Change In Friction Coefficient Research Articles

Numerická analýza ozubového spoje vyrobeného CNC technologií

The objective of the paper is the parametrization and the finite element analysis of mechanical pro­per­ties of a through dovetail joint made with the use of a specific procedure by a 3-axis CNC machine. This corner joint was used for the simulation of the bending load of the joint in the angle plane – by compression, i.e. by pressing the joint together. The deformation fields, the stress distribution, the stiffness and the bending moment of the joints were evaluated. The finite element system ANSYS was used to create two parametric numerical models of the joint. The first one represents an ideal­ly stiff joint – both joint parts have been glued together. The second model includes the contact between the joined parts. This numerical model was used to monitor the response of the joint stiffness to the change of the static friction coefficient. The results of both models were compared both with each other and with similar analyses conducted within the research into ready-to-assemble furniture joints. The results can be employed in the designing of more complex furniture products with higher demands concerning stiffness characteristics, such as furniture for sitting. However, this assumption depends on the correction of the created parametric models by experimental testing.

Tribological analysis of surfactant modified nanolubricants containing CeO2 nanoparticles

Cerium oxide (CeO2) nanoparticles are added to different lubricating oils together with suitable surfactants to obtain modified nanolubricants. Lubricating properties of these surfactant modified nanolubricants have been investigated using a pin on disc tribotester under boundary lubrication conditions. Coconut oil, paraffin oil and a commercial engine oil (SAE15W40) have been used as base oils for the present study. Changes in frictional coefficient and specific wear rate have been studied as a function of nanoparticle concentration in the lubricant together with an estimation of the settling trend of nanoparticles with time. Results show that the frictional force and specific wear rate decrease with increase in concentration of nanoparticles, come to a minimum at a specific concentration level and then increase, showing the presence of an optimum concentration level at which both friction and wear are the least. At this concentration level, coconut oil shows the lowest frictional coefficient and specific wear rate among the three oils studied. The morphology of the pin surfaces after sliding has been studied using atomic force microscopy, optical interferometer and SEM. When CeO2 nanoparticles are added to the lubrication oil together with surfactant modification, settling trend and agglomeration of nanoparticles with time are reduced to a great extent compared to the case in which nanoparticles are added without surfactant modification.

온도변화에 따른 주석 도금한 전기 커넥터의 미동마멸 부식 거동

In this study, we conduct fretting corrosion tests on tin-plated brass coupons to investigate the effect of temperature on fretting corrosion for various span amplitudes. We prepare a coupled fretting corrosion specimens using a tin-plated brass coupon with a thickness of <TEX>$10{\mu}m$</TEX>. One specimen is a flat coupon and the other specimen is a coupon with a protuberance in 1 mm radius, which is produced using 2 mm diameter steel ball. We conduct fretting corrosion tests at <TEX>$25^{\circ}C$</TEX>, <TEX>$50^{\circ}C$</TEX>, <TEX>$75^{\circ}C$</TEX>, <TEX>$100^{\circ}C$</TEX> by rubbing the coupled coupons together at the contact between the flat and protuberance coupons. We measure electric resistance of the contact during the fretting corrosion test period. There is increase in resistance with fretting cycles. It is found that rate of increase in electric resistance becomes faster with increase in testing temperature. Magnitude of friction coefficient increases with fretting span amplitudes. And, change in friction coefficient becomes desensitized to the increment in span amplitude. Assuming that failure cycle is the cycle with an electric resistance of <TEX>$0.01{\Omega}$</TEX>, we find that failure lifetime (<TEX>$N_f$</TEX>) decreases with increase in testing temperature. Furthermore, based on the assumption that the damage rate of the connector is inversely related to the failure cycle, we calculate the activation energy for fretting damage to be 13.6 kJ/mole by using the Arrhenius equation. We propose a method to predict failure cycle at different temperatures for span amplitudes below <TEX>$30{\mu}m$</TEX>. Friction coefficients generally increase with increase in span amplitude and decrease in testing temperature.

