An experimental study on the effects of friction modifiers on wheel-rail dynamic interactions with various angles of attack

By modifying friction to the desired level,the application of friction modifiers(FMs)has been considered as a promising emerging tool in the railway engineering for increasing braking/traction force in poor adhesion conditions and mitigating wheel/rail interface deterioration,energy consumption,vibration and noise.Understanding the effectiveness of FMs in wheel–rail dynamic interactions is crucial to their proper applications in practice,which has,however,not been well explained.This study experimentally investigates the effects of two types of top-of-rail FM,i.e.FM-A and FM-B,and their application dosages on wheel–rail dynamic interactions with a range of angles of attack(AoAs)using an innovative well-controlled V-track test rig.The tested FMs have been used to provide intermediate friction for wear and noise reduction.The effectiveness of the FMs is assessed in terms of the wheel–rail adhesion characteristics and friction rolling induced axle box acceleration(ABA).This study provides the following new insights into the study of FM:the applications of the tested FMs can both reduce the wheel–rail adhesion level and change the negative friction characteristic to positive;stick–slip can be generated in the V-Track and eliminated by FM-A but intensified by FM-B,depending on the dosage of the FMs applied;the negative friction characteristic is not a must for stick–slip;the increase in ABA with AoA is insignificant until stick–slip occurs and the ABA can thus be influenced by the applications of FM.

Ashless Multi-Functional Friction Modifier for Modern Engine Oils

Automotive manufacturers are currently under pressure to improve fuel efficiency,and at the same time,reduce exhaust gas emission.To meet new emission requirements,modern vehicles are equipped with exhaust gas after-treatment devices.However,as sulfated ash,phosphorus and sulfur(SAPS) have a detrimental impact on these after-treatment devices,the use of low-or zero-SAPS additives is favored.Irgalube F 10 A is an additive that does not contain any metal,phosphorus or sulfur.It enables formulators to develop ...

Boundary slip and lubrication mechanisms of organic friction modifiers with effect of surface moisture

Surface moisture or humidity impacting the lubrication property is a ubiquitous phenomenon in tribological systems,which is demonstrated by a combination of molecular dynamics(MD)simulation and experiment for the organic friction modifier(OFM)-containing lubricant.The stearic acid and poly-α-olefin 4cSt(PAO4)were chosen as the OFM and base oil molecules,respectively.The physical adsorption indicates that on the moist surface water molecules are preferentially adsorbed on friction surface,and even make OFM adsorption film thoroughly leave surface and mix with base oil.In shear process,the adsorption of water film and desorption OFM film are further enhanced,particularly under higher shear rate.The simulated friction coefficient(that is proportional to shear rate)increases firstly and then decreases with thickening water film,in good agreement with experiments,while the slip length shows a contrary change.The wear increases with humidity due to tribochemistry revealing the continuous formation and removal of Si–O–Si network.The tribological discrepancy of OFM-containing lubricant in dry and humid conditions is attributed to the slip plane’s transformation from the interface between OFM adsorption film and lubricant bulk to the interface between adsorbed water films.This work provides a new thought to understand the boundary lubrication and failure of lubricant in humid environments,likely water is not always harmful in oil lubrication systems.

Molecules with a TEMPO-based head group as high-performance organic friction modifiers

High-performance organic friction modifiers(OFMs)added to lubricating oils are crucial for reducing energy loss and carbon footprint.To establish a new class of OFMs,we measured the friction and wear properties of N-(2,2,6,6-tetramethyl-1-oxyl-4-piperidinyl)dodecaneamide referred to as C12Amide-TEMPO.The effect of its head group chemistry,which is characterized by a rigid six-membered ring sandwiched by an amide group and a terminal free oxygen radical,was also investigated with both experiments and quantum mechanical(QM)calculations.The measurement results show that C12Amide-TEMPO outperforms the conventional OFMs of glyceryl monooleate(GMO)and stearic acid,particularly for load-carrying capacity,wear reduction,and stability of friction over time.The friction and wear reduction effect of C12Amide-TEMPO is also greatly superior to those of C12Ester-TEMPO and C12Amino-TEMPO,in which ester and amino groups replace the amide group,highlighting the critical role of the amide group.The QM calculation results suggest that,in contrast to C12Ester-TEMPO,C12Amino-TEMPO,and the conventional OFMs of GMO and stearic acid,C12Amide-TEMPO can form effective boundary films on iron oxide surfaces with a unique double-layer structure:a strong surface adsorption layer owing to the chemical interactions of the amide oxygen and free radical with iron oxide surfaces,and an upper layer owing to the interlayer hydrogen-bonding between the amide hydrogen and free radical or between the amide hydrogen and oxygen.Moreover,the intralayer hydrogen-bonding in each of the two layers is also possible.We suggest that in addition to strong surface adsorption,the interlayer and intralayer hydrogen-bonding also increases the strength of the boundary films by enhancing the cohesion strength,thereby resulting in the high tribological performance of C12Amide-TEMPO.The findings in this study are expected to provide new hints for the optimal molecular design of OFMs.

