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Träfflista för sökning "AMNE:(ENGINEERING AND TECHNOLOGY Mechanical Engineering Tribology) srt2:(2015-2019)"

Sökning: AMNE:(ENGINEERING AND TECHNOLOGY Mechanical Engineering Tribology) > (2015-2019)

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1.
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2.
  • Pieringer, Astrid, 1979, et al. (författare)
  • Investigation of railway curve squeal using a combination of frequency- and time-domain models
  • 2016
  • Ingår i: Proceedings of the 12h International Workshop on Railway Noise (IWRN12), Terrigal, Australia, September 12-16. ; , s. 444 - 451
  • Konferensbidrag (refereegranskat)abstract
    • Railway curve squeal arises from self-excited vibrations during curving. In this paper, a frequency- and a timedomainapproach for curve squeal are compared. In particular, the capability of the frequency-domain model topredict the onset of squeal and the squeal frequencies is studied. In the frequency-domain model, linear stabilityis investigated through complex eigenvalue analysis. The time-domain model is based on a Green's functionsapproach and uses a convolution procedure to obtain the system response. To ensure comparability, the samesubmodels are implemented in both squeal models. The structural flexibility of a rotating wheel is modelled byadopting Eulerian coordinates. To account for the moving wheel‒rail contact load, the so-called moving elementmethod is used to model the track. The local friction characteristics in the contact zone is modelled inaccordance with Coulomb's law with a constant friction coefficient. The frictional instability arises due togeometrical coupling. In the time-domain model, Kalker's non-linear, non-steady state rolling contact modelincluding the algorithms NORM and TANG for normal and tangential contact, respectively, is solved in eachtime step. In the frequency-domain model, the normal wheel/rail contact is modelled by a linearization of theforce-displacement relation obtained with NORM around the quasi-static state and full-slip conditions areconsidered in tangential direction. Conditions similar to those of a curve on the Stockholm metro exposed tosevere curve squeal are studied with both squeal models. The influence of the wheel-rail friction coefficient andthe direction of the resulting creep force on the occurrence of squeal is investigated for vanishing train speed. Results from both models are similar in terms of the instability range in the parameter space and the predictedsqueal frequencies.
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3.
  • Winroth, Julia, 1981, et al. (författare)
  • Contact stiffness considerations when simulating tyre/road noise
  • 2017
  • Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 409, s. 274-286
  • Tidskriftsartikel (refereegranskat)abstract
    • Tyre/road simulation tools that can capture tyre vibrations, rolling resistance and noise generation are useful for understanding the complex processes that are involved and thereby promoting further development and optimisation. The most detailed tyre/road contact models use a spatial discretisation of the contact and assume an interfacial stiffness to account for the small-scale roughness within the elements. This interfacial stiffness has been found to have a significant impact on the simulated noise emissions but no thorough investigations of this sensitivity have been conducted. Three mechanisms are thought to be involved: The horn effect, the modal composition of the vibrational field of the tyre and the contact forces exciting the tyre vibrations. This study used a numerical tyre/road noise simulation tool based on physical relations to investigate these aspects. The model includes a detailed time-domain contact model with linear or non-linear contact springs that accounts for the effect of local tread deformation on smaller length scales. Results confirm that an increase in contact spring stiffness causes a significant increase of the simulated tyre/road noise. This is primarily caused by a corresponding increase in the contact forces, resulting in larger vibrational amplitudes. The horn effect and the modal composition are relatively unaffected and have minor effects on the radiated noise. A more detailed non-linear contact spring formulation with lower stiffness at small indentations results in a reduced high-frequency content in the contact forces and the simulated noise.
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4.
  • Lundberg, Oskar, 1980- (författare)
  • On the influence of surface roughness on rolling contact forces
  • 2016
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Road vehicle tyres, railway wheels and ball bearings all generate rolling contact forces which are transferred within a finite area of contact between the rolling element and the substrate. Either it is visible or not for the human eye, a certain degree of roughness is always present on the contacting surfaces and it influences the generation of both vertical and lateral contactforces. The purpose of this investigation is to enhance the understanding and modelling of the influence from small-scale surface roughness on the generation of rolling contact forces. To this end, a computationally efficient method to include roughness-induced contact nonlinearities in the dynamic modelling of rolling contacts is proposed. The method is implemented in a time domain model for vertical wheel–track interaction to model rolling-induced rail vibrations, showing good agreement with measurements. Furthermore, a test rig is developed and used for the investigation of tyre–road rolling contact forces. Detailed studies are performed on the influence of substrate roughness on the resulting contact forces for a tyre tread block which is rolling at different operating conditions. The choice of substrate as well as the rolling velocity and the slip ratio is observed to have significant influence on the resulting friction coefficient. For high slip ratios, stick–slip oscillations appear, exhibiting frequency content which is largely dependent on the choice of substrate. The outcomes of this study can potentially be used to improve future tyre–road contacts with respect to wear, traction and noise generation.
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5.
  • Torstensson, Peter, 1981, et al. (författare)
  • Hybrid model for prediction of impact noise generated at railway crossings
  • 2016
  • Ingår i: Proceedings of the 12h International Workshop on Railway Noise (IWRN12), Terrigal, Australia, September 12-16 (2016). ; , s. 539 - 545
  • Konferensbidrag (refereegranskat)abstract
    • A hybrid model for the prediction of impact noise at railway crossings is presented. The hybrid model combines the simulation of vertical wheel‒rail contact force in the time domain and the prediction of sound pressure level using a linear frequency-domain model. The time-domain model uses moving Green’s functions for the vehicle and track models (accounting for wheel flexibility and a discretely supported rail with space-variant beam properties) and a non-Hertzian wheel‒rail contact model. The time-domain and frequency-domain models are coupled based on the concept of an equivalent roughness spectrum. The model is demonstrated by investigating the influence of axle load, vehicle speed and wheel profile on generated impact noise levels. A negligible influence on impact noise is observed for axle loads in the interval 15 – 25 tonnes. On the other hand, increasing vehicle speed from 80 km/h to 150 km/h, or comparing a nominal S1002 wheel profile with a severely hollow worn profile, result in substantially higher levels of impact noise; for the given wheel and track conditions the differences are in the order of 10 dB(A).
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6.
  • Gomez-Gallegos, A. A., 1983-, et al. (författare)
  • A comparative study assessing the wear behaviour of different ceramic die materials during superplastic forming
  • 2017
  • Ingår i: Materialwissenschaft und Werkstofftechnik. - : Wiley-VCH Verlagsgesellschaft. - 0933-5137 .- 1521-4052. ; 48:10, s. 983-992
  • Tidskriftsartikel (refereegranskat)abstract
    • Superplastic forming is an advanced manufacturing process where metallic sheets are heated to their superplastic region to be then blow formed within a die set. The process allows for the forming of complex parts but it is typically restricted to low volume production and high value pieces. Despite their brittle nature, ceramic dies are a developing technology for superplastic forming as they offer lower production costs and shorter lead times than conventional metallic dies, thus reducing process costs. This work presents a method to assess ceramic die wear by means of a novel test rig developed a at the Advance Forming Research Centre of the University of Strathclyde, Scotland, UK where the superplastic forming die-part interaction can be replicated at laboratory scale. Controllable normal load tests at standard superplastic forming conditions on three different reinforced ceramic materials are carried out with a view to understanding their wear mechanisms and to ultimately identify methods to improve their wear resistance.
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7.
  • Silva-Magalhães, Ana, et al. (författare)
  • In-situ temperature measurement in friction stir welding of thick section aluminium alloys
  • 2019
  • Ingår i: Journal of Manufacturing processes. - : Elsevier. - 1526-6125 .- 2212-4616. ; 39, s. 12-17
  • Tidskriftsartikel (refereegranskat)abstract
    • Friction stir welding (FSW) is a reliable joining technology with a wide industrial uptake. However, several fundamentals of the process such as the temperature inside the stirred zone of the weld and its influence on mechanical properties, are not yet fully understood. This paper shows a method for accurate temperature measurements in multiple locations around the tool, to identify the location of the peak temperature, the temperature variations between the advancing and the retreating side of the tool and its relation to the tool geometry. Both standardised thermocouples in the FSW tool and the novel “tool-workpiece thermocouple” method were used to record temperatures.Bead-on-plate welds in 20 mm thickness AA6082-T6 were produced while the temperatures were measured in three locations on the FSW tool: at the shoulder outer diameter, at the transition from shoulder to probe and at the probe tip. It was found that the hottest point in the stirred zone was 607 °C and was located at the transition between the shoulder and probe, on the retreating-trailing side of the tool. The lowest temperature was found at the probe tip on the retreating-leading side of the tool.The results offer a better understanding of the temperature distribution around a FSW tool. The method presented can be applied to verification of thermal simulation models, tool design optimization, quality assurance and temperature feedback control.
