Wet Friction Coefficient Research Articles

Hydrodynamic Analysis of Pipelines Transporting Capsule for Onshore Applications

Abstract— Rapid depletion of energy resources hasimmensely affected the cargo transportation industry.Efforts have been made to develop newer economic andenvironmental friendly modes for this purpose. Bulk solidscan be transported for long distances effectively in pipelines.Raw materials can be stored in spherical containers(commonly known as capsules) transported through thepipeline. For economical and efficient design of anytransportation mode, both the local flow characteristics andthe global performance parameters need to be investigated.Published literature is severely limited in establishing theeffects of local flow features on system characteristics ofHydraulic Capsule Pipelines (HCPs). The present study focuses on using a well-validatedComputational Fluid Dynamics (CFD) based solver tosimulate the unsteady turbulent flow of a sphericalcapsule as a simplified case in HCPs for onshoreapplications. A novel numerical model has beenemployed in the present study with the aid of thedynamic mesh technique for calculating the pressureand the velocity variations within such pipelines. Thenumerical model comprises a straight test section. Thenumerical model for capsule flow yields realisticresults for the global flow parameters as compared tothe experimental data from the test rig developed inthe present study. The influence of the carrying fluid(water) on the capsule has been verified by estimatingthe shear forces and the friction coefficient. Inaddition, novel models have been developed forpredicting the wet friction coefficient considering thestart-up effect in such systems.

Analysis of Self-Rescue Possibilities for Pedestrians in the Aftermath of Destabilization during a Flood Event

Human safety is paramount in flood disasters. Current research indicates that the majority of fatalities in such disasters are due to people moving in water. Existing studies on human stability in floods have primarily focused on the static resistance of a standing posture against water flow, neglecting the realistic scenario where people need to move and attempt self-rescue in the aftermath of destabilization. This paper introduces an analysis of the stability during the self-rescue process following a fall in floodwaters, providing insights into the baseline risks of human impact in floods. The self-rescue process is defined as the recovery to a standing position after a fall, segmented into four postures: sitting, kneeling, squatting, and standing. Additionally, considering the significant variability of the current method (D×v water depth multiplied by flow velocity) used to assess human stability in floods, this research thoroughly investigates previously undefined parameters, including submerged volume, frontal area, wet friction coefficient, and flow resistance coefficient. This leads to the development of a physically meaningful self-rescue risk assessment formula, which is validated against previous studies for accuracy, with the aim of contributing new insights to flood risk management and public education.

Design of bionic tire tread compounds with pit structures and the improvement mechanism of wear and wet grip resistance

Design of bionic tire tread compounds with pit structures and the improvement mechanism of wear and wet grip resistance

An interactive water lubrication mechanism of γ-LiAlSi2O6 glass-ceramics in friction and wear

Anti-attrition and water lubrication are two areas where ceramics are widely applied. In comparison to pure ceramics, glass-ceramic composite materials are more accessible to machine and manufacture into water lubrication kits. However, current water lubrication theories are mainly applied to ceramic materials such as SiC, Si3N4, Al2O3 and ZrO2. Glass-ceramic water lubrication mechanisms are not involved, in particular, the specific development process of low friction glass-ceramics in the water environment is yet unknown, which limits the application of glass-ceramics. As a result, we developed custom-made γ-LiAlSi2O6 glass-ceramics for a ball and a wafer that were utilized to conduct friction and wear tests. By contrasting the dry and wet friction coefficients between the ball and the wafer, abrasion losses and surface roughnesses of glass-ceramics, particle size distribution and zeta potential of wear debris over time, the water lubrication mechanisms of glass-ceramics in three different friction stages were clarified, the interactive lubrication effects of the electrical double layer and the dynamic fluid pressure ensure that the wet friction coefficient of the glass-ceramics is constant below 0.02.

Multiple Intermolecular Interaction to Improve the Abrasion Resistance and Wet Skid Resistance of Eucommia Ulmoides Gum/Styrene Butadiene Rubber Composite.

A rubber composite was prepared by using methyltriethoxysilane (MTES) to modify silica (SiO2) and epoxidized eucommia ulmoides gum (EEUG) as rubber additives to endow silica with excellent dispersion and interfacial compatibility under the action of processing shear. The results showed that compared with the unmodified silica-reinforced rubber composite (SiO2/EUG/SBR), the bound rubber content of MTES-SiO2/EEUG/EUG/SBR was increased by 184%, and its tensile strength, modulus at 100% strain, modulus at 300% strain, and tear strength increased by 42.1%, 88.5%, 130.8%, and 39.9%, respectively. The Akron abrasion volume of the MTES-SiO2/EEUG/EUG/SBR composite decreased by 50.9%, and the wet friction coefficient increased by 43.2%. The wear resistance and wet skid resistance of the rubber composite were significantly improved.

