| 1. |
- Andersson, Joel, et al.
(författare)
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Simulation of a wear experiment
- 2010
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Ingår i: 14th Nordic Symposium on Tribology. - Luleå : Luleå tekniska universitet. - 9789174391244
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Konferensbidrag (refereegranskat)abstract
- By using a deterministic FFT-accelerated contact mechanical tool to calculate pressure and elastic-plastic deformation, a wear model is utilized to simulate the time dependent wear from a sphere on at contact. The results of the simulated wear are compared to experimental results form a SRV ball on disk tribometer, from which worn surfaces are optically measured. The conditions of the simulation and the experiments are independently adjusted to match. Agreement and diversity shows upon the usefulness and limitation of wear modeling of this type.
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| 2. |
- Björling, Marcus, et al.
(författare)
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EHL friction mapping : the influence of lubricant, roughness, speed and slide to roll ratio
- 2010
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Ingår i: 14th Nordic Symposium on Tribology. - Luleå : Luleå tekniska universitet. - 9789174391244
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Konferensbidrag (refereegranskat)abstract
- A friction test is conducted in a WAM ball on disc test rig. The output from the test is friction coefficient versus entrainment speed and slide-to-roll ratio presented as a 3D friction map. A number of parameters are varied while studying the friction coefficient; surface roughness, base oil viscosity and EP additive package. Entrainment speed, slide to roll ratio and oil temperature are also varied. The results show that the mapping is efficient in showing the different types of friction that may occur in an EHL contact. The results also show that the friction behaviour can be strongly influenced by changing surface roughness as well as base oil viscosity, EP additive content and operating temperature.
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| 3. |
- Emami, Nazanin, et al.
(författare)
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Friction, wear and surface characterization of metal-on-metal implant in protein rich lubrications
- 2010
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Ingår i: 14th Nordic Symposium on Tribology. - Luleå : Luleå tekniska universitet. - 9789174391244
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Konferensbidrag (refereegranskat)abstract
- Although various surface and interface characterization methods have been applied to study the physical wear, corrosion and implant surface interactions with biological environments, presently - in metal on metal (MOM) hip implant- the local and systematic effects of interaction between metal surfaces and protein rich lubrication in body are poorly understood. Materials and Methods: Cobalt-chromium-molybdenium (CoCrMo) alloys have been used in MOM implants extensively. In the present study the samples were immersed in four different biological lubricants (Human serum, synovial fluid, MEM and distill water) for 10 min, 1 hr, and 5 days of immersion and then studied by X-ray Photoelectron Spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). XPS determined the chemistry of elements located whit in the top few nanometers of materials. Friction and wear behavior of CoCrMo substrate in different biological lubricatin were also studied. Results and discussion: Spectra from P2p3/2, O1s, Ca2p3/2, C1s and N1s were collected. Metallic substrates behaved differently when immersed in the same lubricant for different time intervals. The four lubricants reacted differently with metallic surfaces. Larger calcium deposits occurred in supersaturated physiological solutions. Deposition of calcium phosphate was different on CoCrMo alloys depending on the lubricant and the immersion period. Specimens immersed in synovial fluid gave thinner oxide layers and lower calcium phosphate deposits. For all specimens, water immersion resulted in thicker oxide layer. Synovial fluid gave lowest coefficient of friction when distill water gave the highest value. Generally wear was higher for disc in comparison to the pin (in the pin on plate test).
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| 4. |
- Emami, Nazanin, et al.