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8.
  • Malakizadi, Amir, 1983, et al. (författare)
  • Effects of workpiece microstructure, mechanical properties and machining conditions on tool wear when milling compacted graphite iron
  • 2018
  • Ingår i: Wear. - : Elsevier. - 0043-1648 .- 1873-2577. ; 410-411, s. 190-201
  • Tidskriftsartikel (refereegranskat)abstract
    • The aim of the present study was to investigate the tool performance when machining compacted graphite iron (CGI) alloys. A comparison was made between solid solution strengthened CGI including various amounts of silicon (Si-CGI) and the pearlitic-ferritic CGI as a reference material. The emphasis was on examining the influence of microstructure and mechanical properties of the material on tool wear in face milling process. Machining experiments were performed on the engine-like test pieces comprised of solid solution strengthened CGI with three different silicon contents and the reference CGI alloy. The results showed up-to 50% lower flank wear when machining Si-CGI alloys, although with comparable hardness and tensile properties. In-depth analysis of the worn tool surfaces showed that the abrasion and adhesion were the dominant wear mechanisms for all investigated alloys. However, the better tool performance when machining Si-CGI alloys was mainly due to a lower amount of abrasive carbo-nitride particles and the suppression of pearlite formation in the investigated solid solution strengthened alloys.
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9.
  • Kahlin, Magnus (författare)
  • Fatigue Performance of Additive Manufactured Ti6Al4V in Aerospace Applications
  • 2017
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Additive Manufacturing (AM) for metals includes is a group of production methodst hat use a layer-by-layer approach to directly manufacture final parts. In recent years, the production rate and material quality of additive manufactured materials have improved rapidly which has gained increased interest from the industry to use AM not only for prototyping, but for serial production. AM offers a greater design freedom, compared to conventional production methods, which allows for parts with new innovative design. This is very attractive to the aerospace industry, in which parts could be designed to have reduced weight and improved performance contributing to reduced fuel consumption, increased payload and extended flight range. There are, however, challenges yet to solve before the potential of AM could be fully utilized in aerospace applications. One of the major challenges is how to deal with the poor fatigue behaviour of AM material with rough as-built surface.The aim of this thesis is to increase the knowledge of how AM can be used for high performance industrial parts by investigating the fatigue behaviour of the titanium alloy Ti6Al4V produced with different AM processes. Foremost, the intention is to improve the understanding of how rough as-built AM surfaces in combination with AM built geometrical notches affects the fatigue properties.This was done by performing constant amplitude fatigue testing to compare different combinations of AM material produced by Electron Beam Melting(EBM) and Laser Sintering (LS) with machined or rough as-built surfaces with or without geometrical notches and Hot Isostatic Pressing (HIP) treatment. Furthermore, the material response can be different between constant amplitude and variable amplitude fatigue loading due to effects of overloads and local plastic deformations. The results from constant amplitude testing were used to predict the fatigue life for variable amplitude loading by cumulative damage approach and these predictions were then verified by experimental variable amplitude testing.The constant amplitude fatigue strength of material with rough as-built surfaces was found to be 65-75 % lower, compared to conventional wrought bar, in which HIP treatments had neglectable influence on the fatigue strength. Furthermore, the fatigue life predictions with cumulative damage calculations showed good agreement with the experimental results which indicates that a cumulative damage approach can be used, at least for a tensile dominated load sequences, to predict the fatigue behaviour of additive manufactured Ti6Al4V.
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10.
  • Lin, Yen-Ku, et al. (författare)
  • A versatile low-resistance ohmic contact process with ohmic recess and low-temperature annealing for GaN HEMTs
  • 2018
  • Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 1361-6641 .- 0268-1242. ; 33:9
  • Tidskriftsartikel (refereegranskat)abstract
    • Deeply recessed ohmic contacts for GaN-based high electron mobility transistors (HEMTs) are demonstrated. It is shown that low-resistance ohmic contacts can be achieved with recessing beyond the AlGaN Schottky barrier where the ohmic contacts are formed on the sidewall of the recess. This makes the process versatile and relatively insensitive to the exact recess depth. The ohmic contact is based on a gold-free metallization scheme consisting of a Ta/Al/Ta metal stack requiring a low-temperature annealing. Important parameters for this type of ohmic contact process include the metal coverage, slope of the etched sidewall, bottom Ta-layer thickness, as well as annealing temperature and duration. The optimized contact resistance is as low as 0.24 Omega mm after annealing at 575 degrees C. Moreover, this sidewall contact approach was successfully implemented on different epitaxial heterostructures with different AlGaN barrier thickness as well as with and without AlN exclusion layer. All the samples exhibited excellent contact resistances in a wide range of recess depths. The Ta-based, sidewall ohmic contact process is a promising method for forming an ohmic contact on a wide range of GaN HEMT epitaxial designs.
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11.
  • Rodiouchkina, Maria, 1987-, et al. (författare)
  • Material Characterization and Influence of Sliding Speed and Pressure on Friction and Wear Behavior of Self-Lubricating Bearing Materials for Hydropower Applications
  • 2018
  • Ingår i: Lubricants. - Basel : MDPI. - 2075-4442. ; 6:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Nowadays, hydropower plants are forced to have more frequent power control and the self-lubricated bearings used in the applications are one of the most critical components affected by the continuously changing operating conditions. In this study, microstructure and composition of two commercially available bearing materials (Orkot TXM Marine and Thordon ThorPlas) used in hydropower turbines were studied. In addition, the influence of sliding speed and applied pressure on the friction and wear behavior of the materials was investigated systematically for dry sliding conditions. The bearing materials were characterized using X-ray microtomography, Nuclear Magnetic Resonance (NMR) spectroscopy and Inductively Coupled Plasma–Sector Field Mass Spectrometry (ICP-SFMS) techniques. Friction and wear tests were carried out with a polymer pin sliding against a stainless steel (SS2333) plate with a linear reciprocating motion. Test conditions were: room temperature, 9–28 MPa pressure and 10–40 mm/s sliding speed ranges. Surface analysis of the polymer pins and the wear tracks were performed by optical profilometry, Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) techniques. Test results show that, for both materials, the coefficient of friction (COF) is decreasing at higher pressures. Surface analysis reveals higher concentrations of solid lubricants in the transfer layers formed at higher pressures, explaining the decrease in COF. Furthermore, the specific wear rate coefficients are increasing at higher sliding speeds, especially at lower pressures. Results of this study demonstrate that, under dry sliding conditions, changes in sliding speed and pressure have a significant influence on the tribological behavior of these bearing materials.
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12.
  • Puneet, C., et al. (författare)
  • CrAlSiN nanocomposite thin films for high-speed machining applications
  • 2018
  • Ingår i: Materials and Manufacturing Processes. - : Informa UK Limited. - 1042-6914 .- 1532-2475. ; 33:4, s. 371-377
  • Tidskriftsartikel (refereegranskat)abstract
    • CrAlSiN nanocomposite thin films with varying film chemistry were developed on tungsten carbide (WC)specimens using cylindrical cathodic arc physical vapor deposition (c-CAPVD) technique. The physical, mechanical, and tribological properties of all the films were comprehensively investigated for arriving at the film chemistry leading to the best properties with respect to mechanical applications. The best tribo-mechanical properties were obtained in films with Cr/(AlþSi) ratio of 1.2. This coating with best properties was translated on to WC drill bits for machining tests. The Al and Si content has shown major influence on the adhesion strength and phase constitution of the films, with a considerable change in residual stress too. The superior properties achieved could be attributed to the formation of an ear-perfect nanocomposite structure, with the crystalline CrAlN phase surrounded by an amorphous Si3N4 phase. The tool life of the coated CrAlSiN tools was investigated during dry machining of EN 24material. In comparison to the tool life of an uncoated tool and a TiAlSiN-coated tool, the best CrAlSiN coatings synthesized in this study performed exceedingly well. The present study clearly demonstrates the advantages of CrAlSiN over other existing similar coatings for high-speed machining.
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13.
  • Andersson, Robin, 1986, et al. (författare)
  • Integrated analysis of dynamic vehicle-track interaction and plasticity induced damage in the presence of squat defects
  • 2015
  • Ingår i: Proceedings of the 10th International International Conference on Contact Mechanics and Wear of Rail/Wheel Systems, Colorado Springs, USA, August-September 2015.
