Change In Friction Coefficient Research Articles

Numerical and experimental investigation of Johnson–Cook material models for aluminum (Al 6061-T6) alloy using orthogonal machining approach

This research focuses on the study of the effects of processing conditions on the Johnson–Cook material model parameters for orthogonal machining of aluminum (Al 6061-T6) alloy. Two sets of parameters of Johnson–Cook material model describing material behavior of Al 6061-T6 were investigated by comparing cutting forces and chip morphology. A two-dimensional finite element model was developed and validated with the experimental results published literature. Cutting tests were conducted at low-, medium-, and high-speed cutting speeds. Chip formation and cutting forces were compared with the numerical model. A novel technique of cutting force measurement using power meter was also validated. It was found that the cutting forces decrease at higher cutting speeds as compared to the low and medium cutting speeds. The poor prediction of cutting forces by Johnson–Cook model at higher cutting speeds and feed rates showed the existence of a material behavior that does not exist at lower or medium cutting speeds. Two factors were considered responsible for the change in cutting forces at higher cutting speeds: change in coefficient of friction and thermal softening. The results obtained through numerical investigations after incorporated changes in coefficient of friction showed a good agreement with the experimental results.

Experimental study on the location of gas drainage pipeline leak using cellular automata

In recent years, researches on leak detection and location of oil and gas pipeline have attracted considerable attention. A variety of methods have been proposed, including a pipeline-model-based method that predicts pressure distribution along the pipeline and locates the leak through the pressure and flow rate signal on both ends of the pipeline. At present, the most widely used pipeline-model-based methods include the pressure gradient (PG) method and the average friction coefficient (AFC) method. Nevertheless, the pressure gradient PG method which ignores the influences of friction coefficient, temperature, pipe diameter and other factors on the pressure distribution along the pipeline considers the pressure to be linear. The average friction coefficient (AFC) method assumes the friction coefficient and pipe diameter to be constant, yet gas pipeline is nonlinear and complex. Additionally, other uncertain factors such as changes in medium components and working conditions increase the difficulty of accurately describing the pipeline. To solve this problem, this study proposed a cellular automata (CA) model to locate the leak of main gas drainage pipeline. In the cellular automata model, the friction coefficient and diameter change are discretely distributed along the pipeline. The pressure distribution along the pipeline is predicted using flow rate and pressure parameters at both ends of the pipeline. This method assumes a continuous change in the pipeline fluid over time and space, thus improving the location accuracy.

Determining friction coefficient between the base cylinder of rotary screw propulsion unit and various ice types in different daylight surface

Statistical data processing results of friction coefficient change between steel base cylinder of rotary screw propulsion unit and ice of different surface roughness are considered in the article. Experimental values of ice surface roughness complex criterion are given. It is also established that in actual operating conditions the basic factor affecting the friction coefficient change of the base cylinder on ice is represented by the processes connected with the plastic yield of the ice daylight surface irregularities. At this the adhesive component of friction force while operating on rough ice did not exceed the 20% value.

THE INFLUENCE OF REDUCING TEMPERATURE ON CHANGING YOUNG’S MODULUS AND THE COEFFICIENT OF FRICTION OF SELECTED SLIDING POLYMERS

For the polymeric materials, changing of the temperature causes changes in mechanical and tribological properties of sliding pairs. The goal of the present study was to determine the change in Young's modulus and kinetic friction coefficient depending of the temperature. Three thermoplastic polymers, PA6, PET and PEEK, were tested. These materials cooperated in sliding motion with a C45 construction steel disc. As part of the experiment, the Young's modulus tests (by 3-point bending method) and kinetic friction coefficient studies (using pin-on-disc stand) were carried out. The temperature range of mechanical and tribological tests was determined at T = –50°C±20°C. Comparing the results of mechanical and tribological properties, there is a tendency to decrease the coefficient of friction as the Young's modulus increases while reducing the working temperature.

