Action Of Friction Forces Research Articles

Simple preparation of ultra‐thin white g‐C3N4 nano‐sheets and their use as nanofillers to enhance the tribological properties of epoxy composite coating

AbstractGraphite phase carbon nitride (g‐C3N4) has shown great promise as a functional filler in the field of friction. But at present, research in the field of friction mainly focuses on bulk g‐C3N4 or obtaining g‐C3N4 nano‐sheets through inefficient exfoliation strategies, which greatly limits its industrial applications. In the study, a simple and effective secondary calcination method has been developed to successfully fabricate ultrathin white g‐C3N4 nano‐sheets. The mass ratio of the same volume of bulk g‐C3N4 and white g‐C3N4 nano‐sheets was as high as 50:1. Subsequently, the tribological performance of epoxy (EP) composite coatings containing different contents of bulk g‐C3N4 and g‐C3N4 nano‐sheets were researched. The EP composite coatings containing 1 wt.% g‐C3N4 nano‐sheets possess the lowest wear rate and friction coefficient in all samples, which is attributed to the two‐dimensional planar structure and high specific surface area of g‐C3N4 nano‐sheets make it easier to transfer to the dual surface to form the excellent transfer film under the action of friction force, so that the friction mainly occurs between a dual surface and a transfer film, which effectively improves the tribological performance of the coatings.Highlights Ultrathin white g‐C3N4 nano‐sheets were prepared by secondary calcination. EP‐1 wt.% g‐C3N4 nanosheets show the best tribological properties. g‐C3N4 nanosheet is easy to transfer to dual surfaces to form transfer films. This work provides guidance for the application of nanofillers in tribology.

Theoretical studies of obtaining of glass-type finned products by reverse extrusion with active friction forces

The forming process of responsible products made of high-strength alloys, accompanied by significant force loads on the tool is considered. To reduce the technological force of the operation, the forming method of hollow bodies with internal finning in the near-bottom part made of the titanium VT6 alloy under hot deformation conditions is used. The rationale for the rationality of extrusion is carried out taking into account the active friction forces provided by the movement of the die in the direction opposite to the movement of the punch in the manufacture of bodies.

Effective Strains Determination in Continuous Constrained Double Bending with Active Friction Forces

In this work, a new process for severe plastic deformation (SPD) with active friction forces - CCDB Conform R3D2, a variation of the so-called "active bending", which is a continuous two-stage bending in calibers with small relative bending radius, is analyzed. A mechanical scheme of a device for realization of the process with a bending roller is proposed, based on a developed 3D virtual tool for its realization. Using CAD/CAE software 3D simulation, two virtual solutions of the process were compared, differing in terms of the location of the bending roller relative to the axes of the feeding and output rolls. The distribution and magnitude of the effective strains in the volume of the deformed long workpiece in the two bending stages at small relative bending radiuses were analyzed. An analytical expression is developed to determine the effective strains achieved in the SPD operation by constrained continuous bending in calibers with grooved rolls. The strain calculation methodology is based on the results obtained by simulation modelling of the CCB Conform R3D2 process in trapezoidal calibers with a bending roller located above and below the rolls line.

STAMPING BY ROLLING BLANKS USING ADVANCED ENERGY-EFFICIENT INDUCTION HEATING

The article presents the results of development and research of technological schemes of cold forming by rolling (CFR) of blanks. Expansion of the technological capabilities of the processes of COP and improving the quality of products is based on the control of active friction forces and deformability of the processed metals. The main limiting factors in the application of SHO processes are insufficient ductility of metals, which causes the risk of destruction of workpieces, as well as relatively large deformation forces that cause unfavorable operating conditions of the rolling bearing unit. The solution of these problems is facilitated by the transition to hot SHO. However, the problems of manufacturing by the hot SHO method of products from tubular and solid cylindrical billets have been little studied to date. An effective process of billets heating is induction heating, but its application is characterized by relatively low efficiency. In this work, it is recommended to use new materials and technology for the manufacture of induction heaters for the implementation of hot SHO, which open up opportunities for improving induction heating equipment for industrial applications. The use of new generation induction heaters to replace other heating methods in metalworking has significant advantages: higher efficiency; less scattered magnetic fields; less complexity of the coil design; increased geometric freedom; no water cooling is required. In order to study the hot SHO, devices for rolling billets with conical and cylindrical rolls were designed and manufactured. Physical modeling of hot SHO by using solid cylindrical lead billets was carried out. It is experimentally proved that the process of hot SHO allows to achieve significant degrees of deformation even at unfavorable stress-strain state and insignificant power of the equipment. Thus, the process of induction heating of blanks can be quite effective when processing them by hot SHO.

