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1
Abachi, Siamak. „Wear Analysis Of Hot Forging Dies“. Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/12605706/index.pdf.
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WEAR ANALYSIS OF HOT FORGING DIES
ABACHI, Siamak
M. S., Department of Mechanical Engineering
Supervisor: Prof. Dr. Metin AKKÖK Co-Supervisor: Prof. Dr. Mustafa lhan GÖ
KLER December 2004, 94 pages The service lives of dies in forging processes are to a large extent limited by wear, fatigue fracture and plastic deformation, etc. In hot forging processes, wear is the predominant factor in the operating lives of dies. In this study, the wear analysis of a closed die at the final stage of a hot forging process has been realized. The preform geometry of the part to be forged was measured by Coordinate Measuring Machine (CMM), and the CAD model of the die and the worn die were provided by the particular forging company. The hot forging operation was carried out at a workpiece temperature of 1100°
C and die temperature of 300°
C for a batch of 678 on a 1600-ton mechanical press. The die and the workpiece materials were AISI L6 tool steel and DIN 1.4021, respectively. The simulation of forging process for the die and the workpiece was carried out by Finite Volume Method using MSC.SuperForge. The flow of the material in the die, die filling, contact pressure distribution, sliding velocities and temperature distribution of the die have been investigated. In a single stroke, the depth of wear was evaluated using Archard&rsquo
s wear equation with a constant wear coefficient of 1¥
10-12 Pa-1 as an initial value. The depth of wear on the die surface in every step has been evaluated using the Finite Volume simulation results and then the total depth of wear was determined. To be able to compare the wear analysis results with the experimental worn die, the surface measurement of the worn die has been done on CMM. By comparing the numerical results of the die wear analysis with the worn die measurement, the dimensional wear coefficient has been evaluated for different points of the die surface and finally a value of dimensional wear coefficient is suggested. As a result, the wear coefficient was evaluated as 6.5¥
10-13 Pa-1 and considered as a good approximation to obtain the wear depth and the die life in hot forging processes under similar conditions.
2
Sandberg, Joakim. „Development of a Laboratory Test Method for Assessment of Crater Wear Volume on Inserts for Steel Turning“. Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-75569.
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This thesis project was carried out at Sandvik Coromant in Västberga, Sweden with the purpose of developing a new laboratory test method for volumetric assessment of crater wear on inserts for steel turning. The test method was developed with the Sandvik Coromant´s existing crater wear measurement method as a starting point. Crater wear is currently measured as the projected area of exposed substrate, meaning where all coating layers have been removed. Based on earlier research on volume wear assessment, a focus variation microscope was selected to carry out 3D scans. To accurately measure the removed volume, an initial reference scan is required to capture individual variations existing on samples. The insert is then scanned after turning and compared with its reference. Factors affecting accuracy as well as possible improvements were identified as: Sample preparation, scan settings (resolution, quality) and data processing (alignment of scans, volume calculation etc.). Guiding alignment markers were created by laser ablation to help with alignment. CloudCompare software was used to process the scanned 3D point clouds. A step by step routine was developed to ensure consistent results. The repeatability was assessed showing 8% standard deviation in volume for a shallow crater within the coating to 2% for a large crater worn into the substrate. The new method provides the possibility to measure wear while still inside the coating, which has been previously unavailable data. This enables measurement of the contribution of each specific coating layer on the wear resistance such as wear rate of a single layer instead of a combined wear rate for all layers. Detailed coating wear analysis is a valuable tool for development of optimized coatings. The developed wear measurement method was implemented on a case study which demonstrated the capabilities regarding its ability to resolve performance differences in experimental coatings. Additional wear parameters were used beside crater volume to support wear rate analysis and novel ways of representing volume wear parameters were presented.
3
Liu, Qiang. „Control of Wear-Resistance Properties in Ti-added Hypereutectic High Chromium Cast Iron“. Licentiate thesis, KTH, Tillämpad processmetallurgi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-105854.
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High chromium cast iron (HCCI) is considered as one of the most useful wear resistance materials and their usage are widely spread in industry. The wear resistance and mechanical properties of HCCI mainly depend on type, size, number, morphology of hard carbides and the matrix structure (γ or α). The Hypereutectic HCCI with large volume fractions of hard carbides is preferred to apply in wear applications. However, the coarser and larger primary M7C3 carbides will be precipitated during the solidification of the hypereutectic alloy and these will have a negative influence on the wear resistance. In this thesis, the Ti-added hypereutectic HCCI with a main composition of Fe-17mass%Cr-4mass%C is quantitatively studied based on the type, size distribution, composition and morphology of hard carbides and martensite units. A 11.2μm border size is suggested to classify the primary M7C3 carbides and eutectic M7C3 carbides. Thereafter, the change of the solidification structure and especially the refinement of carbides (M7C3 and TiC) size by changing the cooling rates and Ti addition is determined and discussed. Furthermore, the mechanical properties of hypereutectic HCCI related to the solidification structure are discussed. Mechanical properties of HCCI can normally be improved by a heat treatment process. The size distribution and the volume fraction of carbides (M7C3 and TiC) as well as the matrix structure (martensite) were examined by means of scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). Especially for the matrix structure, EBSD is a useful tool to classify the fcc (γ) and bcc (α) phases. In conclusion, low holding temperatures close to the eutectic temperature and long holding times are the best heat treatment strategies in order to improve wear resistance and hardness of Ti-alloyed hypereutectic HCCI.QC 20121130
4
Liu, Qiang. „Microstructure Evaluation and Wear-Resistant Properties of Ti-alloyed Hypereutectic High Chromium Cast Iron“. Doctoral thesis, KTH, Tillämpad processmetallurgi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-128532.
