| 1. |
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| 2. |
- Nybacka, Mikael, et al.
(författare)
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Project: CASTT - Centre for Automotive Systems Technologies and Testing
- 2007
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Annan publikation (populärvet., debatt m.m.)abstract
- Through the Centre for Automotive Systems Technologies and Testing, Luleå University of Technology aims to first of all support automotive winter testing in Northern Sweden. This means to support the local automotive test entrepreneurs and through them their customers: the car manufacturers and their suppliers. To succeed in this task, the center relies on the university's areas of leading research and most importantly on the cooperation between those areas.
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| 3. |
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| 4. |
- Karlsson, Patrik, 1973-, et al.
(författare)
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Galling resistance and wear mechanisms for cold-work tool steels in lubricated sliding against high strength stainless steel sheets
- 2012
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Ingår i: Wear. - Amsterdam : Elsevier. - 0043-1648 .- 1873-2577. ; 286-287, s. 92-97
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Tidskriftsartikel (refereegranskat)abstract
- Tool damage in sheet metal forming of stainless steel is of high concern for the forming industry. In the present work, ingot cast AISI D2 and advanced powder metallurgy tool steel (PM) cold-work tool steels were evaluated and ranked regarding wear mechanisms and galling resistance. Wear tests were performed using a slider-on-flat-surface (SOFS) tribometer in sliding against austenitic–ferritic (duplex) stainless steel sheets at different contact pressures in lubricated conditions. The best galling resistance was observed for the nitrogen alloyed PM tool steels. Abrasive scratching of the tool surfaces and transfer of sheet material due to adhesive wear were the main metal forming tool surface damage mechanisms. By increasing the hardness of one PM sheet metal forming tool grade, the galling resistance was enhanced.
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| 5. |
- Vilardell, A. M., et al.
(författare)
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B2-structured Fe3Al alloy manufactured by laser powder bed fusion : Processing, microstructure and mechanical performance
- 2023
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Ingår i: Intermetallics (Barking). - : Elsevier. - 0966-9795 .- 1879-0216. ; 156
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Tidskriftsartikel (refereegranskat)abstract
- Prealloyed Fe3Al was successfully manufactured by laser powder bed fusion. The best set of process parameters led to parts with a relative density of 99.5 %, a surface roughness, Sa, of 31.5 ± 5.6 μm and a hardness of 319 ± 14 HV0.1. Its microstructure as well as its mechanical properties at room and high temperatures were analyzed. The results of the chemical composition showed minor variations in aluminum content oscillating between 21 and 28 at.% along the melt pool. Additionally, elongated grains were observed to grow parallel to the building direction, as well as the development of a weak 001 texture along the building direction. The mechanical properties were influenced by the temperature. Compression tests showed a loss in strength with the increase in temperature, from a yield strength of 621 ± 40 MPa at room temperature to 89 ± 20 MPa at 650 °C. Reciprocating sliding wear tests showed that fragmentation of the intermetallic at room temperature occurs, whereas plastic deformation dominated at higher temperatures. For all temperatures, tribochemical wear was also present due to the oxidation of wear debris.
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| 6. |
- Li, Xiaojian, 1991, et al.
(författare)
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A new method for performance map prediction of automotive turbocharger compressors with both vaneless and vaned diffusers
- 2021
-
Ingår i: Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering. - : SAGE Publications. - 2041-2991 .- 0954-4070. ; 235:6, s. 1734-1747
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Tidskriftsartikel (refereegranskat)abstract
- A new approach to predict the performance maps of automotive turbocharger compressors is presented. Firstly, a polynomial equation is applied to fit the experimental data of flow coefficient ratios for the centrifugal compressors with both vaneless and vaned diffusers. Based on this equation, the choke and surge flow coefficients under different machine Mach numbers can be quickly predicted. Secondly, a physically based piecewise elliptic equation is used to define compressors’ characteristic curves in terms of efficiency ratio. By introducing the flow coefficient ratio into the efficiency correlation, the empirical coefficients in the piecewise elliptic equation are uniquely calibrated by the experimental data, forming a unified algebraic equation to match the efficiency maps of the compressors with both vaneless and vaned diffusers. Then, a new universal equation, which connects the work coefficient, the impeller outlet flow coefficient and the non-dimensional equivalent impeller outlet width, is derived by using classical aerothermodynamic method. The off-design pressure ratio is predicted based on the equivalent impeller outlet width with less knowledge of the compressor geometry and no empirical coefficients. Finally, three state-of-the-art turbocharger compressors (one with vaneless diffuser, two with vaned diffusers) are chosen to validate the proposed method, and the results show a satisfactory accuracy for the performance map prediction. This method can be used for the preliminary design of turbocharger compressors with both vaneless and vaned diffusers, or to assess the design feasibility and challenges of the given design specifications.
