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1
Zhang, Cheng. "Robotic 3D friction stir welding : T-butt joint." Thesis, Högskolan Väst, Avd för automationssystem, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-8250.
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This Master Thesis was performed in terms of robotic three dimensional friction stir welding with T-butt joint. Friction stir welding (FSW) is a solid state welding method that achieves the weld temperature by friction of a rotating non-consumable tool with the workpiece. Science and technology fast developing requires for higher seam quality and more complex welding joint geometry like 3D welds. In order to acquire high productivity, capacity and flexibility with acceptable cost, robotic FSW solution have been proposed. Instead of the standard FSW machine, using a robot to perform complicated welds such as, three-dimensional. In this report, a solution for weld a 3D T-butt joint, which located in an aluminium cylinder with 1.5 mm thickness using a robot, was developed. Moreover, two new paths were investigated in order to avoid the use of two welds to perform this type of joint. The paths were tested on 2D and on 3D (with a 5050 curvature radius) geometries. Both paths had good results. What is more, the parameter developing methods of FSW process, which is composed of necessary parameter setting, positional compensation was introduced. Specially,the study demonstrates how complicate geometry can be welded using a robot. Also,it shows that TWT temperature control is able to acquire high quality 3D welds. In addition, an analysis of the 2D welding and 3D welding was performed, which exposed that, keeping exactly the same welding conditions, higher lateral forces on the tool were found during 3D welding. Basis on the special case in this paper, when the tool goes like "climbing" the sample, the suffering force of tool decreasing with increasing the height(Z position); nevertheless, when the tool goes like "downhill", the suffering force of tool decreasing with decreasing the height (Z position). What is more, in 2D weld, increasing the downforce (Fz) results increasing the lateral forces which can be Fx and/or Fy. Finally, the future works suggestions were presented in terms of (1) performing the new paths into a real cylinder, (2) performing tensile test on the paths and comparing it with conventional path which weld twice, (3) researching how the downforce (Fz) influence the Fx and Fy during welding of different 3D geometries, (4) how the cooling rate of backing bar influence the seam quality when it is use the same welding parameters and (5) the effect of performing welds in the same welding temperature achieved with different combination of the tool rotational speed and downforce on the material properties
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Arinez, Jorge Francisco. "Reduction of friction in polymeric composites for artificial joint prostheses." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/37044.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1995.Includes bibliographical references (leaves 128-135).
Ultra-high molecular weight polyethylene has been used as a bearing material in artificial joints for more than thirty years. Despite this long period of use and the success which artificial implants have had, material failure and ultimately prosthetic failure still occurs as the result of mechanical wear of the bearing surface. Several wear mechanisms have been proposed as the main causes for failure; however, none is as dominant as the delamination wear of artificial knee prostheses. Delamination wear occurs mainly as the result of cyclic plastic deformation of the surface and subsurface layer which causes cracks to nucleate and propagate in the subsurface leading to the production of wear sheets. This research seeks a new alternative material to prevent the occurrence of delamination wear by the use of a fiber reinforced composite. The use of a fiber-reinforced composite having fibers oriented normal to the sliding direction is known to offer reduced plastic deformation resulting from the high stiffness of fibers and furthermore can inhibit crack nucleation and more importantly propagation since fibers are able to arrest the growth of cracks normal to the fiber axis. This new material has been called homo composite based on the fact that fiber and matrix are made from the same material, namely UHMWPE. This material has shown promising results in friction tests yielding coefficients of 0.05 in bovine lubricated sliding conditions. The optimization of material processing parameters with respect to friction and wear of the homocomposite is also presented.
by Jorge Francisco Arinez.
S.M.
3
KANTURA, JOHN JOSEPH. "TEST RIG DESIGN AND EVALUATION: CHARACTERIZING NONLINEARITY OF FRICTION JOINT." University of Cincinnati / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1046378210.
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Blom, Arvid. "Speed dependent friction in bolt joints." Thesis, KTH, Maskinkonstruktion (Inst.), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-141687.
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Denna rapport undersöker hastighetsberoende friktionsbeteende i zinkpleterade 8.8 M12x1.75 skruvförband med en klämlängd på 82 mm och ett åtdragningsmoment på 120 Nm. Totalt 84 åtdragningar genomförs med nya skruvar, brickor och muttrar för varje åtdragning med utrustning tillhandahållen av Atlas Copco. All data importeras och analyseras i Matlab. Analysen visar att inom en standard avvikelse från medelvärdet kan klämkraften variera med så mycket som 90% beroende på var inom det 10-200 rpms hastighetsspannet skruven drogs åt. Vidare framgår även att restmomentet är mycket beroende av den hastighet som skruven drogs åt vid, med ett restmoment ~5 Nm över slutmomentet för 10 rpm och ~20 Nm över slutmomentet vid 200 rpm. En ursprunglig hypotes tas fram som antar att en utförlig modell av lastfördelningen i skruvensgänga och under skruvens skalle kan användas för att förutse skruvförbandets friktionsbeteende. Denna hypotes övergavs då mätresultat och analys visar att effekten av en förbättrad lastfördelningsmodell inte skulle märkas då spridningen i friktionen är för stor.This report examines the speed dependency of frictional behavior in zinc plated 8.8 M12x1.75 bolt joints with an 82 mm clamping length at a tightening torque of 120 Nm. A total of 84 test tightenings have been performed with new bolts, nuts and washers for each tightening. The tests are performed using equipment supplied by Atlas Copco and all data is imported and analyzed in Matlab. It is found that within one standard deviation of the mean value the clamping force can vary as much as 90% depending on where in the 10-200 rpm speed range the bolt is tightened. Furthermore it is concluded that the residual torque is also highly speed dependent, registering at ~5 Nm above the final torque at 10 rpm and ~20 Nm above at 200 rpm. An initial hypothesis was developed regarding the pressure distribution in the thread and under the bolt head in the hopes that better understanding and modeling of this aspect could help predict frictional behavior in the bolt joint. This hypothesis was abandoned after it is concluded that the impact of an improved pressure model would be much too small to be noticeable due to the already large scatter in frictional coefficients.
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Schroeder, Matthew O. "Biotribology : articular cartilage friction, wear, and lubrication /." Thesis, This resource online, 1995. http://scholar.lib.vt.edu/theses/available/etd-12302008-063639/.
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Sage, R. M. "The mathematical modelling of ball-joints with friction." Thesis, University of Leicester, 1987. http://hdl.handle.net/2381/34822.
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At present the effects of friction are not included in three-dimensional mechanism simulation packages because of the difficulty of determining a friction model for joints such as the spherical joint where the frictional resistance to motion depends not only upon the coefficient of friction and the magnitude of the loading on the joint but also on the pressure distribution within the joint resulting from that loading. Thus the basis of this thesis has been the development of a mathematical model of the effects of friction in a spherical joint which could then be incorporated into a mechanisms simulation program. The model developed has shown that the main factors determining the magnitudes and directions of the frictional effects produced in a spherical joint, apart from the coefficient of friction and the magnitude of the loading, are the extent of the contact area between the ball and the socket and the magnitude of the angle between the axis of rotation of the joint and the direction of the applied load. Experimental results were obtained using apparatus that enabled the frictional moment produced on the socket of a joint to be measured while allowing the angle between the axis of rotation of the ball and the direction of the applied load to be varied between measurements. These results, obtained for a range of values of the coefficient of friction, confirm that this angle is a significant factor in the model and that the model usefully determines the frictional effects produced in a spherical joint.
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Kantura, III John J. "Test rig design and evaluation characterizing nonlinearity of a friction joint /." Cincinnati, Ohio : University of Cincinnati, 2003. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=ucin1046378210.
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Nykänen, Robin. "Simulation of Bolted Joint with Frictional Contacts." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-74490.
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An easy and reliable way to join two or more components is to use a bolted joint. When torque is applied on the bolt head, a clamp force is achieved. However about 90% of this torque will be used just to overcome the friction in the interfaces. To be able to fasten these in an ecient and precise manner the friction in the bolt threads and underhead area is important to understand. This is currently investigated at Atlas Copco by using a friction test rig, FTR, which measures the clamp force, the total torque and the shank torque. To evaluate the test rig and also to be able to evaluate dierent friction models, a parameterised simulation model of a bolted joint is built. This is a 3D-model of the joint containing a bolt, a nut and a test specimen. The stiness and frictional behaviour of the FTR is used in the model to get a good comparison between these two. Dierent contact formulations and settings are tested to achieve a good model. Also, mesh size, step size and material models are evaluated to see the eect of these. The results show a good correlation between the FTR data and the simulation model. For the total torque to clamp force ratio a dierence of about 1% is achieved. The average dierence in shank torque and underhead torque is at 3.1% and -1.6% respectively. The pressure distribution for this model is shown to be unevenly distributed along the threads. This is minimized by softening the contact, but this instead increases the error between the FTR data and the simulation model. For the evaluation of friction models that are based on the contact pressure this needs to be investigated further to nd a good compromise between the contact pressure and the frictional behaviour.
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Owellen, Michael C. "Biotribology: The Effect of Lubricant and Load on Articular Cartilage Wear and Friction." Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/36872.
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This paper presents a biotribological study on cartilage
wear and friction, using a system of cartilage-on-stainless
steel. This study is a part of the ongoing biotribology
research by Dr. Furey at the Virginia Polytechnic
Institute and State University.Two loads (65 N and 20 N) and three lubricants (saline reference, reference + hyaluronic acid, and bovine synovial fluid) were tested and evaluated using several analysis techniques. These techniques included wear analysis by hydroxyproline measurement, scanning electron microscopy (SEM), histologic sectioning and staining, numerical analysis of friction and specimen displacement data, and Fourier transform infrared (FTIR) analysis.
Biochemical wear analysis showed that, under high load, the saline reference generated the most wear, hyaluronic acid produced less wear, and bovine synovial fluid produced the least. Wear was sensitive to load with all three lubricants, but was not significantly affected by the lubricant under low load.
SEM photographs and histologic sections showed evidence of plowing and surface delamination, as well as another wear mechanism that produced wear markings perpendicular to the direction of sliding.
Opaque films remained on the polished stainless steel
disks after saline and hyaluronic acid tests, but not after
synovial fluid tests. FTIR analysis of these films, as
well as fresh and worn cartilage, showed that the cartilage
experienced chemical changes during sliding.
Master of Science
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JOHANNA, DOLK. "Rotary Joint Module for Lenses on Infrared Camera." Thesis, KTH, Maskinkonstruktion (Inst.), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-192635.
