Dependence Of Friction Coefficient Research Articles

Effect of Surface Pressure/Velocity Dependence of Friction Coefficient on Seismic Response of Sliding Base Structure Based on Shaking Table Test

Effect of Surface Pressure/Velocity Dependence of Friction Coefficient on Seismic Response of Sliding Base Structure Based on Shaking Table Test

A comprehensive investigation into the effect of vertical component of ground motion on response of sliding unanchored blocks

This study aims to quantify the effect of the vertical component of ground motion on the seismic response of sliding rigid blocks, in terms of maximum and residual displacements. A multi-stripe analysis approach is employed to examine the response with and without the vertical component under various levels of ground motion intensity. First, a parametric study is conducted using a Coulomb friction model with a constant coefficient of friction that does not account for any dependence of the friction coefficient on velocity or pressure. It is shown that the effect of the vertical component on maximum and residual displacement is more pronounced for ground motions that can barely initiate sliding. Moreover, the influence of the vertical component on the residual sliding displacement is higher than that on the maximum displacement. Subsequently, to account for the friction coefficient dependence on pressure and sliding velocity, two interface cases (steel-steel, and concrete-concrete) are analyzed. It is found that even when a variable coefficient of friction is used, the overall trends observed for a constant coefficient of friction do not change.

Development of a pressure-, velocity-, and acceleration-dependent phenomenological friction model using experimental data of sliding tests between 11 polymers and stainless steel

This paper experimentally investigates the frictional behavior between stainless steel and 11 polymers. Particularly, the dependence of the friction coefficient on the sliding velocity, pressure, and acceleration is quantified. The novelty of this work lies in quantifying the acceleration-dependent nature of friction, correlating it to the well-documented Stick-Slip effect. The experimental setup consisted of two parallel stiff steel beams, one above the other, with a separation of 95 mm, and steel surfaces welded at the inner sides for sliding the polymers. Cylindrical polymer pads were placed between the stainless-steel surfaces and connected to a dynamic actuator to apply the displacement protocol. The protocol consisted of consecutive nominally constant-velocity ramp cycles covering velocities from 1 mm/s to 300 mm/s (with 20 mm/s increments). An additional vertical force was applied with a hydraulic actuator to reach nominal pressures in the polymers between 5 and 80 MPa. The results showed that the friction coefficient depends on the velocity, pressure, and acceleration of the motion, and a phenomenological model on these three variables is proposed. The velocity dependence can be represented through a logarithmic relationship, while the pressure dependence is through an exponential decay relationship. The acceleration dependence was represented through a linear relationship, which could capture the stick-slip effect. Overall, this work contributes to a better understanding of friction for seismic isolation systems. Since friction is the main source of energy dissipation in such structures, the proposed model will allow a higher accuracy in predicting variables of interest during the dynamic analyses of seismically isolated structures with frictional systems.

A quasistatic electro-elastic contact problem with long memory and slip dependent coefficient of friction

In this paper we consider a mathematical model describing a quasistatic frictional contact problem between a deformable body and an obstacle, say a foundation. We assume that the behavior of the material is described by a linear electro-elastic constitutive law with long memory. The contact is modeled with a version of Coulomb's law of dry friction in which the normal stress is prescribed on the contact surface. Moreover, we consider a slip dependent coefficient of friction. We derive a variational formulation for the model, in the form of a coupled system for the displacements and the electric potential. Under a less assumption on the coefficient of friction, we prove the existence result of weak solutions of the model. We can show the uniqueness of solution by adding another condition (3.10). The proofs are based on arguments of time-dependent variational inequalities, differential equations and Banach fixed point theorem.

Numerical analysis of the dependence of damage on friction during deep drawing of asymmetric geometries

The manufacturing of three-dimensional sheet metal components, such as car body parts, heavily relies on deep drawing. With the increasing demand for lightweight measures in the automotive industry due to CO2 limitation requirements, various methods are currently employed to reduce the weight of deep drawn components. However, these methods often overlook the potential for influencing the stress-strain dependent damage state within the component, even though it can greatly affect its performance in subsequent applications, and thus offers lightweight potentials. Friction between the deep drawing tools and the sheet metal is a key factor influencing the stress-strain state, and hence, represents a lever that can be utilized to manipulate the damage state in the component. This paper focuses on the numerical analysis of the dependence of damage on friction during deep drawing. Therefore, a rectangular geometry with an asymmetrical material flow is numerically investigated. A friction ratio is introduced with different constant friction coefficients for the corner of the tools and the straight sides. The established load paths at a chosen reference point are then considered in the form of selected stress and strain characteristics and the numerically predicted damage state is compared. The results are used to derive a recommended friction ratio that leads to less damage in the corner of the geometry. Afterwards strip drawing tool surfaces are modified to manipulate their friction properties using machine hammer peening. Subsequently, the influence of the structures of the strip drawing tool surfaces is quantified using strip drawing tests. The identified contact normal stress dependent friction coefficients are then implemented in the numerical simulation and the established numerical predicted damage state is examined to gain a more comprehensive understanding of how the friction ratio and the structure of the tool surfaces influence the damage state.

