Static Friction Coefficient Research Articles

Study on Friction and Wear Properties of 3D Braided Carbon Fiber

In this paper, the friction and wear properties of 3D braided carbon fiber wet friction material at 2550r/min, 3800r/min and 5100r/min were studied with MM3000 friction and wear tester, and the wear mechanism was studied with SEM. The results show that the average static friction coefficient of friction materials is 0.153; With the increase of rotating speed, the dynamic friction coefficient decreases from 0.095 to 0.087; The volume wear rate decreased from 9.46*10−8cm3/J to 2.58*10−8cm3/J; The friction torque curves at three different speeds are relatively stable, showing the material has good braking stability. 3D braided carbon fiber friction material has fiber fracture and crack on the raised surface of the material after 1500 times of jointing at three different speeds. The mechanism of friction and wear is abrasive wear and fatigue wear.

Determination of Engineering Properties of Coleus Pertinent to the Design of a Digging-cum-Windrowing Unit

Coleus (Solenostemon rotundifolius) is an important minor tuber crop grown in the homesteads of Kerala and Tamil Nadu. There was a demand for mechanisation for harvesting the tuber because the conventional method of harvesting followed was tedious and time-consuming. For the design and development of a coleus harvester with reduced drudgery, the design parameters were selected with respect to the tuber properties. Random sampling was carried out for determining the physical and frictional properties of coleus. The average values of physical properties such as length, width, thickness, geometric mean diameter, sphericity, surface area, volume and bulk density were found out as 44.56 mm, 27.36 mm, 24.50 mm, 30.99 mm, 0.70, 3029.69 mm2, 15786.50 mm3 and 718.21 kg m-3 respectively. The angle of repose was determined as 30.83° and the coefficient of static friction was found out as 0.73, 0.69 and 0.81 on galvanised iron, stainless steel and plywood surfaces respectively. These data were used for the design of various components of the harvester.

Study on the shear-slip process and characteristics of fracture in shale

To clarify the shear-slip process and characteristics of fault, we conducted triaxial shear tests driven by displacement on shale samples with prefabricated sawcut and natural fractures, and the acoustic emission (AE) technology was used to monitor the shear-slip process in real-time. According to the test results, the shear-slip process and mechanical characteristics of sawcut and natural fractures were analyzed. The test results indicate that the shear-slip process of fractures can be divided into four stages, improving the confining pressure will cause more serious plastic failure in the shear-slip process, and the increase of roughness will make the phenomenon of “stress drop” more obvious, which is closely related to the earthquake occurrence. Confining pressure and roughness all have implications for the stress thresholds of each stage. With the transition of shear-slip stages, the effects of confining pressure and roughness on the shear-slip of fractures are more drastic. The maximum static friction coefficient μ0 increases with initial roughness increasing and is independent of confining pressure. Due to the strain-strengthening effect of fracture slip, the average value of dynamic friction coefficient μd under simple shear deformation is greater than the maximum static friction coefficient μ0. Based on AE response characteristics, microcracks development, and rupture scale during the shear-slip process were also explored. AE events are mainly distributed along the inclined fracture. The AE response in different shear-slip stages displays pronounced differences, and the AE evolution and macro mechanical characteristics of fractures show significant time-synchronization. The variation of peak frequency can reflect the rupture scale transformation and the influence of confining pressure and roughness. Additionally, the differences in the morphological evolution of sawcut and natural fractures are mainly reflected in the wear pattern, degree and the rock debris attach amount. Finally, we also discussed the micro-deformation mechanism of asperities during the shear-slip process. This work may provide a reference for the research of fault activation and slip in shale reservoirs.

Characterization of green peppers based on dynamic repose angle

Virtualization of machining process, is of great significance, for the design and research of equipment to improve food quality and safety. Green pepper (GP), a biological origin fruit, displays promising cosmetic, spices and drug values, but its processing is labor and time intensive, which urgently needs equipment to improve productivity. Therefore, this investigation taking the dynamic angle of repose obtained from rotating drum assays as indicator, to explore suitable material and interaction properties for the discrete element method (DEM) to re-produce the processing visually. Primarily, ranges of these properties were experimentally measured. Centrally, values of these properties were categorized and reasonably determined via a set of simulations involving the Plackett-Burman (PB), Steepest Ascent (SA), and Central Combination Design (CCD). Interestingly, the PB demonstrated that coefficients of static friction between particle-steel (CoSP−s) and coefficients of friction and restitution between particle-particle (CoRP−P; CoSP−P; CoLP−P) were significant, their optimal ranges (0.59–0.64, 0.15–0.30, 0.20–0.44, 0–0.05) and values (0.590, 0.299, 0.200, 0.034) were sequentially selected by the SA and CCD respectively. Collectively, suitable properties were determined as the selected and mean values of the significant and insignificant properties, respectively. Importantly, values of these properties have been confirmed via triplicate independent verification simulations.

