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Lubricants, Volume 4, Issue 1 (March 2016)

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Open AccessArticle
Investigation of Couple Stress Fluid and Surface Roughness Effects in the Elastohydrodynamic Lubrication Problems using Wavelet-Based Decoupled Method
Received: 13 December 2015 / Revised: 13 February 2016 / Accepted: 11 March 2016 / Published: 21 March 2016
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Abstract
The standard decoupled method with Newton-generalized minimum residual procedure performs poorly or may break down when used to solve certain elastohydrodynamic lubrication problems. The authors Zargari et al., 2007 presented decoupled and coupled methods in which the limitations of the decoupled method [...] Read more.
The standard decoupled method with Newton-generalized minimum residual procedure performs poorly or may break down when used to solve certain elastohydrodynamic lubrication problems. The authors Zargari et al., 2007 presented decoupled and coupled methods in which the limitations of the decoupled method for some set of physical parameters and slight variation in these values (physical parameters) give a non-convergence solution. To overcome this aspect the wavelet-based preconditioners technique is used in this paper to solve the elastohydrodynamic lubrication problem. The effect of coupled stress fluids on elastohydrodynamic lubrication behavior in smooth, as well as rough, contact is investigated using the proposed method, numerically, in a low-speed-high load condition. The elastohydrodynamic lubrication characteristics computed for couple stress fluids are found to have strong dependence on the couple stress parameter, which shows the versatility and applicability of the proposed method. Full article
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Open AccessArticle
Tribological Behaviour of PVD Coatings Lubricated with a FAP Anion-Based Ionic Liquid Used as an Additive
Received: 9 February 2016 / Revised: 9 March 2016 / Accepted: 11 March 2016 / Published: 17 March 2016
Cited by 6 | Viewed by 1676 | PDF Full-text (4365 KB) | HTML Full-text | XML Full-text
Abstract
This paper studies 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl) trifluorophosphate ionic liquid ([BMP][FAP]) as a 1 wt% additive to a polyalphaolefin (PAO 6) in the lubrication of CrN and TiN PVD coatings. Friction and wear behaviour were determined by using a ball-on-plate reciprocating tribometer at two loads [...] Read more.
This paper studies 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl) trifluorophosphate ionic liquid ([BMP][FAP]) as a 1 wt% additive to a polyalphaolefin (PAO 6) in the lubrication of CrN and TiN PVD coatings. Friction and wear behaviour were determined by using a ball-on-plate reciprocating tribometer at two loads (20 and 40 N) and a reciprocating frequency of 10 Hz. The tribological behaviour of this mixture has also been compared to a traditional oil additive, like zinc dialkyldithiophosphate (ZDDP). As an additive, ionic liquid exhibited an important friction and wear reduction compared to the base oil. However, tests conducted with ZDDP show slightly better results. XPS was used to analyse wear surfaces. The interactions of each additive with the surface contributed to improving the tribological behaviour of the lubricants. Full article
(This article belongs to the Special Issue Nanoparticles and Ionic Liquids in Lubrication)
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Open AccessArticle
Kinetic Friction of Sport Fabrics on Snow
Received: 28 December 2015 / Revised: 3 March 2016 / Accepted: 8 March 2016 / Published: 14 March 2016
Cited by 2 | Viewed by 1835 | PDF Full-text (5433 KB) | HTML Full-text | XML Full-text
Abstract
After falls, skiers or snowboarders often slide on the slope and may collide with obstacles. Thus, the skier’s friction on snow is an important factor to reduce incidence and severity of impact injuries. The purpose of this study was to measure snow friction [...] Read more.
