Dissertations / Theses on the topic '3 point bend test'

This work characterizes the material properties of carbon infiltrated carbon nanotube (CI- CNT) structures. The impacts of temperature, time, and hydrogen flow rates on the material prop- erties of modulus of elasticity and strength are examined and compared. Carbon infiltration levels are assessed through the use of SEM images to determine which parameters give the highest level of infiltration. Through the use of SEM, carbon capping is observed on samples infiltrated for longer times at 900 and 950◦ C, suggesting that the samples are not being infiltrated during the entire desired infiltration period at these temperatures. The highest material properties of modulus and strength were reached when infiltrating the carbon nanotube forests for 150 mins at 850◦ C with hydrogen flowing at 311 sccm (0.0115 m/s). With these parameters, a modulus of 20.4 GPa and strength of 289.8 MPa were attained. The poorest results were seen when the samples were infiltrated at 800◦ C, and is therefore not recommended as an infiltration temperature if high mod- ulus and strength are desired. Density is correlated to strength and modulus and it is seen that there is a strong correlation between higher strength and modulus with higher density.

The increased use of thermoplastics in load carrying components, especially in the automotive industry, drives the needs for a better understanding of its complex mechanical properties. In this thesis work for a master degree in solid mechanics, the mechanical properties of a PA 6/66 resin with and without reinforcement of glass fibers experimentally been investigated. Topics of interest have been the dependency of fiber orientation, residual strains at unloading and compression relative tension properties. The experimental investigation was followed by simulations implementing existing and available constitutive models in the commercial finite element code LS-DYNA. The experimental findings showed that the orientation of the fibers significantly affects the mechanical properties. The ultimate tensile strength differed approximately 50% between along and cross flow direction and the cross-flow properties are closer to the ones of the unfilled resin, i.e. the matrix material. An elastic-plastic model with Hill’s yield criterion was used to capture the anisotropy in a simulation of the tensile test. Residual strains were measured during strain recovery from different load levels and the experimental findings were implemented in an elastic-plastic damage model to predict the permanent strains after unloading. Compression tests showed that a stiffer response is obtained for strains above 3% in comparison to tension. The increased stiffness in compression is although too small to significantly influence a simulation of a 3 point bend test using a material model dependent of the hydrostatic stress.

Thesis (M.S.)--State University of New York at Binghamton, Thomas J. Watson School of Engineering and Applied Science, Department of Mechanical Engineering, 2007.
Includes bibliographical references.

Aluminium matrix composites are among the most promising candidate materials for light weight and high strength applications such as transportation and armour. In a previous study 6061 aluminum matrix composites reinforced with plain weave carbon fiber preform (AS4 Hexcel) were successfully fabricated by squeeze casting using the laminate fabrication technique. This research aims at optimizing the fabrication process in order to achieve improved strength and mechanical properties. It focuses on the liquid infiltration squeeze casting method. Good mechanical bonding between fiber and aluminium is achieved thanks to improved infiltration and impregnation of the fabric by liquid aluminium. Oxidation products at fiber/aluminium interface and porosity are reduced. As a result, composites are produced with overall improved mechanical properties. The flexural strength is increased by up to 19.9% and 15.4% compared to the laminate approach and the reference 6061 aluminium alloy squeeze cast under identical conditions, respectively. Similarly, overall hardness is improved. However, the impact strength is reduced by 7.76% and 25.78% when compared to casts fabricated by the laminate method and the reference aluminium alloy, respectively. The thesis constitutes a good basis for further research on fiber and particle reinforced aluminium matrix composites with the goal of further improving fracture toughness, particularly for gradient materials used in armour applications.

