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1
Bertrand, Loïc. "Hot rolling friction control through lubrication." Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0146.
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Cette thèse porte sur l’amélioration du laminage à chaud, un procédé de fabrication sidérurgique permettant de transformer une brame de métal (10m de long, 1.5m de large et 250mm d’épaisseur) en une bande de tôle bobinée (1000m de long, 1m de large et 2mm d’épaisseur). Afin d’obtenir certaines propriétés mécaniques et de faciliter la phase de laminage, la brame est réchauffée à 1300°C et dégrossi avant d’être envoyé vers le train finisseur où elle est laminée en passant successivement dans plusieurs cages (ensemble de cylindres qui écrasent le métal) et qui permettent de réduire l’épaisseur à la valeur finale souhaitée. Le produit est finalement refroidi puis bobiné avant d’être envoyé au client. La thèse se focalise sur l’amélioration du train finisseur en proposant un contrôle du frottement entre la bande et les cylindres de travail à l’aide d’une lubrification. La lubrification consiste à déposer de l’huile sur le cylindre en vaporisant une émulsion d’eau et d’huile. L’huile déposée modifie l’interface entre la bande et le cylindre et diminue le coefficient de frottement. Cette diminution du coefficient de frottement a plusieurs avantages : elle permet de réduire l’usure des cylindres, d’améliorer l’état de surface de la bande, de réduire l’effort nécessaire de laminage donc la consommation d’énergie et d’augmenter la capacité du train. A l’inverse, un frottement trop bas dû à une lubrification trop importante peut causer un patinage de la bande entrainant l’arrêt du train. Il est donc important de contrôler le niveau de frottement de manière sécurisée. La conception du contrôle s’est faite à travers deux principales étapes : La modélisation et l’identification de l’effet de la lubrification sur le coefficient de frottement, la conception du contrôle du frottementThis thesis is about the improvement of the hot rolling process. This steelmaking process turns a slab (10m long, 1.5m wide, 250mm thick) into a coiled strip (1000m long, 1m wide, 2mm thick). To obtain some metallurgical properties and to make the rolling easier, the slab is heated up to 1300 ° C and roughly rolled before going to the finishing mill. In the finishing mill the strip is rolled through successive stands (set of rolls) to reduce the thickness to its final desired value. The product is finally cooled down and coiled before shipping it to the customers. The thesis focuses on the enhancement of the finishing mill through a friction control between the strip and the work rolls using lubrication. The lubrication consists in building up oil on the rolls by spraying an emulsion of water and oil. The deposited oil changes the contact interface between the strip and the roll and decreases the friction coefficient. The reduction of the friction presents the advantages of: reduce the roll wear, enhance the strip surface quality, decrease the rolling force (reduce then the energy consumption) and increase the mill capability. In the other hand, an insufficient amount of friction due to an overabundance of lubrication can induce a slippage of the strip leading to a stop of the mill. It is important to control the amount of friction in a secure way. The design of the controller was done through two main steps: Modeling and identification of the effect of lubrication on the friction coefficient, designing the friction control
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Li, Yiling. "Optical Measurements of Rolling Friction Coefficients." Licentiate thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-142.
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This thesis presents an optical method to measure the rolling friction coefficientsfor balls rolling freely on a cylindrical surface. Two different models of a ball rollingfreely on a cylindrical surface are established, one is an analytical model and the otheris a numerical model derived from Lagrange equation. The rolling friction coefficientsare evaluated from the position data of the steel balls. The positions data are retrievedfrom images recorded by a high-speed camera. The locating algorithms includingbackground subtraction and ball recognition are presented in detail. The rollingfriction coefficients between different diameter steel balls and a cylindrical aluminumsurface are measured. The angular positions of the balls are predicted by the solutionof the equation of motion (EOM), and good agreements are found between theexperimental and theoretical results. The values of rolling friction coefficientsbetween different diameter steel balls and a cylindrical aluminum surface areevaluated.
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Sutcliffe, Michael Patrick Forbes. "Friction and lubrication in metal rolling." Thesis, University of Cambridge, 1989. https://www.repository.cam.ac.uk/handle/1810/244874.
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This dissertation is concerned with the physical processes which determine friction and lubrication in metal rolling in the mixed lubrication regime, with particular attention paid to the conditions encountered when rolling aluminium foil. Two areas of relevance to the analysis of the rolling process are initially investigated. Firstly, the rheological properties of a typical aluminium foil rolling oil at high pressures and shear rates have been measured using a disc machine. The behaviour of the oil was found to be well described by the Eyring viscous model, at the shear rates and pressure likely to be found in metal rolling. Secondly, the deformation of asperities when the bulk material is deforming has been examined. The theory developed here was found to agree reasonably with experiments. The results of these investigations are used in the analysis of lubrication in metal rolling, considering the hydrodynamic buildup of oil pressure in the entry region and the crushing of the asperities both in the entry region and at the beginning of the work zone. The contact between roll and strip is divided into two regions, that under the asperities and that in the intervening valleys. Calculations for conditions appropriate to strip and foil rolling give the proportion of the two types of contact and the film thicknesses in each region. Measurements of film thicknesses with an experimental mill in a regime where roughness is unimportant were not found to agree well with an existing simple theory of lubrication. This was ascribed to uneven lubrication in the experiments. After taking this into account, the experiments in a regime where roughness was important were found to agree reasonably with the theory developed here. The effect of roughness on traction is measured in a disc machine with elastic contacts. Its behaviour is found to be determined by the bulk properties of the lubricant at the pressures and strain rates under the asperities. Theory and experiments presented in this dissertation lead to a greater understanding of the physical processes determining friction in metal rolling in the mixed lubrication regime. Film thicknesses and friction coefficients in metal rolling may now be estimated with more confidence.
4
Bradbury, Stephen Robert. "Roll pressure distribution in strip rolling." Thesis, Sheffield Hallam University, 1986. http://shura.shu.ac.uk/19386/.
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The determination of the pressure distribution generated along the arc of contact between the rolls and workpiece during the rolling process has been a subject of interest to researchers for many years. Existing rolling theories make assumptions and include simplifications which are not often substantiated by direct measurement techniques in which pressure transducers are located within the roll surfaces. Such techniques are effective but prohibitively expensive since they render the rolls useless for rolling. A technique has been developed in which the pressure distribution and roll separating load are determined from consideration of the elastic deformation of the rolls during operation. By interrupting a rolling pass before completion, the shapes of the deformed rolls are imparted to the workpiece surface. Accurate measurement of the imparted profiles at several sections across the width of the workpiece allows the extent of the elastic deformation of the roll to be determined. An analytical solution based on solid body contact theory was used to determine the pressure distribution responsible for the elastic deformation along each section. The solution incorporates experimentally determined parameters and functions relating to specific mill-stands and schedules. Initial experimental work was undertaken in which the proposed technique was applied to the quasi-static indentation of flat and inclinedstrip specimens. Having established the basic features of the method relating to these modes of deformation the technique was then applied to the cold rolling process in the form of interrupted rolling passes. Tests were undertaken using a two-high laboratory rolling mill reducing the thickness of mild steel strip workpieces. Comparisons between the predicted pressure profiles using the technique developed and those determined by others using pressure transducers show close similarities. A comparison between the predicted roll separating loads and those determined experimentally show a reasonable correlation.
5
Jupp, Simon Peter. "Fundamental modelling of friction during the hot rolling of steel." Thesis, University of Sheffield, 2006. http://etheses.whiterose.ac.uk/14637/.
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Friction is one of the most significant physical phenomena influencing metal forming, yet in comparison with metallurgy, heat transfer and mechanics it remains the least understood. The goal of this project was to develop, on as fundamental a level as possible, a friction model based upon the physics of the process to be applied to the hot rolling of steel. A fundamental friction model was developed based upon the simplified approach to the adhesion theory by Straffelini (Wear, 249, 79-85, 2001), which is an extension of Bowden and Tabor's original adhesion theory. In this work, the simplified approach's dependence on the thermodynamic work of adhesion was exploited to apply it over a wide range of temperatures. The thermodynamic work of adhesion describes the work required to form a new surface and is a function of the surface energy of the contacting materials was estimated using two approaches: Rabinowicz's and the geometric mean rule. Since high temperature surface energy data is not generally available the relative change in Young's modulus with temperature was used to estimate a material's surface energy at a desired temperature. Reciprocating friction experiments, which provided a controlled environment in which to investigate friction, were conducted to verify the application of this theory to high temperature conditions and metal-oxide contacting materials. The fundamental model describing friction was applied to the hot rolling of steel via a friction algorithm using the commercial finite element (FE) code MARC. Simply described the friction algorithm calculated a friction coefficient using material properties, defined by the user, and contact temperatures, taken from the rolling model. This resulted in the friction coefficient predicted throughout the roll bite, compared to an average friction coefficient typically employed in rolling models. The combined friction algorithm-rolling model was validated against laboratory rolling experiments. One of the assumptions of the finite element rolling model is the presence of a thin, continuous and adherent scale layer. To achieve this in the laboratory a two pass rolling schedule was employed; the first pass to remove the furnace scale and the second pass to input the desired deformation. The success of the friction algorithm was determined by comparing the experimental torques and loads to the predictions of the finite element model. The FE model with the friction algorithm predicted the friction coefficient to vary in the roll gap between approximately 0.25 and 0.35 and was able to predict the measured rolling torque with an average error of 15%, which was considered acceptable and the accuracy was increased after the bearing torque was considered. The error in the load predictions compared to the measured loads was 13.5% on average, which was also acceptable.
