SwePub
Sök i SwePub databas

  Extended search

AND is the default operator and can be omitted

Träfflista för sökning "AMNE:(ENGINEERING AND TECHNOLOGY Mechanical Engineering Tribology) "

Search: AMNE:(ENGINEERING AND TECHNOLOGY Mechanical Engineering Tribology)

  • Result 1-50 of 2361
Sort/group result
   
EnumerationReferenceCoverFind
1.
  •  
2.
  • Nybacka, Mikael, et al. (author)
  • Project: CASTT - Centre for Automotive Systems Technologies and Testing
  • 2007
  • Other publication (pop. science, debate, etc.)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.
  •  
3.
  •  
4.
  • Karlsson, Patrik, 1973-, et al. (author)
  • Galling resistance and wear mechanisms for cold-work tool steels in lubricated sliding against high strength stainless steel sheets
  • 2012
  • In: Wear. - Amsterdam : Elsevier. - 0043-1648 .- 1873-2577. ; 286-287, s. 92-97
  • Journal article (peer-reviewed)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.
  •  
5.
  • Vilardell, A. M., et al. (author)
  • B2-structured Fe3Al alloy manufactured by laser powder bed fusion : Processing, microstructure and mechanical performance
  • 2023
  • In: Intermetallics (Barking). - : Elsevier. - 0966-9795 .- 1879-0216. ; 156
  • Journal article (peer-reviewed)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. 
  •  
6.
  • Li, Xiaojian, 1991, et al. (author)
  • A new method for performance map prediction of automotive turbocharger compressors with both vaneless and vaned diffusers
  • 2021
  • In: Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering. - : SAGE Publications. - 2041-2991 .- 0954-4070. ; 235:6, s. 1734-1747
  • Journal article (peer-reviewed)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.
  •  
7.
  •  
8.
  • Bayani, Mohsen, 1981 (author)
  • Squeak and Rattle Prediction for Robust Product Development in the automotive industry
  • 2021
  • Doctoral thesis (other academic/artistic)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.
  •  
9.
  • Pieringer, Astrid, 1979, et al. (author)
  • Investigation of railway curve squeal using a combination of frequency- and time-domain models
  • 2016
  • In: Proceedings of the 12h International Workshop on Railway Noise (IWRN12), Terrigal, Australia, September 12-16. ; , s. 444 - 451
  • Conference paper (peer-reviewed)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.
  •  
10.
  • Karlsson, Patrik, 1973-, et al. (author)
  • Galling resistance evaluation of tool steels by two different laboratory test methods for sheet metal forming
  • 2012
  • In: Lubrication Science. - : John Wiley & Sons. - 0954-0075 .- 1557-6833. ; 24:6, s. 263-272
  • Journal article (peer-reviewed)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.
  •  
11.
  • Caprioli, Sara, 1978 (author)
  • Thermal impact on rolling contact fatigue of railway wheels
  • 2014
  • Doctoral thesis (other academic/artistic)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.
  •  
12.
  • Winroth, Julia, 1981, et al. (author)
  • Contact stiffness considerations when simulating tyre/road noise
  • 2017
  • In: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 409, s. 274-286
  • Journal article (peer-reviewed)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.
  •  
13.
  • Imran, Tajammal (author)
  • Effect of water contamination on the diffused content of hydrogen under stress in AISI-52100 bearing steel
  • 2005
  • Doctoral thesis (other academic/artistic)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.
  •  
14.
  • Skåre, Thomas (author)
  • Dynamiskt belastade tribologiska system under plastisk formning, del II --- analyserade genom akustisk emission
  • 2001
  • Doctoral thesis (other academic/artistic)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.
  •  
15.
  • Lundberg, Oskar, 1980- (author)
  • On the influence of surface roughness on rolling contact forces
  • 2016
  • Doctoral thesis (other academic/artistic)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.
  •  
16.
  • Torstensson, Peter, 1981, et al. (author)
  • Hybrid model for prediction of impact noise generated at railway crossings
  • 2016
  • In: Proceedings of the 12h International Workshop on Railway Noise (IWRN12), Terrigal, Australia, September 12-16 (2016). ; , s. 539 - 545
  • Conference paper (peer-reviewed)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).
  •  
17.
  • Persson, Erik, et al. (author)
  • Clamp Force Accuracy in Threaded Fastener Joints Using Different Torque Control Tightening Strategies
  • 2021
  • In: SAE technical paper series. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191. ; :2021
  • Journal article (peer-reviewed)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.
  •  
18.
  • Karlsson, Patrik, 1973-, et al. (author)
  • Influence of tool steel hard phase orientation and shape on galling
  • 2014
  • In: Advanced Materials Research. - : Trans Tech Publications. - 1022-6680 .- 1662-8985. ; 966-96, s. 249-258
  • Journal article (peer-reviewed)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.
