Static Friction Coefficient Research Articles

A tube heat transfer prediction model considering static friction coefficient of dense particle flow

Particulate material is an important heat transfer medium in industry. The heat transfer process of dense particle flow around tubes has important applications in industrial waste heat and solar energy conversion. However, rapid prediction of particle heat transfer processes is still worth investigating, especially when the particle flow is affected by the coefficient of friction. A heat transfer model of dense particle flow around a tube was established, the effects of particle size, density and static friction coefficient on the heat transfer characteristics were explored, and a heat transfer prediction equation considering the static friction coefficient was constructed originally. The results show that the particle size has the most significant effect on the heat transfer. As the particle size increases from 2 mm to 4 mm, the average effective heat transfer coefficient of the tube decreases from 262.35 W/(m2·K) to 217.31 W/(m2·K). The effect of particle density on the heat transfer is reflected in the difference in the heat capacity of the particles, and has little effect on the flow of the particles. The particle static friction coefficient mainly affects heat transfer by affecting the flow state of the particle flow. The average contact number decreases from 63.9 to 38.9. The relative error of the modified model is reduced from 8.9% to 3.78%.

Olive pit powder as multifunctional pigment for waterborne paint: influence of the bio-based filler on the aesthetics, durability and mechanical features of the polymer matrix

In this work, olive pit powder has been added into a polyurethane-acrylate top-coat paint, evaluating the effect of four different filler amounts on the aesthetics, durability and mechanical features of the composite coatings. The samples were characterized by electron microscopy and colorimetric analyses to assess the possible change in morphology and appearance introduced by the bio-based additive. The durability of the coatings was evaluated by salt spray chamber and UV-B exposures, which evidenced the water absorption tendency of the lignocellulose-based filler and its severe chemical-physical degradation, respectively. Otherwise, the filler based on olive pit causes an increase in the mechanical features of the polymeric matrix, such as abrasion resistance, hardness and static coefficient of friction. Although the coating containing high concentrations of olive pit powder demonstrated poor durability, this study revealed that the bio-based filler can be employed as multifunctional pigment, providing particular aesthetic features, but also improving the mechanical durability performance of polyurethane-acrylate paints.

Modeling contact of Au-coated sphere with rigid flat: Electrical contact resistance, adhesive wear and friction

The electrically conductive coating is an effective means to reduce electrical contact resistance (ECR) of sliding electrical contact, however, the wear resistance of the coated surface influences its reliability and lifetime. The electrical contact performance of coated systems is assessed in this work using the Au-coating/Cu-substrate system. An elastic-plastic coated spherical contact is established with the realistic ductile failure criterion to allow material damage, and the effects of coating thickness and normal loading are investigated. As coating thickness increases, it is found that: the ECR decreases and then increases, presenting minimum value at a thickness independent of normal loading; the static friction coefficient increases which is related to the locations of damage occurrence at sliding inception; the wear coefficient increases to a peak and then decreases. Two wear modes of coated sliding electrical contact are observed, namely debonding mode and detaching mode, where wear particle forms by coating debonding and fracture inside coating, respectively. A critical dimensionless coating thickness, which is the minimum thickness able to protect the coating from debonding, is proposed.

Stick–Slip Characteristic Analysis of High-Speed Train Brake Systems: A Disc–Block Friction System with Different Friction Radii

Inspired by the difference in the friction radii of the pads from the high-speed train brake system, stick–slip experiments for a disc–block friction system with different friction radii were carried out via a test device. Based on the test results, the stick–slip vibration characteristics of the disc–block friction system with variation in the friction radius were analyzed, and the corresponding Stribeck model parameters in exponential and fractional forms were identified. The experimental results show that with an increase in the friction radius the vibration amplitude first increased and then decreased and the frequency of stick–slip vibration increased. The identified Stribeck model parameters show that the decay factors increased, the static friction coefficient decreased, and the dynamic friction coefficient decreased first and then increased as the friction radius increased. Moreover, the identified Stribeck model in an exponential form can more accurately reflect the stick–slip characteristics of a disc–block friction system than the model in a fractional form. It can be further applied in the investigation of the dynamic behaviors of high-speed train brake systems.