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Chertok, Daniel. "Hysteretic friction in the transient rolling contact problem of linear viscoelasticity." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape15/PQDD_0001/NQ37689.pdf.
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Waltersson, Erik, and Göran Eriksson. "Undersökning av steady state och utvärdering av valskraft och friktion vid kallvalsning av aluminium." Thesis, Högskolan Dalarna, Materialvetenskap, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:du-6494.
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The purpose with this thesis was to examine the cold rolling mill located at Högskolan Dalarna and to stabilize the rolling process, to achieve steady state. Experiments with cold rolling of an aluminium strip have given results for rolling force, friction, reduction, strip tension and strain hardening. Results show that steady state has been found for the experiments with roll force and strain hardening, and not been found for the experiments with friction and reduction. Results show that increased strip tension gives lower roll forces. The roll force equation of Stone shows comparable results with reality for dry contact with reductions up to 30 %, but starts being incomparable with higher reductions. The roll force equation of Stone shows a bit higher roll forces than reality gave, but was comparable within reductions from 13 to 50 %. Experiments have shown that the aluminium strip has gone through strain hardening. Experiments show how the set roll gap did not yield the desired thickness reduction, there for the elastic spring constant for the rolling mill was examined and determined to be 417 N / mm for the specific alloy band. The influence of tension strip for roll force was examined and Results confirm the theory about how the roll force is decreased by increasing tension strip. The work rolls started to slip against the alumina strip as high tension strip; 70 N/mm2, gave low roll force; < 15kN.
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Hedmark, Björn, and Per Wallgren. "Influence of ANS Triboconditioning on friction and fatigue in rolling contact configurations." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-75597.
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The automotive industry is constantly being challenged by customers and authorities to enhance the efficiency of the internal combustion engine (ICE) in order to achieve improved fuel consumption and reduced emissions. There are several interfaces within the design of an ICE that causes frictional losses, one of them is the valvetrain. An approach to reducing the friction in the valvetrain of modern engines is to implement cam-follower rollers, resulting in a rolling rather than sliding contact when interacting with the camshaft. The prominent type of wear in rolling contacts is surface fatigue, and specifically a phenomenon called micropitting. The company in collaboration with this project is Applied Nano Surfaces Sweden AB (ANS), located in Uppsala, Sweden. The company have specialized in surface treatment methods of mechanical components. ANS has developed a mechano-chemical treatment method called ANS Triboconditioning, which have shown beneficial friction and wear reducing properties when applied to metal surfaces. This thesis was conducted to investigate how the ANS Triboconditioning would affect the frictional behaviour compared to established surface treatment methods and the occurrence of micropitting in rolling contact configurations. Two types of test programs was implemented into a Wazau UTM 2000 Twin-Disc Tribometer. No clear trend could be established from the micropitting tests and therefore no conclusion regarding if ANS Triboconditioning affects the occurrence of micropitting damage in a positive or negative manner could be stated. The results from the friction test indicated an overall reduction in friction for the test specimens that had been treated with ANS Triboconditioning when compared to specimens that only had been treated with already established surface treatment methods. Summarized, additional tests and analyses are necessary in order to statistically confirm the observed results and determine their respective trends.
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Kalil, Richard Charles Jr. "Evaluation of Frictional Characteristics of Precision Machined Surfaces." Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5000.
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Precision surface finishes are used in a wide variety of applications. From bearing races and rolling elements to parallel slide ways, the frictional characteristics of these surfaces are critical to the performance of the products. Experimental trial and error has shown that certain surfaces outperform others in certain applications, but the specific surface characteristics that make this true have yet to be fully understood. The research goal was to develop an apparatus that can test the coefficient of rolling/sliding friction of different precision machined surfaces and to combine this data with topographic analysis of the surfaces to correlate specific 3-D parameters with the frictional performance of a surface.
The sample treatments consisted of four different surface textures (hard-turned, ground, honed and isotropic finish) and four different relative surface speeds. By monitoring the torque in the sample-mounting shaft under lubricated conditions the coefficient of rolling/sliding friction of each surface was found. Utilizing white light interferometry measurement of the surfaces, a highly detailed map of each surface was obtained.
Using different characteristic values of each machined surface (RMS roughness, asperity density, lay direction, etc.), the frictional behavior of the surfaces were compared to the surface characteristics yielding insight into the relationship between surface finish and friction in rolling/sliding contact. Friction coefficient was found to correlate most strongly with RMS roughness (Sq) and density of surface summits (Sds). These parameters govern mechanical interference of asperities and surface adhesion respectively. These findings suggest that friction coefficients of surfaces could be optimized through manipulation of three-dimensional surface parameters.
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Hutama, Chapin. "Effect of Inclusion of Nanofibers on Rolling Resistance and Friction of Silicone Rubber." University of Akron / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=akron1556118372072796.
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Rudkins, Neil Thomas. "A study of surface friction to improve the Finite-Element simulation of Hot Rolling." Thesis, University of Birmingham, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.511473.
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Sundar, Sriram. "Impact damping and friction in non-linear mechanical systems with combined rolling-sliding contact." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1386245045.
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Dauber, Olaf [Verfasser]. "Elastohydrodynamische Rollreibung in Stahl-Keramik-Kontakten = Elastohydrodynamic rolling friction in steel-ceramics-contacts / Olaf Dauber." Karlsruhe : KIT-Bibliothek, 2001. http://d-nb.info/1014060869/34.
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Bakoglidis, Konstantinos D. "Low Friction and Wear Resistant Carbon Nitride Thin Films for Rolling Components Grown by Magnetron Sputtering." Licentiate thesis, Linköpings universitet, Tunnfilmsfysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-118349.
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The scope of this licentiate thesis is the investigation of carbon based thin films suitable for rolling components, especially roller bearings. Carbon and carbon nitride are materials with advantageous tribological properties and high resiliency. Such materials are required in order to withstand the demanding conditions of bearing operation, such as high loads and corrosive environments. A fundamental condition for coated bearings is that the deposition temperature must be striktly limited. Thus, carbon nitride (CNx) thin films were synthesized here at low temperature of 150 oC by different reactive magnetron sputtering techniques, which are mid-frequency magnetron sputtering (MFMS), direct current magnetron sputtering (DCMS), and high power impulse magnetron sputtering (HiPIMS). While DCMS is a very well studied technique for carbon based films, MFMS and HiPIMS are relatively new sputtering techniques for carbon, and especially CNx depositions. Using different magnetron sputtering techniques, different ionization conditions prevail in the chamber during each process and influence the obtained film properties at a great extent. It was found that bias duty cycles and the amount of working gas ions are key parameters and affect the morphology and microstructure as well as the mechanical response of the films. Moreover, different bias voltages, from 20 V up to 120 V were applied during the processes in order to investigate the changes that the different ion energies induce in the film structure. The structural, mechanical and tribological properties of CNx films are also presented in this licentiate thesis. The morphology of CNx films strongly depends on both the deposition technique and ion energy. The special configuration of MFMS mode produces highly homogeneous and dense films even from low applied bias voltages, while in HiPIMS mode high bias voltages above 100 V must be applied in order to produce films with similar structural characteristics. DCMS is also proven as a good technique for homogeneous and dense films. Low bias voltages do not favor homogeneous structures, thus at 20 V all techniques produced films with columnar structures with intercolumnar voids. High bias voltages influence the N incorporation in the films, with the appearance of re-sputtering of N-containing species and a promotion of sp2 bonding configurations with increasing ion energy. Nevertheless, the different deposition mode influences the sp2 content in different ways, with only MFMS showing a clear increase of sp2 content with increasing bias voltage and HiPIMS showing relatively constant sp2 content. The morphology and microstructure of the CNx films affects their mechanical response, with higher ion energies producing harder films. A dependency of hardness and elastic modulus with increasing ion energy was obtained, where for all deposition modes, hardness and elastic modulus increase linearly with increasing bias voltage. Films with hardness as high as 25 GPa were synthesized by MFMS at 120 V , while the softer film yielded a hardness of 7 GPa and was deposited by HiPIMS at 20 V . The elastic recovery of the films differs with increasing ion energies, presenting a correlation with the C sp2 bond content. The highest elastic recovery of 90% was extracted for the film deposited by MFMS at 120 V and is a value similar to the elastic recovery obtained for FL-CNx films. All films developed compressive residual stresses, depending also on the ion energies and the deposition mode used. It is demonstrated that the induced stresses in the films increase when denser and more homogeneous film morphologies are obtained and with higher Ar intercalcation. Low friction coefficients were obtained for all films between 0.05 and 0.07, although the deposition conditions are not detrimental for the development of friction coefficient. The wear resistance of the films was found to be dependent on the morphology and to some extent on the microstructure of the films. Harder, denser, and more homogeneous films have higher wear resistance. Especially, CNx films deposited by MFMS at 120 V present no wear. The tribological characteristics of the surface of the films were also investigated at nanoscale by a new reciprocal wear test. In this wear test, the recording of the track profile is performed in between consecutive test cycles, eliminating also thermal drift. The very low wear of the films deposited by MFMS at 100 V and 120 V revealed that during the wear test a phase transformation on the surface may take place, possibly graphitization. It is also demonstrated the way that the surface characteristics, such as asperities and roughness affects the tribological measurements. Attention is also turned to the presence of large asperities on the film surface and the way they affect the obtained average friction coefficient and tribological measured data.The series name Linköping Studies in Science and Technology Licentiate Thesis is incorrect. Correct series name is Linköping Studies in Science and Technology. Thesis.
