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  • Journal article
    Kolekar AS, Olver AV, Sworski AE, Lockwood FEet al., 2014,

    Windage and Churning Effects in Dipped Lubrication

    , JOURNAL OF TRIBOLOGY-TRANSACTIONS OF THE ASME, Vol: 136, ISSN: 0742-4787
  • Journal article
    Ponjavic A, di Mare L, Wong J, 2014,

    Effect of pressure on the flow behavior of polybutene

    , Journal of Polymer Science Part B: Polymer Physics, Vol: 52, Pages: 708-715, ISSN: 0887-6266

    The rheology of submicron thick polymer melt is examined under high normal pressure conditions by a recently developed photobleached‐fluorescence imaging velocimetry technique. In particular, the validity and limitation of Reynold equation solution, which suggests a linear through‐thickness velocity profile, is investigated. Polybutene (PB) is sheared between two surfaces in a point contact. The results presented in this work suggest the existence of a critical pressure below which the through‐thickness velocity profile is close to linear. At higher pressures however, the profile assumes a sigmoidal shape resembling partial plug flow. The departure of the sigmoidal profile from the linear profile increases with pressure, which is indicative of a second‐order phase/glass transition. The nature of the transition is confirmed independently by examining the pressure‐dependent dynamics of PB squeeze films. The critical pressure for flow profile transition varies with molecular weight, which is consistent with the pressure‐induced glass transition of polymer melt.
  • Conference paper
    Christodoulias AI, Olver AV, Kadiric A, Sworski AE, Kolekar A, Lockwood FEet al., 2014,

    The efficiency of a simple spur gearbox - A thermally coupled lubrication model

    , Pages: 81-98

    A thermally coupled efficiency model for a simple dip-lubricated gearbox is presented. The model includes elastohydrodynamic (EHL) friction losses in gear teeth contacts as well as bearing, seal and churning losses. An iterative numerical scheme is used to fully account for the effects of contact temperature, pressure and shear rates on EHL friction. The model is used to predict gearbox efficiency with selected transmission oils whose properties were first obtained experimentally through rolling-sliding tribometer tests under representative contact conditions. Although the gearbox was designed using standard methods against a fixed rating, the model was used to study efficiency over a much wider range of conditions. Results are presented to illustrate the relative contribution of different sources of energy loss and the effect of lubricant properties on the overall gearbox efficiency under varying operating conditions.
  • Conference paper
    Maćkowiak S, Gattinoni C, Heyes DM, Brańka AC, Dini Det al., 2014,

    Boundary-controlled barostats for slab geometries in molecular dynamics simulations

    , Pages: 2712-2715
  • Conference paper
    Thaitirarot A, Hills D, Dini D, 2014,

    Contact mechanics of frictional lap joint

    , Pages: 2228-2231
  • Conference paper
    Dini D, Mastrandrea LN, Giacopini M, Bertocchi Eet al., 2014,

    Numerical investigation of the cavitation damage in a high performance engine conrod big end bearing via a mass-conserving complementarity algorithm

    , Pages: 586-589
  • Journal article
    Hills DA, Flicek RC, Dini D, 2014,

    A discussion of: Development of a complete contact fretting test device by J Juoksukangas et al.

    , PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART J-JOURNAL OF ENGINEERING TRIBOLOGY, Vol: 228, Pages: 123-126, ISSN: 1350-6501
  • Conference paper
    Arana C, Evangelou SA, Dini D, 2014,

    Car attitude control by series mechatronic suspension

    , 19th World Congress of the International-Federation-of-Automatic-Control (IFAC), Publisher: ELSEVIER SCIENCE BV, Pages: 10688-10693, ISSN: 2405-8963
  • Journal article
    Quinchia LA, Delgado MA, Reddyhoff T, Gallegos C, Spikes HAet al., 2014,

    Tribological studies of potential vegetable oil-based lubricants containing environmentally friendly viscosity modifiers

    , TRIBOLOGY INTERNATIONAL, Vol: 69, Pages: 110-117, ISSN: 0301-679X
  • Book chapter
    Gurrutxaga-Lerma B, Balint DS, Dini D, Eakins DE, Sutton APet al., 2014,

