Academic literature on the topic 'Unidirectional friction test'
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Journal articles on the topic "Unidirectional friction test":
1
Cai, Peng, Zhongfan Luo, Xuhua Duan, and Xinshao Qin. "Effect of reciprocating and unidirectional sliding motion on the friction and wear of phenolic resin based composite." Industrial Lubrication and Tribology 71, no. 4 (May 7, 2019): 573–77. http://dx.doi.org/10.1108/ilt-07-2018-0277.
Abstract:
Purpose The purpose of this paper is to investigate the effect of reciprocating and unidirectional sliding motions on friction and wear of phenolic resin-based composite. Design/methodology/approach The phenolic resin-based composite was fabricated by hot press molding, and then the tribological properties were tested on a CSM tribometer with two types of friction motion modes – reciprocating friction and unidirectional friction. Findings The results showed that the composite exhibited low friction coefficient in unidirectional test. However, the wear factor recorded under unidirectional sliding condition was 12-16 times higher than the reciprocating friction results. The SEM and optical microscopy test results showed that changing the relative motion mode resulted in different topography of transfer film, which is responsible for the different friction and wear characteristics of the composite under reciprocating and unidirectional friction conditions. Originality/value Effect of different friction modes, reciprocating friction and unidirectional friction, on friction characteristics of the composite is sought. Different topography of transfer film formed under reciprocating and unidirectional friction conditions contributed to the different friction characteristics.
2
Pasco, Corentin, Muhammad Khan, Jaipal Gupta, and Kenneth Kendall. "Experimental investigation on interply friction properties of thermoset prepreg systems." Journal of Composite Materials 53, no. 2 (June 9, 2018): 227–43. http://dx.doi.org/10.1177/0021998318781706.
Abstract:
A comprehensive novel investigation into the characterisation of interply friction behaviour of thermoset prepregs for high-volume manufacturing was conducted. High interply slipping rate and normal pressure typically used for high-volume manufacturing present challenges when preforming carbon fibre reinforced plastics. The study involved multiple reinforcement architectures (woven and unidirectional with the same rapid-cure resin system) which were characterised using a bespoke interply friction test rig used to simulate processing conditions representative to press forming and double diaphragm forming. Under prescribed conditions, woven and unidirectional prepregs exhibit significantly different frictional behaviour. Results demonstrated the unidirectional material obeys a hydrodynamic lubrication mode. For the woven material, a rate-dependent friction behaviour was found at low normal pressure. At higher normal pressure however, the woven material exhibited a friction behaviour similar to that of a dry reinforcement and significant tow displacement was observed. Post-characterisation analysis of test-specimens showed significant resin migration towards the outer edges of the plies, leaving a relatively resin-starved contact interface. The findings generate new knowledge on interply friction properties of thermoset prepreg for high-volume manufacturing applications, yet reveal a lack of understanding of the influence of tow tensions as well as the pre-impregnation level for a range of processing conditions.
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Talib, Anis Adilah Abu, Aidah Jumahat, Mohammad Jawaid, Napisah Sapiai, and Alcides Lopes Leao. "Effect of Wear Conditions, Parameters and Sliding Motions on Tribological Characteristics of Basalt and Glass Fibre Reinforced Epoxy Composites." Materials 14, no. 3 (February 2, 2021): 701. http://dx.doi.org/10.3390/ma14030701.
