Total Friction Research Articles

Friction models for grease lubricated ball-race contacts

In this paper the authors theoretically investigated the influence of the hydrodynamic rolling friction forces in greased ball-race contacts at low loads. Two IVR-EHL transitions equations for hydrodynamic rolling friction forces have been applied to the ball-race contacts in a modified thrust ball bearing by using three types of greases having base oil viscosities between 40 mm2/s and 1000 mm2/s. Based on the total friction torque analytically estimated and experimentally determined has been evidenced the influence of the hydrodynamic rolling friction force on the total friction torque as the most important parameter for both proposed transition equations. The theoretical values of the total friction torque have been experimentally validated. The experiments was realized with a modified tree ball thrust bearing, without cage in a range of speed between 60 rpm and 400 rpm and for a normal load of 1.422 N for each ball.

Experimental Investigation of the Flow Characteristics in Crude Oil Containing Sand and Gas Flowing Along Vertical Pipelines

An experimental study on the flow behavior of crude oil containing sand and air in a vertical pipe with 50 mm diameter was carried out. The experiments were conducted under the following input superficial phase velocities: oil from 0.1 to 2.23 m/s and gas from 0 to 0.34 m/s. Oil was blended with sand in three different volume concentrations, namely, 0.7, 2, and 3%. Two different types of sand were used to investigate the effect of sand size distribution. A comparison between rheological measurements and pipe flow data showed that the stress–strain relationship obtained by the rheometer could be used to predict the transport characteristics in the vertical pipe flow. It was demonstrated that a small gas injection and sand addition can decrease the total pressure and friction pressure gradients. In the oil flow, the injection of air generally increased the friction factor compared to the single-phase flow, especially at low Reynolds numbers. However, the friction factor decreased by adding a small amount of fine sand. The accuracy of the correlation developed in this study was compared with other three correlations widely used in gas–liquid vertical pipe flow.

Magnetic viscoelastic behavior in a colloidal ferrofluid.

Based on the stochastic Langevin equation, we derived the total friction experienced by a tracer particle diffusing in thermally equilibrated colloidal magnetic fluids. This transport property leads to new expressions for its long-time diffusion coefficients, which satisfy an Einstein relation with the frictions of its translational and rotational Brownian motion. Further use of the nano-rheology theory allowed us to derive also the viscoelastic modulus of the colloid from such a property. The temporal relaxation of the viscoelasticity and transport coefficient turns out to be governed by the intermediate scattering function of the colloid. We derived an explicit formula for this evolution function within a hydrodynamic theory to include rotational degrees of freedom of the particles. In the limit of short frequencies, the viscous moduli render a new expression for the static viscosity. We found that its comparison with known experiments, at low and high concentration of ferroparticles in magnetite ferrofluids, is fair. However, comparing the predicted viscoelastic moduli with computer simulations as a function of frequency yields poor agreement.

Investigations on start-up performances of novel hybrid metal rubber-bump foil bearings

In the frequent start-up process of aerodynamic bearings, contact easily occurs between journal and bearing bush. In this research, novel hybrid metal rubber-bump foil bearings (MR-BFBs) were proposed. Based on rough surface contact and ultra-thin film lubrication theory, we studied the start-up performances of MR-BFBs. The results showed that the changes in both RSm and Ra caused great changes in the parameters pmax and A0. The increased start-up times led to a decrease in the load ratio Wc/W0 and the total friction coefficient, and an increase in both the linear velocity, the gas film pressure and the minimum gas film thickness. With the increase in the composite roughness, both the critical rotation speed and start-up time exhibited an upward trend.

Influence of Seasonal River Discharge on Tidal Propagation in the Ganges‐Brahmaputra‐Meghna Delta, Bangladesh