    Dynamic Discrete Dislocation Plasticity

    , ADVANCES IN APPLIED MECHANICS, VOL 47, Editors: Bordas, Publisher: ELSEVIER ACADEMIC PRESS INC, Pages: 93-224, ISBN: 978-0-12-800130-1
  • Conference paper
    Roberts O, Lunt AJG, Ying S, Sui T, Baimpas N, Dolbnya IP, Parkes M, Dini D, Kreynin SM, Neo TK, Korsunsky AMet al., 2014,

    A study of phase transformation at the surface of a zirconia ceramic

    , Publisher: Proceedings of the World Congress on Engineering 2014, Pages: 1173-1177

    Yttria Partially Stabilized Zirconia (YPSZ) is one of the most important engineering ceramic materials in that it displays a whole host of outstanding structural and functional properties. Of particular importance for load-bearing applications is the remarkable fracture toughness of YPSZ that arises from its ability to undergo martensitic transformation, a phase transformation that is dependent on stress, temperature, time, humidity, grain size, and the proximity of an interface. The present study was aimed at revealing the influence of the thermal ageing on the tetragonal to monoclinic phase transformation in the near-surface regions of YPSZ. In order to perform qualitative and quantitative characterisation of the phase composition, three principal microscopic techniques were employed: atomic force microscopy, depth resolved Raman micro-spectroscopy, and synchrotron X-ray diffraction. Satisfactory consistency was achieved between the results obtained using different techniques. Moreover, the data obtained in this way displayed complementarity that provided valuable input for the development of thermodynamic modelling of the complex inter-dependence between phase state and processing history of zirconia ceramics.
  • Journal article
    Mattei L, Campioni E, Accardi MA, Dini Det al., 2014,

    Finite element analysis of the meniscectomised tibio-femoral joint: implementation of advanced articular cartilage models

    , COMPUTER METHODS IN BIOMECHANICS AND BIOMEDICAL ENGINEERING, Vol: 17, ISSN: 1025-5842
  • Journal article
    Heyes DM, Smith ER, Dini D, Zaki TAet al., 2014,

    The method of planes pressure tensor for a spherical subvolume

    , The Journal of Chemical Physics, Vol: 140, Pages: ---
  • Journal article
    Zhang J, Yamaguchi E, Spikes H, 2014,

    The antagonism between succinimide dispersants and a secondary zinc dialkyl dithiophosphate

    , Tribology Transactions, Vol: 57, Pages: 57-65, ISSN: 1040-2004

    Recent years have seen an increase in the concentration of dispersant present in formulated engine oils, while the concentration of antiwear additives has been progressively reduced. However, it is known that the presence of dispersant can, in some cases, detract from the performance of antiwear additives in lubricant blends. In this article, the influence of three succinimide dispersants on the film formation and wear-reducing properties of a secondary zinc dialkyldithiophosphate (ZDDP) has been studied. Both posttreated and non-post-treated dispersants reduce steady-state ZDDP tribofilm formation to a certain extent depending on the dispersant concentration. At very high dispersant concentrations, ZDDP film formation is suppressed almost entirely. This can be restored only marginally by increasing ZDDP concentration, which implies that the absolute dispersant concentration rather than the dispersant : ZDDP ratio controls the impact of the dispersant on ZDDP film formation.Addition of dispersant to ZDDP also caused an increase in wear rate for all three dispersants tested. For one succinimide reported in detail in this article, it is has been shown that the wear rate increases approximately linearly with dispersant concentration and is largely independent of ZDDP concentration over the P weight percentage range studied.
  • Journal article
    Botta F, Dini D, Schwingshackl C, Di Mare L, Cerri Get al., 2013,

    Optimal Placement of Piezoelectric Plates to Control Multimode Vibrations of a Beam

    , Advances in Acoustics and Vibration, Vol: 2013, ISSN: 1687-627X

    Damping of vibrations is often required to improve both the performance and the integrity of engineering structures, for example, gas turbine blades. In this paper, we explore the possibility of using piezoelectric plates to control the multimode vibrations of a cantilever beam. To develop an effective control strategy and optimize the placement of the active piezoelectric elements in terms of vibrations amplitude reduction, a procedure has been developed and a new analytical solution has been proposed. The results obtained have been corroborated by comparison with the results from a multiphysics finite elements package (COMSOL), results available in the literature, and experimental investigations carried out by the authors. © 2013 Fabio Botta et al.
  • Journal article
    Myant CW, fowell M, cann P, 2013,