Abstract:
Basalt fibre is a promising mineral fibre that has high potential to replace synthetic based glass fibre in today’s stringent environmental concern. In this study, friction and wear characteristics of glass and basalt fibres reinforced epoxy composites were studied and comparatively evaluated at two test stages. The first stage was conducted at fixed load, speed and distance under three different conditions; adhesive, abrasive and erosive wear, wherein each composite specimens slide against steel, silicon carbide, and sand mixtures, respectively. The second stage was conducted involving different types of adhesive sliding motions against steel counterpart; unidirectional and reciprocating motion, with the former varied at pressure—velocity (PV) factor; 0.23 MPa·m/s and 0.93 MPa·m/s, while the latter varied at counterpart’s configuration; ball-on-flat (B-O-F) and cylinder-on-flat (C-O-F). It was found that friction and wear properties of composites are highly dependent on test conditions. Under 10 km test run, Basalt fibre reinforced polymer (BFRP) composite has better wear resistance against erosive sand compared to Glass fibre reinforced polymer (GFRP) composite. In second stage, BFRP composite showed better wear performance than GFRP composite under high PV of unidirectional sliding test and under B-O-F configuration of reciprocating sliding test. BFRP composite also exhibited better friction properties than GFRP composite under C-O-F configuration, although its specific wear rate was lower. In scanning electron microscopy examination, different types of wear mechanisms were revealed in each of the test conducted.
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Caliman, Radu. "Tribological Study in Case of Polymeric Composite Materials Reinforced with Unidirectional Carbon Fibers Having Stratified Structure." Applied Mechanics and Materials 657 (October 2014): 422–26. http://dx.doi.org/10.4028/www.scientific.net/amm.657.422.
Abstract:
This paper presents a study of the tribological properties of polymeric composite materials reinforced with unidirectional carbon fibers having stratified structure. Unidirectional reinforces carbon fiber materials are more effective if refer to specific properties per unit volume compared to conventional isotropic materials [. Potential benefits of carbon fibers composite materials are: high resistance to breakage and high value ratios strength/density; resistance to high temperatures; low density and high resistance to wear; low or high friction coefficient. The composites are complex and versatile materials but their behaviour in practice is not fully studied. For instance, polymeric composite materials reinforced with carbon fibers after being investigated in terms of wear, did not elucidate the effect of fiber orientation on wear properties [. Is therefore necessary to investigate the effect of carbon fibers orientation on the friction wear properties of the reinforced composite materials tested to adhesive and abrasive wear. Research work has been done with unidirectional composite materials having overlap 16 successive layers made from a polymeric resin and 60% of carbon fibers. The stratified structure was obtained by compressing multiple pre-impregnated strips, positioned manually. During this experimental work, three types of test samples were investigated: normal, parallel and anti-parallel, taking in consideration the carbon fibre orientation with respect to the sliding direction. The specific wear rate was calculated according to: the mass loss, density, the normal contact surface, the sliding distance and load rating. The friction coefficient is computed function to the friction load and loading value.
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Liu, Bin, Zu Hua Yang, and Jian Song Zhou. "Tribological Behavior of Polyimide/Zinc Oxide Hybrid Films." Advanced Materials Research 105-106 (April 2010): 438–40. http://dx.doi.org/10.4028/www.scientific.net/amr.105-106.438.
Abstract:
A series of polyimide/ZnO films were successfully prepared via a solution process. The friction and wear behavior of the hybrid polyimide films in dry sliding against Si3N4 ball was examined on a DF-PM ball-on-block unidirectional friction and wear test rig. The worn surface morphologies of the films were observed with a scanning electron microscope. It was found that the introduction of zinc oxide led to improving the tribological characteristics and thermal stability of the polyimide films. The polyimide/zinc oxide hybrid films had much better friction-reducing ability and wear-resistance than the neat PI film.
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Cheng, B., and M. Kortschot. "An energy-based model for the wear of unidirectional carbon fiber reinforced epoxy." Journal of Composite Materials 54, no. 28 (June 24, 2020): 4535–44. http://dx.doi.org/10.1177/0021998320935486.
Abstract:
The wear resistance of unidirectional carbon fiber reinforced epoxy under severe abrasive sliding conditions was studied. It was found that unidirectional laminates tested with the fibers parallel to the sliding direction (UDp) were more wear resistant than the same laminates tested with fibers transverse to the sliding direction (UDap) under the same set of test conditions. A novel energy-based model was developed to explain the difference in the wear rates. It was found that the difference in wear rates between the two orientations was due to differences in the average volume to surface area ratio of the debris, the energy required to generate new surfaces, and a new k factor that represents the fraction of the total friction energy used for creating wear particles. Furthermore, wear volume per sliding distance was found to be linearly proportional the total frictional energy dissipation for both orientations. These findings can be used to simplify wear predictions for industrial applications.
