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Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第15334号 / 工博第3213号 / 新制||工||1484(附属図書館) / 27812 / 京都大学大学院工学研究科化学工学専攻 / (主査)教授 大嶋 正裕, 教授 田門 肇, 教授 宮原 稔 / 学位規則第4条第1項該当

Composite materials are widely used in demanding applications in aerospace and other industries. In order to understand the complex behaviour of the composite materials and their components, standardised test methods are used. One example is the double cantilever beam (DCB) test in which the test specimen is loaded in an opening, i.e., tensile mode. Failures in composite materials loaded compression are different from those in tension, for example, kink band or buckling-like failures can occur. In this project, several DCBs are designed and a new fixture which allows for compression testing of a DCB is developed for an existing Instron testing machine. The fixture overcomes a known problem of tensile peak causing the failure of the adhesive at the inner surfaces of the DBC by applying additional compressive loads along the outer surfaces of the DBC. The compressive forces can induce the desired kink band formation so that researchers can better study the failure mode. The conceptual development of the new DCBs and the new fixture are presented. Several prototypes of the specimens and the fixture are modelled using the three-dimensional (3D) computer-aided design software Creo Parametric 2.0.  One of the fixtures is selected to further study. The different DCB specimens are studied in order to obtain information about the kink band using 3D finite element analysis with the software programme Abaqus CAE. The selected fixture is analysed to determine if there are any areas of concern. Finally, the behaviour of the compression stress along the DCB using two pairs of forces is studied. Unfortunately, it is determined that the tensile peak experienced by the adhesive cannot be eliminated by the application of two pairs of compressive loads, one at the free end and the other in the vicinity of the tensile peak. Several suggestions are made for future work which might serve to reduce the tensile peak; e.g., the movable force couple is applied as a surface load instead of a point load. For this, the fixture will have to be modified with a new geometry, although the DCB could be the same. This will allow further work to focus on the combined behaviour of the tensile peak and the fixture.

Ventricular fibrillation is one of the leading causes for Sudden Cardiac Death and is characterized by multiple activation wavefronts. Multiple activation wavefronts originate from a reentrant circuit which requires the presence of a unidirectional block in the path of a propagating excitation wave. It has been proposed that at the cellular level beat to beat alternation in the action potential duration at rapid pacing rates can result in a conduction block. Various mechanisms have been postulated to show the mechanisms of alternans. We use simulated activation in a one dimensional tissue fiber to show the existence of a new mechanism via which alternans can result. We used a new pacing protocol to eliminate alternans at the pacing site, and thus eliminating restitution of action potential duration at this site to reveal existence of alternans down the fiber. Effects on alternans of manipulations of specific ionic currents such as the sodium current (INa), calcium current (ICaL), potassium current (Ikr) and of the diffusion co-efficient (Dx) which simulates reduced expression of connexin 43 were determined. Decrease in sodium conductance, i.e. in excitability by half caused the alternans to occur at the pacing site itself even though APD restitution was eliminated. An increase or decrease in calcium current (ICaL) eliminated alternans throughout the fiber. The use of a novel pacing approach in investigation of alternans, as in this study, furthers our understanding of the mechanism of alternans and may prove helpful in the development of better anti-arrhythmic drugs in the future.