Design of convex‐hull bionic tire tread compounds and mechanism on collaborative improvement of wet resistance and wear resistance

AbstractThe materials or bionic methods available cannot further solve the contradiction between the wear resistance and wet resistance of tire tread compounds. In this study, a convex‐hull bionic tire tread compound was designed and produced according to the difference in wear resistance between two types of tire tread compounds. The effects of the bionic structure on the wear resistance and wet resistance of the tire tread compounds were explored by analyzing the changes in wear loss, wear surface characteristics, and wet friction coefficient. The wear resistance and wet resistance of the convex‐hull bionic tire tread compound were collaboratively improved. The largest increasing rate of wear resistance was 9%, and the largest increasing rates of wet sliding ability on sand paper surface and on smooth glass surface were 3.4% and 4.2%, respectively. The coupling design of materials and bionic structures offers a new way to improve the overall performances of tire tread compounds.

The Effect of Roughness on the Wet Skid Resistance of Tire Tread Compounds

The wet skid resistance is the main performance of automobile tires, and the excellent wet skid resistance can ensure the safety of the car. In this paper, 60 mesh sandpaper, 400 mesh sandpaper, 1000 mesh sandpaper and 2000 mesh sandpaper were used to pre-grind the sample, which changed the surface roughness of the sample; measured the dry and wet friction coefficient of the sample, and the measured friction pair was smooth Glass surface, rough glass surface and 180 grit sandpaper surface. The experimental results show that the rougher the surface of the sample and the surface of the friction pair, the greater the wet friction coefficient and the better the wet skid resistance.

Experimental study on wet skid resistance at different water-film thicknesses

PurposeDriving safety on a wet road is closely related to the wet skid resistance of tires. The purpose of this paper is to reveal the evolution of wet skid resistance at different water film thicknesses and provide some guidance on the design of a tread pattern with improved traction on rainy roads.Design/methodology/approachBrake tests are performed in a laboratory with a viscoelastic tribotester at various water film thicknesses. The initial water film thickness is 3 mm, which decreases with an increase in the test number. Brake friction force is dynamically measured at water film thicknesses ranging from 0 mm to 3 mm.FindingsThe results show that water film thickness exerts a great influence on the forms of tire motion and slip ratio. The tire is much easier to slide on the road with thick water film and also with a considerably thin water film (about 0-1 mm) during a sharp braking process. The brake traction can be very low under this road condition despite the apparently safe quality of the road.Originality/valueThe authors design and establish a new viscoelastic tribotester which is used to simulate the real braking sliding process and study the tribological properties between tire rubber and road surface. The variation in the wet friction coefficient and slip ratio at different water film thicknesses have a great influence on the design of a tread pattern with improved traction on rainy roads.

The influence of road surface texture on the skid resistance under wet conditions

Due to their influence on traffic safety, skid resistance and drainage are important surface properties of a road and their optimization and durability is still focus of ongoing research. Under wet conditions, these two characteristics are connected as a wetted road cannot provide a sufficient skid resistance without a working drainage system. The wet friction is mainly affected by the road surface geometry and the water depth. Herein, we describe a novel numerical approach to study the influence of the surface texture – mainly the microtexture – on the wet friction coefficient. This method is based on the hysteresis effect, which is the main friction force on rough surfaces under wet conditions. We therefore use an already established friction model for dry surfaces and extend its range of application by an additional consideration of water films. A drainage model has been developed to calculate the water film thickness for a given road surface and geometry (pavement surface runoff model) as systematic measurements of water film thicknesses in situ are difficult. The water depth determines the number of contact points between the pavement and the tyre. Based on three-dimensional measurements of a surface texture, the friction coefficient is calculated. By this newly developed model approach, it is possible to identify the main factors influencing wet skid resistance in regard to the pavement surface microtexture and the water film thickness.

