Karl D. Dearn

Finding synergies in fuels properties for the design of renewable fuels - hydroxylated biodiesel effects on butanol-diesel blends.

This article describes the effects of hydroxylated biodiesel (castor oil methyl ester - COME) on the properties, combustion, and emissions of butanol-diesel blends used within compression ignition engines. The study was conducted to investigate the influence of COME as a means of increasing the butanol concentration in a stable butanol-diesel blend. Tests were compared with baseline experiments using rapeseed methyl esters (RME). A clear benefit in terms of the trade-off between NOX and soot emissions with respect to ULSD and biodiesel-diesel blends with the same oxygen content was obtained from the combination of biodiesel and butanol, while there was no penalty in regulated gaseous carbonaceous emissions. From the comparison between the biodiesel fuels used in this work, COME improved some of the properties (for example lubricity, density and viscosity) of butanol-diesel blends with respect to RME. The existence of hydroxyl group in COME also reduced further soot emissions and decreased soot activation energy.

Friction-Induced Transformation from Graphite Dispersed in Esterified Bio-Oil to Graphene

Fabricating high-quality graphene with simple methods has aroused considerable interests in recent years. In this paper, graphite was dispersed in esterified bio-oil as a lubricant for steel/gray cast iron friction pairs, and the shear-induced transformation from graphite to graphene was observed. The tribological behavior during this process, including the influence of the normal load and sliding velocity, was investigated. The products formed after sliding were confirmed by Raman spectroscopy, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The results showed that friction induces exfoliation, accounting for the transformation from graphite into graphene, and the frictional conditions influence the products. It was also found that high loads and low sliding velocities facilitate the formation of high-quality single-layer graphene during sliding, and high loads and low sliding velocities also contributed to obtaining excellent tribological performance for friction pairs. Friction-induced transformation demonstrates a potentially new strategy for in situ graphene preparation.

Lubrication Regimes in High-Performance Polymer Spur Gears

Little has been published on the behaviour of polymer gears operating under lubricated conditions. An experimental and analytical programme was undertaken to classify the regimes of EHL under which polymer spur gears operate. In doing so theoretical film thicknesses were calculated and then used to classify the regime according to Johnsons Map. The effects of lubrication on the operating efficiencies of high-performance polymer gears were interpreted and from these results coefficients of friction were derived. In addition to this the effect of tooth geometry was investigated and the beneficial influence of high-pressure angle tooth geometry is demonstrated. At loads typically associated with polymer gears the operating regime is shown to be mixed film lubrication. When high-pressure angle gears were tested at high loads the operating regime became full film lubrication and relatively little tooth flank damage occurred.

PEEK (Polyether-ether-ketone) Based Cervical Total Disc Arthroplasty: Contact Stress and Lubrication Analysis

This paper presents a theoretical analysis of the maximum contact stress and the lubrication regimes for PEEK (Polyether-ether-ketone) based self-mating cervical total disc arthroplasty. The NuNec® cervical disc arthroplasty system was chosen as the study object, which was then analytically modelled as a ball on socket joint. A non-adhesion Hertzian contact model and elastohydrodynamic lubrication theory were used to predict the maximum contact stress and the minimum film thickness, respectively. The peak contact stress and the minimum film thickness between the bearing surfaces were then determined, as the radial clearance or lubricant was varied. The obtained results show that under 150 N loading, the peak contact stress was in the range 5.9 – 32.1 MPa, well below the yield and fatigue strength of PEEK; the calculated minimum film thickness ranged from 0 to 0.042 µm and the corresponding lambda ratio range was from 0 to 0.052. This indicates that the PEEK based cervical disc arthroplasty will operate under a boundary lubrication regime, within the natural angular velocity range of the cervical spine.