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Dawkins, Jeremy James. "Influence of crystallographic orientation in normal and sliding contacts." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/24713.
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Hili, Joslyn. "Film forming and friction properties of single phase and two phase lubricants in high-speed rolling/sliding contact." Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/7133.
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Single-phase (neat oil) and two-phase (oil-in-water emulsions) lubricants are widely used in metal forming processes, where speeds as high as 20 m s-1 are reached. Most of the previous work done on both neat oil and on oil-in-water emulsions has focused on low speed behaviour (below 5 m s-1) and, as a result, the low speed behaviour of oil-in-water emulsions is well understood. Under these conditions, the lubricating oil film is composed predominantly of oil and the thickness of the film is similar to that for neat oil. However, the behaviour at high speed is entirely different. No experimental film thickness and friction results at speeds above 5 m s-1 are available for neat oil and only one study (Zhu et al., 1994) has reported the film thickness behaviour of oil-in- water emulsions above this speed whereas no friction measurements at speeds above 3.5 m s-1 have been carried out using oil-in-water emulsions. Consequently, to date, the behaviour of neat oil and the relation of emulsion composition to film forming ability at high rolling speeds could not be described. This project is aimed at investigating the mechanism of film formation and the film forming and friction properties of single-phase and two-phase lubricants in high speed rolling/sliding contacts. An EHD test rig was modified to measure film thickness and friction of oil-inwater emulsions in very high speed, rolling/sliding conditions (up to a mean rolling speed of 20 m s-1). Ultrathin film interferometry was used to investigate film thickness while infrared temperature mapping of the contact was used to obtain maps showing the rate of heat input into the surface, from which shear stresses and friction could be calculated. Light induced fluorescence was also employed using a water-soluble and an oil-soluble dye to allow visualization of the contact (at low speeds) and help in investigating the composition of the entrained lubricant at these high speeds. Results showed that, for neat oils, the major factor affecting the film formed at high speed is shear heating. For dilute emulsions at the highest speeds, the film thickness and friction are close to those obtained with pure water. More concentrated emulsions give slightly higher film thicknesses. A comparison of the results with earlier theoretical predictions was carried out. Together with the fluorescence results, this suggested that high speed leads to the entrainment of a micro-emulsion.
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Mutyala, Kalyan Chakravarthi. "Influence of Metallic, Dichalcogenide, and Nanocomposite Tribological Thin Films on The Rolling Contact Performance of Spherical Rolling Elements." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1447751680.
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Lundberg, Oskar. "On the influence of surface roughness on rolling contact forces." Doctoral thesis, KTH, MWL Marcus Wallenberg Laboratoriet, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-193935.
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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.QC 20161013
Centre for Eco2 Vehicle Design
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Shon, Samuel. "An Experimental Study on the Impact of Various Surface Treatments on Friction, Scuffing, and Wear Characteristics of Lubricated Rolling-Sliding Contacts." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1351629351.
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Wilson, Steve Jason. "Traction and Wear Evaluation of a Number of Plastic Materials and Greases under Combined Rolling and Sliding Contact Conditions." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1337191253.
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森, 敏彦, Toshihiko MORI, 健治 広田, Kenji HIROTA, 進幸 千田, Shinkoh SENDA, 貴司 足立, and Takashi ADACHI. "PCR加工による異種材質円管の重ね圧接." 日本機械学会, 2000. http://hdl.handle.net/2237/9034.
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Scholz, Christian [Verfasser], Walter [Gutachter] Reimers, and Mathias [Gutachter] Woydt. "Low friction slip-rolling contacts - Influences of alternative steels, high performance thin film coatings and lubricants / Christian Scholz ; Gutachter: Walter Reimers, Mathias Woydt." Berlin : Bundesanstalt für Materialforschung und -prüfung (BAM), 2015. http://d-nb.info/1121035531/34.
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Keylin, Alexander. "Analytical Evaluation of the Accuracy of Roller Rig Data for Studying Creepage in Rail Vehicles." Thesis, Virginia Tech, 2013. http://hdl.handle.net/10919/49607.
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The primary purpose of this research is to investigate the effectiveness of a scaled roller rig for accurately assessing the contact mechanics and dynamics between a profiled steel wheel and rail, as is commonly used in rail vehicles. The established creep models of Kalker and Johnson and Vermeulen are used to establish correction factors, scaling factors, and transformation factors that allow us to relate the results from a scaled rig to those of a tangent track. �Correction factors, which are defined as the ratios of a given quantity (such as creep coefficient) between a roller rig and a track, are derived and used to relate the results between a full-size rig and a full-size track. Scaling factors are derived to relate the same quantities between roller rigs of different scales. Finally, transformation factors are derived by combining scaling factors with correction factors in order to relate the results from a scaled roller rig to a full-size tangent track. Close-end formulae for creep force correction, scaling, and transformation factors are provided in the thesis, along with their full derivation and an explanation of their limitations; these formulae can be used to calculate the correction factors for any wheel-rail geometry and scaling.For Kalker\'s theory, it is shown that the correction factor for creep coefficients is strictly a function of wheel and rail geometry, primarily the wheel and roller diameter ratio. For Johnson and Vermeulen\'s theory, the effects of creepage, scale, and load on the creep force correction factor are demonstrated. �It is shown that INRETS\' scaling strategy causes the normalized creep curve to be identical for both a full-size and a scaled roller rig. �It is also shown that the creep force correction factors for Johnson and Vermeulen\'s model increase linearly with creepage, starting with the values predicted by Kalker\'s theory. �Therefore, Kalker\'s theory provides a conservative estimate for creep force correction factors. �A case study is presented to demonstrate the creep curves, as well as the correction and transformation factors, for a typical wheel-rail configuration. �Additionally, two studies by other authors that calculate the correction factor for Kalker\'s creep coefficients for specific wheel-rail geometries are reviewed and show full agreement with the results that are predicted by the formulae derived in this study. �Based on a review of existing and past roller rigs, as well as the findings of this thesis, a number of recommendations are given for the design of a roller rig for the purpose of assessing the wheel-rail contact mechanics. �A scaling strategy (INRETS\') is suggested, and equations for power consumption of a roller rig are derived. Recommendations for sensors and actuators necessary for such a rig are also given. Special attention is given to the resolution and accuracy of velocity sensors, which are required to properly measure and plot the creep curves.
Master of Science
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Hasan, Mushfiq. "Investigation of micropitting and wear in rolling/sliding contacts operating under boundary lubrication conditions." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-87215.
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Bousmat, Jonas. "Expériences et modèles du frottement élastomère sur chaussée en roulement/glissement." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEC011.
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Les enjeux de consommation d'énergie et de sécurité ont fait du frottement entre les pneumatiques et la chaussée une propriété importante lors de la conception de nouveaux pneumatiques. Pour mesurer ces efforts de frottement deux cinématiques sont couramment utilisées : la mise en glissement et le roulement/glissement. Les lois de frottement issues des expériences de mise en glissement sont assez bien interprétées. En revanche, le lien qui existe entre ces lois de frottement et le comportement en roulement/glissement est encore mal compris. En particulier, les modèles de roulement/glissement n'incorporent pas la transition entre frottement statique et frottement dynamique, bien que cette phénoménologie soit bien établie expérimentalement. Dans cette thèse, nous proposons différents modèles de frottement en roulement/glissement qui étendent ceux de la littérature en intégrant explicitement la transition de frottement statique/dynamique. Pour tester ces modéles dans le cas du contact pneu/chaussée, nous avons réalisé des expériences selon les deux cinématiques, sur un contact simplifié élastomère/chaussée. A partir des expériences de mise en glissement, les paramètres de la loi de frottement sont identifiés, en fonction de la force normale appliquée, de la vitesse de glissement et de la nature de la chaussée. Ces résultats sont implémentés dans nos modèles, pour produire des prédictions en roulement/glissement, qui sont finalement comparées avec les mesures obtenues en roulement/glissement. De plus, certaines hypothèses des modèles ont été testées par des expériences de visualisation in situ du contact. En particulier nous confirmons, sur une interface élastomère/verre, la présence simultanée d'une zone collée et d'une zone en glissement en conditions de roulement/glissementFor safety and energy consumption issues, tyre friction has become an important property when designing tyres. There are two main kinematic conditions which are commonly used to measure friction forces : the onset of sliding and the rolling/sliding. The friction laws which are extracted from the onset of sliding experiments are rather well interpreted. In contrast, the link between those frictions laws and the rolling/sliding behaviour remains incompletely understood. In particular, the rolling/sliding models do not take into account the transition between static friction and dynamic friction, although it is a well-established phenomenology. In this manuscript, we propose diérent models of friction in rolling/sliding, which extend those of the literature by explicitly integrating a static/dynamic friction transition. To test these models in the case of a tyre/road contact, we performed experiment in the two kinematic conditions, on a simpliéd elastomer/road contact. From the onset of sliding experiments, we identify the parameters of the friction law as functions of the applied normal force, the sliding speed and the type of road. These results are used as inputs in our models to predict the rolling/sliding behaviour, and are eventually compared with the corresponding experiments. In addition, we have tested several assumptions made in the models by performing in situ contact imaging experiments. In particular we con_rm, on an elastomer/glass interface, the simultaneous presence of a sticking and a slipping zone in rolling/sliding conditions
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Palanivel, Sivanesh. "Thermomechanical Processing, Additive Manufacturing and Alloy Design of High Strength Mg Alloys." Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc849628/.