Physical and engineering properties of chickpea (Cicer arietnum L.) for planter design

The design of a chickpea planter and its optimum performance requires physical and engineering properties of the grain varying with cultivars. Such properties include size, shape, mass, density, static friction coefficient, and repose angle etc. The cultivars viz. JG 16, HC 5, KWR 108, IPC 4-1, IPC 5-62, DCP 92-3, IPC 4-98 and JG 14 were investigated at 11.0±1.0 per cent moisture content using standard methodology. The grain size was presented in terms of major, intermediate, minor, and geometric mean diameters as 8.49-9.78, 5.91-7.23, 5.88-6.94, and 6.68-7.89 mm, respectively. The shape of the grain was presented in terms of sphericity which ranged from 0.78-0.81. The thousand seed mass, bulk density, and true density were 198-338 g, 830-880 kg m-3, and 1310-1350 kg m-3, respectively. The static friction coefficient was the least against aluminium followed by galvanised iron and mild steel surfaces with respective ranges of 0.37-0.40, 0.41-0.45, and 0.52-0.56. The angle of repose ranged from 26.4-27.7 degrees. There was a significant varietal difference in different physical and engineering properties of chickpeas except true density and angle of repose, where the difference was non-significant.

Temperature Dependence of the Static Friction Coefficient of Common Recyclable Polymers

According to the classical adhesion explanation for the phenomenon of friction, the friction coefficient between two surfaces is defined as the ratio between the horizontal friction force exerted on each surface and the perpendicular normal force between each surface. There is a paucity of published investigations into the relationship between the contact temperature of a polymer-nonpolymer physical interface and the resultant static friction coefficient at varying temperatures. This study investigates the relationship between temperature and the static friction coefficients of five recyclable thermoplastic polymers in polymer-aluminum interfaces across a range of temperatures. The results demonstrate a generalizable relationship between the static friction coefficient and the contact temperature of polymer-aluminum interfaces which corresponds to polymer-specific phase-change temperatures.

Experimental investigation of the frictional behavior of single glass fiber filament

Fiber friction behaviors are crucial for understanding the ubiquitous frictional damage phenomena in the manufacturing and service processes of multiscale textile reinforcements. This paper investigates the influence of relative velocity and applied load on the frictional behavior between a solitary glass fiber filament and a metal roller. The results of piecewise regression analysis indicate that the apparent coefficient of friction initially decreases with relative velocity, followed by an increase, and subsequently decreases again until stabilizing at higher velocity. Specifically, the maximum values of the coefficient of static friction are observed within the relative velocity range of 1.26–1.68 mm/s, while that of dynamic friction occurs within the range of 0.84–3.94 mm/s; the coefficient of friction reaches stable values within the relative velocity range of 7.87–15.71 mm/s. Under four different tension conditions, the stable values for the coefficient of static friction are 0.336, 0.308, 0.321, and 0.281, while the coefficient of dynamic friction are 0.291, 0.269, 0.273, and 0.232 respectively. Furthermore, the relationship between the coefficient of friction and the applied load reveals that the coefficient of friction decreases as the load increases. Finally, quantitative investigation reveals a strong coupling characteristic between the velocity dependency and load dependency of the apparent coefficient of friction.

Efecto de las condiciones de superficie en obra sobre el coeficiente de fricción estático de materiales metálicos

Se propone una metodología para cuantificar variaciones del coeficiente de fricción estático µ debido a diferentes condiciones de superficie en obra para materiales metálicos con radio de dureza ρ = 0.5 – 2.9. ρ es definido como la relación entre la dureza del material y la del Acero A36. Para cada material, 7 probetas fueron consideradas en las condiciones de obra “limpia”, “comprada”, “pulida” y “corroída”. Los resultados muestran que respecto a la condición “limpia”, si las superficies se mantienen como compradas, µ puede incrementarse o reducirse hasta el 20%, si las superficies se pulen, µ puede incrementarse hasta el 37% y si las superficies se corroen µ puede incrementarse hasta el 410% para ratas de corrosión entre 90 – 670µm/año. Los resultados también muestran que para superficies limpias y para ρ ≤ 1.7, µ es dependiente de ρ y para ρ > 1.7, µ es aproximadamente constante. Un modelo que predice la variación de µ para las condiciones de superficie en obra consideradas fue propuesto.