A kinematic analysis of meshing polymer gear teeth

This article describes an investigation into the contact behaviour of polymeric gear transmissions using numerical finite element (FE) and analytical techniques. A polymer gear pair was modelled and analysed using the ABAQUS software suite and the analytical results were calculated using the BS ISO 6336 rating standard. Before describing the results, the principles of the strategies and methods employed in the building of the FE model have been discussed. The FE model dynamically simulated a range of operating conditions. The simulations showed that the kinematic behaviour of polymeric gears is substantially different from those predicted by the classical metal gear theory. Extensions to the path of contact occur at the beginning and end of the meshing cycle. These are caused by large tooth deflections experienced by polymer gear teeth, as a result of much lower values of stiffness compared to metallic gears. The premature contact (occurring at the beginning of the meshing cycle) is hypothesized to be a factor in pitch line tooth fractures, whereas the extended contact is thought to be a factor in the extreme wear as seen in experiments. Furthermore, the increase in the path of contact also affects the induced bending and contact stresses. Simulated values are compared against those predicted by the international gear standard BS ISO 6336 and are shown to be substantially different. This is particularly for the case for bending stresses, where analytically derived values are independent of contact stiffness. The extreme tooth bending and the differences between analytical and numerical stresses observed in all the simulations suggest that any future polymeric gear-rating standard must account for the effects of load sharing (as a result of tooth deflection) and friction (particularly in dry-running applications).

Interrogating the surface: the effect of blended diesel fuels on lubricity

The lubricating properties of two sustainable alternative diesels blended with ultra low sulphur diesel (ULSD) were investigated. The candidate fuels were a biodiesel consisting of fatty acid methyl esters derived from rapeseed (RME) and gas-to-liquid (GTL). Lubricity tests were conducted on a high frequency reciprocating rig (HFRR). The mating specimen surfaces were analysed using optical microscopy and profilometery for wear scar diameters and profiles respectively. Microscopic surface topography and deposit composition was evaluated using a scanning electronic microscope (SEM) with an energy dispersive spectrometer (EDS). Like all modern zero sulphur diesel fuel (ZSD), GTL fuels need a lubricity agent to meet modern lubricity specifications. It has been proven that GTL responds well to typical lubricity additives in the marketplace. The lubricity of ULSD, GTL and blends of these fuels were significantly improved with the addition of as little as 10% volume of RME, inducing more stable hydrodynamic conditions. Topography measurements showed the formation of a residue when RME was blended in the base fuels and composition analysis indicated a predominately carbon formation on the worn surfaces that correlated with wear scar diameters. On the other hand, the test disc under GTL lubrication showed the smooth and residue free surface. The optimal proportion of blended fuel that created the smallest wear scar diameter was 70% GTL, 20% ULSD and 10% RME.

Nano-MoS 2 and Graphene Additives in Oil for Tribological Applications

Nano-additives have attracted lots of attentions in recent years due to their special performances. A traditional lubricating additive MoS2 with nano-scale and a novel additive graphene were reviewed in this chapter. The synthesis methods, properties, and tribological applications of these two kinds of nano-additives dispersed in media have been reported. Nano-MoS2 has three main nanostructures including nano-ball particles, nano-sheets, and nano-tubes. The wide accepted lubricating mechanisms for the MoS2 nano-balls, nano-sheets, and nano-tubes are nano-bearing effects, slippery roles, and combined actions of rolling and sliding, respectively. Exfoliation and transfer seem to be the main pattern for MoS2 nano-balls. For graphene, the adsorption and tribo-reaction account for its lubricating properties. A synergistic lubricating effect for using graphene and MoS2 together dispersed in oil was found. Graphene was proved to extend the retention of MoS2 on the surfaces and prevent the oxidation of MoS2. Simultaneously, MoS2 prevented the graphene from being ground into small and defective platelets. Both of them help to form a thicker adsorbed and tribo-film which result in a lower friction and wear. Other properties and applications of nano-MoS2 and graphene are also reviewed. It shows that these two nano-additives have diverse functions and great potential for industrial applications.

Wear debris from total joint replacements: evaluation of automated categorisation by scale-invariant feature transforms

AbstractWear debris is a crucial factor in determining the lifespan of a total joint replacement. Not only do particulates between a bearing surfaces increase wear rates through third-body abrasion, but immune reactions can lead to inflammation and osteolysis. In this paper, the use of computer vision to analyse and classify scanning electron microscope images of debris was investigated. UHMWPE debris was generated using an in vitro simulator or a linear tribometer, images were analysed using scale invariant feature transforms and a support vector machine classifier. The accuracy was 77.6% with a receiver operating characteristic area under curve of 92%.

Wear processes in polymer implants

Abstract: Wear processes are discussed for polymers used in a wide variety of implants in the human body, such as in joint replacement implants for the hip and knee. The articulation of metal or ceramic components against a polymer component can lead to the generation of wear debris and the effect this debris may have in the body is examined.