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Detta arbete utfördes på vridledsmodulen för handhållna kameror från T-serien hos företaget FLIR. Vridledsmodulen används för att hålla uppe objektivet och reglerar vinkeln på detta i jämförelse med resten av kameran. FLIR hade tidigare ett flertal lösningar för olika kameramodeller och dessa hade individuella problem när det kom till kvalitet, toleranser och hållbarhet. De tidigare lösningarna skilde sig i vilka komponenter som används och vilket vridmoment som krävs från användaren vid bruk. Företaget sökte en ny lösning för vridledsmodulen; en lösning som var skalbar. Detta innebar att den nya modulen skulle kunna användas i flera kameramodeller med olika användarmoment och olika objektiv med varierande vikt. Användarmomentet skulle kvantifieras genom att utvärdera befintliga lösningar; de funna värdena skulle sedan användas för att finna en ny lösning. Dimensionerna på modulen skulle väljas med hänsyn till dimensionerna på de tidigare lösningarna och gränssnittet mot kamerahuset. I början av projektet utfördes en förstudie genom att titta på tidigare lösningar gjorda av FLIR för att formulera krav på produkten. De verktyg som användes för detta var MATLAB för beräkningar, SolidWorks för CAD och utrustning från verkstaden för att manuellt mäta momentet. För att börja formulera koncept gjordes en brainstorm där de första koncepten förklarades genom skisser, och senare med CAD gjorda i SolidWork. Dessa koncept beräknades på genom att använda MATLAB för att hitta rätt dimensioner och komponenter. Koncepten diskuterades genom att låta berörda parter ge feedback under planerade möten. En Pugh’s matris användes för att utvärdera koncepten emot varandra, för att välja slutkoncept. De slutgiltiga koncepten var av två olika modeller. Det ena kontrollerades genom dimensioner och stålkulor, styrda av kompressionsfjädrar, som klickade i spår i en ytterring. Det andra styrdes endast genom friktionen mellan två ytor som var i kontakt med varandra under lasten från kompressionsfjädrar, där det då inte fanns distinkta klicklägen. Avsikten var att dessa två koncept skulle ha samma moment och att de skulle vara skalbara på samma sätt; genom olika förspänning av fjädrarna i applikationen.This work was done on the rotary joint module of handheld cameras in the T-series made by the company FLIR. The rotary joint module holds the lens and controls the angle in relation to the rest of the camera. FLIR’s current solutions for the rotary joint had various module solutions for different camera models and the solutions have individual problems in quality, tolerances and durability. The current solutions differ in which components that are used, in dimensions and what torque is required by the user. The company was looking for a new solution for the rotary joint module; a solution with scalability. This means that the new module were to fit in several camera models with different torques and with lenses of different weight. The torque needed by the user would be quantified by evaluating solutions used today, where these values would be applied when finding a new solution. The dimensions of the module would be in consideration to the dimensions of the earlier solutions and to the interface between the joint and the camera. In the beginning of the project a pre study was made by looking at the current solutions made by FLIR to form requirements. The tools used for this were MATLAB for calculations, SolidWorks for CAD drawings and workshop tools for manual measurements of the torque. To start forming concepts solving the problem a brainstorm was performed where the ideas were visualized using sketches, and later CAD drawings using SolidWorks. These concepts were calculated using MATLAB to find the right dimensions and components. The concepts were discussed using meetings with interested parties, to get feedback on the work and sort out the better concepts. A Pugh’s matrix was used to evaluate the concepts against each other. The final concepts were of two different models; one controlled by dimensions and steel balls, connected to compression springs, clicking into grooves, and the other controlled merely by the friction between two surfaces provided under load from compression springs, where there were no actual click positions. The intention was that these two would have the same torque and they were scalable in the same way; by pre-tensioning the springs in the application to give different loads.
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Do, Nguyen Ba. "Modeling of Frictional Contact Conditions in Structures." Thesis, Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7123.
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This thesis explores two aspects of modeling the behavior of joint friction in structures. The first aspect deals with the accurate and efficient simulation of a simple system that incorporates the LuGre friction law. Energy transfer and dissipation in a structural joint model is the second topic of this thesis. It is hypothesized that friction could serve to pump energy from one frequency to higher frequencies where it might be dissipated more quickly. Motivation for this study stems from the need to have accurate models of high-precision space structures. Because friction at connecting joints plays a major role in the damping capacity of the structure, a good understanding of this mechanism is necessary to predict the vibratory response and enhance the energy dissipation of the structure.
Simulation results of a dynamic system with LuGre friction show that the system is relatively well-conditioned when the slip velocity is small, and ill-conditioned for large slip velocities. Furthermore, the most efficient numerical method to simulate this system is determined to be an implicit integration scheme. To study the energy transfer and dissipation, two models of a jointed structure with friction are considered. Results from the steady-state forced responses of the two structural systems indicate that friction converted low frequency, single harmonic excitation to multi-harmonic response through internal resonances. However, differences in energy dissipation results between the models show that the response of a frictional system is highly sensitive to system parameters and friction laws. Conclusions and suggestions for future research are also discussed.
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Ren, Ying. "The analysis and identification of friction joint parameters in the dynamic response of structures." Thesis, Imperial College London, 1992. http://hdl.handle.net/10044/1/8904.
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Chang, Timothy C. (Timothy Chan) 1979. "Effects of select fluids on the friction of metal-on-polyethylene joint replacement surfaces." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/30318.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.Includes bibliographical references (leaves 57-61).
Lubricants are important factors in the tribology of total joint arthroplasty (TJA) surfaces, which are primarily comprised of a polished metallic or ceramic component articulating on an Ultra-High Molecular Weight Polyethylene (PE) surface. Wear particles released from the PE surface are the primary cause of TJA failure. The human body responds to the foreign, micro- scale particles by activating a cascade of cytokine responses that ultimately leads to osteolysis and aseptic loosening. Although research in the materials selection and design of TJA components is continually advancing, one of the major intrinsic components that affect the tribological response in joints is overlooked. In particular, the properties and composition of joint fluid directly affect the fluid film and boundary lubrication of artificial prostheses. Since the characteristics of joint fluids are likely to differ from patient to patient as a result of varying disease indications, age, health, gender, and activity level, tribological behavior is also likely to vary significantly. The primary objective of this thesis is to examine the effects of variation in joint fluid composition on tribology. Due to the relative high stresses applied to the knee, the tribological effects related specifically to total knee arthroplasty (TKA) are investigated in detail. Before any joint fluid samples are examined, however, an assay capable of determining appropriate tribological properties is adapted. A unidirectional pin-on-disk (POD) tribometer is therefore selected to measure friction between PE and cobalt-chromium-molybdenum alloy (Co-Cr). Its sufficient precision, short testing time-frame and low cost enables rapid evaluations.
(cont.) Preliminary friction data collected on fluids such as distilled water and bovine serum are used as standards and controls against lubricants in subsequent tests. From this data, the contributions to friction of boundary and fluid-film lubrication in PE on Co-Cr POD systems are discussed. Analysis of these friction properties in conjunction with previously published differences in wear between water and bovine serum leads to a rejection of a hypothesis directly correlating friction and wear. However, since ultimately wear is the important factor in the failure mechanism of TJA, an indirect relationship between friction and wear is investigated and proposed. Friction is then recorded using joint fluids as the lubricant and compared to the standards. Analysis of the joint fluid data demonstrates significance in frictional behavior, indicating that compositional properties affect friction. Moreover, examination of the data reveals large variation in joint fluids. Comparisons of the data to standard lubricants exhibit the potential for large variations in wear among joint fluids.
by Timothy C. Chang.
S.M.
14
Hedström, Gabriel. "Structural and tribological analysis of harvester crane joint." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-69653.
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Grease-lubricated journal bearings are widely used in heavy duty applications, such as construction equipment, agriculture- and forest machines. The main purpose of the grease-lubricated journal bearing is solely to create sustainable rotation of a given application. However, purpose seldom decides complexity of journal bearing design. Depending on application, parameters such as Load , Material and Lubrication immensely increase complexity of the design. Tribology is a highly interdisciplinary subject, which requires knowledge concerning physics, chemistry, metallurgy and solid mechanics. Tribological aspects of a design are frequently regarded as irrelevant. Tribological issues are commonly enlightened in combination with structural design weaknesses. The main aim of the thesis was to analyze two cylinder joints found in a Komatsu Forest 951 crane and establish root cause to the structural and tribological issues. Outline of the approach was divided into three main targets: 1. Investigate mechanical and tribological aspects of the crane design. 2. Understand how these aspects influence the life time of the bearings. 3. Summarize the analysis and suggest improvements based on the discovery. Fundamental structural and tribological design guidelines regarding grease-lubricated journal bearings have been presented in this thesis. Damaged components such as cylinders, pins and journal bearings have been examined at Komatsu Forest’s factory in Umeå. Further, a scanning electron microscopy study has been done at Luleå University of Technology, to determine predominant wear mechanisms in the harvester crane joints. A non-linear finite element model of the crane has been designed to represent pressure distribution in the contact between bearing and pin. The finite element analysis gives a good approximation of the contact but leaves room for further refinements. Temperatures, in the contacts, have not been identified and will be measured outside the time frame of the master’s thesis. Design changes, with respect to discovered structural and tribological issues have been suggested. The suggested improvements can potentially increase the life time of lift cylinders, pins and journal bearings.
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Sun, Tianzhu. "Residual stress development in AA7050 stationary shoulder friction stir welds." Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/residual-stress-development-in-aa7050-stationary-shoulder-friction-stir-welds(9c4066c2-f3cf-4a3d-bfd0-3f6842de1251).html.
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Stationary shoulder friction stir welding (SSFSW) is a recently developed variant of conventional friction stir welding (FSW). Recent studies have shown that SSFSW can join high strength aluminum alloys with improved mechanical strength and reduced distortion as a result of a narrower and more uniform thermal profile. However, a lack of understanding on the residual stress development in the SSFSW process makes it difficult to assess the structural integrity and delays a widespread application of this technique to industry. This dissertation reports the first systematic investigation into the development of residual stress induced by the SSFSW process and comparison between SSFSW and FSW techniques. Welding residual stresses were experimentally assessed with both the contour method and neutron diffraction. The weld microstructure and hardness distributions were characterized and used to understand the formation of residual stresses during the welding process. The results have shown that for both FSW and SSFSW processes, the residual stresses distribute in the form of âMâ shaped profile while the magnitude and size of tensile residual stress zone were effectively reduced (by 25%) in the SSFSW process, even when input welding power was identical. Other improvements seen in the SSFSW process include a reduction in the heat affected zone width, an increase in the minimum hardness and a more uniform through-thickness microstructure and hardness. The dominating welding process parameter affecting the welding residual stress was travel speed as compared to rotation speed and tool downforce. With a 90 degree shaped shoulder, SSFSW has been shown to produce defect-free T-sections by dual fillet welds. For these components, an asymmetrical distribution of microstructure, hardness and residual stresses were found as a consequence of the thermal effects induced by second weld on the first weld. The material softening caused by the first weld provides the potential of utilizing a lower heat input on the subsequent pass so as to optimize the welding parameters.
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Martins, Jorge Miguel Ribeiro. "Joining copper to stainless steel by friction stir diffusion process." Master's thesis, Faculdade de Ciências e Tecnologia, 2013. http://hdl.handle.net/10362/10723.
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Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do Grau de Mestre em
Engenharia MecânicaOne of the major trends in welding and joining technology is to join dissimilar materials taking advantage of individual materials properties. Among these, copper to stainless steel joining has significant industrial applications and importance where e.g. the highest electrical and thermal conductivities are required to engineering materials associated to good corrosion resistance. However, joining these materials is difficult due to their very different chemical composition and thermo-physical properties. Additionally, they easily form intermetallic phases that deteriorate the mechanical strength of the joint. Thus investigating the feasibility of applying alternative processing technologies is relevant. Solid state processes have been investigated for this application, namely friction stir welding. Recently, a variant has been exploited where local diffusion is the fundamental joining mechanism triggered by friction stir. The advantage of friction stir diffusion process is the minimal detrimental effect on both materials, preventing some critical identified problems. Since this process is not well developed, this thesis aimed to study friction stir diffusion process (FSDP) to join copper to stainless steel. Lap joints were produced varying processing parameters, namely, rotation and travel speeds and axial forging force. The effect of processing parameters on the width of effective joining was studied, as well the joints characterization for mechanical resistance properties and microstructural features at the interface. The thermo-mechanical conditions and time during the FSDP resulted in an interface with diffusion between both materials below 3 μm. The shear strength of the lap joints depends on the material thickness involved, but joining efficiencies up to 73.8 % were achieved.
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Olofsson, Johanna. "Friction and Wear Mechanisms of Ceramic Surfaces : With Applications to Micro Motors and Hip Joint Replacements." Doctoral thesis, Uppsala universitet, Institutionen för teknikvetenskaper, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-156801.