Tribological properties of boride based thermal diffusion coatings

Engineering components, e.g. tubing systems for the down-hole applications in the oil and gas industry (in particular, sucker rod pumps, progressing cavity pumps and some other components of the artificial lifting systems), as well as numerous valves and seats, bearings, gears and plungers, require protection against friction and sliding abrasion service conditions. The hard boride based coatings on steels and alloys obtained through the thermal diffusion process have a high potential for these severe application conditions over many other types of coatings as they can be obtained on the entire working surfaces of large size and complex shape products. Intensive tribological studies of the iron boride based coatings on carbon steel obtained at Endurance Technologies Inc. have been conducted using the Cameron–Plint testing unit (reciprocating sliding of the metallic rod under the load over a flat surface of the coated samples). The friction wear loss, friction coefficient and structural changes of the coatings have been studied in dry and lubricating (water–oil) friction conditions, which simulate actual application conditions. It was demonstrated that the obtained boride coatings have the friction loss significantly smaller than untreated steel (e.g. ∼10–30 times in the dry conditions and at least 5 times in the lubricating conditions) with no peeling and flaking-off. The friction coefficients of the boride coatings are steady over the test duration. The influence of the thickness on the boride coatings performance is demonstrated. The encouraging results are explained by the specific coating structure of the hard coating obtained through the thermal diffusion process and the thin ‘tribofilm’ formed during a friction mode.

일정 변위 진폭조건에서의 은도금한 커넥터의 미동마멸부식 거동

Fretting corrosion tests are conducted with a constant displacement amplitude using silver-plated brass coupons to investigate the effect of contact pressure on fretting corrosion. Three behaviors are identified based on the change in electric resistance and friction coefficient during the fretting test period, and the identified behaviors are dependent on the magnitude of the applied load. The failure cycle (Nf) with an electric resistance of 0.1 D cannot be achieved due to the adhesion behavior of the metal and metal contact under the higher applied load of 0.45 N. This suggests that an average contact pressure higher than 159 MPa for the silver-coated con- nector is desirable to gain an almost infinite lifetime. The relationship between the electric contact resistance (R) and the average contact pressure (p) can be written as p = 106.2 × Ω �1.5 . Keywordscontact pressure (접촉압력 ), fretting corrosion (미동마멸부식 ), friction coefficient (마찰계수 ), electric connector (전기 커넥터), electric resistance (전기저항)

Sensing of protein molecules through nanopores: a molecular dynamics study

Solid-state nanopores have been shown to be suitable for single molecule detection. While numerous modeling investigations exist for DNA within nanopores, there are few simulations of protein translocations. In this paper, we use atomistic molecular dynamics to investigate the translocation of proteins through a silicon nitride nanopore. The nanopore dimensions and profile are representative of experimental systems. We are able to calculate the change in blockade current and friction coefficient for different positions of the protein within the pore. The change in ionic current is found to be negligible until the protein is fully within the pore and the current is lowest when the protein is in the pore center. Using a simple theory that gives good quantitative agreement with the simulation results we are able to show that the variation in current with position is a function of the pore shape. In simulations that guide the protein through the nanopore we identify the effect that confinement has on the friction coefficient of the protein. This integrated view of translocation at the nanoscale provides useful insights that can be used to guide the design of future devices.

A speed estimation-based controller for three-phase AC motors having uncertain parameters

This paper investigates and proposes a three-phase AC motor control system combining an adaptive speed estimation method and control algorithms using neural networks to deal with uncertain parameters in dynamic models of the motor such as the rotor’s resistance, as well as the friction coefficient and load changes when the system operates. Some simulation results on Matlab-Simulink are provided to show the efficiency of the proposed speed estimation and speed control method.

A speed estimation-based controller for three-phase AC motors having uncertain parameters

This paper investigates and proposes a three-phase AC motor control system combining an adaptive speed estimation method and control algorithms using neural networks to deal with uncertain parameters in dynamic models of the motor such as the rotor’s resistance, as well as the friction coefficient and load changes when the system operates. Some simulation results on Matlab-Simulink are provided to show the efficiency of the proposed speed estimation and speed control method.