The Application of filled PTFE material in the end sealing of scroll compressor

The feasibility of filling PTFE composite material as the material of the top seal of scroll compressor was studied. Taking a certain type of scroll compressor as an example, had established a mathematical model of sealing strip force, and analysed the change regularity of sealing strip load. The PES, PEEK, the pure PTFE and the Filled PTFEwere respectively matched with the HT250. According to the running parameters of scroll compressor, had designed test conditions, and had carried out the simulation experiment in the end wear testing machine. According to the experimental results, analyzed the four materials of the tribological properties. The volume wear rate, friction coefficient and temperature change of PTFE composites were measured. The morphology of the friction surface and the transfer of composites were observed by scanning electron microscopy. The results show that when the experimental conditions are 200N and 2000r/min, the friction coefficient of friction pairs is less than 0.25, and the volume wear rate is 3.328 * 10−6. When the temperature increases, the friction coefficient has a rising trend, but it rises slowly. In addition, it is found by scanning electron microscope that when the temperature is above 120 degrees, the material will burn and the wear will be intensified. In summary, compared with the actual working conditions of scroll compressor, the PTFE material is used as the sealing strip material, and its friction and wear properties can basically meet the needs of the work

Properties of Coatings Based on Carbon and Nitrogen-Doped Carbon Obtained Using a Pulsed Vacuum Arc Method

Diamond-like carbon coatings on hard-alloy substrates, including coatings doped with nitrogen about 1.0 μm thick have been obtained using a pulse vacuum-arc method. Three types of coatings have been investigated: a carbon diamond-like coating (C), a carbon coating doped with nitrogen (C: N), and a composite coating based on (C: N + C) layers. The coatings have been annealed in atmospheric air at a temperature of 400°C. The tribological characteristics (wear resistance and friction coefficient change dynamics), the adhesion strength, and the microhardness of coatings in the initial state and after annealing have been studied. The composite coating consisting of C: N + C layers surpasses the constituent coatings in properties, both in the initial state and after annealing at a temperature of 400°C.

Remaining Lifetime Prediction for Reliability-based Dry Clutch Control

Increasing requirements for reliability of modern powertrainscan be achieved by predictive maintenance and reliabilitybasedcontrol based on lifetime prediction. This contributionpresents lifetime prediction for a dry clutch, being an essentialcomponent of automated manual transmissions. Modelbaseddevelopment of lifetime prediction requires knowledgeof dry clutch wear, which was identified in previous experiments.The derived wear model allows estimation of characteristicwear-dependent values, like friction lining materiallosses and friction coefficient changes. Based on these estimatedvalues the presented lifetime prediction was developedby fusing these estimated values into a health index (HI) describingthe systems healthiness. Furthermore, the remaininguseful lifetime (RUL) becomes predictable from observationsof health index trend using an exponential weightedmoving average. Eventually, the presented lifetime predictionwas implemented and tested on real-time operating hardwaresimilar to common transmission control units. In order tocontrol the system lifetime in normal operation, target trendsfor health index and predicted remaining useful lifetime weredefined. Based on trend deviations, a fuzzy-logic based controlstrategy was realized, which sets the optimization targetfor a reliability-based control. Thus, the optimization targetcan be varied between comfort-optimized or wear-optimizedclutch engagements. Finally, an outline of reliability-basedcontrol concepts is given.

A neurofuzzy controller for active front steering system of vehicle under road friction uncertainties

In this study, a neurofuzzy controller is proposed to improve vehicle handling in different road friction coefficients. This controller adapts itself to neutralize the effects of unpredictable changes in road friction coefficient on vehicle handling. This adaptive neurofuzzy controller can improve vehicle handling, manoeuvrability and path tracking. First a proportional-integral-derivative (PID) controller is proposed and tuned by using PSO (particle swarm optimization). Then, this tuned PID controller is applied to the vehicle system and training data is gathered. The next step is to train a fuzzy controller by importing thistraining data tothe ANFIS (adaptive neurofuzzy inference system) toolbox of MATLAB software. Then the trained fuzzy controller is applied to a vehicle that exploits AFS (active front steering system). This controller is able to adapt itself during manoeuvres, by using back propagation of error as a learning algorithm. Results show that neurofuzzy controller can improve handling of the vehicle in different road conditions, because neurofuzzy conteroller can adapt itself in unpredictable situations.

In-situ tribochemical formation of self-lubricating diamond-like carbon films

Diamond-like carbon (DLC) films were tribochemically formed from ambient hydrocarbons on the surface of a highly stable nanocrystalline Pt-Au alloy. A sliding contact between an alumina sphere and Pt-Au coated steel exhibited friction coefficients as low as μ = 0.01 after dry sliding in environments containing trace (ppb) organics. Ex situ analysis indicated that the change in friction coefficient was due to the formation of amorphous carbon films, and Raman spectroscopy and elastic recoil analysis showed that these films consist of sp2/sp3 amorphous carbon with as much as 20% hydrogen. Transmission electron microscopy indicated these films had thicknesses exceeding 100 nm, and were enhanced by the incorporation of worn Pt-Au nanoparticles. The result was highly wear-resistant, low-friction DLC/Pt-Au nanocomposites. Atomistic simulations of hydrocarbons under shear between rigid Pt slabs using a reactive force field showed stress-induced changes in bonding through chain scission, a likely route towards the formation of these coatings. This novel demonstration of in situ tribochemical formation of self-lubricating films has significant impact potential in a wide range of engineering applications.