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Surfaces exposed to wear always transform and typically a layer of new structure and composition is formed. This layer, often called tribofilm, changes the friction and wear properties. Tribofilms formed on ceramic surfaces may consist of products from chemical reactions between the materials in contact and the environment or consist of compacted wear debris. In this thesis, focus has been to understand the friction and wear mechanisms of ceramic surfaces, as well as acquiring knowledge about the properties of the new surfaces created during wear. Ultimately, this understanding can be used to develop ceramic systems offering high or low friction, while the material loss in both cases should be minimised. Such ceramics could improve numerous tribological systems and applications, out of which ultrasonic motors, low-friction ceramic coatings and hip joint replacements have been treated in this thesis. Friction and wear tests, and subsequently various surface analyses have been essential for the knowledge about the friction, wear and tribofilm formation. For ultrasonic motors of the studied type, the highest driving force is achieved when the friction is high between the alumina components in the friction drive system. The highest friction was here accomplished with a thick tribofilm on the surfaces. The formation of such tribofilms was favoured by dry conditions, and using an initially rough surface, which increased the initial generation of wear debris. In a detailed investigation of the importance of microtopography on tribofilm formation and friction behaviour, a low-friction, PVD coating of TaC/a-C was studied. This coating showed a very low, stable friction. High sensitivity to the microtopography was demonstrated, smooth coating exhibited a faster build-up of a dense tribofilm of fine ground material on the counter steel surface and subsequently a faster running in and friction decrease. The life span for total hip joint replacements can be prolonged by minimising the wear particles that cause inflammation and subsequent implant loosening. In this work coatings of amorphous/nanocrystalline silicon nitride have shown low wear rate, and hence produce a minimum of wear particles. Furthermore, these particles that are expected to resorb in vivo. This system therefore has potential to reduce problems with inflammation and osteolysis connected to wear particles.
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Fox-Kemper, Baylor 1973. "Eddies and friction : removal of vorticity from the wind-driven gyre." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/39405.
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Thesis (Ph. D.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences and the Woods Hole Oceanographic Institution), 2003.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 299-310).
Inertial terms dominate the single-gyre ocean model and prevent western-intensification when the viscosity is small. This occurs long before the oceanically-appropriate parameter range. It is demonstrated here that the circulation is controlled if a mechanism for ultimate removal of vorticity exists, even if it is active only in a narrow region near the boundary. Vorticity removal is modeled here as a viscosity enhanced very near the solid boundaries to roughly parameterize missing boundary physics like topographic interaction and three dimensional turbulence over the shelf. This boundary-enhanced viscosity allows western-intensified mean flows even when the inertial boundary width is much wider than the frictional region because eddies flux vorticity from within the interior streamlines to the frictional region for removal. Using boundary-enhanced viscosity, western-intensified calculations are possible with lower interior viscosity than in previous studies. Interesting behaviors result: a boundary-layer balance novel to the model, calculations with promise for eddy param- eterization, eddy-driven gyres rotating opposite the wind, and temporal complexity including basin resonances.
(cont.) I also demonstrate that multiple-gyre calculations have weaker mean circulation than single-gyres with the same viscosity and subtropical forcing. Despite traditional understanding, almost no inter-gyre flux occurs if no-slip boundary conditions are used. The inter-gyre eddy flux is in control only with exactly symmetric gyres and free slip boundaries. Even without the inter-gyre flux, the multiple-gyre circulation is weak because of sinuous instabilities on the jet which are not present in the single-gyre model. These modes efficiently flux vorticity to the boundary and reduce the circulation without an inter-gyre flux, postponing inertial domination to much smaller viscosities.
by Baylor Fix-Kemper.
Ph.D.
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Ghods, Farzad. "Finite element modeling of single shear fastener joint specimens: a study of clamp-up, friction and plasticity effects." Thesis, Wichita State University, 2011. http://hdl.handle.net/10057/5168.
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A three dimensional solid finite element model was assembled to investigate the influence of parameters such as friction coefficient, fastener preload and material plasticity on the structural response of Hi-Lok bolted single-lap joints under remote tension/compression loading. Three different specimen types which produce nominal load transfer levels of 6%, 30% and 50% have been investigated. The effects of these parameters where characterized in terms of load transfer, fastener rotation, and stress concentration factor. Friction coefficient has been varied from 0 to 1.25 and the fastener preloads of 1.35lbs, 13.5lbs and 135lbs were assigned for different simulations. Furthermore, constant amplitude load cycles of 15, 20, 30 and 40Ksi were applied in different FE analysis. Results of elastic and isotropic hardening based elastic-plastic material models have been compared and effects of plasticity have been explored.
The analysis results indicate that friction coefficient is the most important parameter and friction has a great influence on load transfer, stress concentration and fastener rotation, for all loading conditions, and for both elastic and elastic-plastic material models. Friction, which is affected by both friction coefficient and clamp-up force, has the most influence on load transfer and stress concentration factor at lower remote loads and smaller amount of load transfer. Plasticity which is more prevalent at high remote loads reduces load transfer and stress concentration factors, especially during tension.Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering.
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Iyer, A. Vishwanath. "Effect of tool shoulder profile on the axial force and joint strength of friction stir spot welded aluminum alloys." Thesis, Wichita State University, 2012. http://hdl.handle.net/10057/5599.
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In many industries, the use of articulated robots has proven to be an efficient and beneficial way in which to reduce manufacturing costs, e.g., by increasing productivity through automating repetitive processes. However, because of their limited payload capacity, articulated robotic arms have found limited use in processes like friction stir welding (FSW), which require precise position control under relatively high process loads. This limitation in payload has restricted the use of robots to low-loading operations in manufacturing. One way to increase the usefulness of robots for FSW is to reduce the process forces to which they are required to react. One potential area of robotic application is friction stir spot welding (FSSW), a variant of FSW. FSSW is typically used to join two overlapped sheet metal workpieces. A significant portion of the process cycle of FSSW is the plunge cycle. The axial (z) load generated in the process can be substantial depending on selection of the weld tool and process parameters. This study is a continuation of the work performed in the first phase on a gantry-style FSW machine to analyze the process feedback forces, mainly the axial force. In the first phase of this project, the level of the axial force required to produce FSSW in an AA2024-T3 bare aluminum sheet, was significantly lowered by reducing the weld tool shoulder diameter from 0.4 inches (10.2 mm) to 0.3 inches (7.6 mm).
Results from the second phase of this project included the influence of three weld tool shoulder geometries, namely concave, convex scrolls, and flat scrolls, on the axial force, mechanical strength (shear strength), and macrostructural properties produced between AA7075-T6 (typical of stringers) and AA2024-T3 (typical of an aircraft skin). The effects of process parameters were analyzed using the design of experiments (DOE) approach. The results of this research suggest that basic and swept FSSW of dissimilar aerospace alloys can be successfully performed at an axial force that is suitable for robotic applications.Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering
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Reardon-Smith, Mardi Jane. "Forces and Frictions of Belonging: Land, People and Changing Environments in Cape York, Australia." Thesis, The University of Sydney, 2021. https://hdl.handle.net/2123/25462.
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This thesis is an anthropological study of people involved in land management in Cape York Peninsula, Australia. It investigates how this diversity of people come to belong in meaningful ways, examining the multi-layered and intercultural situations in which people form, maintain and transform relationships in changing environments. Contemporary Cape York is a site of complex land-tenure arrangements, political struggles and environmental change. Based on 14 months of field research with settler-descended graziers, Aboriginal traditional owners and Queensland Parks and Wildlife Service rangers the thesis investigates how these diverse groups of people articulate, value and experience their social, cultural and practical connections to land. By attending to non-Indigenous people and Aboriginal traditional owners, the analysis grapples with the friction of intercultural engagement in the region. A key argument is that social and cultural differences between groups of people are not fixed or stable. Instead, through various kinds of interactions, social differentiation and cultural norms and practices are re-worked, making an indeterminate space of intercultural encounter that can result in both new forms of difference and inequality, and, importantly, partially shared environmental knowledges, practices and ways of relating to land. Developing the analytical concepts of intercultural mediation and friction, this thesis thus examines how forms of belonging and difference are enacted, experienced and transformed relationally. It contends that relationships to land and forms of belonging are mediated by property rights, manual labour, conservation initiatives, bureaucratic interventions, cattle, fire, seasonality, climate change and invasive species. In the interactions and contingent collaborations among people as well as between people and more-than-human forces, meaningful relationships to land are continually co-produced and reworked. This ethnographic study contributes to a growing body of scholarly work in anthropology and related disciplines that attend to the details of intercultural and multispecies relationships, and to questions of human and non-human belonging in settler-colonial states.
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Niglis, Anton, and Per Öberg. "Modelling High-Fidelity Robot Dynamics." Thesis, Linköpings universitet, Reglerteknik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-119640.
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The field of robotics is in continuous development. Driving forces for the development are higher demands on robot accuracy and being more cost effective in the development process. To reduce costs, product development is moving towards virtual prototyping to enable early analysis and testing. This process demands realistic models and modelling is therefore of utmost importance. In the process of modelling high fidelity robot dynamics many different physical aspects have to be taken into account. Phenomena studied in this thesis stretch from where to introduce flexibilities, mechanical and dynamical coupling effects, and how to describe friction. By using a bottom up approach the effects are analysed individually to evaluate their contribution both to accuracy and computationalcomplexity. A strategy for how to model a flexible parallel linkage manipulator by introducing some crucial simplifications is presented. The elastic parameters are identified using a frequency domain identification algorithm developed in [Wernholt, 2007] and shows that the presented method works well up to a certain level of fidelity. Friction is modelled using empirically derived static and dynamic models. Evaluation of accuracy is conducted through identification of friction models for a real manipulator and it is seen that to capture all existing phenomena in low velocities a dynamic model is needed. It is also seen that friction characteristics vary with temperature and a Kalman filter is suggested to adaptively estimate friction parameters. Finally an implementation of a flexible manipulator model using the software MapleSim is presented. The tool severely simplifies the process of modelling manipulators and enables for export to other environment such as simulation, optimization and control.
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Peterson, Rebecca Hilary. "Friction Bit Joining of Dissimilar Combinations of DP 980 Steel and AA 7075." BYU ScholarsArchive, 2015. https://scholarsarchive.byu.edu/etd/6030.
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Friction Bit Joining (FBJ) is a new technology that allows lightweight metals to be joined to advanced high-strength steels (AHSS). Joining of dissimilar metals is especially beneficial to the automotive industry because of the desire to use materials such as aluminum and AHSS in order to reduce weight and increase fuel efficiency. In this study, FBJ was used to join 7075 aluminum and DP980 ultra-high-strength steel. FBJ is a two-stage process using a consumable bit. In the first stage, the bit cuts through the top material (aluminum), and in the second stage the bit is friction welded to the base material (steel). The purpose of the research was to examine the impact a solid head bit design would have on joint strength, manufacturability, and ease of automation. The solid head design was driven externally. This design was compared to a previous internally driven head design. Joint strength was assessed according to an automotive standard established by Honda. Joints were mechanically tested in lap-shear tension, cross-tension, and peel configurations. Joints were also fatigue tested, cycling between loads of 100 N and 750 N. The failure modes that joints could experience during testing include: head, nugget, material, or interfacial failure. All tested specimens in this research experienced interfacial failure. Welds were also created and examined under a microscope in order to validate a simulation model of the FBJ process. The simulation model predicted a similar weld shape and bond length with 5 percent accuracy. Joints made with external bits demonstrated comparable joint strength to internal bits in lap-shear tension and cross-tension testing. Only external bits were tested after lap-shear tension, because it was determined that external bits would perform comparably to internal bits. Joints made with external bits also exceeded the standard for failure during fatigue testing. Peel tested specimens did not meet the required strength for the automotive standard. Examining specimens under a microscope revealed micro-cracks in the weld. These defects have been shown to decrease joint strength. Joint strength, especially during peel testing, could be increased by reducing the presence of micro-cracks. The external bit design is an improvement from the internal bits for manufacturability and ability to be automated, because of the less-expensive processes used to form the bit heads and the design that lends to ease of alignment.