    The effect of transient motion on Isoviscous-EHL films in compliant, point, contacts

    , Tribology International, Vol: 72, Pages: 98-107, ISSN: 1879-2464

    Laser induced fluorescence was employed to measure lubricant film thickness in a compliant, point, contact during transient motion. Two types of transient sliding motion were investigated: start-up and sudden halting. The effects of acceleration rate and sliding speed on film formation and breakdown were studied.A clear relationship between start-up acceleration and the period of the film formation phase was observed. During sudden halting motion entrapment of fluid occurred in the centre of the contact. This trapped fluid was squeezed out of the contact over several seconds. The size of this entrapment was dependent on the initial sliding speed. The findings are compared to similar results for hard, point, contacts and the implications discussed.
  • Conference paper
    Puthumanapully PK, Amis A, Harris S, Cobb J, Jeffers Jet al., 2013,

    Measurements of the Varus Knee and Their Influence on Implant Design

    , Orthopaedic Proceedings, Publisher: The British Editorial Society of Bone & Joint Surgery, Pages: 89-89, ISSN: 1358-992X

    Introduction:Varus alignment of the knee is common in patients undergoing unicondylar knee replacement. To measure the geometry and morphology of these knees is to know whether a single unicondylar knee implant design is suitable for all patients, i.e. for patients with varus deformity and those without. The aim of this study was to identify any significant differences between normal and varus knees that may influence unicondylar implant design for the latter group.Methodology:56 patients (31 varus, 25 normal) were evaluated through CT imaging. Images were segmented to create 3D models and aligned to a tri-spherical plane (centres of spheres fitted to the femoral head and the medial and lateral flexion facets). 30 key co-ordinates were recorded per specimen to define the important axes, angles and shapes (e.g. spheres to define flexion and extension facet surfaces) that describe the femoral condylar geometry using in-house software. The points were then projected in sagittal, coronal and transverse planes. Standardised distance and angular measurements were then carried out between the points and the differences between the morphology of normal and varus knee summarised. For the varus knee group, trends were investigated that could be related to the magnitude of varus deformity.Results:Several significant differences between normal and varus knees were found, but most of these were small differences unlikely to be clinically significant or have an influence on implant design. However, two strong trends were observed. Firstly, the version of the femoral neck was significantly less for patients with varus knees (mean difference 9°; p < 0.05).The second trend was a significant difference in the sagittal morphology of the medial condyle. The kink angle, the angle formed by the intersection of the circles fitted to the flexion and extension facet surfaces, and their centres (Figure 1) was either absent or small in normal knees (mean 1°). An absent kink angle o
  • Journal article
    Botta F, Marx N, Dini D, de Lieto Vollaro R, Battista Get al., 2013,

    Experimental results for optimal placement of piezoelectric plates for active vibration control of a cantilever beam

    , International Journal of Engineering and Technology, Vol: 5, Pages: 4489-4494, ISSN: 2319-8613

    The fatigue phenomena correlated to the gas turbine blades vibrations can lead to catastrophic failure. To damp the vibrations amplitude typically damping passive systems are used. In the last years the interest in the piezoelectric materials, and their use as damping elements, has received considerable attention by many researchers. Recently different research groups have started to study their use in blades of turbomachinery. Because of their effectiveness strongly depends on their position, some of the authors have proposed ([15], [17]) a new model to find the optimal position to control the multimode vibrations. Such model has been corroborated by experimental results for different combinations of excited eigenmodes ([16], [18]]). In this paper the authors present new experimental results with the aim to increase the knowledge of the optimal position of the piezoelectric plates when different eigenmodes are involved.
  • Journal article
    Botta F, Dini D, de Lieto Vollaro R, 2013,

    A new function for the optimal placement of piezoelectric plates to control multimode vibrations of a rotating beam

    , International Journal of Engineering and Technology, Vol: 5, Pages: 4472-4488, ISSN: 2319-8613

    Damping of vibrations is often required to improve both the performances and the integrity of engiengineering structures, e.g. gas turbine blades. In [24] some of the authors have proposed a new function to control the multimode vibrations of a fixed beam. In this article this methodology has been extended to a rotating cantilever beam. To develop an effective control strategy, and optimize the placement of the active piezoelectric elements in terms of vibrations amplitude reduction, a procedure has been developed and a new analytical solution has been proproposed. The results obtained have been corroborated by comparison with the results from a multi-physics finite elements package (COMSOL) and data from other models available in the literature.
  • Journal article
    Veijgen NK, Masen MA, van der Heide E, 2013,