Safety Aspects of Wet Asphalt Pavement Surfaces through Field and Numerical Modeling Investigations

Good pavement macrotexture has a direct influence on vehicle safety during wet weather conditions by improving vehicle traction and braking ability. Apart from the macrotexture, several other factors, such as environmental, tire, and pavement-related characteristics, affect the wet friction. Most experimental studies had a limited scope of reusability as soon as there was a change in any of the other factors. In recent years, the development of powerful finite element tools has made it possible to simulate complex wet tire–pavement interaction as close as possible to the actual field conditions. However, to the best of the authors’ knowledge, none of the past analytical and numerical studies were able to include the actual pavement surface texture in their analysis. This paper describes an approach to study the effect of actual surface morphologies of asphalt pavements on the wet friction coefficient by using the finite element method. Asphalt surface morphologies representative of open-graded mix to close-graded mix were used in the finite element analysis. The finite element model was duly calibrated with the field investigations conducted with state-of-the-art field equipment. The extreme loss of wet friction, which ultimately led to the risk of hydroplaning, was also studied. The analyses were performed for two water film thicknesses, two tread patterns, and two tire slip ratios. The results from the current study can be used as safety indicators of in-service asphalt pavements under wet and flooded conditions.

Comparisons of PEPT derived charge features in wet milling environments with a friction-adjusted DEM model

The extent to which the discrete element method (DEM) represents particulate flow in wet tumbling mill environments is investigated by adjusting the friction coefficient in the simulation to best match positron emission particle tracking (PEPT) experiments of the same media in steady-state, re-circulating fluids of water and slurry. Porosity and velocity distributions of 5mm, mono-sized glass spheres in a 300mm diameter mill are statistically compared to an equivalent dry DEM model. These show a very high degree of spatial agreement with RMS differences of only 0.11%. Typically, around 80% of the mill volume is found to have identical results. Similar levels of agreement are found for a range of operating speeds from 31% to 75% of critical speed. These demonstrate that a solid particle DEM model of the charge, without an explicit representation of the slurry, is able to accurately capture the motion of the solid charge. Agreement is improved by calibration of the wet friction coefficient. The DEM results indicate that the flow is not particularly sensitive to the exact choice. Small differences between DEM and PEPT are observed in the free surface part of the flow. The presence of fluid slightly slows the fall and compaction of the charge leading to a more slowly moving and higher free surface in the middle of the mill. The flow is also found to be highly three dimensional with significant axial flow generated by the end walls of the mill.

The effect of mineralogy and effective normal stress on frictional strength of sheet silicates

Phyllosilicates are common constituents of upper crustal faults and subduction forearcs. We studied the effect of mineralogy and controlled effective normal stress (between 5 MPa and 100 MPa) on frictional strength. Although the effect of mineralogy on frictional strength of single-phase phyllosilicate gouges has been previously studied, the influence of effective normal stress has not. We conducted water-saturated and vacuum-dry frictional tests on single-phase phyllosilicate gouges using a triaxial apparatus. Minerals included talc, pyrophyllite, kaolinite, lizardite, illite, montmorillonite, chlorite, muscovite, phlogopite, and biotite (particle size <30 μm). Results show friction coefficients between 0.22 – 0.44 (dry) and 0.12–0.38 (wet). Wet strength is always lower than dry strength for the same phyllosilicate, and those with hydrophilic surfaces are especially weakened by water. Tri-octahedral minerals are weaker than di-octahedral minerals with otherwise similar structures. The dependence of friction on interlayer bond strength is less clear than previously suggested. At effective normal stresses > 20 MPa dry friction coefficients are constant, and wet friction coefficients show a small increase. This is attributed to loss of water and increased contact area. The results indicate that frictional strength of clay-rich faults increases at depths less than ≈1 km under hydrostatic pore fluid pressures.

Study on Friction Properties of Cu-Fe-Based Powder Metallurgy Materials under Dry and Wet Friction Conditions

Copper-iron-based friction materials were prepared by powder metallurgy process. The effects of friction velocity and friction pressure on friction and wear behavior of the material under dry and wet friction conditions were investigated with a constant-speed friction machine. The results show that, at low speed friction, the dry friction coefficient is higher than wet friction coefficient and the friction coefficient increases with increasing friction pressure. The reason is that the water film plays an important role in cleaning and lubricating. At high speed friction, there is not much difference between dry and wet friction coefficients and the friction coefficient is not sensitive to friction pressure changes. This is due to the metal matrix high-temperature softening, caused by high speed friction, which controls the friction properties.