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Sheedy, Patrick. "Alleviating concrete placement issues due to congestion of reinforcement in post-tensioned haunch-slab bridges." Thesis, Kansas State University, 2011. http://hdl.handle.net/2097/13251.
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Master of ScienceDepartment of Civil Engineering
Robert Peterman
A flowable hybrid concrete mix with a spread of 17 to 20 inches was created with a superplasticizer to be used in post-tension haunch-slab (PTHS) bridges where rebar congestion is heaviest. The mix would allow for proper concrete consolidation. A conventional concrete mix with a slump of three to four inches was also created to be placed on top of the hybrid mix. The conventional mix would be used to create a sloping surface on the top of the concrete. The two mixes could be combined in the PTHS bridge deck and act as one monolithic specimen. Standard concrete tests such as compressive strength, tensile strength, modulus of elasticity, permeability, freeze/thaw resistance, and coefficient of thermal expansion were determined for the mixes and compared. Core blocks were cast using both mixes and composite cores were drilled. The cores were tested and their composite split-tensile strengths were compared to the split-tensile strengths of cylinders made from the respective mixes. A third concrete mix was made by increasing the superplasticizer dosage in the hybrid concrete mix to create a self-consolidating concrete (SCC) mix with a 24-inch spread. The SCC mix was created as a worst-case scenario and used in the determination of shear friction. Eighty-four push-off shear friction specimens were cast using the SCC mix. Joint conditions for the specimens included uncracked, pre-cracked, and cold-joints. Uncracked and pre-cracked specimens used both epoxy- and non-epoxy-coated shear stirrups. Cold-joint specimens used both the SCC mix and the conventional concrete mix. Joint-conditions of the cold-joint specimens included a one-hour cast time, a seven-day joint with a clean shear interface, and a seven-day joint with an oiled shear interface. The shear friction specimens were tested using a pure shear method and their results were compared to the current American Concrete Institute code equation.
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Gilbert, Gregory S. Jr. "Scaling a Prismatic Revolute Joint (Pr) Manipulator Using Similitude and Buckingham Pi Techniques." Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/36599.
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This thesis presents scaling methods for sizing a prototype micro prismatic revolute (PR) manipulator actuated by permanent magnet (PM) direct current (d.c.) gearmotors. Dimensional analysis was the principle tool used in this investigation, and addressed the problems of scaling a trajectory planner, control law, and gearmotors that exhibit internal nonlinear friction. Similitude methods were used to develop a scaleable two degree-of-freedom trajectory planner from a third order polynomial. Scaling laws were developed from Buckingham's Pi theorem to facilitate the selection process of gearmotors. Nondimensional, nonlinear, differential equations were developed to describe viscous, Coulomb and static friction in comparative PM d.c. motors. From the insights gained through dimensional analysis, a scaleable controller based on the computed torque method was developed and implemented with a cubic trajectory planner. Model and prototype PR manipulator systems were simulated using a hybrid Matlab/Simulink simulation scheme. Experimental systems were constructed with dissimilar model and prototype motors. Control was provided by an AT class PC equipped with 12-bit A/D, D/A cards operating at a sample rate of 100 Hz. The control algorithm was written in Borland 3.1 C for DOS. Results from the experimental testing showed excellent agreement between the test and simulated data and verified the viability of the scaling laws. The techniques presented in this thesis are expected to be applicable to any application that involves scaling PM d.c. micro gearmotors that have significant internal friction terms. These simple, practical tools should be especially beneficial to designers of micro robotic systems.Master of Science
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Faivre, Jimmy. "Développement de liquides synoviaux synthétiques bioinspirés." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSE1230/document.
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La bioinspiration consiste à analyser les systèmes naturels qui se sont adaptés parfaitement à leurs environnements pour développer des solutions ingénieuses. Ce projet de thèse aborde la thématique de la lubrification articulaire dans le but de développer un traitement contre l'ostéoarthrite (OA). Nous nous sommes inspirés des articulations synoviales, systèmes tribologiques très performants grâce aux interactions synergiques entre la structure unique du cartilage et les molécules lubrifiantes (ML) du fluide synovial (SF). Cependant, lors de l'OA des mécanismes inflammatoires et d'érosion mécanique aboutissent à la dégénérescence progressive du cartilage et la dégradation spécifique des ML du SF (aggrécane et lubricine). Des mimes des ML du SF ont été synthétisés reprenant leur structure particulière dite en écouvillon moléculaire (BB), structure responsable de la lubrification. Des tests tribologiques (SFA, tribomètre) ont montré que les BB garantissent à la fois une faible friction et une résistance à l'usure sur des surfaces dures de mica. Ceci est dû à la présence, sur nos EM, de groupements d'ancrage spécifiques assurant l’adsorption sur la surface de mica et à la formation d'enchevêtrements et d’interactions intermoléculaires avec l'acide hyaluronique de haut poids moléculaire, composant essentiel du SF. Des mimes de cartilage à base d'hydrogels de chitosane multicouches ont été également réalisés reprenant les principales propriétés architecturales du cartilage. En combinaison avec nos EM, ces hydrogels, matériaux poroélastiques fragiles, sont capables d’être lubrifiés avec une friction dans la gamme physiologique et une nette amélioration de leur usureBioinspiration consists in the design of materials inspired by biological systems which have developed ingenious solutions to suit their environment. This project deals with bioinspiration for joint lubrication and in particular for the development of treatments for patients suffering from osteoarthritis (OA). To do so, we took our inspiration from joints which are amongst the most efficient aqueous tribological systems. Their unique properties arise from the complex synergistic interactions between cartilage structure and the lubricant macromolecules of the synovial fluid (SF). However, during OA, inflammatory mechanisms as long as mechanical erosion result in the degeneration of cartilage and lubricant macromolecules (aggrecan and lubricin). Polymeric mimes of the SF have been synthesized based on the bottle-brush (BB) architecture of LUB and AGG which is responsible for the joint lubrication. Tribological tests (SFA, tribometer) showed that BB polymers provided mica surfaces with a low friction and a wear protection up to several megapascals, typically in the range of natural joints. This wear protection was essentially due to the incorporation of anchoring groups specific to mica tribopairs on the BB polymers and the intermolecular bridging and entanglements emerging between BB polymers and high molecular weight HA, another main SF component. Cartilage mimes composed of multilayered chitosan hydrogels were designed to mimic the basic features of cartilage. Along with our BB polymers, the hydrogels, which are poroelastic and fragile materials, provided a low friction and a great decrease of wear
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Atwood, Lorne Steele. "Friction Bit Joining of Dissimilar Combinations of GADP 1180 Steel and AA 7085 – T76 Aluminum." BYU ScholarsArchive, 2016. https://scholarsarchive.byu.edu/etd/6400.
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Friction Bit Joining (FBJ) is a method used to join lightweight metals to advanced high-strength steels (AHSS). The automotive industry is experiencing pressure to improve fuel efficiency in their vehicles. The use of AHSS and aluminum will reduce vehicle weight which will assist in reducing fuel consumption. Previous research achieved joint strengths well above that which was required in three out of the four standard joint strength tests using DP980 AHSS and 7075 aluminum. The joints were mechanically tested and passed the lap-shear tension, cross-tension, and fatigue cycling tests. The t-peel test configuration never passed the minimum requirements. The purpose of continuing research was to increase the joint strength using FBJ to join the aluminum and AHSS the automotive industry desires to use specifically in the t-peel test. In this study FBJ was used to join 7085 aluminum and GADP1180 AHSS. The galvanic coating on the AHSS and its increased strength with the different aluminum alloy required that all the tests be re-evaluated and proven to pass the standard tests. FBJ is a two-step process that uses a consumable bit. In the first step the welding machine spins the bit to cut through the aluminum, and the second step applies pressure to the bit as it comes in contact with the AHSS to create a friction weld.
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Ripard, Valentin. "Tribological characterization of greased drive-shaft : Evaluation of constant velocity joint durability." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEI083.
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La modification des besoins clients amène les constructeurs automobiles vers de nouveaux challenges. En effet, en Europe notamment, les véhicules rehaussés type SUV (Sport Utility Vehicle) sont de plus en plus populaires. Or, ces véhicules impliquent une modification de l’implantation des transmissions mécaniques. Ces dernières possèdent alors une angularité plus élevée que pour des berlines par exemple. Cette modification a alors 2 impacts : l’augmentation du glissement dans la transmission mais aussi son influence sur la durabilité des composants. La modification de l’angularité est un des enjeux majeurs de ces dernières années pour les constructeurs. En effet, son augmentation influe sur le rendement des transmissions. Or, avec des normes environnementales de plus en plus contraignantes mais aussi une hausse du prix du pétrole, cet axe d’amélioration représente un facteur d’attractivité pour les constructeurs. De plus, la durabilité des organes reste primordiale. Une voiture se doit d’avoir une transmission fiable ne nécessitant, pour le cas des joints homocinétiques, aucun entretien durant la vie du véhicule. C’est sur cet axe que les travaux suivants ont majoritairement porté. L’objectif de ce manuscrit est de comprendre le mécanisme d’usure des joints homocinétiques côté boîte dits tripode. Une analyse de la cinématique a d’abord été menée afin de reproduire les contacts sur des bancs d’essais. Elle s’est appuyée sur des données issues de la bibliographie mais aussi une simulation de la dynamique des solides. De plus, la création en fabrication additive d’un banc d’observation a permis d’évaluer de façon expérimentale le glissement dans cet organe de transmission. Par la suite, une caractérisation des graisses de transmission utilisée dans le groupe PSA a été effectuée afin de connaître les coefficients de frottement induisant le niveau de vibrations de la transmission pour un client. Ces derniers sont essentiels pour juger l’efficacité énergétique de l’organe. Enfin, une étude de l’usure a permis d’expliquer les mécanismes de défaillance de la lubrification avec des graisses proposant des propriétés mécaniques. Cela permet alors de comprendre les données-clés afin de choisir une graisse assurant une durabilité maximale des organes de transmission et remplissant alors un des deux enjeux cités ci-dessus. Pour le futur, un banc de caractérisation des lubrifiants spécialement conçu pour les contacts de joint tripode a été créé. Il permettra ainsi de caractériser de façon plus complète les lubrifiants du futur pour cet organe essentiel d’une voitureNew customer desires are leading car manufacturers to new challenges. Indeed, enhanced vehicles like SUV (Sport Utility Vehicle) becomes more and more popular, especially in Europe. These vehicles involve some modification over the usual mechanical transmissions designs. This vehicle type has a higher angularity than sedans for example. This desire modification has 2 impacts: the increase of slipping in the transmission and its influence on the durability of the components. The angularity modification remains one of the major lines of research in recent years for car manufacturers. Its increasing influences efficiency. Indeed, this axis of improvement is attractive for manufacturers due to new environmental standards but also an increase in oil price. In addition, a car must have a reliable transmission that does not require, in the case of constant velocity joints, any maintenance during vehicle life. The following work will focus on this objective. The main goal of this manuscript is to understand the wear mechanism of the tripod constant velocity joint (CVJ). An analysis of the kinematics was first conducted to reproduce contacts on test rigs. It relied on data from the bibliography but also a simulation of solid dynamics. In addition, the design of a new observation rig using additive manufacturing made it possible to experimentally reproduce slipping in tripod. Furthermore, a characterization of greases used in Groupe PSA transmissions was performed in order to know the friction coefficients inducing the shudder level of the CVJ. These are also essential in order to judge the efficiency of the component. Finally, a wear investigation is performed to explain the possible lubrication failure mechanisms with greases proposing different mechanical behaviour. This approaches enables the transmission designer to choose a grease ensuring maximum durability of transmission components. Looking ahead, a lubricant characterization rig specially designed for tripod joint contacts has been designed. It will thus allow a more complete characterization of further lubricants to this essential vehicle component
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Wirström, Fredrik. "Development and Validation of Threaded Fastener Test Rig." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-74502.