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High chromium cast iron (HCCI) is considered as one of the most useful wear resistance materials and their usage are widely spread in industry. The mechanical properties of HCCI mainly depend on type, size, number, morphology of hard carbides and the matrix structure (γ or α). The hypereutectic HCCI with large volume fractions of hard carbides is preferred to apply in wear applications. However, the coarser and larger primary M7C3 carbides will be precipitated during the solidification of the hypereutectic alloy and these will have a negative influence on the wear resistance. In this thesis, the Ti-alloyed hypereutectic HCCI with a main composition of Fe-17mass%Cr-4mass%C is studied based on the experimental results and calculation results. The type, size distribution, composition and morphology of hard carbides and martensite units are discussed quantitatively. For a as-cast condition, a 11.2μm border size is suggested to classify the primary M7C3 carbides and eutectic M7C3 carbides. Thereafter, the change of the solidification structure and especially the refinement of carbides (M7C3 and TiC) size by changing the cooling rates and Ti addition is determined and discussed. Furthermore, the mechanical properties of hypereutectic HCCI related to the solidification structure are discussed. Mechanical properties of HCCI can normally be improved by a heat treatment process. The size distribution and the volume fraction of carbides (M7C3 and TiC) as well as the matrix structure (martensite) were examined by means of scanning electron microscopy (SEM), in-situ observation by using Confocal Laser Scanning Microscope (CLSM), Transmission electron microscopy (TEM) and electron backscattered diffraction (EBSD). Especially for the matrix structure and secondary M7C3 carbides, EBSD and CLSM are useful tools to classify the fcc (γ) and bcc (α) phases and to study the dynamic behavior of secondary M7C3 carbides. In conclusion, low holding temperatures close to the eutectic temperature and long holding times are the best heat treatment strategies in order to improve wear resistance and hardness of Ti-alloyed hypereutectic HCCI. Finally, the maximum carbides size is estimated by using statistics of extreme values (SEV) method in order to complete the size distribution results. Meanwhile, the characteristic of different carbides types will be summarized and classified based on the shape factor.QC 20130913
5
Farah, Philipp Wagih [Verfasser], Wolfgang A. [Akademischer Betreuer] Wall, Wolfgang A. [Gutachter] Wall und Manfred [Gutachter] Bischoff. „Mortar Methods for Computational Contact Mechanics Including Wear and General Volume Coupled Problems / Philipp Wagih Farah ; Gutachter: Wolfgang A. Wall, Manfred Bischoff ; Betreuer: Wolfgang A. Wall“. München : Universitätsbibliothek der TU München, 2017. http://d-nb.info/1160381259/34.
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6
Champagne, Matthieu. „« Endommagement utile » et « dialogue surface/volume » : Investigations numérique et expérimentale du comportement des composites C/C sous sollicitations tribologiques“. Thesis, Lyon, INSA, 2014. http://www.theses.fr/2013ISAL0135.
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Le matériau composite carbone/carbone ou C/C est utilisé en temps que matériau de friction en freinage aéronautique. Matériau complexe tant du point de vue de sa description microstructurale que de son comportement sous sollicitations tribologiques, il a été l’objet de nombreuses études visant à mieux comprendre les mécanismes régissant sa réponse (frottement, endommagement, usure) à ces sollicitations. Dans cette étude nous nous focalisons sur l’aspect mécanique de cette réponse. En particulier, nous nous intéressons aux endommagements présents dans le matériau : nous souhaitons étudier tant leurs origines que leur influence sur le comportement du matériau. Pour cela, nous choisissons une approche combinée numérique et expérimentale, nous permettant d’identifier de façon exhaustive ces endommagements puis de construire un modèle numérique tribologique permettant d’étudier les mécanismes d’usure du matériau. Nous montrons comment les mécanismes d’accommodation en volume du 1er corps influent sur les détachements de particules en surface, nous conduisant à parler de dialogue tribologique surface/volume. Le modèle numérique utilise la méthode des éléments discrets pour représenter 1er et 3ième corps simultanément. Un travail est réalisé autour de la représentativité du modèle vis-à-vis des caractéristiques mécaniques du composite C/C. Nous proposons également une démarche de recherche d’un Volume Elémentaire Représentatif sous condition de contact. Ce modèle ainsi que les observations du matériau nous permettent de proposer un scenario de comportement tribologique du composite C/C, en fonction des sollicitations thermomécaniques qui lui sont appliquées et correspondant aux différents types de freinages aéronautiques. Les endommagements identifiés dans le volume du matériau se révèlent être bénéfiques dans certains cas de figure au travers d’un mécanisme de rigidification du matériau intervenant à haute température, ce qui nous conduit à parler d’ « endommagement utile ». Le scenario intègre donc ce phénomène, ainsi que d’autres tant mécaniques que physicochimiques et identifiés par cette étude ou dans la littérature, et montre comment leur équilibre « dynamique » produit le comportement tribologique identifié du matériau pour les différentes gammes de sollicitations qui lui sont appliquéesCarbon/Carbon (or C/C) composite is used as a friction material in aeronautical braking applications. This is a complex material from both microstructural and tribological behavior points of view. Thus, it has been studied through various works for several years, aiming at understanding what mechanisms guide this material response (friction, damage, wear) under tribological conditions. In this study, a focus is performed on mechanical aspects such as damages that occur in the numerical and experimental approach, in view to identify and classify the damages as well as to build a numerical model used to investigate wear mechanisms. It is underlined how first-body accommodation mechanisms have a great influence on particles detachment at the interface, as a surface/volume tribological dialogue take place. This model is based on the Discrete Elements method and represents simultaneously first- and third-body; such model is able to represent fist-body degradation as well as creation and flow of third-body particles. Its representativeness is ensured through experimental comparisons, particularly on mechanical aspects. A procedure is proposed for the research of a Representative Elementary Volume under contact conditions. Model results and material observations allow proposing a global scenario explaining C/C composite behavior under tribological conditions, which are representative of different aeronautical braking cases. Damages, identified in the volume of the first-body, reveal themselves to be sometimes beneficial, and could be characterized as “useful damages”. The scenario takes into account this phenomenon, as well as thermal, mechanical and physicochemical ones, identified from this work or literature. It explains the influences of these parameters on C/C tribology and show how the dynamic equilibrium between them results on the C/C response, particularly its wear mechanism
7
Rec, Matouš. „Návrh testovacího stavu pro stanovení opotřebení u kontaktu železničního kola a kolejnice“. Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2021. http://www.nusl.cz/ntk/nusl-445166.