Влияние свойств дискового тормоза с термоизолированными узлами трения на коэффициент трения покоя

The article is devoted to analytical determination of dependences of the static idle friction coefficient of a disc brake with thermally insulated friction nodes on influencing factors and experimental confirmation of the final result obtained. The design of the new disc brake provides two friction units, each of which uses materials with different operating temperatures. A characteristic feature of the brake is the thermal insulation of friction units, which allows each pair of friction to provide its own temperature conditions. Carbon and steel are used as friction materials. The characteristics of contact interaction of the working elements of the disc brake are calculated: the dependence of a contour contact area on the radius of curvature of the tops of undulation waves, contour pressures on complex roughness criteria, the integral coefficient of friction of the disc brake with thermally insulated friction nodes on influencing factors. Experimental verification of the obtained results was carried out on a full-scale facility, which allows measuring the forces of static friction under conditions of real forces, pressures and geometry of the contact area. As a result of the study, it was found that the stress strain state of the contact area under conditions of static force interaction corresponds to an elastic unsaturated contact. In this case, when calculating the static friction, the mechanical component of the friction coefficient can be neglected. It has been experimentally confirmed that with the increase in the normal pressing force of the disc brake elements, the coefficient of static friction decreases, which indicates the elastic nature of the interaction of micro-dimensions. Carbon-based friction material is characterized by lower values of the static friction coefficient for all specified values of the clamping force.

Moisture Dependent: Physical Properties of Baobab Seeds (Adansonia digitata L.)

Abstract The research investigated physical properties of baobab seeds to determine suitable equipment for the processing of its seeds. Pods of baobab used in the study were collected at a local farm in Ilorin, North Central Nigeria. Physical properties of the samples, such as moisture contents, mass, axial dimensions, shape indices, true and bulk densities, porosity, angle of repose and surface area were determined. The results showed that physical properties of baobab seeds were stable for moisture content, ranging between 12 to 18% dry mass (dm). The 100 seed mass (g) and geometric mean diameter increased from 0.60 g to 0.62 g and 10.12 to 10.27 mm respectively, in the moisture range of 12 to 18% dm. Other studied ranges of physical properties ranges included: average length (12.22 to 12.63 mm), width (10.10 to 10.28 mm), thickness (8.23 to 8.42 mm,), sphericity, (81.23 to 82.56 mm), surface area (319.42 to 332.53 mm2), 50 seed mass (0.60 and 0.62 g), and 1000 seed mass (12 and 12.4 g) within the moisture content range of 12 to 18% dm. The angle of repose of baobab seeds decreased with an increase in moisture content. The maximum value of 29.18o was obtained at 14% moisture content while a minimum value of 24.42o was obtained at 18% moisture. Moisture content had a significant effect on coefficient of friction of baobab seeds on glass, stainless steel, plywood and rubber. In the same moisture range (12-18%), the static coefficient of friction for baobab seeds ranged from 0-739 to 0-905 on stainless steel, 0-960 to 1-190 on galvanized steel, 0-812 to 1-055 on plywood and 0-496 to 0-950 on glass. The least coefficient of friction values were recorded on stainless steel and glass which implies that baobab seeds will move with lower resistance on these surfaces in post-harvest handling. On the other hand, the resistance will be higher on plywood and glass. The data obtained will serve as guide for agricultural and food engineers, food processors and technicians involved in design and construction of post-harvest equipment used for separating, cleaning, milling and other production processes, to which baobab seeds are subjected.