Disertační práce se zabývala vlivem adheze mezi vláknovým (FRC) a částicovým (PFC) kompozitem a složením obou komponent na mechanické vlastnosti a způsob porušování modelových bi-materiálových kompozitních těles při statickém namáhání. Zkoumán byl také vliv způsobu přípravy bi-materiálového kompozitního tělesa na pevnost adheze mezi jeho kompozitními komponentami. K hodnocení mechanických vlastností bi-materiálových PFC/FRC těles byl použit jak 3 tak 4-bodový ohybový test za pokojové teploty a relativní vlhkosti 70%. Modifikovaný vytrhávací test byl použit k měření smykové pevnosti adheze mezi vláknovým a částicovým kompozitem. Tyto výsledky byly korelovány s výsledky ze strukturní a fraktografické analýzy (TGA, SEM). Experimentální data byla poté analyzována pomocí existujících mikromechanických modelů a byl nalezen vztah mezi tuhostí modelových bi-materiálových těles, složením a geometrií uspořádání jejich komponent a pevností adheze mezi těmito komponentami. Na základě těchto výsledků byl navržen optimální způsob vrstvení a přípravy PFC/FRC bimateriálových těles. Navržené postupy byly použity k přípravě a pre-klinickým testům nosných konstrukcí zubních můstků.

The effects of pore density and distribution were investigated on the fatigue crack initiation behavior in an A713 sand cast aluminum alloy plate of 12 mm thickness. The applied stress- the number of cycles to failure (S-N) curves of the samples taken from 2 mm and 5 mm from the free surface were obtained using four-point bend fatigue testing at room temperature, frequency of 20 Hz, stress ratio of 0.1, sinusoidal waveform, and in ambient air. The fatigue strengths of both, the 2 mm and 5 mm samples were 60% of the yield strength (σy=171.9 MPa) of the alloy. Optical microscopy, SEM, and EDS mapping were used to characterize pores and particles in 2 mm and 5 mm samples. The average pore sizes of the 2 mm and 5 mm samples were measured to be 10 to 14 μm, and 14 to 32 μm, respectively. The pore number densities in 5 mm and 2 mm samples were comparable, but higher number densities of non-clustered coarse pores (gas pores) were observed in 5 mm samples. The crack population found after fatigue testing showed a Weibull function of stress level. The peaks of strength distributions of fatigue weak link density of 5 mm and 2 mm samples were measured to be 0.017 mm-2 at 67.6 % σy, and 0.01027 mm-2 at 69.5% σy. Crack populations, when normalized by number densities of gas pores (non-clustered) and number densities of shrinkage pores (clustered), giving crack nucleation rate (crack/pore, mm-2), showed a good fit with the Weibull function in 2 mm and 5 mm samples. Shrinkage and gas pores could both become the main crack initiation sites (i.e. fatigue weak links) in this alloy. Higher nucleation rates of gas pores and shrinkage pores were observed in 5 mm samples compared to those rates in 2 mm samples. At high applied stresses, the 2 mm samples showed better fatigue lives than those of 5 mm samples. Fractured surfaces were analyzed using SEM and found that the main crack initiation were predominately from pores. The pores on the fractured surfaces were counted and their depth and width were measured. It was found that the cracks may not necessarily initiate from coarse pores, but sometimes from shrinkage pores (i.e. group of pores). The depth from the free surface, the width, the size, and the orientation of pores are key factors in increasing the driving force for crack initiation and subsequently those pores turn into long cracks. Moreover, the aspect ratios of pores on the main cracks were measured and found that in 5 mm samples, some pores have an aspect ratios of less than 0.7, which means that these pores are elongated in depth and have a narrow width which increase the stress concentration on the surface, thus, increasing the driving force for crack nucleation.