Self-lubricating coating design strategy for titanium alloy by additive manufacturing

Lowering the coefficient of friction (COF) and improving the wear resistance of titanium alloys are critical for expanding their industrial applications. Herein, we report a novel strategy endowing titanium alloys with superior tribological performance by combining surface texture and solid lubricant: a coating with honeycomb structure was prepared by laser powder-bed fusion and incorporated with polytetrafluoroethylene (PTFE) as solid lubricant. The hybrid coating exhibits stable low COF and zero-wear properties under various service environments: atmosphere, deionized water, seawater, and corrosive acid medium. Under the action of friction force, wear debris can be continuously captured by the hybrid coating while releasing equal volume PTFE lubricant to repair the damaged lubricating film, thereby achieving excellent tribological properties of the coating in various environments. Our findings provide a new approach to improve the friction and wear properties of metal and alloy components.

FORMATION OF QUALITATIVE INDICATORS OF PRODUCTS BY ROLLING STAMPING PROCESSES

The influence of rolling stamping on the service characteristics of products is investigated in the work. Based on the analysis of deformation kinematics, stress-strain state, microstructure and evaluation of deformability of workpiece material, ways to increase geometric accuracy, vacuum tightness, electrolytic stability and mechanical characteristics of product material, as well as ways to improve the material of workpieces for their subsequent processing. The influence of active friction forces on the nature of the material flow during SHO was established, which contributed to the development of new processes that allow to bring the shape and dimensions of the workpiece as close as possible to the finished part. Thus accuracy of the sizes of details corresponds to 7-11th qualities of accuracy, and roughness of the processed surfaces makes Ra = 2,5… 0,63 microns. The process of reshaping the square billets into round ones by the method of SHO is effective, which increases the utilization factor of the metal and reduces the anisotropy of its mechanical properties. The characteristic of flat anisotropy λr, adopted in sheet metal stamping as a characteristic of the ability of the material to form scallops, decreases as a result of reshaping by 70-80%. The relative difference in yield strength in the plane of the sheet decreases from 0.10-0.15 to 0.03-0.05. The ultimate tensile strain increases by 8-10%, and the uniform uniform strain - by 5-8%. This improvement in the characteristics of the material reshaped by rolling blanks leads to the fact that when drawing cylindrical products, the value of scallops decreases by 2-2.5 times, and the value of the maximum degree of drawing increases by 10-15%. This reduces the relative difference in wall thickness along the perimeter of the elongated workpiece, and the change in wall thickness along its height becomes linear. Thus, the use of SHO processes significantly improves the quality characteristics of products.

Simulation of the process of extruding a bar billet into a cylindrical extrusion die with active friction

Backward extrusion processes are widespread when producing various axisymmetric hollow products. This process is characterized by high values of specific pressures. The meaningful task to be achieved is to reduce loads during this process implementation. The use of active friction forces to reduce loads seems to be promising. The use of a floating die with a protrusion on a cylindrical surface, which will facilitate the billet material pushing, is proposed. For theoretical justification of the process, the provision is made to use the finite-element method. The procedure was simulated for different geometric relationships of the tool, the floating extrusion die path velocities and the billet position relative to the extrusion die. The provision is made to analyze the influence of deformation parameters and velocity parameters on the change in force of the studied procedure. Based on the research findings, the conclusions on the expediency of the studied method use for its practical implementation have been made.