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This diploma thesis focuses on the issue of a wear of a railway wheel and a rail. The wear of the components depends on a number of parameters including the contact stress, the contact pressure and the contact surface dimensions. Among the factors determining these parameters belongs primarily the wheel driving gauge, the rail profile and the load of the contact area. Furthermore, the material from which the wheels and rail are made, the roughness and hardness of the functional surfaces and the residual stress in the material have a significant impact on the wear. All the parameters mentioned above are designed for the production of the railway wheels and rails and therefore they meet the standards for the production of these components. However, the existence of the changeable parameters has also a significant impact on the wear. These parameters include the presence of contaminants, or lubricants in contact, the changing driving gauge due to the wear, the slip ratio or the friction coefficient. With the wear being an inevitable process during the application it cannot be eliminated but only controlled. Applying the lubricant into the contact when passing through the arc in order to achieve an ideal coefficient or the maintenance grinding for restoring the driving gauge can serve the purpose. If properly optimized, the importance of the wear research lies in the financial savings. Being the crucial factor for optimization of the intervals between the maintenance grinding, the research is also beneficial. A high-quality wear prediction can be seen as the key field in order to increase the safety of the railway vehicles operation as well. Therefore, the wear research is made using several methods, such as the computational models, the multi-body dynamics software and the technical experiments. This thesis introduces a conceptual design of the test, enabling the wear research via experimental approach. The final device is capable of a simulation of both volume and fatigue wear during the states the railway wheel and railway undergo including riding on the straight track, passing through an arc or a wheel slip during braking.
8
Hlavinková, Vítězslava. „OPTIMALIZACE ANALYTICKÉ METODY VÝPOČTU OPOTŘEBENÍ STAVEBNÍCH OBJEKTŮ“. Doctoral thesis, Vysoké učení technické v Brně. Ústav soudního inženýrství, 2014. http://www.nusl.cz/ntk/nusl-234316.
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The dissertation focuses on the problems associated with determining the amount of wear (finding the remaining technical values) that are being addressed. It deals with an overview of the different methods used. The basic premise of the thesis is a comprehensive overview of the calculation procedure and the methods used. This area of wear does not except the price regulation precisely defined procedure, nor are they addressed the circumstances in which that would be the method to be used. Various possible methods or inaccuracies may result in questioning the expert opinions as at trial. In conclusion of this dissertation is shown how the calculation procedure should wear for what purpose should be used and it is also proposed several alternatives.
9
Sjösten, William, und Victor Vadling. „CFD Simulations of Flow Characteristics of a Piano Key Weir Spillway“. Thesis, Uppsala universitet, Elektricitetslära, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-414861.
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Comprehensive rehabilitation projects of dam spillways are made in Sweden, due to stricter dam safety guidelines for their discharge capacity. The Piano Key Weir (PKW) is an innovative design which has proven effective through several renovation projects made in many countries including France. In this study we investigate the flow patterns around a prototype PKW, located in Escouloubre dam in southern France, with numerical simulations through three different flow cases in Ansys Fluent. A computational domain containing the PKW is created in the CAD software Ansys SpaceClaim for the simulations. Three polyhexcore meshes are further generated using Ansys Fluent Meshing. The three flow cases are then simulated with a Reynolds-averaged Navier-Stokes (RANS) model, coupled with realizable k-epsilon and volume of fluid models. Through an assessment of the discretization error between three meshes, a relative error of one percent is obtained for the discharge rate. The numerical results are qualitatively compared with results from previously conducted physical experiments on this PKW. The RANS model does not capture the water surface undulations (due to turbulence) around the PKW. The effects from under modelled surface undulations are alleviated by inserting an air vent to the PKW, which results in a flow behaviour in good agreement with the physical experiments. Through this alteration, water discharge rates are computed with a maximum discrepancy of five percent compared with the corresponding experimental values. A large eddy simulation should be conducted in the future, to bring further light on air exchange and water interaction phenomena present in the PKW flow pattern.
10
Franco, Correa Iván David. „Étude tribologique à hautes températures de matériaux céramiques structurés à différentes échelles“. Thesis, Limoges, 2019. http://www.theses.fr/2019LIMO0106.