Esse trabalho tem como objetivo estabelecer um método simples de ensaio que permita determinar a resistência à tração e módulo elástico de partículas individuais de agregados graúdos naturais submetidas à carga de compressão. O método de ensaio foi desenvolvido baseado no ensaio de carga pontual (Point Load Test) que permite obter a resistência à tração de partículas. Para a determinação do módulo de elasticidade foi acoplado ao método um LVDT e foi satisfeita a condição para aplicação da teoria de contato de Hertz (contato curvo-plano entre as partículas e as fixações de aplicação da carga). Inicialmente a metodologia foi avaliada utilizando como material de referência partículas de vidro (com geometrias similares aos agregados). Após a validação no vidro, o método de ensaio foi aplicado em agregados graúdos de granito. Propôs-se um método de seleção de partículas com base na sua distribuição de frequência de absorção, com o intuito de reduzir a quantidade de partículas testadas mecanicamente necessárias para obter a distribuição de Weibull da resistência à tração (e módulo de elasticidade). Para tanto, foi feita a determinação da absorção de água individual de centenas de partículas selecionadas por amostragem a esmo da população de agregados. Com base nos resultados, foi possível determinar a distribuição de Weibull da resistência à tração e módulo de elasticidade das partículas. Observou-se que as resistências à tração variaram de 3 a 15 MPa. Os agregados possuíam aproximadamente 10% da população de partículas com resistência à tração inferior a 5 MPa, o que pode influenciar as classes de resistência à compressão de concretos >50MPa. Os módulos elásticos dos agregados também foram variáveis (18-67 GPa) e aproximadamente 10% da população de partículas com módulo elástico <30 GPa. Isso pode limitar o módulo de elasticidade do concreto (que geralmente é em torno de 27 GPa), dependendo do processo de escolha dos agregados. As funções exponenciais inversas fundamentais entre essas propriedades mecânicas e a porosidade foram confirmadas (para valores médios).
The aim of this work is to establish a simple test method to determine the tensile strength and elastic modulus of individual natural aggregate particles subjected to a compression load. The test method was developed based on the Point Load Test, that allows to obtain the tensile strength of particles. For the determination of the elastic modulus, an LVDT was coupled to the method and the condition for application of Hertz contact theory (curved-plane contact between the particles and the load application fixations) was satisfied. Initially, the method was evaluated using glass particles as reference (with geometries similar to aggregates). After validation on the glass, the test method was applied to coarse granite aggregates. A method of particle selection was proposed based on its absorption frequency distribution, in order to reduce the amount of mechanically tested particles required to obtain the Weibull distribution of tensile strength (and elastic modulus). For this purpose, the determination of the individual water absorption of hundreds of particles selected by random sampling of the population of aggregates was made. Based on the results, it was possible to determine the Weibull distribution of the tensile strength and elastic modulus of the particles. The tensile strengths ranged from 3 to 15 MPa. The aggregates had approximately 10% of the particles population with tensile strength less than 5 MPa, which may influence the classes of concrete with compressive strength > 50MPa. The elastic modulus of the aggregates was also variable (18-67 GPa), with approximately 10% of the particle population with elastic modulus <30 GPa. This may limit the elastic modulus of the concrete (usually around 27 GPa) depending on how the aggregates are selected. The fundamental inverse exponential functions between these mechanical properties and the porosity were confirmed (for mean values).

Cold spray is a novel coating method. Due to its low-temperature character, it has a potential to replace the high-temperature thermal spray processes in some applications. The presented work analyzes the microstructure and the phase composition of pure metal coatings deposited by cold spraying and evaluates selected mechanical properties. Specimens prepared by readily used HVOF industrial technology were used for comparison purposes.