Adjustable Tribological Behavior of Glucose-Sensitive Hydrogels.

Stimuli-responsive hydrogels have been considered to have various applications in numerous fields. In the present work, a double-network (DN) hydrogel has been synthesized. The copolymers of 2-acrylamide-2-methylpropane sulfonic acid (AMPS) and acrylamide (AM) [P(AMPS- co-AM)] are prepared as the 1st network and poly(acrylic acid) as the 2nd network. This DN hydrogel is sensitive to glucose by introducing the glucose-sensitive group phenylboronic acid to the network. The tribological properties of this glucose-sensitive DN hydrogel have been investigated using a universal mechanical tester (UMT-5). The tribological results show that the friction coefficient varied with the glucose solution. The friction coefficient increased to a maximum of 0.06, and finally decreased to 0.025 with the increase in the glucose concentration. An adjustable friction coefficient of the hydrogel, between 0.025 and 0.056, was achieved along with the change of lubricant. According to the tribological experimental results and the analysis of the DN structure, it can be deduced that a hydrated layer exists in the interface of the hydrogel. The hydrated layers consisting of water molecules are bounded with the hydrophilic group of the hydrogel network by hydrogen bonds. The change in the number of water molecules leads to the difference in the water content of the hydrogel, which further resulted in the various tribological properties. In addition, the hydrogel's mesh size also has an impact on the change in friction coefficient. In general, the adjustable friction of the hydrogel in a glucose environment is achieved.

Simulation of thermo-mechanical performance of pile geothermal heat exchanger (PGHE) considering temperature-depend interface behavior

Pile geothermal heat exchanger (PGHE) has attracted great interests in recent years, but some new challenges have emerged with its application, especially in understanding its thermo-mechanical behaviors. In this paper, based on the experimental data from a modified direct shear test, a finite element simulation model is developed to investigate the thermo-mechanical behavior of PGHE. The simulation model has been verified by an in-suit test. The influence of interface behavior, thermal loads, and soil properties on the PGHE’s thermo-mechanical behavior has been investigated. The results show that the changes in contact force and friction coefficient has to be considered in a comprehensive way in estimating the influence of thermal load on the bearing capacity of PGHE. Compared with the results without thermal loads, bearing capacity of PGHE shows a decreasing ratio of 8.7%, and an increasing ratio of heating is found to be 13.2%. In addition, the simulation results suggest that without head load imposed, at a certain depth, the axial stress has a linear relationship with the change of temperature, but when a head load is imposed, the linear relationship is only separately valid in each temperature region (heating or cooling). The thermo-mechanical performance of PGHE should be fully considered during the design stage, and this paper has the certain actual reference significance to engineering applications.

A Similarity Solution with Two-Equation Turbulence Model for Computation of Turbulent Film Condensation on a Vertical Surface

In this paper, we presented a similarity solution for turbulent film condensation of stationary vapor on an isothermal vertical flat plate. In this method, some similarity transformations are employed and the set of governing partial differential equations (PDE) of conservation together with transport equations of turbulent kinetic energy and dissipation rate are transformed into a set of ordinary differential equations (ODE). Calculated data for the flow field, velocity profile, wall shear stress, condensate film thickness, turbulent kinetic energy, rate of dissipation, and heat transfer properties are discussed. The effect of Prandtl (Pr) number was also investigated in a wide range of variations. The obtained results showed that at high Prandtl numbers, the velocity profile becomes more uniform across the condensation film and therefore, the kinetic energy of turbulence is reduced. Furthermore, the effect of change in Pr is negligible at high Pr numbers and consequently, the flow parameters have no significant change in this range. The friction coefficient changes linearly through the condensation film and the slope of friction lines diminishes slightly by the Pr number. The rate of turbulent kinetic energy increases linearly from the wall up to about 20% of condensate film, then rises asymptotically and converges to a constant value near the liquid-vapor interface. Also, the rate of turbulent dissipation grows linearly up to 40% of condensate film thickness and then increases slightly while it oscillates.

