Dynamic Friction Coefficient Research Articles

Experimental analysis of long-term skid resistance of steel slag asphalt mixture based on differential wear

ABSTRACT This study aimed to analyse the attenuation law of skid resistance of steel slag asphalt mixture (SSAM) based on differential wear. In this study, an indoor accelerated wear instrument was used to accelerate the wear of the SSAM surface. A pavement laser scanner and a dynamic friction tester measured the three-dimensional morphology and dynamic friction coefficient (μ) of SSAM. Then, the improvement mechanism of steel slag on the skid resistance of SSAM was expounded by analysing the surface microtexture, mineral composition, and chemical composition of aggregates. The results showed no linear relationship between the amount of steel slag and the improvement of SSAM skid resistance. The SSAM with 50% steel slag maximised the differential wear effect and had the largest μ and the richest surface macrotexture. It was recommended that the steel slag content in the SSAM should not exceed 50%. The more mineral composition and higher average hardness of steel slag were the sources of its excellent skid resistance. In addition, it is suggested that the differential wear between mixed aggregates should be considered in the design of skid resistance pavement, and the proportion of different aggregates should be reasonably distributed.

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

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

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

Experimental investigation of the frictional behavior of single glass fiber filament

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

Physico-mechanical properties of seed pile of fodder crops

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

Optimization of microstructure and properties of laser sintered Ni30Cr25Al15Co15Mo5Ti5Y5 high-entropy alloy coatings via controlling plasma

An active suppressing method of laser-induced plasma was proposed to optimize the crystal structure and tribological properties for the surface laser sintering (SLS) of Ni30Cr25Al15Co15Mo5Ti5Y5 high-entropy alloy (HEA) coatings using a pulsed laser with various shielding gases. The results indicate that electron temperature (Te) and the plasma jet volume with no shielding gas or in He atmosphere were higher than those in Ar−He atmosphere. Well- defined phase transitions and significant metal atom diffusion occurred in SLS, and metallurgical bonding occurred with the precipitation of α-AlFe3, α-AlNi, and γ-AlFe2Ni. The lower energy absorbed by the plasma via inverse bremsstrahlung (IB) strengthened interactions between laser and HEA, increasing the microhardness, and reducing the dynamic friction coefficient. This elucidates the crucial influence of plasma control on laser-based additive manufacturing.

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

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

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

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

Frictional sliding of infilled planar granite fracture under oscillating normal stress

This paper investigates the frictional behavior of the infilled rock fracture under dynamic normal stress. A series of direct shear tests were conducted on saw-cut granite fractures infilled with quartz using a self-developed dynamic shear apparatus, and the effects of normal load oscillation amplitude, normal load oscillation period and sliding velocity were studied. The test results reveal that the shear response can be divided into three stages over a whole loading-unloading process, characterized by different time spans and stress variations. Generally, a smaller oscillation amplitude, a longer oscillation period and a fast shear velocity promote the stability of the friction system, which is also confirmed by the Coulomb failure criterion calculated based on the observed periodic apparent friction coefficient. The dynamic strengthening/weakening phenomenon is dependent on the oscillation amplitude and product of sliding velocity and oscillation period (vT). Also, the rate and state friction law incorporating the parameter α that characterizes the normal stress variation is employed to describe the dynamic friction coefficient but exhibits an incompetent performance when handling intensive variation in normal stress. Finally, the potential seismicity induced by oscillating normal stress based on the observed stress drop is analyzed. This work helps us understand the sliding process and stability evolution of natural faults, and its benefits for relative hazard mitigation.

Active control for stick-slip behavior of the marine propeller shaft subjected to friction-induced vibration

A stable rotational speed of the marine propeller shaft is essential to minimize the friction of the supporting bearings and to improve the efficiency of the power system. While, the friction induced vibration of the marine shaft-bearing system seriously affect the performance and reliability of the powertrain. This paper proposes an active control method to suppress the stick-slip behavior of the marine propeller shaft based on state observer. The dynamical response including relative velocity, power spectral density, dynamic friction coefficient and reaction force with various friction model are calculated. The active control with state feedback and internal model principle are applied to track the rotational speed of each segment of the whole shaft. The behavior of the state observer is analyzed through a comparison of actual value and observed value of the tracking for continuously varying speeds. The robustness of controlled system is investigated through comparison of overshoot rate and adjustment time with various control parameters. Moreover, a comparison of the observed velocity between present work and previous reference is conducted to validate the applicability of the proposed frictional model. The active control for friction-induced vibration of marine propeller shaft is thus realized based on the adjustment of control parameters.

