Thesis (M.S.)--Brigham Young University. Dept. of Mechanical Engineering, 2005. / Includes bibliographical references (p. 27-28).

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2006. / Includes bibliographical references (leaves 263-272). Also available in electronic version.

The chemical nature of the Transfer Film (T.F.) or Third-Body Layer (T.B.L.) formed at the friction interface of an automotive friction brake during off-brake motoring has been studied using Energy Dispersive X-ray (E.D.X.) analysis and Scanning Electron Microscopy (S.E.M.). Although these third-body layers are deposited on both mating surfaces of the friction couple, special attention has been paid to those formed on the disc brake rotor surface. Concurrently, detailed investigations have been undertaken examining the temperature-dependent, physico-chemical interactions of friction material constituents with each other, atmospheric oxygen and countermember materials using X-Ray Diffraction (X.R.D.).Evidence is presented relating the tribological performance of the friction pair to both the transfer film thermochemistry and the friction material composition. Among those characteristics describing the tribological performance of the friction couple, particular attention has been applied to the generation of Disc Thickness Variations (D.T.V.) induced by Off-Brake or Non-Braking Wear (O.B.W. or N.B.W.). The critical role of solid lubricants and abrasive friction modifiers and their effectiveness over a range of contact pressures / temperatures has received particular attention. Information obtained using various surface analytical techniques combined with detailed dimensional assessments of the affected triboelements has been used to show the considerable significance of abrasive particle size in determining the overall tribological behaviour of the friction pair, especially with respect to the wear regime and extent encountered at the surface of the countermember during O.B.W.Wear mechanisms are described for the generation of off-brake wear, these varying with friction material formulation. Dynamic and temperature-dependent influences on the level of in-service disc brake rotor runout are named as causes for particular forms of disc thickness variation generated by aggressive friction materials. Keywords: Third-body layer; Transfer film; Tribochemistry; Automotive Friction Braking; Cold Judder; Disc Thickness Variation; Disc Brake; Friction Material.

Smectite clay minerals are among the most common minerals in subduction zone megathrusts faults at shallow depth and in landslide decollements. Consequently, deformation processes at seismic slip rates (ca. 1 m/s) in smectites contribute to control the mechanics of megathrust earthquakes and landslide collapses. To investigate the deformation processes, rotary shear experiments on smectite-rich gouge layers (70/30 wt.% Ca-montmorillonite/opal) were performed. The experiments were conducted at ambient temperature and at 5 MPa normal stress. The gouges were sheared under vacuum (<0.001 mbar) and room humidity (i.e., water depleted) or in the presence of liquid water (i.e., water rich) conditions, at slip rates of 0.0003 <V <1.5 m/s and displacements of 0.1 <d <30 m. The temperature evolution with slip was measured with thermocouples and modelled numerically. Permeability of the gouge layer was measured with the pore pressure oscillation method prior to the rotary experiments. Before and after the experiments, the mineral and amorphous material content in wt.% were determined via quantitative X-ray powder diffraction and the microstructures investigated via scanning and transmission electron microscopy. The activation of deformation processes was strongly controlled by the water content of the gouge layers. Under water depleted conditions, grainsize reduction producing nanoparticles controlled the evolution of the friction coefficient f at all slip rates. Coseismic dynamic weakening (f = 0.2 - 0.3) occurred by combined thermal decomposition or melting (with decreasing water content) and pressurization of water released by dehydration of smectite interlayer. Under water rich conditions, grain size reduction was minor and development of nano-foliations occurred. At all slip rates, the friction coefficient rapidly decreased at the onset of slip. The large initial weakening (to f <0.15) was due to the presence of a film of water lubricating the surfaces of the sub-parallel smectite grains forming the nano-foliation in combination with shear-enhanced water pressurization. Then, friction coefficient evolved depending on the balance between dissipation of pore pressures, dehydration of smectite interlayer and thickening of the nano-foliation layers. At higher displacement and slip rates, sustained dynamic weakening was aided by vaporization of pore water. Expulsion of water determined a switch to deformation processes typical of water depleted conditions. In nature, the presence of liquid water in smectites has a lubricating effect, pressurizes the slipping zone and renders the smectite-rich gouges prone to accommodate large seismic slips. During megathrust earthquakes, such lubricating effect may result in the easy propagation of seismic ruptures in smectite- and water-rich sediments at shallow depths. Similarly, the presence of water can promote large displacements during landslide collapse.