Design and analysis of a novel light-weight, linear actuator driven flexible PET strips robotic gripper

A robotic manipulator consists of a robotic arm and an end-effector. The function of the end-effector or robotic gripper is to allow the robotic arm to grasp and manipulate objects. The traditional hard robotic grippers are prone to poor gripping ability when grasping objects with irregular shape or in-ability to passively adjust force to delicate objects. Soft Robotic grippers were purposely designed to solve these disadvantages. In this work, a novel light weight robotic gripper based on grasping action of holding an object in between two strips of in-elastic flexible material under tensile force developed when pulled is hereby presented. Force analysis of the gripper was carried out as well as validation experiments. Analysis shows that the minimum pulling force to be exerted by the gripper on the grasping strips is directly proportional to the payload mass and the strips lengths. It is also inversely proportional to the coefficient of static friction between the payload-strips interface and the horizontal extent of the payload. Experimental results supported these observations. Moreover the predicted analytical values of gripper pulling force agreed reasonably with the empirically derived values. A proof of concept model of the gripper successfully grasps a 185g object.

Running-in evaluation after a rail grinding process using a pin-on-disk tribometer

Rail grinding as a maintenance strategy plays an important role in controlling rail defects due to rolling contact fatigue, noise reduction, and train stability by reshaping the rail. However, the effect of roughness topography of the rail surface after a grinding process has not been extensively studied in terms of friction coefficient and running-in behaviour.In this work, rail disks specimens with different textures were characterized by different roughness parameters: Ra, Rq, Rt, Rp, Rv, Rz, Ssk, and Sku. All the textures were achieved by varying the amount of material removed and the work speed by using some emery stones with similar properties in rail grinders. The tests were performed by using a pin-on-disk tribometer in dry and grease-lubricated conditions. Pin specimens were manufactured from a wheel section with standard roughness.The results showed that in dry conditions, rail disk specimens with rougher surface patterns yield a higher friction coefficient and higher wear rate. On the other hand, under lubricated conditions, a rough surface does not give a low static friction coefficient in some cases. Additionally, microstructural analyses were carried out on the cross-section of rail specimens and some images were taken from the existing wear scars identifying the wear mechanisms and finding in some textures the presence of a white etching layer (WEL) and a brown etching layer (BEL).

Parameter Calibration and Systematic Test of a Discrete Element Model (DEM) for Compound Fertilizer Particles in a Mechanized Variable-Rate Application

In order to obtain accurate discrete element simulation model (DEM) parameters of compound fertilizer and solve the problem of challenging measurement of contact parameters of compound fertilizer particle, simulation calibration test was carried out by using EDEM simulation soft-ware. This study measured the intrinsic parameters and contact parameters of compound fertilizer particles through physical tests and established a simulation model that corresponds with the actual situation to calibrate the contact parameters of compound fertilizer particles. By using the Blackett-Burman test, the parameters that had a significant impact on the compound fertilizer’s resting angle were determined by the fertilizer-fertilizer collision recovery coefficient, fertilizer-fertilizer rolling friction coefficient, and fertilizer-steel static friction coefficient. Utilizing the steepest ascent test, the ideal value intervals for the three key parameters were identified. Box-Burman response surface analysis was used to establish and optimize the regression model of the rest angle and significant parameters. With the actual rest angle as the target value, the best combination of significant parameters was found, which was used for the simulation verification test. The simulated rest angle was 20.61°, whereas the real rest angle was 19.95°, with a relative error of 3.31%. The results demonstrate that the calibration parameters are essentially accurate representations of the real characteristics, which can serve as a reference point for simulation research and optimization design of variable fertilizer spreader.