Ce projet de thèse se situe dans le cadre de l'étude de la fiabilité prédictive de nouveaux concepts d'assemblages microélectroniques de type « system in package » SiP. L'objectif est de développer une méthodologie de fiabilité prédictive adaptée aux nouveaux concepts d'assemblage qui permet d'optimiser et de prédire les performances dès la phase de conception. Elle est ensuite appliquée sur des projets concrets. Cette méthodologie de fiabilité prédictive fait intervenir des études expérimentales, des simulations thermomécaniques et des analyses statistiques pour traiter les données et évaluer la fiabilité et les risques de défaillance. L'utilisation d'outils de simulation des composants électroniques est bien adaptée pour aider à l'évaluation des zones les plus fragiles, la mise en place des règles de conception et la détermination des paramètres les plus influents avec une réduction du temps de mise en marché d'un produit fiable et une optimisation des performances. Les études réalisées sur le silicium avec deux tests : bille sur anneau et test trois points montrent que le rodage et l'épaisseur ont une influence sur la variation de la contrainte et la déflexion du silicium à la rupture. Avec le test trois points, le déclenchement des fissures est lié à la qualité de sciage et de rodage. Cependant avec le test bille sur anneau, seule la qualité de surface influence le déclenchement des fissures. Le test bille sur anneau est bien adapté pour évaluer la qualité de surface du silicium. Avec les techniques chimiques de réduction de contraintes, comme la gravure humide et plasma, la résistance à la rupture a été considérablement améliorée. Ces tests de rupture sur le silicium ont permis de caractériser la rupture du silicium sous une contrainte de flexion et de compléter les résultats de simulation. Ces travaux démontrent, le besoin et l'utilité du prototypage virtuel des composants électroniques et de l'utilisation d'une méthodologie prédictive dans l'évaluation de la fiabilité en l’appliquant sur des composants réels
This thesis project is a study of the predictive reliability of new microelectronic package concepts such as "system in package" SiP. The objective is to develop a reliable predictive methodology adapted to the new assembly concepts to optimize and to predict the performance at the design phase. Then, the methodology is applied to concrete projects. This methodology of predictive reliability involves the use of experimental studies, thermomechanical simulations and statistical analysis to process the data and assess the reliability and risks of failure. The use of simulation tools for electronic components is well suited to assist in the evaluation of the most fragile areas, the setting up of design rules and the determination of the most influential parameters with a reduction in the setup time market for a reliable and optimized performance. Studies on silicon strength are conducted with two tests: ball on ring test and on three-point bend test show that the grinding and the thickness influence the variation of the stress and deflection of the silicon at break. With the three points bend test, the onset of crack is linked to defects in sawing and grinding zone. However, with the ball on ring test, only the surface quality influences the initiation of cracks. The ball on ring test is well suited for evaluating the quality of the silicon surface. Chemical techniques of stress release, such as wet etching and plasma etching, improve significantly the strength of silicon samples. These tests on silicon dies are used to characterize the breakdown of silicon under bending test and to complete the simulation results. We have demonstrated in this work, the need and the usefulness of the virtual prototyping of electronic components and the use of a predictive methodology in assessing reliability

Aim of this diploma thesis is to choose new pattern wax for Fimes a.s. foundry. New wax should substitute old not fully satisfactory pattern wax which caused problems in technological process resulting in increased number of rejects. New pattern wax should eliminate current problems and help foundry with producing large, thin-walled, high-quality castings. Numbers of pattern waxes supplied by world’s leading wax manufacturers were subjected to laboratory tests and pilot study. This diploma thesis is part of project Alfa TA01010766: „Research and development of production technology large, thin and high quality castings of aluminium alloys “