AN ABSTRACT OF THE THESIS OF Jacob Boone, for the Master of Science degree in Mechanical Engineering, presented on 10/28/2010, at Southern Illinois University Carbondale. TITLE: DESIGN, CONSTRUCTION, AND EVALUTAION OF UNIVERSAL FRICTION TESTER MAJOR PROFESSOR: Dr. Peter Filip Many different types of friction testers are currently available for testing specific frictional applications. Of these machines very few have versatility, and of the ones that do, the amount of versatility is limited. Since friction is a property specific to each system, all operating parameters need to match the specific application as closely as possible in order to obtain accurate data. This requires many research facilities to have several specific friction testers in order to provide the necessary testing capabilities. The goal of this project was to design a Universal Friction Tester (UFT) with enough versatility to reproduce most types of sliding friction situations. This was accomplished by providing a wide range of testing capabilities through the use of interchangeable system components. Results show that the UFT provides quality data over its entire operating range. It was shown that normal pressure, sliding speed, temperature and system stiffness all have drastic effects on frictional performance. By using a borosilicate glass disc, the friction surface was viewed in-situ during testing. This allowed insights into true surface temperature and contact area. In conclusion, the UFT can successfully take the place of several friction testers and thus provide many friction research capabilities while requiring fewer resources. The wide range of testing capabilities will allow the UFT to be used as a research tool for many types of advanced friction studies. Some of these may include true surface temperatures, true contact area, influence of conditions on stick-slip phenomenon, and thermo-elastic instabilities.

Made available in DSpace on 2014-06-11T19:31:26Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-01-24Bitstream added on 2014-06-13T18:42:03Z : No. of bitstreams: 1 clavijo_vgr_dr_arafo.pdf: 969958 bytes, checksum: 57064b07ad94167d21ebb9ba66873da2 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Neste estudo avaliou-se a resistência ao cisalhamento por extrusão de pinos de fibra de vidro, reembasados ou não com compósito, cimentados com dois tipos de cimentos resinosos em dentina intra-radicular, avaliando os segmentos cervical, médio e apical. Selecionaram-se 40 incisivos bovinos com dimensões semelhantes, removendo a porção coronária, padronizando o comprimento das raízes em 14 mm. Após, incluiu-se as raízes em resina acrílica, realizando tratamento endodôntico e, então o preparo dos espaços para os pinos, dividindo- as, em seguida, aleatoriamente em quatro grupos com dez amostras cada. Os elementos do grupo 1 receberam retentores de fibra de vidro cimentados com cimento resinoso RelyX ARC, grupo 2 retentores de fibra de vidro cimentados com cimento resinoso RelyX U100, grupo 3 retentores de fibra de vidro reembasados com resina composta e cimentados com cimento resinoso RelyX ARC e grupo 4 retentores de fibra de vidro reembasados com resina composta e cimentados com cimento resinoso RelyX U100. Ao término dos procedimentos de cimentação, realizou-se a secção dos segmentos radiculares, submetendo, então, os corpos-de-prova ao teste push-out em máquina de ensaios universal, através de ponta ativa cilíndrica com 1 mm de diâmetro, à velocidade de 0,5 mm/min, até extrusão do retentor. Obteve-se os seguintes valores médios de resistência de união, em MPa: grupo 1, terços cervical = 6,22 ± 2,64(a), médio = 4,25 ± 2,01(a) e apical = 4,45± 2,81(a); grupo 2, terços cervical = 5,04 ± 2,34(a), médio = 3,06 ± 2,12(a) e apical = 3,26 ± 2,38(a). grupo 3, terços cervical = 11,85 ± 1,67(b), médio = 11,83 ± 3,84(b) e apical = 10,39 ± 2,44(b). grupo 4, terços cervical = 12,05 ± 1,14(b), médio = 11,98 ± 3,23(b) e apical = 10,96 ± 2,14(b). Submeteram-se os valores à análise de variância e ao teste de Tukey com nível de significância de 5% indicadas... / This study evaluated the bond strength of fiber posts, relined or not with composite resin, luted with resinous cement to radicular dentin, evaluating cervical, median and apical root segments. Fourty bovine incisors, with similar dimensions, were selected and cut 16 mm from the apical limit. The roots were embedded in acrylic resin and the radicular canals were root treated and post space prepared with a depth of 9 mm. Samples were randomly assigned to two groups of ten roots each. Group 1 received glass fiber posts luted with dual-cure resin cement RelyX ARC in association with a bonding system. In Group 2 the same type of posts were relined with composite for further cementation with resin cement RelyX U100. In Group 3, glass fiber post were relined with composite and cemented with resin cement RelyX ARC and in Group 4 glass fiber posts were relined ith composite and cemented with resin cement RelyX U100. After cementation procedures roots were sectioned transversally and three sections, from cervical, medium and apical thirds were obtained. Push-out test was performed in a universal testing machine with a 1 mm diameter steel rod at cross-head speed of 0,5 mm/min until post extrusion. Collected data was statistically analyzed by two- way ANOVA and Tukey HSD test (p<0,05). The measured retention strengths for cervical, medium and apical thirds were: Group 1, cervical thirds = 6,22 ± 2,64(a), medium = 4,25 ± 2,01(a) e apical = 4,45± 2,81(a); group 2, cervical thirds = 5,04 ± 2,34(a), medium = 3,06 ± 2,12(a) and apical = 3,26 ± 2,38(a). Group 3, cervical thirds = 11,85 ± 1,67(b), medium = 11,83 ± 3,84(b) and apical = 10,39 ± 2,44(b). Group 4, cervical thirds = 12,05 ± 1,14(b), medium = 11,98 ± 3,23(b) and apical = 10,96 ± 2,14(b). Glass fiber composite relined posts presented statistically higher retention values in cervical, medium and apical thirds when compared... (Complete abstract click electronic access below)