    Variables influencing the frictional behaviour of in vivo human skin

    , JOURNAL OF THE MECHANICAL BEHAVIOR OF BIOMEDICAL MATERIALS, Vol: 28, Pages: 448-461, ISSN: 1751-6161
  • Journal article
    Gattinoni C, Heyes DM, Lorenz CD, Dini Det al., 2013,

    Traction and nonequilibrium phase behavior of confined sheared liquids at high pressure

    , PHYSICAL REVIEW E, Vol: 88, ISSN: 1539-3755
  • Journal article
    Yang S, Reddyhoff T, Spikes H, 2013,

    Influence of Lubricant Properties on ARKL Temperature Rise and Transmission Efficiency

    , TRIBOLOGY TRANSACTIONS, Vol: 56, Pages: 1119-1136, ISSN: 1040-2004
  • Journal article
    Bertocchi L, Dini D, Giacopini M, Fowell MT, Baldini Aet al., 2013,

    Fluid film lubrication in the presence of cavitation: a mass-conserving two-dimensional formulation for compressible, piezoviscous and non-Newtonian fluids

    , TRIBOLOGY INTERNATIONAL, Vol: 67, Pages: 61-71, ISSN: 0301-679X
  • Journal article
    Rodriguez NV, Masen MA, Schipper DJ, 2013,

    A contact model for orthotropic-viscoelastic materials

    , International Journal of Mechanical Sciences, Vol: 74, Pages: 91-98, ISSN: 0020-7403
  • Journal article
    van Kuilenburg J, Masen MA, van der Heide E, 2013,

    The role of the skin microrelief in the contact behaviour of human skin: Contact between the human finger and regular surface textures

    , TRIBOLOGY INTERNATIONAL, Vol: 65, Pages: 81-90, ISSN: 0301-679X
  • Journal article
    Vengudusamy B, Green JH, Lamb GD, Spikes HAet al., 2013,

    Durability of ZDDP Tribofilms Formed in DLC/DLC Contacts

    , TRIBOLOGY LETTERS, Vol: 51, Pages: 469-478, ISSN: 1023-8883
  • Journal article
    van Arkel RJ, Modenese L, Phillips ATM, Jeffers JRTet al., 2013,

    Hip abduction can prevent posterior edge loading of hip replacements

    , JOURNAL OF ORTHOPAEDIC RESEARCH, Vol: 31, Pages: 1172-1179, ISSN: 0736-0266
  • Journal article
    Veijgen NK, van der Heide E, Masen MA, 2013,

    A multivariable model for predicting the frictional behaviour and hydration of the human skin

    , SKIN RESEARCH AND TECHNOLOGY, Vol: 19, Pages: 330-338, ISSN: 0909-752X
  • Journal article
    Accardi MA, McCullen SD, Callanan A, Chung S, Cann PM, Stevens MM, Dini Det al., 2013,

    Effects of fiber orientation on the frictional properties and damage of regenerative articular cartilage surfaces

    , Tissue Engineering: Parts A, B, and C, Vol: 19, Pages: 2300-2310, ISSN: 1937-3368

    Articular cartilage provides a low-friction, wear-resistant surface for diarthrodial joints. Due to overloading and overuse, articular cartilage is known to undergo significant wear and degeneration potentially resulting in osteoarthritis (OA). Regenerative medicine strategies offer a promising solution for the treatment of articular cartilage defects and potentially localized early OA. Such strategies rely on the development of materials to restore some aspects of cartilage. In this study, microfibrous poly(ɛ-caprolactone) scaffolds of varying fiber orientations (random and aligned) were cultured with bovine chondrocytes for 4 weeks in vitro, and the mechanical and frictional properties were evaluated. Mechanical properties were quantified using unconfined compression and tensile testing techniques. Frictional properties were investigated at physiological compressive strains occurring in native articular cartilage. Scaffolds were sheared along the fiber direction, perpendicular to the fiber direction and in random orientation. The evolution of damage as a result of shear was evaluated via white light interferometry and scanning electron microscopy. As expected, the fiber orientation strongly affected the tensile properties as well as the compressive modulus of the scaffolds. Fiber orientation did not significantly affect the equilibrium frictional coefficient, but it was, however, a key factor in dictating the evolution of surface damage on the surface. Scaffolds shear tested perpendicular to the fiber orientation displayed the highest surface damage. Our results suggest that the fiber orientation of the scaffold implanted in the joint could strongly affect its resistance to damage due to shear. Scaffold fiber orientation should thus be carefully considered when using microfibrous scaffolds.
  • Conference paper
    Oldfield MJ, Dini D, Jaiswal T, Rodriguez y Baena Fet al., 2013,

