Different Coefficients Of Friction Research Articles

Material characterization and inter/intra-particle validation for DEM simulation of urea coating process

Particle coating is a common operation in the controlled-release fertilizer (CRF) industry, where a coating layer is appliedto the urea cores. A discrete element method (DEM) computer simulation was applied to model the coating process for the urea granules using measured model parameters. The accuracy of DEM input parameters for the coating material properties and the physical and mechanical characterizations of urea granules are crucial to the study of particle coating processes. Thus, to enhance the simulation accuracy, information on the material properties (urea granules) is required. In this study, the elasticity parameters, shear modulus, coefficient of restitution (CoR), and coefficient of rolling and static friction (CoRF) and (CoSF) of urea granules are estimated experimentally in addition to the physical characteristics. The sensitivity of the angle of repose of the urea bed was investigated at different coefficients of friction. According to the obtained experimental value of the angle of repose, values of 0.2 and 0.3 for CoRF and CoSF, respectively, were adjusted to obtain consistent urea granules’ motion for simulation and the experiment. Moreover, the spray droplet sizes and velocity distributions were estimated using the video-imaging process technique. Based on this experimental characterization, elasticity parameters and spray properties were integrated into DEM simulation software as input data to perform numerical analysis of the coating process to compare simulation and experimental results, which show uniformity at three different pan speeds with a maximum deviation of 0.033 at 5 rpm. Also, consistency between DEM and experiment results was achieved in terms of average coating thickness (μm) of the selected samples and average intra-particle thickness variation (CoVintra). These results revealed that the coating film thickness is proportional to the rotation speed for the experiment and simulation. To enhance the inter-particle coating uniformity, the effects of the most significant parameters such as pan speed, filling ratio, particle size, spray rate, and spray angle, were examined. A low spray rate, filling ratio, and high pan speed improved the coating uniformity. The particle size and spray angle show considerable influence on the coating uniformity, where larger particle sizes and spray angles tend to reduce the inter-particle coating uniformity.

Effect of pad rotation angle and coefficient of friction on fretting fatigue crack nucleation behavior

Fretting fatigue may occur on surfaces that are in contact, subjected to a normal load, and where there is a cyclic small relative movement between them. It could occur in press-fitted shafts, bolted and dovetail joints, and many other engineering components. It is recognized that the coefficient of friction of the contacting bodies is a primary variable in the fretting process. Also, a recent study indicates that its behavior might be greatly affected by the possible rotation of the pad. Consequently, the aim of this investigation is to evaluate the impact of diverse angles of rotation of the pad and different coefficients of friction on crack initiation angle, location, and life. For this purpose, a numerical model based on a finite element model of a cylinder-plane test configuration is constructed. The Fatemi-Socie damage parameter for multiaxial fatigue is used to evaluate initiation behavior. Firstly, different angles of rotation are applied to the pad, in order to model a lack of stiffness of the test rig, while the coefficient of friction is kept constant and equal to 0.75. Secondly, several coefficients of friction between the pad and the specimen are utilized, while considering a cyclic rotation of the pad between 0.19° and – 0.19°. For the case studied, the results indicate that an increase of the coefficient of friction (μ) may cause a substantial reduction of crack initiation life. However, a variation of μ in the range 0.75 ≤ μ ≤ 0.85 does not produce a significant change in life estimation. This suggests that it cannot be stated that an increase in the coefficient of friction always leads to a reduction in nucleation life. Regarding the angle of initiation of the crack, the results show that an increase of μ causes an approximately linear reduction of the angle. In the case of an increase of the pad angle of rotation, this causes a longer nucleation life and a smaller crack nucleation angle. Even the rotation angle of 0.23° produces an increase of initiation life from 16.6 to 154 thousand cycles. It is concluded that there is a major impact on initiation behavior of the coefficient of friction and the rotation of the pad, which may be due to the lack of rigidity of the test setup. Therefore, controlling the stiffness of the test rig and measuring accurately the coefficient of friction are important factors to consider in fretting fatigue research.

Controllable Friction of an Epoxy Composite via Thermal Treatment

Smart surfaces with controllable friction have generated considerable attention lately. However, most composites prepared with traditional fillers cannot achieve “real-time” friction conversion. Herein, a new smart surface was designed to achieve different friction coefficients (0.65 and 0.12). Different coefficients of friction were reversibly and precisely controlled via heating. Via friction and heating, 1H,1H,2H,2H-perfluorohexyl hexadecane (PHHD), a kind of phase-change material—paraffin wax—was released from the microcapsules, and a stable and complete film was formed. It changed the interface from “solid-solid” to “solid-liquid” in a dry friction state. The composite contains microcapsules that prevent phase separation between PHHD and matrix, which enables the composite to have a long service time and switchable friction performance. In addition, this composite can maintain its extraordinary ability even in harsh environments like UV irradiation. By demonstrating switchable friction based on changes in the interactions between contact interfaces, this work provides a new principle for designing smart tribological composites.