  •  
19.
  • Gomez-Gallegos, A. A., 1983-, et al. (author)
  • A comparative study assessing the wear behaviour of different ceramic die materials during superplastic forming
  • 2017
  • In: Materialwissenschaft und Werkstofftechnik. - : Wiley-VCH Verlagsgesellschaft. - 0933-5137 .- 1521-4052. ; 48:10, s. 983-992
  • Journal article (peer-reviewed)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.
  •  
20.
  • Mill, O., et al. (author)
  • Analysis and development of hydro power research : synthesis within Swedish Hydro Power Centre
  • 2010
  • Reports (other academic/artistic)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...
  •  
21.
  • Munavirov, Bulat, 1986- (author)
  • Ionic lubricants : Molecular features and surface protection mechanisms
  • 2022
  • Doctoral thesis (other academic/artistic)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.
  •  
22.
  • Karlsson, Patrik, 1973-, et al. (author)
  • Influence of tool steel microstructure on friction and initial material transfer
  • 2014
  • In: Wear. - : Elsevier. - 0043-1648 .- 1873-2577. ; 319:1-2, s. 12-18
  • Journal article (peer-reviewed)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.
  •  
23.
  • Karlsson, Patrik, 1973-, et al. (author)
  • Influence of work material proof stress and tool steel microstructure on galling initiation and critical contact pressure
  • 2013
  • In: Tribology International. - Amsterdam : Elsevier. - 0301-679X .- 1879-2464. ; 60, s. 104-110
  • Journal article (peer-reviewed)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
  •  
24.
  •  
25.
  • Cvetkovski, Krste, 1983, et al. (author)
  • Analysis of wear debris in rolling contact fatigue cracks of pearlitic railway wheels
  • 2014
  • In: Wear. - : Elsevier BV. - 0043-1648. ; 314:1-2, s. 51-56
  • Journal article (peer-reviewed)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.
  •  
26.
  • Silva-Magalhães, Ana, et al. (author)
  • In-situ temperature measurement in friction stir welding of thick section aluminium alloys
  • 2019
  • In: Journal of Manufacturing processes. - : Elsevier. - 1526-6125 .- 2212-4616. ; 39, s. 12-17
  • Journal article (peer-reviewed)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.
  •  
27.
  • Engström, Niclas, et al. (author)
  • Road grip test in Arjeplog
  • 2008
  • Reports (other academic/artistic)abstract
    • The Swedish road administration sees a need to improve the road grip estimation capacity for the Swedish road system. The challenge is to find methods to measure road grip fast and reliable. There where six different system types at the tests in Arjeplog, three continuous, two system measuring road grip through deceleration and one system based on GPS and accelerometers. Two system types used air craft runway tires. The other systems used either studded winter tires or friction winter tires. Test runs where performed and road grip where recorded for three different surface types, old system 2000 ice, polished ice and new system 2000 ice. Weather data was collected during the three days. It is clear that all systems can detect changes in road grip. It is clear that continuous systems hold an information advantage over the sequence oriented systems. For measurements of road grip on winter roads, we recommend that rubber compounds adapted for cold conditions are used, as the resolution of the road grip measurement where better. In extreme condition like on polished ice, studded winter tires increase the road grip significantly.
  •  
28.
  • Karlsson, Stefan, 1984-, et al. (author)
  • Non-destructive strength testing of microindented float glass by a nonlinear acoustic method
  • 2023
  • In: Construction and Building Materials. - 0950-0618 .- 1879-0526. ; 391
  • Journal article (peer-reviewed)abstract
    • The present paper describes a method for non-destructive testing of the glass strength. Square 10 × 10 cm2 samples of annealed float glass was inflicted with a controlled defect in the centre of the atmospheric side using Vickers microindentation-induced cracking with a force of 2 N, 5 N and 10 N and compared to an un-indented reference. The samples were non-destructively tested using a nonlinear acoustic wave method resulting in defect values. The average of the defect values was found to linearly correlate to the indentation force in a log–log relationship. The samples were subsequently tested in a ring-on-ring setup that allows for an equibiaxial stress state. The indentation-induced cracking gave practically realistic strength values in the range of 45 to 110 MPa. The individual sample values for failure stress as a function of normalized defect value show linear trends with approximately half of the data within 95% confidence limit. In summary, this study provides an initial proof-of-concept for a non-destructive testing of the strength of glass.
  •  
29.