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Dans le but d’évaluer la performance et de comprendre les mécanismes d'usure, à haute température, de matériaux céramiques, de compositions chimiques différentes (Al2O3, base ZrO2, mullite), à différentes échelles de structure (finement structuré, microstructuré et submillimétrique) et de configurations différentes (monocouche, bicouche et en volume), des revêtements céramiques ont été réalisés par projection plasma à pression atmosphérique sur un substrat céramique silico-alumineux. Les revêtements d’Al2O3, de ZrO2-Al2O3 et de ZrO2- Y2O3 correspondant à la configuration monocouche ont été élaborés avec deux échelles de structure : finement structurée et microstructurée. Tandis que les revêtements de mullite/Al2O3, mullite/ ZrO2-Al2O3 et mullite/ ZrO2-Y2O3 correspondant à la configuration bicouche, ont été réalisés avec la couche supérieure (top coat) de mullite microstructurée sur les sous-couches (bond coat) finement structurés et microstructurés. Les revêtements ont été comparés à des réfractaires électrofondus d’Al2O3 et d’AZS correspondant à la configuration en volume à l’échelle submillimétrique, utilisés comme références en raison de leur grande résistance à l’usure à haute température dans les industries de fabrication du verre et des ciments. Tous les matériaux céramiques ont été exposés à des conditions d’usure par contact glissant (5 N, 20000 tours et 0,10 m.s-1) avec un tribomètre de type bille sur disque à des températures de 25, 500, 750 et 1000 °C. Les résultats indiquent que l’usure des revêtements d’Al2O3, de ZrO2- Al2O3 et de ZrO2-Y2O3 à 25 et 1000 °C est due à une déformation ductile, avec des taux d’usure respectifs de l’ordre de 10-4-10-6 et 10-4-10-5 mm3.N-1.m-1, tandis qu’à 500 et 750 °C l’usure se fait par déformation fragile avec des taux d’usure de l’ordre de 10-3-10-4 mm3.N-1.m-1 pour les deux températures. La résistance à l’usure a été trouvée légèrement supérieure dans les revêtements finement structurés principalement en raison de la ténacité plus élevée. Pour les deux réfractaires électrofondus en volume à échelle submillimétrique, l’usure par déformation ductile est prépondérante à 1000 °C, avec des taux d’usure de l’ordre de 10-4 mm3.N-1.m-1. Pour les systèmes bicouches de mullite, l’usure par déformation fragile a été observée à toutes les températures évaluées, avec des taux d’usure de l’ordre de 10-3-10-4 mm3.N-1.m-1, sans montrer aucune amélioration du fait de la présence d’une sous-couche céramique. En cherchant des solutions plus économiques et pour d’autres applications, le comportement tribologique à haute température a également été étudié sur des revêtements d’Al2O3 finement structurés et microstructurés, réalisés par projection à la flamme oxyacétylénique, plus économique que la projection plasma, ainsi que sur les mêmes revêtements d’Al2O3 réalisés par projection plasma sur un substrat métallique d’Inconel 718, couramment utilisé dans les industries spatiale et aéronautique. Dans les deux cas, les résultats étaient similaires à ceux obtenus par projection plasma sur un substrat réfractaireIn order to evaluate and to understand the wear performance and mechanisms at high temperatures that take place when different chemical compositions (Al2O3, ZrO2, mullite), scales (finely structured, microstructured and submillimetric) and configurations (single layer, bilayer and volume) interact, atmospheric plasma sprayed coatings manufactured on a silicoaluminous ceramic substrate were used. The Al2O3, ZrO2-Al2O3 and ZrO2-Y2O3 coatings correspond to the monolayer configuration, as well as the finely and microstructured scales, while the Mullite/Al2O3, Mullite/ ZrO2-Al2O3 and of Mullite/ ZrO2-Y2O3 correspond to the bilayer configuration, where the outer mullite layer is microstructured and the sub-layers can correspond to finely and microstructured scales. In the same way, the Al2O3 and AZS commercial refractories correspond to the volume configuration and the submillimeter scale, taking into account that these have also been used as references because of the high resistance to wear that they show in glass and cement industries. Subsequently, these ceramic materials were subjected to sliding contact wear conditions (5 N, 20000 rpm and 0,10 ms-1) with a ball on disk tribometer at temperatures of: 25, 500, 750 and 1000 °C. The results indicate that the wear of the Al2O3, ZrO2-Al2O3 and ZrO2-Y2O3 coatings at 25 and 1000 ° C was by ductile deformation, showing wear rates of the order of 10-4-10- 6 and 10-4-10-5 mm3.N-1.m-1 respectively, while at 500 and 750 °C was by brittle deformation with wear rates of the order of 10-3-10-4 mm3.N-1.m-1 for both temperatures, finding a slightly higher wear resistance in finely structured coatings due primarily to toughness. Regarding the two electro-melted volume refractories at submillimetric scale, they showed wear by ductile deformation only at 1000 °C, showing wear rates of the order of 10-4 mm3.N-1.m-1. On the other hand, the mullite bilayer systems showed wear by brittle deformation at all evaluated temperatures, with wear rates of the order of 10-3-10-4 mm3.N-1.m-1, without showing any improvement at all because of the presence of the sub-layers. Finally, aiming to seek more economical options, as well as to give other applications to the materials studied, it has also been determined the influence on wear at high temperature of Al2O3 coatings, finely and microstructured, manufactured by the chep technique of oxy-flame spraying, as well as the same Al2O3 coatings manufactured by plasma spraying on a metallic substrate of Inconel 718, which is used by the space and aerospace industries, obtaining for both cases comparable and similar results to all those obtained previously
