A newly developed measuring device is presented, that allows the evaluation of the frictional behaviour of different materials. The device does not need specific laboratory environment and due to its compact design - similarly the... more
A newly developed measuring device is presented, that allows the evaluation of the frictional behaviour of different materials. The device does not need specific laboratory environment and due to its compact design - similarly the palpation by the fingertip -enables the measurement and differentiation, respectively, of the frictional coefficients under realistic working conditions.
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The wear behaviour of metallic material at elevated temperature is influenced by the formation of various types of layers. Present investigation is undertaken to find the influence of the oxidation kinetics, the adhesion characteristics... more
The wear behaviour of metallic material at elevated temperature is influenced by the formation of various types of layers. Present investigation is undertaken to find the influence of the oxidation kinetics, the adhesion characteristics of the oxide scale and the strength of the test material on the high temperature wear. Towards that purpose two different alloy, 253 MA and PM 1000 are taken as test materials. 253 MA is a Fe based and PM 1000 is a Ni based alloy. Both of them forms Cr 2 O 3 scale on oxidation. The friction coefficient and the thickness loss of 253 MA alloy and PM 1000 alloy are measured and compared as function of temperatures. The morphology of the worn surfaces and the transverse section of the worn surfaces are examined to identify the material removal mechanisms. The results showed that the friction coefficient of PM 1000-PM 1000 is higher than the friction coefficient of 253 MA-PM 1000 up to 873 K. The transverse section of the worn surface showed presence of a...
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The aim of this research is the investigation of surface properties, measurement of friction coefficient and wear rate, and determination of the reliability of selective laser-sintered (SLS) tool elements for use as prototype tools. The... more
The aim of this research is the investigation of surface properties, measurement of friction coefficient and wear rate, and determination of the reliability of selective laser-sintered (SLS) tool elements for use as prototype tools. The tests were carried out on a pin-on-ring machine. The pin was constructed of glass-fiber reinforced polyamide-imide, the ring of laser-sintered phosphorous bronze. During the tests the wear rate, the friction coefficient and the change in surface properties were measured at different temperature and loading conditions. The wear rate and the friction coefficient increase with normal force at temperatures up to 80 °C, but over this temperature the coefficient of friction decreases. No extreme destruction or failure occurred in the sintered structure during the tests.
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This study deals with a comparison between new experiments on the frictional behavior of porous journal bearings and its prediction by previous numerical simulations. The tests were carried out on bearings lubricated with polyalphaolefin... more
This study deals with a comparison between new experiments on the frictional behavior of porous journal bearings and its prediction by previous numerical simulations. The tests were carried out on bearings lubricated with polyalphaolefin (PAO)-based oils of distinct viscosities. The theoretical model underlying the simulations includes the effects of cavitation by vaporization and accounts for the sinter flow by virtue of Darcy's law. The effective eccentricity ratio corresponding to the experimentally imposed load is estimated by an accurate numerical interpolation scheme. The comparison focuses on the hydrodynamic branches of the Stribeck curve by dimensional analysis (DA), where the variations of the lubricant viscosity with temperature are of main interest. The numerically calculated values of the coefficient of friction are found to reproduce the experimentally obtained ones satisfactorily well in terms of overall trends; yet, the former lie predominantly below the measured...
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Abstract Diamond and diamond-like carbon films are well known for their outstanding properties such as high hardness, low coefficient of friction, good thermal conductivity, excellent biocompatibility and electrical insulation. Diamond... more
Abstract Diamond and diamond-like carbon films are well known for their outstanding properties such as high hardness, low coefficient of friction, good thermal conductivity, excellent biocompatibility and electrical insulation. Diamond films with nanocrystalline grains offer added advantages of higher hardness, improved surface finish (less roughness), very high sp3 content, etc. In view of the above, the present investigation is undertaken to explore the possibility of using nanocrystalline diamond films in advanced tribological applications. In this work, a nanocrystalline diamond film is deposited using a unique chemical vapour deposition (CVD) technique. The microstructural features are characterised using atomic force microscopy (AFM). Tribological behaviour of these films is evaluated by means of a reciprocating model tribometer with various lubricants. The worn surfaces are examined using three-dimensional confocal microscopy. The results show that these films have comparable friction coefficient with and without lubricants. Furthermore, they exhibited negligible wear for the tested range of loads.
