Oblique impact of ice hockey and plastic pucks with a rigid surface

The collision of a disk with a rigid surface is analysed in this paper assuming that the disk slides throughout the collision at glancing angles or grips the surface at other angles of incidence. Experimental results are presented for an ice hockey puck and a plastic disk, showing that there is no rolling involved, as assumed in previous studies. Measurements are presented of the outgoing speed, angle and spin as a function of the angle of incidence, and the results are described in terms of the normal and tangential coefficients of restitution plus the coefficient of sliding friction. The experiment would be suitable for use in a student laboratory.

Scaling theory of rubber sliding friction

Current theoretical descriptions of rubber or elastomer friction are complex—usually due to extensive mathematical detail describing the topography of the solid surface. In addition, the viscoelastic properties of the elastomer material itself, in particular if the rubber is highly filled, further increase the complexity. On the other hand, experimental coefficients of sliding friction plotted versus sliding speed, temperature or other parameters do not contain much structure, which suggests that a less detailed approach is possible. Here we investigate the coefficient of sliding friction on dry surfaces via scaling and dimensional analysis. We propose that adhesion promotes viscoelastic dissipation by increasing the deformation amplitude at relevant length scales. Finally, a comparatively simple expression for the coefficient of friction is obtained, which allows an intuitive understanding of the underlying physics and fits experimental data for various speeds, temperatures, and pressures.

MECHANICAL CHARACTERISTICS OF THE RUBBED MAIZE STRAW DURING SCREW CONVEYING

In order to reduce the power consumption of screw conveyor and to improve the productivity, this study investigated such mechanical characteristics of rubbed maize straw as coefficient of sliding friction, angle of repose, internal friction coefficient, cohesion, flow function value and compressible coefficient with respect to its moisture content and density. An experiment was designed and consists of a sliding friction characteristic test-bed, a direct shear apparatus, a self-made device with adjustable density and compression. The results showed that: the coefficient of sliding friction increases with the increase of moisture content and density; the angle of repose and internal friction coefficient each increases with increasing moisture content respectively; there is no significant effect between the moisture content and the cohesion of rubbed maize straw; the flow function value goes up with the increase of the moisture content; also the increase of the moisture content leads to the increased bulk density due to the reduced materials gap and the increased compression coefficient, which makes it hard to compress. The equation of pressure and density was found, and it is suitable for the analysis of compression characteristic of rubbed maize straw. The research results lay a theoretical foundation and a basis for the further study on mechanical properties of maize straw.

Insects use lubricants to minimize friction and wear in leg joints

A protein-based lubricating substance is discovered in the femoro-tibial joint of the darkling beetle Zophobas morio (Insecta). The substance extrudes to the contacting areas within the joint and appears in a form of filiform flows and short cylindrical fragments. The extruded lubricating substance effectively reduces the coefficient of sliding friction to the value of 0.13 in the tribosystem glass/lubricant/glass . This value is significantly lower than 0.35 in the control tribosystem glass/glass and comparable to the value of 0.14 for the tribosystem glass/dry PTFE (polytetrafluoroethylene or Teflon). The study shows for the first time that the friction-reducing mechanism found in Z. morio femoro-tibial joints is based on the lubricant spreading over the contacting surfaces rolling or moving at low loads and deforming at higher loads, preventing direct contact of joint counterparts. Besides Z. morio , the lubricant has been found in the leg joints of the Argentinian wood roach Blaptica dubia .

Scaling Theory of Rubber Sliding Friction

Current theoretical descriptions of rubber or elastomer friction are complex-usually due to extensive mathematical detail describing the topography of the solid surface. In addition, the viscoelastic properties of the elastomer material itself, in particular if the rubber is highly filled, further increase the complexity. On the other hand, experimental coefficients of sliding friction plotted versus sliding speed, temperature or other parameters do not contain much structure, which suggests that a less detailed approach is possible. Here we investigate the coefficient of sliding friction on dry surfaces via scaling and dimensional analysis. We propose that adhesion promotes viscoelastic dissipation by increasing deformation amplitude at relevant length scales. Finally, a comparatively simple expression for the coefficient of friction is obtained, which allows an intuitive understanding of the underlying physics and fits experimental data for various speeds, temperatures and pressures.