Influence of structural factors on the tribological performance of organic friction modifiers

The influence of structural factors on the lubrication performance of organic friction modifiers(OFMs)formulated in Group V(polyol ester oil)base oil was studied using a ball-on-disk tribometer.The results show that OFMs can mitigate friction under heavy loads,low sliding speeds,and high temperatures.These conditions are commonly encountered in internal-combustion engines between cylinder liners and piston rings.The reduction in friction is ascribed to the boundary lubrication film containing the OFM.The chemical composition analysis of the metal disk surface using energy dispersive X-ray spectroscopy(EDS)confirmed the presence of a protective film of OFM on the wear track,albeit inconsistently deposited.Although the adsorption of the OFM on the metal surface was observed to be dependent on the chemical reactivity of the functional groups,levels of unsaturation,and hydrocarbon chain length of the OFM,the frictional performance was not always directly correlated with the surface coverage and tribofilm thickness.This implies that the friction reduction mechanism can involve other localized processes at the interface between the metal surface and lubricant oil.The occasional variation in friction observed for these OFMs can be attributed to the stability and durability of the boundary film formed during the rubbing phase.

Effects of solid friction modifier on friction and rolling contact fatigue damage of wheel-rail surfaces

In railway network,friction is an important factor to consider in terms of the service behaviors of wheel-rail system.The objective of this study was to investigate the effect of a solid friction modifier(FM)in a railway environment.This was achieved by studying the friction,wear,and rolling contact fatigue(RCF)damage on the wheel-rail materials at different slip ratios.The results showed that when a solid FM was applied,the friction coefficient decreased.After the solid FM was separated from the wheel-rail interface,the friction coefficient gradually increased to its original level.With the application of the solid FM,the wear rates of the wheel-rail decreased.In addition,the thickness and hardness of the plastic deformation layers of the wheel-rail materials were reduced.The worn surfaces of the wheel-rail were dominated by pits and RCF cracks.Without the FM,RCF cracks ranged from 84 to 120μm,and subsurface cracks were generated.However,with the FM,RCF cracks ranged from 17 to 97μm and no subsurface cracks were generated.These findings indicate possible methods of improving the performance of railway rolling stock by managing friction,and reducing wear and permanent RCF damage affecting both the wheels and rails.

A Fuel Economy Study in Heavy Duty Diesel Engine Lubricants

Internal combustion engines′ fuel economy is an important role for engine designers,engine manufacturers over the past 30 years,especially passenger car motor oils.In heavy duty diesel engine,over the past 20 years,fuel economy has in some cases been sacrificed for exhaust gas emission optimizations.Now,Heavy Duty Automotive and the related industries have strong interest in fuel economy and the lubricants.It is driven by competitive market forces as well as government mandates and new emission regulations.Japan was the first country in the world to establish and implement heavy duty trucks and buses fuel economy standards.Other countries also have followed either by establishing direct fuel economy standards or greenhouse gas(GHG) emissions standards which are directly tied to fuel economy.This paper is discussing that heavy duty diesel engine lubricants can contribute on fuel economy.The contribution of various aspects of engine oil formulations on fuel economy will be discussed such as lubricant viscosity grade,lubricant additives and friction modifiers.In this paper,the evaluation discussions are based on fuel economy measurements in some bench tests,standardized laboratory engine tests and field tests.