This study investigates the effects of Z-pinning on the delamination performance in opening and shear loading modes in woven fabric reinforced / epoxy composite materials, as well as the effects of friction between specimen crack faces and the Z-pin failure mechanisms involved in mode II delamination. Mode I and mode II delamination tests are carried out on Z-pinned unidirectional (UD) and woven laminates. Both UD and woven laminates exhibit enhanced delamination resistance and crack propagation stability through Z-pinning. The effects of various structural and Z-pin parameters on the mode I and mode II delamination behaviour are separately assessed. The 4ENF testing configuration is deemed as the appropriate mode II configuration for the testing of Z-pinned laminates. A new basic friction rig is used to measure the friction coefficient between crack faces in woven laminates. An additional friction effect attributed to fibre architecture is identified. A specially designed delamination specimen is used to overcome the difficulty of accurately measuring crack propagation in Z-pinned woven fabric materials and aid data reduction using the available analytical methods. The failure mechanisms involved in the mode II delamination of Z-pinned laminates have been investigated with the implementation of a new test. Z-pins fail under shear loading through a combination of resin crushing, laminate fibre breakage, pin shear, pin bending and pin pullout. The balance of the failure mechanisms is shown to be a function of the crack opening constraint, material type, stacking sequence, Z-pin angle and insertion depth to Z-pin diameter ratio. Z-pin and material parameters influencing Z-pinning quality are identified, categorised and quantified. The importance of controlling Z-pin insertion depth is underlined and updated manufacturing procedures are proposed. Partial pinning appears as an advantageous alternative. A reduction in in-plane stiffness and in-plane strength in UD and woven fabric composites is measured, whilst no significant change of in-plane shear stiffness of UD materials is observed. A reduction in the fibre volume fraction is the single most important parameter affecting the in-plane stiffness. The performance of a Z-pinned sub-structural component is investigated. Enhanced loading carrying capacity and damage tolerance is achieved through Z-pinning.

Orientador: Rezende Gomes dos Santos / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-06T09:53:26Z (GMT). No. of bitstreams: 1 Sousa_TonnyfranXavierdeAraujo_M.pdf: 6216112 bytes, checksum: 8c56f86b7dd957a9bef95dc947db6ed6 (MD5) Previous issue date: 2006 / Resumo: O objetivo do trabalho é o desenvolvimento de uma análise comparativa do processo de solidificação de uma liga de alumínio a partir de diferentes graus de superaquecimento. São determinados experimentalmente os principais parâmetros do processo de solidificação afetados pelo grau de superaquecimento e sua influência na formação da microestrutura. Foi escolhida a liga AA5052, contendo cerca de 3% de magnésio pelo seu interesse comercial. A liga foi vazada com três diferentes graus de superaquecimento, em um dispositivo que permite a solidificação unidirecional e o monitoramento, através de um sistema de aquisição de dados, das variações de temperatura em diferentes posições da peça. A partir dos resultados de temperatura são determinados outros parâmetros do processo. Os espaçamentos interdendriticos são determinados a partir das micrografias. Através da análise experimental é determinada a influência do grau de superaquecimento nos seguintes parâmetros relativos ao processo de solidificação: coeficiente de transferência de calor na interface metal/molde, velocidade de avanço da frente de solidificação, gradiente de temperatura em frente à isoterma liquidus, taxa de resfriamento, tempo local de solidificação e espaçamentos interdendriticos primário e secundário. Também é analisada a transição entre a estrutura colunar e equiaxial / Abstract: The objective of this work is the development of a comparative analysis of solidification process of the aluminum 5052 alloy with different overheating ranges. The main parameters of the solidification process, experimentally determined, are affected by the overheating range and its influence on the microstructure arrangement. lt was selected the 5052 alloy, containing about 3% of magnesium, used for commercial purposes. The al1oy was poured with three different overheating ranges in a device which allows the unidirectional solidification and its monitoring through an acquisition data system thru the temperature variation from different positions on the sample. From the temperature results, the process parameters are determined. The dendritic spacing is determined using the micrographs. Through experimental analysis is established the influence of the overheating range at the fol1owing parameters related to solidification process: heat transfer coefficient at the metal/mold interface, solidification rate, thermal gradient at the liquidus isotherm, cooling rate, local solidification time and secondary arm spacing. The change between the structure columnar and equiaxed is also studied. / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica

Service parts management is an integral component of customer satisfaction. The service parts supply chain has a number of unique challenges that differentiate it from retail and manufacturing supply chains. These challenges include: unpredictable and lumpy demand, limited storage capacity, high demand service rate requirements, and high risk of obsolescence. This research focuses on the use of substitution as a policy tool to aid in service part supply chain management; particularly with respect to low inventory and high dollar value components. In one part of this dissertation, a Markov chain is used to model unidirectional substitution with dissimilar part reliability. In addition, this work investigates probabilistic substitution policies that allow substitution to be employed on a partial basis. This research also utilizes a Poisson process to explore steady state optimization with probabilistic substitution for a model in which a non-primary part is utilized solely as a substitute for primary parts. The models demonstrate that both substitution protocols can significantly enhance customer performance benchmarks. Unidirectional substitution policies improve fill rate and backorder levels for the machine upon which substitution is performed. The price of this improvement is the cost of additional ordering and inventory, along with decreased fill rate and backorder performance, on the machine whose parts are used for substitution. Substitution, using a part solely carried for that purpose, increases performance levels without higher inventory levels of either primary part. However, this type of substitution requires the inclusion of an additional inventory part and the associated costs.

