The Formation of Viscous Surface Films by Polymer Solutions: Boundary or Elastohydrodynamic Lubrication?

The film-forming properties of a range of polymer solutions have been studied down to very thin film thickness using ultrathin film interferometry.

It has been found that, at very slow rolling speeds, some polymers generate much thicker films than predicted from theory. It appears that these polymers form adsorbed layers between three and 15 nanometers thick on the two solid surfaces. These layers have a viscosity many times higher than that of the bulk solution. Therefore, under slow speed, low film thickness conditions, the contact effectively operates within a viscous boundary layer, generating an elastohydrodynamic-type film much thicker than predicted from the viscosity of the bulk lubricant. As the speed is raised the contact emerges from this boundary layer and reverts to elastohydrodynamic behavior based upon the viscosity of the bulk polymer solution.     

Right Way of Using Graphene Oxide Additives for Water-Lubricated PEEK: Adding in Polymer or Water?

Water-lubricated polymer is attracting more and more interest from the industry. Adding nanoparticles is considered to be an effective way to improve the tribological performance. In this work, water-lubricated Polyetheretherketone (PEEK)-steel contacts were employed as the objects of study. A careful comparative study was made by investigating the effect of adding graphene oxide (GO) into water or into PEEK. Results show that adding GO into water can significantly reduce the wear and friction coefficient of pure PEEK, which is much more effective than adding GO into PEEK. Under the lubrication of GO aqueous dispersion, the wear of PEEK remains very low even under a harsh condition where the pressure reaches 50 MPa and the linear sliding speed is 0.7 m/s. Neat PEEK and GO/PEEK composites in pure water exhibit serious wear under this harsh condition. The excellent lubricating properties of GO aqueous dispersion are attributed to GO nanosheets entering into solid contacts, which can not only form a protective layer on steel counterpart repairing the worn surface, but also strongly adhere to the PEEK matrix resulting in an in situ-formed GO coating and prevent the scratch by steel counterpart.     

Electric force microscopy investigation of a MEH-PPV conjugated polymer blend: Robustness or frailty?

Electric force microscopy (EFM) was employed in the electrical characterization of a blend of thermoplastic polyurethane (TPU) and poly(2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylenevinylene) (MEH-PPV) conjugated polymer. Although qualitative EFM interpretation is straightforward, its quantitative analysis always relies on approximated models. The extraction of physically reasonable parameters is normally assumed as a proof of validity of the theoretical model employed. In order to gather information about electric properties of this blend and to test the EFM technique itself, two distinct and discordant models were developed in this work to fit experimental EFM data. Even though MEH-PPV is regarded as a conductor in one model and as a dielectric in the other, both models yielded coherent and reasonable electrical properties for this blend. Such unexpected results are used to discuss the robustness or frailty of EFM in the analysis of complex materials.     

Vibroacoustic: The challenges of a mission impossible?

Why it is difficult to solve a vibroacoustic problem; what are the hidden pitfalls that one is called to overcome; are there methods or techniques suggested in other fields of physics that can help to formulate an efficient vibroacoustic prediction model? The authors provide personal answers to these questions and suggest also a classification of the numerous prediction methods proposed in the literature.     

Semi-Empirical Molecular Modeling of Ionic Liquid Tribology: Ionic Liquid–Hydroxylated Silicon Surface Interactions

The interactions between selected ionic liquids and modified silicon surfaces are modeled in this article using semi-empirical methods. The modeled ionic liquids include a series of ionic liquids consisting of imidazolium derivatives with Cl^? as the anion interacting with hydroxylated silicon wafers. A second series consists of symmetrical and asymmetrical dicationic imidazolium derivatives with PF₆ ^? or BF₄ ^? as the anion interacting with hydroxylated single crystal silicon wafers. The tribological properties of these ionic liquids and their interactions with silicon surfaces are modeled using a rolling hydroxylated silicon surface. The ionic liquids are allowed to form a complex with this surface, and the enthalpies of complex formation are seen to correlate with the tribological properties of the ionic liquids.     