Лазерне зміцнення деталей автомобільного транспорту в АПК

The purpose of the work is to determine the effect of laser processing on the microhardness of the zones of ductile cast iron KCh60-3 when it is strengthened by a defocused laser beam and a beam with transverse oscillations. It is also necessary to establish the dependence of friction coefficients on the sliding speed of friction pairs 40H-SCh20 and to determine for these friction pairs the dependence of the intensity of wear on the density of the laser energy flow during the processing of the studied samples. Laser hardening of ductile cast iron KCh60-3 with a defocused beam at a scanning speed of less than 7 mm/s led to shell-type defects and inflows on the surface of the samples. Transverse oscillations of the beam made it possible to exclude similar defects and vary the depth of the solidification zones from the liquid state in the range of 10–800 μm. The maximum depth and width of the hardening zones of cast iron KCh60-3 were 1.8 mm and 11.7 mm respectively. The maximum microhardness values of 12100 MPa were obtained in the remelting zone during processing with transverse beam oscillations. The microstructure of the melting zone is an austenitic-martensitic mixture. A decrease in friction coefficients was observed for all samples up to a sliding speed of 1.5 m/s. The maximum friction coefficients of 0.13–0.145 were obtained for the base material SCh20 with a hardness of 180–210 НВ. The minimum values of friction coefficients of 0.07-0.09 were obtained on samples processed at a laser flux energy density of 46 J/mm2. The obtained results showed that during laser processing of cast iron the microhardness of the hardened layers significantly increases compared to the base material. The developed technology of laser hardening with the use of transverse oscillations of the beam has a higher productivity than when hardening with a defocused beam. Laser hardening of gray cast iron SCh20 and malleable cast iron KCh60-3 using transverse oscillations of the laser beam made it possible to increase processing productivity by 1.5–2.0 times. When using I-20 industrial oil, the increase in energy density during laser hardening of SCh20 cast iron leads to an increase in its wear resistance by 2.5–3.5 times and reduces frictional losses in a pair with 40H steel by 30–60%.

Frictional properties of the décollement in the shallow Nankai Trough: Constraints from friction experiments simulating in-situ conditions and implications for the seismogenic zone

Along subduction zone megathrust faults, the transition from smectite to illite with depth occurs at temperatures of ∼150°C and has long been hypothesized to be one of the dominant controls on the updip limit of the seismogenic zone. Despite this, there have been few experimental studies performed at in-situ conditions to test the frictional stability behavior of subduction zone faults across the smectite-illite transition. In this study, we simulated in-situ temperature-pressure-mineral conditions along the shallow plate boundary in the Nankai Trough, and conducted friction experiments to further constrain the role of smectite-illite transition in seismogenesis in subduction zones. We found that the friction coefficient of the simulated sediment increased with the progress of illitization and followed the Reuss average of friction coefficients of the mineral phases. The obtained friction coefficients and the Coulomb wedge model inferred that the pore pressure conditions around the plate boundary may be over-pressured but not as high as lithostatic pressure. Higher friction coefficients of sediment due to diagenetic processes would be required to sustain pore pressure close to lithostatic along the plate boundary. The velocity dependence of friction coefficient (a−b) was always positive (i.e., velocity strengthening, not seismogenic) except for slip rates less than ∼10 μm/s at 171°C where the smectite-illite transition has almost completed. Therefore, shallow slow earthquakes that occur beneath the outer prism in the Nankai Trough cannot be explained only by the frictional instability of unconsolidated sediment. Since the smectite-illite transition mostly completes at ∼30 km landward from the trough axis, the transition from velocity strengthening to velocity weakening observed at 171°C is caused by temperature-dependent frictional behavior of illite-rich material. Hence, the updip limit of the seismogenic zone in subduction zones is mainly controlled by the frictional properties of illite-rich material, not by the smectite-illite transition.