Body mapping of skin friction coefficient and tactile perception during the dynamic skin-textile interaction

The clothing fabric and skin interact continuously across the many regions of users′ bodies during wear, which can lead to both physical skin damage and discomfort. Therefore, this investigation aimed to explore the regional differences in skin friction, tactile perception, and sensitivity in both females and males during the skin-textile interaction. The static and dynamic friction coefficient and textile perception (texture, stickiness, pleasantness, and discomfort) were measured across the 36 selected testing body areas by using a friction measurement device. The results revealed there was a significant difference in skin friction, tactile perceptions, and sensitivity across the various body regions. The anterior neck had the highest skin friction in both females and males, and participants generally rated higher texture perception in their anterior aspects compared to posterior and lateral regions. There was no significant difference in skin friction, tactile perception ratings, and sensitivity between females and males. Practitioner summary: This study sought to examine regional variations in skin friction, tactile perception, and sensitivity during the skin-textile interaction. There was a significant difference in skin friction, tactile perceptions, and sensitivity across the various body regions and no significant sex effect on skin friction, tactile perception ratings, and sensitivity.

Some technical properties of dried Terminalia chebula (kara halile) for use in harvest and post-harvest processing

Depending on humidity, some technical properties of T. chebula (black halile) dried fruit were investigated. It was observed that various properties, such as dimension, geometric mean diameter, and arithmetic mean diameter, increased linearly with increasing moisture content. With the increase in moisture content, sphericity increased from 57.2% to 67.7%, surface area increased from 487.65 mm2 to 805.03 mm2, porosity increased from 0.49 to 0.59, and the angle of repose increased from 22.77° to 27.86°. However, moisture content, true density, and bulk density decreased from 1.85% to 3.27%, 1469.54 kg/m3 to 1740.22 kg/m3, and 735.64 kg/m3 to 705.99 kg/m3, respectively. When the moisture content increased from 1.85% to 3.27%, the static and dynamic friction coefficient increased from 0.231 to 0.495 and 0.311 to 0.637, respectively. The lowest static and dynamic friction force values were obtained for stainless steel and the highest for rubber surface. When moisture content increased from 1.85% to 3.27%, tensile strength decreased from 446.46 N to 257.59 N. Rupture energy and deformation increased with an increase in the moisture content of the fruit. When the moisture content increased from 1.85% to 3.27%, the rupture energy and deformation increased from 0.09 J to 0.27 J and 0.83 mm to 1.76 mm, respectively.

Analysis of stamping dezincification of DP590 alloyed hot dip galvanized dual phase steel

with the requirements of vehicle lightweight and safety performance, dual phase steel is more and more widely used in vehicles. However, the stamping of the sheet has attracted more attention due to the increased use of dual-phase steels in auto parts. In this paper, the surface morphology, composition, surface kinetic friction coefficient, and plate thickness change rate of stamping plates were detected, calculated, and analyzed respectively. Based on solving the problem of the dezincification defect of DP590 alloyed hot-dip galvanized dual-phase steel during stamping. In addition, the stamping die was also investigated and analyzed, The results showed that the stamping die has deteriorated beyond the service life, resulting in the reduction of the adaptability between the die and the material. More importantly, the low Fe content and high dynamic friction coefficient of the surface of the stamped plate made the zinc layer unable to keep up with the tensile deformation of the substrate during stamping, which was the main factor for the lamellar detachment at the interface between the zinc layer and the substrate. By updating the dies and improving the plate design, the stamping dezincification defects of the sheet have basically disappeared.

