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  • JOURNAL ARTICLE
    Jean-Fulcrand A, Maser MA, Bremner T, Wong JSSet al., 2019,

    Effect of temperature on tribological performance of polyetheretherketone-polybenzimidazole blend

    , TRIBOLOGY INTERNATIONAL, Vol: 129, Pages: 5-15, ISSN: 0301-679X
  • JOURNAL ARTICLE
    Puhan D, Nevshupa R, Wong JSS, Reddyhoff Tet al., 2019,

    Transient aspects of plasma luminescence induced by triboelectrification of polymers

    , Tribology International, Vol: 130, Pages: 366-377, ISSN: 0301-679X

    © 2018 The Authors Transient electric gas discharges that occur around sliding interfaces during contact electrification of polymers were studied at millisecond timescales and with micrometre resolution. Deduced vibrational temperatures indicate cold plasma resulting from positive corona discharge. At millisecond timescales, previously unseen rapid discharge events are observed, and modelling suggests that these result from streamer development, triggered by electron emission from the polymer surface. Those which occur over a period of several seconds are shown to be caused by competition between charge generation and the formation of polymer films. The findings explain the interplay between charging and plasma generation and their dependence on wear processes.

  • JOURNAL ARTICLE
    Vladescu S-C, Putignano C, Marx N, Keppens T, Reddyhoff T, Dini Det al., 2019,

    The percolation of liquid through a compliant seal - an experimental and theoretical study

    , Journal of Fluids Engineering, Vol: 141, Pages: 031101-031101, ISSN: 0098-2202
  • JOURNAL ARTICLE
    Campen S, Smith B, Wong J, 2018,

    Deposition of Asphaltene from Destabilized Dispersions in Heptane-Toluene

    , ENERGY & FUELS, Vol: 32, Pages: 9159-9171, ISSN: 0887-0624
  • JOURNAL ARTICLE
    Dzepina B, Balint D, Dini D, 2018,

    A phase field model of pressure-assisted sintering

    , Journal of the European Ceramic Society, ISSN: 0955-2219

    © 2018 The Authors The incorporation of an efficient contact mechanics algorithm into a phase field sintering model is presented. Contact stresses on the surface of arbitrarily shaped interacting bodies are evaluated and built into the model as an elastic strain energy field. Energy relaxation through deformation is achieved by diffusive fluxes along stress gradients and rigid body motion of the deforming particles maintain contact between the particles. The proposed model is suitable for diffusion deformation mechanisms occurring at stresses below the yield strength of a defect-free material; this includes Nabarro-Herring creep, Coble creep and pressure-solution. The effect of applied pressure on the high pressure-high temperature (HPHT) liquid phase sintering of diamond particles was investigated. Changes in neck size, particle coordination and contact flattening were observed. Densification rates due to the externally applied loads were found to be in good agreement with a new theory which implicitly incorporates the effect of applied external pressure.

  • JOURNAL ARTICLE
    Ebrahimi MT, Dini D, Balint DS, Sutton AP, Ozbayraktar Set al., 2018,

    Discrete crack dynamics: A planar model of crack propagation and crack-inclusion interactions in brittle materials

    , INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, Vol: 152, Pages: 12-27, ISSN: 0020-7683
  • JOURNAL ARTICLE
    Ewen JP, Heyes DM, Dini D, 2018,

    Advances in nonequilibrium molecular dynamics simulations of lubricants and additives

    , FRICTION, Vol: 6, Pages: 349-386, ISSN: 2223-7690
  • JOURNAL ARTICLE
    Ewen JP, Kannam SK, Todd BD, Dini Det al., 2018,

    Slip of Alkanes Confined between Surfactant Monolayers Adsorbed on Solid Surfaces