Analytical model for friction coefficient determination in hydroforming of thin-walled tube elements

Industrial branches where the changes occur with the introduction of the new technologies in a very short period are automobile and aviation industries, because the securing and ergonomic criteria had to be achieved. These demands initialized setting of the new productive philoso-phy, which is based on a modern production like plastic forming and modelling with an incompressible fluid.A tube hydroforming got a significant role in the last five years and is considered as a technology of rapid development. This paper provides researches and analyses of hydroforming of thin-walled tube elements. A work-piece and die contact for hydroforming in a work process manifests with the friction force which has an influence on: axial force, axial punch feed and workpiece wall thick-ness.The stress-strain state and their disposition during the tube hydroforming are foundation where the friction influence in tube hydroforming is based on. It provides an analysis of deformation zones and friction in T shape tube hydroforming. An analytical model of friction coefficient change in hydroforming between a tube and die has been carried out. The main objective of this paper is to suggest new analytical model for friction coefficient determination in hydroforming of thin-walled tube elements which de-scribes process the most realistically. This paper provides an experimental way of needle sensor setting in measuring of the contact friction in T shape tube hydroforming.DOI: http://dx.doi.org/10.5755/j01.mech.19.6.6012

Numerical Analysis of Sliding Friction Coefficient and the Normal Pressure Between the Cable Wire

Abstract In this paper, the wire pressing device is designed, the range of true positive pressure, curves of steel friction coefficient changes with positive pressure. Describe the change trend of friction coefficient is: with the increasing pressure, friction coefficient of cable parallel wire decreased significantly, but when the pressure increases to a certain value, the friction coefficient decline is slowing down, and finally tends to a certain value. The curves of friction coefficient changes with positive pressure, provides a method and basis for the practical engineering of steel wire in the ultimate friction shear stress accurately, set up and stay cable as layered slipping model provides important parameters of bending stress analysis. From the numerical simulation method analyzes the positive pressure parallel wire between the start. This paper first parallel wire contact problem of two cables are analyzed with the classical theoretical solution and the FEM software ANSYS, to verify the feasibility, using ANSYS to solve the contact problem of accuracy and precision. On this basis, the strand steel beam of contact analysis, the preliminary inquiry arching effect on cable parallel wire.

Numerical study of horizontal pneumatic conveying: Effect of material properties

This paper presents a numerical study of the effects of friction and restitution coefficients of particles on horizontal pneumatic conveying by a combined approach of computational fluid dynamics for gas and discrete element method for particles. The flow behaviours are analysed in terms of particle flow pattern, gas pressure drop, solid concentration, particle velocity and transition of flow regime. The results show that in the slug flow regime, an increased friction coefficient or a decreased restitution coefficient results in longer slugs but no change in slug shape. Slug flow cannot be obtained at a low friction coefficient. In the stratified and dispersed flow regimes, the transition between the two regimes and formation of clusters occur due to the changes of friction and/or restitution coefficient. These two coefficients also affect the pressure drop, particle velocity and solid concentration. The resulting effects vary with flow regime. Overall, the effect of restitution coefficient is less significant than that of friction coefficient. It is also found that when gas velocity is varied from high to low values, three flow transition modes may occur depending on friction and restitution coefficients. They are respectively represented by Mode I for dilute-phase only, Mode II for unsmooth transition from dilute-phase to unstable-zone, and finally to slug-flow, and Mode III for smooth transition from dilute-phase to slug-flow. Based on the numerical results, a diagram is established to predict these transition modes as a function of friction and restitution coefficients.

Fretting wear behaviors of hoisting rope wires in acid medium

The fretting wear behaviors of hoisting rope wires in acid medium were investigated in this paper. Fretting wear tests of steel wires were conducted on a self-made fretting wear rig, and their fretting running characteristics, coefficient of friction, dissipated energy and wear morphology were analyzed. The results show that the relative sliding between steel wires can be promoted in the acid medium. As the contact load increases, the fretting of steel wires changes from a slip regime to a mixed one, and the coefficient of friction decreases significantly. Moreover, the coefficient of friction changes from about 1.2 in the dry friction environment to about 0.5 in the acid medium. Energy loss presents the same variation trend. Wear scar depth is larger in the acid medium than in the dry friction environment. The primary wear mechanism in the dry friction environment is peeling as compared to peeling, particle attrition and corrosion in the acid medium.