  • Konferensbidrag (refereegranskat)abstract
    • Despite significant efforts, the mechanisms behind the formation of squats – a form of rolling contact fatigue damage – are not fully understood. This study employs numerical simulations to investigate the propensity of squat initiation in the vicinity of small, isolated rail surface irregularities. Time domain dynamic vehicle–track interaction analysis is used to obtain wheel–rail contact stress distributions, which are mapped onto a continuum finite element model that accounts for plastic deformation of the rail material. The evaluated stress and strain fields are quantified using two RCF impact measures: accumulated effective strain and the Jiang-Sehitoglu multiaxial low cycle fatigue parameter. It is shown that the RCF impact increases with increasing size of the surface irregularity and that clustering of irregularities might strongly promote RCF. The friction coefficient is identified as a very influential parameter. Further, the effect of variations in friction along the rail is evaluated. It is shown that a short rail section of low friction results in fairly high RCF impact.
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14.
  • Andersson, Robin, 1986, et al. (författare)
  • Integrated analysis of dynamic vehicle–track interaction and plasticity induced damage in the presence of squat defects
  • 2016
  • Ingår i: Wear. - : Elsevier BV. - 0043-1648. ; 366-367:SI, s. 139-145
  • Tidskriftsartikel (refereegranskat)abstract
    • Despite significant efforts, the mechanisms behind the formation of squats – a form of rolling contact fatigue (RCF) damage – are not fully understood. This study employs numerical simulations to investigate the propensity of squat initiation in the vicinity of small, isolated rail surface irregularities. Time-domain dynamic vehicle–track interaction analysis is used to obtain wheel–rail contact stress distributions, which are mapped onto a continuum finite element model that accounts for plastic deformation of the rail material. The evaluated stress and strain fields are quantified using two RCF impact measures: accumulated effective strain and the Jiang–Sehitoglu multiaxial low cycle fatigue parameter. It is shown that the RCF impact increases with increasing size of the surface irregularity and that clustering of irregularities might strongly promote RCF. The friction coefficient is identified as a very influential parameter and also the effect of variations in friction along the rail is evaluated.
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15.
  • Gåård, Anders, 1977-, et al. (författare)
  • Nano-scale friction of multi-phase powder metallurgy tool steels
  • 2015
  • Ingår i: Advanced Materials Research. - : Trans Tech Publications. - 1022-6680 .- 1662-8985. ; 1119, s. 70-74
  • Tidskriftsartikel (refereegranskat)abstract
    • Friction is a fundamental phenomenon in tribology involving complex mechanisms between thecontacting surfaces. Measurements of friction are often made using devices with substantially largercontact area than dimensions corresponding to microstructural features of the materials. Hence, for multi-phase materials,influence of particular microstructural constituents is not resolved. In the present work, a tribometerwith a contact area in the nano-scale range was used to map friction for different types of tool steelswith different chemical- and phase composition. Owing to the small tip radius, frictionalcharacteristics of primary carbides and the steel matrix were measured and compared. Dependingon chemical composition, a difference was observed where the coefficient of friction wasapproximately twice higher for the steel possessing highest coefficient of friction, including bothcarbides and the steel matrix.
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16.
  • Haralanova, Valentina, et al. (författare)
  • Failures in gearboxes due to material problems
  • 2016
  • Ingår i: Materials, Methods & Technologies. - 1314-7269. ; 10, s. 112-136
  • Tidskriftsartikel (refereegranskat)abstract
    • Mechanical failures in general can appear because of weak design, wrong handling, and problems during the manufacturing process, material problems etc. This paper is dealing with failures in lifting machinery gearboxes which appear because of material stresses and tribological problems. The study conducted is based on theoretical analysis and analysis of inspection results for failures that have appeared in cranes and other lifting machinery in southern part of Sweden. Investigation shows that besides the surface damages like abrasive and adhesive failures also cracks in the material in different parts appear. Since these types of gearboxes are made in short series, gearbox housings and sometimes also gears are made of welded steel. Hence welding process makes the weld joints brittle; cracks do start and developed until the part fails. Another problem that happens due to welding is wrapping which leads to changes in the geometrical tolerances and that does affect the parallelism of the shafts and the functionality of the gearbox.
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17.
  • Ghasemi, Rohollah (författare)
  • The influence of microstructure on mechanical and tribological properties of lamellar and compacted irons in engine applications
  • 2016
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Lamellar graphite iron (LGI) is commonly used in diesel engine applications such as piston rings–cylinder liner where an excellent combination of physical and tribological properties is essential to avoid scuffing and bore polishing issues. The excellent tribological behaviour of LGI alloys is related to the graphite lamellas, which act as solid lubricant agents by feeding onto the tribosurfaces under sliding conditions. However, increasingly tighter emissions and fuel economy legislations and the higher demands on enhanced power and durability have encouraged both engine designers and manufacturers to introduce pearlitic compacted graphite irons (CGI) as an alternative material replacing LGI, although the poor machinability of pearlitic CGI alloys compared to the LGI remains a challenge.The focus of this study is placed on investigating how the microstructure of LGI and CGI alloys affects their mechanical and tribological properties. This was initially undertaken by investigating representative, worn lamellar cast iron piston rings taken from a two-stroke large-bore heavy-duty diesel engine. As known that it is tribologically essential to keep the graphite open under sliding conditions, in particular under starved lubrication regimes or unlubricated conditions to avoid scuffing issues; however, this study revealed the closure of a majority of graphite lamellas; profoundly for those lamellas that were parallel to sliding direction; due to the severe matrix deformation caused by abrasion. Both microindentation and microscratch testing, which were used to crudely simulate the abrasion under starved lubricated condition in combustion chamber, suggested a novel mechanism of activating the graphite lamellas to serve as lubricating agents in which the matrix deformation adjacent to the graphite initially resulted in fracturing and then extrusion of the graphite lamellas.Additionally, in order to investigate the relation between matrix constituents, mechanical properties and machinability of cast iron materials, solution-strengthened CGI alloys were produced with different levels of silicon and section thicknesses. The results showed significant improvements in mechanical properties and machinability while deteriorating the ductility. Moreover, multiple regression analysis, based on chemical composition and microstructural characteristics was used to model the local mechanical properties of high Si ferritic CGI alloys, followed by implementing the derived models into a casting process simulation which enables the local mechanical properties of castings with complex geometries. Very good agreement was observed between the measured and predicted microstructure and mechanical properties.
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18.
  • Homayoun, Mohammad-Reza, et al. (författare)
  • Effect of Hygrothermal Ageing on Tribological Behaviour of PTFE-Based Composites
  • 2018
  • Ingår i: Lubricants. - : MDPI. - 2075-4442. ; 6:4
  • Tidskriftsartikel (refereegranskat)abstract
    • The present study investigates the influence of hygrothermal ageing on the tribological behaviour of polytetrafluoroethylene (PTFE) polymer composites. Three PTFE composites along with unfilled PTFE were tested in sliding contact against Inconel 625 (a Ni-based alloy) plates in both dry and water-lubricated conditions, utilising a unidirectional pin-on-disc tribometer. The tribo-tests were performed at a constant sliding speed of 0.13 m/s with a normal load of 84N providing an apparent contact pressure of 5 MPa. Hygrothermal conditioning was carried out at two different temperatures, and the water absorption evolution and kinetic parameters were estimated. Various characterisation methods were used to identify the wear mechanisms and influence of hygrothermal ageing on the degradation of the filler/matrix. The different tribological behaviour for different PTFE composites was observed within the ageing timeframe. The wear resistance of the fibre-filled samples was reduced compared to the non-aged ones over the ageing timeframe. However, the friction and wear resistance of the bronze-filled PTFE were enhanced by hygrothermal ageing.
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19.
  • Esmaeili, Ali, 1983, et al. (författare)
  • Thermomechanical cracking of railway wheel treads: a combined experimental and numerical approach
  • 2015
  • Ingår i: Proceedings of the 10th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems (CM2015). ; , s. 8-
  • Konferensbidrag (refereegranskat)abstract
    • In the present study, thermal cracking of railway wheel treads is studied by full-scale brake rig tests and finite element simulations. The focus is on thermomechanical rolling contact fatigue (RCF) life predictions. The wheel tread material is subjected to simultaneous mechanical and thermal loads due to rolling contact and stop braking, respectively. Full-scale tests featuring three series of repeated stop braking cases have been performed at the Railway Technical Research Institute (RTRI) in Japan in a brake rig featuring a tread braked wheel that is in rolling contact with a railwheel. The brake rig test conditions have been simulated numerically using the finite element method. To this end, the effect of “hot bands” on the tread is accounted for as indicated by the experimental findings. Thermomechanical stresses induced by braking as well as Hertzian contact loading on the tread including tractive loads based on a partial slip assumption are considered. The mechanical response of the wheel material ER7 is obtained from a viscoplastic Chaboche material model calibrated against data from cyclic experiments with hold-time from room temperatures up to 650 °C. Finally, a strategy for prediction of fatigue life with respect to ratcheting failure is discussed.