Optimization of the technology for applying discrete coatings in restoration of bronze parts by electrospark alloying

In this work, a multicriteria optimization of the technology for applying discrete coatings by electrospark alloying in the restoration of bronze parts is carried out. As criteria for optimizing the process of electrospark alloying, tribotechnical characteristics were chosen – the wear intensity and friction coefficient of the coating. As adjustable parameters, those design, technological and operational factors that have the greatest influence on the value of optimization criteria are used: coating material; lubricant; operating current; amplitude of electrode oscillations; sliding speed; specific load. As a result of experimental studies, experimental dependences of wear intensity and friction coefficient for various coating materials, sliding speeds and lubrication conditions were obtained. The use of multicriteria optimization of the electrospark alloying technology made it possible to obtain various alternative coating options and technological parameters of their application for various operating conditions. Of the studied coatings, the most effective is a two-layer coating with the first layer SP-2 and an outer layer of the base material bronze BrAZhMts 10-3-1.5, which is explained by the formation of wear-resistant areas based on Mn and Ni. Multiparametric optimization of the electrospark alloying technology made it possible to reveal a combination of structural and technological factors that ensure the formation of discrete coatings with high operational properties in the restoration of bronze parts.

Sliding velocity dependence of kinetic friction coefficient of bronze-filled polytetrafluoroethylene and its application to robustness improvement of friction damper

Sliding velocity dependence of kinetic friction coefficient of bronze-filled polytetrafluoroethylene and its application to robustness improvement of friction damper

Friction Dynamics of Organogels on Artificial Skin Surfaces

Organogels are attractive formulations in cosmetics, food, and pharmaceuticals. They exhibit characteristic frictional and mechanical responses during the collapse of a mesostructure. In this study, the friction dynamics of organogels composed of five different waxes (paraffin wax, microcrystalline wax, ceresin, candelilla wax, and carnauba wax) and liquid paraffin were evaluated using a sinusoidal motion friction evaluation system. All organogels exhibited a velocity dependence of friction coefficient that increased with the acceleration of the contact probe. Depending on the ease of the crystal formation of the waxes in liquid paraffin, hydrocarbon-based waxes formed soft organogels with a low-friction coefficient, whereas ester-based, highly polar waxes formed organogels that were hard and had a high-friction coefficient.

Features of ion nitriding technology multicriteria optimization

In this work, the technology of 30HGSA steel ion nitriding was optimized in terms of tribotechnical characteristics – wear intensity and friction coefficient. When choosing controlled factors, the influence of all existing groups of factors that can affect the process of ion nitriding is taken into account: structural, technological and operational. Friction and wear tests were carried out under conditions that are as close as possible to the actual operating conditions of aircraft parts made of 30HGSA steel. As a result of experiments on friction and wear, tribotechnical characteristics of coatings were obtained depending on structural, technological and operational factors, respectively, to the matrix. The conducted studies showed the presence of three clearly defined zones in the dependences of wear intensity and friction coefficient on specific load at different sliding speeds and technological parameters of ion nitriding: run-in zones, uniform and catastrophic wear. The nature of samples dependences hardened by ion nitriding and heat-treated samples is similar and coincides with modern views on the laws of friction and wear processes. Analysis of tribotechnical characteristics showed the effectiveness of ion nitriding technology in comparison with traditional heat treatment. The optimal processing modes for the studied steel and triboconjugation have been established

Numerical modeling of defect formation in friction stir welding

This study presents an investigation of welding defect formation in joining AZ61 magnesium alloy with friction stir welding by means of a 3D finite element model. The numerical model was created and analyzed in the ABAQUS software. This numerical model uses coupled Eulerian Lagrangian formulation, modified Coulomb's friction law, Johnson-Cook material law, mass scaling technique, and temperature dependent friction coefficient values. The numerical model was validated with experimental results in terms of heat input, temperature distribution, plastic deformation type-amount, and weld defect formation in the weld zone. In friction stir welding, the heat input with a certain tool simply changes directly proportional to the ratio of tool rotation speed to tool feed rate for constant tool compressive force. In the numerical model, as in the experimental study, when the ratio of tool rotational speed to tool feed rate is 2, low heat input results in insufficient plastic deformation, leading to the formation of weld defects in the form of void. When the ratio of tool rotational speed to tool feed rate is 3, however, it was observed that sufficient heat input is provided, and no welding defects occur. The generated numerical model enables the determination of the welding defects that occur in the form of voids in the friction stir welding in a very short processing time. Besides, weld seam geometry can be predicted quite accurately with this model.