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SEGU, DAWIT ZENEBE, PYUNG HWANG, and SEOCK-SAM KIM. "EFFECT OF THE TEMPERATURE ON THE FRICTION AND WEAR PROPERTIES OF BULK AMORPHOUS ALLOY." Surface Review and Letters 21, no. 05 (September 29, 2014): 1450067. http://dx.doi.org/10.1142/s0218625x1450067x.
Abstract:
The present paper report the results of an experimental investigation of the temperature effect on the sliding friction and wear properties of the bulk metallic glass (BMG). To improve the friction and wear properties of the BMG, the disk specimens were developed in the alloy system of Fe 67.6 C 7.1 Si 3.3 B 5.5 P 8.7 Cr 2.3 Mo 2.6 Al 2 Co 1.0 using hot metal and industrial ferro-alloys. The friction and wear test was performed using flat-on-flat contact configuration of unidirectional tribometer and Si 3 N 4 ceramic disk used as a counterpart. The worn surfaces of the BMG were observed by using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). The results indicated that the friction and wear properties of the BMG depend on the glass transition and the formation of protective oxide film. The friction coefficient decreased with increasing temperature, while it increased slightly when the temperature passed the glass transition temperature (Tg). The worn specimens were exposed to abrasion, adhesion, oxidation and plastic deformation. In addition, obvious surface flow characteristics was accompany during wear test.
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Suresh, R., P. Shruthi, R. Sunil Kumar, J. Siva, M. Prem Ananth, and R. Ramesh. "Experimental Investigation of Nano-Composite Coated Stainless Steel (316L) Surfaces under Unidirectional Sliding." Applied Mechanics and Materials 440 (October 2013): 37–41. http://dx.doi.org/10.4028/www.scientific.net/amm.440.37.
Abstract:
This work proposes the investigation of nanosized Titanium Aluminum Nitride (TiAlN) on the Stainless Steel (316L) substrate. A chromium interlayer has been applied over the modified surface which will act as an interlayer between the substrate and hard composite coating. The composite coating was prepared by Magnetron Sputtered-Physical Vapour Deposition (PVD) on chromium coated lapped and textured surfaces of stainless steel substrate. Scratch test was performed to characterize the adherence of the coatings on the substrate. TiAlN surface coating over the textured surface exhibits higher adherence than the lapped surface coating surface. The tribological performance of the wear resistant coatings on lapped and textured surfaces was experimentally investigated by pin on disc tribometer at dry sliding contact conditions under various normal loads. The testing results were compared and the results showed that TiAlN coating on textured surfaces exhibited lower friction coefficient and wear rate than lapped coating surfaces under same testing conditions. Sliding wear characteristics such as coefficient of friction and specific wear rate were investigated.
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Kobykhno, Ilya, Dmytro Honcharenko, Hong Yu Li, Alexey Leonidovich Steshenkov, Jin Bao Xu, and Vladimir Yadykin. "Friction and Wear Characteristics of UD Thermoplastic Tape Based Nanocomposites with Fullerene Soot." Key Engineering Materials 822 (September 2019): 215–23. http://dx.doi.org/10.4028/www.scientific.net/kem.822.215.
Abstract:
A series of unidirectional thermoplastic tapes (UD tapes) specimens based on carbon fibers and polyamide filled with fullerene soot in a concentration of up to 4 wt. % was made. A study of the tribological properties by the 3 Ball on Plate test and Ring on Plate test and was made. Shown that the introduction of fullerene soot up to 2 wt. % decreases scatter of CoF in both ranges of load and velocity. Also, this concentration decreases wear rate almost 2.5 times compare to unfilled specimen. Mechanism of friction and wear was suggested. The obtained tribological results are well consistent with mechanical properties, and agree with previously suggested theory of the effect of fullerene soot on adhesion between polymer and fibers.