AbstractSignificant research efforts have been devoted to understanding river‐tide interactions in estuaries. However, studies on the impact of monsoon‐driven fluctuations of river discharge are limited. Here, the role of varying river discharge on the tidal propagation and tidal limit along the Ganges‐Brahmaputra‐Meghna Delta (GBMD), a macrotidal estuary subject to seasonal and annual river discharge variations, is investigated. The Delft3D hydrodynamic model is validated and applied to an average flood year condition and nine idealized scenarios covering the typical hydrological conditions. Results reveal that the upper limit of the tidal propagation shifts 75 km upstream during the dry season. The residual water level slope and tidal damping rate increase with river discharge beyond 100 km from the estuary mouth. The balance between the generation and dissipation of quarterdiurnal tides shifts spatially as a result of changes in channel convergence and friction and temporally as a function of river discharge, which controls the total friction in the upper tidal river. The balance between tidal dissipation and generation depends on the residual velocity generated by river discharge and the velocity of the principal tides. The maximal generation of quarterdiurnal tides in the upper GBMD depends on the friction generated from the river‐tide interaction. Critical river discharge thresholds produce an optimal condition of dissipation of semidiurnal tides and generation of quarterdiurnal tides through friction at the upper and middle estuary. River discharge above the critical river discharge amount more rapidly dissipates both semidiurnal and quarterdiurnal tides than generates quarterdiurnal tides from nonlinear interactions.

Analisis Kecepatan Kendaraan Akibat Hambatan Samping (Studi Kasus: Jl. Mayor Abd. Karta Wirana Kota Jambi di sekitar Lippo Mall)

This study aims to analyze the vehicle speed due to side friction with the MKJI 1997 method and the analysis of the cumulative distribution of speed using statistical methods. This research was conducted on Jalan Mayor Abd. Karta Wirana Jambi City around Lippo Mall. The results show that the total side friction for events per day on Wednesday is 1175.34 with the lowest incidence of resistance on pedestrians at 48.39 and the highest incidence of friction on incoming and outgoing vehicles of 790.32. Side friction class on Jalan Mayor Abd. Karta Wirana, according to MKJI 1997, is in a high class (VH) with a frequency of weight events exceeding > 900 events per day. While the speed when disturbed is obtained an average of 11, 56 km / hour is at the lowest speed interval 10 - 11 km / hour and the highest speed is 12 - 13 km / hour. The average of undisturbed speed of 30.32 km / h at the lowest speed interval of 20-24 km / hour and the highest is 36-40 km / hour. The difference between these two speeds states that the side drag has a very large effect on speed (a very significant decrease in speed is 61.87%)

Pretensioned prestress friction losses considering contact imperfection at deviators in prestressed concrete girders

Pretensioned prestressed concrete (PC) girders are prefabricated in series to reduce cost and facilitate fabrication efficiency. However, a consensus of the calculation of prestress friction losses at deviators is not achieved yet. The existing calculation methods assume a perfect contact between prestressing tendon and deviator, which is inconsistent with observed imperfect contact in real-life practices. This research considers imperfect contact in the investigation of the friction loss through theoretical analysis and experimentation. Three representative types of deviators are investigated and compared in terms of the magnitude of the friction loss. Modified equations for calculating the friction are proposed through the theoretical study, validated against experiment, and applied to investigate the distribution and effects of friction loss in series girders. The results show that the friction loss due to contact imperfection accounts for a significant percentage (61%) of the total friction loss. The equations without considering contact imperfection underestimated friction loss by up to 54 MPa, overestimated the elongation of tendons by up to 77 mm, and overestimated the camber and crack resistance of series girders by up to 6.6%. This study provides new insights into pretensioned prestress friction loss, and the modified equations are useful to improve the design, fabrication, and evaluation of PC girders.

Origin of Friction in Superlubric Graphite Contacts.

More than thirty years ago, it was theoretically predicted that friction for incommensurate contacts between atomically smooth, infinite, crystalline materials (e.g., graphite, MoS_{2}) is vanishing in the low speed limit, and this corresponding state was called structural superlubricity (SSL). However, experimental validation of this prediction has met challenges, since real contacts always have a finite size, and the overall friction arises not only from the atoms located within the contact area, but also from those at the contact edges which can contribute a finite amount of friction even when the incommensurate area does not. Here, we report, using a novel method, the decoupling of these contributions for the first time. The results obtained from nanoscale to microscale incommensurate contacts of graphite under ambient conditions verify that the average frictional contribution of an inner atom is no more than 10^{-4} that of an atom at the edge. Correspondingly, the total friction force is dominated by friction between the contact edges for contacts up to 10 μm in lateral size. We discuss the physical mechanisms of friction observed in SSL contacts, and provide guidelines for the rational design of large-scale SSL contacts.