A method is presented by which fatigue life predictions of polymer matrix composites may be improved. First a "critical element", whose failure defines global failure of the material. is identified. The global stiffness changes of the specimen during a fatigue test are monitored and taken to be inversely proportional to the increase in applied stress on the critical element. Using a cumulative damage model, the complicated stress history of the critical element is reduced to a "critical element SN curve", which defines the fatigue response of the critical element. The residual strength of the critical element may then be continuously evaluated to predict failure. The statistical nature of material strength is accounted for by forcing the critical element SN Curve to yield a specimen initial strength distribution in fatigue which is equivalent to the quasi-static tensile distribution. In contrast to most methods, the predictions are based on the stiffness history of the specimen in question, rather than on generalized phenomenological models. The critical element SN curve is then applied to (90°/0°) crossply materials to evaluate their fatigue response. Simulations and the variation of experimental parameters are examined for their effect on the predictions. The unidirectional fatigue predictions were vastly improved over the traditional SN Curve. While the crossply predictions were not as good, they still demonstrated the applicability of the critical element SN curve to a material with a different geometry. Additionally. such a method may have application in real-time durability evaluation of composite components. / Master of Science

This thesis is concentrated on the long-term fracture of thick unidirectional glass and carbon fibre composites subjected to transverse stress. The objective was to develop a methodology for predicting the long term lifetime of a composite rotor used as part of a flywheel based energy storage system. The flywheel design is based on accommodating high hoop stresses induced during the high speed rotation. However, the different Poisson's ratios of the constituent materials in the rotor result in a complex stress distribution with significant stresses introduced in a direction transverse to the fibres. The possibility has been raised that the lifetime of the rotor will be limited by crack growth in this transverse direction, originating from defects (pores, cracks etc) that can be introduced into the rotor during its manufacture. The approach explored in this work has been to adopt a fracture mechanics based methodology whereby the rate of crack growth in a thick composite is measured as a function of an applied stress intensity. The basic fracture parameters for the material were measured such that the time taken for a crack to grow to a size sufficient to cause failure under an operating stress could be calculated. The materials were also examined to characterise the nature, size and extent of inherent defects. The stress distribution in the rotor under operating conditions was modelled using finite element analysis. The combination of information on inherent defects, stress directions and crack growth rates enable predictions to be made concerning the likely lifetime of the composites. Proof stress diagrams were also constructed in order to demonstrate an approach to product quality assurance testing. The end point of the work was to identify critical manufacturing defect sizes that could be tolerated under the specified operating conditions. The methodology developed for lifetime predictions was critically assessed and considered to be generally acceptable. The work did however raise some concerns regarding the applicability of a conventional fracture mechanics approach applied to heterogeneous composite systems where the size of the cracks are very small. It is recommended that future work should concentrate on studying this area with an emphasis on crack nucleation studies rather than on further crack propagation work.

In this thesis, the seminal work of Stokes concerning the ow of a Navier-Stokesuid due to a suddenly accelerated or oscillating plate and the ow due to torsionaloscillations of an innitely long rod in a Navier-Stokes uid is extended to a uid withpressure dependent viscosity. The viscosity of many uids varies signicantly withpressure, a fact recognized by Stokes; and Barus, in fact, conducted experiments thatshowed that the variation of the viscosity with pressure was exponential. Given sucha tremendous variation, we study how this change in viscosity aects the nature of thesolution to these problems. We nd that the velocity eld, and hence the structureof the vorticity and the shear stress at the walls for uids with pressure dependentviscosity, are markedly dierent from those for the classical Navier-Stokes uid.