Effect of manganese phosphate conversion coating with different crystal sizes on fatigue life of 20MnCrS5 steel helical gears

Fatigue pitting is the main failure form of automatic transmission gear at present. In this paper, the contact stress of the tooth surface under different coefficients of friction is calculated by the finite element method. The contact fatigue test and transmission performance were carried out on the 20MnCrS5 helical gears after carburizing with different thicknesses of manganese phosphate conversion coating by a special gear test bench. And the influence of the solid lubricating coating on gear contact fatigue performance was deeply discussed. The results show that the contact fatigue life of the gear treated by manganese phosphate conversion coating is improved by more than 100 %, and the manganese phosphate coated gear with a thickness of 12 µm has a higher fatigue life.

Finite Element Modeling of Direct Transition from Concrete Pavement to Asphalt Pavement

The origin of premature distress in direct transitions from Portland cement concrete pavement (PCCP) to asphalt concrete pavement (ACP) constructed as part of TransMilenio pavement repairs has not been investigated and the related literature is limited, therefore, a three-dimensional finite element (FE) model was used to determine the mechanical responses of a direct ACP-PCCP transition under moving vehicular loading in order to identify failure mechanisms. In this sense, a PCCP model was validated with a falling-weight deflectometer (FWD) test, field measurements, and analytical solutions, then a concrete slab (CS) was replaced with flowable fill and asphalt concrete (AC) to create the direct ACP-PCCP transition. The direct transition model considered: 1) the viscoelastic nature of the AC; 2) non-uniform tire-pavement contact pressure; and 3) the bonding variation of the AC-concrete interface of the transition joint using different coefficients of friction (COF) and the Coulomb-type friction model. The results showed 1) relatively high near-surface shear strain of the AC, primarily at the joint and extending 122 mm from the joint; 2) relatively high compressive vertical strain on the subgrade top; and 3) high vertical differential displacement of the joint surface. It is concluded that the AC may prematurely experience near-surface cracking at the vicinity of the joint and rutting from the subgrade, however, increasing the AC-concrete interface bonding may be conservative for fatigue cracking and vertical differential displacement.

Оцінка впливу стабільності характеристик гальмівних механізмів на процес гальмування транспортних засобів

The purpose of the article is to evaluate the influence of the stability of the characteristics of brake mechanisms on the process of braking of passenger vehicles. In the article, using the example of a mixed braking system of a passenger vehicle of segment C, an assessment was made of the influence of the stability of the characteristics of its braking mechanisms on the braking process. The results obtained allow us to conclude that with "cold" and "cooled" brake mechanisms of the vehicle, the values of the mathematical expectation of the friction coefficient and the dispersion of its values are approximately the same. The performed calculation shows that when the friction coefficient changes by 8-20%, the braking torque changes by 20-30%. In this case, the difference between the largest and smallest braking torque can be 50%. Given that the left and right brake mechanisms (due to various reasons) may have different coefficients of friction of the friction surfaces, then the unevenness of the braking forces on the rear axle of the vehicle under consideration can be up to 50%. In order to prevent advanced blocking of the rear wheels during vehicle braking in the event that the actual coefficient of distribution of braking forces between the axles deviates from the calculated value due to the instability of the brake mechanisms, it is necessary to ensure the fulfillment of the condition according to the dependence given in the work. The results obtained can be used in the design of braking systems and the assessment of the braking properties of vehicles, as well as in the examination of road accidents.The instability of the braking torques on the wheels does not have a significant effect on the reduction of the total braking force (braking efficiency) in the presence of amplifiers in the drive, but it significantly affects the stability of the vehicle during braking, since it causes a significant change in the coefficient of distribution of braking forces between the axles and the appearance of their onboard unevenness. The statistical analysis of the coefficients of friction of friction pairs (on the example of a passenger vehicle of segment C) showed their wide spread, which significantly affects the onboard and axial unevenness of the braking forces; for example, for friction linings DTM, the average difference between the friction coefficients on the left and right wheels is 0.17, and the standard deviation is ± 0.08. The difference in the coefficients of friction of friction pairs of different types of brake mechanisms, due to the use of friction linings from different manufacturers, can lead to a change in the coefficient of distribution of brake forces over a wide range.