Con el fin de evaluar el desempeño y comprender los mecanismos de desgaste de materiales cerámicos que se producen a alta temperatura cuando diferentes composiciones químicas (Al2O3, base ZrO2, mullita), diferentes escalas de estructura (finamente estructurado, microestructurado y submilimétrico) y diferentes configuraciones (mono-capa, bi-capa y en volumen) interactúan, fueron realizados recubrimientos cerámicos por proyección térmica de plasma sobre un sustrato cerámico silico-aluminoso. Los recubrimientos de Al2O3, ZrO2-Al2O3 y ZrO2-Y2O3 corresponden con la configuración mono-capa y con las escalas finamente estructurada y microestructurada. Mientras que los recubrimientos de mullita/Al2O3, mullita/ ZrO2-Al2O3 y mullita/ ZrO2-Y2O3 corresponden con la configuración bi-capa, donde la capa superior de los recubrimientos es de mullita microstructurada y las subcapas pueden ser finamente estructuradas y microestructuradas. Dichos recubrimientos fueron comparados con refractarios electrofundidos de Al2O3 y AZS correspondientes con la configuración en volumen y con la escala submilimétrica, los cuales también fueron utilizados como referencias debido a sus altas resistencias al desgaste a altas temperaturas en industrias tales como: la del vidrio y el cemento. Todos los materiales cerámicos fueron sometidos a condiciones de desgaste por contacto deslizante (5 N, 20000 vueltas y 0,10 m.s-1) con un tribómetro de tipo bola-disco a temperaturas de 25, 500, 750 y 1000 °C. Los resultados indican que el desgaste en los recubrimientos de Al2O3 y base ZrO2 a 25 y 1000 °C fue por deformación dúctil, con tasas de desgaste de 10-4-10-6 et 10-4-10-5 mm3.N-1.m-1 respectivamente, mientras que a 500 y 750 °C el desgaste fue por deformación frágil con tasas de desgaste del orden de 10-3-10-4 mm3.N- 1.m-1 para ambas temperaturas y ambos materiales. La resistencia al desgaste en los recubrimientos finamente estructurados fue ligeramente superior debido principalmente a la mayor tenacidad tenacidad a la fractura. Para los dos refractarios electrofundidos en volumen a escala submilimétrica, el desgaste por deformación dúctil fue detectado solo a 1000 °C, con tasas de desgaste del orden de 10-4 mm3.N-1.m-1. Para los sistemas bi-capa de mullita, el desgaste por deformación frágil se observó a todas las temperaturas evaluadas, con tasas de desgaste del orden de 10-3-10-4 mm3.N-1.m-1, sin mostrar ninguna mejora debido a la presencia de una subcapa cerámica. Finalmente, en aras de buscar tanto soluciones más económicas como otras aplicaciones, el comportamiento tribológico a alta temperatura se estudió también en recubrimientos de Al2O3 finamente estructurados y microestructurados, realizados mediante proyección térmica de llama oxiacetilénica, más económica que la proyección de plasma, así como sobre los mismos recubrimientos de Al2O3 realizados mediante proyección de plasma sobre un sustrato metálico de Inconel 718, utilizado comúnmente en las industrias espacial y aeronáutica. En ambos casos, los resultados fueron similares a los obtenidos por plasma o por sustrato refractario
11
Ahmad, Ola. „Stochastic representation and analysis of rough surface topography by random fields and integral geometry - Application to the UHMWPE cup involved in total hip arthroplasty“. Phd thesis, Ecole Nationale Supérieure des Mines de Saint-Etienne, 2013. http://tel.archives-ouvertes.fr/tel-00905519.
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Surface topography is, generally, composed of many length scales starting from its physical geometry, to its microscopic or atomic scales known by roughness. The spatial and geometrical evolution of the roughness topography of engineering surfaces avail comprehensive understanding, and interpretation of many physical and engineering problems such as friction, and wear mechanisms during the mechanical contact between adjoined surfaces. Obviously, the topography of rough surfaces is of random nature. It is composed of irregular hills/valleys being spatially correlated. The relation between their densities and their geometric properties are the fundamental topics that have been developed, in this research study, using the theory of random fields and the integral geometry.An appropriate random field model of a rough surface has been defined by the most significant parameters, whose changes influence the geometry of its excursion. The excursion sets were quantified by functions known as intrinsic volumes. These functions have many physical interpretations, in practice. It is possible by deriving their analytical formula to estimate the parameters of the random field model being applied on the surface, and for statistical analysis investigation of its excursion sets. These subjects have been essentially considered in this thesis. Firstly, the intrinsic volumes of the excursion sets of a class of mixture models defined by the linear combination of Gaussian and t random fields, then for the skew-t random fields are derived analytically. They have been compared and tested on surfaces generated by simulations. In the second stage, these random fields have been applied to real surfaces measured from the UHMWPE component, involved in application of total hip implant, before and after wear simulation process. The primary results showed that the skew-t random field is more adequate, and flexible for modelling the topographic roughness. Following these arguments, a statistical analysis approach, based on the skew-t random field, is then proposed. It aims at estimating, hierarchically, the significant levels including the real hills/valleys among the uncertain measurements. The evolution of the mean area of the hills/valleys and their levels enabled describing the functional behaviour of the UHMWPE surface over wear time, and indicating the predominant wear mechanisms.