Tribological properties of hydrogenated nitrile rubber in confrontation with hard particles under different axial loads

The influence of different axial loads on the tribological properties of Hydrogenated Nitrile Rubber (HNBR) under oil-based mud containing hard particles is studied through experimental and theoretical approaches. Friction and wear tests were performed by using pin-on-disc friction pairs. The findings indicate that the tribological properties of HNBR vary with axial load and wear time. The total friction coefficient can be divided into an adhesion term, a hysteresis term and an abrasive term through the analysis of tribological mechanism. The hysteresis term is due to micro-strain on the HNBR surface and overall deformation of the HNBR specimen. The variation of tribological properties can be well explained through the above theory and the hysteresis term is the main influence factor.

Analysis of Chaotic Response of Frenkel-Kontorova-Tomlinson Model

The Frenkel-Kontorova-Tomlinson (FKT) model represents mechanical systems in which the atomic smooth surfaces of two bodies slide against each other. The model is very sensitive to changes of the system parameters, and ranges from simple stable harmonic to chaotic solutions. The design of the model between two bodies for the dynamic problem, following the network method rules, is explained with precision and run on standard electrical circuit simulation software. It provides the phase diagrams of atom displacement for each atom and the total friction force by the summation of all the atom displacements. This article is focused on studying the effect of the selected time step on the result and in the lack of sensitivity of Lyapunov exponents to assess chaotic behaviour.

Price discovery in a matching and bargaining market with aggregate uncertainty

We introduce aggregate uncertainty into a Rubinstein and Wolinsky (1985)-type dynamic matching and bilateral bargaining model. The market can be either in a high state, where there are more buyers than sellers, or in a low state, where there are more sellers than buyers. Traders do not know the state. They randomly meet each other and bargain by making take-it-or-leave-it offers. The only information transmitted in a meeting is the time a trader spent on the market. There are two kinds of search frictions: time discounting and exogenous exit. We find that as the search frictions vanish, the market discovers the competitive price quickly: the prices offered in equilibrium converge in expectation to the true-state Walrasian price at the rate linear in the total search friction. This rate is the same as it would be if the state were commonly known.

An Experimental Study on Factors Affecting the Friction Coefficients in Electroplated Bolts

Electroplated bolts have been widely used in the automotive industry for many decades. In the present work, for the first time, the role of each layer of the bolt coating (i.e., electroplating, passivation layer, and topcoat layer) on the coefficient of friction of a bolted joint were experimentally and systematically investigated. The coefficient of total friction (μ tot), coefficient of friction between threads (μ th), and coefficient of friction between bearing surfaces (μb ) were calculated by a torque–tension testing system and compared under different experimental conditions. It was found that the μ th, μb , and μ tot on pure Zn plating was slightly different from that on Zn-Ni alloy plating; the black passivation layer had lower μ th, μb , and μ tot than the clear passivate when topcoats were applied; and the topcoat played a dominant role in reducing the μ tot. Other factors including washer material, nut plating, and heat treatment were also studied. Results showed that the aluminum washer gave a dramatically higher μb than the steel washer. The tested plating layers of Zn, Ni, and Zn-Ni alloy on the nut did not significantly affect the μ th. Tested bolts could withstand heat up to 182 °C for 1 h. Higher temperature or longer heating time increased μ th, μb , and μ tot. These findings will increase the understanding of the factors that affect the friction coefficients in electroplated bolts and will help to better design bolted joints.

Developed diamond wire sawing technique with high slicing ability for multicrystalline silicon wafers

ABSTRACT In this work, various reciprocating cycle times of 80, 160, 240, and 320 sec in the diamond wire sawing (DWS) process were adjusted to improve the slicing ability in solar industry. During the same slicing time, the long reciprocating cycle time had less velocity inverse points in comparison with the short reciprocating cycle time. Consequently, the total friction force of the slicing wires used in the DWS process with the short reciprocating cycle time was larger than that of the slicing wires used in the DWS process with the long reciprocating cycle time. It was noting that the lower diamond consumption and better slicing ability in the DWS process with a reciprocating cycle time of 320 sec was obtained in comparison with a reciprocating cycle time of 80 sec. However, since the diamond grits with too high slicing strength to collide the Si material, the serious damages were form on the wafer edge. Therefore, the edge chipping increased to 1.63% as the reciprocating cycle time of 320 sec. The highest mass production yield of 94.22% and the lowest edge chipping of 1.23% for the DWS-sliced mc-Si wafers were obtained as the suitable reciprocating cycle time was 240 sec.