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| 7. |
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| 8. |
- Bayani, Mohsen, 1981
(författare)
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Squeak and Rattle Prediction for Robust Product Development in the automotive industry
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Squeak and rattle are nonstationary, irregular, and impulsive sounds that are audible inside the car cabin. For decades, customer complaints about squeak and rattle have been, and still are, among the top quality issues in the automotive industry. These annoying sounds are perceived as quality defect indications and burden warranty costs to the car manufacturers. Today, the quality improvements regarding the persistent type of sounds in the car, as well as the increasing popularity of electric engines, as green and quiet propulsion solutions, stress the necessity for attenuating annoying sounds like squeak and rattle more than in the past. The economical and robust solutions to this problem are to be sought in the pre-design-freeze phases of the product development and by employing design-concept-related practices. To achieve this goal, prediction and evaluation tools and methods are required to deal with the squeak and rattle quality issues upfront in the product development process. The available tools and methods for the prediction of squeak and rattle sounds in the pre-design-freeze phases of a car development process are not yet sufficiently mature. The complexity of the squeak and rattle events, the existing knowledge gap about the mechanisms behind the squeak and rattle sounds, the lack of accurate simulation and post-processing methods, as well as the computational cost of complex simulations are some of the significant hurdles in this immaturity. This research addresses this problem by identifying a framework for the prediction of squeak and rattle sounds based on a cause-and-effect diagram. The main domains and the elements and the sub-contributors to the problem in each domain within this framework are determined through literature studies, field explorations and descriptive studies conducted on the subject. Further, improvement suggestions for the squeak and rattle evaluation and prediction methods are proposed through prescriptive studies. The applications of some of the proposed methods in the automotive industry are demonstrated and examined in industrial problems. The outcome of this study enhances the understanding of some of the parameters engaged in the squeak and rattle generation. Simulation methods are proposed to actively involve the contributing factors studied in this work for squeak and rattle risk evaluation. To enhance the efficiency and accuracy of the risk evaluation process, methods were investigated and proposed for the system excitation efficiency, modelling accuracy and efficiency and quantification of the response in the time and frequency domains. The demonstrated simulation methods besides the improved understanding of the mechanisms behind the phenomenon can facilitate a more accurate and robust prediction of squeak and rattle risk during the pre-design-freeze stages of the car development.
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| 9. |
- Pieringer, Astrid, 1979, et al.
(författare)
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Investigation of railway curve squeal using a combination of frequency- and time-domain models
- 2016
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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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| 10. |
- Karlsson, Patrik, 1973-, et al.
(författare)
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Galling resistance evaluation of tool steels by two different laboratory test methods for sheet metal forming
- 2012
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Ingår i: Lubrication Science. - : John Wiley & Sons. - 0954-0075 .- 1557-6833. ; 24:6, s. 263-272
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Tidskriftsartikel (refereegranskat)abstract
- Adhesive accumulation of work material on the tool surface is today a major problem in many sheet metal-forming applications. Different laboratory test methods are used to investigate galling with respect to different tool materials, lubricants and process conditions. In the present study, the galling resistance of a modern nitrogen-alloyed powder metallurgy tool steel and an conventional ingot cast D2 type tool steel was evaluated under lubricated sliding against ferritic stainless steel sheets using a commercial pin-on-disc (POD) and an in-house made slider-on-flat-surface (SOFS) tribotester. The investigated tool steels ranked similarly in terms of galling resistanc in both test methods. However, sliding distances to galling were longer for the SOFS equipment due to continuous sliding on new lubricated sheet surface. Best performance was demonstrated by the powder metallurgy tool steel treated to 65 HRC. Differences in friction behaviour and galling initiation were analysed on the basis of the two different working conditions, i.e. open (SOFS) and closed (POD) tribosystems. Copyright © 2012 John Wiley & Sons, Ltd.