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Barjami, Saimir. „A New AC-Radio Frequency Heating Calorimetry Technique for Complex Fluids“. Link to electronic thesis, 2005. http://www.wpi.edu/Pubs/ETD/Available/etd-042805-132440/.
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Dissertation (Ph.D.) -- Worcester Polytechnic Institute.Keywords: random-field interactions; radio frequency field heating; modulation calorimetry technique; heat capacity; aerosil; nematic; isotropic; phase transitions Includes bibliographical references.
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Winkler, Anderson M. „Widening the applicability of permutation inference“. Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:ce166876-0aa3-449e-8496-f28bf189960c.
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This thesis is divided into three main parts. In the first, we discuss that, although permutation tests can provide exact control of false positives under the reasonable assumption of exchangeability, there are common examples in which global exchangeability does not hold, such as in experiments with repeated measurements or tests in which subjects are related to each other. To allow permutation inference in such cases, we propose an extension of the well known concept of exchangeability blocks, allowing these to be nested in a hierarchical, multi-level definition. This definition allows permutations that retain the original joint distribution unaltered, thus preserving exchangeability. The null hypothesis is tested using only a subset of all otherwise possible permutations. We do not need to explicitly model the degree of dependence between observations; rather the use of such permutation scheme leaves any dependence intact. The strategy is compatible with heteroscedasticity and can be used with permutations, sign flippings, or both combined. In the second part, we exploit properties of test statistics to obtain accelerations irrespective of generic software or hardware improvements. We compare six different approaches using synthetic and real data, assessing the methods in terms of their error rates, power, agreement with a reference result, and the risk of taking a different decision regarding the rejection of the null hypotheses (known as the resampling risk). In the third part, we investigate and compare the different methods for assessment of cortical volume and area from magnetic resonance images using surface-based methods. Using data from young adults born with very low birth weight and coetaneous controls, we show that instead of volume, the permutation-based non-parametric combination (NPC) of thickness and area is a more sensitive option for studying joint effects on these two quantities, giving equal weight to variation in both, and allowing a better characterisation of biological processes that can affect brain morphology.
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Raghavan, R. „Effect Of Free-Volume On The Fracture And Fatigue Of Amorphous Alloys“. Thesis, 2008. http://hdl.handle.net/2005/726.
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Bulk metallic glasses (BMGs) are a new class of structural materials and exhibit unique combinations of mechanical properties. As a result, their mechanical behavior has been an active area of scientific pursuit in the recent past and considerable emphasis has been paid to understand plastic deformation in them. It is now well accepted that shear transformation zones (STZs), aided by free volume, are the fundamental carriers of plasticity. At a microscopic level, deformation at low temperatures and high stresses tends to localize into shear bands. Most BMGs posses high fracture toughness despite high yield strengths and poor global ductility. However, the micro-mechanisms of fracture and fatigue in this new class of materials are not fully understood yet. The overall objective of this study is to provide insights into the fracture and fatigue response of amorphous alloys, which is important both from scientific and technological perspectives. The key questions we seek to answer through this study are the following. Do amorphous alloys undergo a ductile-brittle transition (DBT), and if so what are the reasons for it? What are the parameters that influence fatigue crack initiation in amorphous alloys and whether fatigue life can be improved by surface treatments? A related question is whether the BMGs are susceptible to deformation-induced crystallization (DIC). A Zr-based BMG, Zr41.2Ti13.75Cu12.5Ni10Be22.5 was utilized to conduct this study. By comparing the fracture and fatigue behaviors in the as-cast and annealed states {annealing was carried out below the glass transition temperature (Tg) because of established embrittlement effects}, we seek to provide answers for the questions posed above.
We begin by examining the influence of temperature on the toughness of BMGs. Impact toughness measurements show that the annealed samples, which are brittle at room temperature, recover the lost toughness beyond a critical temperature (TDB) and exhibit a sharp DBT. However, the hardness remains unaffected across the TDB. Fractography reveals nano-scale patterning and cleavage fracture in the brittle state, while the formation of thick vein-patterns and shear fracture are characteristics of the ductile state of the annealed samples. We explore various micro-mechanistic possibilities for explaining the features of this transition, including a critical Poisson’s ratio-toughness correlation.
Next, to understand the origins of fatigue crack initiation, we study the un-notched fatigue response of as-cast and sub-Tg annealed Zr-based BMG specimens. Because of embrittlement and nano-crystallization at the crack initiation region, the annealed specimens exhibit a lower fatigue life than the as-cast specimens. Shot-peening of the as-cast specimens did not exhibit significant improvement in their fatigue performance because of competing effects between the compressive residual stress field (CRSF) and deformation-induced softening. To further investigate surface and repeated loading effects, the tribological response of the as-cast Zr-based BMG was compared with specimens annealed above and below the Tg. A good correlation between the hardness (increasing as a function of the annealing temperature) and wear rate was obtained. The formation and peeling of the oxide layer formed during testing was the primary wear mechanism in all the specimens.
Lastly, crystallization was observed within the deformed region of the as-cast Zr-based BMG repeatedly scratched with a sharp diamond indenter. But, transmission electron microscopy (TEM) does not reveal any evidence of crystallization within the indents formed within an electron transparent film formed by laser deposition of the as-cast Zr-based BMG. Absence of crystallization in deformed regions obtained by designing critical experiments, which avoid artifacts generated during sample preparation, suggests that the occasional observation of DIC might be an exception rather than the rule in BMGs.