Modeling and simulation method of trajectory in double-side autonomous grinding considering the dynamic friction coefficient

Modeling and simulation method of trajectory in double-side autonomous grinding considering the dynamic friction coefficient

Relationship between surface characteristics and properties of fiber-reinforced resin-based composites

Fiber-reinforced resin-based composites (FRC) are in line with the concept of sustainable development owing to their excellent performance and have gradually replaced traditional friction materials. Notably, the wear of composites only accounts for about 15% of whole thickness when reaching their service life, so the surface characteristics are important factors affecting comprehensive properties. To make clear the relationship between surface characteristics and properties, especially under oil lubrication, the composites with different surface characteristics have been obtained by introducing constrain and free curing process during composites preparation. Results indicate that the surface porosity increases from 36.3% to 61.2% with the extension of free curing time, and the changes in surface roughness of different composites are consistent with surface porosity, showing an increasing trend. A more uniform and better-connected pore structure is conducive to enhancing the thermal conductivity of FRC. When the surface porosity is about 41.0%, the composite exhibits excellent tensile and interlaminar shear strength owning to better interface bonding. In addition, the dynamic friction coefficient (μd) gradually improved as the surface porosity increases, and the stability of μd is related to the change of surface roughness under continuous braking, the slight change of surface roughness corresponds to a more stable μd. The wear rate of composites first decreases from 0.73 × 10−8 cm3/J (Y1) to 0.50 × 10−8 cm3/J (Y2) and then increases to 1.57 × 10−8 cm3/J (Y6). When the surface porosity is 40–50%, the composite exhibits excellent wear resistance. Most importantly, this study provides solid basic knowledge of the structural design of composites, which is favorable for obtaining expected mechanical and tribological performances.

Experimental Study on Interfacial Friction Characteristics of Reinforced Clay.

Clay is one of the important base materials in slope restoration. The adhesion of clay-rock interface plays a decisive role in the repairing effect on rock slopes. Fibers and polymers are widely used as a clay improvement method in rock slope repair. In this paper, the friction effect of sisal fiber and polyvinyl acetate (PVAc)-reinforced clay was studied through the design of an indoor rock-like interface sliding model test. Using modelled test results and scanning electron microscope (SEM) images, the reinforced clay was analyzed. The test results showed that the critical sliding angle and maximum static friction force of clay decreased with the increase of moisture content. An excess of fiber content and moisture content weakens the coupling effect of fiber-anchoring clay. Fiber content of 0.8% and PVAc content of 2% had the best effect on enhancing the sliding resistance of clay and provided good adhesion for dangerous interfaces of rock slope at 35° and 45°, respectively. PVAc formed a three-dimensional networked elastic membrane structure to improve the skid resistance and dynamic friction coefficient of the clay. The results provide an effective way for soil improvement and ecological restoration.

The sliding-contact factor (ηsc): a novel index for slip risk definition

The causes of slip are multiple and depend on the mechanical and aesthetic characteristics of the surfaces in contact, and on external elements related to the specific situation. The non-slip characteristics of a surface can be evaluated by measuring the dynamic friction coefficient (DCoF). Hazardous conditions generally appear and progress over time as a result of use, aging-related natural degradation, lack of or incorrect cleaning and maintenance. This study focuses on the characteristics of roughness profiles of the surfaces in contact and aims at the identification of those roughness parameters that can allow a more reliable evaluation of both the "slip risk index" and of its change over time due to alterations of surface texture. The sliding-contact factor,ηsc, is identified as a candidate for the evaluation of slip risk, and is represented by a dimensionless number that can be calculated using only the data of some roughness parameters, measured by a handheld instrument (Portable Surface Roughness Measuring Instrument), portable and easy to use. The sliding-contact factorηsc allows the evaluation of the "slip risk index" of dry and water-contaminated surfaces and can increase the accuracy of the assessment of the "slip risk index” if evaluated through the DCoF only.Article HighlightsA new parameter, termed sliding-contact factor ηsc is defined and is correlated with the dynamic friction coefficient.A classification of the slip risk index can be performed by means of the introduced sliding- contact factor ηsc.The present work can represent a basis for the development of a new international standard for slip-risk assessment.

