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  This is an Open Access Journal Open Access journal
   ISSN (Online) 2075-4442
   Published by MDPI Homepage  [140 journals]
  • Lubricants, Vol. 3, Pages 80-90: Wear Tests of a Potential Biolubricant
           for Orthopedic Biopolymers

    • Authors: Martin Thompson, Ben Hunt, Alan Smith, Thomas Joyce
      Pages: 80 - 90
      Abstract: Most wear testing of orthopedic implant materials is undertaken with dilute bovine serum used as the lubricant. However, dilute bovine serum is different to the synovial fluid in which natural and artificial joints must operate. As part of a search for a lubricant which more closely resembles synovial fluid, a lubricant based on a mixture of sodium alginate and gellan gum, and which aimed to match the rheology of synovial fluid, was produced. It was employed in a wear test of ultra high molecular weight polyethylene pins rubbing against a metallic counterface. The test rig applied multidirectional motion to the test pins and had previously been shown to reproduce clinically relevant wear factors for ultra high molecular weight polyethylene. After 2.4 million cycles (125 km) of sliding in the presence of the new lubricant, a mean wear factor of 0.099 × 10−6 mm3/Nm was measured for the ultra high molecular weight polyethylene pins. This was over an order of magnitude less than when bovine serum was used as a lubricant. In addition, there was evidence of a transfer film on the test plates. Such transfer films are not seen clinically. The search for a lubricant more closely matching synovial fluid continues.
      PubDate: 2015-03-25
      DOI: 10.3390/lubricants3020080
      Issue No: Vol. 3, No. 2 (2015)
  • Lubricants, Vol. 3, Pages 91-112: Survey of Damage Investigation of
           Babbitted Industrial Bearings

    • Authors: Lyle Branagan
      Pages: 91 - 112
      Abstract: This survey collects the efforts to understand the sources and consequences of damage to babbitted industrial bearings, which operate by means of a hydrodynamic, or hydrostatic, film. Major individual damage types are discussed in the context of major damage categories.
      PubDate: 2015-04-01
      DOI: 10.3390/lubricants3020091
      Issue No: Vol. 3, No. 2 (2015)
  • Lubricants, Vol. 3, Pages 113-131: Numerical Treatments of
           Slipping/No-Slip Zones in Cold Rolling of Thin Sheets with Heavy Roll

    • Authors: Yukio Shigaki, Rebecca Nakhoul, Pierre Montmitonnet
      Pages: 113 - 131
      Abstract: In the thin sheet cold rolling manufacturing process, a major issue is roll elastic deformation and its impact on roll load, torque and contact stresses. As in many systems implying mechanical contact under high loading, a central part is under “sticking friction” (no slip) while both extremities do slip to accommodate the material acceleration of the rolled metal sheet. This is a crucial point for modeling of such rolling processes and the numerical treatment of contact and friction (“regularized” or not), of the transition between these zones, does have an impact on the results. Two ways to deal with it are compared (regularization of the stick/slip transition, direct imposition of a no-slip condition) and recommendations are given.
      PubDate: 2015-04-02
      DOI: 10.3390/lubricants3020113
      Issue No: Vol. 3, No. 2 (2015)
  • Lubricants, Vol. 3, Pages 132-141: Frictional Characteristics of a Small
           Aerostatic Linear Bearing

    • Authors: Ryosuke Araki, Akihiro Takita, Prin Nachaisit, Dong-Wei Shu, Yusaku Fujii
      Pages: 132 - 141
      Abstract: Frictional characteristics of a small aerostatic linear bearing are accurately evaluated by means of a method, in which the force acting on the moving part of the bearing is measured as the inertial force. An optical interferometer is newly developed to measure the Doppler shift frequency of the laser light reflected on the small moving part. From the measured time-varying Doppler shift frequency, the velocity, the position, the acceleration and the inertial force of the moving part are numerically calculated. It is confirmed that the dynamic frictional force acting inside the bearing is almost proportional to the velocity of the moving part and is similar to the theoretical value calculated under the assumption that the flow inside the bearing is the Couette flow.
      PubDate: 2015-04-02
      DOI: 10.3390/lubricants3020132
      Issue No: Vol. 3, No. 2 (2015)
  • Lubricants, Vol. 3, Pages 142-154: Analysis of the Journal Bearing
           Friction Losses in a Heavy-Duty Diesel Engine

    • Authors: Christoph Knauder, Hannes Allmaier, David Sander, Stefan Reich, Theodor Sams
      Pages: 142 - 154
      Abstract: Internal combustion engines (ICE) for the use in heavy-duty trucks and buses have to fulfil demanding requirements for both vehicle efficiency as well as for emission of greenhouse gases. Beside the piston assembly the journal bearings are among the largest contributors to friction in the ICE. Through a combination of measurements and validated simulation methods the journal bearing friction losses of a state-of-the-art heavy-duty Diesel engine are investigated for a large range of real world operating conditions. To this task recently developed and extensively validated simulation methods are used together with realistic lubricant models that consider the Non-Newtonian behaviour as well as the piezoviscous effect. In addition, the potential for further friction reduction with the use of ultra-low viscosity lubricants is explored. The results reveal a potential of about 8% friction reduction in the journal bearings using a 0W20 ultra-low viscosity oil with an HTHS-viscosity (The HTHS-viscosity is defined as the dynamic viscosity of the lubricant measured at 150 °C and at a shear rate of 106 s
      PubDate: 2015-04-02
      DOI: 10.3390/lubricants3020142
      Issue No: Vol. 3, No. 2 (2015)
  • Lubricants, Vol. 3, Pages 155-163: Experimental Measurements of Journal
           Bearing Friction Using Mineral, Synthetic, and Bio-Based Lubricants

    • Authors: Pantelis Nikolakopoulos, Dimitrios Bompos
      Pages: 155 - 163
      Abstract: The environmental impact of many industrial and naval applications is becoming increasingly important. Journal bearings are crucial components related with the reliable, safe and environmentally friendly operation of rotating machinery in many applications, e.g., in hydroplants, ships, power generation stations. The maintenance activities in certain cases also have considerable environmental impact. Fortunately, it is relatively easy to reduce the impact by changing the way lubricants are being used. Selecting the proper lubricant is important to sharply reduce long-term costs. The best-fit product selection can mean longer lubricant life, reduced machine wear, reduced incipient power losses and improved safety. Suitable basestocks and additives reduce environmental impact. In this paper, three types of lubricants are used in order to examine their effects on the tribological behavior of journal bearings. A mineral oil, a synthetic oil and a bio-based lubricant are experimentally and analytically examined for several configurations of load and journal rotational velocity. The friction forces and the hydrodynamic friction coefficients are calculated and compared. This investigation can assist the correct choice of lubricant in journal bearings with minimized environmental footprint.
      PubDate: 2015-04-03
      DOI: 10.3390/lubricants3020155
      Issue No: Vol. 3, No. 2 (2015)
  • Lubricants, Vol. 3, Pages 164-180: Friction and Lubrication of Large
           Tilting-Pad Thrust Bearings