    , Langmuir, Vol: 34, Pages: 3864-3873, ISSN: 0743-7463

    © 2018 American Chemical Society. The slip and friction behavior of n-hexadecane, confined between organic friction modifier surfactant films adsorbed on hematite surfaces, has been studied using nonequilibrium molecular dynamics simulations. The influence of the surfactant type and coverage, as well as the applied shear rate and pressure, has been investigated. A measurable slip length is only observed for surfactant films with a high surface coverage, which provide smooth interfaces between well-defined surfactant and hexadecane layers. Slip commences above a critical shear rate, beyond which the slip length first increases with increasing shear rate and then asymptotes toward a constant value. The maximum slip length increases significantly with increasing pressure. Systems and conditions which show a larger slip length typically give a lower friction coefficient. Generally, the friction coefficient increases linearly with logarithmic shear rate; however, it shows a much stronger shear rate dependency at low pressure than at high pressure. Relating slip and friction, slip only occurs above a critical shear stress, after which the slip length first increases linearly with increasing shear stress and then asymptotes. This behavior is well-described using previously proposed slip models. This study provides a more detailed understanding of the slip of alkanes on surfactant monolayers. It also suggests that high coverage surfactant films can significantly reduce friction by promoting slip, even when the surfaces are well-separated by a lubricant.

  • CONFERENCE PAPER
    Ferretti A, Giacopini M, Mastrandrea L, Dini Det al., 2018,

    Investigation of the Influence of Different Asperity Contact Models on the Elastohydrodynamic Analysis of a Conrod Small-End/Piston Pin Coupling

    , WCX World Congress Experience

    © 2018 SAE International. All Rights Reserved. Bearings represent one of the main responsible of friction losses in internal combustion engines and their lubrication performance has a crucial influence on the operating condition of the engine. In particular, the conrod small-end bearing is one of the most critical engine parts from a tribological point of view since limited contact surfaces have to sustain high inertial and combustion forces. In this contribution an analysis is performed of the tribological behaviour of the lubricated contact between the piston pin and the conrod small-end of a high performance motorbike engine. An algorithm is employed based on a complementarity formulation of the cavitation problem. A comparison between two different approaches to simulate the asperity contact problem is performed, the former based on the standard Greenwood-Tripp theory and the latter based on a complementarity formulation of the asperity contact problem. A model validation is performed by comparing the results with those obtained adopting the commercial software AVL Excite Power Unit. Similar results are obtained from both the approaches, if a proper calibration of the model input data is performed. However, a remarkable sensitivity is highlighted of the results obtained using the Greenwood/Tripp model to the adjustment parameters. The realistic (engineering) difficulty in defining and identifying the roughness data and their purely statistical nature returns results that may be afflicted by a dose of uncertainty. Considering that results of such simulations usually offer guidelines for a correct design of the coupling, further investigations are suggested to identify a relationship between simply available roughness data and model input, starting from a direct experimental measurements of real roughness profiles.

  • JOURNAL ARTICLE
    Forte AE, Galvan S, Dini D, 2018,

    Models and tissue mimics for brain shift simulations

    , BIOMECHANICS AND MODELING IN MECHANOBIOLOGY, Vol: 17, Pages: 249-261, ISSN: 1617-7959
  • JOURNAL ARTICLE
    Gattinoni C, Ewen JP, Dini D, 2018,

    Adsorption of Surfactants on alpha-Fe2O3(0001): A Density Functional Theory Study

    , JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 122, Pages: 20817-20826, ISSN: 1932-7447
  • JOURNAL ARTICLE
    Guo Y, di Mare L, Li RKY, Wong JSSet al., 2018,

    Cargo Release from Polymeric Vesicles under Shear

    , POLYMERS, Vol: 10, ISSN: 2073-4360
  • JOURNAL ARTICLE
    Hartinger M, Reddyhoff T, 2018,

    CFD modeling compared to temperature and friction measurements of an EHL line contact

    , TRIBOLOGY INTERNATIONAL, Vol: 126, Pages: 144-152, ISSN: 0301-679X
  • JOURNAL ARTICLE
    Heyes DM, Dini D, Smith ER, 2018,

    Incremental viscosity by non-equilibrium molecular dynamics and the Eyring model

    , JOURNAL OF CHEMICAL PHYSICS, Vol: 148, ISSN: 0021-9606
  • JOURNAL ARTICLE
    Hili J, Pelletier C, Jacobs L, Olver A, Reddyhoff Tet al., 2018,