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| 11. |
- Caprioli, Sara, 1978
(författare)
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Thermal impact on rolling contact fatigue of railway wheels
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Rolling contact fatigue (RCF) is a very common and costly damage mechanism for rails and wheels. This thesis investigates the influence of combined thermal and mechanical loading on RCF of railway wheels on the basis of numerical predictions. The established computational framework includes heat flux analyses, (two- and three-dimensional) elastoplastic finite element simulations and subsequent RCF life analyses. The computational framework is employed to quantify the influence of various operational parameters and modelling presumptions such as applied heat and tangential stress characteristics, load application schemes, mesh densities etc. Examples of results include quantifications of how partial slip conditions result in higher plastic strain magnitudes in a thin layer at the wheel tread surface, and differences in material responses between accelerating and braking wheels.The numerical model was extended to incorporate surface initiated cracks. With the extended model it is shown that 1 mm deep cracks have a substantial influence on the state of stress and strain in the bulk material between surface cracks. Further, comparisons between radial (thermal) and inclined (RCF) surface cracks show that the deformation of significantly inclined cracks (30 degrees) is more severe than that of radial cracks. Further, acceleration is found to give larger crack face displacements. However braking tends to induce tensile residual stresses that open the crack mouth, thus allowing fluid penetration that can promote crack growth. Also thermal loading is found to cause a significant crack mouth opening that is decreased by subsequent rolling contact.In a final study numerical RCF predictions are compared to full-scale experimental studies carried out at the Railway Technical Research Institute in Japan. Thermal loading tuned towards measurements by thermocameras and thermocouples are introduced in a truncated loading scheme corresponding to the test configuration. Estimated crack initiation life is found to be in good agreement with test results. The investigation also shows the significant influence of the employed material model. In addition to thermomechanical fatigue analyses, the case of purely thermal fracture has been investigated. This study quantified how the risk of fracture and resulting crack sizes depend on braking conditions and initial surface cracks. The results of this thesis are believed to be of importance in defining and enforcing sustainable operational conditions and maintenance actions. Further, this thesis provides tools to establish root causes and pertinent mitigating actions when thermomechanical wheel cracking nevertheless occurs.
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| 12. |
- Winroth, Julia, 1981, et al.
(författare)
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Contact stiffness considerations when simulating tyre/road noise
- 2017
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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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| 13. |
- Imran, Tajammal
(författare)
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Effect of water contamination on the diffused content of hydrogen under stress in AISI-52100 bearing steel
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Abstract Hydrogen embrittlement is a degradation process of mechanical/tribological properties (toughness, wear etc.) of mating steel surfaces. This is caused by the presence and interaction of hydrogen with applied stresses. Therefore, it is important to quantify the hydrogen content which could be dissolved under applied stresses in steel. Water contamination of lubricants is often considered as a reason of hydrogen embrittlement of rolling bearings. Thus the effect of water and %RH (relative humidity) on the hydrogenation/dehydrogenation of steel was studied experimentally under different operating conditions. Two types of steels were used, that are silver steel and AISI-52100 ball bearing steel. The testing conditions used in various tests, were percent relative humidity (%RH), temperature, rotating bending stresses, uni-axial tensile stress, rolling and sliding in combination with rotating bending stresses. As a first task, the hydrogen content was quantified in as-received specimens of bearing steel. The spread of hydrogen content was measured in radial and axial directions of the as-received bearing steel bars. This was done to show the importance of the internal hydrogen embrittlement effects of the initial hydrogen content. Sample melting technique (SMT) was used to quantitatively analyze the total content of hydrogen in all specimens using a hydrogen analyzer. In addition to this, Elastic Recoil Detection Technique (ERDT) was employed to qualitatively analyze the local hydrogen content distribution in soft and hard AISI-52100 bearing steel. Secondly, the influence of applied stresses on the absorption of hydrogen content into respective steel specimens was studied. A rotating bending set up was used through a lathe machine. Water was used as a source of hydrogen charging of the testing samples in all rotating bending tests. The influence of rotating bending stresses on the absorption of hydrogen was studied in silver steel and in bearing steel bar samples. Further, a universal fatigue testing machine was used to study the effect of cyclic released uni-axial tension on the absorption of hydrogen in the bearing steel. Similarly, the influence of Sliding and Rolling on the absorption/desorption of hydrogen content was studied in combination of rotating bending stresses using the same lathe machine. Mild and water quenched silver steel bar specimens were used to study the influence of quenching and applied stresses on the absorption of hydrogen. Finally, the experiments were conducted on SKF-624 deep groove ball bearing (DGBB) under isolated operating environment. Non water absorbing grease was used as lubricant. Tests were run for 10% of L10 life of deep groove ball bearing. Two different amplitudes of pure radial loading were selected for testing under high and low relative humidity of the operating environment. Total content of hydrogen was measured in the inner ring, outer ring and 7-balls of DGBB (deep groove ball bearing) using the hydrogen analyzer. Results are presented for total dissolved (or absorbed) hydrogen content in various components as a function of bearing shaft revolutions and operating conditions. Results obtained revealed a dependence of total content of hydrogen on the number of inner ring shaft revolutions. Hydrogen seems to accumulate in the specimens with the increase of number of stress cycles or shaft revolutions.