    • Authors: Michał Wasilczuk
      Pages: 164 - 180
      Abstract: Fluid film bearings have been extensively used in the industry because of their unbeatable durability and extremely low friction coefficient, despite a very low coefficient of friction dissipation of energy being noticeable, especially in large bearings. Lubricating systems of large tilting pad thrust bearings utilized in large, vertical shaft hydrogenerators are presented in this paper. A large amount of heat is generated due to viscous shearing of the lubricant large tilting pad thrust bearings, and this requires systems for forced cooling of the lubricant. In the dominant bath lubrication systems, cooling is realized by internal coolers or external cooling systems, with the latter showing some important advantages at the cost of complexity and also, potentially, lower reliability. Substantial losses in the bearings, reaching 1 MW in extreme cases, are a good motivation for the research and development aimed at reducing them. Some possible methods and their potential efficiency, along with some effects already documented, are also described in the paper.
      PubDate: 2015-04-03
      DOI: 10.3390/lubricants3020164
      Issue No: Vol. 3, No. 2 (2015)
  • Lubricants, Vol. 3, Pages 181-196: Running Torque of Slow Speed Two-Point
           and Four-Point Contact Bearings

    • Authors: Amit Joshi, Bhavesh Kachhia, Harsha Kikkari, Mandyam Sridhar, Daniel Nelias
      Pages: 181 - 196
      Abstract: A decoupled slow speed friction torque model has been developed to predict the running torque of a double-arched angular contact bearing when operating as a four-point, as well as a two-point contact bearing. The load distribution model from Amasorrain et al. (2003) and the kinematics model developed by Leblanc and Nelias (2007) have been combined after ignoring centrifugal and gyroscopic effects, a valid assumption for slow speed operation. Results from the model are compared with previous literature data, as well as with tests done on a specially-developed friction torque rig. The comparison with the literature results was done for two specific cases: (i) when only one out of the two contact lines in the four-point contact bearing is active (effectively creating a two-point contact bearing); and (ii) where both contact lines in the four-point contact bearing are active. Further, the comparison was done with a custom-built friction torque rig with FAG QJ309 bearings, again for two cases: (i) bearings mounted with a specific clearance (two-point contact); and (ii) bearings mounted with larger size balls to obtain interference (four-point contact). All tests were performed at low speeds. The sliding friction, which is an important input to the friction torque model, is carefully measured on ball-on-plate test using the same interface roughness, speed and contact pressure conditions as seen in the QJ309 friction test. The model comparison with experimental results is covered. The comparison is found to be encouraging, with the RMS difference being less than 7% between the model and experimental data for a four point contact.
      PubDate: 2015-04-09
      DOI: 10.3390/lubricants3020181
      Issue No: Vol. 3, No. 2 (2015)
  • Lubricants, Vol. 3, Pages 197-221: Grease Aging Effects on Film Formation
           under Fully-Flooded and Starved Lubrication

    • Authors: Tiago Cousseau, Beatriz Graça, Armando Campos, Jorge Seabra
      Pages: 197 - 221
      Abstract: Several film thickness measurements were performed with three fresh and aged lubricating greases, their base and bled oils under a wide range of operating conditions using a ball-on-disc test rig with optical interferometry. The analysis of the film thickness measurements is in agreement with the observations of several authors and adds some important aspects regarding separate film properties in EHL contacts. At full film lubrication and moderate to high speeds, the bled oil showed a similar behavior of its lubricating greases. At fully-flooded condition, low speeds and thin films, it was observed that the thickener lumps play a major role on film formation, overcoming the bled oil effects. A relationship between thickener type and film formation was evidenced. The same trends were observed under starved lubrication, where the thickener type that contributes the most to locally increase the film thickness follows the order of PP > Ca > Li. The aging process of the greases was shown to change their rheological response in different manners—softening or hardening—depending on the grease formulation. Grease aging increased the film thickness under fully-flooded and starved lubrication, regardless of the level of degradation.
      PubDate: 2015-04-09
      DOI: 10.3390/lubricants3020197
      Issue No: Vol. 3, No. 2 (2015)
  • Lubricants, Vol. 3, Pages 222-243: Rolling Friction Torque in Ball-Race
           Contacts Operating in Mixed Lubrication Conditions

    • Authors: Mihaela Bălan, Luc Houpert, Ana Tufescu, Dumitru Olaru
      Pages: 222 - 243
      Abstract: Based on a theoretical model and an experimental methodology for defining the friction torque for lubricated conditions in a modified thrust ball bearing having only three balls, the authors experimentally investigated the influence of the lubricant parameter Λ on friction torque for mixed IVR (isoviscous rigid) and EHL (elastohydrodynamic) lubrication conditions. The experiments were conducted using ball diameters of 3 mm, 3.97 mm and 6.35 mm loaded at 0.125 N, 0.400 N and 0.633 N. Two oils of viscosity 0.08 Pa·s and 0.05 Pa·s were used and rotational speed was varied in the range 60–210 rpm to obtain a lubricant parameter Λ varying between 0.3 and 3.2. The experiments confirmed that the measured friction torque can be explained using hydrodynamic rolling force relationships respecting the transition from an IVR to an EHL lubrication regime.
      PubDate: 2015-04-13
      DOI: 10.3390/lubricants3020222
      Issue No: Vol. 3, No. 2 (2015)
  • Lubricants, Vol. 3, Pages 244-255: In Vitro Wear Testing of a CoCr-UHMWPE
           Finger Prosthesis with Hydroxyapatite Coated CoCr Stems

    • Authors: Andrew Naylor, Sumedh Talwalkar, Ian Trail, Thomas Joyce
      Pages: 244 - 255
      Abstract: A finger prosthesis consisting of a Cobalt-chromium (CoCr) proximal component and an Ultra-high-molecular-weight-polyethylene (UHMWPE) medial component (both mounted on hydroxyapatite coated stems) was evaluated to 5,000,000 cycles in an in vitro finger simulator. One “test” prosthesis was cycled through flexion-extension (90°–30°) with a dynamic load of 10 N, whilst immersed in a lubricant of dilute bovine serum. Additionally, a static load of 100 N was applied for 45 s every 3000 cycles to simulate a static gripping force. A second “control” prosthesis was immersed in the same lubricant to account for absorption. Gravimetric and Sa (3D roughness) measurements were taken at 1,000,000 cycle intervals. Micrographs and Sa values revealed negligible change to the CoCr surfaces after 5,000,000 cycles. The UHMWPE also exhibited no distinctive Sa trend, however the micrographs indicate that polishing occurred. Both the CoCr and UHMWPE test components progressively decreased in weight. The CoCr control component did not change in weight, whilst the UHMWPE component gained weight through absorption. To account for the disparity between surface and gravimetric results, the hydroxyapatite coatings were examined. Micrographs of the test stems revealed that the hydroxyapatite coating was partially removed, whilst the micrographs of the control stems exhibited a uniform coating.
      PubDate: 2015-04-13
      DOI: 10.3390/lubricants3020244
      Issue No: Vol. 3, No. 2 (2015)
  • Lubricants, Vol. 3, Pages 256-280: Thermo-Hydrodynamic Analysis of a Plain
           Journal Bearing on the Basis of a New Mass Conserving Cavitation Algorithm

