Frictional Work Research Articles

Relative displacement of the tendon and subsynovial connective tissue using ultrasound captures different phenomena than mechanical tendon shear

The most common finding in carpal tunnel syndrome is fibrosis and thickening of the subsynovial connective tissue (SSCT). While the SSCT mediates tendon gliding in the carpal tunnel, this histopathology suggests excessive shear forces are involved in injury development. Ultrasound is often used to quantify relative motion between the finger flexor tendons and SSCT as an indirect measure of “shear-strain”; however, the underlying mechanical implications of using ultrasound are not well understood. The middle flexor digitorum superficialis (FDS) tendon of 8 cadavers was moved in a combination of 2 wrist postures (neutral, flexed), 3 velocities (5, 10, 15cm/s), and 3 forces (10, 20, 30N) to assess ultrasound-based FDS-SSCT relative displacement while simultaneously quantifying tendon frictional work in the carpal tunnel. We found independent velocity effects for both constructs (relative displacement, ηp2=0.862, p<0.05; frictional work, ηp2=0.937, p<0.05), indicating ultrasound captured viscous gliding resistance owing to the gel-like inter-fibrillar matrix of the SSCT. FDS-SSCT relative displacement also increased independently in a flexed wrist posture (p=0.010) and with greater tendon force (p=0.036), likely representing strain dependant changes with tendon position. Alternatively, we found a significant posture×force interaction on tendon frictional work (p<0.01), due to, in part, greater surface friction against the transverse carpal ligament with a flexed wrist and high force. While ultrasound provided a different interpretation compared to direct measurement of mechanical shear, FDS-SSCT relative displacement successfully localized viscoelastic shear-strain, which may help elucidate the role of hand motion in SSCT pathology and CTS.

Comparison of Conventional Sprocket Drum and Sprocket Drum with Modified Design

Abstract Seats in conventional sprocket drums are symmetrical. Due to the set general direction of sprocket drum revolutions resulting from the direction of rock transport, the wear of the seat bottoms and teeth flanks may be reduced by introducing the asymmetry of the profile of the sprocket drum seats. The proposed modification of sprocket drum seats’ profile consists of inclining the seat bottom towards the expected direction of the basic drum revolutions. The work compares the loads on the seats and teeth of a conventional drum with its profile conforming to the standard to a modified drum with an asymmetric profile of seats. For the general direction of sprocket drum revolutions, the maximum values of all forces are higher for a standard drum than for a modified drum. The profile asymmetry substantially shortens the friction path of the horizontal link front torus on the seat bottom and relative total friction work on the seat bottom and lessens the occurrence probability of the slide of the horizontal link rear torus on the tooth flank. The modification of the profile causes also the asymmetric wear of link joints. The total relative friction work is considerably reduced in the front joint as compared to a conventional drum, and the total relative friction work in the rear joint is increasing at the same time.

Numerical Research on Tribological Performance of Textured Liner Surface Under Different Combustion Modes

With the increasingly stringent requirements on energy saving and environmental-friendly for internal combustion (IC) engine, new concepts like novel combustion mode and surface texturing technology have emerged. In order to have deep understanding about the application effects of surface texturing into IC engine with new combustion mode, a mixed lubrication calculation model considering surface textures on cylinder liner together with different combustion modes has been built in the present work based on a four-cylinder diesel engine. The numerical research was conducted on the change of the surface tribological performance of textured cylinder liner under different combustion modes. The simulation results indicate that compared with the conventional combustion (CC) mode, the combustion phase of premixed charge combustion ignition (PCCI) mode and retarded injection (RI) mode varies and their in-cylinder peak pressure is different at the beginning of power stroke due to different injection strategies applied, which lead to significant differences between piston ring radial working loads. Near TDC, the mixed lubrication duration of PCCI and RI mode increases slightly in comparison to that of CC mode, and these three boundary lubrication durations are almost same. However, the thickness of lubricant film between friction pair of three modes is quite different, resulting in their different tribological properties. Among these parameters, the dimensionless total friction force (DTFF) and the dimensionless friction work of PCCI mode increase by 82.37% and 18.41% at most, respectively, while those of RI mode decrease by 36.50% and 12.45% at most, respectively, compared with the same parameters of CC mode. Therefore, the variations in tribological property of the textured cylinder liner–piston ring (CLPR) with different combustion modes should not be ignored.