Study on surface modification of paper friction material by optimization design of clutch disk construction equipment for automobile AT

Automatic transmission mechanism of automobiles has progressed especially in passenger cars the ratio of AT vehicles has become extremely large. As a result, the production quantity of clutch discs, which is one of the parts of the transmission mechanism, is also increasing, and parts manufacturers pay great effort to secure production volume and quality. A lot of parts to transmit power are incorporated in the automatic transmission inside of the car. In the clutch disc, there are various sizes and shapes according to specifications such as transmission torque. In the clutch disc which is the object of this research, a friction material made of special paper as a base material is adhered to both sides of a base material (iron type sheet metal) grooving processing for improving cooling efficiency is done on the surface of the friction material There. Since the quality of the disc directly affects the driving performance of the car, the quality of the friction surface is strictly controlled, in particular. The technical problem of a wet process clutch disc (DISC) having an important function about shifting is securing of stability of the power transmission torque in the catalytic action of shifting performance gain and DISC aspect each other automatic. That stabilization of the DISC board thickness precision controls in particular the change of the skin friction coefficient and reduces a shock phenomenon at the time of the shifting; have technical grounds. In this research, we designed the method of construction equipment which improved quality and productivity of DISC.

Estimating coke fracture toughness using acoustic emissions and changes in coefficient of friction during scratch testing

Acoustic emission profiles generated during scratch testing of a range of metallurgical coke samples were recorded and linked to the concurrent energy release, dispersal or absorption on coke fracture or damage. Three different signatures were identified, which were based on the simultaneous measurement of acoustic and total energy release profiles, and these signatures could be correlated with both the microstructure and microtexture of the coke being traversed at the time. The acoustic emission signature for fracture or damage to the coke reactive maceral derived constituents (RMDC) was correlated to the rank of the parent coal or coal blend, with the signature number generally increasing with increasing rank. Conversely, the signature numbers did not vary with parent coal rank for fracture or damage to the inertinite maceral derived constituents (IMDC), with the majority of IMDC fractures associated with a release of mechanical energy. The incidence of the signature associated with a release of mechanical energy (type 1) became increasingly dominant from RMDC to RMDC-IMDC interfaces to IMDC. Conversely, signature types associated with a dispersal (type 2) or absorption (type 3) of mechanical energy become increasingly dominant from IMDC to RMDC-IMDC interfaces to RMDC. The findings suggest acoustic emissions recorded during scratch testing and their subsequent characterisation can be used to indicate the fracture toughness of a given coke. This study contributes towards a broader program of research to improve understanding of the factors which influence the strength of coke and its microtextural constituents and interfaces, and how this relates to the properties of the parent coals.

Wire Mesh Dampers for Semi-Floating Ring Bearings in Automotive Turbochargers: Measurements of Structural Stiffness and Damping Parameters

The current work introduces a new semi-floating ring bearing (SFRB) system developed for improving the rotordynamic and vibration performance of automotive turbochargers (TCs) at extreme operation conditions, such as high temperature, severe external force excitation, and large rotor imbalance. The new bearing design replaces outer oil films, i.e., squeeze film dampers (SFDs), in TC SFRBs with wire mesh dampers (WMDs). This SFRB configuration integrating WMDs aims to implement reliable mechanical components, as an inexpensive and simple alternative to SFDs, with consistent and superior damping capability, as well as predictable forced performance. Since WMDs are in series with the inner oil films of SFRBs, experimentally determined force coefficients of WMDs are of great importance in the design process of TC rotor-bearing systems (RBSs). Presently, the measurements of applied static load and ensuing deflection determine the structural stiffnesses of the WMDs. The WMD damping parameters, including dissipated energy, loss factor, and dry friction coefficient, are estimated from the area of the distinctive local hysteresis loop of the load versus WMD displacement data recorded during consecutive loading-unloading cycles as a function of applied preload with a constant amplitude of motion. The changes in WMD loss factor and dry friction coefficient due to increases in preload are more significant for the WMDs with lower density. The present work shows, to date, the most comprehensive measurements of static load characteristics on the WMDs for application into small automotive TCs. More importantly, the extensive test measurements of WMD deflection versus increasing static loads will aid to anchor predictions of future computation model.

The Importance of the Scalp in Head Impact Kinematics.