    • Authors: Shivam Alakhramsing, Ron van Ostayen, Rob Eling
      Pages: 256 - 280
      Abstract: Accurate prediction of cavitation is an important feature in hydrodynamic bearing modeling. Especially for thermo-hydrodynamic modeling, it is crucial to use a mass-conservative cavitation algorithm. This paper introduces a new mass-conserving Reynolds cavitation algorithm, which provides fast convergence and easy implementation in finite element models. The proposed algorithm is based on a variable transformation for both the pressure and mass fraction, which is presented in the form of a complementary condition. Stabilization in the streamline and crosswind direction is provided by artificial diffusion. The model is completed by including a simple and efficient thermal model and is validated using the numerical values of a reference plain journal bearing experiment under steady-state conditions. In addition, a transient analysis is performed of a journal bearing subjected to a harmonic load. It is shown that the proposed cavitation algorithm results are in good agreement with the reference measurement results. Moreover, the algorithm proves to be stable and requires only a small number of iterations to convergence in the Reynolds-based finite element model.
      PubDate: 2015-04-13
      DOI: 10.3390/lubricants3020256
      Issue No: Vol. 3, No. 2 (2015)
  • Lubricants, Vol. 3, Pages 281-310: Nonlinear Dynamic Response of an
           Unbalanced Flexible Rotor Supported by Elastic Bearings Lubricated with
           Piezo-Viscous Polar Fluids

    • Authors: Mustapha Lahmar, Benyebka Bou-Saïd
      Pages: 281 - 310
      Abstract: On the basis of the V. K. Stokes micro-continuum theory, the effects of couple stresses on the nonlinear dynamic response of the unbalanced Jeffcott’s flexible rotor supported by layered hydrodynamic journal bearings is presented in this paper. A nonlinear transient modified Reynolds’ equation is derived and discretized by the finite element method to obtain the fluid-film pressure field as well as the film thickness by means of the implicit Euler method. The nonlinear orbits of the rotor center are determined by solving the nonlinear differential equations of motion with the explicit Euler’s scheme taking into account the flexibility of rotor. According to the obtained results, the combined effects of couple stresses due to the presence of polymer additives in lubricant and the pressure dependent viscosity on the nonlinear dynamic response of the rotor-bearing system are significant and cannot be ignored or overlooked. As expected, these effects are more noticeable for polymers characterized by higher length molecular chains.
      PubDate: 2015-04-16
      DOI: 10.3390/lubricants3020281
      Issue No: Vol. 3, No. 2 (2015)
  • Lubricants, Vol. 3, Pages 311-331: How Does Dissipation Affect the
           Transition from Static to Dynamic Macroscopic Friction?

    • Authors: Naum Gershenzon, Gust Bambakidis, Thomas Skinner
      Pages: 311 - 331
      Abstract: Description of the transitional process from a static to a dynamic frictional regime is a fundamental problem of modern physics. Previously, we developed a model based on the well-known Frenkel-Kontorova model to describe dry macroscopic friction. Here, this model has been modified to include the effect of dissipation in derived relations between the kinematic and dynamic parameters of a transition process. The main (somewhat counterintuitive) result is a demonstration that the rupture (i.e., detachment front) velocity of the slip pulse which arises during the transition does not depend on friction. The only parameter (besides the elastic and plastic properties of the medium) controlling the rupture velocity is the shear to normal stress ratio. In contrast to the rupture velocity, the slip velocity does depend on friction. The model we have developed describes these processes over a wide range of rupture and slip velocities (up to 7 orders of magnitude) allowing, in particular, the consideration of seismic events ranging from regular earthquakes, with rupture velocities on the order of a few km/s, to slow slip events, with rupture velocities of a few km/day.
      PubDate: 2015-04-16
      DOI: 10.3390/lubricants3020311
      Issue No: Vol. 3, No. 2 (2015)
  • Lubricants, Vol. 3, Pages 332-345: Correlation between System Entropy and
           Structural Changes in Lubricating Grease

    • Authors: Erik Kuhn
      Pages: 332 - 345
      Abstract: Lubricating greases are colloid disperse systems consisting of a base oil and a thickener (additional additives). The lubricant is modeled as a tribological system, and the reaction of a fluid friction stress is investigated. The energetic situation of the volume element is analyzed and the system entropy described. The description of the structural degradation and the used entropy was realized with the help of rheometer tests.
      PubDate: 2015-04-24
      DOI: 10.3390/lubricants3020332
      Issue No: Vol. 3, No. 2 (2015)
  • Lubricants, Vol. 3, Pages 346-364: Materials and Their Failure Mechanisms
           in Total Disc Replacement

    • Authors: John Reeks, Hong Liang
      Pages: 346 - 364
      Abstract: Adults suffering from lower back pain often find the cause of pain is degenerative disc disease. While non-surgical treatment is preferred, spinal fusion and total disc replacement remain surgical options for the patient. Total disc replacement is an emerging and improving treatment for degenerative discs. This paper provides a review of lumbar disc replacement for treatment of lower back pain. The mechanics and configuration of the natural disc are first discussed, followed by an introduction of treatment methods that attempt to mimic these mechanics. Total disc replacement types, materials, and failure mechanisms are discussed. Failure mechanisms primarily involve biochemical reactions to implant wear, as well as mechanical incompatibility of the device with natural spine motion. Failure mechanisms include: osteolysis, plastic deformation of polymer components, pitting, fretting, and adjacent level facet and disc degeneration.
      PubDate: 2015-04-28
      DOI: 10.3390/lubricants3020346
      Issue No: Vol. 3, No. 2 (2015)
  • Lubricants, Vol. 3, Pages 365-380: Relationship between Supplied Oil Flow
           Rates and Oil Film Thicknesses under Starved Elastohydrodynamic

    • Authors: Taisuke Maruyama, Tsuyoshi Saitoh
      Pages: 365 - 380
      Abstract: Many studies have already considered starved lubrication. However, there have been no reports on the oil film thicknesses under steady starved EHL (elastohydrodynamic lubrication), where the ultra-low volume of oil supplied per unit time is uniform. The present study examined the relationship between the supplied oil flow rate and oil film thickness under steady starved lubrication. A ball-on-disk testing machine was used in experiments to measure the oil film thickness by means of optical interferometry. A microsyringe pump was used to accurately control the supplied oil flow rate. The supplied oil flow rate was kept constant, and the minimum oil film thickness was measured for 1 h after the start of the tests to determine the relationship between the supplied oil flow rate and oil film thickness.
      PubDate: 2015-04-28
      DOI: 10.3390/lubricants3020365
      Issue No: Vol. 3, No. 2 (2015)
  • Lubricants, Vol. 3, Pages 381-393: Prediction of Wear in Crosslinked
           Polyethylene Unicompartmental Knee Arthroplasty

    • Authors: Jonathan Netter, Juan Hermida, Cesar Flores-Hernandez, Nikolai Steklov, Mark Kester, Darryl D'Lima
      Pages: 381 - 393
      Abstract: Wear-related complications remain a major issue after unicompartmental arthroplasty. We used a computational model to predict knee wear generated in vitro under diverse conditions. Inverse finite element analysis of 2 different total knee arthroplasty designs was used to determine wear factors of standard and highly crosslinked polyethylene by matching predicted wear rates to measured wear rates. The computed wear factor was used to predict wear in unicompartmental components. The articular surface design and kinematic conditions of the unicompartmental and tricompartmental designs were different. Predicted wear rate (1.77 mg/million cycles) was very close to experimental wear rate (1.84 mg/million cycles) after testing in an AMTI knee wear simulator. Finite element analysis can predict experimental wear and may reduce the cost and time of preclinical testing.
      PubDate: 2015-05-07
      DOI: 10.3390/lubricants3020381
      Issue No: Vol. 3, No. 2 (2015)
  • Lubricants, Vol. 3, Pages 394-412: The Synovial Lining and Synovial Fluid
           Properties after Joint Arthroplasty