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Stauch, Tilo. „Lokalisation und Volumenberechnung von femoralem Schaftabrieb an explantierten, zementierten Hüftendoprothesenschäften vom Typ CF-30 und dessen Relevanz als Faktor der aseptischen Lockerung“. Doctoral thesis, 2012. http://hdl.handle.net/11858/00-1735-0000-000D-F1ED-F.
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McAfee, James. „Wear resistant coatings for agricultural wear applications“. 1986. http://catalog.hathitrust.org/api/volumes/oclc/15473362.html.
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Thesis (M.S.)--University of Wisconsin--Madison, 1986.Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 63-67).
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Tsai, Pang-Yen. „Improved wear resistance of sawteeth“. 1993. http://catalog.hathitrust.org/api/volumes/oclc/32463249.html.
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Thesis (M.S.)--University of Wisconsin--Madison, 1993.Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 50-53).
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Hoggatt, Ross. „Robust drill wear monitoring utilizing multiple sensors“. 1992. http://catalog.hathitrust.org/api/volumes/oclc/25776433.html.
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Thesis (M.S.)--University of Wisconsin--Madison, 1992.Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 117-122).
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Perez, Briceño Guillermo A. „Wear resistant coatings for wood machining applications“. 1986. http://catalog.hathitrust.org/api/volumes/oclc/15029494.html.
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Thesis (M.S.)--University of Wisconsin--Madison, 1986.Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 121-123).
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Lenling, William James. „The evaluation and development of wear resistant coatings“. 1986. http://catalog.hathitrust.org/api/volumes/oclc/15497216.html.
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Thesis (M.S.)--University of Wisconsin--Madison, 1986.Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 95-97).
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Patel, J., S. Lal, K. Nuss, Stacy-Paul Wilshaw, Rechenberg B. von, R. M. Hall und J. L. Tipper. „Recovery of low volumes of wear debris from rat stifle joint tissues using a novel particle isolation method“. 2018. http://hdl.handle.net/10454/15561.
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YesLess than optimal particle isolation techniques have impeded analysis of orthopaedic wear debris in vivo. The purpose of this research was to develop and test an improved method for particle isolation from tissue. A volume of 0.018 mm3 of clinically relevant CoCrMo, Ti-6Al-4V or Si3N4 particles was injected into rat stifle joints for seven days of in vivo exposure. Following sacrifice, particles were located within tissues using histology. The particles were recovered by enzymatic digestion of periarticular tissue with papain and proteinase K, followed by ultracentrifugation using a sodium polytungstate density gradient. Particles were recovered from all samples, observed using SEM and the particle composition was verified using EDX, which demonstrated that all isolated particles were free from contamination. Particle size, aspect ratio and circularity were measured using image analysis software. There were no significant changes to the measured parameters of CoCrMo or Si3N4 particles before and after the recovery process (KS tests, p > 0.05). Titanium particles were too few before and after isolation to analyse statistically, though size and morphologies were similar. Overall the method demonstrated a significant improvement to current particle isolation methods from tissue in terms of sensitivity and efficacy at removal of protein, and has the potential to be used for the isolation of ultra-low wearing total joint replacement materials from periprosthetic tissues.
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Raebel, Suzanne. „The fabrication and evaluation of wear resistant saw blade inserts“. 1991. http://catalog.hathitrust.org/api/volumes/oclc/24510583.html.
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Thesis (Ph. D.)--University of Wisconsin--Madison, 1991.Vita. Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves : 204-217).
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Liu, Tien-I. „Development of crankshaft multifacet drills and on-line drill wear monitoring“. 1987. http://catalog.hathitrust.org/api/volumes/oclc/17911727.html.
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Thesis (Ph. D.)--University of Wisconsin--Madison, 1987.Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 118-124).
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Lee, Jae-Won. „Force analyses of drill point geometry for optimal design and wear prediction“. 1986. http://catalog.hathitrust.org/api/volumes/oclc/15171391.html.
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Thesis (Ph. D.)--University of Wisconsin--Madison, 1986.Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 140-145).
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Goggin, Eimear Mary. „Weak convergence of conditional probabilities“. 1988. http://catalog.hathitrust.org/api/volumes/oclc/19339508.html.
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Thesis (Ph. D.)--University of Wisconsin--Madison, 1988.Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 128-130).
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Stange, Alan Lawrence. „Multiple weak boson signals at hadron supercolliders“. 1992. http://catalog.hathitrust.org/api/volumes/oclc/28686396.html.
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27
Cariaga, Joselito D. „A predictive procedure for wear, pitting, and scoring of gears based on combined thermal and mechanical stresses“. 1997. http://catalog.hathitrust.org/api/volumes/oclc/39286962.html.
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Thesis (Ph. D.)--University of Wisconsin--Madison, 1997.Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 325-336).
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Tam, Kwa-Sur. „Hybrid inverter for HVDC/weak AC system interconnection“. 1985. http://catalog.hathitrust.org/api/volumes/oclc/13593525.html.
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29
Chen, Jie. „Microstructure, wear and corrosion properties of methane plasma source ion implanted 304 stainless steel and Ti-6A1-4V“. 1993. http://catalog.hathitrust.org/api/volumes/oclc/31370179.html.
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Thesis (Ph. D.)--University of Wisconsin--Madison, 1993.Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 148-153).
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Talcott, Paul David. „Why the weak can win healthcare politics in postwar Japan /“. 1999. http://catalog.hathitrust.org/api/volumes/oclc/47007842.html.