La present tesi doctoral s’ha centrat en el repte d’aconseguir, mitjançant Fabricació Additiva (FA), models per a assaig quirúrgic, sota la premissa que els equips per fer-los haurien de ser accessibles a l’àmbit hospitalari. L’objectiu és facilitar l’extensió de l’ús dels prototips com a eina de preparació d’operacions quirúrgiques, transformant la pràctica mèdica actual de la mateixa manera que en el seu moment ho van fer tecnologies com les que van facilitar l’ús de radiografies. El motiu d’utilitzar FA, en lloc de tecnologies més tradicionals, és la seva capacitat de materialitzar de forma directa les dades digitals obtingudes de l’anatomia del pacient mitjançant sistemes d’escanejat tridimensional, fent possible l’obtenció de models personalitzats. Els resultats es centren en la generació de nou coneixement sobre com aconseguir equipaments d’impressió 3D multimaterials accessibles que permetin l’obtenció de models mimètics respecte als teixits vius. Per facilitar aquesta buscada extensió de la tecnologia, s’ha focalitzat en les tecnologies de codi obert com la Fabricació per Filament Fos (FFF) i similars basades en líquids catalitzables. La recerca s’alinea dins l’activitat de desenvolupament de la FA al CIM UPC, i en aquest àmbit concret amb la col·laboració amb l’Hospital Sant Joan de Déu de Barcelona (HSJD). El primer bloc de la tesi inclou la descripció de l’estat de l’art, detallant les tecnologies existents i la seva aplicació a l’entorn mèdic. S’han establert per primer cop unes bases de caracterització dels teixits vius -sobretot tous- per donar suport a la selecció de materials que els puguin mimetitzar en un procés de FA, a efectes de millorar l’experiència d’assaig dels cirurgians. El caràcter rígid dels materials majoritàriament usats en impressió 3D els fa poc útils per simular tumors i altres referències anatòmiques. De forma successiva, es tracten paràmetres com la densitat, la viscoelasticitat, la caracterització dels materials tous a la indústria, l’estudi del mòdul elàstic de teixits tous i vasos, la duresa d’aquests, i requeriments com l’esterilització dels models. El segon bloc comença explorant la impressió 3D mitjançant FFF. Es classifiquen les variants del procés des del punt de vista de la multimaterialitat, essencial per fer models d’assaig quirúrgic, diferenciant entre solucions multibroquet i de barreja al capçal. S’ha inclòs l’estudi de materials (filaments i líquids) que serien més útils per mimetitzar teixits tous. Es constata com en els líquids, en comparació amb els filaments, la complexitat del treball en processos de FA és més elevada, i es determinen formes d’imprimir materials molt tous. Per acabar, s’exposen sis casos reals de col·laboració amb l’HJSD, una selecció d’aquells en els que el doctorand ha intervingut en els darrers anys. L’origen es troba en la dificultat de l’abordatge d’operacions de resecció de tumors infantils com el neuroblastoma, i a la iniciativa del Dr. Lucas Krauel. Finalment, el Bloc 3 té per objecte explorar nombrosos conceptes (fins a 8), activitat completada al llarg dels darrers cinc anys amb el suport dels mitjans del CIM UPC i de l’activitat associada a treballs finals d’estudis d’estudiants de la UPC, arribant-se a materialitzar equipaments experimentals per validar-los. La recerca ampla i sistemàtica al respecte fa que s’estigui més a prop de disposar d’una solució d’impressió 3D multimaterial de sobretaula. Es determina que la millor via de progrés és la de disposar d’una pluralitat de capçals independents a fi de capacitar la impressora 3D per integrar diversos conceptes estudiats, materialitzant-se una possible solució. Cloent la tesi, es planteja com seria un equipament d’impressió 3D per a models d’assaig quirúrgic, a fi de servir de base per a futurs desenvolupaments.
La presente tesis doctoral se ha centrado en el reto de conseguir, mediante Fabricación Aditiva (FA), modelos para ensayo quirúrgico, bajo la premisa que los equipos para obtenerlos tendrían que ser accesibles al ámbito hospitalario. El objetivo es facilitar la extensión del uso de modelos como herramienta de preparación de operaciones quirúrgicas, transformando la práctica médica actual de la misma manera que, en su momento, lo hicieron tecnologías como las que facilitaron el uso de radiografías. El motivo de utilizar FA, en lugar de tecnologías más tradicionales, es su capacidad de materializar de forma directa los datos digitales obtenidos de la anatomía del paciente mediante sistemas de escaneado tridimensional, haciendo posible la obtención de modelos personalizados. Los resultados se centran en la generación de nuevo conocimiento para conseguir equipamientos de impresión 3D multimateriales accesibles que permitan la obtención de modelos miméticos respecto a los tejidos vivos. Para facilitar la buscada extensión de la tecnología, se ha focalizado en las tecnologías de código abierto como la Fabricación por Hilo Fundido (FFF) y similares basadas en líquidos catalizables. Esta investigación se alinea dentro de la actividad de desarrollo de la FA en el CIM UPC, y en este ámbito concreto con la colaboración con el Hospital Sant Joan de Déu de Barcelona (HSJD). El primer bloque de la tesis incluye la descripción del estado del arte, detallando las tecnologías existentes y su aplicación al entorno médico. Se han establecido por primera vez unas bases de caracterización de los tejidos vivos – principalmente blandos – para dar apoyo a la selección de materiales que los puedan mimetizar en un proceso de FA, a efectos de mejorar la experiencia de ensayo de los cirujanos. El carácter rígido de los materiales mayoritariamente usados en impresión 3D los hace poco útiles para simular tumores y otras referencias anatómicas. De forma sucesiva, se tratan parámetros como la densidad, la viscoelasticidad, la caracterización de materiales blandos en la industria, el estudio del módulo elástico de tejidos blandos y vasos, la dureza de los mismos, y requerimientos como la esterilización de los modelos. El segundo bloque empieza explorando la impresión 3D mediante FFF. Se clasifican las variantes del proceso desde el punto de vista de la multimaterialidad, esencial para hacer modelos de ensayo quirúrgico, diferenciando entre soluciones multiboquilla y de mezcla en el cabezal. Se ha incluido el estudio de materiales (filamentos y líquidos) que serían más útiles para mimetizar tejidos blandos. Se constata como en los líquidos, en comparación con los filamentos, la complejidad del trabajo en procesos de FA es más elevada, y se determinan formas de imprimir materiales muy blandos. Para acabar, se exponen seis casos reales de colaboración con el HJSD, una selección de aquellos en los que el doctorando ha intervenido en los últimos años. El origen se encuentra en la dificultad del abordaje de operaciones de resección de tumores infantiles como el neuroblastoma, y en la iniciativa del Dr. Lucas Krauel. Finalmente, el Bloque 3 desarrolla numerosos conceptos (hasta 8), actividad completada a lo largo de los últimos cinco años con el apoyo de los medios del CIM UPC y de la actividad asociada a trabajos finales de estudios de estudiantes de la UPC, llegándose a materializar equipamientos experimentales para validarlos. La investigación amplia y sistemática al respecto hace que se esté más cerca de disponer de una solución de impresión 3D multimaterial de sobremesa. Se determina que la mejor vía de progreso es la de disponer de una pluralidad de cabezales independientes, a fin de capacitar la impresora 3D para integrar diversos conceptos estudiados, materializándose una posible solución. Para cerrar la tesis, se plantea cómo sería un equipamiento de impresión 3D para modelos de ensayo quirúrgico, a fin de servir de base para futuros desarrollos.