FINDING THE TRAJECTORYOF MOVEMENT OF A MATERIAL PARTICLE ON THE INNER SURFACE OF A VERTICAL CYLINDER AT THE SIDE SUPPLY OF MATERIAL

The movement of material particles on the inner surface of the cylinder takes place in cyclones. Due to the complexity of the aerodynamics of the process, theoretical developments can not be used as a basis for calculating the design and efficiency of their operation. Because of this, a number of simplifications are allowed in the theoretical provisions, as a result of which the calculated data do not coincide with the experimental data. The use of modern software products, which have great graphics capabilities, allows you to get new results in solving such problems in the form of high-quality graphic illustrations. The aim of the study is to determine the motion of a material particle that enters the inner surface of a vertical cylinder with a given initial velocity. A number of simplifications were introduced in the calculations: air resistance, the effect of particles on each other, their size, etc. were not taken into account. Accompanying Frenet and Darboux triangles were used to find the trajectory. Differential equations of motion of a material particle on the inner surface of a vertical cylinder are compiled. The equations are solved using the MatLab system. It is established that the velocity of particles that fall on the inner surface of the cylinder decreases to a certain value, and then begins to increase. For specific conditions (coefficient of friction and radius of the cylinder), the value of the minimum speed to which the movement of particles is slowed down is approximately the same and does not depend on the value of the initial speed. This means that there is a minimum value of the initial velocity at which the particle will not slow down when it hits the surface of the cylinder. Since particles with different coefficients of friction at the initial stage of their movement on the cylinder are poorly scattered on its surface, for the effective operation of the cyclone you need to make an inlet window of sufficient size in the vertical direction.

Numerical Simulation and Parametric Analysis of Fatigue Crack in UIC60 Rail Thermite Welded Joint

The mechanism of rail-wheel contact is the most essential field of study in railway engineering since it requires extensive application expertise, diagnostic skills, and a trustworthy analysis technique. In this research the fatigue life of a UIC60 rail AT weld under vertical load and its parametric effect has been studied, and for that a three-dimensional elastic-plastic finite element model is created using ANSYS space-claim software, and then finite element method is employed to analyse the full-scale model of wheel-track and weld system with realistic three-dimensional solution. Model assembly components include axle, wheel, and thermite-welded rail. Simulation of contact between wheel and UIC60 rail weld with crack on weld at angles of 30 and 60 degrees with different coefficients of friction between the weld wheel contact and between crack surfaces was carried out under vertical loadings. In general, the Hertz contact theory assumptions are taken into consideration throughout the analysis, and the impacts on fatigue life are given by using damage mechanics method. The results of the wheel/weld fatigue crack analysis have been displayed to demonstrate the influence of different parameters on the fatigue life of cracks. The purpose of this study is to identify and safeguard the rail against failure, as well as to ensure the safety of passengers and to reduce the cost of maintaining the rail system.

Математичне моделювання процесу розділення матеріалу на стаціонарних гвинтових поверхнях

The motion of material particles on gravitational surfaces is used in special devices for their separation by physical and mechanical properties. For this purpose stationary screw surfaces of a constant step are applied. The purpose of the study is to investigate helical surfaces with different design parameters in order to improve their separation ability through mathematical and geometric modeling of the process without making surface models. The problem of constructing the trajectory of a material particle on the surface under the action of its own weight is preceded by the problem of finding the trajectory on an inclined plane. Modern software products make it possible not only to find the trajectory of the particle, but also to show it on the surface and even make an animation, which essentially replaces high-speed camera recording. This approach makes it possible to study the kinematic parameters of motion on different helical surfaces without full-scale samples of these surfaces, which significantly reduces the cost of finding the desired surfaces. The trajectories of the particle on the surface of the helical conoid and the deployable helicoid are obtained. It is established that when moving on the surface of a helical conoid, the particle in the presence of friction first accelerates, and then stops at a considerable distance from its axis. To prevent this, its need to take a limited compartment of the conoid both in height and on its periphery. When a particle moves on the surface of a helicoid, its velocity becomes constant over time, and the trajectory after that will be a helical line. The developed approaches make it possible to study the process of material separation not only after stabilization of motion, but also during the transition process, as it became possible to visualize it. This will allow you to choose the surface compartment of the optimal size, which will provide the desired productivity of separation due to the dispersion of particles with different coefficients of friction on its surface. Key words: material particle, trajectory, material separation, helical conoid, helicoid

Research of resistance forces in the contact zone between the seal and the floor of a mobile robotic air cushion platform