Full textAbstract:
The recent emphasis on magnesium alloys can be appreciated by following the research push from several agencies, universities and editorial efforts. With a density equal to two-thirds of Al and one-thirds of steel, Mg provides the best opportunity for lightweighting of metallic components. However, one key bottleneck restricting its insertion into industrial applications is low strength values. In this respect, Mg-Y-Nd alloys have been promising due to their ability to form strengthening precipitates on the prismatic plane. However, if the strength is compared to Al alloys, these alloys are not attractive. The primary reason for low structural performance in Mg is related to low alloying and microstructural efficiency. In this dissertation, these terminologies are discussed in detail. A simple calculation showed that the microstructural efficiency in Mg-4Y-3Nd alloy is 30% of its maximum potential. Guided by the definitions of alloying and microstructural efficiency, the two prime objectives of this thesis were to: (i) to use thermomechanical processing routes to tailor the microstructure and achieve high strength in an Mg-4Y-3Nd alloy, and (ii) optimize the alloy chemistry of the Mg-rare earth alloy and design a novel rare—earth free Mg alloy by Calphad approach to achieve a strength of 500 MPa.
Experimental, theoretical and computational approaches have been used to establish the process-structure-property relationships in an Mg-4Y-3Nd alloy. For example, increase in strength was observed after post aging of the friction stir processed/additive manufactured microstructure. This was attributed to the dissolution of Mg2Y particles which increased the alloying and microstructural efficiency. Further quantification by numerical modeling showed that the effective diffusivity during friction stir processing and friction stir welding is 60 times faster than in the absence of concurrent deformation leading to the dissolution of thermally stable particles. In addition, the investigation on the interaction between dislocations and strengthening precipitate revealed that, specific defects like the I1 fault aid in the accelerated precipitation of the strengthening precipitate in an Mg-4Y-3Nd alloy. Also, the effect of external field (ultrasonic waves) was studied in detail and showed accelerated age hardening response in Mg-4Y-3Nd alloy by a factor of 24.
As the bottleneck of low strength is addressed, the answers to the following questions are discussed in this dissertation: What are the fundamental micro-mechanisms governing second phase evolution in an Mg-4Y-3Nd alloy? What is the mechanical response of different microstructural states obtained by hot rolling, friction stir processing and friction stir additive manufacturing? Is defect engineering critical to achieve high strength Mg alloys? Can application of an external field influence the age hardening response in an Mg-4Y-3Nd alloy? Can a combination of innovative processing for tailoring microstructures and computational alloy design lead to new and effective paths for application of magnesium alloys?
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Pisklák, Jan. "Vliv přimknutí na tření ve valivém ložisku." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2013. http://www.nusl.cz/ntk/nusl-230584.
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This master’s thesis describes the influence of conformity on friction in rolling bearings. The coefficient of friction is measured on an experimental machine - Mini Traction Machine 2 – using ball-on-disc method. The results are plotted in graphs which showing the dependence of the coefficient of friction at spin-to-roll ratio for specific conformity, normal load and speed in the contact area. The influence of load, speed or different lubricant viscosity is verified for a given value of conformity. Experimentally obtained data are compared with the mathematical model developed in MatLab, within this thesis.
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Ainegren, Mats. "Roller skis' rolling resistance and grip characteristics : influences on physiological and performance measures in cross-country skiers." Doctoral thesis, Mittuniversitetet, Institutionen för teknik och hållbar utveckling, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-16446.
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The aim of this thesis was to investigate roller ski characteristics; classical and freestyle roller skis’ rolling resistance coefficients (μR) and classical style roller skis’ static friction coefficients (μS), and to study the influence of different μR and μS on cross-country skiers’ performance and both physiological and biomechanical indices. The aim was also to study differences in skiing economy and efficiency between recreational skiers, female and male junior and senior elite cross-country skiers.The experiments showed that during a time period of 30 minutes of rolling on a treadmill (warm-up), μR decreased significantly (p<0.05) to about 60-65 % and 70-75 % of its initial value for freestyle and classical roller skis respectively. Also, there was a significant influence of normal force on μR, while different velocities and inclinations of the treadmill only resulted in small changes in μR.The study of the influence on physiological variables of a ~50 % change in μR showed that during submaximal steady rate exercise, external power, oxygen uptake, heart rate and blood lactate were significantly changed, while there were non-significant or only small changes to cycle rate, cycle length and ratings of perceived exertion. Incremental maximal tests showed that time to exhaustion was significantly changed and this occurred without a change in maximal power, maximal oxygen uptake, maximal heart rate and blood lactate, and that the influence on ratings of perceived exertion was non-significant or small.The study of classical style roller skis μS showed values that were five to eight times more than the values of μS reported from on-snow skiing with grip-waxed cross-country skis.The subsequent physiological and biomechanical experiments with different μS showed a significantly lower skiing economy (~14 % higher v̇O2), higher heart rate, lower propulsive forces coming from the legs and shorter time to exhaustion (~30 %) when using a different type of roller ski with a μS similar to on-snow skiing, while there was no difference between tests when using different pairs of roller skis with a (similar) higher μS.The part of the thesis which focused on skiing economy and efficiency as a function of skill, age and gender, showed that the elite cross-country skiers had better skiing economy and higher gross efficiency (5-18 %) compared with the recreational skiers, and the senior elite had better economy and higher efficiency (4-5 %) than their junior counterparts, while no differences could be found between the genders.Syftet med denna avhandling var att undersöka fristils- och klassiska rullskidors rullmotståndskoefficienter (μR) och klassiska rullskidors statiska friktionskoefficienter (μS) samt effekter av olika μR och μS på längdskidåkares prestation vid rullskidåkning på rullande band. Syftet var även att undersöka s.k. åkekonomi och mekanisk verkningsgrad mellan motionärer och kvinnliga och manliga junior- och seniorlängdskidåkare på elitnivå.Experimenten visade att under en period av 30 minuters kontinuerligt rullande, på rullande band, så sjönk μR signifikant (p<0.05) till 60-65 % och 70-75 % av initiala värden, för fristils- respektive klassiska rullskidor. Undersökandet av olika normalkrafter, hastigheter och lutningars påverkan på μR resulterade i en signifikant, negativ korrelation för μR som funktion av normalkraft, medan olika hastigheter och lutningar endast medförde små förändringar av μR.Studien som undersökte fysiologiska effekter av olika μR visade, vid submaximala konstanta arbetsbelastningar, att yttre effekt, syreupptagning, hjärtfrekvens och blodlaktat förändrades signifikant vid ~50 % förändring av μR. Försökspersonernas frekvens och sträcka per frekvens samt skattning av upplevd ansträngning resulterade dock i mestadels icke signifikanta eller små förändringar. Protokollen med successivt ökande arbetsbelastning (maxtest) resulterade i signifikant förändrad tid till utmattning, vid ~50 % förändring av μR. Detta inträffade utan signifikant skillnad i maximal syreupptagning, hjärtfrekvens och blodlaktat, vilket även mestadels gällde för skattning av upplevd ansträngning.Experimenten som undersökte klassiska rullskidors μS visade att dessa erhöll värden som är fem till åtta gånger högre än vad som rapporterats från studier av μS på snö med fästvallade skidor.Den efterföljande studien som undersökte fysiologiska och biomekaniska influenser av olika μS visade, vid submaximala konstanta arbetsbelastningar, att åkekonomin försämrades (~14 % högre syreförbrukning), hjärtfrekvensen ökade, den framåtdrivande kraften från benen på rullskidorna minskade samt att det blev kortare tid till utmattning (~30 %), vid maxtest, när skidåkarna använde rullskidor med en μS i likhet med vad som rapporterats för skidåkning på snö. För arbetsförsöken med olika rullskidor av olika fabrikat med en högre, och likartad, μS förelåg ingen skillnad i de undersökta variablerna.Studien som undersökte åkekonomi och mekanisk verkningsgrad som funktion av prestationsnivå, ålder och kön, visade att elitskidåkarna hade bättre åkekonomi och verkningsgrad (5-18 %) i jämförelse med motionärerna, att seniorerna hade bättre åkekonomi och verkningsgrad (4-5 %) än juniorerna och att ingen skillnad kunde konstateras mellan könen.
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Jandora, Radek. "Výpočtové modelování dynamických projevů v kontaktu kola a kolejnice s obecnou geometrií kontaktních povrchů." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2012. http://www.nusl.cz/ntk/nusl-234020.
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During life of railway vehicles, shape irregularities develop on wheels and rails because of wear. The shape irregularities then affect forces in wheel-rail contact and cause further damage of contact surfaces, vibrations and noise and increase risk of derailment. A numerical simulation of railway vehicle motion with more details on contact surfaces geometry was created to investigate dynamic contact loads in wheel-rail contact. A variety of methods can be used to evaluate forces in rolling contact, the method chosen for this study was algorithm CONTACT based on boundary element method. Four studies are presented in this papers: contact loads from a wheel with a flat and with a wavy tread pattern, loads on wavy rail and load in a curve. The first three studies investigated effects of existing wear patterns, the last one looked for cause of common wear pattern developing on rails. Results of the studies with worn components used showed that the worst kind of shape irregularities is a flat present on wheel. This type of shape cause loss of contact and following impacts. The study of ride in curve showed that cause of high wear in curves, especially those with small radii, is caused by vibration of wheelset. This vibration is then caused by different length of inner and outer rail and wheels travelling along a different path.