    • Authors: Michael Kung, John Markantonis, Scott Nelson, Patricia Campbell
      Pages: 394 - 412
      Abstract: The lubrication of the cartilaginous structures in human joints is provided by a fluid from a specialized layer of cells at the surface of a delicate tissue called the synovial lining. Little is known about the characteristics of the fluids produced after a joint arthroplasty procedure. A literature review was carried out to identify papers that characterized the synovial lining and the synovial fluids formed after total hip or knee arthroplasty. Five papers about synovial lining histology and six papers about the lubricating properties of the fluids were identified. The cells making up the re-formed synovial lining, as well as the lining of interface membranes, were similar to the typical Type A and B synoviocytes of normal joints. The synovial fluids around joint replacement devices were typically lower in viscosity than pre-arthroplasty fluids but the protein concentration and phospholipid concentrations tended to be comparable, suggesting that the lining tissue function was preserved after arthroplasty. The widespread, long-term success of joint arthroplasty suggests that the lubricant formed from implanted joint synovium is adequate for good clinical performance in the majority of joints. The role the fluid plays in component wear or failure is a topic for future study.
      PubDate: 2015-05-18
      DOI: 10.3390/lubricants3020394
      Issue No: Vol. 3, No. 2 (2015)
  • Lubricants, Vol. 3, Pages 413-436: Wear Performance of UHMWPE and
           Reinforced UHMWPE Composites in Arthroplasty Applications: A Review

    • Authors: Juan Baena, Jingping Wu, Zhongxiao Peng
      Pages: 413 - 436
      Abstract: As the gold standard material for artificial joints, ultra-high-molecular-weight polyethylene (UHMWPE) generates wear debris when the material is used in arthroplasty applications. Due to the adverse reactions of UHMWPE wear debris with surrounding tissues, the life time of UHMWPE joints is often limited to 15–20 years. To improve the wear resistance and performance of the material, various attempts have been made in the past decades. This paper reviews existing improvements made to enhance its mechanical properties and wear resistance. They include using gamma irradiation to promote the cross-linked structure and to improve the wear resistance, blending vitamin E to protect the UHMWPE, filler incorporation to improve the mechanical and wear performance, and surface texturing to improve the lubrication condition and to reduce wear. Limitations of existing work and future studies are also identified.
      PubDate: 2015-05-18
      DOI: 10.3390/lubricants3020413
      Issue No: Vol. 3, No. 2 (2015)
  • Lubricants, Vol. 3, Pages 437-446: An Insight to High Humidity-Caused
           Friction Modulation of Brake by Numerical Modeling of Dynamic Meniscus
           under Shearing

    • Authors: Liangbiao Chen, Gang Chen, James Chang
      Pages: 437 - 446
      Abstract: To obtain an insight to high humidity-caused friction modulation in brake pad-rotor interface, the adhesion phenomenon due to a liquid bridge is simulated using an advanced particle method by varying the shearing speed of the interface. The method, called generalized interpolation material point for fluid-solid interactions (GIMP-FSI), was recently developed from the material point method (MPM) for fluid-solid interactions at small scales where surface tension dominates, thus suitable for studying the partially wet brake friction due to high humidity at a scale of 10 m. Dynamic capillary effects due to surface tension and contact angles are simulated. Adhesion forces calculated by GIMP-FSI are consistent with those from the existing approximate meniscus models. Moreover, the numerical results show that capillary effects induce modulations of adhesion as slip speed changes. In particular, the adhesion modulation could be above 30% at low speed. This finding provides insights into how the high humidity-caused friction could cause modulations of brake, which are unable to be achieved by conventional models. Therefore, the numerical analysis helps to elucidate the complex friction mechanisms associated with brakes that are exposed to high humidity environments.
      PubDate: 2015-05-19
      DOI: 10.3390/lubricants3020437
      Issue No: Vol. 3, No. 2 (2015)
  • Lubricants, Vol. 3, Pages 1-2: Acknowledgement to Reviewers of Lubricants
           in 2014

    • Authors: Lubricants Office
      Pages: 1 - 2
      Abstract: The editors of Lubricants would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2014:[...]
      PubDate: 2015-01-09
      DOI: 10.3390/lubricants3010001
      Issue No: Vol. 3, No. 1 (2015)
  • Lubricants, Vol. 3, Pages 3-13: Experimental Performance Study of a High
           Speed Oil Lubricated Polymer Thrust Bearing

    • Authors: Jie Zhou, Barry Blair, John Argires, Donald Pitsch
      Pages: 3 - 13
      Abstract: With the demand for turbomachinery to operate at higher speeds, loads, and power, fluid film bearings that support turbomachinery must be capable of operating in these more demanding applications. Thrust bearings operating at high speeds and loads can experience high surface temperatures and thin fluid film thickness. Typically, babbitt (white metal) is the bearing lining material for most turbomachinery bearings but is limited in operating temperature and allowable film thickness. Polymer based materials are alternative materials that can operate at high temperatures and with thin films and have been in use for many decades in high load applications, such as electric submersible pumps (ESP). Test results of polymer lined thrust bearings subjected to modern turbomachinery speeds and loads are presented and compared to babbitt lined bearings of the same design and under similar conditions. The test results show polymer lined thrust bearings can operate at higher bearing unit loads than babbitt.
      PubDate: 2015-01-21
      DOI: 10.3390/lubricants3010003
      Issue No: Vol. 3, No. 1 (2015)
  • Lubricants, Vol. 3, Pages 14-26: Wear Performance of Sequentially
           Cross-Linked Polyethylene Inserts against Ion-Treated CoCr, TiNbN-Coated
           CoCr and Al2O3 Ceramic Femoral Heads for Total Hip Replacement

    • Authors: Christian Fabry, Carmen Zietz, Axel Baumann, Rainer Bader
      Pages: 14 - 26
      Abstract: The aim of the present study was to evaluate the biotribology of current surface modifications on femoral heads in terms of wettability, polyethylene wear and ion-release behavior. Three 36 mm diameter ion-treated CoCr heads and three 36 mm diameter TiNbN-coated CoCr heads were articulated against sequentially cross-linked polyethylene inserts (X3) in a hip joint simulator, according to ISO 14242. Within the scope of the study, the cobalt ion release in the lubricant, as well as contact angles at the bearing surfaces, were investigated and compared to 36 mm alumina ceramic femoral heads over a period of 5 million cycles. The mean volumetric wear rates were 2.15 ± 0.18 mm3·million cycles−1 in articulation against the ion-treated CoCr head, 2.66 ± 0.40 mm3·million cycles−1 for the coupling with the TiNbN-coated heads and 2.17 ± 0.40 mm3·million cycles−1 for the ceramic heads. The TiNbN-coated femoral heads showed a better wettability and a lower ion level in comparison to the ion-treated CoCr heads. Consequently, the low volumes of wear debris, which is comparable to ceramics, and the low concentration of metal ions in the lubrication justifies the use of coated femoral heads.
      PubDate: 2015-02-16
      DOI: 10.3390/lubricants3010014
      Issue No: Vol. 3, No. 1 (2015)
  • Lubricants, Vol. 3, Pages 27-53: On the Characteristics of Misaligned
           Journal Bearings