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20.
  • Mallipeddi, Dinesh, 1987, et al. (författare)
  • Effect of Running-In (Load and Speed) on Surface Characteristics of Honed Gears
  • 2019
  • Ingår i: Tribology Transactions. - : Informa UK Limited. - 1040-2004 .- 1547-397X. ; 62:3, s. 412-418
  • Tidskriftsartikel (refereegranskat)abstract
    • The initial running-in cycles alter the surface integrity characteristics and influence gear performance. This article shows how the surface characteristics of honed spur gears evolved due to the combined effect of running-in load (0.9 or 1.7 GPa) and speed (0.5 or 8.3 m/s) in Forschungsstelle fur Zahnräder und Getriebebau tests. Running-in affected the surface layers to a depth of 5 µm. High running-in load promoted plastic deformation of asperities, created microstructural changes associated with surface cracks, and relaxed residual stresses. It also enhanced the amount of phosphorous from extreme pressure (EP) additives at the surface. The surface contact fatigue failure—that is, micropitting—was promoted by running-in speed rather than load.
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21.
  • Mallipeddi, Dinesh, 1987, et al. (författare)
  • The effect of manufacturing method and running-in load on the surface integrity of efficiency tested ground, honed and superfinished gears
  • 2019
  • Ingår i: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 131, s. 277-287
  • Tidskriftsartikel (refereegranskat)abstract
    • This study compares gear surface characteristics generated by grinding, honing and superfinishing of case-hardened steel, including the evolution during efficiency testing with two different prior running-in loads (0.9 GPa and 1.7 GPa). The most influential factor was surface roughness. Micro-pitting was associated with surface asperities and hence only seen in ground and honed gears, while being absent for super-finished gears. The micro-pitting was enhanced by running-in load, but only for rough surfaces. Deformation-induced localized microstructure impact was associated with cracks. Residual stresses reached similar levels after efficiency testing. Phosphorous content in the gear surface was connected to surface roughness and running-in load.
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22.
  • Melk, Latifa, et al. (författare)
  • Mechanical and thermal performances of UHMWPE blended vitamin E reinforced carbon nanoparticle composites
  • 2018
  • Ingår i: Composites Part B. - : Elsevier. - 1359-8368 .- 1879-1069. ; 146, s. 20-27
  • Tidskriftsartikel (refereegranskat)abstract
    • Ultrahigh molecular weight polyethylene (UHMWPE) is a known to be the material of choice for bearing components in joint arthroplasty. However, oxidation wear of UHMWPE components is considered to be a major drawback limiting the lifespan of implants. Vitamin E was considered as a promising antioxidant to prevent long-term oxidation and reduce the wear degradation of UHMWPE material. Nevertheless, there are limited results on the improvements of vitamin E on the mechanical and thermal properties of UHMWPE. In this study, we investigated the incorporation of 0.5–3 wt.% carbon nanoparticles: Multiwalled Carbon Nanotubes (MWCNTs), Graphene (GO) and Nanodiamonds (ND) on the mechanical and thermal properties of UHMWPE blended vitamin E (UHMWPE-E). Surface analysis of the composite powders showed well-dispersed carbon nanoparticles within the UHMWPE-E matrix. Thermogravimetric (TGA) and Differential Scanning Calorimetry (DSC) were used to study the thermal behavior of the nanocomposites. It was found that the addition of GO, MWCNTs and ND improved the thermal stability of the nanocomposites compared to neat UHMWPE-E. However, the addition of carbon nanoparticles had no significant effect on the crystallization parameters of the composites. In addition, the incorporation of MWCNT and ND improved significantly the fracture toughness of the composites. The addition of 0.7 wt.% ND and 1 wt.% MWCNT increased the fracture toughness from 5.93 MPa m1/2 for neat UHMWPE-E to 7.38 and 9.19 MPa m1/2 respectively. The enhanced fracture toughness and thermal stability of the nanocomposites could be due to the successful powder processing technique where an optimized mixing and ball milling parameters were used.
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23.
  • Casanueva, Carlos, 1981-, et al. (författare)
  • Comparison of wear prediction models for different contact conditions
  • 2016
  • Ingår i: Proceedings of the 24th Symposium of the International Association for Vehicle System Dynamics (IAVSD 2015), Graz, Austria, 17-21 August 2015. - : CRC Press. - 9781138028852 - 9781498777025 ; , s. 871-878
  • Konferensbidrag (refereegranskat)abstract
    •  Simulation of wheel and rail wear allows to predict long term profile evolution and thus, study the consequences of wheel damage in the dynamic behaviour of the vehicle, or study future maintenance requirements. Several models have been developed which try to solve the wear issue by relating the energy dissipated in the wheel-rail contact to the worn out material, from which two can be highlighted (Tg/A and Archard) which have significant differences on contact level. Even though, the prediction of long term wheel profile evolution has been validated with these two models, which means that for regular applications they seem to have an equivalent behaviour. In this work similarities and differences between the long term wear prediction methodologies are analysed, discussing their actual limitations. Then, these differences are exploited in specific operational cases to compare their wear prediction performance.
  •  
24.
  • Hoier, Philipp, 1988, et al. (författare)
  • Flank wear characteristics of WC-Co tools when turning Alloy 718 with high-pressure coolant supply
  • 2017
  • Ingår i: Journal of Manufacturing Processes. - Dearbord, Mich. : Society of Manufacturing Engineers, North American Manufacturing Research Institution. - 1526-6125 .- 2212-4616. ; 30:Supplement C, s. 116-123
  • Tidskriftsartikel (refereegranskat)abstract
    • In the present study, the tool wear mechanisms of uncoated cemented tungsten carbide (WC-Co) tools during machining Alloy 718 with high-pressure coolant supply are investigated. Worn flank faces are analyzed by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). With increasing spiral cutting length, larger areas on the tool surface are subjected to erosion of Co-binder by the coolant jet impact. Moreover, the amount and morphology of workpiece-precipitates adhered on worn flank surfaces are influenced significantly by the extent of flank wear land (due to increasing spiral cutting length). The reasons for the obtained results are addressed with respect to the underlying mechanisms. Possible implications for the tool wear behavior are discussed.
  •  
25.
  • Tofique, Muhammad Waqas, 1986-, et al. (författare)
  • Development of the distributed dislocation dipole technique for the analysis of closure of complex fractures involving kinks and branches
  • 2018
  • Ingår i: European journal of mechanics. A, Solids. - : Elsevier. - 0997-7538 .- 1873-7285. ; 69, s. 168-178
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper presents the development of the distributed dislocation dipole technique (DDDT) for the analysis of straight, kinked and branched cracks where parts of the cracks may close during loading. The method has been developed for plane problems. Crack cases in which closure occurs are analyzed by reformulating the Buecicner's principle, taking into account the contact stresses at the contacting portions of the crack surfaces. Stress intensity factors corresponding to opening and the in-plane sliding mode of deformation at the crack tips are computed. Several test cases involving straight, kinked and/or branched cracks where parts of the cracks undergoes crack surface closure when subjected to the outer loading are analyzed. The results obtained from the DDDT are compared to those obtained from a Finite Element Method (FEM) analysis of the same crack cases. This comparison shows that the computation of stress intensity factors for the cases involving crack surface closure are less accurate than those for fully open crack cases. However, for the cases under consideration, the stress intensity factors were still computed with a maximum difference of approximately 2 per cent compared to the FEM calculations if Jacobi polynomial expansions of at least the twelfth order were used to represent the crack surface opening and sliding displacements. In most cases under consideration, sixth order Jacobi polynomial expansions were sufficient to obtain results within that margin of deviation.
  •  
26.