Numerical Analysis of the Die Forging of Porous Blanks in a Die with the Implementation of Active Friction Forces

This paper provides the results of simulating the hot die forging of porous powder preforms with active friction forces applied along the lateral surface of the blank under deformation due to internal cohesion in the die–material system. The study covers the evolution of the distribution of the relative density over the blank cross section at different stages of deformation, the stress-strain state, and the total strain force while varying the boundary loading conditions by changing the initial compression force applied to elastic elements that prevent the die from displacement. It is shown that the active friction forces that act on the periphery of the forged piece adjacent to the die inner side result in areas with a significantly higher deformation intensity compared to deformations in the center of the blank volume. In this case, the volume of the high deformation intensity area and the maximum values of deformation increase with a decrease in the initial compression force of the springs and, accordingly, with an increase in the die displacement value during the deformation. The automatic displacement of the die due to the internal cohesion in the die–deformed material system leads to a decrease in the total deformation force, and the deformation force increases with a decrease in the die displacement value during deformation.

The influence of hardening on the operational properties of soil-cutting tools

Today, soil cutting tools are mainly made from carbon steels, which are heat treated to provide high hardness and strength. However, at present, the durability of such a hardened soil-cutting tool of both domestic and foreign manufacturers is far from perfect. One of the reasons for the insufficient resistance to abrasive wear of a soil-cutting tool subjected to hardening by heat treatment may be its heating by frictional force in contact with the soil. As a result of such heating, the steel undergoes additional tempering, which leads to a decrease in the surface hardness of the cutting edge of the tool by almost 2 times - 49-50 HRC to 22-34 HRC, depending on the intensity of metal heating. This circumstance was established during metallographic studies of samples cut from the shares of the KB-01 body of the PBS-4 plow. One of the ways to solve this problem is to obtain a wear-resistant layer on the surface of the soil-cutting tool, which is not subject to the negative effects of reheating during operation, for example, from alloyed white cast iron by the method of plasma-powder surfacing. Metallographic studies showed that the deposited layer has a hardness of more than 62 HRC. At the same time, such types of heat treatment as hardening, normalization or annealing do not have a noticeable effect on the hardness of the deposited layer. Metallographic studies of the deposited metal after operation also showed the absence of noticeable changes in its microstructure and hardness. This indicates that reheating from the action of friction forces does not have a significant effect on the properties of a soil-cutting tool strengthened by plasma-powder surfacing, which contributes to an increase in its duration of operation.

Effect of active action friction forces on technological parameters of backward extrusion

The parameters of deformation degree at theoretical and experimental researches of cold backward extrusion processes of hollow glasses-type products are considered. The dependences of their relationship with the relative degree of deformation and the scale of their conformity are suggested. The published results of experimental and theoretical studies on the impact of technological parameters of the backward extrusion process of hollow products in the conditions of active friction forces to reduce the deformation force and stress-strain state of the billet are analyzed. Insuffi ciently studied features of the process and the possibility for expanding of the application fi eld of the backward extrusion method with the active action of friction forces are noted. The method for calculating of the deformation rate required to determine the current stress in the implementation of the hot backward extrusion process.

Numerical analysis of porous blank die forging in the die with the implementation of active friction forces

The paper provides the results of simulating the hot die forging of porous powder preforms with active friction forces applied along the lateral surface of the deformable blank by means of internal cohesion in the die-material system. The study covers the evolution of relative density distribution over the blank cross section at different stages of deformation, stress-strain state and total strain force while varying the loading boundary conditions by changing the initial compression force applied to elastic elements that prevent the die from displacement. It is shown that active friction forces acting on the periphery of the forging adjacent to the die inner side result in areas with a significantly higher deformation intensity compared to deformations in the center of the blank volume. At the same time, the volume of the high deformation intensity area and maximum values of deformation increase with a decrease in the spring initial compression force and, accordingly, with an increase in the die displacement value during deformation. Automatic die displacement due to internal cohesion in the die-deformable material system leads to a decrease in the total deformation force, and with a decrease in the die displacement value during deformation, the deformation force increases.