  • Krishna, Visakh V, et al. (author)
  • Long term rail surface damage considering maintenance interventions
  • 2020
  • In: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 460
  • Journal article (peer-reviewed)abstract
    • A new methodology to estimate costs for wear and Rolling Contact Fatigue (RCF) on rails that cause a major portion of track maintenance costs is presented. It is demonstrated for a standard UIC-Y25 bogie and the FR8RAIL bogie, a softer and cross-braced iteration of the former, based on running conditions for the Swedish iron-ore line. Various non-linearities in the vehicle and track models have been considered. The rail profile evolution and the surface-initiated fatigue on the rail surface for different track radii with progressive tonnage are calculated using iterative multibody simulations. Additionally, the impact of maintenance measures on the long-term rail profile evolution has been considered with optimal preventive rail grinding actions implemented at fixed tonnage intervals based on the recommendations from EN13231-5. The rail profile attributes after 100 Mega Gross Tonnes passage are presented and discussed for both running gears. In doing so, the methodology addresses the long-term ‘track-friendliness’ of running gears considering wear, RCF and the intermediate track maintenance strategies.
  •  
30.
  • Malakizadi, Amir, 1983, et al. (author)
  • Effects of workpiece microstructure, mechanical properties and machining conditions on tool wear when milling compacted graphite iron
  • 2018
  • In: Wear. - : Elsevier. - 0043-1648 .- 1873-2577. ; 410-411, s. 190-201
  • Journal article (peer-reviewed)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.
  •  
31.
  • Anderberg, Cecilia, et al. (author)
  • Cylinder Liners and Consequences of Improved Honing
  • 2006
  • In: Proceedings of Nordtrib conference 2006, Helsingor, Danemark. ; , s. 13-
  • Conference paper (peer-reviewed)abstract
    • The demands on decreased environmental impact from vehicles are resulting in a strong push for decreased engine oil and fuel consumption. Engine oil and fuel consumption are to a great extent controlled by the topography of the cylinder liner surface.Recent engine tests have shown a promising reduction in oil consumption when using cylinder liners with a smoother finish than the current plateau honing.One approach to produce smoother liner surfaces is to replace SiC ceramic honing stones with diamond tools. However, event though the diamond honing process results in higher productivity, improved demands of quality control is needed to monitor the degree of cold worked material - “blechmantel” (German), and the resulting risk of increased wear and scuffing.A number of petrol and diesel engine cylinder liners have been mapped to be able to verify the quality and consequences, in terms of wear and function, of the honing process. A new mapping method, combining SEM images and quantitative image analysis with traditional 2D profilometry has been developed and tested in this study. The liners where tested in a reciprocating rig of 8 mm stroke and with a frequency of 10 Hz, simulating the top-dead center conditions in a running engine.The tests where carried out in high- and low pressure conditions with smooth respectively rough liner roughnesses against PVD coated piston rings. The developed surface mapping method was employed before and after the test to study effect of running-in wear on the surface, features characterized with the SEM- and the 2D profilometer.The results show that combining SEM- and profilometric methods gives a good picture of the effects of varying the cylinder liner pressure and roughness. The core roughness decrease more for diesel liners than for petrol liners. In average (rough and smooth liners) the diesel core roughness decrease 265% while the petrol liners average on a 60% decrease. Blechmantel- and Irregularities ratio show a high sensitivity to varying conditions and decrease 1180% to 100% for the diesel liners while the parameters increase between 106% to 18% for all the petrol liners. A probable cause is the more severe diesel high pressure run-in conditions are able to effectively “truncate” the plateaux and remove residing plastically deformed un-cut honing residues while the less severe petrol liner conditions not manage to remove the blechmantel and irregularities in an important extent.
  •  
32.
  • Kahlin, Magnus (author)
  • Fatigue Performance of Additive Manufactured Ti6Al4V in Aerospace Applications
  • 2017
  • Licentiate thesis (other academic/artistic)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.
  •  
33.
  • Dahlén, Leon, et al. (author)
  • Vegetable and synthetic hydraulic fluids to improve the overall efficiency of a hydrostatic transmission
  • 2001
  • In: Journal of Synthetic Lubrication. - : Wiley. - 0265-6582 .- 1557-6841. ; 17:4, s. 263-276
  • Journal article (peer-reviewed)abstract
    • The purpose of the investigation reported here was to determine whether or not a hydrostatic transmission can act as an alternative to a conventional one, and, if so, to ascertain to what extent the fluid type contributes to an improvement in the efficiency of the hydrostatic transmission. The results presented in this paper are derived from an experimental field test of the hydrostatic transmission of a belt conveyor. This belt conveyor is one part in an ore-transport line at LKAB mining company in Kiruna. The hydrostatic transmission replaced a conventional transmission consisting of an electric motor, a belt drive and a gearbox. The hydrostatic transmission was operated using three different hydraulic fluids: Shell Tellus TX 68, a conventional mineral oil; Mobil SHC 526, a synthetic fluid; and Binol Hydrap II, a vegetable fluid. All fluids have the same ISO viscosity grade, VG 68. The measurements on the transmission show a 3% overall efficiency improvement when using vegetable and synthetic hydraulic fluids compared with the mineral oil. The current at the start of the transmission was reduced by a factor of 6, compared to that of the conventional transmission. The installed 110 kW electric motor was replaced with one of 55 kW. The test also showed that a closer study of all operating conditions, and a selection of components suited to the size of the load, can improve the overall efficiency of the hydrostatic transmission.