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Threaded fastener is one of the most common ways to join components. Having a method to test threaded fasteners is key when designing a joint and even more a nutrunner. A joint is often tightened by a torque applied on the head. The applied torque is equal to three quantities in the joint, the thread torque, the underhead torque and the clamp force. To measure these quantities are the propose of a friction test rig. A test rig was built last year to be able to do that in a flexible and effective way. But the test rig built last year does not have the possibility to measure the underhead torque. A new transducer is constructed to add that possibility. The transducer is constructed by using methods such as concept generation, strength calculations, FEM simulations and a comparison of sensors are made. An easy way to change the stiffness is also investigated but no possible solution could be found. Some modifications and trims are also done on the test rig and also a comparison with the older BLM rig. A validation is made of how good the rig perform is also done. The results shows in favour for the FTR but precise results is not possible to determine.
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Bartošík, Jan. "Vliv velikosti hlavice na procesy tření a mazání v TEP kyčle." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2015. http://www.nusl.cz/ntk/nusl-231946.
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This diploma thesis concerns itself with the experimental study of friction and lubrication in the artificial hip joint depending on the head size. Measurements were made in a hip joint simulator based on the principle of pendulum. For the friction measurements artificial joints, made from three material combinations and two diameters, from two companies were used. The measurements show that the material combination has a more significant effect to friction coefficient than the head size. Using a bigger head size shows a decrease in friction coefficient for all material combinations when compared to a smaller head size. For the measurement of lubrication film the colorimetric interferometry was applied. A metal-on-glass contact pair was used, where the glass cups were made according to the real measurements of the joint cups. Four types of hip replacements with diameters of 28 and 36 mm with two different diametral clearance were measured during a constant motion of 210 seconds. Measurements show, that the lubrication film in the hip joint with a small diametral clearance increases very fast over the 800 nm value. Contact surfaces in the hip joint with a large diametral clearance aren’t separated by the lubrication film, resulting in a damage of the chromium coating in cup. A thick lubrication film results in a higher friction coefficient, when compared with hip joints with a very thin or no lubrication film.
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Ehmaida, Mutyaa M. "Friction and lubrication behaviour of hip resurfacing metal-on-metal and ZTA ceramic on CFR peek implants with various diameters and clearances : friction and lubrication behaviour of hip resurfacing Co-Cr-Mo and zirconia toughened alumina ceramic heads against carbon fibre reinforced poly-ether-ether-ketone cups with various diameters and clearances have been investigated using serum-based lubricants." Thesis, University of Bradford, 2012. http://hdl.handle.net/10454/5665.
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Total hip joint prostheses made of CoCrMo heads versus ultra high molecular weight polyethylene (UHMWPE) cups have a limited lifetime, mainly due to the wear of the UHMWPE cups as a result of high friction between the articulating surfaces leading to osteolysis and implant loosening with revision surgery becoming inevitable in more active patients. Tribology plays an important role in developing the design, minimizing wear and reducing friction of hip joint prostheses in order to improve their long-term performance, with good lubricating properties. Metal-on-metal hip resurfacing prostheses have shown significantly lower wear rates compared with conventional metal-on-polyethylene implants and thus osteolysis is potentially reduced leading to increased lifetime of the prosthesis. Nevertheless, excessive wear of metal-on-metal joints leads to metal ion release, causing pseudo-tumours and osteolysis. An alternative approach to such bearings is the use of newly developed carbon fiber-reinforced poly-ether-ether-ketone (CFR PEEK) acetabular cups articulating against ceramic femoral heads due to their better wear resistance compared to UHMWPE. In this study, therefore, friction and lubrication properties of large diameter, as cast, Co-Cr-Mo metal-on-metal hip resurfacing implants with various diameters and clearances have been investigated and compared to those of the newly developed zirconia toughened alumina (ZTA) ceramic femoral heads articulating against carbon fiber reinforced poly-ether-ether-ketone (CFR PEEK) acetabular cups with different diameters and clearances. Friction hip simulator was used to measure frictional torque and then friction factors were calculated along with Sommerfeld numbers leading to Stribeck analysis and hence the lubricating mode was also investigated. This involved using lubricants based on pure bovine serum (BS) and diluted bovine serum (25 vol. %BS+75 vol. %distilled water) with and without carboxymethyl cellulose (CMC) (as gelling agent). Standard Rheometer was used to measure lubricant viscosity ranged from 0.0014 to 0.236 Pas at a shear rate of 3000 . Pure bovine serum, diluted bovine serum without CMC and with CMC (25BS+75DW+0.5gCMC and +1gCMC) showed pseudoplastic flow behaviour up to shear rate of ~139 s⁻¹ above which a Newtonian flow with significant increase in shear stress was observed. The viscosity flow curves for the 25BS+75DW+2gCMC, +3.5gCMC and +5gCMC showed only shear thinning up to a shear rate of 3000 . The shear rate application modified the flow behaviour of bovine serum from a pseudoplastic to a Newtonian flow depending on its purity and CMC content. This will cause a different frictional behaviour depending on joint diameter and clearance, as seen in this work. The experimental data were compared with theoretical iv predictions of the lubricating regimes by calculating theoretical film thickness and lambda ratio. The metal-on-metal Biomet ReCaps showed similar trends of Stribeck curves, i.e. friction factors decreased from ~0.12 to ~0.05 as Sommerfeld numbers increased in the range of viscosities ~0.001-0.04Pas indicating mixed lubrication regimes above which the friction factor increased to ~0.13 at a viscosity of 0.236Pas. The Stribeck analyses suggested mixed lubrication as the dominant mode with the lowest friction factor in the range ~0.09 - ~0.05 at the physiological viscosities of ~0.01 to ~0.04 Pas and that such joints can be used for more active patients as compared to the conventional total hip replacement joints with 28mm diameter. The Stribeck curves for all ZTA ceramic-on-CFR PEEK components illustrated a similar trend with BS fluids showing higher friction factors (in the range 0.22-0.13) than the diluted BS+CMC fluids (in the range 0.24-0.05). The friction tests revealed boundary-mixed lubrication regimes for the ZTA ceramic-on-CFR-PEEK joints. The results, so far, are promising and suggest clearly that the newly developed ZTA ceramic femoral heads articulating against CFR PEEK cups have similar friction and lubrication behaviour at optimum clearances to those of currently used metal-onmetal hip resurfacing implants at the range of viscosities 0.00612 to 0.155Pas. These results clearly suggest that the ZTA ceramic-on-CFR-PEEK joints showed low friction at the physiological viscosities of ~0.01Pas in the range ~0.1-0.05, suggesting that these novel joints may be used as an alternative material choice for the reduction of osteolysis. The result of this investigation has suggested that the optimum clearance for the 52mm diameter MOM Biomet ReCaps could be ~170μm. However, 48 and 54mm joints showed lower friction due to clearances to be >200μm. For the 52mm ZTA ceramic-on-CFR-PEEK joints the optimum clearance seems to be ≥ 630μm radial clearance. These results suggested that increased clearance bearings have the potential to generate low friction and hence no risk of micro- or even macro-motion for the ceramic-on-CFR-PEEK joints. This study found no correlation between theoretical predictions and experimental data for all metal-onmetal and ZTA ceramic-on-CFR PEEK bearings at the physiological viscosity (0.0127Pas). However, at lubricant viscosity of 0.00157Pas, the theoretical prediction of lubrication regime correlated well with the experimental data, both illustrating boundary lubrication. As expected, a decrease in viscosity resulted decrease in the film thickness.
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Balounová, Hana. "Studium tření náhrad kyčelního kloubu." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2013. http://www.nusl.cz/ntk/nusl-230585.
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Diploma thesis deals with analysis of coefficient of friction in total hip prosthesis for several materials bearing with presence of bovine serum as substitute of synovial fluid occurred in natural joint. Behavior of coefficient of friction is observed on Mini Traction Machine. Results are plotted at graphs representing dependence of coefficient of friction on time. There are described effects of several kinematic conditions, the influence of used material and the effect of the method of contact lubrication. The experiments analyze how the formation of lubricant film with a layer of adsorbed protein affects coefficient of friction.
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Crudu, Monica. "Étude expérimentale et numérique des joints hydrauliques." Thesis, Poitiers, 2012. http://www.theses.fr/2012POIT2283/document.
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Ce travail est une contribution à l'étude du comportement des joints en translation. Un modèle numérique, basé sur la théorie inverse, est développé pour en prédire les performances. La principale contribution consiste dans le traitement des effets hydrodynamiques liés à la région d'entrée du contact. Les résultats numériques sont ensuite validés par comparaison avec lesmesures expérimentales. Ces dernières sont obtenues sur un dispositif original, conçu et réalisé au laboratoire INOE 2000 IHP de Bucarest. Ce banc reproduit les conditions réelles de fonctionnement d'un joint hydraulique et permet de mesurer la force de frottement à pression et vitesse constantes. La comparaison des résultats numériques et expérimentaux a été effectuéepour un joint de tige en forme de "U" à des pressions de service comprises entre 4 MPa et 20 MPa et pour deux vitesses de translation. Dans un premier temps, on a idéalisé le problème en considérant que les surfaces en contact tige-joint sont lisses. Si l'épaisseur du film est supérieure à la rugosité de la tige, les résultats numériques qu'on a obtenus sont en bonne corrélation avecles résultats expérimentaux. Dans le cas contraire, le modèle doit être amélioré. Cette amélioration a été entreprise de manière originale. En effet, la théorie inverse est appliquée à la distribution de pression statique du contact obtenue à partir de la simulation par éléments finis de l'assemblage d'un joint rugueux et d'un arbre lisse. La rugosité moyenne (Ra) de la surface dujoint en contact avec la tige a été choisie égale à la rugosité moyenne mesurée du joint étudié. Les résultats ainsi obtenus améliorent sensiblement la corrélation avec les mesures eThis work is a contribution to the study of reciprocating seals behavior. A numerical model, based on the inverse hydrodynamic lubrication theory, is developed to predict their performances. The main contribution consists in the treatment of the hydrodynamic effects in the entry region of contact. The numerical results are validated by comparison with experimentalones, obtained on an original experimental device, design and conceived in the laboratory INOE 2000 IHP of Bucharest. This bench reproduces actual operating conditions of a hydraulic seal and measures the friction force at constant pressure and speed. The comparison of experimental and numerical results was carried out for a "U" type rod seal at different operating pressuresvarying from 4 MPa up to 20 MPa and for two reciprocating speeds. Initially, we idealized the problem by assuming that the surfaces in contact are smooth. The numerical results obtained are in good correlation with experimental ones if the film thickness is greater than the rod roughness. Otherwise, the model must be improved. This improvement was undertaken in an original way. The inverse lubrication theory is applied to the dry frictionless contact pressure distribution, obtained from a FEM simulation of a rough seal and a smooth rod assembly. The average roughness (Ra) of the seal surface in contact with the rod is chosen equal to the measured average roughness of the studied seal. The results obtained significantly improve the correlationwith experimental measurements. The roughness distribution on the entry region of contact appears to have an important influence on the numerical results
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Odehnal, Lukáš. "Vývoj součinitele tření a mazacího filmu v implantátu kolenní náhrady v průběhu cyklu chůze." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2021. http://www.nusl.cz/ntk/nusl-442825.