Modeling the Process of Obtaining Bars from Aluminum Alloy 01417 by Combined Rolling-Extruding Method with Application of the Deform-3D Complex

The results of computer simulation of the process of combined rolling-extruding of longish deformed semi-finished products from alloy 01417 are presented. A feature of the research is that continuously cast bars with a diameter of 12.5 mm obtained using an electromagnetic mold are used as a workpiece. This makes it possible to increase the manufacturability of processing and to obtain after rolling-extruding billets for drawing with a diameter of 5 mm with a large resource of plastic and strength properties. For this case the technological parameters and temperature and speed conditions of combined processing have not yet been studied, therefore, their analysis was performed using the Deform-3D software package. It has been revealed that the feasibility of the rolling-extruding process is significantly affected by the frequency of rotation of the rolls. Moreover, the process becomes unstable when the value of this parameter is 4 rpm, which can be explained by insufficient degrees of deformation during rolling, and consequently by the small value of the active friction forces acting on the contact surface of the metal with the rolls. As a result of this, the processing temperature conditions also change, which is also demonstrated using the developed computer model. As a result, it was found that for the stable course of the combined rolling-extruding process at the CRE-200 unit of a continuously cast billet with a diameter of 12.5 mm from alloy 01417 at a heating temperature of the billet of 550 °C and a tool of 200 °C, degree of deformation during rolling 44% and drawing ratio during extruding 18.6 the frequency of rotation of the rolls should be at least 8 rpm. The simulation data used during the implementation of the process at the combined processing unit CRE-200, the results of which made it possible to finally obtain electrotechnical wire with a diameter of 0.5 mm from 01417 alloy that meets the requirements of TS 1-809-63-2018.

Метод определения мест утечек в водопроводе путем контроля градиента давления

The objective was to develop a method for determining leaks in a branchless water pipeline section, when a pressure drop in the pipe under the action of friction forces is observed. The problem of detecting leaks can be solved by developing new methods for monitoring the operation of water supply and distribution systems. A well-known method for detecting leaks in branchless pipelines consists in determination of the coordinates of the intersection point of lines that characterize the pressure change in the pipe before and after the leak incident. On this basis, a method is proposed for determining several leak locations in the water supply system with fewer necessary measurements. A well-known method for determining leaking sites in a horizontal water supply section with a constant pipe diameter was analysed. One disadvantage of this method is that determination of a leaking site may require numerous measurements to establish the ratio of the pipeline length to the most likely minimum length of the interval between nearby leak points. The developed method for detecting water leaks by monitoring the pressure gradient eliminates this drawback. A method of equivalent points was proposed, which allows the number of necessary measurements to be significantly reduced. Formulas were obtained for estimating the multiplicity of reducing the number of necessary measurements in the proposed method. It was determined that, upon an excessive increase in the number of leak points, the specified multiplicity decreases to zero. However, this indicates a completely obsolete water supply system, which requires replacement

Numerical simulation of backward extrusion process with local acting of active friction forces

This article presented the results of numerical analysis of the deformation forces calculation on the backward extrusion of box-shaped details including the active friction forces action. It is shown on the example of aluminium box-shaped details, that the numerical methods of the analysis based on finite elements method, give accurate results. This allows us to recommend numerical methods for calculation of the force values acting on the working tool in backward extrusion. In addition, a numerical research enables to predict the shape change of the workpieces at any stage of the backward extrusion process. All this allows drawing conclusions about the quality of the box-shaped parts and more considerably take into account the characteristic features of the deformation during the development of the technological process.

A Cold-Pressing Method Combining Axial and Shear Flow of Powder Compaction to Produce High-Density Iron Parts

Highly performance methods for cold pressing (cold die forging) of preforms from iron powder with subsequent heat treatment and producing ready parts made of powder are described in the paper. These methods allow fabricating parts with smooth surfaces and improved mechanical characteristics—porosity, tensile strength. Application of the traditional design set-up with a single-axial loading is restricted to high stresses in the dies to deform the preforms that lead to cracks formation. New powder compaction schemes by applying active friction forces (shear-enhanced compaction) make it possible to unload dies and produce high-quality parts by cold pressing. The scheme allows moving the die in the direction of the material flow with a velocity that exceeds the material flow velocity.