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| 14. |
- Skåre, Thomas
(författare)
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Dynamiskt belastade tribologiska system under plastisk formning, del II --- analyserade genom akustisk emission
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The dynamic friction process and contact surface between tool and working material in a plastic forming process is hard to describe in mathematical form and hard to monitor and control in real time. High production speed and highly optimised forming operations result in great demands on the control equipment. Especially if the influence from variations due to the tool, work material and the friction surfaces between working material and tool can not be minimised and are essential for the quality of the product. Friction surfaces can be monitored with acoustic emission (AE) and the AE-signal depends on the lubrication between the friction surfaces. The power of the AE-signal increases with ungreased friction surfaces compared in more effectively lubricated surfaces. Differences in detected acoustic emission between different lubricants can be measured and this information can be used to classify different lubricants and the performance in the investigated forming operation. Acoustic emission from a forming operation contains measurable information from events as galling (welded work material on tool), wear of tool, penetration of lubricant, stick-slip, wrinkling necking of sheet material and cracking in tool-material or working material. The detected acoustic emission is directly proportional to the mechanical power consumption in a friction surface and can therefore be used to estimate the forces on the friction surfaces. A change in the tribological parameters, as material in contact, the efficiency of lubricants, the roughness of the friction surfaces, relative velocity between the friction materials and contact pressure can be monitored with acoustic emission. Mounting and adjusting of tool parts or correction of holding forces in deep drawing operations can be optimised by minimising acoustic emission due to influence of boundary layer friction and wrinkling. Critical friction surfaces can be monitored with consideration to the wear of the friction surfaces. The momentary acoustic emission contains information about the status of wear at the friction surfaces and if the wear is a wear-in or a wear-out process. A further development of the acoustic emission monitoring, primarily regarding methodology, the performance of the measurement equipment and methods of analysing measured data, should lead an increased implementation of the method, measuring and monitoring different forming operations and production lines. This will in the end result in new ways to increased production quality and improved quality check. This work is divided in two volumes, ''Dynamically loaded tribo-systems in plastic forming operations, part I --- actuated by cyclic mechanical stress'' and ''Dynamically loaded tribo-systems in plastic forming operations, part II --- monitored by acoustic emission''. Part I deal with the subjects magnetostrictive actuators, vibration actuated tribosystems and vibration assisted wire drawing. Part II deals with the monitoring of tribosystems using acoustic emission.
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| 15. |
- Lundberg, Oskar, 1980-
(författare)
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On the influence of surface roughness on rolling contact forces
- 2016
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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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| 16. |
- Torstensson, Peter, 1981, et al.
(författare)
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Hybrid model for prediction of impact noise generated at railway crossings
- 2016
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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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| 17. |
- Persson, Erik, et al.
(författare)
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Clamp Force Accuracy in Threaded Fastener Joints Using Different Torque Control Tightening Strategies
- 2021
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Ingår i: SAE technical paper series. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191. ; :2021
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Tidskriftsartikel (refereegranskat)abstract
- The assembly of threaded fasteners may seem straightforward. However, there are many factors to consider to achieve quality tightened joints, including the joint material, threaded fastener, and coatings. Additionally, there are many assembly tool types and torque application strategies to choose from. This investigation studies the tightening speed dynamics when using torque as a control method. The clamp force obtained in the joint changes when tightening at high speed or when the speed varies greatly during tightening. This type of tightening is called highly dynamic. Highly dynamic torque control tightening strategies are studied, such as impact, pulse, and inertia-controlled methods, and compared with the continuous drive strategy, which is a standard dynamic torque tightening method. The clamp force and its scatter caused by the torque accuracy in the assembly tool type are investigated for the abovementioned torque application strategies. The study also focuses on the different results obtained from the International Organization for Standardization’s (ISO) 16047:2005 (Fasteners-Torque/clamp force testing) standard compared to a production-like setup.