Elastomer vs. ceramic in cyclically loaded contact: What wears less?

Here we compare the wear performance of silica and polyurethane in a vacuum gripper. The problem is modeled numerically by evaluating the energy dissipated at the interface, and experimentally by examining surface damage in contact subjected to cyclic normal loading. In the numerical model, the energy dissipated during unloading is found to be negligible with respect to that of loading. Changing the contact geometry has a good effect in terms of frictional work reduction, but this is not as significant as the effect obtained by changing the material. Replacing silica with polyurethane reduces the frictional work by a factor of at least 20. The latter finding is qualitatively validated in experiments.

Suggested Research Method for Testing Selected Tribological Properties of Friction Components in Vehicle Braking Systems

Abstract The braking system is one of the most important systems in any vehicle. Its proper functioning may determine the health and life the people inside the vehicle as well as other road users. Therefore, it is important that the parameters which characterise the functioning of brakes changed as little as possible throughout their lifespan. Multiple instances of heating and cooling of the working components of the brake system as well as the environment they work in may impact their tribological properties. This article describes a method of evaluating the coefficient of friction and the wear speed of abrasive wear of friction working components of brakes. The methodology was developed on the basis of Taguchi’s method of process optimization.

Slosh Damping Caused by Friction Work Due to Contact Angle Hysteresis

The damping ratio of low-gravity sloshing induced by the friction work due to contact angle hysteresis is calculated using a newly developed semianalytical sloshing analysis method for arbitrary axisymmetric tanks. The damping ratio is estimated for the first mode for the case with small contact angle and its variation, as a fundamental study for propellant sloshing. First, the relation between the friction force and the change in the contact angle caused by contact angle hysteresis is derived from the equilibrium among the friction force and the three surface tensions. Next, the virtual work done by the friction force is calculated to determine the nonlinear damping term to be introduced into the modal equation for sloshing. Physical considerations are made for the dependencies of the damping ratio on the Bond number and filling level. Although the damping term arises from the second-order small term in the friction force, the damping ratio can reach the same order as the viscous damping ratio for low Bond numbers because, due to the hysteresis nonlinearity, the friction damping ratio increases with decreasing Bond number more markedly than the viscous ratio.

Analysis of vorticity dynamics for hump characteristics of a pump turbine model

Conventional parameters based on CFD methodology for the investigation on hump characteristics of a pump turbine cannot reflect the dynamic interaction mechanism between the runner and the fluid. This research presents a dynamic interaction mechanism of a pump turbine operating in the hump region. First, vorticity dynamic parameters were obtained based on the theory of vorticity dynamics. Second, 3-D unsteady flow simulations were performed in a full pump turbine model using the SST k-ω turbulence model, and numerical results have a good agreement with the experiments. Then, analysis was carried out to determine the relation between the vorticity dynamic parameters and hump characteristics. The results indicate that the theory of vorticity dynamics has an advantage in evaluating the dynamic performance of a pump turbine. The energy transfer between the runner and the fluid is through vorticity dynamic parameters-pressure and friction terms, in which the pressure term accounts for the most. Furthermore, vortex generation mainly results from the skin friction. Combining vorticity dynamic analysis with the method of Q-criterion indicates that hump characteristics are related to the reduction of the surface normal pressure work and vortex motion on the suction surfaces close to the leading edges in the runner, and the increase of skin friction work in the stay-guide vanes.

On the influence of conformity on wheel–rail rolling contact mechanics

The aim of this work is to assess the effects of conformity on local contact related quantities at the wheel–rail interface such as traction distributions, subsurface stresses and frictional work distributions. For this purpose conformal contact analyses are carried out by means of Finite Element (FE) models, and also with the exact rolling contact theory approach developed by Kalker, which has been appropriately adapted by the authors in order to take into account some of the effects of conformity. On the other hand, equivalent cases are analysed without taking into account the effects of conformity. In this way, the validity of the hypothesis of non-conformity is evaluated in different cases with varying degrees of conformity.