A Multifunctional Borate Ester/Amide for Engine Oils

Global economic and pollution concerns are having a major impact on how modern engine oils are being formulated.Modern engine oil specifications mandate reduced levels of phosphorus and sulfur to protect the efficacy of pollution control devices.In addition,modern engine oil must also be more fuel efficient than earlier generations to reduce greenhouse gas emissions and the impact of high priced gasoline and diesel fuel to the consumer.At the same time,oxidation,wear,and corrosion performance of the oil must not be compromised.Multifunctional additives are useful formulation tools that help formulators meet these tough new challenges.One such additive is the organo-borate ester/amide.Originally conceived as an organic friction modifier,this patented technology is really a multifunctional additive that addresses the global economic and pollution concerns.With the addition of boron,this unique commercial organic friction modifier also imparts antioxidancy,antiwear and anticorrosion properties to engine oil.In addition,the organo-borate ester/amide is compatible with pollution control devices because it does not contain sulfur or phosphorus.Work is on going to uncover additional beneficial properties of this chemistry.

Study and Development of a Screener Test for Fuel Economy Passenger Car Motor Oil

Fuel economy regulations have been issued in many countries to save energy,and it is one of the most essential performance requirements for Passenger Car Motor Oil(PCMO) this decade.The performance is also important to reduce green house gas(GHG) emissions.Automotive,Oil and Additive industries have been developing fuel economy tests in fired engine for PCMO.The ASTM 5 Car test was started in 1982 and ASTM Sequence Ⅵ series test was also developed by the industries as one of fuel economy tests after the 5 Car test.However,the fired engine(combustion) test condition is more complicated and the combustion mode in engine introduce high variability into a fuel economy measurement.Screening by bench testing is complicated by the difficulty to reproduce friction conditions of all of engine parts.Based on the background,a motored engine friction torque test(MEFT) was developed as one of the solutions for fuel economy screening test.Using a newly developed MEFT,key additive chemistries were evaluated and compared in the test,and it distinguished the differences in additive chemistries,in addition to those in viscosity and friction modifiers.The Sequence Ⅵ-D FEI 1(Seq.Ⅵ-D FEI 1) and chassis dynamometer vehicle tests were also conducted in this study,and the test data has shown an excellent correlation among MEFT,Seq.Ⅵ-D FEI 1 and chassis dynamometer vehicle tests.

Improving Local Temperature Rise in Rotational Incremental Sheet Forming Process by Modifying Forming Parameters Using Response Surface Method

In rotational incremental sheet forming( RISF) process,the friction heating of rotational tool could lead to local temperature rise of the sheet and cause the improvement of sheet's formability.Lightweight metal,such as magnesium alloy,could be deformed by RISF without additional heating. The objective of this study is to investigate the effects of forming parameters,namely,tool rotational speed,feed-rate,step size and wall angle,on the local temperature rise. Using response surface methodology and central composite design( CCD) experimental design,the significance,sequence of parameters and regression models would be analyzed with AZ31 B as the experimental material,and 3D response surface plots would be shown. Combined with actual processing conditions,the measures to improve the local temperature rise by modifying each parameter would be discussed in the end. The results showed that hierarchy of the parameters with respect to the significance of their effects on the local temperature at the side wall was: feed-rate,step size,and rotational speed,while at the bottom it was: feed-rate,step size,wall angle, and rotational speed, and no significant interaction appeared. It was found that the most significant parameter was not rotational speed,but feed-rate,followed by step size,for both test positions. In addition, the local temperature would increase by elevating step size,wall angle,rotating rate,and bringing down of feed-rate.

The effect of ethanol fuel dilution on oil performance and MoDTC tribofilms formation and composition

Ethanol has emerged as a promising alternative to fossil fuels,but its use can lead to significant dilution in lubricants,particularly during cold start or heavy traffic.This dilution can affect the performance of additives,including friction modifiers like molybdenum dithiocarbamate(MoDTC),which are designed to reduce friction under extreme contact conditions.Prior research suggests that ethanol may impact the performance of MoDTC,prompting this study’s goal to investigate the effects of ethanol on MoDTC tribofilms and their friction response under boundary lubrication conditions.Therefore,reciprocating tribological tests were performed with fully formulated lubricants containing MoDTC with varying ethanol concentrations.The results indicate that a critical ethanol dilution level inhibits friction reduction by MoDTC activation,resulting in friction coefficients(COFs)similar to the base oil.Surfaces tested with simple mixtures of polyalphaolefin(PAO)+MoDTC showed increased COFs with added ethanol.Analysis of tested surfaces using Raman spectroscopy,X-ray photoelectron spectroscopy(XPS),and X-ray absorption spectroscopy near the edge structure(XANES)revealed the presence of sulfates,MoO_(3),MoS_(2),and MoS_(x)O_(y)compounds in the tribofilms formed on the surfaces,with and without ethanol diluted in the lubricant.However,the addition of ethanol increased the sulfates and MoO_(3)content of the tribofilms at the expense of friction-reducing compounds such as MoS_(2)and MoS_(x)O_(y).These findings suggest that ethanol dilution in lubricants containing MoDTC creates an oxygen-rich interfacial medium that favors the formation of compounds with insufficient friction-reducing capabilities.