    • Authors: Joon Jang, Michael Khonsari
      Pages: 27 - 53
      Abstract: Journal bearing misalignment arise generally from the shaft deformation under load, deflection of the shaft, manufacturing and assembly errors, improper installation, and asymmetric loading. During operations, misalignment has a considerable effect on the static and dynamic performances. It could cause wear, vibration and even system failure. In this article, a literature review of misalignment of the journal bearings is presented. The basic theory for the misalignment and some results for the circular journal bearing are also presented to show the general trends of the misalignment.
      PubDate: 2015-03-16
      DOI: 10.3390/lubricants3010027
      Issue No: Vol. 3, No. 1 (2015)
  • Lubricants, Vol. 3, Pages 54-79: Characterization of Thermal Stability of
           Synthetic and Semi-Synthetic Engine Oils

    • Authors: Anand Tripathi, Ravikrishnan Vinu
      Pages: 54 - 79
      Abstract: Engine oils undergo oxidative degradation and wears out during service. Hence it is important to characterize ageing of engine oils at different simulated conditions to evaluate the performance of existing oils and also design new formulations. This work focuses on characterizing the thermo-oxidative degradation of synthetic and semi-synthetic engine oils aged at 120, 149 and 200 °C. Apparent activation energy of decomposition of aged oils evaluated using the isoconversional Kissinger-Akahira-Sunose technique was used as a thermal stability marker. The temporal variation of stability at different ageing temperatures was corroborated with kinematic viscosity, oxidation, sulfation and nitration indices, total base number, antiwear additive content and molecular structure of the organic species present in the oils. At the lowest temperature employed, synthetic oil underwent higher rate of oxidation, while semi-synthetic oil was stable for longer time periods. At higher temperatures, the initial rate of change of average apparent activation energy of synthetic oil correlated well with a similar variation in oxidation number. A mixture of long chain linear, branched, and cyclic hydrocarbons were observed when semi-synthetic oil was degraded at higher temperatures.
      PubDate: 2015-03-17
      DOI: 10.3390/lubricants3010054
      Issue No: Vol. 3, No. 1 (2015)
  • Lubricants, Vol. 2, Pages 162-176: Windage Power Losses of Ordinary Gears:
           Different CFD Approaches Aimed to the Reduction of the Computational

    • Authors: Franco Concli, Carlo Gorla, Augusto Della Torre, Gianluca Montenegro
      Pages: 162 - 176
      Abstract: Efficiency improvement is one of the main challenges in all fields of design. The reduction of power losses is becoming a great concern also in the design of power transmissions. For this reason it is important to have specific models available in order to quantify the power losses during the design stage. The power losses of a gear transmission can be subdivided into bearing losses, seal losses, meshing losses and hydraulic losses. Although literature provides models for the prediction of losses related to bearings or to gear meshing, for the calculations of the losses generated by the interaction with the lubricant, only few and simplified models are available. For this reason the authors recognize that a general purpose method is required in order to overcome this lack of fit and to improve the capability to predict the efficiency of gearboxes. Being able to compare different design solutions means being able to improve the efficiency, reduce the operating temperature and, consequently, improve the reliability of the system. In this paper, the windage losses generated by a single rotating gear have been studied exploiting different numerical approaches. The results obtained have been compared with measurements showing good agreement.
      PubDate: 2014-10-15
      DOI: 10.3390/lubricants2040162
      Issue No: Vol. 2, No. 4 (2014)
  • Lubricants, Vol. 2, Pages 177-192: Influence of Temperature on the
           Frictional Properties of Water-Lubricated Surfaces

    • Authors: Troels Røn, Seunghwan Lee
      Pages: 177 - 192
      Abstract: The influence of temperature on the lubricating properties of neat water for tribopairs with varying bulk elasticity moduli and surface hydrophilicity, namely hard-hydrophobic interface (h-HB), hard-hydrophilic interface (h-HL), soft-hydrophobic interface (s-HB), and soft-hydrophilic interface (s-HL), has been investigated. With increasing temperature, the coefficients of friction generally increased due to the decreasing viscosity of water. This change was more clearly manifested from soft interfaces for more feasible formation of lubricating films. Nevertheless, dominant lubrication mechanism appears to be boundary and mixed lubrication even for soft interfaces at all speeds (up to 1200 mm/s) and temperatures (1 to 90 °C) investigated. The results from this study are expected to provide a reference to explore the temperature-dependent tribological behavior of more complex aqueous lubricants, e.g., those involving various additives, for a variety of tribosystems.
      PubDate: 2014-10-15
      DOI: 10.3390/lubricants2040177
      Issue No: Vol. 2, No. 4 (2014)
  • Lubricants, Vol. 2, Pages 193-205: Development and Validation of a Wear
           Model to Predict Polyethylene Wear in a Total Knee Arthroplasty: A Finite
           Element Analysis

    • Authors: Bernardo Innocenti, Luc Labey, Amir Kamali, Walter Pascale, Silvia Pianigiani
      Pages: 193 - 205
      Abstract: Ultra-high molecular weight polyethylene (UHMWPE) wear in total knee arthroplasty (TKA) components is one of the main reasons of the failure of implants and the consequent necessity of a revision procedure. Experimental wear tests are commonly used to quantify polyethylene wear in an implant, but these procedures are quite expensive and time consuming. On the other hand, numerical models could be used to predict the results of a wear test in less time with less cost. This requires, however, that such a model is not only available, but also validated. Therefore, the aim of this study is to develop and validate a finite element methodology to be used for predicting polyethylene wear in TKAs. Initially, the wear model was calibrated using the results of an experimental roll-on-plane wear test. Afterwards, the developed wear model was applied to predict patello-femoral wear. Finally, the numerical model was validated by comparing the numerically-predicted wear, with experimental results achieving good agreement.
      PubDate: 2014-11-18
      DOI: 10.3390/lubricants2040193
      Issue No: Vol. 2, No. 4 (2014)
  • Lubricants, Vol. 2, Pages 206-222: Modeling and Forecasting of Depletion
           of Additives in Car Engine Oils Using Attenuated Total Reflectance Fast
           Transform Infrared Spectroscopy

    • Authors: Ronald Nguele, Hikmat Al-Salim, Khalid Mohamad
      Pages: 206 - 222
      Abstract: On average, additives make up to 7% of a typical lubricant base. Commonly, they are blended with lube oils to enhance specific features thereby improving their qualities. Ultimately, additives participate in the performance of car engine oils. Using an analytical tool, attenuated total reflectance fast transform infrared spectroscopy, various grades of car engine oils, at different mileages, were analyzed. Sulfate oxidation and wear were found to trigger chemical processes which, in the long run, cause lubricant degradation while carbonyl oxidation was observed to occur only at a slow rate. Based upon data obtained from infrared spectra and using a curve fitting technique, mathematical equations predicting the theoretical rates of chemical change due to the aforementioned processes were examined. Additive depletions were found to obey exponential regression rather than polynomial. Moreover, breakpoint (breakpoint is used here to denote the initiation of deterioration of additives) and critical mileage (critical mileage defines the distance at which the lubricant is chemically unusable) of both samples were determined.
      PubDate: 2014-11-26
      DOI: 10.3390/lubricants2040206
      Issue No: Vol. 2, No. 4 (2014)
  • Lubricants, Vol. 2, Pages 223-236: Detection of Elemental Composition of
           Lubricating Grease Using Laser Induced Breakdown Spectroscopy