Heat Transfer Coefficient of Zinc Phosphate Coating with Metal Soap during Cold Backward Extrusion

In cold forging, the temperature difference between the workpiece and the tool is small and thus deformation analysis is rarely coupled with thermal analysis. However, the friction coefficient of zinc phosphate coating with metal soap has a large temperature dependence. Consideration of the effects of workpiece and tool temperature change on the friction coefficient is thus expected to improve the analytical accuracy of cold forging. Thermally coupled cold forging analysis requires thermal conductivity, specific heat, heat transfer coefficient between the workpiece and the tool, in addition to the temperature dependence of flow stress and friction coefficient. The heat transfer coefficient between workpieces coated with zinc phosphate with metal soap and tools is investigated in this paper. Cold backward extrusion was performed with a 50% reduction of area, and the temperature history in the punch was measured with a thermocouple. The forging speed was 1, 3, and 10 spm. FEM analysis was performed to simulate the experiment by considering the temperature dependence of flow stress and friction coefficient. The heat transfer coefficient was estimated at 20 kW/(m2•°C) by comparing the experimental result and calibration curves.

The amphoteric cartilage surface tested in the pH Range from 2.0 to 9.0

Background: Phospholipids adsorbed to negatively-charged proteoglycan matrix form phospholipid (membrane), have negatively charged surface (-PO4-) and are hydrophilic. Strong adsorption and strong cohesion are necessary for phospholipids to provide a good lubricant. The surface energy of spherical lipid bilayers have "bell-curve" shaped has amphoteric character and lowest surface energy at a pH 7.4 ± 1 of the natural joint. Objectives: The amphoteric character of the natural surface of the articular cartilage was determined by measuring the surface energy of the model spherical bilayer lipid membrane. It was found that the friction (f) vs. pH 2.0 to 9.0 of the pair (cartilage/cartilage) has the amphoteric character by exposing "bell-curve" shaped with an isoelectric point (IEP). Methods: The friction coefficient (f) was measured with the sliding pin-on-disc tribotester the friction between two surfaces (cartilage/cartilage) pair. The method of interfacial tension measurements of the spherical lipid bilayer model vs the pH over the range 0.2 to 9.0 was used. Results: The dependence of friction coefficient between two cartilage surfaces on the pH over the range 2.0 to 9.0 is demonstrated by a “bell - curve” in Fig. 2(A). The surface energy of a model spherical bilayer lipid membrane vs. the pH has the character of a “bell - curve” with an (IEP) is shown in Fig. 2(B). Conclusion: The amphoteric effect on friction between the bovine cartilage/cartilage contacts has been found to be highly sensitive to the pH of an aqueous solution. In this paper we demonstrate experimentally that the pH sensitivity of cartilage to friction provides a novel concept in joint lubrication on charged surfaces. The change in friction was consistently related to the change of charge density of an amphoteric surface.

A friction model of fractal rough surfaces accounting for size dependence at nanoscale

Traditional laws of friction believe that the friction coefficient of two specific solids takes a constant value. However, molecular simulations revealed that the friction coefficient of nanosized asperity depends strongly on contact size and asperity radius. Since contacting surfaces are always rough consisting of asperities varying dramatically in geometric size, a theoretical model is developed to predict the friction behavior of fractal rough surfaces in this work. The result of atomic-scale simulations of sphere-on-flat friction is summarized into a uniform expression. Then, the size dependent feature of friction at nanoscale is incorporated into the analysis of fractal rough surfaces. The obtained results display the dependence of friction coefficient on roughness, material properties, and load. It is revealed that the friction coefficient decreases with increasing contact area or external load. This model gives a theoretical guideline for the prediction of friction coefficient and the design of friction pairs.

Characterising the friction coefficient between rubber O-rings and a rigid surface under extreme pressures

Previous research into the friction behaviour of elastomers has typically focused on the effects of velocity, contact pressure, counter surface and lubrication on the coefficient of friction. O-ring type elastomer seals are common in many different industries. Friction plays a critical role during the setting and in service of these components. An experimental O-ring friction testing rig has been developed that can measure the effects of sliding speed and hydrostatic pressure on elastomer friction. Finite element analysis (FEA) packages can adopt fixed friction coefficients or ones that are pressure dependent. For the latter case, the dependence of the frictional behaviour is typically obtained from the instantaneous stress response at any given pressure and then related to the normal force response. The friction rig described in this paper uses industry standard dimensions for the O-ring gland, the pre-compression levels, extrusion gap size and pressure rating. The coefficient of friction is derived by dividing the measured friction force by the normal force, which was determined using an FEA modelling approach, as it could not be measured directly. Finally, a relationship between the frictional velocity and surface roughness is obtained in order to provide a frequency dependent Coefficient of Friction (CoF) that is easily translatable between surfaces.