The best way to reduce the risk of head injury (up to 69% reduction) is to wear a helmet. In recent years, the improvement of helmet standard tests focused on reproducing realistic impact conditions and including the effect of rotational acceleration. However, less importance has been given to the development of a realistic headform. The goal of this work was to evaluate the role of scalp tissue in head impact kinematics; both with respect to its mechanical properties and with respect to its sliding properties. An EN960 and HIII headform were subjected to linear and oblique impacts, respectively, both with and without porcine scalp attached. Different speeds, impact locations and impact surfaces were tested. Standard linear drop tests (EN960) showed that the scalp reduced the impact energy by up to 68.7% (rear impact). Oblique head impact tests showed how the headform-anvil friction coefficient changes when the HIII is covered with scalp, affecting linear and rotational accelerations. Therefore, the scalp plays an important role in head impacts and it should be realistically represented in headforms used for impact tests and in numerical models of the human head.

Study of the Plain Bearings of Modified Wood for Heavy-Loaded Friction Assemblies

The article describes the structure of a self-lubricating plain bearing of modified wood for heavy-loaded friction assemblies and production technology. A method is developed to define the wood’s coefficient of friction on steel and the friction machine MI–1M is upgraded. The sliding friction coefficient changes within 0.06–0.11, depending on the load.

Effect of temperature on wear and tribofilm formation in highly loaded DLC-steel line contacts

Abstract In the present study the tribological properties of DLC coatings are analysed by performing Stribeck experiments with a block on ring (BoR) configuration, developed for a rotational tribometer, under different temperatures operated with a conventional 5W30 engine oil. Both, block and ring are made of steel and surface hardened, whereby a-C:H coating with CrN adhesion and CrC gradient layer is deposited on the latter. Results reveal, that the amount of formed Zinc dialkyldithiophosphate (ZDDP) tribofilms can be linked directly to changes of wear volume and boundary friction coefficient (COF). Furthermore, wear and tribofilms can trigger topological surface adaptations, leading to a different frictional behaviour in the fluid lubrication regime as well. Optical, energy dispersive X-ray (EDX) and thermoelastohydrodynamic (TEHD) numerical analysis were carried out in order to gain a holistic understanding of phenomena taking place in DLC/steel tribosystems. Findings indicate, that anticipated positive effects of DLC coatings are partly suppressed due to the onset of these films under conditions relevant in automotive engines.

Effect of Adverse Weather Conditions on Vehicle Braking Distance of Highways

The effect of adverse weather conditions on the safety of vehicles moving on different types of roads and measuring its margin of safety have always been a major research issue of highways. Determining the exact value of friction coefficient between the wheels of the vehicle and the surface of the pavement (usually Asphalt Concrete) in different weather conditions is assumed as a major factor in design process. An appropriate method is analyzing the dynamic motion of the vehicle and its interactions with geometrical elements of road using dynamic simulation of vehicles. In this paper the effect of changes of friction coefficient caused by the weather conditions on the dynamic responses of three types of vehicles: including Sedan, Bus, and Truck based on the results of Adams/car Simulator are investigated. The studies conducted on this issue for different weather conditions suggest values ranging from 0.04 to 1.25. The results obtained from simulation based on Adams/car represent that the friction coefficient in values of 0.9, 0.8, 0.7, 0.6 do not effect on braking distance significantly and it is possible to attribute them all to dry weather condition. However, as it was anticipated the values of 0.5, 0.4, 0.28 and 0.18 have significant differences in braking distance. Hence, the values of 0.5, 0.4, 0.28 and 0.18 can be attributed to wet, rainy, snowy and icy conditions respectively.

The friction and wear properties of steel wire rope sliding against itself under impact load

Friction and impact between steel wire rope always exist in multi-layer winding hoist during the winding-in process, in particular for an ultra-deep coal mine. To understand the friction and wear mechanisms of wire rope among the layers in the winding hoist, a series of sliding friction experiments were carried out using a self-made friction test rig. The results show that the coefficient of friction (COF) of the wire rope changes little with increasing load and stabilizes at approximately 0.73, but decreases with the sliding velocity under dry-friction condition. However, under lubrication condition, there is almost no effect of the contact load and sliding velocity on the COF, which stabilizes at approximately 0.35. Additionally, the temperature rise is concentrated at the contact area, and it increases with the load and the sliding velocity. The maximum temperature rise with the lubrication is much lower, approximately 10 °C, than that under the condition of dry-friction, which is approximately 103 °C. Furthermore, the maximum of the COF under the impact load is significantly lower than that for the stable contact friction. With the impact and sliding velocities increase, the maximum COF under the impact load experiences a slight increase and reaches a maximum value of approximately 0.36. As the impact load increases, the COF changes little, but the impact process occurs more than once.