  •  
34.
  • Tam, Eric, 1980 (author)
  • Tailoring of Transition Metal Silicides as Protective Thin Films on Austenitic Stainless Steel
  • 2011
  • Doctoral thesis (other academic/artistic)abstract
    • The objective of this study is to make use of transition metal silicides in a novel way as protective thin films on engineering metals. It can then be possible to take advantage of the potentially good corrosion resistance of metal silicides while compensating for their brittle nature by the ductile bulk material. Transition metal silicide thin films based on the systems of Ti-Si, Cr-Si, Fe-Si, Ni-Si were fabricated by means of ion-beam co-sputter deposition on 304 stainless steel substrates, with or without subsequent annealing treatment. Thin film characterisation was done by means of X-ray photoelectron and X-ray diffraction analysis. For the films in crystalline form after annealing, the silicides were well-characterised by means of both techniques. The co-sputtered films showed short-range ordered structures, but the possible silicide phases could be depicted from the core-level XPS spectra of the transition metal peaks defined by the crystalline forms. Except for the Cr-Si system, the phase formation sequence during annealing processes was possible to predict by means of Pretorius’ effective heat of formation (EHF) model provided that the initial thin film compositions were determined. The corrosion properties of the as-deposited silicide films and the uncoated stainless steel specimens were assessed by means of polarisation measurements in dilute hydrochloric (HCl) and sulphuric (H2SO4) acid solutions. All silicide-coated specimens showed lower current densities along the measured potentials than the uncoated steel, suggesting their lower reactivity. Among the silicide films, the Ti-Si and Ni-Si based films showed the best corrosion properties and Si content above 60 at.% for all films facilitated high integrity Si-oxide layer development, whereby corrosion properties improved. Further studies conducted on the Ni-Si system showed that composition is a more important design factor than structure. When considering their tribological properties, Rockwell-C adhesion tests and reciprocating sliding wear tests proved the silicide films to be well-adhering on the substrates and to show lower specific wear rate (10e-13 m3/Nm) than that (10e-12 m3/Nm) of the uncoated steel. It is supposed that transition metal silicides can act as protective thin films on stainless steel as well as any other engineering materials as far as good adhesion is guaranteed.
  •  
35.
  • Vernersson, Tore V, 1968, et al. (author)
  • Wear of Railway brake block materials at elevated temperatures : pin-on-disc experiments
  • 2012
  • In: Proceedings of Eurobrake 2012. - FISITA.
  • Conference paper (peer-reviewed)abstract
    • An experimental study on a pin-on-disc rig is presented where the wear of some brake block materials at controlled elevated disc temperatures are reported. It is found for the three studied organic composite materials that the (specific) wear rate increases radically at a temperature of about 500 oC. For temperatures below 500 oC, the wear rate is found to increase with temperature. The cast iron material shows an increase of the wear rate up to 500 oC, after which a transition in the wear mechanism occurs and the wear rate is decreasing with increasing temperature. The studied sinter material shows a weak dependence of the wear rate with temperature.
  •  
36.
  •  
37.