    The significance of rate dependency in blade insertions into a gelatin soft tissue phantom

    , 1st International Conference on Biotribology (ICoBT), Publisher: ELSEVIER SCI LTD, Pages: 226-234, ISSN: 0301-679X
  • Journal article
    Cann P, Dini D, 2013,

    International Conference on Biotribology (ICoBT)

    , TRIBOLOGY INTERNATIONAL, Vol: 63, Pages: 1-1, ISSN: 0301-679X
  • Conference paper
    Myant C, Cann P, 2013,

    In contact observation of model synovial fluid lubricating mechanisms

    , 1st International Conference on Biotribology (ICoBT), Publisher: ELSEVIER SCI LTD, Pages: 97-104, ISSN: 0301-679X
  • Journal article
    Thaitirarot A, Hills DA, Dini D, 2013,

    Contact mechanics of frictional lap joints

    , JOURNAL OF STRAIN ANALYSIS FOR ENGINEERING DESIGN, Vol: 48, Pages: 321-329, ISSN: 0309-3247
  • Journal article
    Rodriguez NV, Masen MA, Schipper DJ, 2013,

    A model for the contact behaviour of weakly orthotropic viscoelastic materials

    , INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES, Vol: 72, Pages: 75-79, ISSN: 0020-7403
  • Journal article
    Gurrutxaga-Lerma B, Balint D, Dini D, Eakins D, Sutton Aet al., 2013,

    A dynamic discrete dislocation plasticity method for the simulation of plastic relaxation under shock loading

    , Proceedings of the Royal Society A: Mathematical, Physical & Engineering Sciences, Vol: 469, ISSN: 1364-5021

    In this article, it is demonstrated that current methods of modelling plasticity as the collective motion of discrete dislocations, such as two-dimensional discrete dislocation plasticity (DDP), are unsuitable for the simulation of very high strain rate processes (106 s−1 or more) such as plastic relaxation during shock loading. Current DDP models treat dislocations quasi-statically, ignoring the time-dependent nature of the elastic fields of dislocations. It is shown that this assumption introduces unphysical artefacts into the system when simulating plasticity resulting from shock loading. This deficiency can be overcome only by formulating a fully time-dependent elastodynamic description of the elastic fields of discrete dislocations. Building on the work of Markenscoff & Clifton, the fundamental time-dependent solutions for the injection and non-uniform motion of straight edge dislocations are presented. The numerical implementation of these solutions for a single moving dislocation and for two annihilating dislocations in an infinite plane are presented. The application of these solutions in a two-dimensional model of time-dependent plasticity during shock loading is outlined here and will be presented in detail elsewhere.
  • Journal article
    Van Der Heide E, Zeng X, Masen MA, 2013,

    Skin tribology: Science friction?

    , FRICTION, Vol: 1, Pages: 130-142, ISSN: 2223-7690
  • Journal article
    Rodriguez NV, Masen MA, Schipper D-J, 2013,

    Tribologically modified surfaces on elastomeric materials

    , PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART J-JOURNAL OF ENGINEERING TRIBOLOGY, Vol: 227, Pages: 398-405, ISSN: 1350-6501
  • Journal article
    Moorhouse BS, Reddyhoff T, Ward-Close M, Ryan MP, Shollock BAet al., 2013,

    Formation of wear resistant coatings on Ti-6Al-4V by calciothermic reduction

    , SURFACE & COATINGS TECHNOLOGY, Vol: 221, Pages: 214-221, ISSN: 0257-8972
  • Journal article
    Ponjavic A, Wong JSS, 2013,

    The effect of boundary slip on elastohydrodynamic lubrication

    , RSC Advances, Vol: 4, Pages: 20821-20829, ISSN: 2046-2069
  • Journal article
    Hart AJ, Muirhead-Allwood S, Porter M, Matthies A, Ilo K, Maggiore P, Underwood R, Cann P, Cobb J, Skinner JAet al., 2013,

    Which Factors Determine the Wear Rate of Large-Diameter Metal-on-Metal Hip Replacements?