Određivanje nekih inženjerskih osobina irskih sorti krompira

Irish potato (Solanum Tuberosum) is a nutritive diet in the food chain supply of the Nigerian populace. Apart from the agronomic practices and production level in the country, limited data that exist on engineering properties of the adapted varieties are either scanty or non-existent in print form. Three locally varieties namely Nicola, Bartita and Bawondoya were investigated for some physical and frictional properties using standard laboratory procedures and equipment. The measured parameters are data resource for indigenous processors and machinery and equipment fabricators. The data obtained were subjected to simple descriptive statistics using Microsoft Excel package for computing the mean, range and the standard deviation. The mean, standard deviation and range values for axial diameters (major, intermediate and minor), geometry diameter, sphericity, aspect ratio, mass, volume, density and surface area in varietal order of 'Nicola', 'Bartita' and 'Bawondoya' are (43.61±3.72mm-63.82±7.95mm; 39.41±2.99mm-44.1±2.38mm; 33.41±2.67-5.90±2.87mm); 40.81±1.87mm - 44.02±2.87 mm; 0.70±0.07 - 0.94±0.06; 0.63±0.10 -1.02±0.11; 43.2±4.69g - 52.8±9.9g; 43.3±5.4cm3 - 49.8±10 cm3 ; 1.001±0.057 g/cm3 -1.065±0.076 g/cm3 and from43.30±476.20 mm2 to 6113.63±811.26 mm2 respectively. Bulk density values of 701.43 kg/m3 , 673.30 kg/m3 and 672.86 kg/m3 were obtained in respective order as above. Peel-weight proportion of 2.5%, 2.76% and 1.9% were obtained at 80.6%, 79.4% and 81.4% moisture content (w.b) levels for the sampled weight of Nicola, Bartita and Bawondoya varieties respectively. The frictional parameters results indicate an angle of repose 15⁰ was obtained for both Bartita and Bawondoya varieties while 130 was obtained for Nicola variety. Average values of 0.68, 0.61 and 0.52 were obtained as coefficients of static friction for Bartita, Bawondoya and Nicola varieties respectively.

Physico-mechanical properties of seed pile of fodder crops

The purpose of the study is to study and analyze the physical and mechanical properties of the seed pile of fodder crops. The results of determining the physico-mechanical properties of the seed pile of fodder crops obtained in the combing clover plants with a comb of the combing drum of the harvesting machine are presented. The basic principles and methods of classical mechanics, mathematical analysis, and statistics were used in this study. It was found that the stiffness of the stems of the seed pile at a humidity of 40-60% is in the range of 0.07-0.008 N / m2. At the same time, with a moisture content of 35-65%, its bulk mass is 80-185 kg/ m3, respectively. The minimum value of the angle of the natural slope of the clover seed pile is 48o, and its maximum value reaches up to 90o; the value of the static friction coefficient at a humidity of 40-60% is within 0.98-1.02, and the value of the dynamic friction coefficient is within 0.5-0.7. The pile's temperature is directly proportional to the storage time; during self-heating, the appearance of the pile gradually changes depending on the storage time and temperature duration.

基礎滑りを利用した木造住宅の最大滑動量と強振動の計測震度の関係

Sliding bases decrease the seismic load to structures. They make both the decrease of the maximum displacement response and the slide displacement of the structure. In this paper, sliding bases are adopted to a Japanese wooden house. Both the demand base shear and the maximum slide displacement of houses are proposed. As a result, the sliding bases with 0.2 static friction coefficient makes that no slide displacement is calculated in rare earthquakes. And the storey displacement angle of the house with 2.0 bearing wall sufficiency ratio is less than 1/120 rad in extremely rare earthquakes. Some observed earthquakes make the slide displacement over 600mm.

On the discontinuous dynamics of a class of 2-DOF frictional vibration systems with asymmetric elastic constraints

<abstract><p>In this paper, the discontinuous dynamic behavior of a two-degree-of-freedom frictional collision system including intermediate elastic collision and unilateral elastic constraints subjected to periodic excitation is studied by using flow switching theory. In this system, given that the motion of each object might have a velocity that is either greater than or less than zero and each object experiences a periodic excitation force that has negative feedback, because the kinetic and static friction coefficients differ, the flow barrier manifests when the object's speed is zero. Based on the discontinuity or nonsmoothness of the oscillator's motion generated by elastic collision and friction, the motion states of the oscillator in the system are divided into 16 cases and the absolute and relative coordinates are used to define various boundaries and domains in the oscillator motion's phase space. On the basis of this, the G-function and system vector fields are used to propose the oscillator motion's switching rules at the displacement and velocity boundaries. Finally, some dynamic behaviors for the 2-DOF oscillator are demonstrated via numerical simulation of the oscillator's stick, grazing, sliding and periodic motions and the scene of sliding bifurcation. The mechanical system's optimization designs with friction and elastic collision will benefit from this investigation's findings.</p></abstract>

