Static Friction Coefficient Research Articles

Measurement of Physical Properties of Sorghum Seeds and Calibration of Discrete Element Modeling Parameters

This study aimed to improve the measurement accuracy of the discrete element method (DEM) simulation parameters of sorghum seeds for enhanced model accuracy. We measured the intrinsic and contact parameters of sorghum seeds, extracted the outline of the seeds by 3D scanning, and used the multi-spherical particle model filling method in the EDEM (Version 2020) software to obtain the simulation model of the seeds. By simulating the free-fall, slope slip, slope rolling, and rolling experiments of sorghum seeds–photosensitive resin material, we calibrated the collision restitution coefficient of the sorghum seeds–photosensitive resin material to 0.690, static friction coefficient to 0.345, and rolling friction coefficient to 0.040. Through the steepest ascent search and central composite design experiments, we calibrated the collision restitution coefficient of sorghum seeds–sorghum seeds to 0.400, the static friction coefficient to 0.450, and the rolling friction coefficient to 0.043. The angle of repose of the parameter combination and the angle of repose of the physical experiment (33.82°) were verified, and the relative errors of the coefficients were 0.7%, 0.25%, and 0.3%, respectively, indicating that the established model had a high simulation accuracy and reliability. These results show that the established sorghum seeds model and the optimally calibrated parameter combination are effective for DEM studies on sorghum seeds.

Study on the Multi-Directional Static Friction Properties of High Performance Yarns

Abstract To further optimise the bullet-proof performance of textile reinforced composites, multi-directional friction tests of aramid and ultra-high molecular weight polyethylene (UHMWPE) yarns were carried out by the slope method. The influence of the included angle between the high-performance yarns on the static friction coefficient for aramid and UHMWPE yarns was studied by measuring the friction coefficient. The relationship between the static friction coefficient and the included angle among the high-performance yarns was discussed. The results showed that the friction coefficient of aramid yarns was higher than that of UHMWPE yarns. Especially, at the same included angle between high-performance yarns, the static frictional coefficient of aramid yarns is 50% higher than that of UHMWPE yarns. In accordance with expectations, the static friction coefficient decreases with the increased included angle between high-performance yarns, and the included angle of high-performance yarns changes from 0º to 90º. The trend of rapid decline appeared when the included angle between high-performance yarns changed from 0º to 15º. For the actual result, the static friction coefficient of aramid and UHMWPE yarns is less than 0.3, which needs to be improved to increase the bullet-proof performance of textile composites.

包膜肥料接触参数DEM标定研究

To simulate the interactions between the coated fertilizer particles and the fertilizer discharging components accurately, the coated fertilizer contact parameters were calibrated using the discrete element method (DEM). Based on the angle of repose test, single-factor simulations were performed on the coefficient of restitution (COR), coefficient of static friction (COSF) and coefficient of rolling friction (CORF) between particles, and the internal relationship between the level change of each factor and the static angle of repose (SAOR) was determined. The CCD test was used to calibrate the contact parameters between particles. When the COR, COSF and CORF between particles are 0.625, 0.175, and 0.037, respectively, the simulation value of SAOR is 24.173°, and the relative error from the real value is 1.230%, which indicates that the calibrated fertilizer particle contact parameters are accurate and reliable.

ESTABLISHMENT AND CALIBRATION OF DISCRETE ELEMENT MODEL OF KING GRASS STALK BASED ON THROWING TEST

In order to better use the discrete element method (DEM) to study the cutting and throwing process of King Grass (KG) stalk in mechanical harvesting, the DEM model and contact parameters of KG stalk were studied in this paper. By using the Multi-sphere method, the DEM model of KG stalk was established in EDEM software. Through the impact bounce test and slope sliding test, the stalk-steel coefficient of static friction, stalk-steel coefficient of restitution and stalk-stalk coefficient of restitution were calibrated as 0.372, 0.656 and 0.523, respectively. Based on the stacking test, using the response surface methodology, the optimal values of stalk-stalk coefficient of static friction, stalk-stalk coefficient of rolling friction, stalk-steel coefficient of rolling friction were calibrated as 0.393, 0.072 and 0.144, respectively. The throwing test bench of stalk was designed, and the actual and simulation throwing test were carried out. The relative error of throwing distance in bench test and simulation test under four throwing speeds was 1.15%, 7.76%, 8.88% and 10.46%, respectively. The throwing trajectory curve of the simulation test is consistent with that of the actual test, which verifies the accuracy of the DEM model and contact parameters of KG stalk.