Application and Control Method of Electromagnetic Synchronizer for Double Rotor Motor Power Coupling System

On the double rotor motor power coupling system existing now, electromagnetic coupling of the inner motor is the only way to transmit engine power to drive axle. And this leads to the low transmission efficiency when the vehicle is driven by the engine. Aiming at this issue, this paper proposes the improvement measure, which is to add the electromagnetic synchronizer between the input shaft and the output shaft. According to the thinking of this measure, the paper analyzes the operating process of the electromagnetic synchronizer. Then using quadratic optimal control theory, the optimal PID control method is designed to control the duty ratio of the electromagnetic synchronizer driving voltage. In order to test the validity of the method, the paper builds the simulation model in Matlab/Simulink software. The simulation results indicate that the optimal PID control method can effectively control the work process of electromagnetic synchronizer. It can achieve the balance between frictional work and longitudinal jerk, and decrease the impact reasonably when the electromagnetic synchronizer switching its state.

Effects of curve radius and rail profile on energy saving in heavy haul achieved by application of top of rail friction modifier

Energy saving achieved by application of top of rail (TOR) friction modifier (FM) in heavy haul are modeled, and the effects of curve radius and rail profile on the energy saving are discussed. A vehicle model for a C70 freight car running on the track of a heavy haul line was established. The coefficient of friction and Kalker coefficient were adjusted to simulate the creepage/force relationship when the TOR FM is applied to the wheel/rail interface. Friction work is used to represent the energy dissipation due to wheel/rail creepage. Energy saving achieved by applying TOR FM was calculated. The energy saving was studied under different operating conditions, and the effects of track curve radius and rail profile were studied. It is found that the curve radius of the track has significant influence on the energy saving. The energy saving was also found to behave differently on new and worn rails. The dramatic increase of lateral creepage on new rail when FM is applied and the decrease of the difference of wheel rolling radius when the rail profile changes from new to worn were found to be the main reasons that cause the difference.

Study of kinetic performance effect on wheel and rail wear using computer simulation

The study object is a “wheel - rail” system. The subject is the computer simulation of the system elements wear. The work objective is to investigate the wheel and rail wear dependence on the kinetic performance parameters. The problems solved here are analysis of the earlier proposed mathematical functions describing the kinetic performance for the presence of extremes, the functional behavior (growth, decrease, monotonicity, and unimodality, etc.) in various parameter ranges; implementation of the computer simulation of the wheelpair movement by rail with the quantitative estimation of the wheel and rail wear with various kinetic performance parameters; to determine qualitative influence patterns of the kinetic wear performance. The simulation is fulfilled by the software package “Universal Mechanism”. As a result, values of various characteristics related to wear (power, total and specific friction work) under different conditions of the kinetic friction performance are obtained. The conclusions are as follows. The kinetic friction performance parameters must be considered as they can significantly affect the wear within the range of the actual operating conditions in the course of the computer simulation. Under some conditions, there are cases when an increase in the friction coefficient is accompanied by a decrease in depreciation. It is proposed to continue the research in two main areas: determining the influence patterns on the kinetic friction performance and wear of the multiple actual factors, and studying the dynamic (at variable slip velocity) feature of friction effect on the parameter wear through the same procedure.

Power dissipation modeling in wheel/rail contact: Effect of friction coefficient and profile quality

This work investigates the power dissipation in a wheel/rail system through friction work modeling. In order to identify the effect of the friction coefficient on the power dissipation in the wheel/rail contact, several simulations were performed using a three-dimensional multibody model of a railway vehicle implemented in the software package VI-Rail Adams. The power dissipation and wear rates of the inner and outer wheels of the first bogie of the vehicle running over a curve of a metro line were calculated for different friction coefficients varying from 0.2 to 0.7. The total frictional work was obtained from the resultant force and slip in a reference point. The wear was also analyzed according to the Tγ method including the spin, in combination with Kalker׳s simplified theory Fastsim, assuming that the wear is proportional to the frictional work. Two sets of rail and wheel profiles were studied in order to determine the effect of the profile׳s quality on the power dissipation and wear rates. To this end simulations and power calculations were performed with a friction coefficient of 0.4.