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In this review, we have presented scanning probe microscopy across dimensions from large samples like single cells, via single biomolecules and nanometer small ion induced defects on crystal surfaces to subatomic features like electronic... more
In this review, we have presented scanning probe microscopy across dimensions from large samples like single cells, via single biomolecules and nanometer small ion induced defects on crystal surfaces to subatomic features like electronic orbitals and single electron spins. Scanning probe microscopy is on its way to a standard laboratory method: subatomic features can be imaged, and with magnetic resonance force microscopy it has even left the two-dimensional surface regime. Perhaps in the not too distant future 3D-imaging of ( ...
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... The holding time of indentation was 5 s in all cases. Both loading and unloading times were 10 s. The experimental results were corrected for the thermal drift of the equipment, and for the uncertainty in the zero position, following... more
... The holding time of indentation was 5 s in all cases. Both loading and unloading times were 10 s. The experimental results were corrected for the thermal drift of the equipment, and for the uncertainty in the zero position, following the method proposed by Oliver et al. [36]. ...
Research Interests: Materials Engineering, Chemical Engineering, Materials Science, Nanoindentation, Transmission Electron Microscopy, and 11 moreTribology, Atomic Force Microscopy, Nanocrystalline Material, Manufacturing Engineering, Composite Material, Diamond, X ray diffraction, Elastic Modulus, X Ray Photoelectron Spectroscopy, Friction Coefficient, and Electron Energy Loss Spectroscopy
High sliding wear resistance is generally attributed to high hardness and high mechanical strength. Novel near net shape process technologies such as metal injection moulding (MIM) or lost foam casting (LF) lack forming processes that... more
High sliding wear resistance is generally attributed to high hardness and high mechanical strength. Novel near net shape process technologies such as metal injection moulding (MIM) or lost foam casting (LF) lack forming processes that typically increase strength. Consequently, the materials exhibit large-grained microstructures with low defect densities. Commercial copper alloys (CuSn8, CuNi9Sn6, CuSn12Ni2) well known for good sliding properties were produced using MIM and LF and characterised in the current study. Their wear and friction behaviour was compared to conventionally produced variants in a lubricated, reciprocating sliding test against steel. The results showed an equal or superior wear resistance and lower friction levels for large-grained microstructures evolving in MIM and LF. SEM, FIB and EBSD studies revealed a tribolayer on the surface and a tribologically transformed layer (TTL), composed of a nano-crystalline zone or partially rotated grains, and selective harden...
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In many fields of industry, abrasion and erosion processes are dominant wear mechanisms that reduce lifetime of costly machine parts. Wear resistance against abrasion and/or impact or the ability to withstand other complex mechanical... more
In many fields of industry, abrasion and erosion processes are dominant wear mechanisms that reduce lifetime of costly machine parts. Wear resistance against abrasion and/or impact or the ability to withstand other complex mechanical actions are often required. In order to quantify the specific properties of material that are applied in such fields, several test methods are in use. A certain discrepancy can be seen between the systems approach and the aim to get information about suitability of materials for practical applications simply from specific material tests. This paper gives an overview over a selection of relevant test equipment and procedures. In addition, some examples are given for advanced studies on materials behaviour combining tribological test, material analyses repectively materialography, and mathematical methods in order to support - for selected cases - the acquired correlation of materials properties and wear resistance under severe conditions.
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Two theoretical mass-conservative models for the tribological evaluation of porous journal bearings are investigated rigorously. The first model supposes that the lubricating fluid film is fully contiguous in the range between two angles,... more
Two theoretical mass-conservative models for the tribological evaluation of porous journal bearings are investigated rigorously. The first model supposes that the lubricating fluid film is fully contiguous in the range between two angles, i.e. effects due to cavitation are excluded. The fluid pressure distribution is determined numerically by solving a modified Reynolds equation which governs the fluid film and accounts for the porous surface and the well-known Darcy's law that describes the flow through the porous matrix in the usual manner. These equations are supplemented with the integral angular momentum equation applied to the fluid film and the integral mass balance between the flow rates of the lubricant entering into and leaking from the clearance, respectively. Considering the second theoretical model, we again solve the Laplace equation governing the pressure distribution due to Darcy's law that holds in the porous bearing seat, but adopt a modification of the Elr...