(författare)
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Novel bio nano-composite for biomedical application
- 2010
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Ingår i: 14th Nordic Symposium on Tribology. - Luleå : Luleå tekniska universitet. - 9789174391244
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Konferensbidrag (refereegranskat)abstract
- Carbon nanoforms exhibit exceptional physical and chemical properties due to their nano-scale dimensions. They also have very high aspect ratio which makes them an excellent reinforcement material for polymer composites. Hydroxyapatite (HA) is the prime constituent of bone generation because of its ability to bond chemically with living bone tissues and positively affect the osteoblasts; this is due to its similar chemical composition and crystal structure to apatite in the human skeletal system. Ultra high molecular weight polyethylene (UHMWPE) is already used as implant material in high stress bearing areas such as hip and knee prosthesis. Wear debris of ultra high molecular weight polyethylene cause osteolysis which is a major reason of long-term failure of total hip replacements.In this study carbon nanoforms together with hydroxyapatite (HA) nanoparticles were used as reinforcement in UHMWPE matrix in order to produce high strength and wear resistant biocomposites with better bioactivity character. Solvent casting and melt blending methods was used during the preparation of this bio-nano composite. The phase compositions and the surface morphology of the nanocomposite material have been studied using X-ray diffraction (XRD), scanning electron microscopy (FE-SEM), and micro-Raman spectroscopy. Nanoindentation technique was used to determine the elastic modulus and hardness of the nanocomposites with different weight% of HA and carbonnanoforms concentrations. The tribologic behaviour of this nano composite was studied using pin-on-plate method. Wear and friction of the produced nano-composites were studied in different biological lubrications.
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| 5. |
- Gebretsadik, Daniel, et al.
(författare)
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Tribological properties of composite multilayer coating
- 2010
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Ingår i: 14th Nordic Symposium on Tribology. - Luleå : Luleå tekniska universitet. - 9789174391244
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Konferensbidrag (refereegranskat)abstract
- The use of surface coatings is emerging as one of the most important approaches in reducing friction and wear in various tribological applications. Even though single layer coatings have a wide range of applications, the performance of the single layer alone may not always be adequate to meet the desired tribological property requirements. Hence, coatings consisting of multi-layers to meet different property requirements in demanding applications are required. In this study, the tribological properties of a graded composite multilayer coating with a specific layer sequence of MoS2:Ti/MoS2:TiBN/TiBN/TiB2/Ti deposited on tool steel substrate have been investigated at temperatures of 40°C and 400°C respectively. The experimental results from the tests at 40°C have shown that the friction coefficient value rangesbetween 0.02 and 0.034. It was found that the deposition parameters influenced the friction and durability of the coatings. Higher substrate bias was found to result in higher friction and the coating deposited at high substrate bias and low N2 flow showed the lowest durability. The friction coefficient and durability of the coatings were found to be highly dependent on temperature. At high temperature, the friction coefficient increases almost three fold and the durability decreases significantly.
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| 6. |
- Golchin, Arash, et al.
(författare)
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Break-away friction of PTFE materials in lubricated conditions
- 2010
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Ingår i: 14th Nordic Symposium on Tribology. - Luleå : Luleå tekniska universitet. - 9789174391244
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Konferensbidrag (refereegranskat)abstract
- This study investigates the tribological characteristics at the initiation of sliding (break-away friction) of several polytetrafluoroethylene (PTFE) based materials including virgin PTFE (PP), PTFE filled with 25% black glass (PG), PTFE filled with 40% Bronze (PB), PTFE filled with 25% Carbon (PC), and PTFE filled with 20% glass fibre and 5% Molybdenum disulphide (PM), as well as standard white-metal Babbitt (BA) in lubricated sliding contact with a steel counter-face. Experiments were carried out using a reciprocating tribo-meter in the block on plate configuration with the specific goal of determining the friction characteristics at break-away under varying conditions. Apparent contact pressures of 1 to 8 MPa were applied with oil temperature levels of 25° to 85°C. Bronze- and carbon-filled PTFE and virgin PTFE were found to provide generally lower break-away friction and less variation in break-away friction over the course of testing than the other tested materials. Break-away friction tests after an extended stop under loading found bronze- and carbon-filled PTFE and virgin PTFE to be minimally affected by the extended stop whereas Babbitt produced a significant increase in break-away friction in the first cycle after stopping. Break-away friction for the four tested materials after an extended stop returned to pre-stop values after 1 stroke.
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| 7. |
- Grahn, Mattias, et al.
(författare)
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Effect of ZDDP on friction and wear in fretting contacts
- 2010
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Ingår i: 14th Nordic Symposium on Tribology. - Luleå : Luleå tekniska universitet. - 9789174391244
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Konferensbidrag (refereegranskat)abstract
- The effect of ZDDP on fretting wear was investigated in a ball on flat machine. The results confirm previous work that anti-wear agents may reduce friction and wear in fretting contacts. It was further found that temperature, adsorption time and base oil polarity were all important parameters affecting the ability of ZDDP to protect the surfaces against fretting wear.