Application of ultrasonic testing method for determining defects of hot-deformed powder materials

The article is devoted to the analysis of elastic and plastic characteristics of composite materials during hot stamping. The purpose of this work is to offer optimal conditions for hot plasticity of composite porous material with determination of temperature conditions of hot stamping excluding the appearance of defects in the structure. Production of details of the difficult form by method of hot stamping from preparations of the cylindrical form is followed by development of barrel on a peripheral surface. Sludge sintered porous blanks, and sediment compact material, accompanied by a nonuniform height lateral deformation. In connection with the action of friction forces on the contact surfaces, this leads to the formation of a “barrel”. The heterogeneity of the deformed state is associated with the appearance of tangential tensile stresses on the free surface of the workpiece. If they exceed some critical degree of transverse deformation, cracks appear on the side surface, which leads to gas saturation (oxidation) of the inner layers of the forging, to the ingress of grease into them and its pressing into the volume of the part during hot stamping. In the end, this significantly reduces the properties of hot-stamped parts. Conclusion: the methods of determining the elastic characteristics depending on the geometric parameters of the workpieces, the applied strain energy, body density and temperature dependence of the plasticity characteristics of the hot deformation of the powder material are сonsidered.

Frictional magnetic curves in 3D Riemannian manifolds

In this study, we investigate the special type of magnetic trajectories associated with a magnetic field [Formula: see text] defined on a 3D Riemannian manifold. First, we consider a moving charged particle under the action of a frictional force, [Formula: see text], in the magnetic field [Formula: see text]. Then, we assume that trajectories of the particle associated with the magnetic field [Formula: see text] correspond to frictional magnetic curves ([Formula: see text]-magnetic curves[Formula: see text] of magnetic vector field [Formula: see text] on the 3D Riemannian manifold. Thus, we are able to investigate some geometrical properties and physical consequences of the particle under the action of frictional force in the magnetic field [Formula: see text] on the 3D Riemannian manifold.

Why is the heel particularly vulnerable to pressure ulcers?

In this article, the vulnerability of the soft tissues of the heel to pressure ulcers (injuries) is explained from a biomechanical engineering perspective, and emerging technologies for protecting the heel, particularly low-friction garments, are reviewed. Sustained deformations in the soft tissue of the weight-bearing posterior heel cause progressive cell and tissue damage due to loss of homeostasis in the cells, as the cytoskeleton and plasma membranes of the affected cells lose integrity and functionality. This deformation damage onsets and evolves rapidly when there is no relief of the tissue distortion (e.g. in supine motionless lying). Hence, prevention should be timely and be applied across all patient populations that are at risk. In particular there is a need to protect tissues from the action of frictional forces that are shearing not only the skin but also the deep tissue structures of the heel. The internal anatomy and physiology of the posterior heel, the common hospital conditions (lying supine, head of the bed elevated) and medical conditions involving neuropathy and perfusion impairments may impose specific risk for heel (pressure) ulcers. There is growing evidence that low-friction-fabric garments may provide added benefits in preventing heel ulcers when used in addition to standard clinical and technology-supported pressure ulcer prevention strategies, as the low-friction fabric structures absorb frictional forces before these are able to considerably distort the susceptible heel tissues.

Research of forming of thin-walled axisymmetric cone-shaped parts

This article presents a new method based on the process of beading, which allows reducing polythickness of the part wall along generatrix. The proposed method differs from known approaches in the fact that it is presented active friction forces exerted on the both surfaces of the blank. These forces are provided by usage of the elastic die and cone. This method was researched using computer simulation andexperiment. In the experiment it was used the stamping tool, which implements the proposed method.

Formation of Fiber Materials by Pneumatic Spraying of Polymers in Viscous-Flow States

Using a novel ejection spraying unit and relying on new approaches, fibers are formed by the method of pneumatic melt blowing of polycarbonate, polypropylene, and polyethylene terephthalate. The proposed approach is based on the concepts of atomization of the polymer melt flow as a preferential regime for fibermaterial formation. From the analysis of the values of numerical characteristics in the zone of atomization and the physical background of the criteria under study a conclusion is drawn that the essential role in destruction of the jet belongs to the formation of a boundary layer in the melt under the action of friction forces, followed by its separation. An assumption is made on the prevailing action of the separating destruction of the melt jet via the mechanism of ‘skinning’ of the boundary layer of the melt due to a shorter time of its persistence compared to the development of the Kelvin–Helmholtz instability.