Coupling Friction with Visual Appearance

We present a novel meso-scale model for computing anisotropic and asymmetric friction for contacts in rigid body simulations that is based on surface facet orientations. The main idea behind our approach is to compute a direction dependent friction coefficient that is determined by an object's roughness. Specifically, where the friction is dependent on asperity interlocking, but at a scale where surface roughness is also a visual characteristic of the surface. A GPU rendering pipeline is employed to rasterize surfaces using a shallow depth orthographic projection at each contact point in order to sample facet normal information from both surfaces, which we then combine to produce direction dependent friction coefficients that can be directly used in typical LCP contact solvers, such as the projected Gauss-Seidel method. We demonstrate our approach with a variety of rough textures, where the roughness is both visible in the rendering and in the motion produced by the physical simulation.

Fretting wear behaviour of nickel foam struts used in fuel cell applications

In any proton-exchange membrane fuel cell, the bipolar plates grab attention because of the high production cost and heavyweight. Hence, the open-cell nickel foams are considered as an alternative to these grooved plates. The reliability of the metallic foams used as flow distributors and gas diffusion layers plays a vital role in the fuel cell's overall performance. Fretting wear damage of the metal foam at strut/strut interface and strut/supporting frame interface due to the vehicular vibrations and pressurized fuel flow is expected to affect the performance and is investigated. This paper discusses the fretting wear behaviour of nickel foam strut that constitutes open-cell nickel foam based on laboratory tests. The experiments are performed by using two different contact configurations: steel ball on wrought nickel flat and nickel strut on wrought nickel flat. The test results reveal the fretting friction coefficient's dependence on the normal load, surface roughness and contact geometry. Although the nickel strut versus nickel flat fretting wear tests showed a low coefficient of friction, severe damages were observed on the nickel struts’ worn surfaces compared to the wrought nickel flat. Scanning electron microscope images of worn scars on nickel foam struts indicate the presence of shallow grooves, craters, micro-cracks and delamination craters at higher loads.

Calculation of the dependence of friction coefficient of locomotive composite ridge brake shoes on pressing force and braking speed

JSC “FRITEX” has developed non-asbestos ridge composite brake shoes UR 01-01 with a reduced coefficient of friction, which, in contrast to the cast iron ridge brake shoes currently used on locomotives, have high wear resistance and more stable frictional properties at high speeds. They are much lighter than traditional cast iron shoes, resulting in lower logistics costs and easier replacement by service departments. However, the new materials used for the production of the shoe, as well as its innovative design, which combines the two types of materials, require a detailed study of its frictional properties. For this, the braking modes of a locomotive equipped with UR 01-01 shoes were simulated in a full-scale unit of a brake mechanism on an inertial stand at fixed pressures and speeds. Based on the results of the experiments, the values of the friction coefficients of the brake shoes were determined and the dependence of the friction coefficient of the shoes on the pressing force and braking speed was established. The data obtained were used in braking calculations for an electric locomotive of the VL80 series, including the determination of the braking distance, holding a single locomotive by the parking brake on a slope, and ensuring the antiskid braking due to higher values of the friction coefficient of the UR 01-01 shoe at high speeds. The composite ridge brake shoe ensures compliance with the standard values of the braking distance, antiskid braking and slope parking for the VL80 series electric locomotive. In this case, the use of these composite shoes is possible without changes in the device of the lever transmission of the electric locomotive. It is necessary to conduct running brake tests to make approbation of obtained empirical dependence of the friction coefficient of new shoes on the pressing force and the braking speed of the locomotive and its widespread use in the calculation of brake systems.

Size Effects and Mechanisms in the Friction and Wear Processes of Ceramics Based on Zirconium Dioxide

This paper presents a study of the tribological properties of ceramics based on ZrO2 stabilized with CaO in a ceramic-ceramic friction pair. The influence of the scale factor on the coefficient of friction in the micro- and nanoscale is established. A qualitative correlation of the theoretical and experimental curves is shown for friction coefficient dependence on the body-counterbody contact force. Friction and wear micromechanisms at a micro- and nanoscale are proposed for the investigated TZP ceramics.