    High-Speed Elastohydrodynamic Lubrication by a Dilute Oil-in-Water Emulsion

    , Tribology Transactions, Vol: 61, Pages: 287-294, ISSN: 1040-2004

    © 2018 Society of Tribologists and Lubrication Engineers. When a concentrated contact is lubricated at low speed by an oil-in-water emulsion, a film of pure oil typically separates the surfaces (stage 1). At higher speeds, starvation occurs (stage 2) and the film is thinner than would be expected if lubricated by neat oil. However, at the very highest speeds, film thickness increases again (stage 3), though little is known for certain about either the film composition or the mechanism of lubrication, despite some theoretical speculation. In this article, we report the film thickness in a ball-on-flat contact, lubricated by an oil-in-water emulsion, at speeds of up to 20 m/s, measured using a new high-speed test rig. We also investigated the sliding traction and the phase composition of the film, using fluorescent and infrared microscopy techniques. Results show that, as the speed is increased, starvation is followed by a progressive change in film composition, from pure oil to mostly water. At the highest speeds, a film builds up that has a phase composition similar to the bulk emulsion. This tends to support the “microemulsion” view rather than the “dynamic concentration” theory.

  • JOURNAL ARTICLE
    Kanca Y, Milner P, Dini D, Amis AAet al., 2018,

    Tribological properties of PVA/PVP blend hydrogels against articular cartilage

    , JOURNAL OF THE MECHANICAL BEHAVIOR OF BIOMEDICAL MATERIALS, Vol: 78, Pages: 36-45, ISSN: 1751-6161
  • JOURNAL ARTICLE
    Kanca Y, Milner P, Dini D, Amis AAet al., 2018,

    Tribological evaluation of biomedical polycarbonate urethanes against articular cartilage

    , JOURNAL OF THE MECHANICAL BEHAVIOR OF BIOMEDICAL MATERIALS, Vol: 82, Pages: 394-402, ISSN: 1751-6161
  • JOURNAL ARTICLE
    Lu J, Reddyhoff T, Dini D, 2018,

    3D Measurements of Lubricant and Surface Temperatures Within an Elastohydrodynamic Contact

    , TRIBOLOGY LETTERS, Vol: 66, ISSN: 1023-8883
  • JOURNAL ARTICLE
    Marx N, Fernandez L, Barcelo F, Spikes Het al., 2018,

    Shear Thinning and Hydrodynamic Friction of Viscosity Modifier-Containing Oils. Part I: Shear Thinning Behaviour

    , TRIBOLOGY LETTERS, Vol: 66, ISSN: 1023-8883
  • JOURNAL ARTICLE
    Marx N, Fernández L, Barceló F, Spikes Het al., 2018,

    Shear Thinning and Hydrodynamic Friction of Viscosity Modifier-Containing Oils. Part II: Impact of Shear Thinning on Journal Bearing Friction

    , Tribology Letters, Vol: 66, ISSN: 1023-8883

    © 2018, The Author(s). In a companion paper, the temporary shear thinning behaviour of a series of viscosity-modifier (VM)-containing blends was studied over a wide shear rate and temperature range [Marx et al. in Tribol Lett, https://doi.org/10.1007/s11249-018-1039-5]. It was found that for almost all VMs the resulting data could be collapsed on a single viscosity versus reduced strain rate curve using time–temperature superposition. This made it possible to derive a single equation to describe the viscosity–shear rate behaviour for each VM blend. In the current paper, these shear thinning equations are used in a Reynolds-based hydrodynamic lubrication model to explore and compare the impact of different VMs on the film thickness and friction of a lubricated, isothermal journal bearing. It is found that VMs reduce friction and especially power loss markedly at high shaft speeds, while still contributing to increased hydrodynamic film thickness at low speeds. The model indicates that VMs can contribute to reducing friction in two separate ways. One is via shear thinning. This occurs especially at high bearing speeds when shear rates are large and can result in a 50% friction reduction compared to the equivalent isoviscous oil at low temperatures for the blends studied. The second is via their impact on viscosity index, which means that for a set viscosity at high temperature the low-shear-rate (and thus the high shear rate) viscosity of a high-VI oil, and consequently its hydrodynamic friction, will be lower at low temperatures than that of a low-VI oil. The identification and quantification of these two alternative ways to reduce friction should assist in the design of new, fuel-efficient VMs.