PARAMETER CALIBRATION OF DISCRETE ELEMENT SIMULATION MODEL OF WHEAT STRAW-SOIL MIXTURE IN HUANG HUAI HAI PRODUCTION AREA

At present, there is a lack of accurate discrete element simulation model and parameters in the equipment in Huang Huai Hai double cropping production area, which hinders the optimization and improvement of equipment operation effect. In this paper, the discrete element method is used to study the interaction between soil-touching components and wheat straw-soil mixture to improve the performance of equipment. Firstly, the Hertz-Mindlin with JKR Cohesion contact model is selected for the wheat straw-soil mixture to calibrate the parameters. Then, the method of combining physical test and simulation test is used to calibrate the parameters, the cylinder lifting method is used to determine the buildup angle of wheat straw soil mixture, and the Plackett-Burman screening method and the steepest climbing test are used to determine the optimal combination range of soil-straw static friction coefficient, soil-straw dynamic friction coefficient and soil-soil dynamic friction coefficient contact model parameters. Using Box-Behnken optimization research and development of key components such as soil contact of seedbed preparation test, the regression equation of the stacking angle of wheat straw soil mixture was obtained, and the variance and interaction effect of the regression model were analysed. The regression model was used to find the optimal solution in Design-Expert software with an angle of repose of 41.23°, which yielded a soil-straw static friction factor of 0.072, a soil-straw dynamic friction factor of 0.78, and a soil-soil dynamic friction factor of 0.068, with an angle of repose error of 1.43%, indicating that the contact model parameters are reliable, and the parameters can provide a reference and theoretical basis for the study of the key components of the seedbed preparation equipment such as touching soil in the Yellow and Huaihai Sea two-maturity zone.

Determination of Discrete Element Modelling Parameters of Adzuki Bean Seeds

Using discrete element simulation to reveal the interaction between seed and seed metering devices (SMD) is an important method for developing SMDs. However, due to the lack of discrete element modeling (DEM) parameters of adzuki bean seeds (ABS) in existing literature, it is difficult to develop a suitable SMD. In this study, the DEM parameters of ABS were determined by a combination of physical tests and virtual calibration. Initially, the intrinsic parameters, contact parameters, and angle of repose (AOR) of ABS were measured. The parameters significantly affected AOR were then screened out by Plackett–Burman test. Furthermore, the Steepest Ascent test was used to determine the optimal interval value of significant parameters. Finally, the optimal values of significant parameters were obtained by the Box–Behnken test with an AOR of 23.93° and an error of 0 as targets. The results showed that the coefficient of static friction of ABS–ABS, coefficient of static friction of ABS-photosensitive resin plate, and coefficient of rolling friction of ABS–ABS significantly affected the AOR, and their optimal values were 0.302, 0.282, and 0.043, respectively. The verification test showed that the relative error between simulated and measured values of AOR was 0.67%. This indicated that the determined DEM parameters were accurate and reliable. The results from the study can provide a reference for the selection of DEM parameters in the mechanized seeding process of ABS.

Shear lid motion in DEM shear calibration and the effect of particle rearrangement on the internal friction angle

Shear cell tests are now commonly applied in particulate calibration procedures for the discrete element method. Usually, only the shear stresses at the shear plane in the particle bed are examined in short-time instances. This work aimed to find the regularities between the internal friction angle, the vertical position of the shear lid, and the rearrangements of particles in the layers during the shear test with the time instance duration of tens to hundreds of seconds. The Schulze RST Ring Shear Tester was used to compare real experiments to numerical DEM models of non-cohesive materials. The shear tests were investigated for different contact models and DEM input parameters. We also simultaneously monitored the overall specimen stiffness, material dilatancy during calibration, and shear stress. Particle bed stiffness increases with increasing shear modulus and coefficient of static friction for two contact models. The internal friction angle, which is a bulk property of the material determined by a set of particle properties, determines the ability (or resistance) to make displacements of rigid non-deformable particles in the shear testing process. The angle of the resultant of the vector of particle motion in space from the horizontal plane correlates with the angle of internal friction (at each location of the shear cell).