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| 18. |
- Karlsson, Patrik, 1973-, et al.
(författare)
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Influence of tool steel hard phase orientation and shape on galling
- 2014
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Ingår i: Advanced Materials Research. - : Trans Tech Publications. - 1022-6680 .- 1662-8985. ; 966-96, s. 249-258
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Tidskriftsartikel (refereegranskat)abstract
- Conventionally manufactured cold work tool steel is often used in sheet metal forming as die material. Due to the forging process, the as-cast network structure of carbides is broken into elongated particles. Depending on the tool cross-section, the orientation and shape of carbides in the active tool surface is different. In the present research, the influence of tool steel hard phase orientation and shape on galling was investigated. D2 type tool steel was cut in three different orientations and tested in lubricated sliding conditions against AISI 304 austenitic stainless steel. Tests were performed using a Slider-On-Flat-Surface and galling was detected by changes in friction and post-test microscopy. The lubricant was Castrol FST8 using 5 g/m2 sheet material. Results showed a strong correlation between sliding distance to galling and tool steel hard phase orientation and shape at low loads, whereas high load contact resulted in early galling in all cases. Material transfer was observed mainly to the tool steel matrix. The worst performance was observed for specimens cut so that the tool steel hard phase, M7C3 carbides in the D2 steel, were oriented along the sliding direction, which resulted in longer open tool matrix areas contacting the sheet material.
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| 19. |
- Gomez-Gallegos, A. A., 1983-, et al.
(författare)
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A comparative study assessing the wear behaviour of different ceramic die materials during superplastic forming
- 2017
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Ingår i: Materialwissenschaft und Werkstofftechnik. - : Wiley-VCH Verlagsgesellschaft. - 0933-5137 .- 1521-4052. ; 48:10, s. 983-992
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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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| 20. |
- Mill, O., et al.
(författare)
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Analysis and development of hydro power research : synthesis within Swedish Hydro Power Centre
- 2010
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The market for hydropower re-investments in Sweden is approx 2.5 billion SEK/yr the coming decade. Large investments will also be carried out in Swedish tailing dams. This will result in challenging projects and need of experts. A crucial factor for a successful management of these challenges is the supply of engineers and researchers with hydro power and dam skills and knowledge. Swedish Hydro Power Centre (Svenskt vattenkraftcentrum, SVC) is a competence centre for university education and research environments within hydro power and mining dams. SVC comprises of two knowledge areas: Hydraulic Engineering and Hydro Turbines and Generators, respectively. SVC builds high-quality and long term sustainable knowledge at selected universities...
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| 21. |
- Munavirov, Bulat, 1986-
(författare)
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Ionic lubricants : Molecular features and surface protection mechanisms
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis ionic liquids (ILs) are investigated as prospective candidates for lubrication. Three custom synthesized phosphonium orthoborate type ILs were extensively studied from the prospective of molecular structuring both in bulk and at the interface and from the prospective of their lubricating performance as neat lubricants and as additives in oils. A wide selection of contact geometries and surface finishes has been utilized to broaden the applicability of the achieved results. Tribological performance of orthoborate ILs when used as additives in oils was additionally benchmarked against two commercial ILs - phosphonium phosphate, phosphonium phosphinate.Studies on the bulk molecular mobility in the orthoborate ILs performed by means of Pulsed Field Gradient Nuclear Magnetic Resonance (PFG NMR) clearly showed that the distinct molecular organisation in these systems depends on the chemical structure of orthoborate anion. These results demonstrated a clear correlation with tests of the tribological performance of neat orthoborate ILs, where friction reduction, wear protection and particularities of surface interactions were shown to be clearly defined by anion chemistry. Moreover, this finding was further proven to be relevant when using ILs as additives in oils. A comparison of tribological performance of orthoborate ILs with phosphinate and phosphate ILs showed that a change in anion structure could basically revert the tribological performance of oil solution: from lower to higher friction and wear when compared to the neat oil lubricity.One of the orthoborate ILs - trihexyltetradecylphosphonium bis(mandelato)borate (PBMB) – was selected for a thorough study when used as a sacrificial oil additive. A joint PFG NMR and Quartz Crystall Microbalance (QCM) study demonstrated the build-up of a PBMB rich film on a electrically charged surface. This provided an experimental prove for the possibility of electrostatically driven physisorption of ILs. Tribological tests performed on the same oil composition demonstrated that PBMB when reaching the surface triggered tribochemical reactions and formation of a surface protective tribofilm. Phosphonium orthoborate ILs demonstrated an outstanding performance (decreasing wear by up to 92% and friction by up to 50%) in lubricated mechanical contacts, both when used as neat lubricants and when used as additives. These results are based on an extensive study employing a wide variation in contact geometries, surface finish and motion type. The details of such performance are investigated through an extensive surface analysis and further linked to the chemical structure of the anion.