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Luks, Tomáš. "Okrajové podmínky ve válcovací mezeře při válcování za tepla a za studena." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2016. http://www.nusl.cz/ntk/nusl-255769.
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Boundary conditions in the roll gap play an important role in modelling of rolling processes. In the roll gap we can observe the following: changes of rolling pressure, changes of relative velocity, influences of oxides and lubrication, etc. When taking into account all conditions mentioned above the determination of the boundary conditions is not trivial and extensive measurements are necessary. Therefore, this thesis is dealing with design of temperature and force sensors specified for the determination of friction coefficient and heat transfer coefficient in contact. The temperature sensor with an installed thermocouple measures subsurface temperature for a given depth; and then the inverse heat conduction task is used to compute temperature and heat flux on the surface. Several temperature sensors were designed and used for measuring in pilot mill and industrial rolling mill as well. The thermal responses of different sensors were compared in the numerical simulations. The inverse calculations were tested for various rolling conditions. A durability of the sensors was also studied in industrial rolling conditions. The contact stresses in the roll gap were measured by a pin, which was in direct contact with the rolled material. The forces on the top of the pin were measured by a three-axes piezoelectric force transducer and recalculated to the contact stress and friction coefficient. The sensor was implemented in a work roll and tested when rolling aluminium and steel slab for different rolling conditions. The results were compared with the integrative force sensor ROLLSURF.
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Persson, Ann-Sofie. "Flow and Compression of Granulated Powders : The Accuracy of Discrete Element Simulations and Assessment of Tablet Microstructure." Doctoral thesis, Uppsala universitet, Institutionen för farmaci, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-208808.
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Simulations are powerful and important tools for gaining insight into powder processes. Ultimately, simulations have the potential to replace experiments. Thus, accurate models and insight into the essential factors for descriptions of powder behaviour are required. In this thesis, discrete element method (DEM) simulations of granule flow and compression were evaluated to deduce parameters and potential models essential for the experimental and numerical correspondence. In addition, the evolution in tablet microstructure during compression was studied using mercury porosimetry. Granule flow was measured using angle of repose, discharge rate, and shear. The granular flow depended primarily on particle shape and surface texture due to the mutual influence of these two parameters on the inter-particle forces. Rolling friction stabilised both the heap formation and promoted shear in the elastic quasi-static flow regime. Thus, rolling friction was established to be an essential simulation parameter for the correspondence to experiments. Current compression models often neglect the elastic compact deformation during particle loading. In this thesis, two fundamentally different models were evaluated with focus of including the elastic deformation. The first model comprised a maximal particle overlap, where elastic deformation commences. The second model accounted for the contact dependence and impingement at high relative densities. This model was based on a truncated-sphere followed by a Voronoi extension. The validity of the models was demonstrated by the elastic qualitative correspondence to experimental compressions for ductile materials. In tablets, the void (inter-granular pore) diameter was dependent on the degree of compression. Thus, the degree of compression provides an indication of the tablet microstructure. The microstructure was subsequently observed to be related to the tablet tensile strength as inferred from a percolation threshold required for formation of coherent tablets. In summary, this thesis has shed light onto the potential of simulating flow and compression of granulated pharmaceutical powders using DEM. Continuous work in the area are required to further improve the models to increase the experimental and numerical correspondence.
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Zahradník, Radek. "Vliv topografie třecích povrchů na kontaktní únavu." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2010. http://www.nusl.cz/ntk/nusl-229384.
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This master thesis deals with influence of topography of friction surfaces on rolling contact fatigue. This influence is examined by newly reconstructed R-MAT station, whose reconstruction and fully report about it, is part of this master thesis. Influence is examined on area with higher surface's roughness which it wasn't examined before. Further research is made on area of surfaces with topographical modification with higher surface's roughness.
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Bonniot, Thomas. "Fatigue crack growth under non-proportional mixed-mode loading in rail steel : From experiment to simulation." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLX096/document.
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Les rails de Chemins de fer sont soumis à de la fatigue de roulement due au passage répété des roues de train, ce qui induit différents types de fissures, telles que les Squats. Ces fissures sont soumises à un chargement de mode mixte non-proportionnel I + II + III, dans des proportions variables le long du front, avec des phases de compression, ce qui rend la prédiction de leur trajet et de leur vitesse délicate.La cinétique de fissuration en mode I a été déterminée dans de l’acier à rail R260, pour des rapports R positifs et négatifs, ainsi que la cinétique de mode mixte II & III corrigée des effets de frottement. Les Facteurs d’Intensité des Contraintes (FICs) effectifs ont été obtenus à partir des sauts de déplacements dans le plan et hors plan mesurés en surface, le long de la fissure. De ces lois cinétiques, il ressort que ni le mode I seul, ni les modes de cisaillement seuls ne peuvent expliquer la fissuration des rails. C’est donc la combinaison des trois modes, suivant des trajets de chargement complexes, qui en est responsable.Des essais de fissuration par fatigue en mode mixte non-proportionnel I + II ont ensuite été réalisés, suivant des trajets de chargement représentatifs de ceux subis par les squats. La stéréo corrélation d’images a été utilisée pour obtenir les champs de déplacements en pointe de fissure. Les méthodes classiques de mesure des FICs à partir de champs de déplacements n’étant pas adaptées, du fait des efforts de contact et frottement entre les lèvres de fissure, de nouvelles méthodes ont été développées. Les trajets et vitesses de fissuration ont été étudiés au regard de ces FICs effectifs. Il apparait que la prédiction du trajet à partir du critère de la contrainte tangentielle maximale n’est pas très fiable, mais peut être améliorée par la prise en compte de la plasticité en pointe de fissure ainsi que des efforts de contact/frottement entre les lèvres de fissure. Les vitesses de propagation obtenues se corrélèrent bien avec une combinaison des trois FICs effectifs dans une loi de type « Paris ».De ces essais, il ressort que du fait de la rugosité de la fissure, l’enchevêtrement d’aspérités et le frottement réduisent considérablement les FICs effectifs. Et cela même en l’absence de compression normale, ce qui ne peut être modélisé par une simple loi de Coulomb. De plus, l’usure des lèvres de fissure a aussi une forte influence sur les FICs effectifs. Le challenge pour les applications structurelles est donc non seulement de choisir le critère de bifurcation et la loi cinétique les plus appropriés, mais également de prendre en compte la rugosité et l’usure des lèvres de fissure, afin d’estimer correctement les FICs effectifs à utiliser dans ces modèles.Pour les applications industrielles, une approche d’ingénieur, simplifiée, a été proposée afin de prendre en compte le frottement induit par la rugosité dans l’estimation des trajets de chargements effectifs à partir des trajets nominaux. Cette approche a été validée sur des essais de mode mixte séquentiel I + II & IIIRails are submitted to Rolling Contact Fatigue due to repeated passages of train wheels, which induces several types of cracks, such as Squat-type cracks. Those cracks undergo non-proportional mixed-mode I + II + III loading, including compression phases, in variable proportions along the crack front, making the prediction of their paths and growth rates a challenge.Mode I crack growth kinetics, for positive and negative R ratios, were first determined in R260 steel, as well as friction-corrected crack growth kinetics for fully-reversed combined mode II and III. The effective Stress Intensity Factors (SIFs) were deduced from the measured in-plane and out-of-plane crack face sliding displacements. From those kinetic laws, it was deduced that neither pure mode I, nor pure shear mode loadings can explain the crack growth rates observed in rails. A combination of those three loading modes, according to complex loading paths had thus to be prospected.Non-proportional mixed-mode I + II fatigue crack growth tests were then performed, following representative loading paths. Stereo digital image correlation was used to measure the near-tip displacement field. Post-treatment methods generally used to deduce the effective SIFs from these fields were inappropriate because of contact and friction stresses along the crack face. New methods were thus developed. The crack paths and growth rates were analyzed, using the effective SIFs. Crack path prediction by the maximum tangential stress criterion was found not to be very reliable, but substantially improved when crack tip plasticity and the presence of contact and friction stresses along the crack faces were taken into account. The measured crack growth rates correlated well with a combination of the three effective SIFs in a Paris-type law.From these experiments, it appears that due to crack face roughness, asperities interlocking and friction substantially reduce the effective SIFs, even without any normal compression, which cannot be captured by a simple Coulomb’s law. Besides, crack faces wear also has a large influence on the effective SIFs. The challenge for structural applications is thus not only to choose the most appropriate bifurcation criterion and crack growth law, but also to take crack face roughness and wear into account, in order to estimate the correct effective SIFS to use in these models.For industrial applications, a simple engineering approach was proposed to integrate roughness-induced friction in the estimation of the effective loading path from the nominal one. This approach was validated on sequential mixed-mode I + II & III experiments
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Cozza, Ronaldo Câmara. "Estudo do desgaste e atrito em ensaios micro-abrasivos por esfera rotativa fixa em condições de força normal constante e pressão constante." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/3/3151/tde-26082011-143752/.