Traditionally mobile robotic platforms are used in modern production facilities when performing transport operations, as well as in the process of assembling the finished product. With the increase in the load capacity of such platforms, the cost of their operation increases. But the use of an air cushion as a payload mass compensation system can increase their energy efficiency and reduce the cost of their operation. As a result, the scope of their possible application increases significantly. The article presents the main tasks that can be solved with the help of mobile robotic platforms on an air cushion in the complex automation of production. The use of an air cushion increases the energy efficiency of the transport system, which is a very urgent task. The design of the layout of such a platform is presented. The emphasis is placed on the importance of using a pressure seal, which allows achieving virtually zero clearance between it and the floor. A possible arrangement of such an air cushion sealing unit is shown. The computational model of this node built for finite element modeling in the ANSYS Workbench environment is presented. The main calculation cases that occur at various stages of the functioning of a mobile robotic air cushion platform are listed. The deformations of the seal for these cases are shown and the values of the normal force occurring in the contact zone of the seal and the floor for each of them are determined. The contact area of the seal and the floor in each case is also indicated. The dependences reflecting the change in the normal force of the simulation process with different coefficients of friction for the seal-floor pair are constructed. The behavior of the considered compaction unit of the mobile robotic platform in the process of its movement, depending on the direction of movement, is modeled.

Geometry design and dynamic analysis of a modified cycloid reducer with epitrochoid tooth profile

This study proposes a design method for a modified cycloid reducer with an epitrochoid tooth profile. The reducer used here has one contact pattern and non-pin rollers like a planocentric reducer. This feature makes the designed reducer easier to be manufactured compared to conventional cycloid reducers, which are difficult to manufacture due to tolerances. The tooth profile characteristics for nine different design scenarios for the cycloid reducer were analyzed with respect to the tooth thickness ratio and the distance from the center of the rolling circle. It was observed that the inflection point, which was calculated from the radius of curvature, was a major factor influencing the design of the cycloidal tooth profiles. A mathematical model for the force analysis of the designed reducer was developed, and variations in force distribution between the internal and external gears as well as the efficiency of the cycloid reducer were calculated according to different coefficients of friction. Involute and cycloid gears with a difference of one tooth between the internal and external gears were designed and manufactured, and finite element analysis showed that the cycloid gear had higher rigidity than the involute gear.

Evaluation of the influence of friction in a multi-leaf spring on the working conditions of a truck driver

This article presents a simulation study of the suspension system in a vehicle that weighs approximately 12 tons (class N2). The authors have tested the influence of experimentally determined values of friction coefficients on the energy dissipated in the multi-leaf spring. The study was carried out using finite element analysis with LS-DYNA software. A nonlinear vibration model of the complete spring was developed, including the variable friction forces between the leafs. The model takes into account the sprung and unsprung mass of the chassis. Numerical tests were carried out using three different coefficients of friction (determined experimentally) for a selected speed of the car. Random realizations of the road micro-profile (type A, B, C) recommended by ISO 8608 were used. The results of the tests were presented in the form of acceleration curves in the vertical direction, comparative plots of daily vibration exposure A(8) and vibration transmission coefficient (T), and the distributions of RMS acceleration in frequency of one-third octave bands. This data was used to assess the quality of the vibration isolation system between the front suspension of the vehicle and the driver’s seat.

Special Issue on Tribology of Additive Manufacturing

Special Issue on Tribology of Additive Manufacturing

Plane frictional receding contact of a thin layer pressed onto a substrate by finite pressure distributions

A frictional receding contact problem of an infinitely long layer pressed by different finite pressure distributions onto a half-plane of the same linear elastic material is solved with the distributed dislocation technique. Solutions are obtained for when the layer is subject to three different pressure distributions: finite patch of constant pressure, square-root bounded (Hertzian) pressure and square-root singular pressure. The contact tractions, the locations of slip and separation, and the slope of the layer at remote points are found for different coefficients of friction and for different widths of pressure distribution. A universal relationship is deduced between the total slip, the remote slope of the layer and the shear traction.

Effects of coefficient of friction and coefficient of restitution on static packing characteristics of polydisperse spherical pebble bed

The effects of the coefficient of friction and coefficient of restitution on the static packing characteristics of a polydisperse spherical pebble bed are numerically investigated using the discrete element method. Several important static packing characteristics under different coefficients of friction and restitution are presented and discussed. The results show that the coefficients of friction and restitution impose opposite effects on the packing heights and global packing factor. Neither the coefficient of friction nor restitution affected the oscillation width of the wall, whereas their effects are primarily reflected in the oscillation amplitude of the radial local packing factor and the axial local packing factor distribution at the top of the pebble bed. In both the contact force distribution and coordination number distribution, a left-shifted phenomenon appearing as the coefficient of friction occurred, and only the magnitude of the maximum frequency is affected when the coefficient of restitution changed from 0.1 to 0.9. In all simulation cases, the effects of the coefficients of friction and restitution are similar to that of cross-impact.