  • Kumar, Mayank, 1991- (author)
  • Friction in threaded fasteners : Influence of materials and tooling
  • 2022
  • Doctoral thesis (other academic/artistic)abstract
    • Threaded fasteners represent the most common type of machine element, with a unique function that facilitates ease of assembly and disassembly. This ease of disassembly allows machine parts to be reused, refurbished, and recycled. Easy as these components are to assemble, several factors must be considered to achieve the desired clamp force and to utilize the fastener to its full load capacity. The research presented in the thesis compares different tightening strategies and assembly tools to show that the clamp force and it´s scatter are influenced by the variation in the coefficient of friction (CoF) to a much larger extent than by the accuracy of an assembly tool. The research therefore focus on understanding the frictional response in a threaded fastener joint during tightening.A range of design and assembly factors are considered to identify how to increase reliability of the threaded fastener joints. These factors include tightening speed, coating, surface topography, fastener storage conditions, cutting fluid residue and joint material. A torque-controlled, two-step tightening method was mainly used in the studies as it is widely practiced across the production floor of the motor vehicle and general industries to tighten threaded fastener joints. A state-of-the-art friction test rig (FTR) was built to quantify variations in the CoF in the thread and under-head contacts during tightening. Coatings and contact surfaces are also characterized using SEM, FIB, indenters, and optical microscopes to gain an insight to find the likely reasons behind CoF variation. Fasteners with different Zn-based coatings were tightened on plates with surface topographies similar to those found in the motor vehicle industry. The samples were not cleaned before the testing but used "as-received" from the supplier. The degree of damage to the joint surface and fastener thread from the tightening depends on the hardness of the coating. The hardest coating (Zn-Ni) remained relatively unchanged but gave twice as high CoF in the under-head contact compared to the softest coating (Zn-flake). The under-head friction often dominates the tightening process and may be significantly affected by the joint surface topography and the level of cleanliness. In the automotive industry, many parts to be assembled are not thoroughly cleaned, increasing the risk of cutting fluid residue on the joint surface. Different types of cutting fluids were compared in a study with fasteners tightened against “as-received" and cleaned plates. It was shown that CoF might drastically decrease depending on the coating and cutting fluid types. An ester-based fluid performed best, providing the lowest CoF in the under-head contact due to its higher viscosity and polarity. A water-based fluid showed a significantly larger scatter. Water can also influence friction due differences in humidity and temperature. Sometimes fasteners are stored outside a factory which could lead to water diffusion in the coating in hot-humid climate or condensation of water on the fastener surface when it is brought from the outside storage at sub-zero temperatures into the production hall. Water on the coating and inside of it could lead to low CoF, with overtightening and fastener failure as a result. Four Zn-based coatings were compared and showed different response depending on the coating structure and topcoat. Another way to reduce CoF is to use variable speed tightening. It will also increase productivity, as it is faster. It will also improve operator ergonomics, as it gives much lower reaction torque. Much higher CoF was found for EPZ coating when tightened at a constant and very low speed, 5 rpm, due to cohesion that resulted in material transfer, compared to CoF during high, variable speed tightening. At the same time, speed had negligible influence on the CoF when using soft Zn-flake coating as the coating easily sheared off, acting as a solid lubricant.A soft coating is also practical when used in contact with parts made using additive manufacturing (AM). The AM parts are often rough, but a soft coating can mitigate an increase in the under-head CoF. An interesting finding was that the cheapest solution of using an uncoated fastener works very well. An anti-corrosion oil on the plain fastener helped in achieving low CoF. When the AM plate was machined, the CoF and surface damage significantly increased due to the lay of the surface topography created by machining. The findings presented in the thesis increase understanding of how various design and assembly factors govern friction in the thread and under-head contacts. The under-head contact dominates friction response. A proper selection and adjustment of these factors will help design engineers to optimize joint designs and achieve high fastener strength utilization.
  •  
38.
  • Glavatskih, Sergei, et al. (author)
  • Tribotronics facilitates e-maintenance implementation
  • 2011
  • In: Proceedings of the 24th International Congress on Condition Monitoring and Diagnosis Engineering Management. - : COMADEM International. ; , s. 501-506
  • Conference paper (peer-reviewed)abstract
    • Our modern society depends to a great extent on the functionality and efficiency of all the mechanical machinery that we see around us and use every day. All these machines involve numerous tribological contacts. A contact between two surfaces that are in motion relative to each other will result in friction and wear.A constant trend towards more compact mechanical systems with higher power densities requires them to operate in increasingly severe conditions, which heavily influence tribological contacts. They, in turn, affect machine efficiency and impose a limit on machine reliability and service life. Present tribological systems are passive, i.e. their performance cannot be tuned on-line. The purpose of tribotronics is to control so-called loss outputs in a tribo-mechanical system: friction, wear, vibration, etc. Such a system includes sensors, a control unit and actuators. A tribotronic system is thus autonomous and self-adjusting. This allows for on-line tuning of the tribological components for the best performance. This paper illustrates how tribotronic systems can facilitate e-maintenance and thus provide foundation for the best maintenance decisions.
  •  
39.
  • Lin, Yen-Ku, et al. (author)
  • A versatile low-resistance ohmic contact process with ohmic recess and low-temperature annealing for GaN HEMTs
  • 2018
  • In: Semiconductor Science and Technology. - : IOP Publishing. - 1361-6641 .- 0268-1242. ; 33:9
  • Journal article (peer-reviewed)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.
  •  
40.
  • Rodiouchkina, Maria, 1987-, et al. (author)
  • Material Characterization and Influence of Sliding Speed and Pressure on Friction and Wear Behavior of Self-Lubricating Bearing Materials for Hydropower Applications
  • 2018
  • In: Lubricants. - Basel : MDPI. - 2075-4442. ; 6:2
  • Journal article (peer-reviewed)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.
  •  
41.