  • JOURNAL ARTICLE
    Masen M, Cann PME, 2018,

    Friction measurements with molten chocolate

    , Tribology Letters, Vol: 66, ISSN: 1023-8883

    A novel test is reported which allows the measurement of the friction of molten chocolate in a model tongue–palate rubbing contact. Friction was measured over a rubbing period of 150 s for a range of commercial samples with different cocoa content (85–5% w/w). Most of the friction curves had a characteristic pattern: initially a rapid increase occurs as the high-viscosity chocolate melt is sheared in the contact region followed by friction drop as the film breaks down. The exceptions were the very high (85%) and very low (~ 5%) cocoa content samples which gave fairly constant friction traces over the test time. Differences were observed in the initial maximum and final friction coefficients depending on chocolate composition. Generally, the initial maximum friction increased with increasing cocoa content. At the end of the test, the rubbed films on the lower slide were examined by optical microscopy and infrared micro-reflection spectroscopy. In the rubbed track, the chocolate structure was severely degraded and predominately composed of lipid droplets, which was confirmed by the IR spectra. The new test provides a method to distinguish between the friction behaviour of different chocolate formulations in a rubbing low-pressure contact. It also allows us to identify changes in the degraded chocolate film that can be linked to the friction profile. Further development of the test method is required to improve simulation of the tongue–palate contact including the effect of saliva and this will be the next stage of the research.

  • JOURNAL ARTICLE
    Menga N, Carbone G, Dini D, 2018,

    Do uniform tangential interfacial stresses enhance adhesion?

    , Journal of the Mechanics and Physics of Solids, Vol: 112, Pages: 145-156, ISSN: 0022-5096

    © 2017 Elsevier Ltd We present theoretical arguments, based on linear elasticity and thermodynamics, to show that interfacial tangential stresses in sliding adhesive soft contacts may lead to a significant increase of the effective energy of adhesion. A sizable expansion of the contact area is predicted in conditions corresponding to such scenario. These results are easily explained and are valid under the assumptions that: (i) sliding at the interface does not lead to any loss of adhesive interaction and (ii) spatial fluctuations of frictional stresses can be considered negligible. Our results are seemingly supported by existing experiments, and show that frictional stresses may lead to an increase of the effective energy of adhesion depending on which conditions are established at the interface of contacting bodies in the presence of adhesive forces.

  • JOURNAL ARTICLE
    Milner PE, Parkes M, Puetzer JL, Chapman R, Stevens MM, Cann P, Jeffers JRTet al., 2018,

    A low friction, biphasic and boundary lubricating hydrogel for cartilage replacement

    , ACTA BIOMATERIALIA, Vol: 65, Pages: 102-111, ISSN: 1742-7061
  • JOURNAL ARTICLE
    Reddyhoff T, Underwood RJ, Sayles RS, Spikes HAet al., 2018,

    Temperature measurement of debris particles in EHL contacts

    , SURFACE TOPOGRAPHY-METROLOGY AND PROPERTIES, Vol: 6, ISSN: 2051-672X
  • JOURNAL ARTICLE
    Shen L, Denner F, Morgan N, van Wachem B, Dini Det al., 2018,

    Capillary waves with surface viscosity

    , JOURNAL OF FLUID MECHANICS, Vol: 847, Pages: 644-663, ISSN: 0022-1120
  • JOURNAL ARTICLE
    Spikes H, 2018,

    Stress-augmented thermal activation: Tribology feels the force

    , FRICTION, Vol: 6, Pages: 1-31, ISSN: 2223-7690
  • JOURNAL ARTICLE
    Stevenson H, Parkes M, Austin L, Jaggard M, Akhbari P, Vaghela U, Williams HRT, Gupte C, Cann Pet al., 2018,

    The development of a small-scale wear test for CoCrMo specimens with human synovial fluid

    , Biotribology, Vol: 14, Pages: 1-10

    © 2018 The Authors A new test was developed to measure friction and wear of hip implant materials under reciprocating sliding conditions. The method requires a very small amount of lubricant (<3 ml) which allows testing of human synovial fluid. Friction and wear of Cobalt Chromium Molybdenum (CoCrMo) material pairs were measured for a range of model and human synovial fluid samples. The initial development of the test assessed the effect of fluid volume and bovine calf serum (BCS) concentration on friction and wear. In a second series of tests human synovial fluid (HSF) was used. The wear scar size (depth and volume) on the disc was dependent on protein content and reduced significantly for increasing BCS concentration. The results showed that fluid volumes of <1.5 ml were affected by evaporative loss effectively increasing the protein concentration resulting in anomalously lower wear. At the end of the test thick deposits were observed in and around the wear scars on the disc and ball; these were analysed by Infrared Reflection-Absorption Spectroscopy. The deposits were composed primarily of denatured proteins and similar IR spectra were obtained from the BCS and HSF tests. The analysis confirmed the importance of SF proteins in determining wear of CoCrMo couples.