Influence of Material Characteristics of Hoppers on Particle Flow Behavior

In the previous study, different structures of hoppers were proposed. And the dust suppression performance of hoppers were evaluated. In this paper, different materials of hoppers were selected.And influence of different material on particle behaviors were studied based on the discrete element method (DEM). Results shows that the wall material with low collision recovery coefficient for the hopper has positive effect on suppressing dust diffusion.and the wall material with high static friction coefficient showed little effect on the particle flow state through the hopper.

Determination of the physicomechanical characteristics of black chickpea grains

In this study, some physicomechanical characteristics of black chickpea grains, which have rich content, were investigated. Dimensional and volumetric properties, colour characteristics, and frictional and mechanical properties were examined within the physicomechanical properties of the grains. Compression tests were carried out for the behaviour of black chickpea against mechanical force, both force and deformation characteristics of black chickpea grains were determined, and they were used at three different loading speeds (30 mm min-1, 50 mm min-1, 70 mm min-1). The size dimension, such as width, length, and thickness values, were found as 6.68 mm, 8.85 mm, and 6.26 mm, and the mass was 0.25 g, respectively. The highest $a^*$ and $b^*$, $L^*$ values were determined as 4.31, -0.27, and 18.87, respectively. The values of the static friction coefficient of the black chickpea grains on different friction surfaces (PVC, galvanized sheet, laminate, plywood, and rubber) were observed on the rubber surface with the highest. In the mechanical test results, the highest force value was found on the 50 mm min-1 width (Y-) axis, and the highest hardness value was found on the thickness (Z-) axis at the 30 mm min-1 loading speed.

基于坍落度试验的湿粘性水田泥浆颗粒离散元参数分析及标定

In order to obtain the discrete element contact parameters of wet and viscous paddy field mud particles, an accurate numerical simulation model was constructed. Firstly,, the paddy field mud with an average particle size of 0.2 mm was taken as the research object, and the basic physical parameters and rheological behavior laws were obtained through physical measurements and rotational rheological tests. Based on the slump test, combined with the particle scaling theory and Johnson-Kendall-Roberts (JKR) model, and the slump and slump-flow values were taken as response values, the Plackett-Burman test, the steepest climb test and the Box-Behnken test were designed by Design-Expert software to complete the simulation parameters calibration. The optimal significance parameters are as follows: 0.096 J/m2 for the JKR surface energy of mud, 0.13 for the mud-mud restitution coefficient and 0.6 for the mud-steel static friction coefficient. Finally, the mud slump and fluidity verification tests showed that the relative errors between the simulation values and the physical values of slump and slump-flow are 1.73% and 0.42%, and the average error of torque is 2.47%, and the parameters are accurate and reliable. The calibration method can accurately construct the discrete element model of wet-viscous particles, which provides basic data and technical guidance for the coupling mechanism of paddy machinery-mud.