After falls, skiers or snowboarders often slide on the slope and may collide with obstacles. Thus, the skier’s friction on snow is an important factor to reduce incidence and severity of impact injuries. The purpose of this study was to measure snow friction of different fabrics of ski garments with respect to roughness, speed, and contact pressure. Three types of fabrics were investigated: a commercially available ski overall, a smooth downhill racing suit, and a dimpled downhill racing suit. Friction was measured for fabrics taped on a short ski using a linear tribometer. The fabrics’ roughness was determined by focus variation microscopy. Friction coefficients were between 0.19 and 0.48. Roughness, friction coefficient, and friction force were highest for the dimpled race suit. The friction force of the fabrics was higher for the higher contact pressure than for the lower one at all speeds. It was concluded that the main friction mechanism for the fabrics was dry friction. Only the fabric with the roughest surface showed friction coefficients, which were high enough to sufficiently decelerate a sliding skier on beginner and intermediate slopes. Full article
(This article belongs to the Special Issue Friction and Lubricants Related to Human Bodies)
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Open AccessArticle
Friction of Human Skin against Different Fabrics for Medical Use
Received: 1 December 2015 / Revised: 11 February 2016 / Accepted: 19 February 2016 / Published: 1 March 2016
Cited by 10 | Viewed by 2788 | PDF Full-text (2169 KB) | HTML Full-text | XML Full-text
Abstract
Knowledge of the tribology of human skin is essential to improve and optimize surfaces and materials in contact with the skin. Besides that, friction between the human skin and textiles is a critical factor in the formation of skin injuries, which are caused [...] Read more.
Knowledge of the tribology of human skin is essential to improve and optimize surfaces and materials in contact with the skin. Besides that, friction between the human skin and textiles is a critical factor in the formation of skin injuries, which are caused if the loads and shear forces are high enough and/or over long periods of time. This factor is of particular importance in bedridden patients, since they are not moving about or are confined to wheelchairs. Decubitus ulcers are one of the most frequently-reported iatrogenic injuries in developed countries. The risk of developing decubitus ulcers can be predicted by using the “Braden Scale for Predicting Pressure Ulcer Risk” that was developed in 1987 and contains six areas of risk (cognitive-perceptual, immobility, inactivity, moisture, nutrition, friction/shear), although there are limitations to the use of such tools. The coefficient of friction of textiles against skin is mainly influenced by: the nature of the textile, skin moisture content and ambient humidity. This study will investigate how skin friction (different anatomical regions) varies, rubbing against different types of contacting materials (i.e., fabrics for medical use) under different contact conditions and their relationship in the formation and prevention of decubitus ulcers. Full article
(This article belongs to the Special Issue Friction and Lubricants Related to Human Bodies)
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Open AccessReview
The Role of Solid Lubricants for Brake Friction Materials
Received: 11 December 2015 / Revised: 18 February 2016 / Accepted: 19 February 2016 / Published: 29 February 2016
Cited by 13 | Viewed by 2558 | PDF Full-text (748 KB) | HTML Full-text | XML Full-text
Abstract
This review article comprises of three parts. Firstly, reports of brake manufacturers on the beneficial impact of solid lubricants for pad formulations are surveyed. Secondly, since tribofilms were identified to play a crucial role in friction stabilization and wear reduction, the knowledge about [...] Read more.
This review article comprises of three parts. Firstly, reports of brake manufacturers on the beneficial impact of solid lubricants for pad formulations are surveyed. Secondly, since tribofilms were identified to play a crucial role in friction stabilization and wear reduction, the knowledge about tribofilm structures formed during automotive braking was reviewed comprehensively. Finally, a model for simulating the sliding behavior of tribofilms is suggested and a review on modelling efforts with different model structures related to real tribofilms will be presented. Although the variety of friction composites involved in commercial brake systems is very broad, striking similarities were observed in respect to tribofilm nanostructures. Thus, a generalization of the tribofilm nanostructure is suggested and prerequisites for smooth sliding performance and minimal wear rates have been identified. A minimum of 13 vol % of soft inclusions embedded in an iron oxide based tribofilm is crucial for obtaining the desired properties. As long as the solid lubricants or their reaction products are softer than magnetite, the main constituent of the tribofilm, the model predicts smooth sliding and minimum wear. Full article
(This article belongs to the Special Issue Tribofilms and Solid Lubrication)
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Open AccessReview
A Review of Transfer Films and Their Role in Ultra-Low-Wear Sliding of Polymers
Received: 16 January 2016 / Revised: 3 February 2016 / Accepted: 16 February 2016 / Published: 26 February 2016
Cited by 20 | Viewed by 1912 | PDF Full-text (2140 KB) | HTML Full-text | XML Full-text
Abstract
In dry sliding conditions, polytetrafluoroethylene (PTFE) composites can form thin, uniform, and protective transfer films on hard, metallic counterfaces that may play a significant role in friction and wear control. Qualitative characterizations of transfer film morphology, composition, and adhesion to the counterface suggest [...] Read more.