  • JOURNAL ARTICLE
    Tan Z, Dini D, Rodriguez y Baena F, Forte AEet al., 2018,

    Composite hydrogel: A high fidelity soft tissue mimic for surgery

    , Materials and Design, Vol: 160, Pages: 886-894, ISSN: 0264-1275

    © 2018 The Authors Accurate tissue phantoms are difficult to design due to the complex non-linear viscoelastic properties of real soft tissues. A composite hydrogel, resulting from a mix of poly(vinyl) alcohol and phytagel, is able to reproduce the viscoelastic responses of different soft tissues due to its compositional tunability. The aim of this work is to demonstrate the flexibility of the composite hydrogel in mimicking the interactions between surgical tools and various soft tissues, such as brain, lung and liver. Therefore compressive stiffness, insertion forces and frictional forces were used as matching criteria to determine the hydrogel compositions for each soft tissue. A full map of the behaviour of the synthetic material is provided for these three characteristics and the compositions found to best match the mechanical response of brain, lung and liver are reported. The optimised hydrogel samples are then tested and shown to mimic the behaviour of the three tissues with unprecedented fidelity. The effect of each hydrogel constituent on the compressive stiffness, needle insertion and frictional forces is also detailed in this work to explain their individual contributions and synergistic effects. This study opens important opportunities for the realisation of surgical planning and training devices and tools for in-vitro tissue testing.

  • JOURNAL ARTICLE
    Vakis AI, Yastrebov VA, Scheibert J, Nicola L, Dini D, Minfray C, Almqvist A, Paggi M, Lee S, Limbert G, Molinari JF, Anciaux G, Aghababaei R, Restrepo SE, Papangelo A, Cammarata A, Nicolini P, Putignano C, Carbone G, Stupkiewicz S, Lengiewicz J, Costagliola G, Bosia F, Guarino R, Pugno NM, Mueser MH, Ciavarella Met al., 2018,

    Modeling and simulation in tribology across scales: An overview

    , TRIBOLOGY INTERNATIONAL, Vol: 125, Pages: 169-199, ISSN: 0301-679X
  • JOURNAL ARTICLE
    Verschueren J, Gurrutxaga-Lerma B, Balint DS, Sutton AP, Dini Det al., 2018,

    Instabilities of High Speed Dislocations

    , PHYSICAL REVIEW LETTERS, Vol: 121, ISSN: 0031-9007
  • JOURNAL ARTICLE
    Vladescu S-C, Marx N, Fernandez L, Barcelo F, Spikes Het al., 2018,

    Hydrodynamic Friction of Viscosity-Modified Oils in a Journal Bearing Machine

    , TRIBOLOGY LETTERS, Vol: 66, ISSN: 1023-8883
  • JOURNAL ARTICLE
    Yang S, Wong JSS, Zhou F, 2018,

    Ionic Liquid Additives for Mixed and Elastohydrodynamic Lubrication

    , Tribology Transactions, Vol: 61, Pages: 816-826, ISSN: 1040-2004

    © 2018, © 2018 The Authors. Published with license by Taylor & Francis Group, LLC. Ionic liquids (ILs), both as pure lubricants and as lubricant additives, have been demonstrated extensively to exhibit excellent tribological performance in terms of friction and wear reduction in the boundary lubrication (BL) regime. Because engineering contacts experience boundary and mixed as well as full film lubrication depending on operating conditions, it is crucial to examine whether lubrication regimes other the BL regime can also benefit from the use of ILs. The objective of this work is to investigate the tribological performance of IL additives in the mixed lubrication (ML) and the elastohydrodynamic lubrication (EHL) regimes. Polyethylene glycol (PEG) was used as the base fluid. ILs were synthesized in situ by dissolving lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) in PEG. Friction and film thickness measurements were employed to investigate the effectiveness of IL additives at room temperature, 60°C, and 80°C at various loads and slide–roll ratios (SRRs). The effect of IL additives on the rheological behavior of PEG was also investigated. The EHL film thickness increases with increasing IL concentration. EHL friction is, however, only mildly affected by IL additives. In the ML regime, IL additives can reduce friction and metal wear compared to pure PEG in mild conditions. It is conjectured that IL forms sacrificial layers and protects the rubbing surfaces.

