How birds fly determines the shape of their eggs
Business, Brexit, and collaboration: Imperial hosts government reception
Staff and student contributions recognised at Imperial Garden Party
Most Tribology Group publications are universally accessible thanks to EPSRC Open Access funding
This paper examines the fundamental mechanisms of synovial fluid lubrication in artificial joints. Film thickness measurements were made for bovine serum solutions in a model test device. In contact imaging was also carried out to aid interpretation of these results. The results indicated that two types of film are formed; a boundary layer of adsorbed protein molecules, which are augmented by a high-viscosity fluid film generated by hydrodynamic effects. The high-viscosity film is due to inlet aggregation of protein molecules forming a gel which is entrained into the contact preferentially at low speeds. As the speed increases this gel appears to shear thin, giving much lower lubricant film thickness. Results suggest that protein-containing fluids do not obey classical Newtonian EHL models.
A bearing interface of an apparatus, the apparatus having a first element and a second element configured to move relative to each other during operation of the apparatus, the first element comprising a first bearing surface configured to engage at least a portion of a second bearing surface of the second element thereby defining a contact zone between the first bearing surface and the second bearing surface, the first bearing surface having at least one recess indented into the first bearing surface, wherein the dimension of the recess in ...
The study "Contribution of the Pubofemoral Ligament to Hip Stability: A Biomechanical Study" by Martin, Khoury, Schröder, Johnson, Gómez-Hoyos, Campos, and Palmer found that cutting the hip capsular ligament allowed a large increase in femoral internal rotation, particularly in the flexed hip, causing subluxation to occur. In addition to providing new data on the role of the pubofemoral ligament, it raises the question of whether hip joint surgeons should repair the capsule-what are the likely consequences?-and whether any beneficial effects persist in long-term clinical follow-ups. For now, hip capsular repair seems a sound adjunct to hip arthroscopic surgery.
© 2016 Elsevier Ltd.The microstructure of most hard steels used in tribological applications is inhomogeneous at a micro-scale. This results in local variations in chemical composition and mechanical properties. On a similar scale, tribofilms formed by ZDDP and other anti-wear additives are commonly observed to exhibit a patch-like morphology. ZDDP tribofilms formed under controlled contact conditions on four different steel grades were carefully studied with a new AFM technique to analyse the relationship between the steel microstructure and the tribofilm morphology. Tribofilms were found to be thinner on residual carbides than on the martensitic matrix in all grades containing residual carbides. In most cases, the difference in tribofilm thickness is larger than the carbide protrusion.
© 2016 The Authors.This paper presents a comparison between the results from numerical modelling and experiments to shed light on the mechanisms by which surface texture can reduce friction when applied to an automotive cylinder liner. In this configuration, textured features move relative to the piston-liner conjunction and to account for this our approach is to focus on the transient friction response to individual pockets as they pass through, and then leave, the sliding contact. The numerical approach is based on the averaged Reynolds' equation with the Patir & Cheng's flow factors and the . p-θ Elrod-Adams mass-conserving cavitation model. The contact pressures that arise from the asperity interactions are solved simultaneously to the fluid flow solution using the Greenwood and Tripp method. The experimental data is produced using a pin-on-disc set up, in which laser textured pockets have been applied to the disc specimen. Under certain conditions in the mixed and boundary lubrication regimes, both model and experimental results show . i) an increase in friction as the pocket enters the contact, followed by . ii) a sharp decrease as the pocket leaves the contact, and then . iii) a gradual decay back to the pre-entrainment value. From the evidence obtained for the first time from the proposed combined modelling and experimental investigation conducted under carefully controlled conditions, we suggest that these three stages occur due to the following mechanisms: . i) a reduction in fluid pressure due to the increased inlet gap, . ii) inlet suction as the cavitated fluid within the pocket draws lubricant into the contact, and . iii) film thickness decay as oil is squeezed out of the contact. The interplay of these three mechanisms is shown to control the response of micro-textured surfaces under all lubrication regimes.
We implement an original Boundary Element methodology to study the reciprocating contact mechanics between linear viscoelastic materials. Results are shown for the case of a rigid sphere sinusoidally driven in sliding contact with a viscoelastic half-space. We observe the presence of multi-peaked pressure and displacement distributions; the hysteric friction curve is finally shown for different values of the frequency.
© 2016The perception of many food attributes is related to mechanical stimulation and friction experienced in the tongue-palate contact during mastication. Friction in the tongue-palate is determined by the changing film properties (composition, component distribution, thickness) in the conjunction. We suggest this evolution is essentially determined by tongue-palate film loss rather than shear flow entrainment which predominates in conventional bearing lubrication. The paper reports friction measurements in a simulated tongue-palate contact for a range of high and low fat dairy foods. A reciprocating, sliding contact with restricted stroke length (< contact width) was used; under these conditions there is negligible shear-entrainment of fluid from outside the contact area. The tongue-palate contact was simulated by a PDMS ball and glass surface. The effect of hydrophobic and hydrophilic surfaces on friction was investigated for different fat contents (0, 4.2, 9.5% wt fat). Friction was measured over 60 s of rubbing. Significant differences were observed in the friction change with time for different fat contents (μ 9.5 < μ 4.2 < μ 0 wt%) and for different surface energy conditions (μ hydrophilic < μ hydrophobic). Post-test visualisation of the rubbed films showed that low friction coefficient was associated with the formation of a thin oil film on deposited particulate solids.
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