  • Vedantha Krishna, Amogh, 1990-, et al. (författare)
  • Potential approach towards effective topography characterization of 316L stainless steel components produced by selective laser melting process
  • 2018
  • Ingår i: European Society for Precision Engineering and Nanotechnology, Conference Proceedings - 18th International Conference and Exhibition, EUSPEN 2018. - Bedford : euspen. - 9780995775121 - 0995775125 ; , s. 259-260
  • Konferensbidrag (refereegranskat)abstract
    • In this paper, an attempt is made to explain the surface texture of Selective Laser Melting (SLM) parts more satisfyingly than the existing methods. Investigations were carried out on the 316L stainless steel SLM samples. To account for most of the surface conditions, a truncheon artefact was employed for the analysis. A Stylus Profilometer was employed as a metrology tool for obtaining the 3D surface measurements. A methodology is proposed to extract and characterize the topographic features of Additive Manufactured (AM) surfaces. Here, the overall roughness of the surface is segregated into the roughness of the powder particles and the waviness due to thermal and the "staircase" effects. Analyzing these features individually results in an increased understanding of the AM process and an opportunity to optimize machine settings.
  •  
27.
  • Zhang, Yafan, et al. (författare)
  • Thermomechanical Analysis and Characterization of a Press-Pack Structure for SiC Power Module Packaging Applications
  • 2017
  • Ingår i: IEEE Transactions on Components, Packaging, and Manufacturing Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 2156-3950 .- 2156-3985. ; 7:7, s. 1089-1100
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper presents an experimental methodology for the characterization of thermomechanical displacement and friction properties in a free-floating press-pack structure, and evaluation of the tensile stress on the semiconductor die through simulation of different mechanical and thermal loading conditions. The press-pack structure consists of a single silver-metallized (1 μm) silicon carbide die (400 μm) in contact with rhodium-coated (0.4 μm) molybdenum square plates. The thermomechanical displacements in the press-pack structure have been obtained using the digital image correlation technique, and the mean random error has been $± $0.1 μm, which is approximately 10 ppm of the measured length (10.5 mm). The developed experimental method has led to an analytical estimation of friction coefficients on the interfaces' silicon carbide-molybdenum and molybdenum-copper. The results demonstrate that the thin silver layer behaves as a solid film lubricant. A 2-D finite-element model representing the experimental setup has been implemented. The difference in displacement between measurement and simulation is less than 8%. Furthermore, the coinfluence of the design parameters on the thermomechanical performance of the stacked structure has been analyzed through simulations. Finally, design guidelines to reduce the tensile stress on the silicon carbide die have been proposed regarding free-floating press-pack power electronics packaging.
  •  
28.
  • Nyberg, Erik, 1986-, et al. (författare)
  • Additives to Improve Tribological Properties of Ionic Liquid as Base Fluids
  • 2017
  • Konferensbidrag (refereegranskat)abstract
    • Room temperature ionic liquids (RTILs) have several properties which make them interesting candidates as base fluids for extreme conditions. However, a lack of compatibility with tribo-improving additives combined with an often overly aggressive nature is limiting their use as base fluids. To overcome these drawbacks, hydrocarbon-imitating RTIL base fluids have recently been developed. These lubricants aim for a more balanced interaction with metal surfaces while enabling compatibility with common additives, so that the reactivity with the lubricated surface can be tuned in a manner similar to hydrocarbon base oil–additive systems. In this work, the effects of several common additives in the novel RTIL were examined by laboratory tribotesting. Surface analysis was performed in order to study the lubrication mechanisms.
  •  
29.
  • Joshi, Abhishek, 1985 (författare)
  • Electrical Characterisations of Bearings
  • 2019
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Mechanical bearings are an integral part of industry, and are used in various places in order to reduce friction between two interacting surfaces and are used to transmit power and loads. Mechanical bearings are one of the most extensively used components within the wind industry, but on the other hand they are also one of the most dominantly failing failed components. In order to increase the feasibility of wind energy, and to make the wind power more sustainable, a reduction in operation and maintenance cost of wind energy is important. The failures in bearings in the wind energy sector and other industries increased after the introduction of switched power electronic switches (Insulated Gate Bipolar Transistors, or IGBT) within the power converters. The reasons of early failures have been linked to the presence of a common mode voltage at the neutral of the converter and its coupling on the shaft, where the bearings are located. The system is also vulnerable to different types of bearing currents, which are discussed in this report. A small voltage in range of 10's of volts could lead to large electric-field stress of 30 to 40 V/µm in a bearing depending on nominal film thickness at the operating point. The build-up of large electric field stresses in the bearing leads to ohmic electrical conduction through the bearing. Presently, the mitigation techniques mainly discharge the voltage across the bearing by providing a low resistance path for the flowing current using different methods, such as carbon brushes,  or shaft rings, but damages due to bearing current activity and early failures still exist. Another way to mitigate bearing currents is to use filters in the electrical connections, to obstruct or to reduce the amplitude of the bearing currents, but they fail to completely eliminate them. The use of insulating coating on surfaces of the bearing and ceramic rolling elements helps to provide a high resistive path for the current in case of DC voltage, but act capacitively and let the current pass through the bearing when high frequency circulating type bearing currents flow in the system. Nevertheless, to device a successful mitigation technique, it is important to fully understand the electrical breakdown and discharge activity within the bearing’s insulation (i.e., the lubricating film) along with electrical properties of the bearing during running conditions. In our research, we have focused on understanding the electrical properties of the mechanical bearing at different operating conditions and elaborating it through an electrical circuit model. The components of this electrical circuit model are found out experimentally through different laboratory tests. The mechanical bearing is sometimes found to behave as an insulator of electricity and is hence characterizecharacterised by an impedance during the ‘Insulating state’ of the bearing in the model. The impedance in this insulating state is further categorized as a parallel combination of a resistor and a capacitor (parallel RC branch), which corresponds to the ‘real’ and ‘imaginary’ part of the measured bearing impedance. Furthermore, when the bearing enters in into a partial breakdown state, the voltage across the bearing is ‘discharged’, resulting in flow of current through the bearing until the voltage across the bearing again recovers. The Electrical electrical characterization characterisation of bearing lubricants has been performed in order to find out the relevant electrical properties, such as relative permittivity, electrical conductivity and electric breakdown strength at rather short gaps. The electrical behaviorbehaviour of the mechanical bearing at different operating conditions such as rotational speed, mechanical load along with magnitude, frequency and shape of applied voltage has been found out experimentally in order to understand and elucidate the electrical properties of a mechanical bearing in operation.
  •  
30.
  • Joshi, Abhishek, 1985 (författare)
  • Electrical characterization of mechanical bearings
  • 2015
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • Mechanical bearings are an integral part of industry, and are used in various places to reduce friction between two interacting surfaces and are used to transmit power and loads. Mechanical bearings are one of the most extensively used components within the wind industry, but on the other hand they are also one the most dominantly failed components. To increase the feasibility of wind energy, and to make the wind power more sustainable, a reduction in operation and maintenance cost of wind energy is important. The failures in bearings in wind energy sector and other industries increased after introduction of switched power electronic switches (Insulated Gate Bipolar Transistors or IGBT) within the power converters. The reasons of early failures have been linked to presence of common mode voltage at the neutral of the converter and its coupling on the shaft, where the bearings are located. The system is also vulnerable to different types of bearing currents, which are discussed in this report.Presently, the mitigation techniques mainly discharge the voltage across the bearing by providing a low resistance path for the flowing current using different methods, such as carbon brushes, shaft rings, but damages due to bearing current activity and early failures still exist. Another way to mitigate bearing currents is to use filters in the electrical connections, to obstruct or to reduce the amplitude of the bearing currents, but they fail to completely eliminate them. The use of insulating coating on surfaces of the bearing and ceramic rolling elements helps to provide high resistive path for current in case of DC voltage, but act capacitively and let the current pass through the bearing when high frequency circulating type bearing currents flow in the system. Nevertheless, to device a successful mitigation technique, it is important to fully understand the electrical breakdown and discharge activity within the bearing’s insulation (i.e., the lubricating film) along with electrical properties of bearing during running conditions.In our research, we have focused on understanding the electrical properties of the mechanical bearing at different operating conditions and elaborating it through an electrical circuit model. The components of this electrical circuit model are found out experimentally through different laboratory tests. The mechanical bearing is sometimes found to behave as an insulator of electricity and is hence characterized by an impedance during the ‘Insulating state’ of the bearing in the model. The impedance in this insulating state is further categorized as a parallel combination of resistor and a capacitor (parallel RC branch), which corresponds to the ‘real’ and ‘imaginary’ part of the measured bearing impedance. Furthermore, when the bearing enters in a partial breakdown state, the voltage across the bearing is ‘discharged’ resulting in flow of current through the bearing until the voltage across the bearing again recovers. Electrical characterization of bearing lubricants has been performed to find out the relevant electrical properties such as relative permittivity, electrical conductivity and electric breakdown strength at rather short gaps. The electrical behavior of the mechanical bearing at different operating conditions such as rotational speed, mechanical load along with magnitude, frequency and shape of applied voltage has been found out experimentally in order to understand and elucidate the electrical properties of a mechanical bearing in operation.