Multi-objective Optimization of Machine Tool Spindle-Bearing System

In this study, a multi-objective optimization is performed for the design of a spindle-bearing system based on particle swarm optimization (PSO). Multiple objectives, such as natural frequencies, static stiffness, and total friction torque are considered in this design optimization. Bearing preload and bearing locations are selected as the design variables. Pareto-optimal solutions are used to support the selection of optimal values of the design parameters. A finite element model is established for the analysis and design of the spindle system with four angular contact ball bearings. Two optimization processes are performed with the PSO technique. The first process involves the first two natural frequencies and friction torque of the spindle, whereas the second process focuses on the spindle’s static stiffness and friction torque. The simulation results show noticeable improvement in the objectives compared with those of the primitive spindle. The experiments conducted on an actual spindle system fabricated with the optimal design demonstrate the benefits of the optimal design. The proposed design method is expected to be very useful in the design optimization of machine tool spindle systems subjected to various customer-oriented objectives.

Changes in Total Friction in the Engine, Friction in Timing Chain Transmissions and Engine Emissions Due to Adding TiO2 Nanoparticles to Engine Oil

The main aim of the study was to evaluate changes in total friction in the engine, friction in its timing chain transmissions and engine emissions resulting from adding TiO2 nanoparticles to engine oil. The applicable engine oils and factors affecting their features were discussed. The drive from the crankshaft to the camshaft in an internal combustion engine is usually carried out by means of a cogged belt transmission or a chain transmission when high mileage is required without service operations. The engine performance of analyzed SI engine was obtained from the literature. The dependency of engine emission on engine operating speed was obtained using data from tests of a very similar engine under standard test conditions described in the literature. The changes in engine characteristics caused by varying internal friction conditions were estimated using the engine performance characteristic and engine friction losses, particularly in valve train chain transmission. The friction in such a chain transmission operating under oil lubrication conditions can be determined using its analytical model and measured friction torque occurring between the chain rollers and the pins. The analytical model was developed using the finite element method and additional mathematical formulas. The proposed model allowed obtaining weight and mass inertial moments of all valve train transmission components. The friction torque in contact zone chain roller–pin was obtained using the elaborated physical pendulum method for different conditions of lubrication, namely, without oil, with pure engine oil, and with engine oil containing TiO2 nanoparticles. The engine oil SAE 10W-40 with/without dispersed 2% wt. TiO2 nanoparticles was used during tests. The preparation process of studied oils was described. The resulted values of the friction torque in the chain transmission operating in different conditions of lubrication and changes in engine emission have been presented for tests before and after addition of TiO2 nanoparticles into engine oil. During the measurements it was observed that the addition of 2% TiO2 nanoparticles into engine oil reduced the total friction losses by 7–7.7%. Additionally, it was demonstrated that the timing drive and valve train generate about 14.4–18% of overall engine friction losses. Based on the results obtained from a comparative analysis of emission in the other engine with similar power characteristics, the mentioned total friction losses can change the emission of the following compounds in the analyzed SI engine: 17–19% for CO, 8–9% for CO2, 13–17% for NOx, and 12–16% for HC. Such changes were dependent on the engine speed. The smallest changes in engine were registered for the rotation speed of 2500 rpm. The oil consumption in the engine and its impact on the PM emission was estimated. The additional arrangements facilitating the extrapolation of the obtained friction results to the cases of using other oils and the method of measuring the PM emission on the test stand were proposed.

Modeling Surface Riblets Skin Friction Reduction Effect with the Use of Computational Fluid Dynamics

Towards the minimization of fuel consumption and aicraft emissions reduction, many disruptive technologies have been proposed in aviation industry regarding the improvement of aircraft aerodynamic performance. Among others, these technologies involve innovative passive and active flow control methodologies and techniques. A passive flow control methodology which is studied in the current work is the implementation of riblets, which are inspired by shark skin morphology, on a NACA 0012 airfoil. The main purpose of riblets is to alter the boundary layer characteristics near the wall region in such a way that the total skin friction decreases, resulting in an overall drag reduction of the aircraft with a straightforward impact on fuel consumption and thus emissions. The riblets are implemented in the Reynolds Averaged Navier Stokes equations with appropriate source terms in the turbulent dissipation transport equation. Two turbulence models are used, the k-? SST linear eddy viscosity model and the Baseline Reynolds Stress model which also uses the transport equation of the specific rate of turbulence dissipation (?). The computational results are compared with available experimental data of NACA 0012 with surface riblets attached. Drag and skin friction coefficients are presented for various angles of attack and the maximum potential benefit from riblet use is evaluated regarding aerodynamic performance and consequently reduction of emissions and fuel consumption.