    • Authors: Cherry Dhiman, Martha Reddy, Kamal Gulati, Mohd. Khan
      Pages: 223 - 236
      Abstract: The elemental composition of lubricating soft grease used in rail engines are studied using laser induced breakdown spectroscopy (LIBS) technique. LIBS spectra of fresh, partially used and fully used grease samples are recorded using time-gated ICCD spectrometer for verification of compositional degradation of the used grease. LIBS spectra of grease samples are analyzed by comparing with emission spectra of elements published by NIST standard database. Many spectral lines of impurity elements like Fe, Cu, Ba, Mg, Mn, Ni, S, Zn, Si, Pb, Ti, Ca and Al present in the grease in ppm or ppb level in trace level concentrations are observed in excess in the used grease mainly due to wear and tear. On the other hand in fresh grease, spectral lines of Ca, Al and Na are observed predominantly.
      PubDate: 2014-12-18
      DOI: 10.3390/lubricants2040223
      Issue No: Vol. 2, No. 4 (2014)
  • Lubricants, Vol. 2, Pages 237-248: Recycled and Virgin HDPEs as Bleed
           Inhibitors and Their Rheological Influences on Lubricating Greases
           Thickened with PP and mPP

    • Authors: Ravi Dixena, Eltepu Sayanna, Rajendra Badoni
      Pages: 237 - 248
      Abstract: Polypropylene (PP) thickened lubricating grease exhibits high oil bleed tendency at low temperatures, which makes it a promising candidate for low temperature applications. At elevated temperatures, PP thickened lubricating grease exhibits excessive oil bleeding, which limits its use at high temperatures. Excessive oil bleed adversely affects the lubricating performance of the PP thickened grease. The present work is focused on the study of the oil bleed tendency of PP and Maleated Polypropylene (mPP) thickened greases at various temperatures by incorporating virgin and recycled high density polyethylene (HDPE) into the thickener system. Grease containing various percentages of PP and mPP thickeners were prepared and modified with different percentages of virgin and recycled HDPE. Polymers were characterized through differential scanning calorimetry (DSC) techniques. The oil bleed performance of these greases was evaluated by the conical sieve method (ASTM D 6184) at various temperatures. Storage (G′) and loss modulus (G″) of greases was determined by rheometry at 25 °C. Incorporation of HDPE and recycled HDPE in PP thickened grease decreased oil bleeding compared to the base grease.
      PubDate: 2014-12-18
      DOI: 10.3390/lubricants2040237
      Issue No: Vol. 2, No. 4 (2014)
  • Lubricants, Vol. 2, Pages 113-123: Tribofilm Formation As a Result of
           Complex Interaction at the Tool/Chip Interface during Cutting

    • Authors: German Fox-Rabinovich, Iosif Gershman, Mohamed Hakim, Mohamed Shalaby, James Krzanowski, Stephen Veldhuis
      Pages: 113 - 123
      Abstract: Tribofilms are dynamic structures that form at the interface during frictional sliding. These films play a significant role in friction control, particularly under heavy loaded/high temperature conditions, such as those found at the cutting tool/chip interface. The thermodynamic aspects of tribofilm formation are discussed here. Thermodynamic analysis of entropy production during friction shows that there are two types of tribofilms that affect the wear behavior of a cutting tool: (1) tribofilms forming as a result of the surface modification of the cutting tools with further tribo-oxidation; and (2) tribofilms that form as a result of material transfer from the contacting frictional body (the workpiece) during the tool/chip interaction. Experimental examples are presented, outlining the beneficial role of both types of tribofilms.
      PubDate: 2014-07-21
      DOI: 10.3390/lubricants2030113
      Issue No: Vol. 2, No. 3 (2014)
  • Lubricants, Vol. 2, Pages 124-136: Growth Control of Microbial in Miscible
           Cutting Fluids Using Ultraviolet Radiation

    • Authors: Eduardo Bianchi, Paulo Aguiar, Olavo de Arruda, Francine Piubeli
      Pages: 124 - 136
      Abstract: Considering the issues involved in industrial cutting and machining systems, and, in particular, the problems arising from the use of cutting fluids in these systems, this study presents the results of an analysis that points to a safe and efficient way to reduce contaminated microbial cutting fluids using ultraviolet radiation. The study proposes a transmitter system of simple ultraviolet radiation, safe and easy to obtain. The results of this study showed that the action of ultraviolet radiation on microorganisms in metalworking fluids is very effective and leads to a significant reduction of the load of microorganisms. In addition, no changes were observed during the experimental period that would lead to impairments in the performance of the activities of the cutting fluid used. Given the results, we can conclude that the use of ultraviolet radiation in the prevention and control of contamination is an important contribution to the durability of cutting fluids in machining and grinding operations.
      PubDate: 2014-09-02
      DOI: 10.3390/lubricants2030124
      Issue No: Vol. 2, No. 3 (2014)
  • Lubricants, Vol. 2, Pages 137-161: The Preparation of Graphene Oxide and
           Its Derivatives and Their Application in Bio-Tribological Systems

    • Authors: Jianchang Li, Xiangqiong Zeng, Tianhui Ren, Emile van der Heide
      Pages: 137 - 161
      Abstract: Graphene oxide (GO) can be readily modified for particular applications due to the existence of abundant oxygen-containing functional groups. Graphene oxide-based materials (GOBMs), which are biocompatible and hydrophilic, have wide potential applications in biomedical engineering and biotechnology. In this review, the preparation and characterization of GO and its derivatives are discussed at first. Subsequently, the biocompatibility and tribological behavior of GOBMs are reviewed. Finally, the applications of GOBMs as lubricants in bio-tribological systems are discussed in detail.
      PubDate: 2014-09-24
      DOI: 10.3390/lubricants2030137
      Issue No: Vol. 2, No. 3 (2014)
  • Lubricants, Vol. 2, Pages 44-65: Graphite and Hybrid Nanomaterials as
           Lubricant Additives

    • Authors: Zhenyu Zhang, Dorin Simionesie, Carl Schaschke
      Pages: 44 - 65
      Abstract: Lubricant additives, based on inorganic nanoparticles coated with organic outer layer, can reduce wear and increase load-carrying capacity of base oil remarkably, indicating the great potential of hybrid nanoparticles as anti-wear and extreme-pressure additives with excellent levels of performance. The organic part in the hybrid materials improves their flexibility and stability, while the inorganic part is responsible for hardness. The relationship between the design parameters of the organic coatings, such as molecular architecture and the lubrication performance, however, remains to be fully elucidated. A survey of current understanding of hybrid nanoparticles as lubricant additives is presented in this review.
      PubDate: 2014-04-24
      DOI: 10.3390/lubricants2020044
      Issue No: Vol. 2, No. 2 (2014)
  • Lubricants, Vol. 2, Pages 66-89: Abrasive Resistant Coatings—A

    • Authors: Linmin Wu, Xingye Guo, Jing Zhang
      Pages: 66 - 89
      Abstract: Abrasive resistant coatings have been widely used to reduce or eliminate wear, extending the lifetime of products. Abrasive resistant coatings can also be used in certain environments unsuitable for lubrications. Moreover, abrasive resistant coatings have been employed to strengthen mechanical properties, such as hardness and toughness. Given recently rapid development in abrasive resistant coatings, this paper provides a review of major types of abrasive coatings, their wearing mechanisms, preparation methods, and properties.
      PubDate: 2014-05-21
      DOI: 10.3390/lubricants2020066
      Issue No: Vol. 2, No. 2 (2014)
  • Lubricants, Vol. 2, Pages 90-112: Reducing Friction and Wear of
           Tribological Systems through Hybrid Tribofilm Consisting of Coating and