RESULTS OF THEORETICAL STUDIES OF A COULTER WITH A SEED DEFLECTOR, A SOIL DISRUPTURER, AND A FURROW PRESS WHEEL

Качественный посев это не только равномерное распределением семян по длине рядка, но и их заделка на заданной глубине, позволяющая получить высококачественный урожай зерновых культур. Это достигается использованием рядового способа посева зерновых культур при помощи двухдисковых сошников, которые производят укладку посевного материала в борозду, что позволяет получить непосредственный контакт семян с почвой. Сеялки с такими рабочими органами используются как в традиционных, так и в минимальных технологиях возделывания зерновых культур. В статье представлены результаты теоретических исследований экспериментального сошника с направителем семян, рыхлителем почвы закрытого типа и бороздным прикатывающим катком с шиной из каучукового массива, определены зависимости для нахождения ударного коэффициента трения скольжения, а также зависимости скорости центра катка и семени после соударения. Статья посвящена улучшению качественных показателей посева семян зерновых культур сеялкой с экспериментальным сошником и содержит результаты теоретического исследования конструктивных и режимных параметров сошника с направителем семян, рыхлителем почвы закрытого типа и бороздным прикатывающим катком с шиной из каучукового массива. High-quality sowing is not only a uniform distribution of seeds along the length of the row, but also their seeding at a given depth, which allows getting a high-quality crop of grains. This is achieved by using an ordinary method of grain crops sowing using double-disc coulters, which place seeds in the furrow allowing direct contact of the seeds with the soil. Seeders with such working bodies are used in both traditional and minimal technologies for the cultivation of grain crops. The article presents the results of theoretical studies of an experimental coulter with a seed deflector, a closed-type soil cultivator and a furrow press wheel with a rubber mass tire. The dependences for finding the impact coefficient of sliding friction, as well as the dependence of the speed of the wheel center and seed after impact are determined. The article is devoted to the task of improving the quality indicators of sowing seeds of grain crops by a seeder with the experimental coulter and contains the results of a theoretical study of the design and operating parameters of the coulter with a seed deflector, a closed-type soil disrupturer and a furrow press wheel with a rubber mass tire.

Friction and Shear Properties of Pine Biomass and Pellets

Knowledge on the mechanical properties of granular biomass is important for the design and efficient operation of equipment used for handling, storage, and processing. Their mechanical properties are used as a measure of material quality. In this study, the mechanical properties of granular biomass obtained from pines (sawdust, shavings, long shavings, and pellets) were determined under a moisture content range of 10–50%. The coefficient of sliding friction µ of four construction materials was determined using a 210-mm-diameter direct shear tester (Jenike’s shear box). To measure the shear resistance of the biomass materials (represented as torque T), a prototype vane tester was constructed. The characteristics of shear resistance with respect to time T(t) were determined for material samples under normal pressure p ranging from 5 to 30 kPa and a vane rotation rate of 3 rpm. Measurements were performed for five geometries of the rotor, reflecting typical deformation conditions encountered in the processing of granular biomass. The coefficient of sliding friction was found to be affected by the type of material, moisture content, and normal compressive pressure. Depending on the biomass material, the highest µ, which ranged from 0.50 to 0.62, was obtained for black steel, whereas the lowest µ, which ranged from 0.27 to 0.52, was obtained for aluminum. The lowest coefficient of sliding friction was observed for dry materials and high normal pressure. The torque T was observed to be affected by the rotor shape, material, normal pressure, and moisture content. The parameters presented provide information useful for the design of transport equipment and processing of granular wood biomass.

TRIBOLOGICAL PROPERTIES OF DIAMON D-LIKE CARBON COATINGS AT FRICTION JOINTS LUBRICATED WITH IONIC LIQUID

The paper reports the study of a-C: H and a-C:H:Si diamond-like carbon coatings obtained in plasma-assisted chemical vapour deposition processes PACVD. The influence of the coatings on tribological properties of tribopairs under dry friction and in lubrication with synthetic oil PAO-8 and selected ionic liquid was evaluated. To perform the analysis, 100Cr6 steel samples uncoated and coated with a-C:H and a-C:H:Si were compared. Surface topography studies were performed using an atomic force microscope. Using SEM with an EDS analyser, the surface morphology of the coatings was observed, and the elements contained in the coatings were identified. Tribotests were carried out in a ball-on-disc tribotester under dry friction and with lubricants. The characteristics of the texture of the samples before and after the tribotests were determined using a confocal microscope in an interferometric mode. The test results showed that the tribo-pairs with a-C:H in lubrication with ionic liquid had the best tribological characteristics, i.e., the lowest coefficient of sliding friction.

Numerical Study of Particle Morphology Effect on the Angle of Repose for Coarse Assemblies Using DEM

The morphologies of coarse particles are usually irregular and play a dominant role in the mechanical behaviors of the particle assemblies. This paper quantitatively studies the effect of particle shape on the angle of repose, which is an important macroscopic parameter for ballast materials, via laboratory tests and numerical simulations by means of the discrete element method (DEM). Forty ballast particle templates and four simply created clump templates are reconstructed using an image-based method and quantified with two shape factors, sphericity and convexity. A series of simulations are conducted with the coefficient of sliding friction between particles changing from 0.2 to 0.6 at an interval of 0.1 to study its influence on various shapes of particles, and an appropriate value of sliding friction coefficient is chosen for the comparison of particle shape effect. The results show that increasing sphericity and convexity can significantly decrease the angle of repose, and the real ballast model gives a more realistic angle of repose behaviors as that of laboratory tests compared to simply created models. By analyzing the characteristics of particle motions and contacts from a microscopic perspective, the mechanism of particle shape attributed to the formation of granular aggregation is also discussed and revealed in this research.