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31
Liao, Jih-Sheng. „Stability of near-surface excavations in weak rock and soil“. 1988. http://catalog.hathitrust.org/api/volumes/oclc/18773509.html.
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Thesis (Ph. D.)--University of Wisconsin--Madison, 1988.Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 125-139).
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Chung, Tsungting. „Weak against strong Republic of China-United States trade negotiations, 1980-1989 /“. 1992. http://catalog.hathitrust.org/api/volumes/oclc/29681858.html.
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33
Cheng, Ching-Ling. „Absorption and disposition of poorly water soluable weak bases application to delavirdine“. 1997. http://catalog.hathitrust.org/api/volumes/oclc/68799275.html.
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34
Seuntjens, Jeffrey Michael. „Understanding weak links through the processing of (RE)Ba₂Cu₃O₇ ̲[delta]“. 1990. http://catalog.hathitrust.org/api/volumes/oclc/24122719.html.
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Thesis (Ph. D.)--University of Wisconsin--Madison, 1990.Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 127-134).
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Whipple, Mark Scott. „A numerical investigation of convection in an atmosphere with weak symmetric stability“. 1989. http://catalog.hathitrust.org/api/volumes/oclc/20586119.html.
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Thesis (M.S.)--University of Wisconsin--Madison, 1989.Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 95-97).
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Al, Amri Mohammed Dhaifallah. „In-vitro wear of enamel opposing titanium porcelain a thesis submitted in partial fulfillment ... for the degree of Master of Science in Prosthodontics ... /“. 2004. http://catalog.hathitrust.org/api/volumes/oclc/68962642.html.
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37
Armellini, Debora B. „Wear characteristics of titanium and aluminum oxide when opposed by titanium a thesis submitted in partial fulfillment ... for the degree of Master of Science in Prosthodontics ... /“. 1999. http://catalog.hathitrust.org/api/volumes/oclc/68900918.html.
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Cho, Nhansook. „Weak convergence of stochastic integrals and stochastic differential equations driven by martingale measure and its applications“. 1994. http://catalog.hathitrust.org/api/volumes/oclc/31493948.html.
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Thesis (Ph. D.)--University of Wisconsin--Madison, 1994.Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 142-144).
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Ping, Huican. „The observation of the weak radiative hyperon decay xi0-> lambda0 pi0 gamma at KTeV/E799, Fermilab“. 2005. http://catalog.hathitrust.org/api/volumes/oclc/70807305.html.
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40
Jarjoura, Ibrahim F. „In vitro wear rate of multiple substrates and their antagonistic enamel and CoCr abraders a study submitted in partial fulfillment ... for the degree of Master of Science degree in Biomaterials ... /“. 2004. http://catalog.hathitrust.org/api/volumes/oclc/68962665.html.
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Raymond, Chad. „Rational resistance to a weak authoritarian state the political economy of Vietnamese farmers from collectivization to Doi Moi /“. 2000. http://catalog.hathitrust.org/api/volumes/oclc/47285656.html.
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42
Naujok, Roberta Rae. „Weak acid chemistry and photoisomerization of azobenzene surfactants at the liquid/liquid electrochemical interface optical second harmonic generation spectoscopy“. 1997. http://catalog.hathitrust.org/api/volumes/oclc/38554003.html.
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43
O'Kray, Hal. „The hydration of a high alkali porcelain and its effect on In Vitro human enamel wear, flexure and impact strength a study submitted in partial fulfillment ... for a Master of Science degree in Biomaterials ... /“. 2001. http://catalog.hathitrust.org/api/volumes/oclc/68944131.html.
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44
Tambra, Tussavir Rafique. „In-vitro wear of enamel opposing yttria-stabilized-partially-tetragonal-zirconia (YPSZ) core material and porcelains specifically designed for use with all-ceramic restorations a thesis submitted in partial fulfillment ... for the degree of Master of Science in Prosthodontics ... /“. 2002. http://catalog.hathitrust.org/api/volumes/oclc/67878284.html.
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45
ŠEBOR, Ondřej. „Bodové měření průtoku vody v povrchových tocích pro zpřesnění kontinuálního monitoringu průtoku“. Master's thesis, 2014. http://www.nusl.cz/ntk/nusl-180521.
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The thesis is divided into theoretical and practical part. The theoretical part includes issues associated with runoff and discharge, methods for discharge measurement and measurements of uncertainties. The practical part of the thesis describes a specific process flow measurement in Kopaninský and Jenínský stream. There is a familiarization with the water flow velocity measurement and comparison methods of volume measurement discharge with continuous measurement. The results of the practical part served to refine the rainfall-runoff processes in research catchment areas. Refined values of the flow rate were used as input data for the calculation of the runoff coefficient and for quantifying the losses of nutrients from the catchment areas. Calculation of the runoff coefficient and nutrient losses were compared for the original and the revised equation discharge curve. Volume measurement discharge has shown that the different conditions above measurement weir during continuous monitoring lead to the uncertainties of measurement. That´s why one has to approach to each flowmeasurement individually and consider the situation in a particular installation.
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Suhy, Patricia. „A study to examine the effects of mood states on the patient's ability to wean from the mechanical ventilator a research report submitted in partial fulfillment ... /“. 1987. http://catalog.hathitrust.org/api/volumes/oclc/68788023.html.
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47
Tidjani, Bassirou. „Why vocational training under adversarial industrial relations and weak unions does not work a case study of the French and American machine tool industries during the 1980's /“. 1992. http://catalog.hathitrust.org/api/volumes/oclc/28705359.html.
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