Semi-Empirical Molecular Modeling of Ionic Liquid Tribology: Ionic Liquid–Aluminum Oxide Surface Interactions

The interactions between the selected ionic liquids (ILs) and aluminum oxide surfaces are modeled in this report using theoretical methods. A wide range of ILs and their interactions with an aluminum oxide surface are modeled using the PM5 semi-empirical method. The ILs modeled in this study contain imidazolium (C_{3, 4, 6, 8 or 10}mim) or ammonium cations including (C₆H₁₃)₃NH⁺, (C₈H₁₇)₃NH⁺, C₈H₁₇NH₃ ⁺, (C₂H₅)₃NH⁺, and (C₈H₁₇)NH₃ ⁺. The anions include Cl⁻, Br⁻, PF₆ ⁻, (CF₃SO₂)₂N⁻, and (C₂F₅SO₂)₂N⁻. The interactions of these ILs with an Al–O surface are modeled in a stepwise manner. The lowest energy forms of the individual ILs are determined, and these ILs are allowed to form a complex with the Al–O surface. The resulting reaction enthalpies of ionic liquid-surface complex formation are seen to correlate with the tribological properties of the ILs. The strongest correlations occur within those ILs containing similar cations.     

EHL Performance of the Lubricant With Shear Strength: Part I — Boundary Slippage and Film Failure

This paper analytically investigates the isothermal line contact elastohydrodynamic lubrication of three lubricants with much different shear strengths under the nondimensional operating parameters of w = 2.15e-4 and U = 2.53e-10 applying the lubricant ideal viscoplastic rheological model. The boundary slippage of the low-shear-strength lubricant occurring in the EHL inlet zone was found and results in a much thinner film compared to the classical EHL theory prediction. The film boundary slippage and its growth with the slide/roll ratio variation of tile low-shear\- strength lubricant exhibit special phenomena, which are much different from those of the high-shear-strength lubricant. The easy occurrence of film failure in concentrated contact in the case of high sliding speed, heavy load, large slide/roll ratio, and low-shear-strength lubricant was concluded due to the severe friction heating on the surface conjunction and the lubricant thermal desorption on tile lubricant/surface boundary. The EHL film failure mechanism was further recognized.     

Bright-field TEM imaging of single molecules: Dream or near future?

We examine the suitability of spherical aberration (C(S))-corrected (CS) and uncorrected (UC) transmission electron microscopes (TEM) for conventional bright-field imaging of radiation-sensitive materials. We have chosen an individual molecule suspended in vacuum as a hypothetical example of a well-defined radiation-sensitive sample. We find that for this particular sample, CS instruments provide about 30% improvement over an UC instrument in terms of signal/noise ratio per unit electron dose at 300kV. The lowest imaging doses can be achieved in CS instruments equipped with high-brightness electron source operated at low incident electron energies. Our calculations suggest that it may be possible to image individual, iodine- or bromine-substituted organic molecules in bright-field mode, at doses lower than the accepted values for radiation damage of aromatic molecules.     

The biomechanics of plate fixation of periprosthetic femoral fractures near the tip of a total hip implant: cables, screws, or both?

Femoral shaft fractures after total hip arthroplasty (THA) remain a serious problem, since there is no optimal surgical repair method. Virtually all studies that examined surgical repair methods have done so clinically or experimentally. The present study assessed injury patterns computationally by developing three-dimensional (3D) finite element (FE) models that were validated experimentally. The investigation evaluated three different constructs for the fixation of Vancouver B1 periprosthetic femoral shaft fractures following THA. Experimentally, three bone plate repair methods were applied to a synthetic femur with a 5 mm fracture gap near the tip of a total hip implant. Repair methods were identical distal to the fracture gap, but used cables only (construct A), screws only (construct B), or cables plus screws (construct C) proximal to the fracture gap. Specimens were oriented in 15 degrees adduction to simulate the single-legged stance phase of walking, subjected to 1000 N of axial force, and instrumented with strain gauges. Computationally, a linearly elastic and isotropic 3D FE model was developed to mimic experiments. Results showed excellent agreement between experimental and FE strains, yielding a Pearson linearity coefficient, R2, of 0.92 and a slope for the line of best data fit of 1.06. FE-computed axial stiffnesses were 768 N/mm (construct A), 1023 N/mm (construct B), and 1102 N/mm (construct C). FE surfaces stress maps for cortical bone showed Von Mises stresses, excluding peaks, of 0-8 MPa (construct A), 0-15 MPa (construct B), and 0-20 MPa (construct C). Cables absorbed the majority of load, followed by the plates and then the screws. Construct A yielded peak stress at one of the empty holes in the plate. Constructs B and C had similar bone stress patterns, and can achieve optimal fixation.     