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O ensaio de desgaste micro-abrasivo por esfera rotativa vem conquistando elevada aceitação em universidades e centros de pesquisa, sendo amplamente adotado em estudos envolvendo desgaste abrasivo de materiais. Dois modos de desgaste abrasivo podem ser observados neste tipo de ensaio: rolamento resulta quando as partículas abrasivas rolam sobre a superfície do corpo-de-prova, enquanto riscamento é observado quando as partículas abrasivas deslizam sobre o mesmo; o tipo do modo de desgaste abrasivo apresenta uma significante influência sobre o comportamento de um sistema tribológico. Diversos trabalhos envolvendo coeficiente de atrito durante ensaios de desgaste abrasivo estão disponíveis na literatura, mas somente uma pequena parcela dedicaram-se ao estudo do coeficiente de atrito desenvolvido em ensaios de desgaste micro-abrasivo conduzidos por esfera rotativa. Adicionalmente, pesquisas preliminares reportaram que os resultados são dependentes da variação de pressão, ocasionada pela condução de ensaios sob condições de força normal constante. Logo, o propósito desta Tese de Doutorado é pesquisar a relação entre coeficiente de atrito e modos de desgaste abrasivo em ensaios desgaste micro-abrasivo por esfera rotativa, em condições de força normal constante e pressão constante. Ensaios ball-cratering foram conduzidos com esferas de aço AISI 52100 e um corpo-de-prova de aço-ferramenta AISI H10. A pasta abrasiva foi preparada com partículas de carbeto de silício (SiC) preto (tamanho médio de partícula de 3 m) e água destilada. Diferentes valores de força normal constante e pressão constante foram definidos para os experimentos. As forças normal (N) e tangencial (T) foram monitoradas continuamente durante os ensaios e a relação entre T/N foi calculada para fornecer uma indicação do coeficiente de atrito atuante no sistema tribológico esfera / partículas abrasivas / corpo-de-prova. Em todos os casos, análises por Microscopia Óptica das crateras de desgaste revelaram somente a presença de desgaste abrasivo por riscamento. Entretanto, observações mais detalhadas, conduzidas por Microscopia Eletrônica de Varredura, indicaram que diferentes níveis desgaste abrasivo por rolamento atuaram ao longo dos riscos, fenômeno nomeado de micro-rolling abrasion (microrolamento). Além disso, os resultados obtidos mostraram, também, que: i) a distância de deslizamento apresenta significante influência sobre a transição entre os modos de desgaste abrasivo, ii) para os valores de força normal constante e pressão constante adotados, o coeficiente de atrito manteve-se, aproximadamente, na mesma faixa de valores e iii) o coeficiente de atrito é independente da taxa de desgaste.The micro-scale abrasive wear test by rotative ball has gained large acceptance in universities and research centers, being widely used in studies on the abrasive wear of materials. Two wear modes are usually observed in this type of test: rolling abrasion results when the abrasive particles roll on the surface of the tested specimen, while grooving abrasion is observed when the abrasive particles slide; the type of wear mode has a significant effect on the overall behaviour of a tribological system. Several works on the friction coefficient during abrasive wear tests are available in the literature, but only a few were dedicated to the friction coefficient in micro-abrasive wear tests conducted with rotating ball. Additionally, recent works have identified that results may also be affected by the change in contact pressure that occurs when tests are conducted with constant applied force. Thus, the purpose of this work is to study the relationship between friction coefficient and abrasive wear modes in ball-cratering wear tests conducted at constant normal force and constant pressure. Micro-scale abrasive wear tests were conducted with a ball of AISI 52100 steel and a specimen of AISI H10 tool steel. The abrasive slurry was prepared with black silicon carbide (SiC) particles (average particle size of 3 m) and distilled water. Two constant normal force values and two constant pressure values were selected for the tests. The tangential and normal loads were monitored throughout the tests and their ratio was calculated to provide an indication of the friction coefficient. In all cases, optical microscopy analysis of the worn craters revelated only the presence of grooving abrasion. However, a more detailed analysis conducted by SEM has indicated that different degrees of rolling abrasion have also occurred along the grooves. The results have also shown that: i) the sliding distance presents an important role on the wear mode transition, ii) for the selected values of constant normal force and constant pressure, the friction coefficient presented, approximately, the same range of values and ii) the friction coefficient was independent of the wear rate.
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Shahzamanian, Sichani Matin. "Wheel-rail contact modelling in vehicle dynamics simulation." Licentiate thesis, KTH, Spårfordon, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-127949.
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The wheel-rail contact is at the core of all research related to vehicle-track interaction. This tiny interface governs the dynamic performance of rail vehicles through the loads it transmits and, like any high stress concentration zone, it is subjected to serious damage phenomena. Thus, a clear understanding of the rolling contact between wheel and rail is key to realistic vehicle dynamic simulation and damage analyses. In a multi-body-system simulation package, the essentially demanding contact problem should be evaluated in about every millisecond. Hence, a rigorous treatment of the contact is highly time consuming. Simplifying assumptions are, therefore, made to accelerate the simulation process. This gives rise to a trade-off between accuracy and computational efficiency of the contact models in use. Historically, Hertz contact solution is used since it is of closed-form. However, some of its underlying assumptions may be violated quite often in wheel-rail contact. The assumption of constant relative curvature which leads to an elliptic contact patch is of this kind. Fast non-elliptic contact models are proposed by others to lift this assumption while avoiding the tedious numerical procedures. These models are accompanied by a simplified approach to treat tangential tractions arising from creepages and spin. In this thesis, in addition to a literature survey presented, three of these fast non-elliptic contact models are evaluated and compared to each other in terms of contact patch, pressure and traction distributions as well as the creep forces. Based on the conclusions drawn from this evaluation, a new method is proposed which results in more accurate contact patch and pressure distribution estimation while maintaining the same computational efficiency. The experience gained through this Licentiate work illuminates future research directions among which, improving tangential contact results and treating conformal contacts are given higher priority.QC 20130911
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Kongo, Konde Ange. "Modélisation du roulement d'un pneumatique d'avion." Thesis, Aix-Marseille 1, 2011. http://www.theses.fr/2011AIX10009.
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Ce travail de thèse présente la démarche utilisée pour construire un modèle éléments finis en statique ou en dynamique d'un pneumatique d'avion gros porteur prenant en compte la géométrie, la structure matérielle complexe, les différents matériaux et leurs propriétés ainsi que les interactions entre le pneumatique et le sol (contact, frottement et couplage thermomécanique). Des essais ont été effectués afin d'identifier les paramètres géométriques et matériaux.Ces simulations utilisant une approche Lagrangienne et une approche mixte Eulérienne/Lagrangienne ont été réalisées sur le modèle proposé. La seconde approche qui réduit considérablement le temps de calcul a été validée pour simuler le roulement en dérapage du pneumatique. Le modèle permet ainsi d'estimer le torseur des efforts dans le contact pneumatique /sol. Nous montrons l'influence des paramètres de chargement (charge verticale, pression de gonflage et vitesse de roulage) et de l'angle de dérapage sur le moment d'autoalignement (MZ) et sur le potentiel d'adhérence (µY) correspondant au rapport entre l'effort latéral et l'effort vertical dû au poids de l'avion. Nous présentons aussi une étude de sensibilité aux paramètres géométriques et matériels.Des essais de Coulomb et de diffusion thermique ont permis d'identifier la loi d'évolution du coefficient de frottement en fonction de la température (béton, asphalte) et l'évolution de la température dans l'épaisseur du pneumatique. Ceci a permis de prendre en compte les effets thermiques dans le modèle et de proposer un modèle de couplage thermomécanique qui met en évidence la décroissance de µY et la chute rapide de MZ vers des valeurs négatives au-delà d'un angle de dérapage critique βmax variant avec les conditions de chargement du pneumatique. Ces variations sont observées expérimentalementThis PhD Thesis presents the approach adopted for the setting of numerical model based on Finite Element Method for jumbo-jet tire. The model takes into account the real geometry, the complex material structure, the various materials and their properties as well as the interactions between the tire and the ground (contact, friction and thermal-mechanical coupling due to friction). Tests are performed in order to identify geometrical and material parameters.Static and dynamic simulations using a Lagragian approach and an Eulerian/ Lagrangian mixed approach were performed on this proposed model. This second approach which significantly reduces the computational cost time was validated for cornering tire simulation. The model allows thereby to estimate the forces in the tire/ ground contact patch. We show the influency of loading parameters (vertical load, inflating pressure and rolling velocity) and of the slip angle on the self aligning torque (MZ) and on the lateral friction coefficient (µY) corresponding on the ratio between lateral force and vertical load due to the aircraft weight. We also present a sensitivity study on geometrical and material parameters.Coulomb's and thermal diffusion tests were performed in order to identify the friction coefficient law as function of temperature (on concrete and asphalte surfaces) and the temperature evolution in the aircraft tire thickness. These tests allowed to take into account thermal effects in the model and to propose a thermal-mechanical coupling model which emphasized the decreasing of µY and the rapid vanishing of MZ towards zero beyond a critical slip angle βmax varying with the tire loading conditions. These variations were observed experimentally
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Singh, Harpal. "An Investigation of Material Properties and Tribological Performance of Magnetron Sputtered Thin Film Coatings." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1449850005.
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Munther, Per A. "The effect of material and process parameters on the frictional conditions in hot flat rolling of steels." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0008/NQ30633.pdf.
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Pavelec, Jiří. "Vývoj lineárního posuvu pro UHV STM/AFM." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2011. http://www.nusl.cz/ntk/nusl-229812.