Nanomaterials for lubricating oil application:A review

Friction and wear are ubiquitous,from nano-electro-mechanical systems in biomedicine to large-scale integrated electric propulsion in aircraft carriers.Applications of nanomaterials as lubricating oil additives have achieved great advances,which are of great significance to control friction and wear.This review focuses on the applications of nanomaterials in lubricating oil and comprehensively compares their tribological characteristics as lubricating oil additives.Statistical analysis of tribology data is provided and discussed accordingly;moreover,the interaction between nanomaterials and sliding surface,lubricating oil,other additives,and synergistic lubrication in nanocomposites are systematically elaborated.Finally,suggestions for future research on nanomaterials as lubricating oil additives are proposed.Hence,this review will promote a better fundamental understanding of nanomaterials for lubricating oil application and help to achieve the superior design of nanoadditives with outstanding tribological performances.

Lubricatio mechanism of a strong tribofilm by imidazolium ionic liquid

Friction modifiers(FMs)are surface-active additives added to base fluids to reduce friction between rubbing surfaces.Their effectiveness depends on their interactions with rubbing surfaces and may be mitigated by the choice of the base fluid.In this work,the performance of an imidazolium ionic liquid(ImIL)additive in polyethylene-glycol(PEG)and 1,4-butanediol for lubricating steel/steel and diamond-like-carbon/diamond-like carbon(DLC-DLC)contacts were investigated.ImIL-containing PEG reduces friction more effectively in steel-steel than DLC-DLC contacts.In contrast,adding ImIL in 1,4-butanediol results in an increase in friction in steel-steel contacts.Results from the Raman spectroscopy,X-ray photoelectron spectroscopy(XPS),and focused ion beam-transmission electron microscopy(FIB-TEM)reveal that a surface film is formed on steel during rubbing in ImIL-containing PEG.This film consists of two layers.The top layer is composed of amorphous carbon and are easily removed during rubbing.The bottom layer,which contains iron oxide and nitride compound,adheres strongly on the steel surface.This film maintains its effectiveness in a steel-steel contact even after ImIL additives are depleted.Such film is not observed in 1,4-butanediol where the adsorption of ImIL is hindered,as suggested by the quartz crystal microbalance(QCM)measurements.No benefit is observed when the base fluid on its own is sufficiently lubricious,as in the case of DLC surfaces.This work provides fundamental insights on how compatibilities among base fluid,FM,and rubbing surface affect the performance of IL as surface active additives.It reveals the structure of an ionic liquid(IL)surface film,which is effective and durable.The knowledge is useful for guiding future IL additive development.

Functionalization of alumina particles to improve the performance of eco-friendly brake-pads

Abrasives,such as oxides of alumina(Al),silica(Si),zirconia(Zr),chromium(Cr)etc.,are added to raise the friction level and also to remove the glaze on the disc so that surface will be rejuvenated continuously during braking and will contribute to maintain the desired friction level.However,these inorganic particles have less adhesion with the resin/binder and hence are easily dug out during wearing process contributing to higher wear.If efforts are made to enhance the filler‐matrix adhesion,not only the wear of friction material(FM)should reduce,the particles may stay for a longer time on the tribo‐surface of the pads to contribute fully towards controlling the coefficient of friction(μ).In the present study,alumina particles were selected for siloxane treatment to improve the filler‐matrix adhesion.Two types of eco‐friendly(free from asbestos and Cu)brake‐pads were developed using alumina as a theme ingredient(treated and untreated)keeping all the parent formulation identical.An additional type of brake‐pads without alumina particles was also developed to observe the effect of abrasive particles on the tribo‐performance.The performance properties(physical,mechanical,and tribological)of brake‐pads were compared when evaluated in identical conditions.The tribotesting was done on full‐scale brake inertia dynamometer following the procedure in Japanese automobile standard(JASO C 406).It was observed that siloxane treatment affected both friction and wear of brake‐pads in a beneficial way.Wear resistance got increased 35%for siloxane treated pads.Worn surfaces were analysed using scanning electron microscopy(SEM)and energy dispersive X‐ray(EDAX)technique.