Determination of physical and interaction parameters of green pepper (Zanthoxylum armatum): Investigation of the mechanism of significant factors against the repose angle

Physical and interaction parameters of green pepper with contact surfaces are necessary for the development of processing equipment, which may contribute to improving food quality and safety. Green pepper (Zanthoxylum armatum), a renewable plant-derived food, shows high economic value, but its physical and interaction parameters remain unclear. Thus, this work aimed to systematically explore the needed physical and interaction parameters for the design of equipment to process green peppers. Physical and external interaction parameters (particle-to-PVC) were experimentally determined. Based on the discrete element method (DEM), the mechanism of significant parameters against the repose angle (AOR) was investigated using significance analysis, range analysis, and effect analysis. Significance analysis identified that internal interaction parameters (particle-to-particle) were all significant. Furthermore, range analysis demonstrated the optimal ranges of significant factors. Importantly, effect analysis constructed the optimized action model of significant factors against the AOR. Finally, suitable parameters for particles were verified with a restitution coefficient of 0.269, static friction coefficient of 0.932, and rolling resistance coefficient of 0.163. To the best of our knowledge, this represents the first time that the physical and interaction parameters of green pepper were determined. Predictably, these findings may contribute to the development of green pepper processing equipment worldwide.

Design and Development of Site Specific Grape Vineyard Fertilizer Applicator Prototype

The current fertiliser application methods for grape vines are labour intensive and lead to overuse of fertiliser. Frequent rain and vineyard orchard wash over often pollute water sources. Therefore, the right amount and placement of fertiliser can not only improve crop growth but also reduce the risk of chemicals to human health and the environment. To overcome the above problems a site specific fertiliser applicator for grape vineyard with mechanical sensing system was developed. The sensing system was designed to apply fertiliser to the root zone of the plant canopy. An experimental unit was developed to optimise design and operation parameters for fertiliser production per plant. The urea's physical and engineering qualities were determined for metering mechanism design. The average value of bulk density, angle of repose, urea grain diameter, grain weight in single flute measured were 0.759 ± 0.011 gcm −3 , 26.22 ± 1.18°, 3.38 ± 0.23 mm, 1.46 ± 0.04 g, respectively. The coefficient of static friction with plywood, galvanised iron and mild steel with painted surface were observed 0.3177 ± 0.0092, 0.2868 ± 0.0077, and 0.3177 ± 0.0092, respectively. For fertiliser given per plant, the effect of exposure length was p < 0.001. The sensor device opens the delivery tube for fertiliser in 0.9–0.95s.

Multiphase-Based Optimal Slip Ratio Tracking Control of Aircraft Antiskid Braking System via Second-Order Sliding-Mode Approach

This article addresses a novel multiphase-based real-time optimal slip ratio tracking control problem of an aircraft antiskid braking system (ABS) based on the second-order sliding-mode approach. First, a comprehensive dynamic model of an aircraft ABS is established, in which the coupling mechanism of the longitudinal, the vertical, and the pitching dynamics of the aircraft are thoroughly considered. Second, for the aircraft ABS with high nonlinearity, since the measurements of aircraft velocity and acceleration cannot be transmitted to the aircraft ABS in time, the second-order sliding-mode differentiator (SMD) will be designed to estimate them simultaneously. Then, the optimal slip ratio signal, which formulates the maximum friction coefficient, will be updated based on the static friction coefficient model with real-time measured and estimated signals. Furthermore, a novel multiphase-based slip ratio regulation algorithm integrated with the second-order sliding-mode control strategy is proposed on the basis of runway characteristics to track the optimal slip ratio signal, which can not only stop the aircraft faster but prevent the mainwheel from final locking. Finally, the simulation results are presented to demonstrate that the aircraft antiskid braking algorithm proposed in this article can effectively prevent the mainwheel from locking under different runway conditions, and significantly improve the braking efficiency.

Friction Coefficients for Droplets on Solids: The Liquid-Solid Amontons' Laws.