Static and dynamic coefficient of friction in friction pairs of disc-pad brakes

Problem This scientific article is devoted to the value of static and dynamic coefficients of friction of disc-pad brakes. The issue of disc-pad brake wear is very acute because the safety of using the machine itself depends on its reliable operation. Therefore, the relevance of the chosen topic cannot be doubted. Goal. The aim is to establish patters of influence of the main operational parameters of friction pairs of a model disc-pad brake on the potential and kinematic coefficient of friction. Methodology. The methods of analytical mechanics and the theory of elasticity were used in the article. Results. Theoretical and experimental studies of the static (former rest) and dynamic coefficients of friction in the frictional interaction of materials FK-24A - steel 35KhNL were carried out on a model disk-shoe brake in a long-term braking mode. At the same time, it was established in the range of real impulse loads implemented during braking in the contact area of the friction lining with the brake disc, the stress-strain state of the contact according to the criterion of micro deformation in the contact corresponds to the elastic-plastic property. The elastic and plastic properties of materials appear when, in each individual case, the total stresses exceed the yield strength or reach its limit. With an increase in the impulse force of the normal pressing of the pad lining to the treadmill of the disc friction, the static coefficient of friction tends to increase, and with an increase in the static coefficient of mutual overlap kvz.s, it tends to decrease with the elastic-plastic property of materials. When choosing materials for friction pairs, the dynamic coefficient of friction must include the value of the static coefficient of friction and be at least 20% greater than the calculated value of the dynamic coefficient of friction. Practical value An increase in the static and dynamic friction coefficient in the friction pairs of a disk-pad brake leads to an increase in the plastic deformation of their microprotrusions. The data obtained can be used in the design of disc-shoe brakes

Determination Method of Core Parameters for the Mechanical Classification Simulation of Thin-Skinned Walnuts

Simulation can be used to visualize the mechanical classification of walnuts. It can collect microscopic information about walnuts in the classification roller and guide its optimization design. In this process, simulation parameters are essential factors that ensure the effectiveness of the simulation. In this study, the crucial parameters of thin-skinned walnut particles in classification simulation were determined by combining the discrete element method (DEM) and physical tests. Firstly, the moisture content, shear modulus, stacking angle, and some contact parameters in the shell and kernel were obtained by drying test, compression test, cylinder lifting test, and physical test of contact parameters, respectively. A walnut model was constructed using reverse modeling technology. Then, the ranges of the rest contact parameters were determined using simulation inversion based on the Generic EDEM Material Model database. Second, the parameters significantly influencing the stacking angle were screened via the Plackett–Burman test using contact parameters as factors and stacking angle as the index. The results revealed that the walnut–walnut static friction coefficient, walnut–walnut rolling friction coefficient, and walnut–steel plate static friction coefficient significantly affect the stacking angle. The steepest ascent experiment produced the optimal value intervals of crucial parameters. Besides, a quadratic regression model of important parameters was built using the Box–Behnken test to achieve the optimal parameter combination. The stacking and classification experiments verified that the stacking angle and morphology are mostly similar under calibration parameters without any considerable differences. The relative error was only 0.068%. Notably, the relative error of the average staying time of walnut in the classification roller was 0.671%, and the dimensionless distribution curves of stay time were consistent. This study provides technological support to the simulation analysis of walnut classification and recommends novel methods and references to determine the parameters of other shell materials.

Simulation and Validation of Discrete Element Parameter Calibration for Fine-Grained Iron Tailings

In order to improve the calculation efficiency of a discrete element EDEM (Discrete Element Method) numerical simulation software for micron particles, the particle model is linearly enlarged. At the same time, the parameters of the amplified particles were calibrated according to the Hertz-Mindlin with JKR (Johnson-Kendall-Roberts) contact model to make the amplified particles have the same particle flow characteristics as the actual particles. Actual tests were utilized to gather the angle of repose of the microfine iron tailings, which was then used as a reference value for response surface studies based on the JKR contact model from six factors connected to the fine iron tailings particles. The Plackett-Burman test was used to identify three parameters that had a significant effect on the rest angle: static friction factor; rolling friction factor; and JKR surface energy. The Box-Behnken experiment was used to establish a second-order regression model of the rest angle, and the significant parameters and the optimized parameters were: surface energy JKR coefficient 0.459; particle-particle static friction coefficient 0.393; and particle-particle dynamic friction coefficient 0.393, with a dynamic friction coefficient between particles of 0.106. By entering the parameters into the discrete element program, the angle of repose generated from the simulations was compared with the real test values, and the error was 1.56%. The contact parameters obtained can be used in the discrete element simulation of the amplified particles of fine-grained iron tailings, providing an EDEM model reference for the numerical simulation of fine-grained iron tailings particles. There is no discernible difference between the actual and simulated angles.