In dry sliding conditions, polytetrafluoroethylene (PTFE) composites can form thin, uniform, and protective transfer films on hard, metallic counterfaces that may play a significant role in friction and wear control. Qualitative characterizations of transfer film morphology, composition, and adhesion to the counterface suggest they are all good predictors of friction and, particularly, wear performance. However, a lack of quantitative transfer film characterization methods and uncertainty regarding specific mechanisms of friction and wear control make definitive conclusions about causal relationships between transfer film and tribological properties difficult. This paper reviews the state of the art in the solid lubricant transfer film literature and highlights recent advances in quantitative characterization thereof. Full article
(This article belongs to the Special Issue Tribofilms and Solid Lubrication)
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Open AccessArticle
Quantitative Analysis of Retrieved Glenoid Liners
Received: 30 June 2015 / Revised: 1 December 2015 / Accepted: 26 January 2016 / Published: 4 February 2016
Cited by 1 | Viewed by 1355 | PDF Full-text (1665 KB) | HTML Full-text | XML Full-text
Abstract
Revision of orthopedic surgeries is often expensive and involves higher risk from complications. Since most total joint replacement devices use a polyethylene bearing, which serves as a weak link, the assessment of damage to the liner due to in vivo exposure is very [...] Read more.
Revision of orthopedic surgeries is often expensive and involves higher risk from complications. Since most total joint replacement devices use a polyethylene bearing, which serves as a weak link, the assessment of damage to the liner due to in vivo exposure is very important. The failures often are due to excessive polyethylene wear. The glenoid liners are complex and hemispherical in shape and present challenges while assessing the damage. Therefore, the study on the analysis of glenoid liners retrieved from revision surgery may lend insight into common wear patterns and improve future product designs. The purpose of this pilot study is to further develop the methods of segmenting a liner into four quadrants to quantify the damage in the liner. Different damage modes are identified and statistically analyzed. Multiple analysts were recruited to conduct the damage assessments. In this paper, four analysts evaluated nine glenoid liners, retrieved from revision surgery, two of whom had an engineering background and two of whom had a non-engineering background. Associated human factor mechanisms are reported in this paper. The wear patterns were quantified using the Hood/Gunther, Wasielewski, Brandt, and Lombardi methods. The quantitative assessments made by several observers were analyzed. A new, composite damage parameter was developed and applied to assess damage. Inter-observer reliability was assessed using a paired t-test. Data reported by four analysts showed a high standard deviation; however, only two analysts performed the tests in a significantly similar way and they had engineering backgrounds. Full article
(This article belongs to the Special Issue Friction and Lubricants Related to Human Bodies)
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Open AccessArticle
Direct Laser Interference Patterning: Tailoring of Contact Area for Frictional and Antibacterial Properties
Received: 25 September 2015 / Revised: 7 January 2016 / Accepted: 20 January 2016 / Published: 27 January 2016
Cited by 19 | Viewed by 2173 | PDF Full-text (3745 KB) | HTML Full-text | XML Full-text
Abstract
Surface functionalization by topographic micro- and nano-structures in order to achieve unique properties, like super-hydrophobicity or ultrahigh light absorption, is a common strategy in nature. In this paper, direct laser interference patterning (DLIP) is presented as a promising tool allowing for the generation [...] Read more.
Surface functionalization by topographic micro- and nano-structures in order to achieve unique properties, like super-hydrophobicity or ultrahigh light absorption, is a common strategy in nature. In this paper, direct laser interference patterning (DLIP) is presented as a promising tool allowing for the generation of such surface patterns on technical surfaces in order to mimic these biological surfaces and effects. Friction optimization and antibacterial effects by DLIP are exemplarily described. Topographic surface patterns on the micro- and nano-scale demonstrated a significant reduction in the coefficient of friction and bacterial adhesion. It was shown that in both cases, the control of the contact area between surfaces or between surface and bacteria is of utmost importance. Full article
(This article belongs to the Special Issue Friction and Lubricants Related to Human Bodies)
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Open AccessEditorial
Acknowledgement to Reviewers of Lubricants in 2015
Received: 27 January 2016 / Accepted: 27 January 2016 / Published: 27 January 2016
Cited by 1 | Viewed by 1127 | PDF Full-text (145 KB) | HTML Full-text | XML Full-text
Abstract
The editors of Lubricants would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2015. [...] Full article
Lubricants EISSN 2075-4442 Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert
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