Tribocorrosive behaviour of commonly used temporomandibular implants in a synovial fluid-like environment: Ti–6Al–4V and CoCrMo

The temporomandibular joint implant metal alloys, Ti6Al4V and CoCrMo, (n = 3/group) were tested under free-potential and potentiostatic conditions using a custom-made tribocorrosion apparatus. Sliding duration (1800 cycles), frequency (1.0 Hz) and load (16 N) mimicked the daily mastication process. Synovial-like fluid (bovine calf serum, pH = 7.6 at 37 °C) was used to simulate the in vivo environment. Changes in friction coefficient were monitored throughout the sliding process. Changes in surface topography, total weight loss and roughness values were calculated using scanning electron microscopy and white-light interferometry. Finally, statistical analyses were performed using paired t-tests to determine significance between regions within each metal type and also independent sample t-tests to determine statistical significance between metal alloy types. Ti6Al4V demonstrated a greater decrease of potential than CoCrMo, a higher weight loss from wear (Kw = 257.8 versus 2.62 µg; p < 0.0001), a higher weight loss from corrosion (Kc = 17.44 versus 0.14 µg; p < 0.0001) and a higher weight loss from the combined effects of wear and corrosion (Kwc = 275.28 versus 2.76 µg; p < 0.0001). White-light interferometry measurements demonstrated a greater difference in surface roughness inside the wear region in Ti6Al4V than CoCrMo after the sliding (Ra = 323.80 versus 70.74 nm; p < 0.0001). In conclusion, CoCrMo alloy shows superior anti-corrosive and biomechanical properties.

Measuring Free-Flow Speed Considering Water Depth

In this paper, we propose a method of measuring free flow speed according to different water depth in the ponding situation. With different water depth, changes of tire-road friction coefficient caused by reduction of the wheel load are different. This coefficient brings great effect to vehicles free flow speed. In order to reveal this phenomena, observations data obtained in the year 2009 at the number 202 state road in Japan, which runs through Fukuoka, Itosima. By measuring the recording data, we got the speed range corresponding to different water depth. The purpose of this study is to obtain variation of free flow speed according to different water depth and lay foundations for numerical modeling in the future.

Model-based parameter identification of comprehensive friction behaviors for giant forging press

A new experimental apparatus was set up to investigate the actual friction characteristics on the basis of speed control of the serve system. A modified friction model was proposed due to real time varying deformation resistance. The approach to identify the parameters of comprehensive friction behaviors based on the modified model was proposed and applied to the forging press. The impacts on parameters which the external load had were also investigated. The results show that friction force decreases with velocity in the low velocity regime whereas the friction force increases with the velocity in the high velocity regime under no external load. It is also shown that the Coulomb friction force, the maximum static friction force and the vicious friction coefficient change linearly with the external load taking the velocity at which the magnitude of the steady state friction force becomes minimum as the critical velocity.

The influence of high-frequency vibrations on derailment stability coefficient of cars at wheel flange climbing on the rail

Purpose. Taking into account the traffic safety priority on the railway transport the search of factors promoting increase of derailment stability coefficient is an actual task. Purpose of the paper is the influence researches of the high-frequency vibrations on the train traffic safety parameter. In this case the special form of the wheel rim, at which its rigidity changes according to the harmonious law, was considered as a source of vibrations. Methodology. For the analysis of the vibration influence on the change of friction coefficient values the methods of so called vibrational mechanics were used. For determination of vibration amplitudes through moving the wheel flange points the finite-elements method was also used in the paper. Findings. During calculations it was established that the derailment stability coefficient to a great extent depends on the friction coefficient between wheel and rail. The paper shows that the friction coefficient in turn is influenced by the high-frequency vibrations. The form of the wheel rim was considered as a vibration source and the parameters characterizing vibration were calculated. It was given the quantitative estimation of the friction coefficient change under the vibration influence. It was also scientifically based the high-frequency vibration influence on the derailment stability coefficient. Originality. The paper proved the possibility of high-frequency vibration influence on the derailment stability coefficient. The studies theoretically substantiated the traffic safety increase in the presence of vibrations in the contact area of the wheel flange with the rail caused by special form of the wheel disc. Practical value. It is shown that the use of undulating wheel disc form do not constitute a threat to the traffic safety, and the availability of high-frequency vibration can reduce the derailment probability.