    , JOURNAL OF BONE AND JOINT SURGERY-AMERICAN VOLUME, Vol: 95A, Pages: 678-685, ISSN: 0021-9355
  • Journal article
    van Kuilenburg J, Masen MA, van der Heide E, 2013,

    Contact modelling of human skin: What value to use for the modulus of elasticity?

    , PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART J-JOURNAL OF ENGINEERING TRIBOLOGY, Vol: 227, Pages: 349-361, ISSN: 1350-6501
  • Journal article
    Le Rouzic J, Reddyhoff, Tom, 2013,

    Development of Infrared Microscopy for Measuring Asperity Contact Temperatures

    , Journal of Tribology, Vol: 135, Pages: 021504-021504, ISSN: 0742-4787
  • Journal article
    Ponjavic A, Chennaoui M, Wong JSS, 2013,

    Through-Thickness Velocity Profile Measurements in an Elastohydrodynamic Contact

    , Tribology Letters

    The through-thickness flow profile of a lubricant within an elastohydrodynamic contact is challenging to obtain due to its small thickness. Yet, this information is crucial to the accurate friction estimation of the tribological system. In this work, a novel fluorescence based technique has been developed to extract such information in situ. The local through-thickness flow profiles map within a tribological contact is obtained for the first time. The profiles obtained are position depends with slip boundary condition observed in high normal stress locations.
  • Journal article
    Kolekar AS, Olver AV, Sworski AE, Lockwood FEet al., 2013,

    The efficiency of a hypoid axle-a thermally coupled lubrication model

    , TRIBOLOGY INTERNATIONAL, Vol: 59, Pages: 203-209, ISSN: 0301-679X
  • Journal article
    Vengudusamy B, Green JH, Lamb GD, Spikes HAet al., 2013,

    Influence of hydrogen and tungsten concentration on the tribological properties of DLC/DLC contacts with ZDDP

    , WEAR, Vol: 298, Pages: 109-119, ISSN: 0043-1648
  • Journal article
    Ingram M, Underwood R, Denyer P, Cann Pet al., 2013,

    The development of a laboratory screening method to optimize lubrication maintenance of high voltage equipment

    , NLGI Spokesman, Vol: 76, Pages: 9-21, ISSN: 0027-6782

    Imperial College and National Grid Electricity Transmission carried out a study to evaluate lubrication maintenance of electrical switchgear used throughout the network. A discussion on this project covers the switchgear components and lubrication requirements; identification of lubricant degradation mechanisms; development of pertinent screening tests; survey of current lubricants used; and recommendations for the future.
  • Journal article
    Underwood RJ, Kocagoz SB, Smith R, Sayles RS, Siskey R, Kurtz SM, Cann PMet al., 2013,

    A protocol to assess the wear of head/neck taper junctions in large head metal-on-metal (LHMoM) hips

    , ASTM Special Technical Publication, Vol: 1560 STP, Pages: 209-234, ISSN: 0066-0558

    Researchers have hypothesized that the increased revision rate of LHMoM (Large Head Metal-on-Metal) hips compared to MoM hip resurfacings may be attributed to corrosion and wear at the head neck taper junction. Studies have reported visual evidence of fretting and corrosion at the taper junction, but no method has been described in the literature to quantify the amount of material lost from the taper junction. This paper describes a measurement protocol using a Taylor Hobson Talyrond Roundness instrument that allows the simultaneous measurement of surface form (wear) and surface topography (roughness). The methodology allows the measurement of the taper angle, geometry of worn region (depth, length), 3D surface maps and surface topography of the head conical taper. The accurate quantification of the taper geometry, wear and topography is essential to the understanding of the in vivo wear and corrosion mechanisms of taper junctions in LHMoM hips. Copyright © 2013 by ASTM International.
  • Journal article
    Underwood RJ, Fowell M, Sayles R, Kurtz SM, Cann Pet al., 2013,