Moisture dependent engineering properties of Musa balbisiana seeds

AbstractEngineering properties of wild banana seeds at different moisture content (8.66%, 12%, 16%, 20%, and 24% db) were investigated. Physical dimensions, seed surface area (SA), seed volume (SV), and thousand seed mass (M1000) increased linearly with increase inmoisture content. While porosity decreased linearly from 42.33% to 38.89%, bulk density (ρb) and true density (ρt) increased from 513.59 to 564.72 and 890.56–924.09 kg m−3, respectively. The angle of repose increased linearly from 29.84 to 36.48 with moisture content. The increased moisture content also caused an increase in static coefficient of friction for surfaces made of stainless steel, glass, and plywood. The thermal conductivity (λ) and volumetric specific heat (ρcp) were found to increase linearly from .17 to .20 Wm−1 K−1, and .58 to .99 MJ m−3 K−1, and thermal diffusivity (α) decreased from .31 to .19 (×10−6 m2 s−1) with a increase in moisture content.Practical applicationsThe research aimed to study the engineering properties of wild banana seeds as a function of moisture content as they are necessary to design equipment for handling, aeration, storage, and processing. Moreover, it helps in predicting flow and handling behavior during processing, including hopper flow, and conveying through feeders and other handling equipment. Furthermore, thermal properties are helpful in engineering, process design and modeling the thermal behavior of food products during storage, processing, and transportation.

Physical properties of four rice cultivars grown in Indian temperate region

Setting up of non-standard unit operations could result in cracking of rice grains during milling, leading to accumulation of broken rice and generation of inferior quality product. Therefore, it is very much important to study physical properties of rice for designing of appropriate rice processing machinery that would minimise post-harvest losses during milling operation. Hence, the present investigation was aimed to study physical properties of four rice cultivars (SR-4, K-39, Mushq Budij and pigmented) grown in Kashmir. Brown and polished rice variants of the four cultivars were studied for grain dimensions, equivalent diameter (ED), geometric mean diameter (GMD), arithmetic mean diameter (AMD), volume, surface area, sphericity, aspect ratio, bulk density (BD), true density (TD), porosity, thousand kernel weight, static coefficient of friction and colour. In general, polishing of rice led to significant (p<0.05) reduction in grain dimensions, volume, surface area, thousand kernel weight (TKW), ‘a’ and ‘b’ values and static coefficient of friction (SCOF). However, there was increase in sphericity, porosity and ‘L’ values of rice kernels after polishing. Amongst cultivars, brown SR-4 rice had the largest length (6.36 mm), GMD (3.30 mm) and AMD (3.73 mm), respectively. However, polished K-39 rice had the highest BD (790.0 kg/m3), TD (1540.0 kg/m3) and porosity (48.70) amongst cultivars. Moreover, unpolished pigmented rice had the highest TKW (23.03 g). In addition, the minimum SCOF was observed when rice kernels were allowed to slide through glass surface with the lowest value observed for pigmented variety (0.40). The present research will be beneficial in fabricating machines for rice processing industry which would be helpful in eliminating post-harvest losses that occur during milling operation.

Physical properties of white-fleshed and yellow-fleshed cassava (Manihot esculenta) foam powder

This study evaluated the physical properties of cassava foam powder (CFP) produced from white and yellow cassava by foam mat drying, and compared them with cassava pulp powder (CPP). Cassava foams were prepared, dried and milled to foam powder. The white CFP and yellow CFP had a true density of 1.466 g/cm3 and 1.534 g/cm3, respectively. The flow properties determined include Carr's index (CI), angle of repose (θ) and coefficient of static friction (μs). Micrographs of the CFP revealed that the foam powders were irregular, coalesced, and larger in size than CPP. The rehydration kinetics showed an estimated equilibrium water gain (WGeq) of 0.725–1.680 g/g at temperatures between 30 °C and 70 °C. Adsorption isotherm of the powders was best fit by the Halsey model. There were significant correlations between packed density and angle of repose (r = 0.972), CI (r = 0.970) and mean particle size (r = −0.957).

Performance evaluation of friction dampers considering different metal pairs and loading rates

Metal friction dampers are widely applied for structural energy dissipation and shock absorption, and their dynamic performance needs further study. Cyclic loading tests were conducted on 30 specimens to evaluate the effects of loading sequence and rate under high speed (20 mm/s ∼ 60 mm/s) and low speed (0.2 mm/s ∼ 3 mm/s). The friction pairs included five types: brass-hot rolled steel with untreated surfaces (B-HS), brass-hot rolled steel with polished surfaces (B-PHS), brass-stainless steel (B-SS), stainless steel-hot rolled steel with untreated surfaces (SS-HS), and stainless steel-hot rolled steel with polished surfaces (SS-PHS). The test results showed that all specimens exhibited plump rigid-plastic hysteresis behavior under different loading rates, and the mechanical indices of the specimens met the discreteness requirements of FEMA-356. The loading rates obviously influenced the normal force loss and friction coefficient of the friction interfaces. The static friction coefficients for the five metal friction pairs were recommended, and analytical models of the dynamic friction coefficient concerning loading rate were established. It was suggested that the B-HS, B-PHS, SS-HS, and SS-PHS friction pairs should be pre-friction within the travel range before use, and the friction coefficient of the B-SS and SS-HS friction pairs should be calibrated after the first loading.