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This master´s thesis deals with the experimental analysis of the coefficient of friction and lubrication film in total knee replacement. The experiments are performed on a knee joint simulator, with an implemented module for measuring friction. To observe film formation, fluorescent microscopy is used. The experiments are mainly focused on a detailed description of the influence of parameters occurring during the gait cycle. This approach should significantly help in describing the tribological processes that occur in the total knee replacement. The results confirm previous investigations in terms of axial load, where the coefficient of friction decreases with the increasing load. In the case of lubrication film, no significant changes are observed. On the contrary, while investigating the influence of SRR, noticeable changes in film formation are observed while the coefficient of friction being unaffected. While describing the whole gait cycle, precise results are obtained only in the first half of the cycle as the second half is accompanied by the occurrence of large deviations from a rapid decrease of load. This work provides a better understanding of the field of lubrication film in total knee replacements. Moreover, thanks to the simultaneous measurement of the coefficient of friction and the observation of the contact area, it is possible to draw better conclusions than if the experiments had been carried out separately.
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Plaine, Athos Henrique. "Estudo do processo de soldagem a ponto por fricção de juntas dissimilares entre ligas de alumínio e titânio." Universidade Federal de São Carlos, 2016. https://repositorio.ufscar.br/handle/ufscar/8598.
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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Multimaterial structures between aluminum and titanium alloys are a technologically attractive field of research and their increasing use in the transportation sector for weight and emission reduction is part of the motivation of this study. The currently used techniques are either too expensive or limited in performance, especially by excessive formation of undesirable intermetallic compounds, opening opportunities for innovation in this area. Friction spot welding (FSpW), a solid state joining process recently developed by Helmholtz Zentrum Geesthacht, has proven to be one of the promising technologies for joining dissimilar materials as it involves short steps and low thermal cycles, also with the advantages of adding no weight to the structure and having geometrical compatibility to replace rivets. The present work studies the feasibility in welding AA5754-H22/Ti6Al4V and AA6181-T4/Ti6Al4V joints through FSpW. In addition, it is intended to establish the microstructure/ properties / process relationships of the resultant joints, in order to understand the formation and growth of the joining interface and its consequences on the mechanical performance. The proposed joints are produced in overlap configuration through different combinations of parameters, which were established by statistical methods involving design of experiments, and later submitted to mechanical and metallurgical characterization. The results reveal that Al/Ti dissimilar joints with high strength and reproducibility can be produced by using FSpW. The mechanical behavior of the joints presents a strong dependence on the intermetallic thickness formed at the bounding interface, identified as TiAl3. Tool rotational speed and dwell time are key process parameters in controlling the resistance of welded joints. Moreover, the bending load associated to differences in stiffness and/or thickness of the welded specimen appears as an important variable influencing the crack propagation path during shear and fatigue tests.
Estruturas multimateriais entre ligas de alumínio e titânio são um campo de estudo atrativo tecnologicamente e seu uso crescente no setor de transportes, visando à redução de peso e de emissão de gases, faz parte da motivação deste trabalho. As técnicas de soldagem utilizadas atualmente na união de tais materiais são limitadas em certos aspectos, sobretudo pela formação excessiva de compostos intermetálicos indesejáveis, abrindo caminhos para inovação nesta área. A soldagem a ponto por fricção (FSpW) tem demonstrado ser uma das alternativas promissoras na união de materiais dissimilares, destacando-se principalmente por ser um processo de poucas etapas, sem adição de peso, com baixos ciclos térmicos e compatibilidade geométrica para substituir rebites. O presente trabalho estuda a viabilidade técnica da soldagem dissimilar das juntas AA5754-H22/Ti6Al4V e AA6181-T4/Ti6Al4V através do processo FSpW. Ao mesmo tempo busca estabelecer a relação microestrutura / propriedades / processamento, a fim de compreender a possível formação e crescimento dos compostos intermetálicos na região interfacial e as suas consequências no desempenho das juntas. As juntas foram produzidas em configuração de sobreposição por diferentes combinações de parâmetros, estabelecidas por metodologias estatísticas de planejamento de experimentos, e posteriormente submetidas à caracterização mecânica e metalúrgica. Os resultados obtidos demonstram que soldas de boa qualidade e reprodutibilidade podem ser produzidas através do processo de soldagem proposto. O comportamento mecânico apresenta uma forte dependência em relação à espessura dos compostos intermetálicos formados na camada interfacial, constituída principalmente por grãos alongados de TiAl3, sendo a velocidade de rotação da ferramenta e o tempo de mistura parâmetros de processo chaves no controle da resistência das juntas soldadas. Ademais, a carga de flexão associada à diferença de rigidez e/ou espessura entre as ligas de alumínio e titânio demonstra ser uma variável importante nos ensaios de cisalhamento e fadiga, influenciando o caminho de propagação das trincas.
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Dhamari, Ruby Dharma Adji Aerospace Civil & Mechanical Engineering Australian Defence Force Academy UNSW. "The effects of water displacing corrosion preventatives on the fatigue behaviour of mechanically fastened aluminium joints." Awarded by:University of New South Wales - Australian Defence Force Academy. School of Aerospace, Civil and Mechanical Engineering, 2005. http://handle.unsw.edu.au/1959.4/38668.
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Two failure mechanisms in a double lap joint are investigated. Analytical models of net-section and gross-section failure modes are proposed to describe these mechanisms. The effects of lamping force, interference fit, maximum axial load and WDCP on fatigue performance of the joint are included in the models. The effect of WDCP is assumed to give a reduction in friction coefficient. Three types of stress reduction factors are proposed in the net-section failure model to account for these parameters. The stress reduction factors modify stress range that is used in crack growth calculation. If there are no effects of these parameters, the stress reduction factors are equal to one. Two types of fretting stress are introduced in gross-section failure model to describe either sliding contact or incipient sliding contact on faying surface. The fretting stress is combined with body stress to modify stress range. The net-section failure model predicts that fatigue life is increasing as interference fit, clamping force and friction coefficient increase. The gross-section failure model predicts that fatigue life is decreasing as clamping force and friction coefficient increase. Both models predict that fatigue life is decreasing as maximum axial load increases. Transition of the failure mode occurs earlier as friction coefficient and interference fit increase, while it is delayed as maximum axial load increases. A transition parameter is proposed to establish a relationship between the four main parameters. The transition parameter is expressed in a polynomial equation. It gives an optimum combination of the four main parameters in order to achieve relatively higher fatigue life by having gross-section failure mode. Finite element analysis and fatigue testing are performed to validate the models. The finite element and the analytical models show that stress concentration factor at the edge of the hole is decreasing as clamping force increases. The rate of decrease of stress concentration factor is increasing as friction coefficient increases. While stress concentration factor on the faying surface is increasing as clamping force and friction coefficient increase. Fatigue testing reveals that the fatigue life of the joint is in good agreement with the predicted fatigue life of the proposed models.
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Gadari, M’hammed El. "Étude expérimentale et numérique du comportement des joints à lèvre." Thesis, Poitiers, 2013. http://www.theses.fr/2013POIT2304/document.
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Cela fait environ soixante ans que l'on s'intéresse à la compréhension et à la modélisation du comportement Elastohydrodynamique (EHD) des joints à lèvres. Cependant, on peut considérer que, jusqu'à présent, leur modélisation n'a pas été totalement et rigoureusement traitée. En effet, même si de nombreuses études ont été consacrées à cette modélisation, plusieurs questions ont été soulevées et font toujours l'objet de controverses entre les chercheurs, à savoir l'impact sur les performances des joints à lèvre de l'effet des surfaces texturées de l'arbre, de la loi adoptée pour le comportement mécanique des joints à lèvre, de la démarche utilisée pour l'élaboration de la matrice de compliance (matrice de souplesse), de l'importance de supposer l'arbre lisse ou rugueux, ainsi que la valeur du rapport entre la largeur du contact et la longueur d'onde du défaut suivant la direction circonférentielle de la lèvre.Dans cette thèse, nous avons tenté d'apporter de façon rigoureuse des réponses claires et précises à toutes ces questions en élaborant et en validant un outil de simulation EHD complet pour les joints à lèvre qui tienne compte de presque tous les paramètres, à savoir une loi de comportement du matériau du joint précise, une matrice de souplesse rigoureusement validée et un arbre qui peut être lisse, rugueux et/ou texturé. De plus, un second modèle analytique est proposé. Il traite le comportement vibratoire du "squeeze film", en tenant compte de la non linéarité des caractéristiques intrinsèques du joint et du filmIt's about sixty years that we are interested in understanding and modeling the Elastohydrodynamic behavior (EHD) of rotary lip seals. However, we can consider that, until now, their modeling has not been accurately treated. Even though many studies have been devoted to this model, several questions have been raised and are still the subject of controversy among researchers, namely the parameters influencing on the rotary lip seals performance, such as: the shaft surface textured, the law adopted for the mechanical behavior of lip seals, the approach used to develop the matrix of compliance, the importance of assuming the smooth or rough shaft, and finally the ratio between the width of contact and the wavelength according the circumferential direction of the lip roughness.The main goal of this thesis is to answer rigorously these questions by developing and validating a numerical tool for EHD rotary lip seals modeling, that takes into account: the lip law behavior, the compliance matrix rigorously validated by assuming smooth shaft case, or rough and textured shaft case. In addition, an analytical approach is proposed, models the vibratory behavior of the "squeeze film". This implies a nonlinear comportment that is taken into account
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Le-Tien, Luc. "Ansätze zur entkoppelten Regelung von mechanisch gekoppelten Doppelgelenken eines DLR-Medizinroboters." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-39460.
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In dieser Arbeit werden die Methoden zur Modellierung, Identifikation, Regelung und Reibungskompensation von DLR-Medizinrobotern mit elastischen und differentiell getriebenen Gelenken vorgestellt. In der Praxis zeigt sich, dass bei den DLR-Medizinrobotern sowohl die Gelenkelastizität als auch die Gelenkverkopplung innerhalb des Doppelgelenks in der Modellierung und Regelung berücksichtigt werden muss. Daher ist es das Hauptziel dieser Arbeit, eine Regelungsstruktur zu entwickeln, die das gewünschte Folge- und Einschwingverhalten erreicht. Zur Regelung wird mit Hilfe der modalen Entkopplung ein MIMO – Zustandsregler für die Doppelgelenkstruktur eingeführt, der auf der Rückführung der antriebsseitigen Positionen und abtriebsseitigen Drehmomente sowie deren Ableitungen basiert. Für die medizinischen Anwendungen spielt die Positionsgenauigkeit, die durch die hohe Reibung stark beeinflusst wird, eine entscheidende Rolle. Um die Positioniergenauigkeit des Roboters zu verbessern, wird ein Reibungsbeobachter entwickelt, der eine passive Reibungskompensation ermöglicht. Da der Reibungsbeobachter nur den Momentenfehler, nicht aber den Positionsfehler integriert, wird diese Kompensation außer zur Positionsregelung auch zur Verbesserung der Qualität der Drehmoment- und Impedanzregelung eingesetzt. Für die gesamte Regelungsstruktur aus Zustandsregler und Reibungsbeobachter wird global asymptotische Stabilität des gesamten nichtlinearen Roboters nachgewiesen. Diese Regelungsstruktur wird derzeit in zahlreichen Anwendungen mit den DLR-Medizinrobotern benutzt und validiert.
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Nordlund, Erling. "Impact mechanics of friction joints and percussive drills." Doctoral thesis, Luleå tekniska universitet, Geoteknologi, 1986. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-16974.