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Cao, Jialiang, Huan Teng, Wurong Wang, Xicheng Wei, and Hongshan Zhao. "Tribological Properties of the 40Cr/GCr15 Tribo-Pair under Unidirectional Rotary and Reciprocating Dry Sliding." Coatings 12, no. 5 (April 20, 2022): 557. http://dx.doi.org/10.3390/coatings12050557.
Abstract:
The unidirectional rotary and reciprocating sliding experiments of the 40Cr pin/GCr15 disc tribo-pair were carried out on the MFT-5000 Rtec friction and wear tester under the same test conditions with a sliding speed of 0.2 m/s and a load of 150 N. Compared with reciprocating sliding, the tribo-pair in rotary sliding exhibits a stabler friction coefficient and better wear resistance. By analyzing the wear surface morphologies of the two pins, the main wear mechanism was found to be adhesive wear. For the tribo-layer of pin under reciprocating sliding, the surface microstructure plastically converges and forms a ridge from both sides to the middle, while a vortex structure is generated in the tribo-layer of pin under rotating sliding. The metamorphic structure and mircohardness of tribo-layer caused by the sliding forms are the key factors affecting the tribological properties.
Dissertations / Theses on the topic "Unidirectional friction test":
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Takeda, Sho. "A Study of the Consolidation Process of Cu from Powder to Plate by Compression Shearing Method." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEC047.
Abstract:
Compression shearing method at room temperature (COSME-RT)’ est une technique de moulage de matériaux (en particulier de métaux) de la poudre à la plaque en appliquant une force biaxiale simultanée à la température ambiante et dans une atmosphère ambiante. COSME-RT diffère des techniques de moulage conventionnelles en ce sens qu'il peut fabriquer des matériaux sans processus de chauffage et peut ainsi développer de nouveaux matériaux qui ne peuvent pas être formés par des procédés conventionnels. Cependant, le mécanisme de consolidation des matériaux de COSME-RT n’a pas été clarifié en raison de la difficulté de contrôler le processus. Pour contrôler le processus de consolidation des matériaux métalliques avec COSME-RT, j'ai tenté deux expériences visant à contrôler la force de cisaillement: (1) la suppression de la force de cisaillement en dispersant des particules solides de lubrifiant dans des particules de poudre de Cu; et (2) le test de frottement unidirectionnel sur l'échantillon de poudre comprimée uniaxiale pour créer et observer le changement de la condition de liaison dans la direction de la profondeur de l'échantillon. En conséquence, j'ai réussi à acquérir de nouvelles connaissances sur le processus de consolidation des plaques de Cu de poudre de COSME-RT et à construire le nouveau modèle de consolidation du Cu de COSME-RTCompression shearing method at room temperature (COSME-RT) is a molding technique for materials (especially metals) from powder to plate by applying simultaneous biaxial force at room temperature and an ambient atmosphere. COSME-RT differs from conventional molding techniques in that it can fabricate materials without a heating process and can thus develop new materials that cannot be formed by conventional methods. However, the consolidation mechanism of materials by COSME-RT has not been clarified because of the difficulty of controlling the process. To control the consolidation process of metal materials by COSME-RT, I attempted two experiments to control the shearing force: (1) the suppression of the shearing force by dispersing solid lubricant particles into Cu powder particles; and (2) the unidirectional friction test on the uniaxial compressed powder sample to create and observe the change of the bonding condition in the depth direction of the sample. As a result, I successfully obtained new knowledge about the consolidation process of Cu plate from powder by COSME-RT and built the new consolidation model of Cu by COSME-RT
Conference papers on the topic "Unidirectional friction test":
1
Menezes, Pradeep L., Kishore, and Satish V. Kailas. "Effect of Directionality of Grinding Marks on Friction at Different Surface Roughness Using Inclined Scratch Test." In World Tribology Congress III. ASMEDC, 2005. http://dx.doi.org/10.1115/wtc2005-64000.