The empirical laws of dry friction between two solid bodies date back to the work of Amontons in 1699 and are pre-dated by the work of Leonardo da Vinci. Fundamental to those laws are the concepts of static and kinetic coefficients of friction relating the pinning and sliding friction forces along a surface to the normal load force. For liquids on solid surfaces, contact lines also experience pinning and the language of friction is used when droplets are in motion. However, it is only recently that the concept of coefficients of friction has been defined in this context and that droplet friction has been discussed as having a static and a kinetic regime. Here, we use surface free energy considerations to show that the frictional force per unit length of a contact line is directly proportional to the normal component of the surface tension force. We define coefficients of friction for both contact lines and droplets and provide a droplet analogy of Amontons’ first and second laws but with the normal load force of a solid replaced by the normal surface tension force of a liquid. In the static regime, the coefficient of static friction, defined by the maximum pinning force of a droplet, is proportional to the contact angle hysteresis, whereas in the kinetic regime, the coefficient of kinetic friction is proportional to the difference in dynamic advancing and receding contact angles. We show the consistency between the droplet form of Amontons’ first and second laws and an equation derived by Furmidge. We use these liquid–solid Amontons’ laws to describe literature data and report friction coefficients for various liquid–solid systems. The conceptual framework reported here should provide insight into the design of superhydrophobic, slippery liquid-infused porous surfaces (SLIPS) and other surfaces designed to control droplet motion.

Simulation and Experiment of the Spiral Digging End-Effector for Hole Digging in Plug Tray Seedling Substrate

Usually the planters used in agricultural machinery face two problems: The planters have to spread the soil twice using the tray seed planter, and it is difficult for them to dig the holes before planting. This study has designed a spiral digging end-effector to dig holes in parallel effectively and quickly so that the seeds can be planted in the holes easily. A spiral digging end-effector was designed with five spiral bits, a synchronous belt, a cylinder, a gear motor, and a connecting plate based on the tray size and the pumpkin seed characteristics. Before the optimization of the end-effector’s parameters, the substrate discrete element model parameters were calibrated using the method of “material funneling” applied for the EDEM discrete element model simulation. The contact parameters and model parameters (substrate–substrate static friction coefficient, substrate–substrate rolling friction coefficient, and surface energy) that have significant impacts on the substrate AOR (angle of repose) were selected by applying the Plackett–Burman Design and the path of steepest ascent method, and their respective optimal value range were determined. The optimal parameter values were obtained through the Central Composite Design response surface analysis test, and the parameters of the spiral digging end-effector were optimized combining the substrate particle simulation. The verification test results indicate that the substrate discrete element model parameters were accurate and reliable if the substrate static friction coefficient was 0.427; the substrate rolling friction coefficient was 0.039, and the surface energy was 0.228. When the cone angle is 30°, the spiral angle is 80°, and the rotational speed is 240 r/min, the section width at the hole depth of 13 mm is 23.1 mm, and the particle overflow proportion is about 2.05%. Compared with the protrusions penetrating end-effector, soil porosity is increased, and soil aeration is improved. Therefore, the spiral digging end-effector can effectively and quickly dig holes in the seedling substrate and can sow pumpkin seeds, which provides a research basis for the design and improvement of automatic pumpkin seed sowing equipment.

MoSi2–MoS2 composite antifriction material

A new high-temperature antifriction composite material 90 % MoSi2 + 10 % MoS2 was developed with a static friction coefficient of less than 0.3. The material is functional at temperatures up 1500 °C under neutron irradiation in an inert gas environment. Modes of initial MoSi2 and MoS2 powder mixture preparation and hot pressing of the resulting charge in a vacuum induction unit in graphite molds were worked out at a temperature of 1600–1650 °C, specific hot pressing pressure of 25 MPa, and holding for 1 h at these values of temperature and pressure. Tribotechnical properties of the material depending on the compression force in the friction pair and on the counterbody material hardness were investigated. It was shown that the higher the compression force and the harder the counterbody material in the friction pair, the lower the coefficient of friction. The effect of temperature on the physical, mechanical and heat-transfer properties of the material was established. As the temperature increases from 20 to 1000 °C, the material compressive strength decreases from 1388 to 739 MPa. An increase in the temperature from 25 to 400 °C leads to an increase in the specific heat capacity from 427 to 596 J/(kg·K) and the coefficient of heat conductivity from 2.35 to 3.41 W/(m·K). Plain bearings made of this material successfully passed durability and reactor tests.