2303 超音波を利用した小型軽量なセミアクティブ回転ダンパの基礎研究 : 乾摩擦と湿摩擦の比較(J23-1 メカニカルシステムとその知能化(1),J23 メカニカルシステムとその知能化,2005年度年次大会)

In this study, basic research of small semi-active rotation damper in which friction coefficient is controlled by utilizing ultrasonic vibration is dealt with. Experimental rotational friction damper system using ultrasonic brake is introduced as a testing mechanism. Maximum (rotational) coefficient of static friction and coefficient of (rotational) dynamic friction are identified thorough experimental analysis. In this paper, difference in dry and wet friction coefficient variation is investigated. It is shown that the semi-active control does not work in wet friction.

Measurement, Analysis, Evaluation, and Restoration of Skid Resistance on Streets of Muscat

This research was undertaken to study the problems of skidding, particularly during the wet season. Thirty-nine typical street sections of known service age and traffic were selected from the Muscat area for field investigation. Six age groups were used, ranging from ⩽0.5 to &gt;10 years, with five to eight road sections in each group. Traffic-level categories were low, medium, and high. Field measurements of dry and wet friction coefficients were undertaken for 6 months using a pendulum skid tester and a motometer decelerometer mounted on a test car. Site measurements included surface temperature, length of skidding, texture depth, and assessment of pavement condition. Cored samples 100 mm in diameter were visually evaluated and laboratory tested. The experimental work included determination of asphalt mix content and gradation, Los Angeles abrasion, and acid-insoluble residue of the extracted aggregates. Various relationships between friction coefficient and the relevant independent variables were developed. A predictive relationship between the friction coefficient and the skid length was obtained. Minimum required values of friction coefficient were recommended for safe performance. On the basis of criteria such as those proposed in this study, recommendations were made to immediately maintain eight streets to increase their skid resistance followed by others with different maintenance priorities to improve skid resistance. Open-graded friction courses are strongly recommended to reduce wet-weather skidding. The results of this research will have a positive effect on constructing and maintaining roads to reduce skidding accidents.

Experimental characterization of sliding and impact friction coefficients between steam generator tubes and avb supports

Experiments are described that were designed to determine the sliding and the impact friction coefficients between steam generator tubes and anti-vibration bar supports. The test environments were air and water at ambient conditions, in order to allow bracketing of actual steam generator conditions. Two tube/AVB combinations were tested. The first combination consisted of materials used in a recent flow test program on a 5 X 12 U-tube bundle during which the turbulence and fluid-elastic responses of that tube bundle were characterized with different AVB clearances. The said flow test program was also successful in the experimental determination of “work rates” between tubes and AVBs with different boundary conditions, while the tubes were excited by different flow dependent forcing mechanisms. The second combination of materials consisted of an Inconel 600 tube matched with an AVB sample retrieved from an operating steam generator. Results of the present tests on the two material combinations show some differences in the dry friction coefficients, but relatively good agreement between the wet friction coefficients. In addition, friction coefficients were determined to be mostly independent of normal force and sliding velocity. Finally, friction coefficients for oblique impacts were quite similar to those for sliding motion under preload. Interpretation of the test results for normal or near normal impacts justifies use of a single friction coefficient for all combinations of tube to AVB interactions (possibly excluding rocking and rotation) in non-linear finite element, time-domain computer simulations of the tube/AVB dynamics under turbulence and/or fluid-elastic excitations.

ゴムのウェット摩擦係数の温度依存性に関する研究 ＩＩ ゴムのウェット摩擦係数と粘弾性値の関係

ゴムのウェット摩擦係数の温度依存性を粘弾性の温度依存性から記述する. 球状の突起を乗り越える時のゴムのエネルギー損失を竹村•湊による式を拡張して求め, 摩擦試験機の条件を考慮すると摩擦係数μ=3.45•βS•E′-1/4•E′S+1/8が得られた. 摩擦係数は British Pendulum Tester による測定値を用い, 摩擦路面はセイフティーウォークを使用した. 上式においてβS は tanδによる関数であり, tanδ, E′はともにν=摩擦速度/路面突起間隔で定義される変形周波数における測定値である.摩擦係数測定時の変形周波数は4500Hzであり, 粘弾性測定は10Hzで行ったので, 時間温度換算則を用いて, 摩擦試験温度を粘弾性測定温度に変換した. E′Sは測定時のゴム試料の低周波変形を考慮したものである. 上式の妥当性を検証するため, 15種のゴムの摩擦係数の測定値と計算値を比較したところ良い一致を見た. 更に, 摩擦係数の温度依存性を小さくするためには, 粘弾性の温度依存性を小さくしなければならないことを示した.