Abstract:
Surface topography of a tool plays an important role as it predominantly controls the frictional behavior at the interface. In the present study, Inclined Scratch Tester was used to understand the effect of directionality of surface grinding marks on coefficient of friction and transfer layer formation. EN8 steel flats were ground to attain different surface roughness with unidirectional grinding marks. Then Al-Mg alloy pins were scratched against the prepared EN8 steel flats. Grinding angle (angle between direction of scratch and grinding marks) was varied between 0° and 90° during the scratch tests. It was observed that the coefficient of friction and transfer layer formation depend primarily on the directionality of grinding marks of the harder mating surface, and independent of surface roughness of harder mating surface. The grinding angle effect on coefficient of friction was attributed to the variation of plowing component of friction with grinding angle.
2
Menezes, Pradeep L., Kishore, Y. Sasidhar, and Satish V. Kailas. "Role of Surface Topography on Friction and Transfer Layer Formation: A Study Using Inclined Scratch Test." In World Tribology Congress III. ASMEDC, 2005. http://dx.doi.org/10.1115/wtc2005-63999.
Abstract:
Tribological interaction between two contacting surfaces is influenced by many factors such as relative motion, normal load, environment, and lubrication apart from surface characteristics of the mating surfaces. Though surface characteristics such as roughness was dealt by many researchers for decades, the other important characteristic of surfaces, surface topography, has not got its share of attention. In the present investigation, basic studies were conducted using Inclined Scratch Tester to understand the role of surface topography on friction and transfer layer formation. A tribological couple made of copper pin against EN8 flat was used in the tests. Two surface parameters of steel flats — roughness and texture — were varied in tests. Care was taken to ensure that the surface roughness, measured along the scratch direction, had similar values for different textures, namely Unidirectional, 8-ground, and Random. It was observed that the transfer layer formation and the coefficient of friction along with its two components, namely adhesion and plowing, are controlled by the nature of surfaces and are independent of surface roughness. The plowing component of friction was highest for the surface that promotes plane strain conditions near the surface and was lowest for the surface that promotes plane stress conditions near the surface.
3
San Andre´s, Luis, and Adolfo Delgado. "Identification of Force Coefficients in a Squeeze Film Damper With a Mechanical Seal: Part I — Unidirectional Load Tests." In ASME Turbo Expo 2006: Power for Land, Sea, and Air. ASMEDC, 2006. http://dx.doi.org/10.1115/gt2006-90782.
Abstract:
Squeeze film dampers (SFDs) with low levels of external pressurization and poor end sealing are prone to air entrapment, thus not generating enough damping capability. Single frequency, unidirectional load tests were conducted on a SFD test rig replicating a commercial jet-engine configuration. The damper journal is 2.54 cm in length and 12.7 cm in diameter, with nominal clearance of 0.127 mm. The SFD feed end is flooded with oil, while the discharge end contains a recirculation groove and four orifice ports, and a mechanical seal ring in contact with the damper journal. A wave spring pushes the ring ensuring tight sealing to prevent gas ingestion. The mechanical seal also serves to contain the lubricant within the squeeze film land for extended periods of time and; while in operation, to prevent contamination of the ball bearing cartridge. The measurements conducted without and with lubricant in the squeeze film lands, along with a frequency domain identification procedure, render the mechanical seal dry-friction force and viscous damping force coefficients as functions of frequency and motion amplitude. The end seal arrangement is quite effective in eliminating side leakage and preventing air entrainment into the film lands. Importantly enough, the dry friction force, arising from the contact forces in relative motion, increases significantly the test element equivalent viscous damping coefficients. The identified system damping coefficients are thus frequency and motion amplitude dependent, albeit decreasing rapidly as the motion parameters increase. Identified squeeze film force coefficients, damping and added mass, agree well with predictions based on the full film, short length damper model.
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Kovalchenko, Andriy, Oyelayo Ajayi, Ali Erdemir, George Fenske, and Izhak Etsion. "Tribological Behavior of Oil-Lubricated Laser Textured Surfaces in Conformal Flat and Point Contacts." In World Tribology Congress III. ASMEDC, 2005. http://dx.doi.org/10.1115/wtc2005-64309.