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The aim of this diploma thesis is to develop a linear positioning stage for Ultra High Vacuum (UHV) environment. Simple prototypes of the linear positioning stage were designed and incorporated as part of a multiaxis sample manipulator for a UHV Scanning Tunneling Microscopy / Atomic Force Microscopy (STM/AFM). Different types of position encoders and linear guideways are discussed. Implementation of the homodyne interferometer as an optimization tool for a slip-stick based linear stage is described. Scalar diffraction theory is used to model the diffraction grating optical position encoder behavior.
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Trollé, Benoît. "Simulation multi-échelles de la propagation des fissures de fatigue dans les rails." Thesis, Lyon, INSA, 2014. http://www.theses.fr/2014ISAL0033.
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Sous l’effet des sollicitations mécaniques répétées induites par les passages des trains, on observe l’apparition de fissures de fatigue de contact dans les rails. Une fois amorcées, celles-ci peuvent se propager et mener à la rupture du rail. Dans un contexte d’intensification du trafic et d’augmentation globale des vitesses de circulation, il devient stratégique pour SNCF d’optimiser sa politique de maintenance. Afin de définir des pas de surveillance adaptés et une planification optimisée des opérations de maintenance, une meilleure connaissance des mécanismes d’endommagement par fatigue du rail s’avère nécessaire. Tendre vers cette stratégie de maintenance prédictive passe par la mise en place d’outils de simulation numérique adaptés. Dans ce contexte, une chaîne d’outils a été développée : détermination des sollicitations transmises au rail, des champs de contraintes et de déformations résiduelles, localisation des zones critiques vis-à-vis du risque de fissuration. L’étape suivante consiste à estimer le risque lié à la présence de fissures et à étudier leurs propagations. Elle constitue une partie des objectifs de ces travaux de thèse. La résolution du problème tri-dimensionnel d’une structure fissurée, avec contact et frottement entre les lèvres, est effectuée grâce à un modèle tri-dimensionnel éléments finis étendus multi-échelles. Ce modèle fait appel à une formulation mixte stabilisée où chaque champ est écrit à l’aide d’enrichissement. La fissure est représentée grâce à une stratégie implicite-explicite. Le problème est résolu à l’aide du solveur non-linéaire LATIN. Une étude empirico-numérique a permis de proposer des formules a priori assurant à la méthode de résolution un taux de convergence proche de l’optimal. La simulation de la propagation des fissures de fatigue est réalisée à l’aide de critères spécifiques, adaptés à un chargement multi-axial et non-proportionnel, et d’une loi de propagation dédiée en mode mixte. La confrontation des résultats de simulation avec des essais réalisés sur une configuration cylindre-plan a validé la stratégie X-FEM/LATIN à deux échelles. Tous ces développements ont été implémentés dans le code de calcul éléments finis CAST3M. Des contraintes résiduelles réalistes, provenant d’un logiciel externe, ont été introduites. Cette étape a requis la mise en place d’une procédure de transfert des champs entre les deux maillages (celui utilisé pour le calcul des contraintes résiduelles et celui utilisé pour la résolution du problème de mécanique élastique linéaire de la rupture). L’étude de la flexion du rail a révelé l’influence de ce phénomène uniquement lors du passage du chargement sur la fissure.Enfin, une étude numérique a montré la très forte influence de l’orientation du chargement tangentiel, des contraintes résiduelles et de la présence de plusieurs fissures sur la direction et les vitesses de propagation des fissures de fatigueTo optimize the rail grinding strategy, the prediction of crack growth rates has a vital role. Contact, with friction between the crack faces, notably occurs in rolling contact fatigue (RCF) problems. These time-dependent, multi-axial, non proportional loadings may lead to a crack initiation and propagation, and sometimes to the development of very complex 3D crack network. Numerical simulations of frictional fatigue crack are efficiently performed using the eXtended Finite Element Method (X-FEM). Within this method, the mesh does not need to conform to the crack geometry. Most difficulties associated to complex mesh generation around the crack and the re-meshing steps during the propagation are hence avoided. A 3D two-scale frictional contact fa-tigue crack model developed within the X-FEM framework is presented. It allows the use of a refined discretization of the crack interface independent from the underlying finite element mesh and adapted to the frictional contact crack scale. The model is used here to analyze the crack propagation, rate and direction, under rolling contact fatigue. The wheel-rail contact loading is modeled as a traveling hertzian load. The stress intensity factors are computed at the crack tips during the wheel passage. Criteria for determining crack growth direction under multiaxial non proportional conditions and mixed mode Paris’ law are used. Actual residual stresses are accounted for in the simulation. They are determined thanks to a dedicated model used at SNCF in which the asymptotic mechanical state of the rail is computed when submitted to cyclic loads. A non-uniform elastic-plastic stabilized state is calculated and introduced, by projection of the mechanical fields onto the finite element mesh, in the crack propagation simulation. All this strategy has been implemented in CAST3M and is now used to model 3D frictional crack growth under RCF
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Jakel, Roland. "Das neue Kontaktmodell in Mechanica WF 4.0 mit Reibung : Theoretische Grundlagen und Anwendungsbeispiele." Universitätsbibliothek Chemnitz, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-200900787.
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Der Vortrag stellt das neue, unendlich reibungsbehaftete Kontaktmodell der FEM-Berechnungssoftware Pro/ENGINEER Mechanica in der Version Wildfire 4.0 von PTC vor. Dabei werden sowohl die Grundlagen des reibungsfreien Kontaktes als auch die Theorie des unendlich reibungsbehafteten Kontaktmodells behandelt sowie die Grundlagen der zur numerischen Lösung in der Software verwendeten Penalty- und Newton-Raphson-Methode erläutert.
Als Anwendungsbeispiel für das reibungsfreie Kontaktmodell wird ein Zylinderrollenlager vollständig mit sämtlichen Wälzkontakten für verschiedene Lager- und Einbauspiele berechnet, die Ergebnisse umfassend dargestellt sowie eine analytische Gegenrechnung nach der Hertzschen Theorie ausgeführt, die sehr gute Übereinstimmung mit der numerischen Simulation zeigt. Für das reibungsbehaftete Kontaktmodell wird exemplarisch eine geschrumpfte Welle-Nabe-Verbindung unter Torsion berechnet. Diese wird einer analytischen Lösung sowie verschiedenen 2D-Idealisierungen (ebener Spannungszustand, ebener Dehnungszustand, 2D-Axialsymmetrie) gegenübergestellt.
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Giner, Navarro Juan. "Advances Techniques for Time-Domain Modelling of High-Frequency Train/Track Interaction." Doctoral thesis, Universitat Politècnica de València, 2017. http://hdl.handle.net/10251/90637.
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[EN] The aim of the present Thesis is to develop models for the study of very high-frequency phenomena associated with the coupling dynamics of a railway vehicle with the track. Through these models, this Thesis intends to address squeal noise as a particular case of rolling noise when the train negotiates a small radius curve.
Wheel/rail interaction is the predominant source of noise emission in railway operations. Rolling contact couples the wheel and the rail through a very small area, characterised by strongly non-linear and non-steady state dynamics that differentiates rolling noise from any other noise problem. Wheel/rail contact problem is studied based on Kalker's variational theory and the local falling behaviour of the coefficient of friction is introduced by means of a regularisation of Coulomb's law. Its implementation shows that the influence of the falling friction on the creep curves can be assumed negligible, thus rolling contact is finally modelled using a constant coefficient of friction.
Flexibility is introduced in railway substructures through the Finite Element (FE) method in order to cover the high-frequency range. This work adopts a rotatory wheelset model that takes computational advantage of its rotational symmetry. It also develops a cyclic flexible rail model that fixes the translational contact force in a spatial point of the mesh through a technique called Moving Element (ME) method. A modal approach is used to reduce significantly the number of degrees of freedom of the global problem and a diagonalisation technique permits to decouple the resulting modal equations of motion in order to increase the computational velocity of the time integrator.
Simulations in curving conditions in the time domain are carried out for constant friction conditions in order to study if the proposed interaction model can reproduce squeal characteristics for different curve radii and coefficients of friction.[ES] El objetivo de la presente Tesis es desarrollar modelos para el estudio de fenómenos de muy alta frecuencia asociados a la dinámica acoplada de un vehículo ferroviario con la vía. A través de estos modelos, esta Tesis pretende abordar el fenómeno de los chirridos como un caso particular de ruido de rodadura en condiciones de curva cerrada. La interacción rueda/carril es la fuente predominante de ruido en las operaciones ferroviarias. El contacto es el responsable del acoplamiento entre la rueda y el carril a través de un área muy pequeña caracterizada por una dinámica fuertemente no lineal y no estacionaria. El problema de contacto rueda/carril se estudia mediante la teoría variacional de Kalker y la caída local del coeficiente de fricción se introduce por medio de una regularización de la ley de Coulomb, que muestra que su influencia sobre las curvas de fluencia se puede despreciar. Como consecuencia, el coeficiente de fricción se considera constante. La flexibilidad se introduce en las subestructuras ferroviarias a través del método de los Elementos Finitos (EF) para cubrir el rango de las altas frecuencias. La Tesis adopta un modelo de eje montado rotatorio que toma ventaja computacional de su simetría rotacional. También desarrolla un modelo de carril flexible y cíclico que fija la fuerza de contacto en un punto espacial de la malla mediante el método de los Elementos Móviles (EM). Se utiliza un enfoque modal para reducir significativamente el número de grados de libertad del problema global; las ecuaciones de movimiento resultantes en coordenadas modales se desacoplan mendiante una técnica de diagonalización para aumentar la velocidad computacional del integrador temporal. Las simulaciones en condiciones de curva en el dominio del tiempo se llevan a cabo en condiciones de fricción constante con el objetivo de estudiar si el modelo de interacción propuesto puede reproducir las características del chirrido en curva para diferentes radios de curva y coeficientes de fricción.