  • Puneet, C., et al. (author)
  • CrAlSiN nanocomposite thin films for high-speed machining applications
  • 2018
  • In: Materials and Manufacturing Processes. - : Informa UK Limited. - 1042-6914 .- 1532-2475. ; 33:4, s. 371-377
  • Journal article (peer-reviewed)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.
  •  
42.
  • Andersson, Robin, 1986, et al. (author)
  • Integrated analysis of dynamic vehicle-track interaction and plasticity induced damage in the presence of squat defects
  • 2015
  • In: Proceedings of the 10th International International Conference on Contact Mechanics and Wear of Rail/Wheel Systems, Colorado Springs, USA, August-September 2015.
  • Conference paper (peer-reviewed)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.
  •  
43.
  • Andersson, Robin, 1986, et al. (author)
  • Integrated analysis of dynamic vehicle–track interaction and plasticity induced damage in the presence of squat defects
  • 2016
  • In: Wear. - : Elsevier BV. - 0043-1648. ; 366-367:SI, s. 139-145
  • Journal article (peer-reviewed)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.
  •  
44.
  • Ganvir, Ashish, 1991-, et al. (author)
  • Tribological performance assessment of Al2O3-YSZ composite coatings deposited by hybrid powder-suspension plasma spraying
  • 2021
  • In: Surface and Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 409
  • Journal article (peer-reviewed)abstract
    • The advent of high-throughput plasma spray systems that allow axial feeding encourages the study of using liquid feedstock for various next-generation functional applications. The current study explores the benefit of such a plasma spray system to deposit hybrid powder-suspension Al2O3-YSZ ceramic matrix composite (CMC) coatings for tribological applications. The tribological performance of the hybrid processed CMC coatings was assessed using scratch, ball-on-plate wear and erosion tests and compared with that of monolithic powder-derived Al2O3 coatings. As-deposited and tribo-tested coatings were characterized using Scanning Electron Microscopy, X-ray Diffraction and Energy Dispersive Spectroscopy to analyse their microstructure and phase constitution. The results showed that the tribological performance of the hybrid powder-suspension Al2O3-YSZ CMC coating was significantly improved by enhancing the wear resistance under scratch, dry sliding ball-on-plate and erosion tests as compared to the conventional APS deposited monolithic Al2O3 coating. About 36% decrease in the dry sliding ball-on-plate specific wear rate and up to 50% decrease in the erosion wear rate was noted in the hybrid powder-suspension Al2O3-YSZ CMC coating as compared to the conventional APS deposited monolithic Al2O3 coating. The study concludes that the hybrid powder-suspension route can create CMC coatings with unique multi-length scale microstructures which can be attractive for combining different tribological attributes in the same coating system.
  •  
45.
  • Gåård, Anders, 1977-, et al. (author)
  • Nano-scale friction of multi-phase powder metallurgy tool steels
  • 2015
  • In: Advanced Materials Research. - : Trans Tech Publications. - 1022-6680 .- 1662-8985. ; 1119, s. 70-74
  • Journal article (peer-reviewed)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.
  •  
46.
  • Moghaddam, Pouria Valizadeh (author)
  • On the role of microstructure in wear of nanostructured carbide-free bainitic steels
  • 2020
  • Doctoral thesis (other academic/artistic)abstract
    • The significance of steel production for the development of sustainable society and economy is immense. Today’s fast growing global economy poses an increasing demand for improving the properties of steel. The development of nanostructured carbide-free bainitic steel with an excellent combination of strength and toughness is an attempt to satisfy this global demand. During austempering, the precipitation of cementite can be suppressed by addition of approximately 1.5 wt% silicon and a duplex microstructure comprising of extremely fine aggregates of retained austenite and bainitic ferrite can be obtained. Owing to their excellent mechanical properties, these novel steels exhibit considerable potential to replace quenched and tempered bearing steel or pearlitic rail steel. In these applications, wear play a crucial role in determining the performance of the components. However, the majority of studies have been limited to mechanical properties of these steels but not much attention has been paid to their tribological behaviour. Notably, the role of retained austenite and bainitic ferrite on wear performance has not yet fully understood. Furthermore, machining process is an inevitable step in the manufacturing of metal products. During the machining, contact temperature can rise to several hundred degrees. However, high temperature tribological behaviour of these steels in conjunction with coated cutting tool has not yet been addressed. Therefore, the aim of the present research work is to gain a deeper understanding of the correlation between microstructure and tribological performance of carbide-free bainitic steels in various conditions.To achieve this aim, tribological behaviour of nanostructured carbide-free bainitic steels has been investigated under dry rolling/sliding, sliding and two-body abrasive wear conditions. A number of steel grades were austempered under a wide range of temperatures and durations to obtain different carbide-free bainitic microstructures. The results have been compared with that of quenched and tempered bearing steel. Moreover, high temperature tribological behaviour of carbide-free bainitic and 316L stainless steels during interaction with TiAlN PVD coating has also been studied under dry reciprocating sliding condition.The results show that a relatively higher retained austenite content and its stability enhance wear resistance under rolling/sliding condition. Moreover, wear performance of carbide-free bainitic steel has been found to be superior to that of the quenched and tempered bearing