Proper selection of cutting parameters and cutting tool angle to lower the specific cutting energy during high speed machining of 7050-T7451 aluminum alloy

Cleaner production and sustainability are of vital importance in the field of machining processes where great amount of energy is consumed. Reducing the energy consumption during machining process can significantly improve the environmental and economical performance of manufacturing systems. To achieve this, calculation of energy consumption during the metal cutting process is required. This paper investigates the specific cutting energy consumption for the serrated chip formation of 7050-T7451 aluminum alloy in high speed machining. The cutting energy consumption during serrated chip formation mainly includes such three components as plastic deformation energy in the primary deformation zone, friction work between the tool–chip interface and kinetic energy of the flowing chip. The predictive models of these three energy components are developed for orthogonal cutting mode, and the influences of cutting speed, undeformed chip thickness and tool rake angle on the cutting energy consumption are revealed. Meanwhile, the theoretical energy consumptions under different undeformed chip thicknesses are validated with the high speed orthogonal cutting experiments of 7050-T7451 aluminum alloy. Based on the research results, when high cutting speeds are applied in order to improve the machining efficiency, large positive rake angle tools and large undeformed chip thicknesses are recommended if the rigidity of the machining system and the machining surface quality can be guaranteed.

Relaxation damping in contacts under superimposed normal and torsional oscillation

It was recently shown that if a contact of two purely elastic bodies with no sliding is subjected to oscillations in normal and tangential directions, a kind of damping occurs due to relaxation of tangential stress in areas of intermittent contact, despite the absence of sliding and corresponding frictional work. In the present paper we show that the same mechanism acts in contacts with superimposed normal and torsional oscillations. A closed-form solution for the torsional and combined (torsional/tangential) relaxation dissipation for a contact of arbitrary bodies of revolution is presented.

Analysis of tribotechnical characteristics of self-fluxing coating under rolling and sliding at non-stationary loading

This article discusses the possibility of self-fluxing nickel-based alloy for the friction pairs operating under rolling with sliding. The aim of research was to determine the kinetics of changes in the physical and mechanical, anti-wear and anti-friction properties of the sprayed coating of self-fluxing powder PG-AN9 among transmission oil. The method of assessment of tribotechnical properties of the coating is proposed in the start-up mode at step increase in load to the appearance of the first signs of the setting of the contact surfaces. It was established an increase of the normal operation period in sprayed coatings at 5,42 times for the coating thickness increases to 1,2 mm due to effective lubricating effect, low friction coefficient, reducing the specific friction work and reducing the degree of surface coating layers plasticizing by the lubricant components. The results can be used by specialists in the field of repairing and rebuilding worn parts of machines and mechanisms.

Study on the penetration performance of concept projectile for high-speed penetration (CPHP)

Two-group penetration tests of Concept Projectile for High-speed Penetration (CPHP) are carried out with striking velocity ranging from 1130 m/s to 1650 m/s. Almost all projectiles are integral after penetration except the one at striking velocity 1650 m/s. The maximum dimensionless Depth of Penetration (DOP) reaches 78.9 at striking velocity 1415 m/s with the concrete strength as 33.4 MPa. It further confirms that CPHP has excellent structural stability and penetration performance into concrete target at high striking velocities. The penetration performances of CPHP made of different materials are also compared. It indicates that the strength and ductility of material jointly control the penetration performance of CPHP. The mass loss of CPHP distributes not only in its nose but also in its shank. The CPHP nose still keeps ogival and the surface of CPHP shank recedes inward. Furthermore, the mass loss mechanism is studied by metallographic observation. It indicates that the heat transformed from frictional work between target and projectile is the main cause of Heat Affected Zone (HAZ), and the peeling of molten surface layer is the main cause of mass loss. Several White Narrow Bands (WNBs) in CPHP nose tip contribute minor mass loss due to its rare number and limited dimensions. Finally, the analytical model for DOP of CPHP was derived. The model prediction is validated by the available experimental result.