Simple crack propagation model of pressure-sensitive adhesives

We propose a simple mechanical model describing viscoelasticity, cavitation growth and crack propagation during the debonding process in pressure-sensitive adhesives (PSAs). Typical materials of PSA are made of block copolymers and they are usually very soft and highly dissipative, and can stick on a variety of surfaces under low pressure in short time. The debonding process of PSA is governed by very complicated dynamics, for example, deformation of the adhesive layer, cavity expansion and coalescence. Our model is a modified version of that proposed by Yamaguchi et al (2006 Eur. Phys. J. E 20 7). We extended his simple model to be applicable to the final rupture process and applied the model to some cases, where we studied the effects of the change of PSA layer's thickness, separation speed and friction coefficient. Our results are qualitatively in good agreement with the experimental data.

Flow of Newtonian and non-Newtonian fluids in a concentric annulus with a rotating inner cylinder

We examine the characteristics of helical flow in a concentric annulus with radii ratios of 0.52 and 0.9, whose outer cylinder is stationary and inner cylinder is rotating. Pressure losses and skin friction coefficients are measured for fully developed flows of water and a 0.4% aqueous solution of sodium carboxymethyl cellulose (CMC), when the inner cylinder rotates at the speed of 0∼62.82 rad/s. The transitional flow has been examined by the measurement of pressure losses to reveal the relation between the Reynolds and Rossby numbers and the skin friction coefficients. The effect of rotation on the skin friction coefficient is largely changed in accordance with the axial fluid flow, from laminar to turbulent flow. In all flow regimes, the skin friction coefficient increases due to inner cylinder rotation. The change of skin friction coefficient corresponding to the variation of rotating speed is large for the laminar flow regime, becomes smaller as the Reynolds number increases for the transitional flow regime, and gradually approaches zero for the turbulent flow regime. The value of skin friction coefficient for a radii ratio of 0.52 is about two times larger than for a radii ratio of 0.9. For 0.4% CMC solution, the value of skin friction coefficient for a radii ratio of 0.52 is about four times larger than for a radii ratio of 0.9.

The effect of temperature on wear and friction of a high strength steel in fretting

This paper investigates the effect of temperature (between 24°C and 450°C) on the wear rate and friction coefficient of a high strength alloy steel (Super-CMV) in gross sliding fretting in air. It was found that whilst there was significant loss of material from the contact during fretting at room temperature, the overall loss of material from the contact had become negative even with a modest increase in temperature to 85°C. At temperatures greater than 85°C, negative wear was maintained, with the coefficient of friction dropping monotonically with increasing temperature up to 450°C. It is proposed that the changes in wear rate and friction coefficient were due to changes in the way that the oxide particles sintered to form a protective debris bed, with sintering of the oxide debris particles at these low temperatures being promoted by the nano-scale at which the oxide debris is formed.

A simple model for friction evolution infretting

The coefficient of friction (COF) has a large influence on the material response due to fretting, and the value of the COF evolves during fretting. Friction is usually low for early cycles and increases to reach a stabilized value at locations where slip occurs between the contacting bodies. Of the fretting studies utilizing the finite element method to evaluate fretting damage metrics, only one has accounted for the evolution of friction. The majority of studies have used a constant COF equal to the stabilized value. This is not appropriate for low cycle cases where the COF is transient for the majority of the duration or for high cycle cases where the changes in COF affect the stabilized cyclic stress–strain response due to the history dependence of the material behavior. The evolution of the COF is caused by the modification of the interface between contacting materials as a result of wear processes. The wear process changes with cycling, and progresses from initial roughening from metal to metal contact, followed by accumulation of debris, followed by saturation of the debris quantity and morphology and a stabilized response. These processes are each associated with energy dissipation, which can therefore be related to the COF evolution. In this study, a simple expression for the evolution of the COF has been developed that is dependent on accumulated frictional energy dissipation density. This allows the COF to be modified in a finite element model as a function of history and location based on an experimentally measured relationship between energy dissipation andCOF.