steel. However, under sliding condition, the effect of retained austenite on wear heavily depends on sliding speed. At low sliding speed and under adhesive-dominated wear condition, higher retained austenite content results in improved wear performance due to the higher work hardenability. In contrast, at high sliding speed where oxidative wear is dominant, a microstructure with the lowest content of retained austenite exhibits the highest wear resistance. The higher amount of bainitic ferrite provides a hard underlying substrate for a thin and mechanically stable compositional mixed layer and thereby enhances the wear resistance. The formation and microcracking of a brittle white etching layer of quenched and tempered steel is responsible for its inferior wear resistance. Under two-body abrasive wear conditions, higher retained austenite content leads to improved wear resistance. A microstructure providing an optimum combination of hardness and toughness shows the best abrasive wear resistance. During reciprocating sliding, the tribological response of carbide-free bainitic steel is altered with increasing temperature. Higher temperature results in severe material transfer from carbide-free bainitic steel to TiAlN coated cemented carbide. Furthermore, at elevatedtemperature, a porous oxide layer grows on the transferred materials and reduce friction coefficient.In summary, there is no simple and general relationship between microstructure and wear resistance. Depending upon the dominant wear mechanisms and operating conditions, retained austenite and bainitic ferrite affect the wear behaviour in radically different manners.
  •  
47.
  • Haralanova, Valentina, et al. (author)
  • Failures in gearboxes due to material problems
  • 2016
  • In: Materials, Methods & Technologies. - 1314-7269. ; 10, s. 112-136
  • Journal article (peer-reviewed)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.
  •  
48.
  •  
49.
  • Cervantes, Michel, et al. (author)
  • Porjus U9A full-scale hydropower research facility
  • 2008
  • In: Hydro technology and the evironment for the new century. - Foz do Iguassu.
  • Conference paper (peer-reviewed)abstract
    • Hydropower still faces complex scientific and technical challenges in order to secure the availability and reliability of the power plants despite more than a century of development. The main challenge is due to new market constrains such as electrical market deregulation and introduction of renewable sources of energy. The major problem is related to the dynamic of the rotor involving several fields: hydraulics, power engineering and mechanics. On the other side, the large and growing hydropower world market represents an opportunity for technically advanced companies offering better efficiency. The difficulty to scale rigorously any technical advance makes full-scale experiment a necessity. World unique facilities are available at Porjus, Sweden, for this purpose. The Porjus Hydropower Centre is composed of a Francis (U8) and a Kaplan (U9) turbine of 10 MW, each exclusively dedicated to education, research and development. In order to further investigate specific issues related to availability and reliability, a project was initiated in 2006. The main objective is to make U9 a full-scale hydropower laboratory able firstly to furnish the necessary data for the development of rotor-dynamic models but also turbines and bearings. To this purposes more than 200 sensors have been installed to measure displacements, forces, pressure, film thickness, strains... The work presents an overview of the newly upgrade facility as well as some of the problems faced during the instrumentation of the machine.
  •  
50.
  • Hakeem, Abbas Saeed, et al. (author)
  • Synthesis and characterization of alkaline earth and rare earth doped sialon Ceramics by spark plasma sintering
  • 2021
  • In: International journal of refractory metals & hard materials. - : Elsevier. - 0263-4368. ; 97
  • Journal article (peer-reviewed)abstract
    • Several sialon ceramics compositions were synthesized by selecting metal oxides (MOs) in the nanosize range as additives in the oxynitride network. Nanosized precursors, including Si3N4, SiO2, AlN, Al2O3, and MO (MO =MgO, CaO, SrO, BaO, Y2O3, La2O3, CeO2, Nd2O3, Eu2O3, Dy2O3, Er2O3 and Yb2O3,) were used in the present study. Probe sonication and spark plasma sintering techniques were used for mixing the powder precursors and subsequent synthesis of sialon ceramics at a relatively low temperature of 1500 ◦C. Formation of α-sialon(general formula represented by Mm/vSi12-(m+n)Alm+nOnN16-n) was investigated for m and n values of 1.1 and 0.6, respectively and their structural, morphological, thermal, and mechanical properties were evaluated. The synthesized samples were characterized using X-ray diffractometry and field emission scanning electron microscopy to study the effect of the MOs on the microstructure and resulting densification, hardness, fracture toughness, thermal expansion, and thermal conductivity. The sialon samples synthesized using the selected MOs exhibited similar relative densities in the range of 96 to 99% among all the samples and Vickers hardness (HV10) values, in the range of 15 to 20.8 GPa, depending on the type of MO. However, RE MOs exhibited a higher HV than AE MOs.Fracture toughness (KIc) was ~4 MPa⋅m1/2 for most of the samples, but the sample doped with Yb2O3 had the highest KIc of 6.3 MPa⋅m1/2. The thermal conductivity decreased as the atomic number (atomic radii) of the AE increases and in the case of RE exhibited a random tendency. On the other hand, the thermal expansion coefficient increased with increasing atomic radii of the AE, and a mixed trend, with values in the range of 2.63 to2.83 ppm⋅K-1, was observed for RE doped sialon ceramics. These behaviors are attributed to the resulting morphology and structure of alpha sialon comprised of both equiaxed and elongated grains. The properties of these sialon ceramics could be tailored by the proper selection of suitable precursors and synthesis parameters.