The effect of contact friction forces on the stress - strain state of an inclined base during the construction of buildings on complex terrain

The paper considers the interaction of contact friction forces in the system “base - inclined foundation - holding structure” and their influence on the stress-strain state of the soil base in the zone of the foundation structure’s adjacency to the holding structure. The main features of the contact friction forces’ distribution, the places of their application and the calculation algorithm are determined. The design scheme of the inclined foundation is developed taking into account the occurrence of a generalized total friction force. Based on the obtained dependences, the additions and refinements to the existing methodology for calculating foundations on an inclined soil base using a variable stiffness coefficient have been made.

Discrete analytical model for lateral mechanical behavior of cable-saddle system in suspension bridges

AbstractFrictional resistance, typically provided by the bottom and sides of saddle, is essential for counterpoising unbalanced cable tension between adjacent spans. In most practices, however, the friction from the saddle sides is ignored due to the lack of an effective calculation method of lateral forces, giving rise to serious anti-slip issues, especially for multi-tower suspension bridges. For this reason, the lateral forces between the main cable and saddle are studied in this paper. A similar formula of lateral force in specification is first investigated to reveal its theoretical basis and limitations. Considering each cable wire as an individual discrete body, an analytical model with recursive algorithm is then developed, which allows to calculate the contact forces layer by layer. Based on this, the effects of possible errors are quantified, and the sensitivity of lateral forces to key parameters, such as friction coefficient, extra pressure, arrangement and diameter of the wires, is subsequently discussed in detail. The results show that the existing formula evolved from the Janssen theory is insufficient for anti-slip assessment of the main cable. The transverse gap of saddle trough has a limited increase effect on the lateral force. As the wire arrangement widens, the lateral force grows rapidly and then approaches a certain value. The lateral force is negatively related with the friction coefficient, and the extra pressure can create great yet regular influence on the distribution of lateral pressure. Finally, the Taizhou Yangtze River Bridge is taken as a case example for an application of the proposed model. It is found that 32.2% of the total friction comes from the lateral friction when two vertical friction plates are used, confirming that the anti-slip capacity of cable-saddle system can be greatly improved by adequately utilizing the lateral friction.

Characterization of a Microscale Superlubric Graphite Interface.

Direct characterizations of the two component surfaces of a solid-solid interface are essential for understanding its various interfacial mechanical, physical, and electrical behaviors. Particularly, the fascinating phenomenon termed structural superlubricity, a state of nearly zero friction and wear, is sensitively dependent on the interface structure. Here we report a controllable pick-and-flip technique to separate a microscale contact pair for the characterization of its two component surfaces for van der Waals layered materials. With this technique, the interface of a graphite superlubric contact is characterized with resolution from microscale down to the atomic level. Imaging of the graphite lattice provides direct proof that this superlubric interface consists of two monocrystalline surfaces incommensurate with each other. More importantly, the structure-property relationship for this contact is investigated. Friction measurements combined with fully atomistic molecular dynamics reveal that internal structures [internals steps, pits, and bulges buried underneath the topmost graphene sheet(s)] have negligible contribution to the total friction; in contrast, external defects lead to a high friction. These results help us to better understand the structure of highly oriented pyrolytic graphite and the fundamental mechanisms of structural superlubricity, as well as to guide the design of superlubricity-based devices.

On the processing properties and friction behaviours during compaction of powder mixtures

ABSTRACT Iron-based powder mixtures were prepared by dry and wet mixing method. The friction properties during compaction were tested by measuring the internal and external friction coefficient. The test results showed that the wet mixing process could realise the homogeneity of lubricant and improve the processing properties of the powder mixtures. With 0.6 wt-% lubricants, wet mixing powder mixtures have a flow rate of 29.6 s/50 g, an apparent density of 3.18 g cm–3, a repose angle of 35.5°, and the friction coefficient during the compaction is 0.223. An equation to calculate the total (both internal and external) friction forces during the compaction process is proposed, and then the factors influencing the friction coefficient during compaction were quantitatively analysed.