  • JOURNAL ARTICLE
    Yu M, Arana C, Evangelou SA, Dini D, Cleaver GDet al., 2018,

    Parallel Active Link Suspension: A Quarter-Car Experimental Study

    , IEEE-ASME TRANSACTIONS ON MECHATRONICS, Vol: 23, Pages: 2066-2077, ISSN: 1083-4435
  • JOURNAL ARTICLE
    Arana C, Evangelou SA, Dini D, 2017,

    Series Active Variable Geometry Suspension application to comfort enhancement

    , CONTROL ENGINEERING PRACTICE, Vol: 59, Pages: 111-126, ISSN: 0967-0661
  • JOURNAL ARTICLE
    Bodnarchuk MS, Dini D, Heyes DM, Breakspear A, Chahine Set al., 2017,

    Molecular Dynamics Studies of Overbased Detergents on a Water Surface

    , LANGMUIR, Vol: 33, Pages: 7263-7270, ISSN: 0743-7463
  • JOURNAL ARTICLE
    Bodnarchuk MS, Doncom KEB, Wright DB, Heyes DM, Dini D, O'Reilly RKet al., 2017,

    Polyelectrolyte pK(a) from experiment and molecular dynamics simulation

    , RSC ADVANCES, Vol: 7, Pages: 20007-20014, ISSN: 2046-2069
  • JOURNAL ARTICLE
    Campen S, di Mare L, Smith B, Wong JSSet al., 2017,

    Determining the Kinetics of Asphaltene Adsorption from Toluene: A New Reaction-Diffusion Model

    , ENERGY & FUELS, Vol: 31, Pages: 9101-9116, ISSN: 0887-0624
  • JOURNAL ARTICLE
    Cann P, Masen M, 2017,

    The 3<sup>rd</sup>International Conference on Biotribology (ICoBT) Imperial College London, 11-14<sup>th</sup>September 2016

    , Biotribology, Vol: 11, Pages: 1-2
  • JOURNAL ARTICLE
    Ciniero A, Le Rouzic J, Baikie I, Reddyhoff Tet al., 2017,

    "The origins of triboemission - Correlating wear damage with electron emission"

    , WEAR, Vol: 374, Pages: 113-119, ISSN: 0043-1648
  • JOURNAL ARTICLE
    Ciniero A, Le Rouzic J, Reddyhoff T, 2017,

    The Use of Triboemission Imaging and Charge Measurements to Study DLC Coating Failure

    , COATINGS, Vol: 7, ISSN: 2079-6412
  • JOURNAL ARTICLE
    De Laurentis N, Cann P, Lugt PM, Kadiric Aet al., 2017,

    The Influence of Base Oil Properties on the Friction Behaviour of Lithium Greases in Rolling/Sliding Concentrated Contacts

    , TRIBOLOGY LETTERS, Vol: 65, ISSN: 1023-8883
  • JOURNAL ARTICLE
    Delgado MA, Quinchia LA, Spikes HA, Gallegos Cet al., 2017,

    Suitability of ethyl cellulose as multifunctional additive for blends of vegetable oil-based lubricants

    , JOURNAL OF CLEANER PRODUCTION, Vol: 151, Pages: 1-9, ISSN: 0959-6526
  • JOURNAL ARTICLE
    Dench J, Morgan N, Wong JSS, 2017,

    Quantitative Viscosity Mapping Using Fluorescence Lifetime Measurements

    , TRIBOLOGY LETTERS, Vol: 65, ISSN: 1023-8883
  • JOURNAL ARTICLE
    Ewen JP, Echeverri Restrepo S, Morgan N, Dini Det al., 2017,

    Nonequilibrium molecular dynamics simulations of stearic acid adsorbed on iron surfaces with nanoscale roughness