Calibration of Contact Parameters for Moist Bulk of Shotcrete Based on EDEM

To obtain the contact parameters of the moist bulk of shotcrete accurately and quickly, this study calibrated the contact parameters of the moist bulk of shotcrete by physical stacking test and simulation method. Based on the Hertz–Mindlin with JKR (Johnon–Kendall–Roberts) model, the discrete element simulation is carried out. Using P-BD to screen seven initial parameters, it is found that JKR surface energy, rolling friction coefficient between particles and restitution coefficient of particle impact have significant effects on the angle of repose of the moist bulk of shotcrete. According to B-BD, the second-order regression model of angle of repose and significance parameters was established. Three significant parameters were obtained: JKR surface energy 0.418 J/m2, rolling friction coefficient 0.06 and static friction coefficient 1. The angle of repose obtained by simulation is compared with the physical test value, and the relative error is 1.88%. The results show that the calibration method proposed in this study can accurately simulate the physical stacking test, and can provide a reference for the calibration of contact parameters of the moist bulk of shotcrete.

鉄道各所へのウルトラファインバブル水の応用

In the present study, two experimental examples as the applications by ultrafine bubble for railway fields are introduced. The first one was confirmed the cleaning effects of ultrafine bubble water on the brush cleaning machine used in the station buildings. It was found that the removal rate was increased by using ultrafine bubble in the brush cleaning machine compared to the tap water. However, it was also shown that the removal rate increased or decreased with respect to the number of rotations of the brush and the pressing force, and there were some conditions in which the effect of the ultrafine bubble could not be confirmed. In this experiment, it was shown that unevenness on the floor surface and dirt, and microbubbles grew from ultrafine bubble may be important for cleaning effect and understand of the mechanism. The second one was shown an interesting effect that the friction reduction effect by microcloth with ultrafine bubble water. In this experiment, the static frictional coefficient and dynamic frictional coefficient of the microcloth with tap water and ultrafine bubble water were measured on the glass plate. As the results, it was found that both frictional coefficients were decreased by ultrafine bubbles but when the glass plate was not dirty, both frictional coefficients did not decrease.

A new device for the combined measurement of friction and through-thickness deformation on ex vivo skin samples

Skin irritation is a common phenomenon that becomes a real concern when caused by the use of medical devices. Because the materials used for the design of these devices are usually carefully selected for chemical compatibility with the skin, it is reasonable to assume that the irritations result from the mechanical interaction between the devices and the skin. The aim of this work was to develop a new device to study both the shear strains in the layers of the skin, using Digital Image Correlation (DIC), and the friction behaviour of ex vivo skin interacting with objects. Pig skin samples with various surface preparations were tested in friction experiments involving different contacting materials encountered in the conception of medical devices. The measure of the static and dynamic coefficients of friction as well as the length of adhesion has highlighted the great influence of skin surface conditioning on friction properties. Strain maps obtained through DIC provided insights into the impact of friction and adhesion effects on shear strain distribution in the skin as a function of depth beneath its surface.

A numerical tool to predict powder behaviour for pharmaceutical handling and processing

In this article, we discuss the potential of a numerical model to predict the behaviour of powders during pharmaceutical handling and processing. The model is based on the discrete element method (DEM) where simple experiments are required to calibrate the model used such as angle of repose tests. In a first step, the numerical calibration provided the coefficient of static friction and surface energy of the powders tested. This model has been validated with experimental data in different configurations: powder and granule settling by vibration, powder flow within a polydisperse system and mixing study in a rotary drum. Each comparison with the experimental data leads to a good accuracy of the model. In a second step, the method was used to predict numerically the granule formation during the wet granulation process and the manufacture of tablets during the compression process. Therefore, mixing (segregation), compression (mass uniformity and homogeneity of the components in the tablet) or cohesion problems can be modelled and predicted in order to limit some of the manufacturing problems during the industrialisation of pharmaceutical products such as granules or tablets, providing a scale-up of the process.