弾性すべり支承における静摩擦係数を考慮した免震建物の設計手法について

We have illustrated the response changes in the design method for considering the static friction coefficient of elastic sliding bearings in the design of seismic isolated buildings. We also compared the actually observed seismic motion with the response of this design method. According to the results, the design formula and analysis model can reproduce the actual seismic motion, and the response shear force and response displacement change depending on the type of seismic wave when the static friction coefficient is taken into consideration. Therefore, the proposed design method considering the coefficient of static friction is considered appropriate.

Effect of ethylene and propylene oxide-modified polysiloxanes in coating materials on the friction coefficient

In this study, the static and kinetic friction coefficients and their effect on the noise generation were investigated by preparing the coating agent using polyurethane resin, polysiloxane, ethylene and propylene oxide (EO/PO)-modified polysiloxane, PP wax, carbon black, and SiO2. The difference between the static and kinetic friction coefficients decreased with the fraction of (EO/PO)-modified polysiloxane while sharply increasing with the friction velocity. The differences in these friction characteristics reduced the magnitude of noise generation, and the matting property was also increased by the addition of PP wax.

Effect of dynamic friction and static friction in finite element analysis of carbon fiber preform

AbstractThis paper aims to improve the accuracy of the finite element analysis for the preform shape transformation according to the difference in the type of carbon fiber and friction force. The carbon fiber type (Toray T700, Zoltek), the fiber direction (0°/90°, ± 45°), and the frictional force were measured, which occurred between the fiber and the mold and between the fiber and the fiber. A comparative experiment was conducted through actual preform production by designating it as a variable for element analysis. The analysis was conducted according to the difference between the static friction coefficient and the dynamic friction coefficient in the molding analysis. Within the range of the Coulomb equation, the shear angle changing was compared with the actual preform shape to show similar results.

Static friction coefficient depends on the external pressure and block shape due to precursor slip

Amontons’ law states that the maximum static friction force on a solid object is proportional to the loading force and is independent of the apparent contact area. This law indicates that the static friction coefficient does not depend on the external pressure or object shape. Here, we numerically investigate the sliding motion of a 3D viscoelastic block on a rigid substrate using the finite element method (FEM). The macroscopic static friction coefficient decreases with an increase in the external pressure, length, or width of the object, which contradicts Amontons’ law. Precursor slip occurs in the 2D interface between the block and substrate before bulk sliding. The decrease in the macroscopic static friction coefficient is scaled by the critical area of the precursor slip. A theoretical analysis of the simplified models reveals that bulk sliding results from the instability of the quasi-static precursor slip caused by velocity-weakening local friction. We also show that the critical slip area determines the macroscopic static friction coefficient, which explains the results of the FEM simulation.

Evaluation of particle models of corn kernels for discrete element method simulation of shelled corn mass flow

Bulk handling behavior of grains can be studied experimentally, but large-scale investigations of grain flow especially at the commercial scale are expensive, time consuming, and are therefore limited in the treatment factors that can be evaluated in any one study. Recent research has demonstrated the potential of discrete element method (DEM) in simulating grain flow in handling operations. However, application of DEM for simulating grain flow, requires development of appropriate particle models for each grain type. In this study, particle models comprised of one to four overlapping spheres were developed for shelled corn and tested. With these models, measurement of bulk properties, namely bulk density and angle of repose, both involving bulk flow were simulated using EDEM™ software with published data of material and interaction properties of shelled corn as inputs associated with each particle shape. Predicted time for the complete outflow from the bulk density test hopper (hopper emptying time), designated as simulation time in the study, was also recorded as another discriminant for model selection. Variable inputs into the simulation modeling were material properties particle shape, particle size distribution, Poisson's ratio, shear modulus, and density and interaction properties particle coefficients of restitution, static friction, and rolling friction. Computation time is critical in DEM modeling so single sphere particle models were emphasized over multi-sphere particles in the research even though multi-sphere particles represent the corn kernel shape more precisely because their simplicity can provide markedly reduced computation times to complete simulations. Predicted results for hopper emptying time, bulk density, and angle of repose were compared to experimental results or published data to select the most appropriate particle models for simulating bulk behavior of corn kernels in free-flowing grain applications using DEM. From the study, the most appropriate particle model (particle shape/physical properties combination) for corn kernels involved a single-sphere shape particle shape with a particle coefficient of restitution of 0.30, particle coefficients of static friction of 0.30 for corn-corn contact and 0.20 for corn-steel contact, particle coefficient of rolling friction of 0.05, normal particle size distribution with a standard deviation factor of 0.4, and particle shear modulus of 20 MPa.