Modelling and simulation are more and more upcoming tools in various fields in engineering. Most tasks request specialization in terms of the technical background as well as of the mathematical methods used. In this paper an overview is... more
Modelling and simulation are more and more upcoming tools in various fields in engineering. Most tasks request specialization in terms of the technical background as well as of the mathematical methods used. In this paper an overview is given about some commonly available software tools for simulation with respect to the specific conditions in the field of tribology as an interdisciplinary subject. Aspects of geometry, material characteristics and chemical processes have to be considered. The combination resp. integration of different simulation aims is currently a very interesting task. The focus on processes in the nano domain led to new highly specific simulation tools like molecular dynamics, which enables the simulation of complex tribological processes. Some examples of modelling and simulation are given based on research projects as the are currently running or have been recently finished at the Austrian Center of Competence for Tribology: Targets of these works are problems ...
Economic and societal changes and technological development guide the focus of tribology research. “Classical” tasks, such as the improvement of materials or the tuning of a lubricant, have long been replaced by a function-oriented... more
Economic and societal changes and technological development guide the focus of tribology research. “Classical” tasks, such as the improvement of materials or the tuning of a lubricant, have long been replaced by a function-oriented aggregate design, including specifications defined by needs arising from production and the environment. Tribology faces, among other remarkable changes, a paradigm shift according to the tendency to replace classic internal combustion engine (ICE) drivetrains with electric drives. How tribology will develop, and which research topics will prevail in the future, are being explored by several studies based on the experience of experts. The variety of contributions to journals and conferences provide an indicator of the importance of such tasks or topics. Here, a report on the ECOTRIB 2019—7th European Conference on Tribology held in Vienna, Austria, is presented. From the available information, an even stronger integration of other disciplines into tribolo...
Objective During osteoarthritis progression, cartilage degrades in a manner that influences its biomechanical and biotribological properties, while chondrocytes reduce the synthesis of extracellular matrix components and become apoptotic.... more
Objective During osteoarthritis progression, cartilage degrades in a manner that influences its biomechanical and biotribological properties, while chondrocytes reduce the synthesis of extracellular matrix components and become apoptotic. This study investigates the effects of inflammation on cartilage under biomechanical stress using biotribological tests. Methods Bovine osteochondral grafts from five animals were punched out from the medial condyle and treated with or without pro-inflammatory cytokines (interleukin-1β [IL-1β], tumor necrosis factor-α [TNF-α], IL-6) for 2 weeks. After incubation, biotribological tests were performed for 2 hours (alternating 10 minutes test and pause respectively at 39°C, 180 N, 1 Hz, and 2 mm stroke). Before and after testing, the cartilage surface was imaged with a 3-dimensional microscope. During testing, the coefficient of friction (COF) was measured, while gene expression analysis and investigation of metabolic activity of chondrocytes were car...
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Osteochondral defects in middle-aged patients might be treated with focal metallic implants. First developed for defects in the knee joint, implants are now available for the shoulder, hip, ankle and the first metatarsalphalangeal joint.... more
Osteochondral defects in middle-aged patients might be treated with focal metallic implants. First developed for defects in the knee joint, implants are now available for the shoulder, hip, ankle and the first metatarsalphalangeal joint. While providing pain reduction and clinical improvement, progressive degenerative changes of the opposing cartilage are observed in many patients. The mechanisms leading to this damage are not fully understood. This protocol describes a tribological experiment to simulate a metal-on-cartilage pairing and comprehensive analysis of the articular cartilage. Metal implant material is tested against bovine osteochondral cylinders as a model for human articular cartilage. By applying different loads and sliding speeds, physiological loading conditions can be imitated. To provide a comprehensive analysis of the effects on the articular cartilage, histology, metabolic activity and gene expression analysis are described in this protocol. The main advantage of tribological testing is that loading parameters can be adjusted freely to simulate in vivo conditions. Furthermore, different testing solutions might be used to investigate the influence of lubrication or pro-inflammatory agents. By using gene expression analysis for cartilage-specific genes and catabolic genes, early changes in the metabolism of articular chondrocytes in response to mechanical loading might be detected.
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Metal matrix composites are very inhomogeneous materials, and their properties depend on various parameters (production process, constituents, their interfaces, etc.). The influence of SiC microparticles (40 μm) reinforcement and graphite... more
Metal matrix composites are very inhomogeneous materials, and their properties depend on various parameters (production process, constituents, their interfaces, etc.). The influence of SiC microparticles (40 μm) reinforcement and graphite macroparticles (200–800 μm) addition on the mechanical properties of Al–Si A356 alloy, produced by compocasting, has been assessed using macro- and nanoscale measurements of hardness and modulus of elasticity. The Al makes over 90 wt% of the A356 alloy, so the nanoscale measurements were performed on different α phase regions on each material (core of α phase, eutectic α phase, and α phase near the phase boundaries α phase/secondary phases). The results showed that there is no direct correlation between mechanical properties on macro- and nanoscale. The nanoscale results also showed that the secondary phases (SiC and graphite particles) can have significant effect on the mechanical properties on the atomic level, i.e. in the α phase regions very close to the secondary phases.