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Impact-loaded conical and cylindrical friction joints are studied theoretically and experimentally. The system considered consists of a long, straight, cylindrical and linearly elastic rod which is impacted axially at one end, and which has a body attached by means of a friction joint at the opposite end. The conditions are such that the wave propagation is 1-D in the rod and can be neglected in the attached body. Slip and energy dissipation due to an impact load are determined. The theoretical results of the impact-loaded conical friction joints exhibit phenomena which sometimes have spectacular appearance. The agreement between theoretical and experimental results is fair. The influence of blow frequency and thrust on the performance of a percussive rock drill is studied theoretically. The drill considered consists of hammer, adapter, rod and bit. Two different rock drills are studied. The first is a simple drill with constant characteristic impedance throughout the drill. The second is a prototype of a high frequency percussive rock drill. The efficiency and the maximum (maximum tensile) and minimum (maximum compressive) stresses are determined. For the simple drill the average efficiency in the range from soft to hard rock is only weakly dependent on the blow frequency up to relatively high blow frequencies but strongly dependent for extremely high blow frequencies. It is also found that the maximum and minimum stresses in the drill in the range from soft to hard rock are only weakly dependent on the blow frequency up to high frequencies but strongly dependent for extremely high frequencies. The maximum stress increases and the minimum stress decreases with thrust.Godkänd; 1986; 20070108 (mlk)
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Mussa, Abdulbaset. "A study on wear characteristics of high strength steels under sliding contact." Licentiate thesis, Karlstads universitet, Institutionen för ingenjörsvetenskap och fysik (from 2013), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-77660.
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In the last decades, significant improvements regarding the design, materials and technology of rock drills have been made. Likewise, in sheet metal forming, forming tools experience very high contact pressures when processing high strength steel sheets. In both applications components operate under extremely tough contact conditions that result in an accelerated component failure. Enhancements on mechanical properties of components material subjected to extreme contact conditions are highly required in order to withstand the application loads and prevent severe wear. The present thesis was focused on understanding of machinery component damage mechanisms under severe contact conditions. A case study of worn components used in rock drilling and sheet metal cold work was carried out. Thread joints from rock drilling and punches from sheet metal pressing were selected for the investigation. For these components, sliding contact under high contact pressure is a common load condition under the components usage. Then, to understand and quantify the influence of contact parameters, load and surface quality on material performance, laboratory simulations were performed. The results were used for a comparative analysis of the typical damage mechanisms observed in the tests and the case study of the components. The case study results showed that the threaded surfaces underwent severe plastic deformation due to the high-pressure sliding contact. The microstructure beneath the worn surface was altered and surface cracks and delamination were frequently observed at the worn surface. The dominant damage mechanism found on the investigated punches was adhesive wear. Material transfer adds friction stresses at the punch surface and ultimately, with repeated punch strokes, it leads to initiation and propagation of fatigue cracks. Wear process in thread joint and punch wear was simulated using the SOFS. The worn specimens tested experimentally showed similar wear mechanisms obtained in the case study. The thread joint wear simulation showed that the total damage at the worn surface was a result of adhesive wear, plastic deformation, and initiation and propagation of fatigue cracks. In addition, the results showed that the type of motion had a significant influence on the worn volume and crack initiation, and more severe wear was observed at reciprocal motion. The punch wear simulation showed that the friction quickly increased as work material from metal sheets transferred to the disc surface. The rate of the material transfer was strongly dependent on the combination of sheet material and tool steel. Further, the present experimental simulations were applicable to characterize and predict wear of components in the application.Components used in rock drilling and sheet metal forming operate under harsh contact conditions that result in an early-life component failure. Wear and fatigue are considered as the most common damage mechanism for these components. Commonly, the service life of a component is designed based on its fatigue life. However, wear might have a significant effect on the components life too. Wear results in a surface damage that in turn may cause a fatigue crack initiation. Therefore, knowledge about wear of materials and components is a key factor in design and prediction of the lifetime of the components. In order to predict wear of a certain component, a thorough understanding of the component with regards to its material properties, application loads and working environment, and damage mechanisms is required. The overall aim of the present work was to define the typical wear mechanisms occurred on machinery components used in rock drilling and sheet metal forming. A comparative analysis of the case studies and results from performed laboratory tests simulated wear mechanisms in the applications highlighted wear mechanisms and factors influencing severity of wear in the applications. Obtained information is crucial for ranking and selection of the best material in the applications.
The presentation will will be via zoom. PhD student will together with the supervisors will be in Karlstad while the opponent is in Luleå.
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Karim, Yassine. "Caractérisation robuste de liaisons amortissantes avec dispositifs piezo-électriques pour la réduction de vibrations de structures." Phd thesis, Conservatoire national des arts et metiers - CNAM, 2013. http://tel.archives-ouvertes.fr/tel-00953330.
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L'étude présentée dans ce document a pour objet l'étude de différents modes de réduction de vibrations dans les structures avec liaisons. Le premier mode étudié se base sur la dissipation d'énergie apportée par la déformation d' éléments piézoélectriques connectés à un circuit électrique adapté. Le second mode proposé se base sur la propriété de la liaison boulonnée à changer les fréquences propres d'une structure en fonction du serrage appliqué. Cette propriété est utilisée avec plusieurs lois de contrôle du serrage afin d'éviter les plages de fréquences critiques. Ensuite une étude probabiliste est effectuée pour déterminer la robustesse de la réduction de vibrations par rapport à la variation de certains paramètres du modèle. Cette étude de robustesse est effectuée à travers des méthodes stochastiques non-intrusives, parmi lesquelles une méthode originale proposée. Elle permet une réduction de la taille du modèle stochastique à résoudre, ce qui réduit très considérablement le temps de calcul sans perte de qualité significative.
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Ericsson, Mats. "Fatigue Strength of Friction Stir Welded Joints in Aluminium." Doctoral thesis, Stockholm, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-160.
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Tilaveridis, Ioannis. "Detection of friction variations in bolted joints during tightening." Thesis, KTH, Reglerteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-213389.
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Tightening describes the process of rotating a screw with the purpose of binding two surfaces together. It is widely applied in the assembly process of structures, where bolted joints are used to connect the different parts with each other, e.g. robot arms, vehicles, aircrafts. A certain torque is applied with a tool in order to develop the desired clamping force that keeps the surfaces together. A challenge during this process is the fact that friction variations occur unexpectedly, thus increasing the risk of not achieving the necessary clamping force to ensure successful tightening. In this thesis, a diagnosis method is implemented in order to detect friction variations during highly dynamic tightening. Different detection algorithms are investigated (e.g. CUSUM, Particle Filter, Linear regression), and an approach that makes use of the torque and angle signals while estimating the clamping force is implemented. Investigations of signal noise and filtering operations during data extraction are conducted, and the signal channels are evaluated with regards to accuracy and noise bias. An approach using a sliding window is used to estimate the torque rate, and the CUSUM detection algorithm is implemented to indicate variations and provide a diagnostic report. The analysis is performed using a highly dynamic tightening strategy programmed in an electrical tightening tool, allowing for the process to be conducted in milliseconds. Investigations of the tuning parameters of the detection algorithm are also conducted, and value thresholds are identified. Finally, a statistical analysis of the system’s behaviour, as well as the influence of the operator holding the tool, is performed for evaluation.Åtdragning beskriver processen att rotera en skruv i syfte att binda två ytor ihop. Det tillämpas allmänt i monteringsprocessen av strukturer, där skruvförband används för att ansluta de olika delarna med varandra, t.ex. robotarmar, fordon, flygplan. Ett visst vridmoment appliceras med ett verktyg för att utveckla önskad klämkraft som håller ytorna ihop. En utmaning under denna process är att friktionsvariationer uppträder oväntat, vilket ökar risken för att inte uppnå den nödvändiga klämkraften för att säkerställa en framgångsrik åtdragning. I denna avhandling implementeras en diagnosmetod för att detektera friktionsvariationer vid hög dynamisk åtdragning. Olika detekterings algoritmer undersöks (t.ex. CUSUM, Partikelfilter, Linjärregression), och ett tillvägagångssätt som utnyttjar vridmoment- och vinkelsignalerna vid uppskattning av klämkraften implementeras. Undersökningar av signalbrus samt filtreringsoperationer under datautvinningen utförs, och signalerna utvärderas. Ett variabelt fönster används för att uppskatta vridmomentet, som används i detekteringsalgoritmen för att indikera variationer och utföra en diagnostisk rapport. Analysen utförs med en starkt dynamisk åtdragningsstrategi, programmerad i ett elektriskt åtdragningsverktyg, vilket gör att processen kan utföras på millisekunder. Undersökningar av parametrarna för detekteringsalgoritmen genomförs också, och värdetrösklarna identifieras. Slutligen utförs en statistisk analys av systemets beteende, liksom påverkan av operatören som håller verktyget, för utvärdering.
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Doering, Kenneth Thomas Nathaniel. "Fatigue of friction stir welded lap joints with sealants." Diss., Rolla, Mo. : Missouri University of Science and Technology, 2009. http://scholarsmine.mst.edu/thesis/pdf/Doering_09007dcc80627994.pdf.
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Thesis (M.S.)--Missouri University of Science and Technology, 2009.Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed April 9, 2009) Includes bibliographical references (p. 118-127).
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Lång, Marcus. "Static Friction in Slip Critical Bolt Joints : Coefficient of Friction in Steel, Aluminium and ED Coated Steel." Thesis, Karlstads universitet, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-55223.
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This project was performed together with ÅF Industry AB in Trollhättan, Sweden. ÅF’s expertise in Trollhättan is oriented towards the automotive industry. It was conducted within the section of CAE and safety where they, for instance, dimension bolt joints in the cars. Bolt joints play an important role in the automotive industry. Slip critical bolt joints are used widely throughout the vehicles. With lack of good test data, the bolt joints need to be dimensioned conservatively. This may lead to that bolt joints are over-dimensioned, adding more mass to the car. On the contrary, the availability of reliable test data enables designers to optimize joint dimensions to achieve a safe design with minimized mass. A mechanical testing configuration has been designed as well as a testing procedure for a test to determine the static friction value between mating surfaces in bolt joints. The testing configuration has been used to perform tests to find the static friction coefficient in different materials. The study contains varied combinations of steel, aluminium and ED-Coated steel. The study resulted in tables with levels of probability. The developed test configuration is robust and relatively simple to use and is recommended for further use. For improved statistical significance, it was noted that more samples should be used than was used in this study. The aluminium has a smoother surface finish and that could be the reason why its coefficient of friction is lower than steel. It is therefore considered important to also include surface roughness when presenting coefficient of friction results.
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Wang, Na. "Greffage de polymères biomimétiques sur implants articulaires en polyéthylène : contrôle du comportement tribologique." Phd thesis, Université Claude Bernard - Lyon I, 2013. http://tel.archives-ouvertes.fr/tel-00966017.
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Les maladies ostéoarticulaires représentent environ 10% de l'ensemble des pathologies identifiées en France chaque année. Pour l'instant aucun traitement permettant la réparation du tissu cartilagineux n'est vraiment disponible, hormis la pose d'un implant articulaire. Mais, malgré de nombreux efforts pour développer de nouveaux matériaux pour les implants articulaires leur durée de vie in vivo s'avère souvent très décevante par rapport aux extrapolations faites à partir de simulations ex-vivo. Les discordances entre les durées de vie in vivo et ex vivo sont principalement imputées aux conditions d'essais ex vivo insuffisamment réalistes vis-à-vis des propriétés physico-chimiques des lubrifiants biologiques. Dans ce contexte, ce travail vise à agir sur la réactivité physicochimique des surfaces frottantes des implants articulaires en UHMWPE afin de maîtriser l'accrochage des molécules lubrifiantes de type phospholipidique et ainsi d'augmenter leurs performances tribologiques. Les résultats montre que l'activation physichochimique des surfaces de UHMWPE par des couche de MPC peut diminuer l'usure des surfaces polymères d'implant mais cela nécessite un contrôle de la qualité de la couche MPC greffée (densité surfacique, épaisseur, accrochage chimique, adsorption physico-chimique) afin de garantir une bonne tenue mécanique et tribologique. D'autre part il a été montré que la présence de lubrifiant biologique (substitut du fluide synovial à base de liposomes) réduit l'usure des surfaces de UHWPE même si la couche de MPC est peu dense et peu épaisse
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Mahdavi, Shahri Meysam. "Fatigue Assessment of Friction Stir Welded Joints in Aluminium Profiles." Doctoral thesis, KTH, Materialteknologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-92157.