  •  
31.
  • Hedberg, Yolanda S., et al. (författare)
  • Can Cobalt(II) and Chromium(III) ions released from joint prostheses influence the friction coefficient?
  • 2015
  • Ingår i: ACS Biomaterial Science and Engineering. - : American Chemical Society (ACS). - 2373-9878. ; 1:8, s. 617-620
  • Tidskriftsartikel (refereegranskat)abstract
    • Cobalt chromium molybdenum alloys (CoCrMo) are commonly used as articulating components in joint prostheses. In this tribocorrosive environment, wear debris and metal ionic species are released and interact with proteins, possibly resulting in protein aggregation. This study aimed to investigate whether this could have an effect on the friction coefficient in a typical material couple, namely CoCrMo-on-polyethylene. It was confirmed that both Co(II) and Cr(III) ions, and their combination, at concentrations relevant for the metal release situation, resulted in protein aggregation and its concomitant precipitation, which increased the friction coefficient. Future studies should identify the clinical importance of these findings.
  •  
32.
  • Albinsson, Anton, 1989, et al. (författare)
  • Validation of vehicle-based tyre testing methods
  • 2019
  • Ingår i: Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering. - : SAGE Publications. - 2041-2991 .- 0954-4070. ; 233:1, s. 18-27
  • Tidskriftsartikel (refereegranskat)abstract
    • The development process for passenger cars is both time- and resource-consuming. Full vehicle testing is an extensive part of the development process that consumes large amount of resources, especially within the field of vehicle dynamics and active safety. By replacing physical testing with complete vehicle simulations, both the development time and cost can potentially be reduced. This requires accurate simulation models that represent the real vehicle. One major chal- lenge with full vehicle simulation models is the representation of tyres in terms of force and moment generation. The force and moment generation of the tyres is affected by both operating conditions and road surface. Vehicle-based tyre testing offers a fast and efficient way to rescale force and moment tyre models to different road surfaces, in this study the Pacejka 2002 model. The resulting tyre model is sensitive to both the operating conditions during testing and the road surface used. This study investigates the influence of the slip angle sweep rate and road surface on the lateral tyre force characteristics of the fitted tyre model. Tyre models fitted to different manoeuvres are compared and the influence on the full vehicle behaviour is investigated in IPG Carmaker. The results show that by using the wrong road surface, the resulting tyre model can end up outside the tolerances specified by the ISO standard for vehicle simulation model verifi- cation in steady-state cornering. The use of Pacejka 2002 models parameterized in a steady-state manoeuvre to simulate the vehicle behaviour in sine-with-dwell manoeuvres is also discussed.
  •  
33.
  •  
34.
  • Larsson, Joakim, 1989-, et al. (författare)
  • The effect of bearing length on the surface quality of drawn wire
  • 2019
  • Konferensbidrag (refereegranskat)abstract
    • In wire drawing, the geometry of drawing dies influences the performance of the wire process. This study investigates the effect of bearing lengths on the surface quality of the drawn wire. Wire drawing tests were done using an industrial wiredrawing machine utilizing drawing dies with different bearing lengths. The influence of bearing length on surface quality is discussed.
  •  
35.
  • Minovski, Blago, 1986, et al. (författare)
  • A numerical investigation of thermal engine encapsulation concept for a passenger vehicle and its effect on fuel consumption
  • 2019
  • Ingår i: Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering. - : SAGE Publications. - 2041-2991 .- 0954-4070. ; 233:3, s. 557-571
  • Tidskriftsartikel (refereegranskat)abstract
    • Increasingly tough regulations for emission levels and a growing demand for an environmentally clean motor industry impose high requirements in modern automotive development. During recent decades, carmakers have been utilizing various strategies to minimize energy losses in the powertrain to meet legislative and market demands. A great part of research efforts has been focused on improving engine performance during cold starts characterized by increased friction losses. Thermal engine encapsulation is an effective design choice to reduce engine friction in applications with frequent cold starts. In the present work, a coupled 1-D–3-D system-level approach is used to investigate the effects of a novel engine-mounted encapsulation concept featuring air shutters on fuel consumption in a Volvo S80 passenger vehicle. Simulations are performed for sequences of the Worldwide harmonized light vehicles test cycle (WLTC) drive cycle, which include different time intervals of engine inactivity when the car is parked in air of an quiescent ambient temperature. The results show that engine encapsulation with high area coverage (97%) can retain engine oil temperature above 19°C for up to 16 h after engine shutdown at an ambient temperature of 5°C, leading to 2.5% fuel saving during engine warm-up when cold starts occur between 2 and 8 h after key-off. Encapsulations with a lower area coverage (90%) have proven to be less effective, with fuel saving of 1.25% as the temperatures of the oil and engine structures decrease more quickly after key-off compared to the fully enclosed encapsulation.
  •  
36.
  • White, B. T., et al. (författare)
  • The contribution of iron oxides to the wet-rail phenomenon
  • 2016
  • Ingår i: Civil-Comp Proceedings. - Stirlingshire, Scotland : Civil-Comp Press. - 1759-3433. ; 110
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper reviews the current literature regarding iron oxide formation in the wheel-rail contact in order to assess the possible role of iron oxides in the "Wet-Rail" phenomenon, which causes low adhesion between the wheel and the rail. The paper discusses the structure and formation of oxides from a chemical perspective before analysing the direct tribological effects and outlining the techniques that have been used to study the oxide layers. This paper also suggests how knowledge of the subject could be expanded and how further understanding of the "Wet-Rail" phenomenon could lead to better mitigation methods, resulting in both economic and safety benefits.
  •  
37.
  • Carlberger, Andreas, 1992, et al. (författare)
  • An iterative methodology for the prediction of dynamic vehicle–track interaction and long-term periodic rail wear
  • 2018
  • Ingår i: Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit. - : SAGE Publications. - 0954-4097 .- 2041-3017. ; 232:6, s. 1718-1730
  • Tidskriftsartikel (refereegranskat)abstract
    • In this study, a versatile numerical method for the prediction of long-term growth of rail roughness is presented and its functionality is demonstrated for the development of rail corrugation on small radius curves. The procedure includes two sub-modules: (1) a time-domain model for the simulation of dynamic vehicle–track interaction in a wide range of frequencies by using a commercial software for multibody dynamics and (2) a post-calculation of sliding wear based on the Archard’s model in combination with a non-Hertzian and transient wheel–rail contact model. The structural flexibility of the wheelset is accounted for by using the finite element method. The rail wear generated by a large number of passing trains is assessed by recurrently updating the rail surface based on the wear depth calculated in each post- processing step. The current work sets out from a previous study in which a model for the prediction of long-term growth of rail roughness on small radius curves was developed in a general-purpose programming language. By transfer- ring the model into a commercial software, the aim is to develop an engineering tool that is more applicable for different operational conditions, such as various vehicle and track designs and track alignments. The proposed method is verified by comparing the simulation results against those obtained with the pre-existing software. Conditions similar to a 120 m radius curve on the Stockholm metro exposed to corrugation growth on the low rail are considered. The corrugation is found to be generated by the leading wheelsets. The prevailing wavelength-fixing mechanisms are identified and discussed.
  •  
38.
  • Yu, Rixin, et al. (författare)
  • Statistics conditioned to isoscalar surfaces in highly turbulent premixed reacting systems
  • 2019
  • Ingår i: Computers and Fluids. - : Elsevier BV. - 0045-7930. ; 187, s. 69-82
  • Tidskriftsartikel (refereegranskat)abstract
    • The paper aims at clarifying some issues associated with evaluation of surface-averaged quantities in Direct Numerical Simulation (DNS) of a turbulent reacting flow. For a quantity ϕ(t, x) averaged over an isosurface c(t,x)=c^ of a reaction progress variable c, there exist at least two different definitions of surface averages; an area-weighted surface average 〈ϕ〉 s | c^,t and an unweighted surface average 〈ϕ〉 v | c^,t . These two fine-grained averages can also be extended to coarse-grained surface averages 〈ϕ〉 S | c^,ϵ,t and 〈ϕ〉 V | c^,ϵ,t over an interval of c^≤c(t,x)≤c^+ϵ. In a highly turbulent medium, the difference 〈ϕ〉 s −〈ϕ〉 v between the area-weighted and unweighted surface averages can be significant for most quantities ϕ of basic interest. The sign of this difference depends on the sign of the correlation between ϕ and |∇c|, can be opposite for different ϕ or even for different isosurfaces of the same scalar field ϕ. For a quantity ϕ that can become singular in the zero-gradient points |∇c|(t,x)=0, its unweighted or area-weighted surface averages can still be bounded. The difference between area-weighted and unweighted surface averages of 1/|∇c| or |∇c| is relevant to explaining the well-known, but still challenging controversy between available data on the influence of turbulence on the local flame thickness.