Ecological cutting: Feasible or not?

This paper describes the results of a two-year research project on ecological cutting, in which four different applications, namely, cutting, pocket milling, face milling, and drilling, were investigated under dry and lubricated conditions. A traditional cutting fluid and an environmentally friendly cutting fluid were used for the latter. TiN-, Ti (C,N), and (Ti,Al)N-coated tools were tested, together with commercially-available multilayer coated tools, to analyse to what extent the use of coatings could reduce or even eliminate the need for cutting fluids. The machined materials include an unalloyed steel, I.0503, a low alloyed steel, 1.2312, a stainless steel, 1.4306, and cast iron, ADI. End-of- life tests were done in all cases and the wear of the tools was examined with SEM. The research showed that the results are strongly dependent on the application. For cutting, coated tools result in the best tool lives although tools used under lubricated conditions still outperform their dry used counterparts. For milling, dry machining is advantageous. The drilling tests showed better results under lubricated conditions mainly due to the cooling and chip removal capacity of the lubricants. In this case, the (Ti,Al)N-coated drill out-performed the commercially available coated tool.     

Test of a Fluid-Film Wave Bearing at 350°C with Liquid Lubricants

A novel fluid-film wave bearing has been run at a higher temperature (350°C) than ever before with a perfluoropolyether (PFPE)-K liquid lubricant. Additionally, the wave journal bearing (45 mm diameter and 24 mm long) completed an 8-h endurance test at the NASA Glenn Research Center. The lubricant was PFPE-K XHT 500. After being maintained at 350° C for 8 h, the bearing temperature was raised to 356°C for the last 30 min of the run. The speed was 29,000 rpm and the load ranged from 2670 to 3560 N. The bearing was perfectly stable both dynamically and thermally. The observed temperature was more than 150°C above that run with current turbine engine lubricants. The use of high-temperature bearings as tested here would allow efficiency increases of more than 5% in aero or terrestrial turbine engines.     

Cost Effective Upgrade of a Thermal Evaporator with a Dual Mini E‐beam Evaporator with Focus on the Evaporation of Platinum

Abstract

The addition of two mini e‐beam evaporators (Tectra) to a commercially available thermal evaporator (Fullam EFFA) is described. The design allows the integration of the e‐beam attachments via two simple adapters and a rotary sample holder, which allows the independent and subsequent evaporation of two metals on up to four substrates without breaking the vacuum. Problems and solutions regarding the evaporation of a variety of metals, with focus on platinum, are discussed.     

Short pitch corrugation of railway tracks with wooden or concrete sleepers: An enigma solved?

British Railways (BR) in the 1970s observed an increased level of short pitch corrugation after the electrification of the West Coast main line, which involved (among other things) the change from wooden to concrete sleepers. Here, using a simple model for the two systems, we find a different sensitivity to lateral creepage, a doubled growth at the “pinned-pinned” resonance regime shifted from about 600 to about 1000 Hz, but a reduced growth in the 300-600 Hz range, where most data for both systems seem to lye. Hence, despite it would be tempting to associate the increased corrugation simply to the increased (doubled) peak of normal load, there is discrepancy in the corresponding wavelength predicted by the model. Hence, there is still an “enigma” about the reasons for the enhanced corrugations.     

Quantal acetylcholine release: vesicle fusion or intramembrane particles?

Images of vesicle openings in the presynaptic membrane have regularly been shown to increase in number after stimulation of cholinergic nerves. However, with a very few exceptions, the occurrence of vesicle openings is delayed in time with respect to the precise moment of transmitter release. In contrast, a transient change in the size and distribution of intramembrane particles (IMPs) has constantly been found as a characteristic change affecting the presynaptic membrane in a strict time coincidence with the release of acetylcholine quanta. This is illustrated here in a rapid-freezing experiment performed on small specimens of the Torpedo electric organ during transmission of a single nerve impulse. A marked change affected IMPs in the presynaptic membrane for 3-4 ms, i.e., a population of IMPs larger than 10 nm momentarily occurred in coincidence with the passage of the impulse. The nicotinic receptors, abundantly visible in the postsynaptic membranes, also underwent very fleeting structural changes during synaptic transmission. In conclusion, for rapidly operating neurotransmitters like acetylcholine, a characteristic IMP change was regularly found to coincide in the presynaptic membrane with the production of neurotransmitter quanta, whereas images of vesicles fusion were either delayed or even dissociated from the release process. This is discussed in connection to the different modes of release recently described for other secreting systems.     