Flexible and Wireless Normal‐Tangential Force Sensor Based on Resonant Mechanism for Robotic Gripping Applications

AbstractThe ability to detect both normal and tangential forces is essential for robotic tactile systems, while most available sensors implement this function at the cost of complex electrode structure and wiring. Here a fully flexible sensor for wireless detection of normal and tangential force based on resonant mechanism is reported. The components of the sensor are designed and optimized to meet the requirement, and the sensor shows good sensitivity, hysteresis characteristics, response time, and stability in the wired test. Wireless operation is carried out through inductive coupling, and the collected spectrum of reflection coefficient can reflect both normal force and tangential force information. In the case of individual input, the sensitivity is −0.19 MHz kPa−1 to normal force in the range of 0–200 kPa, and −0.031 dB kPa−1 to tangential force in the range of 0–50 kPa. As proofs of concept, maximum static friction coefficient tests and robotic gripping experiments are demonstrated for preliminary determination of surface roughness and material identification respectively. In particular, a total recognition accuracy of 92.5% is achieved by random forest‐based machine learning for balls with different materials in the gripping experiment.

Comparative Study of Engineering Properties of Four Selected Cowpea (Vigna Unguiculata) Varieties

Poor mechanization of cowpea (Vigna unguiculata L. Walp.) in Nigeria is due to unavailability of handling machine due to large number of variations in engineering properties of the crop. To design a functioning machine for the mechanization of the crop, engineering properties of its local varieties is needed. The four local varieties selected are Small White, Big White, Drum and Milk cowpea. The selected engineering properties investigated are size, shape, weight, density, bulk density, angle of repose and coefficient of friction. The seeds were bought from Wаѕо market in Ogbоmоѕо, Oуо State Nigeria. The selected properties were measured using standard methods. The results of the experiments showed that; Mean Length; small white (7.99 mm), milk (10.30 mm), big white (10.40 mm) and drum (10.71 mm); Breadth; small white (6.53 mm), milk (7.37 mm); big white (7.60 mm) and drum (7.98 mm);Thickness; milk (5.00 mm); small white (5.41 mm), drum (5.61mm), and big white (5.92 mm); Unit weight; drum (0.63 g), small white (0.64 g), big white (0.56 g), and milk (0.63 g); Sphericity; milk (0.70), drum (0.74), big white (0.78) and small white (0.82);Angle of repose, small white (26.01), big white (26.05), drum (24.16) and milk (27.52).The average values of static coefficient of friction on the different verities (mild steel, stainless and glass) were, small white (0.45, 0.44, 0.42); big white (0.45, 0.44, 0.44), milk (0.44, 0.44, 0.43) and drum (0.45, 0.44 and .044) respectively. The results from this experiment showed that in the design and manufacturing of operating system for handling and processing of the crop, effect of engineering properties of different cowpea varieties must be incorporated. Keywords: Engineering properties, cowpea, design, processing equipment, manufacturing, verities.

Calibration and Testing of Discrete Element Simulation Parameters for Urea Particles

The lack of accurate simulation model parameters in the optimization design process of variable fertilizer application devices has resulted in large errors between simulation and theoretical calculation results, which has restricted the development of variable fertilizer application devices to a certain extent. Additionally, there are few scholars studying urea granules, so many parameters of urea granular fertilizer cannot be directly obtained from the literature. The aim of this study is to calibrate a set of simulation parameters by combining physical and simulation tests. In this study, intrinsic parameters were systematically determined, including the particle size, particle density, elastic modulus, Poisson’s ratio and their static friction coefficients, rolling friction coefficients and restitution coefficients of urea particles. By performing the urea particle stacking test, the static friction coefficient between urea particles was calibrated to 0.27, and the rolling friction coefficient between particles was 0.11. To check the reliability of the calibration parameters, the simulation and physical tests of the repose angle and bulk density of urea particles were compared, and the results show that the relative error of repose angles and bulk density of urea particles was 0.78% and 1.19%, respectively. Through the simulation of the mechanical variable fertilizer discharger and the comparison test of the benchtop fertilizer discharging performance, the maximum relative error between the simulation and physical test fertilizer discharge is 3.69% when the working length of the outer sheave is 25 mm; the maximum relative error between the simulation and physical test fertilizer discharge is 3.39% when the working length is 35 mm; the maximum relative error between the simulation and physical test fertilizer discharge is 6.86% when the working length is 45 mm; the maximum relative error between the simulation and physical test fertilizer discharge is 4.95% when the working length is 55 mm. The maximum relative error between the simulated and physical test fertilizer discharge was 6.86% at 45 mm opening and 4.95% at 55 mm opening, and the results show that the urea particle calibration parameters are reliable. The results of this study can provide a theoretical reference for the optimization design and simulation study of variable fertilizer application devices.