SIMULATION OF A SINGLE THIRD-BODY PARTICLE IN FRICTIONAL CONTACT

Contact of a single third-body particle between two plates is simulated using the Boundary Element Method. The particle is considered as deformable, and the Coulomb’s law of friction is assumed at the contact interface. The normal pressure distribution and tangential stress distribution in contact as well as the macroscopic force and force moment are calculated. Several movement modes are shown to be possible: rolling, rotation, or sticking during the loading. It is found that, differing from rigid particles, the state of particle may change during the loading. The particle may stick to the plates initially, but rotation may occur when the load becomes larger. Examples with the same and different coefficients of friction are presented to show kinematics of particle. The method can be further applied to simulation of multiple third-body particles.

Learning-Based Analysis of a New Wearable 3D Force System Data to Classify the Underlying Surface of a Walking Robot

Biped humanoid robots that operate in real-world environments need to be able to physically recognize different floors to best adapt their gait. In this work, we describe the preparation of a dataset of contact forces obtained with eight force tactile sensors for determining the underlying surface of a walking robot. The data is acquired for four floors with different coefficient of friction, and different robot gaits and speeds. To classify the different floors, the data is used as input for two common computational intelligence techniques (CITs): Artificial neural network (ANN) and extreme learning machine (ELM). After optimizing the parameters for both CITs, a good mapping between inputs and targets is achieved with classification accuracies of about 99%.

Methods of enlarging material to the concentration table

Abstract Concentration tables are one of the oldest oscillatory enrichments with over 100 years of tradition. On this type of distribution tables are made according to material mass in many recurring cycles induced by appropriate drives. So-called wet tables are the devices most often used for coal enrichment in Polish mines because this process generates very high costs, high water consumption and pollution of the environment, as well as the need for, among others, water and mud management is increasingly being replaced mainly in areas poor in water by the modern model of the air concentration table – FGX produced in China. The process of enrichment on this type of table itself runs in a manner comparable to the method of wet enrichment with the difference that the FGX is distributed on a perforated plate, in this case we deal with air pollution. Department of Machinery Engineering and Transport's attempts to use the differences in coefficients of friction in over-resonance screens have shown that it is possible effective separation of grains with different coefficients of friction. The article presents a theoretical analysis and presents the results of performed dry enrichment trials using different coefficients of friction. The summary presents the advantages of using the enrichment method using the differences in friction coefficients and test results.

Modeling the movement of broadcast on the concentration table

Abstract The article attempts to analyze the work of the concentration table, on which the distribution of the material under investigation takes place. The efficiency of separation or otherwise enrichment depends on the drive that puts the concentration table plate into an asymmetrical reciprocating movement. The most frequently used solutions are concentration tables, on which the distribution of enriched material takes place in an aqueous medium commonly called wet enrichment. The AGH University of Science and Technology conducted simulation tests of material enrichment on a concentration table using the differences in friction coefficient commonly referred to as dry enrichment, i.e. without an additional medium. The article presents the effects of simulations that have been carried out for reference materials characterized by different friction coefficients and densities. The summary presents the analysis of obtained effects of computer simulations of material movement with different coefficients of friction. The simulations were carried out for variables: the frequency of vibrations of the concentration table and the angle of inclination of the table of the concentration table. It has been shown that it is possible to enrich the material by changing the above-mentioned operating parameters of the device.

Computational modeling of child’s swallowing to simulate choking on toys

ABSTRACTChoking occurs more frequently in children and senior citizens than in other groups. Obstruction materials are varied, including food or foreign bodies such as toys and coins. The number of choking accidents has not decreased because its mechanism remains unclear; the manner in which such accidents occur cannot be observed. The purpose of this study is to visualize choking on toys by using a computer simulation, Swallow Vision®, after creating a new child model of swallowing. An organ model for the simulation was created from the CT of a 9-month-old boy and videofluorographic images during swallowing for a 9-month-old girl. The organ models were defined as hyperelastic and contained particles that moved by forced displacement. The toy models were spheres with diameters of 10 and 15 mm and different coefficients of friction and restitution. The applied calculation method was the Hamiltonian Moving Particle Simulation. The results demonstrated that the simulation could visualize how a toy model obstructed the upper airway in the pharynx and larynx. Moreover, the ball size and the coefficients of friction and restitution affected the site obstructed. As choking accidents were successfully visualized using the Swallow Vision®, The computer simulation is expected to advance research on understanding the choking mechanism.