The 25th anniversary of BUA for the assessment of osteoporosis: time for a new paradigm?

The measurement of broadband ultrasonic attenuation (BUA) in cancellous bone at the calcaneus for the assessment of osteoporosis was first described within this journal 25 years ago. It was recognized in 2006 by Universities UK as being one of the '100 discoveries and developments in UK Universities that have changed the world' over the past 50 years. In 2008, the UK's Department of Health also recognized BUA assessment of osteoporosis in a publication highlighting 11 projects that have contributed to '60 years of NHS research benefiting patients'. The BUA technique has been extensively clinically validated and is utilized worldwide, with at least seven commercial systems currently providing calcaneal BUA measurement. However, there is still no fundamental understanding of the dependence of BUA upon the material and structural properties of cancellous bone. This review aims to provide an 'engineering in medicine' perspective and proposes a new paradigm based upon phase cancellation due to variation in propagation transit time across the receive transducer face to explain the non-linear relationship between BUA and bone volume fraction in cancellous bone.     

Tribological behaviour of antiwear additives used in hydraulic applications: Synergistic or antagonistic with other surface-active additives?

This paper examines the friction and antiwear (AW) properties using SRV (Schwing–Reib–Verschleiss) tribometer and film-forming properties using atomic force microscope (AFM) of one simple model formulation containing solely AW additive and seven oils containing mixture of additives including three zinc-based packages (ZP), ZP with additional AW additives, ZP with extreme pressure (EP) additives, ZP with viscosity index improvers (VII) and one zinc-free ashless package in steel/steel contacts. VII-containing oil show lower boundary and mixed friction coefficients than the other oils. Although all AW additive-containing oils formed tribofilms, AW properties of ZPs appear to be affected antagonistically by EP additives while synergistically by VII. Zn-free additives investigated in this study show higher wear than ZPs.     

Wear Performance Forecasting of Chopped Fiber–Reinforced Polymer Composites: A New Approach Using Dimensional Analysis

Solid particle erosion of polymer matrix composites is a complex process in which wear occurs from the target surface by impingement of rigid sand particles in an air medium. The rate of material removal (RMR), also referred to as the erosion rate, mainly depends on target material parameters and the erosion conditions such as impact angle, impact velocity, and erodent size. A new semi-empirical model for prediction of the erosion rate of polymer matrix composites has been developed using a dimensional analysis technique based on Buckingham's π theorem. The predictive model analytically rests upon parameters related to chopped glass fiber composites, erodent (target material properties), and operating variables that mainly affect the erosion process of chopped glass fiber–vinyl ester resin composites. The forecasting ability of the predictive model has been assessed and verified by experimental investigations for chopped glass fiber–reinforced vinyl ester resin (VGF) composites. Validation of the theoretical erosion rates obtained from the predictive model showed that they were in good agreement with the experimentally determined erosion rates, where the average error range was estimated to be ～10 to ～20%.     

ASME Section Ⅲ Stress Analysis of a Heat Exchanger Tubesheet with a Misdrilled Hole and Irregular or Thin Ligaments

A stress analysis is described for a nuclear steam generator tubesheet with a thin, or irregular ligament, associated with a mis-drilled hole using the rules of ASME （American Society of Mechanical Engineers） B ＆ PV Section Ⅲ and non-mandatory Appendix A, Article A-8000 for stresses in perforated flat plates. The analysis demonstrates the proper application of the NB-3200 rules for this special application, with discussion of the differences between an actual tube hole deviation and what is assumed in ASME Appendix A. This is a companion paper to ＂Technical Justification Supporting Operation with a Tube Installed in a Mis-Drilled Hole of a Steam Generator Tubesheet＂.