    • Authors: Shuichiro Yazawa, Ichiro Minami, Braham Prakash
      Pages: 90 - 112
      Abstract: The role of surface protective additives becomes vital when operating conditions become severe and moving components operate in a boundary lubrication regime. After protecting film is slowly removed by rubbing, it can regenerate through the tribochemical reaction of the additives at the contact. However, there are limitations about the regeneration of the protecting film when additives are totally consumed. On the other hand, there are a lot of hard coatings to protect the steel surface from wear. These can enable the functioning of tribological systems, even in adverse lubrication conditions. However, hard coatings usually make the friction coefficient higher, because of their high interfacial shear strength. Amongst hard coatings, diamond-like carbon (DLC) is widely used, because of its relatively low friction and superior wear resistance. In practice, conventional lubricants that are essentially formulated for a steel/steel surface are still used for lubricating machine component surfaces provided with protective coatings, such as DLCs, despite the fact that the surface properties of coatings are quite different from those of steel. It is therefore important that the design of additive molecules and their interaction with coatings should be re-considered. The main aim of this paper is to discuss the DLC and the additive combination that enable tribofilm formation and effective lubrication of tribological systems.
      PubDate: 2014-06-23
      DOI: 10.3390/lubricants2020090
      Issue No: Vol. 2, No. 2 (2014)
  • Lubricants, Vol. 2, Pages 1-10: The Application of Molecular Dynamics in
           Fullerene-Based Journal Bearing Simulation

    • Authors: Alexey Kornaev, Leonid Savin, Mikhail Nozdrichkin
      Pages: 1 - 10
      Abstract: The article is devoted to modeling of the molecular microscopic journal bearing. The walls and the lubricant of the bearing are fullerene-like molecules. On the basis of similarity theory and analysis of the dimensions, the similarity criterion is proposed. This criterion characterizes the convergence of a numerical solution. The test calculation is also made to evaluate the quality of the proposed criterion.
      PubDate: 2014-02-24
      DOI: 10.3390/lubricants2010001
      Issue No: Vol. 2, No. 1 (2014)
  • Lubricants, Vol. 2, Pages 11-20: Lubricants for Metal Belt Continuously
           Variable Transmissions

    • Authors: Keiichi Narita
      Pages: 11 - 20
      Abstract: This paper reviews the effects of lubricant additives and base stock used in metal belt continuously variable transmissions (CVT) fluids on the CVT transmission torque capacity. Additive formulation composed of phosphorus anti-wear agent, calcium detergent, and dispersant improved the friction coefficient between the metals. The analysis on the post-test surface suggests that the friction behavior strongly depends on the local morphology of the tribofilms derived from lubricant additives. Examining the effect of base stock on the torque capacity in actual belt CVTs revealed that SN (synthetic naphthene) exhibited 10% higher torque capacity than that of PAO (polyalphaolefin). It is believed that the difference in the torque capacity is due to the difference in the oil-film shearing force generated by the relative sliding between the belt and pulley.
      PubDate: 2014-02-25
      DOI: 10.3390/lubricants2010011
      Issue No: Vol. 2, No. 1 (2014)
  • Lubricants, Vol. 2, Pages 21-43: Lubricants in Pharmaceutical Solid Dosage

    • Authors: Jinjiang Li, Yongmei Wu
      Pages: 21 - 43
      Abstract: Lubrication plays a key role in successful manufacturing of pharmaceutical solid dosage forms; lubricants are essential ingredients in robust formulations to achieve this. Although many failures in pharmaceutical manufacturing operations are caused by issues related to lubrication, in general, lubricants do not gain adequate attention in the development of pharmaceutical formulations. In this paper, the fundamental background on lubrication is introduced, in which the relationships between lubrication and friction/adhesion forces are discussed. Then, the application of lubrication in the development of pharmaceutical products and manufacturing processes is discussed with an emphasis on magnesium stearate. In particular, the effect of its hydration state (anhydrate, monohydrate, dihydrate, and trihydrate) and its powder characteristics on lubrication efficiency, as well as product and process performance is summarized. In addition, the impact of lubrication on the dynamics of compaction/compression processes and on the mechanical properties of compacts/tablets is presented. Furthermore, the online monitoring of magnesium stearate in a blending process is briefly mentioned. Finally, the chemical compatibility of active pharmaceutical ingredient (API) with magnesium stearate and its reactive impurities is reviewed with examples from the literature illustrating the various reaction mechanisms involved.
      PubDate: 2014-02-25
      DOI: 10.3390/lubricants2010021
      Issue No: Vol. 2, No. 1 (2014)
  • Lubricants, Vol. 1, Pages 75-94: On the Interactions of Additives in
           Metalworking Fluids with Metal Surfaces

    • Authors: Joachim Schulz, Ekkard Brinksmeier, Daniel Meyer
      Pages: 75 - 94
      Abstract: Metalworking fluids (MWF) play a significant role in manufacturing processes, such as machining or forming. Consequently, a high number of MWF with varying chemical composition are commercially available. However, the working mechanisms of the MWF are still object of discussion in science and application. This paper addresses the possible interactions of additives with metal surfaces taking the characteristic conditions in machining and forming processes as well as the chemical properties of the surface and the additives into account. The new model for possible interaction of additives with the metal surface is considered and supported by experimental data. This new model does not imply reaction layers as tribological active layer anymore.
      PubDate: 2013-11-15
      DOI: 10.3390/lubricants1040075
      Issue No: Vol. 1, No. 4 (2013)
  • Lubricants, Vol. 1, Pages 95-101: Nanomaterials in Lubricants: An
           Industrial Perspective on Current Research

    • Authors: Boris Zhmud, Bogdan Pasalskiy
      Pages: 95 - 101
      Abstract: This paper presents an overview on the use of various classes of nanomaterials in lubricant formulations. The following classes of nanomaterials are considered: fullerenes, nanodiamonds, ultradispersed boric acid and polytetrafluoroethylene (PTFE). Current advances in using nanomaterials in engine oils, industrial lubricants and greases are discussed. Results of numerous studies combined with formulation experience of the authors strongly suggest that nanomaterials do indeed have potential for enhancing certain lubricant properties, yet there is a long way to go before balanced formulations are developed.
      PubDate: 2013-11-20
      DOI: 10.3390/lubricants1040095
      Issue No: Vol. 1, No. 4 (2013)
  • Lubricants, Vol. 1, Pages 102-131: Experimental Investigations of
           Biological Lubrication at the Nanoscale: The Cases of Synovial Joints and
           the Oral Cavity