  •  
Skapa referenser, mejla, bekava och länka
  • Result 1-50 of 2361
Type of publication
journal article (1206)
conference paper (741)
doctoral thesis (133)
licentiate thesis (88)
reports (80)
other publication (50)
show more...
book chapter (31)
research review (19)
editorial collection (6)
book (6)
editorial proceedings (1)
show less...
Type of content
peer-reviewed (1828)
other academic/artistic (515)
pop. science, debate, etc. (17)
Author/Editor
Larsson, Roland (298)
Prakash, Braham (257)
Glavatskih, Sergei (146)
Almqvist, Andreas (141)
Emami, Nazanin (123)
Höglund, Erik (123)
show more...
Hardell, Jens (122)
Shi, Yijun (111)
Marklund, Pär (104)
Olofsson, Ulf (83)
Pelcastre, Leonardo (56)
Jacobson, Staffan (53)
Kassfeldt, Elisabet (52)
Olofsson, Ulf, 1962- (49)
Björling, Marcus, 19 ... (47)
Lundberg, Jan (40)
Minami, Ichiro (40)
Mu, Liwen (38)
Jacobson, Bo (37)
Westerberg, Lars-Gör ... (34)
Rosén, Bengt - Göran ... (33)
Björling, Marcus (32)
Wahlström, Jens (29)
Wall, Peter (29)
Baart, Pieter (29)
Dimkovski, Zlate, 19 ... (28)
Lyu, Yezhe, 1987- (28)
Li, Jinxia (26)
Abbasi, Saeed, 1973- (25)
Sellgren, Ulf (25)
Berglund, Kim, 1982- (25)
Lugt, Piet (25)
Zhu, Jiahua (25)
Wiklund, Urban (23)
Lu, Xiaohua (22)
Oldenburg, Mats (22)
Nyberg, Erik, 1986- (22)
Pettersson, Anders (21)
Cervantes, Michel (21)
Norrby, Thomas (21)
McCarthy, Donald (21)
Mäki, Rikard (21)
Hansen, Jonny (21)
Ekberg, Anders, 1967 (20)
Harris, Kathryn L (20)
Nielsen, Jens, 1963 (19)
Kabo, Elena, 1972 (19)
Feng, Xin (18)
Jacobson, Staffan, P ... (18)
Golchin, Arash (18)
show less...
University
Luleå University of Technology (1485)
Royal Institute of Technology (431)
Chalmers University of Technology (195)
Uppsala University (124)
Halmstad University (88)
Lund University (67)
show more...
RISE (57)
Karlstad University (25)
Jönköping University (19)
Mid Sweden University (19)
Linköping University (18)
University West (17)
University of Skövde (17)
Örebro University (15)
Högskolan Dalarna (13)
Stockholm University (9)
Blekinge Institute of Technology (9)
University of Gothenburg (6)
Linnaeus University (6)
VTI - The Swedish National Road and Transport Research Institute (6)
Swedish University of Agricultural Sciences (5)
Umeå University (3)
Södertörn University (3)
University of Gävle (2)
Karolinska Institutet (2)
Malmö University (1)
show less...
Language
English (2296)
Swedish (48)
Russian (12)
German (1)
Estonian (1)
Chinese (1)
show more...
Persian (1)
Ukranian (1)
show less...
Research subject (UKÄ/SCB)
Engineering and Technology (2360)
Natural sciences (123)
Medical and Health Sciences (12)
Social Sciences (2)
Agricultural Sciences (1)

Year

Kungliga biblioteket hanterar dina personuppgifter i enlighet med EU:s dataskyddsförordning (2018), GDPR. Läs mer om hur det funkar här.
Så här hanterar KB dina uppgifter vid användning av denna tjänst.

 
pil uppåt Close

Copy and save the link in order to return to this view