  •  
39.
  • Radovan, Drazumeric, et al. (författare)
  • Truing of diamond wheels - Geometry, kinematics and removal mechanisms
  • 2018
  • Ingår i: CIRP Annals - Manufacturing Technology. - : Elsevier BV. - 1726-0604 .- 0007-8506. ; 67:1, s. 345-348
  • Tidskriftsartikel (refereegranskat)abstract
    • An investigation is made into traverse truing of diamond grinding wheels using various truing grit types, grit sizes and truing parameters. Geometry and kinematics of the truing contact are modeled. Specific energies are found to depend on truing-grit size but not on truing parameters, indicating little to no size effect. Removal mechanisms are analyzed via SEM examination of diamond- and truing-wheel swarf. A fundamental relationship is established relating the truing compliance number to the truing efficiency, which encompasses truing parameters and truing- and diamond-grit sizes. Recommendations are made for optimum conditions to minimize force-constrained truing time.
  •  
40.
  • Söderberg, Rikard, 1963, et al. (författare)
  • An information and simulation framework for increased quality in welded components
  • 2018
  • Ingår i: CIRP Annals - Manufacturing Technology. - : Elsevier BV. - 1726-0604 .- 0007-8506. ; 67:1, s. 165-168
  • Tidskriftsartikel (refereegranskat)abstract
    • The recent trend toward using simulation models with real-time data as digital twins is rapidly increasing in industry. In this paper, a digital framework supporting real-time geometrical quality control of welded components, is presented. The concept is based on a structured process model for all operations included in typical welding, strategies for selective assembly, automatic adjustment of fixtures and optimization of weld sequence. The concept utilizes recently developed algorithms for fast welding simulation and in-line scanning to be used in the optimization loop of an automated welding station—a digital twin for a welding cell.
  •  
41.
  • Kumar, Mayank, 1991-, et al. (författare)
  • Influence of cutting fluid on reliability of threaded fastener joints
  • 2019
  • Ingår i: SAE technical paper series. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191. ; :December
  • Tidskriftsartikel (refereegranskat)abstract
    • This study reports on the effect of cutting fluids on friction behavior of the threaded fasteners. Underhead and thread friction are measured during tightening process of the hex-head threaded fasteners coated with different zinc-based coatings: electroplated zinc, zinc flake, and electroplated zinc nickel, commonly used in the automotive industry. The tests and data analysis are conducted considering ISO 16047 as a baseline. Test conditions are set close to the actual production conditions found in the motor vehicle industry. Water-based and ester-based cutting fluids are selected to unveil their impact on the reliability of the threaded fastener joints. It is shown that a change in the underhead interface conditions from dry to lubricated drastically reduces friction for the electroplated zinc and zinc nickel coatings.
  •  
42.
  • Almeida, Diogo, 1991-, et al. (författare)
  • Dexterous manipulation with compliant grasps and external contacts
  • 2017
  • Ingår i: IEEE International Conference on Intelligent Robots and Systems. - : IEEE. - 2153-0858 .- 2153-0866. ; 2017-September, s. 1913-1920
  • Konferensbidrag (refereegranskat)abstract
    • We propose a method that allows for dexterous manipulation of an object by exploiting contact with an external surface. The technique requires a compliant grasp, enabling the motion of the object in the robot hand while allowing for significant contact forces to be present on the external surface. We show that under this type of grasp it is possible to estimate and control the pose of the object with respect to the surface, leveraging the trade-off between force control and manipulative dexterity. The method is independent of the object geometry, relying only on the assumptions of type of grasp and the existence of a contact with a known surface. Furthermore, by adapting the estimated grasp compliance, the method can handle unmodelled effects. The approach is demonstrated and evaluated with experiments on object pose regulation and pivoting against a rigid surface, where a mechanical spring provides the required compliance.
  •  
43.
  • Gutkin, Renaud, et al. (författare)
  • A physically based model for kink-band growth and longitudinal crushing of composites under 3D stress states accounting for friction
  • 2016
  • Ingår i: Composites Science And Technology. - : Elsevier Ltd. - 0266-3538 .- 1879-1050. ; 135, s. 39-45
  • Tidskriftsartikel (refereegranskat)abstract
    • A material model to predict kink-band formation and growth under a 3D stress state is proposed. 3D kinking theory is used in combination with a physically based constitutive law of the material in the kink-band, accounting for friction on the microcracks of the damaged material. In contrast to existing models, the same constitutive formulation is used for fibre kinking and for the longitudinal shear and transverse responses, thereby simplifying the material identification process. The full collapse response as well as a crush stress can be predicted. The model is compared with an analytical model, a micromechanical finite element analysis and crushing tests. In all cases the present model predicts well the different stages of kink-band formation and crushing.
  •  
44.
  • Bolzon, Micheal, 1990, et al. (författare)
  • Effects of Wheel Configuration on the Flow Field and the Drag Coefficient of a Passenger Vehicle
  • 2019
  • Ingår i: International Journal of Automotive Technology. - : Springer Science and Business Media LLC. - 1976-3832 .- 1229-9138. ; 20:4, s. 763-777
  • Tidskriftsartikel (refereegranskat)abstract
    • The effects of wheel rotation, rim coverage area, fan spokes, spoke sharpness, and tread pattern on the flow field and drag coefficient of a passenger vehicle were investigated. Force measurements and wake surveys were taken on a 1/5th scale passenger vehicle at a Reynolds number of 2.0 × 106. The wake surveys were conducted at three planes. Vorticity, total pressure coefficient, and local drag coefficient plots are presented. Wheel rotation reduced the drag coefficient of all of the wheel configurations tested, which generally agrees with literature. Wheel rotation reduced the front wheel’s jetting vortex’s drag while increasing the drag from the center of the front wheel to the upper rim track. Reducing the rim coverage area increased the drag coefficient. This increase was attributed to an increased jetting vortex drag and a change in flow separation around the front wheel. The fan spoke rim performed the worst, regardless of rotation. Rounding the spoke edges reduced the drag coefficient of a rotating wheel. The tread pattern slightly reduced the shoulder vortex vorticity and slightly increased the separation around the front wheel.
  •  
45.
  • Fröhling, Robert, et al. (författare)
  • Preface: Special issue on heavy haul
  • 2019
  • Ingår i: Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit. - : SAGE Publications. - 0954-4097 .- 2041-3017. ; 233:6, s. 595-595
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
  •  
46.
  • Chen, Zhe (författare)
  • Surface Integrity and Fatigue Performance of Nickel-based Superalloys
  • 2017
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Due to global warming, the demand for more efficient gas turbines has increased. A way to achieve this, is by increasing the operating temperature of the gas turbine. Therefore, nickel-based superalloys have been developed to withstand these extreme temperatures and loads, especially in the hot sections. Today, the way of operating land-based gas turbines is changing. Instead of running for long periods of time, the operation is becoming more flexible, with ever-increasing cyclic loads and number of start and stop cycles. To handle the increased stress and cycles, component resistance to fatigue failures need to be improved.Surface integrity is critical to fatigue performance, since fatigue cracks normally initiate at a surface. Machining changes the surface integrity which can result in worse fatigue resistance. The work presented in this Ph.D. thesis was conducted in collaboration with Siemens Industrial Turbomachinery AB in Finspång, Sweden. Surface integrity changes which are induced during machining and their effects on fatigue performance have been studied on the alloy Inconel 718. Inconel 718 is a widely-used nickel-based superalloy for high temperature applications in modern gas turbines.Broaching, milling, and wire electrical discharge machining, related to component manufacturing in turbo machinery industries, were included in this study. Machining induced surface defects provide preferential sites for fatigue crack initiation which influence the fatigue performance of the alloy. If compressive residual stresses are induced during machining, they benefit the fatigue life by retarding fatigue crack initiation away from surface regions. Shot peening was performed on machined Inconel 718, by which high compressive residual stresses are deliberately induced. It results in enhanced fatigue performance.The high temperatures in gas turbines generally deteriorate the surface integrity. Recrystallization often occurs in the highly deformed surface layer. Microstructural degradation, in the form of α-Cr precipitates, have also been frequently observed in the deformed surface and sub-surface microstructure. Oxidation at elevated temperatures degrades the surface integrity and thereby also the fatigue performance. Fatigue cracks are preferably initiated at oxidized surface carbides, if thermal exposure has been made prior to the test. It is even worse when high temperatures relax the beneficial surface compression induced by shot-peening and thereby lowering the fatigue resistance.Machinability of a newly developed nickel-based superalloy, AD 730TM, and the surface integrity induced during turning have also been studied in this thesis project. AD 730TM is a candidate for turbine disc applications with an operating temperature above 650 °C. At such high temperatures, Inconel 718 is no longer stable and its mechanical properties start to degrade.To summarize, the results from this thesis work show the importance of understanding surface integrity effects for fatigue applications, especially in harsh environments. Moreover, the knowledge gained through this work could be used for surface enhancement of turbine components which are subjected to a high risk of fatigue failure. These will contribute to more efficient and flexible power generation by gas turbines.