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| 22. |
- Karlsson, Patrik, 1973-, et al.
(författare)
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Influence of tool steel microstructure on friction and initial material transfer
- 2014
-
Ingår i: Wear. - : Elsevier. - 0043-1648 .- 1873-2577. ; 319:1-2, s. 12-18
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Tidskriftsartikel (refereegranskat)abstract
- An investigation was conducted to study the influence of tool steel microstructure on initial material transfer and friction. Two different powder metallurgy tool steels and an ingot cast tool material were tested in dry sliding against 1.4301, 1.4162, Domex 355 MC and Domex 700 MC sheet materials. It was found that tool steel hard phase heights influence initial material transfer and friction. The coefficient of friction increased with decreasing tool steel hard phase heights at 50 N normal load and initial material transfer occurred around protruding hard phases. At higher load of 500 N the sheet material adhered to both the tool steel matrix and hard phases. Coefficient of friction decreased with increasing proof strength of the sheet material at 500 N normal load.
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| 23. |
- Karlsson, Patrik, 1973-, et al.
(författare)
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Influence of work material proof stress and tool steel microstructure on galling initiation and critical contact pressure
- 2013
-
Ingår i: Tribology International. - Amsterdam : Elsevier. - 0301-679X .- 1879-2464. ; 60, s. 104-110
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Tidskriftsartikel (refereegranskat)abstract
- EN 1.4301 (austenitic), EN 1.4509 (ferritic), EN 1.4162 (duplex) and EN 1.4310 C1000 (metastable austenitic) stainless steels were tested in lubricated sliding against an ingot cast EN X153WCrMoV12 and powder metallurgy nitrogen alloyed Uddeholm Vancron 40 tool steels to reveal critical to galling contact pressure, Pcr. The calculated Pcr were higher for steels with higher strength. At P>Pcr, due to plastic flow of sheet material, the tool is damaged substantially and wear-induced matrix damage causes rapid galling initiation. At P
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- Cvetkovski, Krste, 1983, et al.
(författare)
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Analysis of wear debris in rolling contact fatigue cracks of pearlitic railway wheels
- 2014
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Ingår i: Wear. - : Elsevier BV. - 0043-1648. ; 314:1-2, s. 51-56
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Tidskriftsartikel (refereegranskat)abstract
- In the current study a severe subsurface crack network in a railway wheel has been studied and compared to typical rolling contact fatigue cracks found in the wheel tread surface. Microstructural characteristics, chemical composition and microhardness within the cracks and around crack faces were examined. While the two damage types are principally different, both showed similar crack characteristics, with short cracks branching along the main crack paths and a discontinuous sheared layer of wear debris and metallic flakes within them. Analyses of the wear debris showed that it does not originate from external contamination or being the result of corrosion primarily. Instead it has most likely been produced by shear deformation and wear mechanisms within crack faces caused by mixed-mode crack growth. Although microstructural appearance at lower magnification seemed to differ from the bulk material, at high magnification a lamellar structure was observed consisting of layers of deformed metallic flakes and particles of the base metal. Auger electron spectroscopy was used to analyze these sheared layers; higher concentration of oxygen was measured in between flakes, indicating the presence of oxides and flakes being of similar chemical composition as the base material. A possible explanation is that these layers are created due to high shear forces and friction between crack faces in the service of the wheel. With continued rolling the material being sheared by the cyclic relative motion of the crack faces disintegrates into smaller wear debris particles with concurrent oxidation.
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