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Objective Cobalt and chromium (CoCr) ions from metal implants are released into the joint due to biotribocorrosion, inducing apoptosis and altering gene expression in various cell types. Here, we asked whether CoCr ions... more
Objective Cobalt and chromium (CoCr) ions from metal implants are released into the joint due to biotribocorrosion, inducing apoptosis and altering gene expression in various cell types. Here, we asked whether CoCr ions concentration-dependently changed viability, transcriptional activity, and inflammatory response in human articular chondrocytes. Design Human articular chondrocytes were exposed to Co (1.02-16.33 ppm) and Cr (0.42-6.66 ppm) ions and cell viability and early/late apoptosis (annexin V and 7-AAD) were assessed in 2-dimensional cell cultures using the XTT assay and flow cytometry, respectively. Changes in chondrocyte morphology were assessed using transmitted light microscopy. The effects of CoCr ions on transcriptional activity of chondrocytes were evaluated by quantitative polymerase chain reaction (qPCR). The inflammatory responses were determined by measuring the levels of released pro-inflammatory cytokines (interleukin-1β [IL-1β], IL-6, IL-8, and tumor necrosis fa...
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Purpose The paper aims to focus on the individual contribution of water to the lubrication regimes in articular joints because understanding of these regimes is crucial not only for the treatment of diseases like osteoarthritis but also... more
Purpose The paper aims to focus on the individual contribution of water to the lubrication regimes in articular joints because understanding of these regimes is crucial not only for the treatment of diseases like osteoarthritis but also for the development of new implants to have a longer service cycle. Design/methodology/approach Cartilage specimen and the synovial fluid were both isolated from bovine knee joints that are enclosed by a synovial membrane under sterile conditions of a biosafety Level 2 (BSL2) cabinet. Subchondral bone was removed from the cartilage because it not only creates a stable base to place the specimen on the holder, but it also acts as a primary shock absorber protecting the overlaying cartilage under high-impact loads. A specimen holder specially designed for tests and was attached to the linear oscillation (SRV) test machine. The SRV test machine provides a reciprocating sliding motion between the cartilage samples that are submerged into the selected bio...
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Abstract Automotive parts made of ultra-high strength steels are produced by press hardening in order to obtain high-strength components. During this process, formed parts are pressed against tools at high temperature, which ultimately... more
Abstract Automotive parts made of ultra-high strength steels are produced by press hardening in order to obtain high-strength components. During this process, formed parts are pressed against tools at high temperature, which ultimately yields to tool damage. Tool damage is especially detrimental since it not only affects the quality of the parts but also causes higher material consumption and reduces maintenance intervals. The extent of tool damage is determined by the process parameters but their influence is not yet clearly understood. The aim of this work is to investigate the influence of input process parameters on tool wear and maximum drawing force. To this end, a novel test rig is designed in order to reproduce typical press hardening conditions under well-controlled laboratory conditions. This set up is used to modify selected input parameters according to a Design of Experiments in order to investigate their impact on tool wear and drawing force. The results obtained can be summarised into two simple equations, which depend only on the most dominant parameters. This method allows a quantitative optimisation of the press hardening process, as illustrated by a practical example.
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Porous sliding elements (especially porous bearings) as well as polymer sliding elements are used in large quantities and in many different applications. For special applications metallic sliding elements with hybrid lubrication... more
Porous sliding elements (especially porous bearings) as well as polymer sliding elements are used in large quantities and in many different applications. For special applications metallic sliding elements with hybrid lubrication (graphite-oil-compound, multiphase composites, MMC) are used. The valuation of the friction and wear behaviour of those "selflubricating" sliding elements "free of maintenance" enables to provide mechanical engineers with information in order to achieve suitable design and functional and life time estimations. The present state, especially with respect to standardisation of testing, is discussed. In addition some specific questions on quality criteria of the sliding elements concerned are asked where selected examples of research topics and investigations, carried out in research projects at the (previous) Tribology and Engineering Design Section of the Vienna University of Technology, and at the Austrian Center of Competence for Tribology or partners, respectively, are presented.