[CAT] L'objectiu de la present Tesi és desenvolupar models per a l'estudi de fenòmens de molt alta freqüència associats amb la dinàmica acoblada d'un vehicle ferroviari amb la via. Aquests models permeten simular el soroll de rodament encara que, en particular, aquest treball es proposa abordar el fenomen del soroll grinyolant produït quan el tren negocia un radi de curvatura estret. La interacció roda/carril és la font predominant de l'emissió de soroll en les operacions ferroviàries. El contacte acobla la roda i el carril a través d'una àrea molt reduïda que es caracteritza per una dinàmica fortament no lineal i no estacionària. El problema de contacte roda/carril s'estudia mitjançant la teoria variacional de Kalker i el descens local del coeficient de fricció s'introdueix per mitjà d'una regularització de la llei de Coulomb, què demostra que la seua influència en les corbes de fluència es pot suposar insignificant. Per tant, s'utilitza un coeficient de fricció constant per a modelar el contacte. La flexibilitat s'introdueix en les subestructures de ferrocarril a través del mètode d'Elements Finits (EF) per tal de cobrir el rang d'alta freqüència. La present tesi adopta un model d'eix muntat rotatori que s'aprofita de la seua la simetria rotacional per a augmentar la eficiència computacional. També desenvolupa un model de carril flexible i cíclic que fixa la força de contacte en un punt espacial de la malla a través del mètode dels Elements Mòbils (EM). S'empra un enfocament modal per reduir significativament el nombre de graus de llibertat del problema global, al temps que s'implementa una tècnica diagonalització que permet desacoblar les equacions modals de moviment per a augmentar la velocitat computacional de l'integrador temporal. Les simulacions en les condicions de corba en el domini del temps es duen a terme per a condicions de fricció constant per tal d'estudiar si el model d'interacció proposat pot reproduir les característiques del soroll grinyolant per a diferents radis de corba i coeficients de fricció.
Giner Navarro, J. (2017). Advances Techniques for Time-Domain Modelling of High-Frequency Train/Track Interaction [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/90637
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Ghodssi, Reza. "A study of rolling friction in Microelectromechanical Systems (MEMS)." 1992. http://catalog.hathitrust.org/api/volumes/oclc/31734070.html.
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Thesis (M.S.)--University of Wisconsin--Madison, 1992.Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 43-46).
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Lin, Chih-Pin, and 林志賓. "Inverse Analysis for Estimating Friction Coefficient in Strip Rolling." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/21204405199856564673.
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碩士國立中山大學
機械與機電工程學系研究所
91
Abstract The rolling is an efficient and economical approach for the manufacturing of strip or plate metals, it plays an important role because of its versatility and its high production rate in the manufacture of various products with uniform cross-sectional area. Without the knowledge of the influences of the variables such as friction conditions, material properties, and workpiece geometry on the process mechanics, it will not be possible to design and control the equipment adequately, or to predict and prevent the occurrence of failures. According to modeling by numerical has become a major tool in rolling research. By using the proper criterion, de-pending upon the production requirements along with the modeling results, the process efficiency, productivity and quality can be increased and the down time of the mill and cost operation can be reduced. In this study, investigated that it do not consider to work hardening and consider to work hardening during the rolling process from Von Karman theory. We can realize friction coefficient, reduction ratio, rolling force, rolling torque, neutral point, and pressure distribution relation, then from measuring rolling force, torque, neutral point can inverse to solve friction coefficient and pressure distribution. Result that we found the error of direct and inverse solution about rolling friction coefficient was less than 5 %, and the coef-ficient of friction was found to increase with reduction and rolling force and neutral point.
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Hsieh, Cheng-Hsin, and 謝姃馨. "Analytic Study on Nonlinear Rolling Isolation System with Viscous or Friction Damper." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/50273913944892375618.
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碩士國立臺灣大學
土木工程學研究所
98
Abstract The vibration period of many linear isolation systems are 2 to 3 seconds which is close to the predominant period of near-fault earthquake, and resonance may occur. For this reason, nonlinear isolation systems are developed to avoid resonance. The frequency of nonlinear isolation system is not fixed, so it can keep the structure from resonance. Numerical simulation is conducted for nonlinear isolation system and the corresponding linear system under free vibration, sine wave, far-field and near-fault earthquake. The linear and nonlinear isolations performance of the system due to harmonic and seismic excitations will also be demonstrated and investigated in this study. In the proposed system, a mass block is pin connected to a set of circular rolling disk. If the pin is connected eccentrically to the center of the disk, the restoring force becomes nonlinear. In addition, energy is dissipated by adding viscous damper or friction damper. The nonlinear governing equation of motion for the eccentric rolling isolation system is derived based on Lagrange’s equation. The isolation frequency as a function of the eccentricity and initial angle will be investigated through free vibration analysis. By the numerical simulation of free vibration, the results show that if the eccentricity or initial angle is small, the dynamic behavior of the system is almost the same as the linear rolling behavior. When the ground excitation input is sine wave and its frequency equal to the linearized frequency, the numerical simulation results show that if no dissipation mechanism, the linear system will be divergent, but nonlinear systems will be stable because of its nonlinear behavior. When the viscous damper dissipation mechanism is adopted, under resonant frequency of the sine wave, linear isolation system is no longer divergent, but the maximan response of the nonlinear system is only about 50% of the linear system. When the PGA of El Centro and Chi-Chi earthquakes varies from 0.05 to 1 (g), the result shows that the superior of the nonlinear system over the linear system becomes more obvious as PGA increases. Therefore, with viscous damping, the nonlinear isolation system performs better than the linear one in both acceleration ratio and maximum displacement under sine wave, far field under or near fault earthquakes excitation. When isolation install friction damper, under far field and near-fault earthquake excitation, the best design of friction parameters are very close. Under resonant frequency of sine wave, the response of linear system will be divergent if the friction parameter is not big enough, while nonlinear system is stable and no resonance occurs at same dutam. Then change the PGA of two earthquakes, the range from 0.05 to 1 (g), the result shows that the displacement of the linear isolation system is closer to that of the nonlinear one.With the increases of PGA, nonlinear isolation display the better isolation effect, but linear system don’t have this advantage. Summarized above, with friction damper, the response of nonlinear systems and linear systems are similar, but if the PGA of near-field and far-field earthquakes becomes larger, nonlinear isolation system shows more and more effect than linear system. Thus, by appropriate design, the nonlinear rolling isolation system is feasible in this research.
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Li, Yufeng. "Generalized empirical dimensionless formulas of coefficient of friction in concentrated sliding-rolling contacts." 1988. http://catalog.hathitrust.org/api/volumes/oclc/19481499.html.
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Thesis (Ph. D.)--University of Wisconsin--Madison, 1988.Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 153-160).
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Cousseau, Tiago. "Film thickness and friction in grease lubricated contacts. Application to rolling bearing torque loss." Tese, 2013. http://hdl.handle.net/10216/73993.
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Cousseau, Tiago. "film thickness and friction in grease lubricated contacts. application to rolling bearing torque loss." Doctoral thesis, 2013. https://repositorio-aberto.up.pt/handle/10216/69532.
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Xu, Dan [Verfasser]. "Dry rolling friction and wear of elastomer systems and their finite element modelling / von Dan Xu." 2009. http://d-nb.info/998937657/34.
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Yao, Xin-Yi, and 姚欣儀. "Effect of friction stir processing and subsequent cold rolling on mechanical properties of Mg-Li alloy." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/34w9u8.
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碩士國立東華大學
材料科學與工程學系
107
Magnesium-lithium alloy has good room temperature formability, but its strength is low due to lithium addition. In this study, the mechanical properties and microstructures of LZ91 and LAZ941 alloys after the friction stir process (FSP) with different rotational speeds and subsequent cold rolling on FSP were investigate. The results show that the grains are remarkably refined after FSP. The minimum grain size of FSP-LZ91 100rpm is 8.9μm, which is due to the lower heat input at a lower rotation speed. It also displays the best yield and ultimate tensile strengths, which are 137.6 MPa and 150.8 MPa, respectively. It is consistent with the Hall-Petch equation, the smaller grain size the greater yield strength. On the other hand, the FSP-LAZ941 has the contrary phenomenon compare with the LZ91, and has the best strength after FSP at a higher rotation speed of 300 rpm, and its yield strength and ultimate tensile strength were 187.7MPa 221.0MPa, respectively. The reason was considered that the precipitation of θ-Li2MgAl phase occur during the FSP at higher rotation speed. After the subsequent cold rolling on FSP, the alloys show the obvious grain refinement and the work hardening due to the large amount of plastic deformation. The mechanical properties were improved, but the elongation decreased. FSP-LAZ941 300rpm following CR40% cold rolling displays optimal properties. The hardness was 89.9HV; yield strength and ultimate tensile strength were 229.6MPa and 298.5MPa, respectively. From the SEM fracture analysis results, the fracture surfaces show the dimple structures.