Manufacturing of textile preforms involve preform compaction which influences the fibre volume fraction and level of crimp in the final laminates affecting the laminate properties. The preform compaction behaviour is highly non-linear and depends on a number of tow-level factors which in turn is guided by filament-level interactions. Hence experimentally predicting the compaction behaviour of a preform, made of large fibre bundles, remains as an obstacle to the understanding of the compaction mechanics due to the stochastic effects of filament-level interactions. This thesis proposes a novel multi-scale modelling technique which predicts the compaction behaviour of large fibre bundles or tows. The model considers real inter-fibre frictional interactions; the friction coefficients are obtained by carrying out friction tests on carbon fibres. Since the inter-fibre friction varies with the inter-fibre orientation, experiments are done to study the effects of fibre orientation on friction. The tests have shown a significant increase in coefficient of friction (from 0.2 to 0.45) for parallel tows due to bedding and entanglement of fibres in comparison to the friction between perpendicular tows. Modelling of the filament-level compaction behaviour requires inter filament friction coefficient which is not equal to the tow friction. In addition, the filaments within a tow can slip relative to each other. Therefore, inter filament friction can influence tow friction. Hence filament friction is determined from tow friction and used in the compaction models. Numerical models of compaction of large fibre bundles are developed which use this experimentally-obtained fibre friction coefficient as input. The solid model requires extensive computational effort. A two-dimensional (2D) model has been developed where the bending and torsional behaviour are incorporated with the help of springs. This 2D model has resulted in improved computational efficiency compared to the solid model (that is, a 99% improvement in CPU time for a 37 filament assembly). The model is then extended to tow- and fabric-levels. The tow-scale results are in close agreement (~5%) with validation tests. A further 3D modelling technique using beam elements has been presented as a further scope which is able to use the level of compaction obtained from the 2D model and also overcomes the limitations of the 2D model. This 3D modelling technique has shown 88% reduction in CPU time compared to that of solid model of same fibre bundle.

Made available in DSpace on 2014-10-09T12:50:35Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:02:02Z (GMT). No. of bitstreams: 1 00490.pdf: 1118936 bytes, checksum: f9cd6a3b97f699bbd0c0f82b0a8731b0 (MD5) / Dissertacao (Mestrado) / IEA/D / Instituto de Fisica, Universidade de Sao Paulo - IF/USP

In mumerical contact simulations with friction, the simple Coloumb law is usually employed. Standard plasticity models are difficult to use since the balance enforced on the contact surface typically only involves balance of traction vectors, and does not use the full stress tensor on the interface. In this work we describe an approach that allows for the use of the stress tensor, thus opening up the possibility of using more advanced plasticity models. We exemplify this approach by implementing the Drucker-Prager pressure sensitive plasticity model.