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For the investigation of piston ring and cylinder liner systems, screening tests are usually run with pure engine oil as the only lubricant. Due to the fact that the combustion chamber of a cylinder is filled with a high-pressure... more
For the investigation of piston ring and cylinder liner systems, screening tests are usually run with pure engine oil as the only lubricant. Due to the fact that the combustion chamber of a cylinder is filled with a high-pressure gas-fuel-mixture, we assume that the piston ring and cylinder liner contact is lubricated by a mixture of oil and fuel rather than by pure oil. As numerous investigations already deal with the effect of oil on the piston ring and cylinder liner system, we will concentrate in this paper on the effect of diesel, especially the effect of the admixture of bio-diesel, on the wear behavior of such a system.
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253 MA alloy and PM 1000 alloy are used for application requiring exposure to high temperature. Both alloys form Cr 2 O 3 protective layer on exposure to elevated temperature. As these alloys are designed for elevated temperature... more
253 MA alloy and PM 1000 alloy are used for application requiring exposure to high temperature. Both alloys form Cr 2 O 3 protective layer on exposure to elevated temperature. As these alloys are designed for elevated temperature applications, it is expected that ...
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Cermet coatings such as WC-Co, Cr 3 C 2 -NiCr obtained by thermal spraying are well known for their tribological application. The strength and toughness and in turn the wear resistance of these coatings can be increased by depositing them... more
Cermet coatings such as WC-Co, Cr 3 C 2 -NiCr obtained by thermal spraying are well known for their tribological application. The strength and toughness and in turn the wear resistance of these coatings can be increased by depositing them in nanocrystalline form. Thus the objective of the present investigation is to evaluate the wear performances of the Cr 3 C 2 -25(Ni20Cr) coating having a nanocrystalline grain size. Towards that purpose, nanocrystalline Cr 3 C 2 -25(Ni20Cr) powder was deposited on steel substrate by High Velocity Oxy Fuel (HVOF) spraying. The micro-structural features and mechanical properties of the coating were determined. The sliding wear behaviour of the said coating was evaluated as a function of temperature with the help of an elevated temperature wear test rig. The morphology of the worn surfaces and the regions beneath the worn surfaces were examined using SEM. The results of this study show that the friction coefficient of the coating decreased with increasing test temperature up to 873 K. The study also identified three different wear mechanisms.
Tribologie ist die Wissenschaft von Reibung und Verschleis. Dabei handelt es sich um physikalische Prozesse, die uberall im Alltag auftreten konnen — vom Kontakt der Schuhsohle mit dem Fusboden bis zu den Reifen in Wechselwirkung mit der... more
Tribologie ist die Wissenschaft von Reibung und Verschleis. Dabei handelt es sich um physikalische Prozesse, die uberall im Alltag auftreten konnen — vom Kontakt der Schuhsohle mit dem Fusboden bis zu den Reifen in Wechselwirkung mit der Fahrbahn oder den Bremsen bei Fahrzeugen. Erforscht wird, wie man Verschleis und Reibung vermindert oder gar verhindert, aber auch, wie man Reibung moglichst effizient realisiert (z.B. bei Bremsen). Friedrich Franek beschaftigt sich unter anderem mit den Eigenschaften von Schmierstoffen und den Folgen, die eine Veranderung ihrer Eigenschaften mit sich bringt. Der Forscher will herausfinden, wie sich Gebrauchsqualitaten entwickeln und ob es Produkte mit verbesserter Stabilitat gibt. Dazu werden beispielsweise Alterungszustande innerhalb weniger Tage simuliert, die in einem realen Aggregat erst nach Monaten oder Jahren auftreten.
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Sliding contacts of copper alloys and steels can commonly be found in numerous machine elements. The interactions of copper alloys and additives under mixed and boundary lubri¬cation conditions are far less understood than those of mating... more
Sliding contacts of copper alloys and steels can commonly be found in numerous machine elements. The interactions of copper alloys and additives under mixed and boundary lubri¬cation conditions are far less understood than those of mating steel bodies. Furthermore, copper alloys can be sensitive to the formation of soft and heavily wearing surface layers (e. g. CuS) making some additives inapplicable. The lubrication properties of various additives in model copper-alloy /steel sliding contacts were evaluated. Of major interest were various esters: 2 variants of sulfurised fatty acid methyl esters (S-FAME) and glycerol monooleat (GMO). The properties and performance were compared to those of base oil, "classical" zinc-dialkyl-dithio-phosphate (ZDDP) additivated oil and two commercially available fully formulated oils. Further the influence of alloy composition was investigated by carrying out tests on a variety of bronzes and brasses. The test rig used for tribometrological...
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The articles of this volume will be reviewed individually.