    The development of a standard method for assessing wear of explanted metal-on-metal hip joints

    , ASTM Special Technical Publication, Vol: 1560 STP, Pages: 130-145, ISSN: 0066-0558

    The concerns surrounding the current generation of metal-on- metal (MoM) hips and the regulatory requirements regarding the reporting of revised MoM components highlight the need for a standardised method for measuring the wear of explanted MoM hip components. This paper reviews the published measurement and analysis protocols used in studies of explanted MoM hips. Because of differences in the measurement and analysis techniques, it is not reliable to directly compare measurements between studies. This paper considers the requirements for a standardised measurement protocol and forms the rationale for a proposed international standard. Copyright © 2013 by ASTM International.
  • Journal article
    Hills DA, Flicek RC, Dini D, 2013,

    Sharp contact corners, fretting and cracks

    , Frattura ed Integrita Strutturale, Vol: 7, Pages: 27-35

    Contacts with sharp edges subject to oscillatory loading are likely to nucleate cracks from the corners, if the loading is sufficiently severe. To a first approximation, the corners behave like notches, where the local elastic behaviour is relieved by plasticity, and which in turn causes irreversibilities that give rise to crack nucleation, but also by frictional slip. One question we aim to answer here is; when is the frictional slip enveloped by plastic slip, so that the corner is effectively a notch in a monolithic material? We do this by employing the classical Williams asymptotic solution to model the contact corner, and, in doing so, we render the solution completely general in the sense that it is independent of the overall geometry of the components. We then re-define the independent parameters describing the properties of the Williams solution by using the inherent length scale, a procedure that was described at the first IJFatigue and FFEMS joint workshop [1]. By proceeding in this way, we can provide a self-contained solution that can be 'pasted in' to any complete contact problem, and hence the likelihood of crack nucleation, and the circumstances under which it might occur, can be classified. Further, this reformulation of Williams' solution provides a clear means of obtaining the strength (defined by crack nucleation conditions) of a material pair with a particular contact angle. This means that the results from a test carried out using a laboratory specimen may easily be carried over to any complicated contact problem found in engineering practice, and a mechanical test of the prototypical geometry, which may often be quite difficult, is avoided.
  • Journal article
    Leong JY, Reddyhoff T, Sinha SK, Holmes AS, Spikes HAet al., 2013,

    Hydrodynamic friction reduction in a MAC-hexadecane lubricated MEMS contact

    , Tribology Letters, Vol: 49, Pages: 217-225, ISSN: 1023-8883

    Recent research has shown that hydrodynamic lubrication is an effective means of reducing friction in high sliding micro-electromechanical systems (MEMS). At high speeds, however, such lubrication can lead to increased friction due to viscous drag. This article describes a series of hydrodynamic tests on a silicon MEMS contact lubricated with a blend of hexadecane and a multiplyalkylated cyclopentane (MAC). Results show that the presence of the MAC reduces hydrodynamic friction compared with neat hexadecane. Such behaviour is contrary to conventional hydrodynamic theory, since the viscosity of the MAC - a mixture of di and tri(2 octyldodecyl)cyclopentane - is significantly higher than that of neat hexadecane. This effect increases with MAC concentration up to an optimum value of 3 wt%, where the hydrodynamic friction coefficient at 15,000 rpm is reduced from 0.5 to 0.3. Above this concentration, friction begins to rise due to the overriding effect of increasing viscosity. The viscosity of the blended lubricant increased monotonically with MAC concentration, when measured using both a Stabinger and an ultrahigh shear viscometer. In addition to this, no reduction in friction was observed when a squalane-hexadecane blend of equal viscosity was tested. This suggests that some property of the MAC-hexadecane lubricant, other than its viscosity, is influencing hydrodynamic lubrication. A tentative explanation for this behaviour is that the MAC induces the liquid to slip, rather than shear, close to the silicon surfaces. This hypothesis is supported by the fact that the friction reducing ability of the MAC blend was inhibited by the inclusion of octade-cylamine - a substance known to form films on silicon surfaces. Furthermore, the MAC reduces friction in the mixed regime, in a manner suggesting that the formation of a viscous boundary layer. This unusual behaviour may have useful implications for reducing hydrodynamic friction in liquidlubricated MEMS devices. © Sprin

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