Orientador: Marcelo Ferrarezi de Andrade / Banca: José Roberto Cury Saad / Banca: Fabio Luiz Camargo Villela Berbert / Banca: Hugo Henriques Alvim / Banca: Victor Humberto Orbegoso Flores / Resumo: Neste estudo avaliou-se a resistência ao cisalhamento por extrusão de pinos de fibra de vidro, reembasados ou não com compósito, cimentados com dois tipos de cimentos resinosos em dentina intra-radicular, avaliando os segmentos cervical, médio e apical. Selecionaram-se 40 incisivos bovinos com dimensões semelhantes, removendo a porção coronária, padronizando o comprimento das raízes em 14 mm. Após, incluiu-se as raízes em resina acrílica, realizando tratamento endodôntico e, então o preparo dos espaços para os pinos, dividindo- as, em seguida, aleatoriamente em quatro grupos com dez amostras cada. Os elementos do grupo 1 receberam retentores de fibra de vidro cimentados com cimento resinoso RelyX ARC, grupo 2 retentores de fibra de vidro cimentados com cimento resinoso RelyX U100, grupo 3 retentores de fibra de vidro reembasados com resina composta e cimentados com cimento resinoso RelyX ARC e grupo 4 retentores de fibra de vidro reembasados com resina composta e cimentados com cimento resinoso RelyX U100. Ao término dos procedimentos de cimentação, realizou-se a secção dos segmentos radiculares, submetendo, então, os corpos-de-prova ao teste push-out em máquina de ensaios universal, através de ponta ativa cilíndrica com 1 mm de diâmetro, à velocidade de 0,5 mm/min, até extrusão do retentor. Obteve-se os seguintes valores médios de resistência de união, em MPa: grupo 1, terços cervical = 6,22 ± 2,64(a), médio = 4,25 ± 2,01(a) e apical = 4,45± 2,81(a); grupo 2, terços cervical = 5,04 ± 2,34(a), médio = 3,06 ± 2,12(a) e apical = 3,26 ± 2,38(a). grupo 3, terços cervical = 11,85 ± 1,67(b), médio = 11,83 ± 3,84(b) e apical = 10,39 ± 2,44(b). grupo 4, terços cervical = 12,05 ± 1,14(b), médio = 11,98 ± 3,23(b) e apical = 10,96 ± 2,14(b). Submeteram-se os valores à análise de variância e ao teste de Tukey com nível de significância de 5% indicadas... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: This study evaluated the bond strength of fiber posts, relined or not with composite resin, luted with resinous cement to radicular dentin, evaluating cervical, median and apical root segments. Fourty bovine incisors, with similar dimensions, were selected and cut 16 mm from the apical limit. The roots were embedded in acrylic resin and the radicular canals were root treated and post space prepared with a depth of 9 mm. Samples were randomly assigned to two groups of ten roots each. Group 1 received glass fiber posts luted with dual-cure resin cement RelyX ARC in association with a bonding system. In Group 2 the same type of posts were relined with composite for further cementation with resin cement RelyX U100. In Group 3, glass fiber post were relined with composite and cemented with resin cement RelyX ARC and in Group 4 glass fiber posts were relined ith composite and cemented with resin cement RelyX U100. After cementation procedures roots were sectioned transversally and three sections, from cervical, medium and apical thirds were obtained. Push-out test was performed in a universal testing machine with a 1 mm diameter steel rod at cross-head speed of 0,5 mm/min until post extrusion. Collected data was statistically analyzed by two- way ANOVA and Tukey HSD test (p<0,05). The measured retention strengths for cervical, medium and apical thirds were: Group 1, cervical thirds = 6,22 ± 2,64(a), medium = 4,25 ± 2,01(a) e apical = 4,45± 2,81(a); group 2, cervical thirds = 5,04 ± 2,34(a), medium = 3,06 ± 2,12(a) and apical = 3,26 ± 2,38(a). Group 3, cervical thirds = 11,85 ± 1,67(b), medium = 11,83 ± 3,84(b) and apical = 10,39 ± 2,44(b). Group 4, cervical thirds = 12,05 ± 1,14(b), medium = 11,98 ± 3,23(b) and apical = 10,96 ± 2,14(b). Glass fiber composite relined posts presented statistically higher retention values in cervical, medium and apical thirds when compared... (Complete abstract click electronic access below) / Doutor