Full textAbstract:
Friction stir welding (FSW) is a low heat input solid state welding technology. It is often used for fabrication of aluminium alloys in transportation applications including railway, shipbuilding, bridge structures and automotive components. In these applications the material is frequently subject to varying load conditions and fatigue failure is a critical issue. In most cases standard codes and fatigue guidelines for aluminium welded joints address only welded structures with conventional welding methods but not those with FSW procedure. In the scope of this thesis fatigue life assessment of friction stir welded components was performed using theoretical approaches along with finite element method (FEM). The further aim of this study was to generate a basis for standardization of fatigue assessment of friction stir welded joints. Friction stir welded hollow aluminium panels of alloy 6005A are investigated. The panels are used for train wall sides, train floors, deck and bridges. Each panel is made of several profiles that are joined with the friction stir welding method. Fatigue bending tests were performed for profiles in these panels. Fatigue cracks and failure appeared at notches in the profiles. With FEM simulations critical positions for crack initiation and failure were identified. The method of critical distance was used to analyse and estimate the fatigue life. It was shown that the failure location and fatigue limit could be predicted for both base metal and weld location. Choice of welding procedure (clamping condition) can significantly influence the fatigue life. It was shown that for some panels the critical distance method was not able to explain the failure in the weld. In this case fracture mechanics together with residual stress analysis were used successfully to predict the failure. Assuming homogeneous material properties throughout the weld and the base material, FEM analysis for T and overlap joints as well can provide a reasonable fatigue prediction. This suggests that the same assumption can be extended to complex components for failure analysis of the friction stir welded joints when using the critical distance method. Fatigue assessment of friction stir welded joints was also performed using standard codes Eurocode 9 and IIW. Fatigue curves of traditional fusion welded joints were used. The results are in reasonable agreement with experimental data and FEM predictions.QC 20120330
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Vaziri, Mojgan. "Water Resistance of Scots Pine Joints Produced by Linear Friction Welding." Thesis, Nancy 1, 2011. http://www.theses.fr/2011NAN10059/document.
Full textAbstract:
Le soudage du bois est une technique d'assemblage sans adhésif de deux pièces de bois, leur soudure étant produite par friction mécanique sous pression des deux pièces. Ce procédé, applicable à des pièces de bois plates, d'essences identiques ou différentes, se prête à la fabrication de meubles et à la menuiserie. Cependant, le joint obtenu n'est pas de classe "extérieur", ce qui le réserve à un usage "intérieur". En effet, un joint destiné à une utilisation extérieure ou en milieu à humidité variable doit présenter une résistance élevée à l'eau. L'objectif principal de cette thèse est d'étudier la résistance à l'eau du bois soudé. A cet effet, des méthodes d'essais complémentaires et non-destructrices ont été utilisées, comme le scanner ou l'imagerie par résonance magnétique (IRM). L'influence des paramètres de soudage et des propriétés du bois sur, d'une part, la formation et la propagation des fissures dans la ligne de soudure, et sur, d'autre part, la densité et l'absorption d'eau de la soudure a été ainsi étudiée. Les expériences de cette thèse seront menées sur des échantillons de pin (Pinus sylvestris) de dimensions 200 mm x20 mm x 40 mm, coupés dans la direction longitudinale du fil du bois. La Norme Européenne EN 205 a servi de cadre pour déterminer la résistance des échantillons de pin en traction-cisaillement. Les méthodes d'essais (non-destructrices) ont été utilisées selon leur pertinence: le scanner a servi à étudier la formation et la propagation des fissures; l'imagerie par résonance magnétique (IRM) a permis quant à elle de caractériser la pénétration et l'infiltration d'eau dans le bois soudé.Le mécanisme d'adhérence du pin a été étudié grâce à la RMN MAS (spectrométrie à résonance magnétique nucléaire avec polarisation croisée et rotation à l?angle magique) du carbone13 et à la micro-densitométrie par rayons X. Ces différentes méthodes, non destructrices, offrent l'avantage d'une analyse non invasive et l'élimination de facteurs parasites liés à la préparation et à la coupe du bois. Voici en résumé les résultats obtenus les plus marquants: (1) Le scanner et l'imagerie par résonance magnétique (IRM) sont des méthodes de recherche particulièrement polyvalentes et adaptées à l'étude des bois soudés. (2) L'utilisation de bois de coeur, une pression de soudage de 1.3 Mpa et un temps de soudage de 1.5 s permettent d'augmenter la résistance à l'eau du pin soudé. (3) Des tests d'optimisation ont montré que la résistance du pin en traction-cisaillement est plus sensible aux variations de temps de soudage qu'au temps de refroidissement et qu'elle peut être optimisée à plus de 9.7 MPa en respectant une pression de 1.3 Mpa, un temps de soudage > 3.5 s et un temps de refroidissement < 60 s. (4) La résistance à l'eau du bois soudé peut être améliorée dans une certaine mesure en faisant varier paramètres de soudage et propriétés des essences, mais dans tous les cas, le recours à un imperméabilisant naturel et écologique reste nécessaire. (5) Le pin soudé possède une résistance à l'eau et en traction-cisaillement inhabituellement élevée, cela pouvant s'expliquer par une teneur en composés extractifs augmentée. (6) Des essais sous IRM ont montré que les causes de rupture du joint varient suivant l'essence: faible résistance à l'eau de la ligne de soudure dans le cas du hêtre soudé, retrait et expansion du bois dans le cas du pin soudé. (7) Les extractifs du pin améliorent nettement la résistance à l'eau du joint soudé, mais à un niveau qui ne lui permet cependant pas la certification "extérieur" sans protection. En revanche, il peut être certifié "semi-extérieur" avec protectionWood welding is a mechanical friction process allowing the assembly of timber without any adhesives. The process consists of applying mechanical friction, under pressure, alternately to the two wood surfaces to be welded. This process can be applied to weld two flat pieces of timber, originating from the same or different tree species, and can be used in the manufacture of furniture and wood joinery. The only limitation is that the joint is not exterior-grade, but only suitable for interior joints. Exterior use, or use in an environment with varying humidity demands water resistance of the welded joints. The main objective of this thesis is to study the water resistance of the welded wood. This is complemented with special attention to non-destructive test methods such as X-ray Computed Tomography (CT-) scanning and Magnetic Resolution Imaging (MRI). The influence of welding parameters and wood properties on crack formation and crack propagation in the weldline was investigated. The influence of these parameters on weldline density and water absorption in the weldline were also studied. Investigations in this thesis are based on welded samples of Scots pine (Pinus sylvestris) of the dimensions 200 mm × 20 mm × 40 mm which were cut in the longitudinal direction of the wood grain. The tensile-shear strength of the welded Scots pine samples were determined using European standard EN 205. Different non-destructive methods such as X-ray Computed Tomography (CT-) scanning to study crack formation and propagation, and magnetic Resolution Imaging (MRI) to characterize water penetration and the distribution mechanism in welded wood were used. Solid state CPMAS 13C NMR spectrometry and X-ray microdensitometry investigations were carried out to study the mechanism of adhesion in Scots pine. These various non-destructive methods offer the advantage of non-invasive analysis and the elimination of any artifacts present due to preparation and sectioning. The most important results are summarized as follows: (1) X-ray Computed Tomography (CT-) scanning and Magnetic Resolution Imaging (MRI) are versatile research methods applicable to investigations of welded woods. (2) Water resistance of welded Scots pine can be increased using heartwood, a welding pressure of 1.3 MPa, and a welding time of 1.5 s. (3) Optimization tests showed that the tensile-shear strength of Scots pine was more sensitive to welding time changes than holding time and could be optimized to more than 9.7 MPa using 1.3 MPa welding pressure, > 3.5 s welding time, and < 60 s holding time. (4) Changing welding parameters and wood properties can increase water resistance of welded wood to some extent, but treating the weldline with certain natural and environmentally-friendly water repellents is still necessary. (5) Welded Scots pine shows unusually high water resistance and tensile-shear strength. This may be explained by there being more extractives compounds in Scots pine. (6) MRI experiments showed that the origin of the joint failure in welded beech is poor water resistance of the weldline, while swelling and shrinkage of wood are the main reasons for joint failure of welded Scots pine. (7) Extractives in Scots pine dramatically improve water resistance of the welded joint, but not to a level to classify the joint as an unprotected exterior grade. However, it can qualify as a joint for protected semi-exterior application
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Mjali, Kadephi Vuyolwethu. "Analysing the effect of FSP on MIG-laser hybrid welded 6082-T6 AA joints." Thesis, Nelson Mandela Metropolitan University, 2007. http://hdl.handle.net/10948/563.
Full textAbstract:
Friction Stir Processing (FSP) of aluminium alloys has been used to modify and improve the microstructure and relevant properties of fusion welded aluminium alloys. The effect of FSP on MIG-Laser Hybrid (MLH) welded aluminium alloy 6082-T6 mechanical and microstructural properties has been studied in this research. The FSP process was used on 6mm thick aluminium alloy plates and a tool was designed specifically for FSP, and the effect of varying speeds was analysed before the final FSP welds were made. The effect of FSP was analysed by optical microscopy, tensile, microhardness and fatigue testing. The aim of the study was to determine whether the FSP process has a beneficial influence on the mechanical properties and metallurgical integrity of MIG-Laser Hybrid welded 6082-T6 aluminium alloy with varying gap tolerances. Three welding processes were compared, namely combined Friction Stir Processing on MIG-Laser hybrid process (FSP-MLH), MLH and Friction Stir Welding (FSW) as part of the analysis. (FSP was carried out on MLH components when it was found that FSP is not an entirely complete welding process but rather a finishing process per se.) The aim of this dissertation is to investigate the effects of the FSP process on the weld quality of MLH welded joints and also to compare this to individual processes like FSW and MLH. This investigation was undertaken in order to gain an understanding of the effect of these processes on fatigue performance and microhardness distribution on aluminium alloy 6082-T6 weld joints.
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Oyedemi, Kayode. "Increasing the gap tolerance in friction stir welded joints of AA6082-T6." Thesis, Nelson Mandela Metropolitan University, 2012. http://hdl.handle.net/10948/d1012325.
Full textAbstract:
This research project was conducted to increase weld gap tolerance in Friction Stir Welding (FSW) of 8 mm thick aluminum alloy 6082 – T6. Investigation was done on I-STIR PDS platform and a Johnford milling machine. The research project involved tool-pin design with varying re-entrant features and varying parameters as a method of weld gap closing to produce successful welds. Direction of spindle rotation and dwell time were established as part of a preliminary study. Clockwise spindle rotation with 20 seconds dwell time allows sufficient plasticity and improved material flow which assisted in achieving welds with prior 30 percent weld gap of the plate thickness. Final welds were made using three rotational speeds and feed rates with sufficient plunging to prevent root defects. Analysis of the results were detailed which include vickers microhardness test, tensile test and metallographic observation to access the suitability of the weld structure. From the set of tool-pins designed, the flare tool-pin gave a well-defined weld nugget with improved stirring at the weld root. Also, with a concave shoulder, right hand threaded tool-pin and counterclockwise flutes undergoing a clockwise spindle rotation, plasticized material flow was upward which was beneficial in reducing the amount of plate thinning. The right hand thread counter clockwise flute with a flute machined in the foot exhibited superior tensile strength for welds containing 30 percent weld gap.