  •  
47.
  • Mu, Liwen, et al. (författare)
  • Lignin from Hardwood and Softwood Biomass as a Lubricating Additive to Ethylene Glycol
  • 2018
  • Ingår i: Molecules. - : MDPI. - 1431-5157 .- 1420-3049. ; 23:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Ethylene glycol (EG)-based lubricant was prepared with dissolved organosolv lignin from birch wood (BL) and softwood (SL) biomass. The effects of different lignin types on the rheological, thermal, and tribological properties of the lignin/EG lubricants were comprehensively investigated by various characterization techniques. Dissolving organosolv lignin in EG results in outstanding lubricating properties. Specifically, the wear volume of the disc by EG-44BL is only 8.9% of that lubricated by pure EG. The enhanced anti-wear property of the EG/lignin system could be attributed to the formation of a robust lubrication film and the strong adhesion of the lubricant on the contacting metal surface due to the presence of a dense hydrogen bonding (H-bonding) network. The lubricating performance of EG-BL outperforms EG-SL, which could be attributed to the denser H-bonding sites in BL and its broader molecular weight distribution. The disc wear loss of EG-44BL is only 45.7% of that lubricated by EG-44SL. Overall, H-bonding is the major contributor to the different tribological properties of BL and SL in EG-based lubricants.
  •  
48.
  • Nikas, Dimitrios, 1984 (författare)
  • Influence of combined thermal and mechanical loadings on pearlitic steel microstructure in railway wheels and rails
  • 2018
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • One of the most important aspects in railway operation is the interaction between rail and wheel. The contact patch between these two components is around the size of a small coin, and since high loads act on this small area, stresses will give rise to wear and damage in both components. Frictional forces on the surface of wheels and rails caused by recurring train acceleration, braking, curving and occasional slippage can cause cyclic plastic deformation and heating, which in turn causes an aligned, anisotropic microstructure with altered mechanical behaviour. Control of material property degradation is an important topic for guiding maintenance, as well as ensuring safety of railways, since it will allow for a more accurate prediction of material wear and lifetime. The thesis focuses on the mechanical properties of railway wheel and rail steels after exposure to elevated temperatures and plastic deformation. Specifically examined are the carbon wheel steels, UIC ER7T and ER8T (~0.55 wt. %C) and rail steel R260 (~0.72 wt. %C). During their service life, the surface layers of rails and wheels are subjected to very high rolling contact loads. These lead to accumulation of large shear strains close to the running surface. Moreover the high thermal loads that wheels experience when block brakes are used can cause severe degradation of the material microstructure, more specifically spheroidisation of the pearlite, which combined with plastic deformation (that makes the material more prone to spheroidisation) can lead to severe deterioration of the material’s mechanical properties. Both un-deformed and pre-strained wheel materials were heat treated at various temperatures from 250°C to 600°C for various durations, and the change in room temperature hardness was analysed. Additionally, Electron Backscatter Diffraction Analysis (EBSD) was used to evaluate if orientation gradients in the pearlitic colonies affect the spheroidisation of the pearlitic microstructure, that is observed at higher temperatures. Uniaxial (tension-compression) and biaxial (including torsion) low cycle fatigue tests were performed to study the behaviour of R7T and R8T material at different temperatures. The influence of hold times as well as the ratchetting behaviour with mean stress effects were also studied. Virgin rail material was twisted using a biaxial machine to various shear strain levels to create a microstructure representative for the surface layer observed in field samples. The microstructure was characterised using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and hardness measurements. The results showed that wheel material hardening due to strain ageing takes place at around 300°C while microstructural degradation caused softening at higher temperatures. Spheroidisation of the pearlite started to become visible at 450°C for the un-deformed material and at around 400°C for the pre-strained. The spheroidised areas appear to have lost their initial orientation gradients after spheroidisation and obtain a more uniform orientation. Cyclic tests at elevated temperature revealed cyclic hardening at around 300°C, as an effect of dynamic strain ageing. At higher temperatures, cyclic softening followed due to a combination of increasing thermal activation and spheroidisation. Biaxial testing showed a more severe effect of strain hardening and shorter fatigue life. For the rail material, the dislocation density was found to increase with increasing shear strain. The flow stresses calculated using microstructural parameters such as dislocation density and interlamellar spacing of the pearlite seem to agree well with those evaluated from hardness measurements.
  •  
49.
  • Shahzamanian Sichani, Matin, 1986- (författare)
  • On Efficient Modelling of Wheel-Rail Contact in Vehicle Dynamics Simulation
  • 2016
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The wheel-rail contact is at the core of all research related to vehicletrackinteraction. This tiny interface governs the dynamic performanceof rail vehicles through the forces it transmits and, like any high stressconcentration zone, it is subjected to serious damage phenomena. Thus,a clear understanding of the rolling contact between wheel and rail is keyto realistic vehicle dynamics simulation and damage analysis.In a multi-body dynamics simulation, the demanding contact problemshould be evaluated at about every millisecond for several wheel-rail pairs.Hence, a rigorous treatment of the contact is highly time-consuming.Simplifying assumptions are therefore made to accelerate the simulationprocess. This gives rise to a trade-o between the accuracy and computationaleciency of the contact model in use.Conventionally, Hertz+FASTSIM is used for calculation of the contactforces thanks to its low computational cost. However, the elliptic patchand pressure distribution obtained by Hertz' theory is often not realisticin wheel-rail contact. Moreover, the use of parabolic traction bound inFASTSIM causes considerable error in the tangential stress estimation.This combination leads to inaccurate damage predictions.Fast non-elliptic contact models are proposed by others to tacklethis issue while avoiding the tedious numerical procedures. The studiesconducted in the present work show that the accuracy of these models iscase-dependent.To improve the accuracy of non-elliptic patch and pressure estimation,a new method is proposed. The method is implemented in an algorithmnamed ANALYN. Comparisons show improvements in patch and, particularly,pressure estimations using ANALYN.In addition, an alternative to the widely-used FASTSIM is developed, named FaStrip. Unlike FASTSIM, it employs an elliptic traction boundand is able to estimate the non-linear characteristic of tangential stressdistribution. Comparisons show more accurate estimation of tangentialstress and slip velocity distribution as well as creep forces with FaStrip.Ultimately, an ecient non-elliptic wheel-rail contact model consistingof ANALYN and FaStrip is proposed. The reasonable computationalcost of the model enables it to be used on-line in dynamics simulationand its accuracy can improve the damage predictions.
  •  
50.
  • Agic, Adnan, 1967-, et al. (författare)
  • Dynamic effects on cutting forces with highly positive versus highly negative cutting edge geometries
  • 2019
  • Ingår i: International Journal on Interactive Design and Manufacturing. - : Springer Science and Business Media LLC. - 1955-2513 .- 1955-2505. ; 13:2, s. 557-565
  • Tidskriftsartikel (refereegranskat)abstract
    • Understanding the influence of the cutting edge geometry on the development of cutting forces during the milling process is of high importance in order to predict the mechanical loads on the cutting edge as well as the dynamic behavior on the milling tool. The work conducted in this study involves the force development over the entire engagement of a flute in milling, from peak force during the entry phase until the exit phase. The results show a significant difference in the behavior of the cutting process for a highly positive versus a highly negative cutting edge geometry. The negative edge geometry gives rise to larger force magnitudes and very similar developments of the tangential and radial cutting force. The positive cutting edge geometry produces considerably different developments of the tangential and radial cutting force. In case of positive cutting edge geometry, the radial cutting force increases while the uncut chip thickness decreases directly after the entry phase; reaching the peak value after a certain delay. The radial force fluctuation is significantly higher for the positive cutting edge geometry. The understanding of such behavior is important for modelling of the milling process, the design of the cutting edge and the interactive design of digital applications for the selection of the cutting parameters.
  •  
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