Abstract:
The effects of laser surface texturing (LST), which involves the creation of an array of microdimples on the surface with laser, on friction and wear behavior of oil-lubricated steel surfaces were evaluated. Tests were conducted in unidirectional sliding in both the conformal and non-conformal contact configurations with a pin-on-disc test rig using fully formulated synthetic oil lubricant. In conformal contact, LST expanded the operating conditions for mixed and hydrodynamic lubrication regimes to higher loads and slower speeds i.e. the Stribeck curve was shifted to the left. LST was also observed to reduce the magnitude of friction coefficients in the boundary regime. For the non-conformal contact configuration, LST produced more wear on the rubbing counterface compared to untreated surfaces. This also accelerated the run-in process in the tests with LST treated surfaces.
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Fais, Collier, Muhammad Ali, Isaiah Yasko, Rick Walker, and Anbara Lutfullaeva. "Experimental Performance Evaluation of Fixed-Geometry Hydrodynamic Thrust Bearings With Variable Taper Depths." In ASME 2021 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/imece2021-70459.
Abstract:
Abstract This paper presents experimental performance characteristics of fixed-geometry hydrodynamic thrust bearings machined to different helical taper depths. Theoretical analysis based on the Reynold’s equation states that under favorable conditions, these taper depths can produce and maintain load-supporting hydrodynamic pressure yet result in characteristically different oil-film pressure distribution profiles and magnitudes of friction torque. These characteristic performance indicators have not previously been observed experimentally for unidirectional fixed-geometry hydrodynamic thrust bearings with helically tapered pads. An experimental test rig was developed by re-purposing a horizontal milling machine capable of subjecting the test bearings to speeds up to 1,265 rpm and axial loads up to 250 lbf (1,112 N). Under various combinations of constant speed, load, and lubrication supply conditions, the steady-state oil-film pressure distribution across the bearing pad and active friction torque are measured. The effects of variable taper-depth on hydrodynamic pressure distribution and friction torque are compared and discussed.
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San Andre´s, Luis, and Adolfo Delgado. "Identification of Force Coefficients in a Squeeze Film Damper With a Mechanical End Seal: Centered Circular Orbit Tests." In STLE/ASME 2006 International Joint Tribology Conference. ASMEDC, 2006. http://dx.doi.org/10.1115/ijtc2006-12041.
Abstract:
The damping capability of squeeze film dampers (SFDs) relies on adequate end sealing to prevent air ingestion and entrapment. The paper presents the parameter identification, procedure and damping coefficients, of a test SFD featuring a mechanical seal that effectively eliminates lubricant side leakage. The test damper reproduces an aircraft application intended to contain the lubricant in the film lands for extended periods of time. The test damper journal is 2.54 cm in length and 12.7 cm in diameter, with a nominal clearance of 0.127 mm. The SFD feed end is flooded with oil, while the discharge end contains a recirculation groove and four orifice ports. In a companion paper (ASME GT2006-90782), single frequency - unidirectional load excitation tests were conducted, without and with lubricant in the squeeze film lands, to determine the seal dry-friction force and viscous damping force coefficients. Presently, tests with single frequency excitation loads rendering circular centered orbits excitations are conducted to identify the SFD force coefficients. The identified parameters include the overall system damping and the individual contributions from the squeeze film, dry friction and structural damping. The identified system damping coefficients are frequency and motion amplitude dependent due to the dry friction interaction at the mechanical seal interface. Identified squeeze film force coefficients, damping and added mass, are in good agreement with predictions based on the full film, short length damper model.
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Lorenzo Martin, C., O. O. Ajayi, S. Torrel, N. Demas, A. Erdemir, and R. Wei. "Effect of Coating Thickness on Tribological Performance of CrN in Dry Sliding Contact." In ASME/STLE 2012 International Joint Tribology Conference. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/ijtc2012-61172.