    • Authors: Javier Sotres, Thomas Arnebrant
      Pages: 102 - 131
      Abstract: Interactions between surfaces are ubiquitous phenomena in living organisms. Nature has developed sophisticated strategies for lubricating these systems, increasing their efficiency and life span. This includes the use of water-based lubricants, such as saliva and synovial fluid. These fluids overcome the limitations of water as a lubricant by the presence of molecules such as proteins, lipids, and polysaccharides. Such molecules may alter surface interactions through different mechanisms. They can increase viscosity enabling fluid-film lubrication. Moreover, molecules adsorb on the surfaces providing mechanisms for boundary lubrication and preventing wear. The mentioned molecules have typical sizes in the nanometer range. Their interaction, as well as the interaction with the entrapping surfaces, takes place through forces in the range of nanonewtons. It is therefore not surprising that the investigation of these systems have been boosted by development of techniques such as scanning probe microscopies and the surface force apparatus which allow studying tribological processes at the nanoscale. Indeed, these approaches have generated an enormous amount of studies over the last years. The aim of this review is to perform a critical analysis of the current stage of this research, with a main focus on studies on synovial joints and the oral cavity.
      PubDate: 2013-11-25
      DOI: 10.3390/lubricants1040102
      Issue No: Vol. 1, No. 4 (2013)
  • Lubricants, Vol. 1, Pages 132-148: Phosphate Esters, Thiophosphate Esters
           and Metal Thiophosphates as Lubricant Additives

    • Authors: David Johnson, John Hils
      Pages: 132 - 148
      Abstract: Phosphate esters, thiophosphate esters and metal thiophosphates have been used as lubricant additives for over 50 years. While their use has been extensive, a detailed knowledge of how they work has been a much more recent development. In this paper, the use of phosphate esters and thiophosphate esters as anti-wear or extreme pressure additives is reviewed with an emphasis on their mechanism of action. The review includes the use of alkyl phosphates, triaryl phosphates and metal containing thiophosphate esters. The mechanisms of these materials interacting with a range of iron and steel based bearing material are examined.
      PubDate: 2013-12-18
      DOI: 10.3390/lubricants1040132
      Issue No: Vol. 1, No. 4 (2013)
  • Lubricants, Vol. 1, Pages 61-74: Employing Acoustic Emission for
           Monitoring Oil Film Regimes

    • Authors: Mhmod Hamel, Abdulmajid Addali, David Mba
      Pages: 61 - 74
      Abstract: The major purpose of a gear lubricant is to provide adequate oil film thickness to reduce and prevent gear tooth surface failures. Real time monitoring for gear failures is important in order to predict and prevent unexpected failures which would have a negative impact on the efficiency, performance and safety of the gearbox. This paper presents experimental results on the influence of specific oil film thickness on Acoustic Emission (AE) activity for operational helical gears. Variation in film thickness during operations was achieved by spraying liquid nitrogen onto the rotating gear wheel. The experimental results demonstrated a clear relationship between the root mean square (r.m.s) value of the AE signal and the specific film thickness. The findings demonstrate the potential of Acoustic Emission technology to quantify lubrication regimes on operational gears.
      PubDate: 2013-07-03
      DOI: 10.3390/lubricants1030061
      Issue No: Vol. 1, No. 3 (2013)
  • Lubricants, Vol. 1, Pages 22-47: Nanotribological Behavior of Carbon Based
           Thin Films: Friction and Lubricity Mechanisms at the Nanoscale

    • Authors: Costas Charitidis, Elias Koumoulos, Dimitrios Dragatogiannis
      Pages: 22 - 47
      Abstract: The use of materials with very attractive friction and wear properties has raised much attention in research and industrial sectors. A wide range of tribological applications, including rolling and sliding bearings, machining, mechanical seals, biomedical implants and microelectromechanical systems (MEMS), require thin films with high mechanical strength, chemical inertness, broad optical transparency, high refractive index, wide bandgap excellent thermal conductivity and extremely low thermal expansion. Carbon based thin films like diamond, diamond-like carbon, carbon nitride and cubic boron nitride known as “super-hard” material have been studied thoroughly as the ideal candidate for tribological applications. In this study, the results of experimental and simulation works on the nanotribological behavior of carbon films and fundamental mechanisms of friction and lubricity at the nano-scale are reviewed. The study is focused on the nanomechanical properties and analysis of the nanoscratching processes at low loads to obtain quantitative analysis, the comparison obtain quantitative analysis, the comparison of their elastic/plastic deformation response, and nanotribological behavior of the a-C, ta-C, a-C:H, CNx, and a-C:M films. For ta-C and a-C:M films new data are presented and discussed.
      PubDate: 2013-04-02
      DOI: 10.3390/lubricants1020022
      Issue No: Vol. 1, No. 2 (2013)
  • Lubricants, Vol. 1, Pages 48-60: Interaction between Lubricants Containing
           Phosphate Ester Additives and Stainless Steels

    • Authors: David Johnson, Matthew Bachus, John Hils
      Pages: 48 - 60
      Abstract: One way to improve fuel efficiency in today’s jet aircraft engines is to create an environment for higher operating temperatures and speeds. New and improved lubricants and bearing materials must be developed to remain stable in these elevated operating temperatures. Three lubricants, with varying amounts of tricresyl phosphate added as an anti-wear/extreme pressure additive were tested on two different stainless steels at varying temperatures ranging from 300 °C to 350 °C in vacuum. Significant decomposition of the lubricant base-stocks and the phosphate ester additive did occur in most of the trials resulting in the formation of carboxylic acids and phenols. In these cases a film containing phosphorus was deposited onto the stainless steel substrate.
      PubDate: 2013-05-17
      DOI: 10.3390/lubricants1020048
      Issue No: Vol. 1, No. 2 (2013)
  • Lubricants, Vol. 1, Pages 3-21: A Review of Ionic Liquid Lubricants

    • Authors: Anthony Somers, Patrick Howlett, Douglas MacFarlane, Maria Forsyth
      Pages: 3 - 21
      Abstract: Due to ever increasing demands on lubricants, such as increased service intervals, reduced volumes and reduced emissions, there is a need to develop new lubricants and improved wear additives. Ionic liquids (ILs) are room temperature molten salts that have recently been shown to offer many advantages in this area. The application of ILs as lubricants in a diverse range of systems has found that these materials can show remarkable protection against wear and significantly reduce friction in the neat state. Recently, some researchers have shown that a small family of ILs can also be incorporated into non-polar base oils, replacing traditional anti-wear additives, with excellent performance of the neat IL being maintained. ILs consist of large asymmetrical ions that may readily adsorb onto a metal surface and produce a thin, protective film under boundary lubrication conditions. Under extreme pressure conditions, certain IL compounds can also react to form a protective tribofilm, in particular when fluorine, phosphorus or boron atoms are present in the constituent ions.
      PubDate: 2013-01-21
      DOI: 10.3390/lubricants1010003
      Issue No: Vol. 1, No. 1 (2013)
  • Lubricants, Vol. 1, Pages 1-2: Welcome to Lubricants, a New Open Access
           Journal for Interdisciplinary Research in the Field of Tribology

    • Authors: James E. Krzanowski
      Pages: 1 - 2
      Abstract: Welcome to Lubricants, a new open access journal for researchers and practitioners working in the field of tribology. The journal will publish peer-reviewed research papers, reviews, letters and communications, as well as papers on research ideas and proposals. The concept of open access is exciting because it allows free access of all publications to anyone, resulting in the widest dissemination possible for the authors publishing in the journal. In addition, publication is rapid, and full use can be made of color figures which are published at no additional cost to the authors. The contents of the journal will nonetheless be archival and articles can therefore have a long-term impact. [...]
      PubDate: 2012-07-02
      DOI: 10.3390/lubricants1010001
      Issue No: Vol. 1, No. 1 (2012)
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