitrary directed surface tears formed during the tread grinding of the disk friction, the material of which has high brittleness, hardness and reduced thermal conductivity. At the same time, the microcracks spread on the grain boundary in the surface layer of the disk metal. The plastic deformation causes a decrease in the density of the metal surface layer of the disc or an increase in its specific volume. The plastically deformed during the electrothermechanical friction layer cannot increase freely in the volume of the near-surface layer of the tread of the brake disc friction. At the same time, in the surface layer of the disk there are stresses of compression, and in the rest of its part we can observe the tensile stress. This argument assumes that the deformed surface layer is not even partially in a state of creep. Plastic deformation causes a decrease in the density of the metal of the surface layer of the disc an increase in its specific volume. Plastic deformation by electromechanical friction the layer cannot freely increase in volume. This is prevented by the non - deformed metal the surface layer of the friction path of the brake pulley. Depending on the temperature, the metal can be in an elastic and plastic creep state, the elastic force does not appear, and the deformation proceeds without the metal striving to restore the shape.

회주철의 마찰용접 특성에 관한 연구 - 입열량 이론식을 중심으로 -

Joining of grey cast iron by fusion welding has much difficulties for its extremely low ductility and low toughness because of the flake form of the graphite. And the brittle microstructure, i.e. ledeburite may be formed during fusion welding by its rapid cooling rates. By these kinds of welding problem, preheat and post heat treatment temperature must be increased to avoid weld crack or welding problems. In order to avoid these fusion welding problem, friction welding of cast iron was carried out for improving joint soundness, establishing friction welding variables. There is no factor for evaluating friction weldability in continuous drive type friction welding. In this point of view,this study proposed the parameters for calculating friction weld heat input. The results obtained are as follows ; 1. There was a close relationship between tensile strength and flash appearance of friction welded joint. 2. Tensile strength was decreased and flash was severely oxidized as increasing frictional heating time. 3. As increased forging pressure P2, flash had a large crack and tensile strength was decreased. 4. As powdered graphite by rotational frictional force induced flat surface and hindered plastic flow of metal ,tensile strength of welded joint was decreased. 5. Heat input for continuous drive type friction welding could be calculated by the factors of P1, P2 and upset distance(δ).

Time-independent description of rapidly driven systems in the presence of friction: Multiple scale perturbation approach

The dynamics of a classical system driven by a rapidly oscillating field (with frequency ω) in the presence of friction has been investigated using the multiple scale perturbation theory (MSPT). By exploiting the idea of separation of time scales, the slow motion has been computed in a systematic expansion in the inverse of ω to the order ω(-3). This perturbation series can be viewed as a generalization of the calculation presented by Landau and Lifshitz for Kapitza's pendulum (where the point of suspension is moved periodically) in the presence of friction. The radiation induced dynamics of the system is found to be described by an effective time-independent potential with friction that controls the slow motion. The explicit appearance of friction in our computed effective potential is a manifestation of the dynamical effect due to the fast motion. The present study demonstrates that MSPT can be used to understand and predict the classical dynamics of a driven system in the presence of friction.

Friction welding of pipe to plate: estimate of heat input and comparison with MAG welding

In welding of a thin plate, welding deformation is a severe problem. It is difficult to correct the welding deformation after welding. Therefore, the welding deformation should be avoided before or during welding. As the welding deformation is generated by thermal cycle during welding, it is thought low heat input joining process is efficient to decrease the welding deformation. In this study, friction welding was proposed as lower heat input welding process than arc welding. MAG welding was also carried out to compare welding deformation and heat input. However, it is difficult to compare heat input between friction welding and arc welding. Because, there in no general heat input calculation in friction welding and does not define the weld line in friction welding. To compare the heat input directly, pipe circumference was assumed to weld line and calculated heat input by simplified heat input rate, which was proposed by authors. The appearance of friction welded joint was sound and tensile tests revealed the fracture occurred at the base metal of plate. In friction welding, the deformation of plate was smaller than that in MAG welded joints. Heat input in friction welding was 10-30% in MAG welding by direct comparison for same dimension of joints. The time for welding was also smaller in friction welding. Friction welding is small deformation and efficiency process for joining of pipe and thin plate.

パイプと板材の摩擦圧接―入熱量の推定とＭＡＧ溶接法との比較―

In welding of a thin plate, welding deformation is a severe problem. It is difficult to correct the welding deformation after welding. Therefore, the welding deformation should be avoided before or during welding. As the welding deformation is generated by thermal cycle during welding, it is thought low heat input joining process is efficient to decrease the welding deformation. In this study, friction welding was proposed as lower heat input welding process than arc welding. MAG welding was also carried out to compare welding deformation and heat input. However, it is difficult to compare heat input between friction welding and arc welding. Because, there in no general heat input calculation in friction welding and does not define the weld line in friction welding. To compare the heat input directly, pipe circumference was assumed to weld line and calculated heat input by simplified heat input rate, which was proposed by authors. The appearance of friction welded joint was sound and tensile tests revealed the fracture occurred at the base metal of plate. In friction welding, the deformation of plate was smaller than that in MAG welded joints. Heat input in friction welding was 10-30% in MAG welding by direct comparison for same dimension of joints. The time for welding was also smaller in friction welding. Friction welding is small deformation and efficiency process for joining of pipe and thin plate.

Spatially quantized friction with a lattice periodicity

Using a two-dimensional frictional force microscope (2D-FFM), we investigated the two-dimensional nature of spatially quantized friction with a lattice periodicity on an atomic scale. As a result, in addition to the well-known stick-slip behavior along the scanning direction, we found the appearance of friction with square-wave behavior which works across the scanning direction. To explain the observed two-dimensional friction with the lattice periodicity, we proposed a two-dimensional stick-slip model which predicts spatially quantized adhesions and jumps with the lattice periodicity. By calibrating displacements due to frictional forces using the lateral force curve, we obtained quantitative agreements between predicted and experimentally deduced displacements on an atomic scale. We also observed the fluctuation of the spatially quantized friction. Further, the two-dimensional stick-slip model with an effective adhesive region enabled us to explain individual sawtooth and square-wave behaviors in more detail. This model also enabled us to interpret a normal load dependence of the frictional force hysteresis as a normal load dependence of the effective adhesive region. Besides, by comparing the normal load dependence of the frictional force hysteresis on layered materials such as MoS 2 with that on the three-dimensional NaF(100) crystal surface, we made clear that the atomic-scale facial friction works on layered materials, in contrast to the near single-atom friction on the three-dimensional one.

Atomic-scale friction observed with a two-dimensional frictional-force microscope.

Using the two-dimensional frictional-force microscope, we studied the two-dimensional nature of the atomic-scale friction between a ${\mathrm{Si}}_{3}$${\mathrm{N}}_{4}$ tip and the cleaved ${\mathrm{MoS}}_{2}$ surface. As a result, we confirmed the existence of two-dimensionally discrete friction with the lattice periodicity of the ${\mathrm{MoS}}_{2}$ surface. In addition to the well-known stick-slip behavior, we found the appearance of friction with square-wave behavior which works across the scanning direction, although it is contradictory to the assumption of classical friction. We found that this friction is due to spatially discrete adhesion and jumps with the lattice periodicity, which is explained by the two-dimensional stick-slip model not only qualitatively but also quantitatively. We also observed the fluctuation of the discrete jumps. Further, using the two-dimensional stick-slip model with an effective adhesive radius, we explain the sawtooth and square-wave behaviors due to each discrete jump in more detail.