Abstract:
One of the most commonly used tribological thin-film coatings is Chromium Nitride (CrN), typically deposited by PVD process. Examples of current applications of this coating include cutting and forming tools: ICE piston ring, hydrodynamic pumps, etc. In selecting coating for tribological applications, one of the critical parameter is the coating thickness. In the present work, we experimentally studied the effect of coating thickness on friction and wear performance of CrN coatings under unidirectional sliding. Test were conducted with ∼ 1, 5 and 10 microns thick coatings deposited on a hardened H-13 steel substrate by plasma enhanced magnetron sputtering (PEMS) process. The friction behavior was strongly dependent on coating thickness, especially at relatively low loads. At higher load however, the thinner coating (1 μm) was quickly worn through while the thicker ones (5 and 10 μm) remained intact. Wear in both, the counterface WC material and the coating was also observed to depend on coating thickness. The observed effect on coating thickness on tribological behavior is attributed to differences in the microstructure and mechanical behaviors of coatings as function of thickness.
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Lorenzo Martin, C., O. O. Ajayi, S. Torrel, G. R. Fenske, and R. A. Erck. "Experimental Investigation of Transition in Lubrication Regime for Thin-Film Coated Surfaces." In ASME/STLE 2012 International Joint Tribology Conference. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/ijtc2012-61171.
Abstract:
Friction and wear behavior of lubricated sliding contact is determined by the operating lubrication regime. A useful approach to determining the operating lubrication regime is the calculation of the λ ratio, which is defined as the ratio of lubricant fluid film thickness (h), and the composite surface roughness (ơ) of contacting surfaces (λ = h/ơ). Thin-film tribological coatings are increasingly being used for application in lubricated machine elements such as gears and bearings. It is usually assumed by design engineers that application of thin-film coatings has no effect on fluid-film lubrication. This paper presents our experimental investigation of the impact of several (5) commercially available coatings on lubrication regime during a unidirectional sliding contact. Using a ball-on-flat contact configuration and lubricated with PAO basestock oil, tests were conducted in which the λ ratio was varied as a function of time, for both uncoated and coated flat specimen. In test with uncoated flat, the various distinctive lubrication regime of hydrodynamic, mixed and boundary were observed as indicated by the measured friction coefficient (Stribeck Curve). In tests with some of the coatings, especially the carbon based DLCs, there was no obvious distinctive transition in lubrication regime. In other coatings (ex. TiCN), various lubrication regime were also observed; although the rate of transition from one regime to the other was different. The effects of coatings are attributed to their inherent mechanical and tribological properties as well as their impact on the run-in process.
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Zum Gahr, Karl-Heinz, and Mario Mann. "Effect of Surface Microtexturing on Friction at Unidirectional Sliding Depending on Lubricant Viscosity." In ASME/STLE 2012 International Joint Tribology Conference. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/ijtc2012-61042.
Abstract:
Effect of surface microtexturing with spherical dimples of 60 μm diameter on friction behaviour of steel 100Cr6/sapphire pairs was studied as function of lubricant viscosity. Tests were run at unidirectional sliding up to 0.30 m/s using a pellet-on-disc geometry with flat contact area and drip lubrication with liquids such as glycerine-water solutions, distilled water and different mineral oils without additives. The texture pattern was produced on the polished sapphire discs by laser ablation processes. Friction force and film thickness of the lubricating liquid were continuously measured during the tests at different sliding velocities. Results showed that effectiveness of microtexturing in reducing friction and increasing load-carrying capacity depended on viscosity of the lubricant, operating conditions such as sliding velocity and applied load as well as texture parameters.
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Aluko, O. "A Parametric Study on Failure of Pin-Loaded Unidirectional-Woven Composite Joints." In ASME 2013 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/imece2013-63961.
Abstract:
An analysis was performed to predict the failure load of unidirectional and woven pinned loaded composite joints using the characteristic curve model. The characteristic dimensions used to determine the characteristic curve were evaluated from stress functions without experimental tests. A parametric study was carried out for different coefficient of friction ranging between 0 and 0.15 to evaluate the effect of friction on joints failure using Tsai-Wu failure criterion along the characteristic curve. A comparison of analytical results with the available experimental data showed that the friction coefficient of 0.05 generally gave the best prediction for the joint configurations evaluated.