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| 8. |
- Kang, Shaojie, et al.
(författare)
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Two-dimensional finite element analysis of elastic-plastic deformation in asperity-asperity collision
- 2010
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Ingår i: 14th Nordic Symposium on Tribology. - Luleå : Luleå tekniska universitet. - 9789174391244
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Konferensbidrag (refereegranskat)abstract
- The collision of cylindrical asperities is simulated by means of a commercial multiphysics software in this paper. The model combines a computational structure mechanics approach with a contact algorithm. Numerical results are first compared to classical Hertzian theory. Effects of the bulk material under the mating surfaces have been included in the simulation. Materials of top and bottom surfaces have been assigned different properties. Development of plastic deformation and friction are presented along the process of collision. Strain hardening is included in the elastic-plastic deformation. The effect of interference change and friction coefficient variation on deformation and friction has been studied. Deformed shape and subsurface residual stress in asperity are output parameters from this study.
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| 9. |
- Kankanala, Anusha, et al.
(författare)
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The tribological behaviour under rolling/sliding conditions of carbide-free bainitic steel austempered at different temperatures
- 2010
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Ingår i: 14th Nordic Symposium on Tribology. - Luleå : Luleå tekniska universitet. - 9789174391244
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Konferensbidrag (refereegranskat)abstract
- The dry rolling/sliding wear behaviour of Si alloyed carbide free bainitic steel austempered at different temperatures and sliding distances has been evaluated. Three different batches of samples were austempered in a salt bath maintained at 250, 300 and 350 °C respectively for 1h. Rolling with 5% sliding wear tests were performed with each batch of samples for different test cycles, namely 6000, 18000 and 30000 cycles respectively, in order to study the wear performance of these specific steels. An in-depth microstructural characterization has been carried out before and after the wear tests in order to link the wear behaviour to the microstructure of each sample. The wear resistance has been expressed by means of the specific wear calculated from the mass loss after the tests. The worn surfaces were analyzed by the scanning electron microscopy and X-ray diffraction techniques. Micro-hardness profiles were also obtained to analyze strainhardening effects beneath the contact surfaces. The results indicate that the harder material exhibited overall lower wear rates for all test cycles studied i.e., the one austempered at 250°C showed superior rolling/sliding wear resistance than the rest. It is also interesting to note that the hardness increment and thickness of the hardened layer increases with increasing the austempering temperature and number of test cycles.Furthermore the results appear to indicate that the initial roughness of the samples has no major effect on the outcome of the results. The higher wear performance of the sample austempered at 250°C has been attributed to its superior mechanical properties provided by its finer microstructure. It has been evidenced that all samples suffer the TRIP phenomenon since, after wear, no retained austenite could be detected by XRD.
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| 10. |
- Li, Jinxia, et al.
(författare)
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Measurements of grease flow in channels with restrictions using μPIV
- 2010
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Ingår i: 14th Nordic Symposium on Tribology. - Luleå : Luleå tekniska universitet. - 9789174391244
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Konferensbidrag (refereegranskat)abstract
- Grease is commonly used to lubricate various machine components such as rolling element bearings, open gears etc. Better understanding of the flow properties of grease will contribute to understanding the lubrication mechanism in bearings and flow in lubrication systems. In an earlier paper Micro Particle Image Velocimetry (μPIV) techniques were used to study the flow in a rectangular channel. The present paper is an extension of this work where restrictions were applied in such a channel, which creates a much more complex velocity field. The grease is seeded with fluorescent particles, which are illuminated by a double-pulsed laser. The test geometries that are used in this study are a channel with one flat restriction and one with two flow restrictions in a similar channel. The stationary grease mass-flow and the two dimensional velocity fields have been monitored for different pressure drops. For the channel with one flat restriction, the flow was measured to be symmetric at the inlet and outlet, and the distance for the flow to fully develop is comparable with the height of the channel; Slow motion was followed near the step corner at the inlet. For the channel with two flow restrictions, the vector profiles show that the maximum velocity appears at the restrictions; In-between the two restrictions, a part of the grease is not moving. This particularly applies to cases with low-pressure drop and where high consistency grease was used.
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