    , Tribology International, Vol: 107, Pages: 264-273, ISSN: 0301-679X

    © 2016 The Authors Nonequilibrium molecular dynamics (NEMD) simulations have been used to examine the structure and friction of stearic acid films adsorbed on iron surfaces with nanoscale roughness. The effect of pressure, stearic acid coverage, and level of surface roughness were investigated. The direct contact of asperities was prevented under all of the conditions simulated due to strong adsorption, which prevented squeeze-out. An increased coverage generally resulted in lower lateral (friction) forces due to reductions in both the friction coefficient and Derjaguin offset. Rougher surfaces led to more liquidlike, disordered films; however, the friction coefficient and Derjaguin offset were only slightly increased. This suggests that stearic acid films are almost as effective on contact surfaces with nanoscale roughness as those which are atomically-smooth.

  • JOURNAL ARTICLE
    Ewen JP, Gattinoni C, Zhang J, Heyes DM, Spikes HA, Dini Det al., 2017,

    On the effect of confined fluid molecular structure on nonequilibrium phase behaviour and friction

    , Physical Chemistry Chemical Physics, Vol: 19, Pages: 17883-17894, ISSN: 1463-9076

    © the Owner Societies 2017. A detailed understanding of the behaviour of confined fluids is critical to a range of industrial applications, for example to control friction in engineering components. In this study, a combination of tribological experiments and confined nonequilibrium molecular dynamics simulations has been used to investigate the effect of base fluid molecular structure on nonequilibrium phase behaviour and friction. An extensive parameter study, including several lubricant and traction fluid molecules subjected to pressures (0.5-2.0 GPa) and strain rates (104-1010s-1) typical of the elastohydrodynamic lubrication regime, reveals clear relationships between the friction and flow behaviour. Lubricants, which are flexible, broadly linear molecules, give low friction coefficients that increase with strain rate and pressure in both the experiments and the simulations. Conversely, traction fluids, which are based on inflexible cycloaliphatic groups, give high friction coefficients that only weakly depend on strain rate and pressure. The observed differences in friction behaviour can be rationalised through the stronger shear localisation which is observed for the traction fluids in the simulations. Higher pressures lead to more pronounced shear localisation, whilst increased strain rates lead to a widening of the sheared region. The methods utilised in this study have clarified the physical mechanisms of important confined fluid behaviour and show significant potential in both improving the prediction of elastohydrodynamic friction and developing new molecules to control it.

  • JOURNAL ARTICLE
    Forte AE, Gentleman SM, Dini D, 2017,

    On the characterization of the heterogeneous mechanical response of human brain tissue

    , BIOMECHANICS AND MODELING IN MECHANOBIOLOGY, Vol: 16, Pages: 907-920, ISSN: 1617-7959
  • JOURNAL ARTICLE
    Guegan J, Kadiric A, Gabelli A, Spikes Het al., 2017,

    Reply to the 'Comment on "The Relationship Between Friction and Film Thickness in EHD Point Contacts in the Presence of Longitudinal Roughness'' by Guegan, Kadiric, Gabelli, & Spikes' by Scott Bair

    , TRIBOLOGY LETTERS, Vol: 65, ISSN: 1023-8883
  • JOURNAL ARTICLE
    Guo Y, di Mare L, Li RKY, Wong JSSet al., 2017,

    Structure of Amphiphilic Terpolymer Raspberry Vesicles

    , POLYMERS, Vol: 9, ISSN: 2073-4360
  • JOURNAL ARTICLE
    Gurrutxaga-Lerma B, Balint DS, Dini D, Sutton APet al., 2017,

    A Dynamic Discrete Dislocation Plasticity study of elastodynamic shielding of stationary cracks

    , JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, Vol: 98, Pages: 1-11, ISSN: 0022-5096
  • JOURNAL ARTICLE
    Gurrutxaga-Lerma B, Shehadeh MA, Balint DS, Dini D, Chen L, Eakins DEet al., 2017,

    The effect of temperature on the elastic precursor decay in shock loaded FCC aluminium and BCC iron

    , INTERNATIONAL JOURNAL OF PLASTICITY, Vol: 96, Pages: 135-155, ISSN: 0749-6419

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