Development of an Innovative Attachment Determining Friction Parameters for Quality Assessment in Sustainable Processing

New trends forcing the attractiveness of products in sustainable processing make it necessary to search for innovative methods of measuring their quality. For various biological materials, their physical properties, such as friction parameters in addition to their texture, are very important. Friction determines the course of many technological operations, e.g., transport, cleaning, sorting, fractionation, storage, and dosing of materials. An innovative friction adapter was developed for biological raw materials and tested on samples of self-produced soap. A 3D printing method for the production of this attachment was used. The soap sample loads were 100, 200, and 500 g, and the measurements of frictional resistance were carried out in contact with dry or water moistened synthetic leather, in comparison with sandpaper. For all tested variants (surfaces × loads), the initial friction of soap ranged from 0.853 N to 5.316 N, dynamic friction from 0.123 N to 3.542 N. The static and dynamic friction coefficients ranged from 0.019 to 0.151 and 0.006 to 0.131, respectively. The developed adapter for testing the friction coefficient ensures easy and quick assembly of the analyzed sample, its quick exchange and stable operation in both measurement directions, i.e., pushing and pulling the sample, as well as the possibility of using a lower applied load.

TRIBOLOGICAL INVESTIGATION OF THE AUTOMOTIVE GRADE ALUMINIUM ALLOY WITH EPOXY PRIMER COATING

Mechanical surface preparation is a common technique for removing contaminants from surface metal layers. Unlike chemical preparation, it does not require special safety measures, including those for disposal of by-products or toxic materials, thus making it more accessible for different industries. We investigated tribological testing as the experimental method to determine the quality of the coating and the influence of the initial mechanical surface treatment. Samples were made of aluminium alloy EN AW 5083 H111 that was shot blasted with white cast aluminium with resulting surface roughness of Rz=38.908 μm. Samples were further coated with Lankwitzer EvoCor 164 2-component epoxy primer. Tribological test realised on nanotribometer is described and output parameters have been analysed: friction coefficient and penetration depth. Ball-on-flat, dry contact tribological setup was used, with 100 mN normal load, under linear reciprocating motion. Dynamic friction coefficient and penetration depth curves during one tribological test were analysed indicating the moment when the coating exhibited first failure. The test has shown that tribological tests with low loads can be used for quality testing of thin coatings, including the influence of the mechanical surface preparation on the coating adhesion.

Establishment and Analysis of the Relationship Model between Macro-Texture and Skid Resistance Performance of Asphalt Pavement

Pavement surface texture evaluation is mainly analyzed based on elevation data in previous research, and attention also need to be paid to wavelength information. Furthermore, a well-established relationship model between surface texture and skid resistance for real road sections still needs further investigation to help provide useful information on appropriate maintenance time considering skid resistance attenuation. In this research, the macro-texture of asphalt pavement was evaluated from different aspects, including elevation, wavelength information, and geometry, and the relationship models between the macro-texture and skid resistance (at both low and high speeds) were established and compared using the multiple linear regression (MLR) and back propagation (BP) neural network to recommend a suitable one. In order to achieve this, this study monitored anti-skidding performance and the macro-texture of six road sections for 18 months. Firstly, the Dynamic Friction Coefficient (DFC) test and core drilling were conducted on site at three different service times. Additionally, a laboratory accelerated loading test was carried out on specimens prepared by similar material composition to one of the road sections, and the British Pendulum Number (BPN) was tested after different passes of loading. Secondly, 3D laser scanning was carried out on core samples from road sections and laboratory specimens after different passes of loading. The correlation degree between macro-texture indexes and anti-skidding performance was analyzed with the grey correlation entropy analysis method. Finally, the relationship models between the anti-skidding performance at high and low speeds and macro-texture were established based on the MLR and BP neural network. The results indicate that the macro-texture indexes calculated based on elevation data to characterize vertical irregularities have a good correlation with the skid resistance despite the different service times and pavement types. Compared with the BP neural network model, the MLR model has low correlation and noticeable error. The relationship model between F60 (DFC at the speed of 60 km/h) and macro-texture could be well established by the BP neural network. In addition, the relationship between F20, BPN, and pavement surface macro-texture is poor, making it impossible to establish a model with good correlation. Generally, it is recommended to use the BP neural network to establish the relationship model between macro-texture and skid resistance.