The Initiation of Frictional Motion—The Nucleation Dynamics of Frictional Ruptures

AbstractFrictional interfaces lose stability via earthquake‐like ruptures, which are close analogues of shear cracks that are well‐described by fracture mechanics. Interface ruptures, however, need to be first formed—or nucleated. Rupture nucleation therefore determines the onset of friction, replacing the concept of a characteristic “static friction coefficient”. Utilizing rupture arrest at an imposed barrier, we experimentally determine nucleation locations, times and stresses at the origin of each subsequent rupture event. This enables us study the nucleation process via real‐time measurements of real contact area and local strain. Nucleation events initiate as 2D patches that expand at nearly constant velocities, vnuc, that are orders of magnitude lower than the dynamic rupture velocities described by conventional fracture mechanics. We find that: (a) Nucleation has location‐dependent stress thresholds, (b) vnuc is roughly proportional to the local stress level, (c) the nucleation process continues until the patch size reaches Ltran ∼ LG, the Griffith length for the onset of dynamic fracture (d) scaling time by τ = Ltran/vnuc, nucleation patches exhibit self‐similar dynamics (e) dynamic ruptures' cohesive zones are not fully established until significantly beyond Ltran. Many details of nucleation are governed by the local contact area topography, which is roughly invariant under successive rupture events in mature interfaces. Topography‐dependent details of the nucleation process include: precise nucleation site location, patch geometry, critical stress thresholds and the proportionality constant of vnuc with stress. We believe that these results shed considerable light on both how frictional motion is triggered and earthquake initiation.

Determination of The Static Friction Coefficient of Some Materials Used for Anti-slip Safety with ANOVA

The surface conditions of ground surface coatings, which are widely used in working environments exposed to various pollutants, were evaluated from a safety perspective. In this work, static and dynamic friction coefficients and safe angle of inclination between some floor coverings exposed to different pollutants for various reasons and some shoe sole materials that are widely used in working environments were determined. The interaction between soil, floor, and surface contaminations were evaluated statistically. In particular, the ground surface contaminated with contaminants such as water and surface cleaners, which significantly reduce the security of the floor is studied. ANOVA results showed that the floor covering, shoe sole samples, and floor contaminants were significant for each variable of the friction coefficient (μ) (p

Parameter Calibration of Xinjiang Paperbark Walnut Kernels by Discrete Element Simulation

To solve the problem of the lack of an accurate model for mechanized transportation and grading of walnut kernels, this paper took the shelled walnut kernels as the research object and calibrated the parameters of the discrete element model of walnut cracking kernels with the discrete element simulation software EDEM. The physical parameters of cracking kernels were measured by experiments, and the Hertz–Mindlin model was used to simulate the repose angle of cracking kernels. The contact parameters, such as the particle collision recovery coefficient, the static friction coefficient, and the rolling friction coefficient, were determined by the two-level factor test, steepest ascent test, and response surface test, respectively. Subsequently, the Hertz–Mindlin model with bonding contact was exploited to conduct the simulation of cracking kernels bending test based on the calibrated contact parameters. Finally, the normal contact stiffness, tangential contact stiffness, critical tangential force, and normal force of cracking kernels were determined by response surface analysis. It was shown that the relative error between the simulated values and the experiment results was 3.00 ± 1.31%. These results indicated that the calibrated parameter values are reliable, and could be used for the mechanized transportation and grading of walnut kernels.

Numerical Analysis of Factors Affecting the Burden Surface and Porosity Distribution in the Upper Part of the Blast Furnace

A proper burden and porosity distribution of the bed in the upper shaft are important prerequisites for realizing a stable and efficient operation of the ironmaking blast furnace. The discrete element method was used to investigate the effects of the static friction coefficient between burden particles and shaft angle on the burden profile and porosity distribution in the bed formed by charging the burden with a bell-less charging equipment. The results indicate that a large static friction coefficient makes the particles stay closer to the impact point (i.e., where they fall) from the rotating chute. A large mixed region of the burden bed decreases the gas permeability, and an increase in the burden particle roughness will worsen this problem. The burden surface shape becomes flatter with an increase in the shaft angle. These findings explain the effect of particle properties and wall geometry on the inner structure of the burden bed.