A novel Lagrangian approach for the stable numerical simulation of fault and fracture mechanics

The simulation of the mechanics of geological faults and fractures is of paramount importance in several applications, such as ensuring the safety of the underground storage of wastes and hydrocarbons or predicting the possible seismicity triggered by the production and injection of subsurface fluids. However, the stable numerical modeling of ground ruptures is still an open issue. The present work introduces a novel formulation based on the use of the Lagrange multipliers to prescribe the constraints on the contact surfaces. The variational formulation is modified in order to take into account the frictional work along the activated fault portion according to the principle of maximum plastic dissipation. The numerical model, developed in the framework of the Finite Element method, provides stable solutions with a fast convergence of the non-linear problem. The stabilizing properties of the proposed model are emphasized with the aid of a realistic numerical example dealing with the generation of ground fractures due to groundwater withdrawal in arid regions. A numerical model is developed for the simulation of fault and fracture mechanics.The model is implemented in the framework of the Finite Element method and with the aid of Lagrange multipliers.The proposed formulation introduces a new contribution due to the frictional work on the portion of activated fault.The resulting algorithm is highly non-linear as the portion of activated fault is itself unknown.The numerical solution is validated against analytical results and proves to be stable also in realistic applications.

A versatile method in the space domain to study short-wave rail undulatory wear caused by rail surface defects

This paper examines the development of short-wave undulatory wear caused by vehicles running over defects on rail surfaces. The track model used was obtained using a Rational Fraction Polynomial (RFP) method modified using genetic algorithms. This produces an extremely accurate and simple wheel-track model requiring minimum computational times. As corrugation formation simulations in the time domain require such a large number of thousands of wheelset passovers, it was essential to develop such a simple but precise model. A non-linear Hertzian spring was used to study the interaction between wheel and rail. Wear is considered to be proportional to the friction work, as some other authors assume for this type of problems, emerging upon contact. This model has been validated by comparing its results with experimental results of undulatory wear measured on a track. The developed tool enables the evolution of rail wear to be studied for different ride conditions that are not affordable to study experimentally. Some of the factors studied in the paper are: the influence of the frequency at which the partially worn rail surface profile is updated during the wear evolution simulation; the influence of the train speed dispersion that usually exists around the nominal speed; the influence of the position of the rail defect within a span between two sleepers; and the influence of the train׳s nominal speed.

Frictional effects in biomimetic scales engagement

Scales engagement can contribute significantly to nonlinear bending behavior of elastic substrates with rigid biomimetic scales. In this letter, we investigate the role of friction in modulating the nonlinearity that arises due to self-contact of scales through an analytical investigation. We model the friction as dry Coulomb's type friction between rigid links and the substrate is taken to be linear elastic. Our results reveal that frictional effects give rise to two possible locking mechanisms, namely static friction lock and kinetic friction lock. These locks arise due to a combination of interfacial behavior and geometry. In addition to these extremes, the frictional behavior is found to increase the stiffness of the structure. This dual nature of friction which influences both the system operation and its terminal limit results in the maximum relative frictional work to lie at intermediate friction coefficients and not at the extremes of the frictional limits.

Prediction of the Nuclear Fuel Rod Abrasion in the Probability Sense

The paper deals with the upper and lower limits estimation of the friction work and fretting wear in the contact of nuclear fuel rods with fuel assembly (FA) spacer grid cells. The friction work is deciding factor for the prediction of the fuel rod cladding abrasion caused by FA vibration. Design and operational parameters of the FA components are understood as random variables defined by mean values and standard deviations. The gradient and three sigma criterion approach is applied to the calculation of the upper and lower limits of the friction work and fretting wear in particular contact surfaces between the fuel rod cladding and some of spacer grid cells. The fuel assembly vibration is excited by pressure pulsations of the cooling liquid generated by main circulation pumps in the coolant loops of the NPP primary circuit. The method is applied for hexagonal type nuclear fuel assembly in the VVER type reactors.