碩士
國立臺北科技大學
土木與防災研究所
99
This study presents the mechanical behavior of hybrid fiber reinforced plastic (HFRP) composite beam. There are two methods to increase the stiffness of pultruded glass fiber reinforced plastic (GFRP) beam and change the failure mode. First method is the GFRP beam filled with epoxy mortar. Second method is the GFRP beam wrapping different fiber sheet consisting of carbon fiber, basalt fiber and hybrid fiber. A series of beam tests will conduct under 3-point bending test to know the force-displacement relationship, stiffness, failure strength and failure mode of the GFRP beam. The Timoshenko beam theory and the finite element method were applied to analyze the profiles, using material properties estimated. Finally compare the experimental result, numerical and analytic result. Both results show the stiffness of GFRP beam filled with epoxy mortar is twice larger than GFRP beam, and the HFRP composite beam displays excellent strength.

碩士
國立交通大學
材料科學與工程學系所
102
In this study, we investigated the qualitative analysis of stress corrosion cracks for Mg-5wt.%Sn alloy by employing 3-point bending test which was different from slow strain rate test regarded as quantitative measurement. We focused on analyzing the correlation between pittings and stress corrosion cracks by using the method mentioned above as well as the discussion of the crack propagation path of Mg-5wt.%Sn under different concentration of Cl- (1,3.5,7wt.%). The result indicated that the route of stress corrosion crack of Mg-5wt.%Sn was obvious intergranular type. We suspected that this behavior could be attributed to the second phase Mg2Sn which was 5~10μm and distributed along the grain boundary after heat treatment. As a result, with the galvanic effect of Mg2Sn and the high chemical activity of grain boundary , we suggested that the prior stress corrosion path of Mg-5wt.%Sn could be grain boundary. The phenomenon that number of pittings for Mg-5wt.%Sn increased with increasing Cl- concentration could be observed through Scanning Electron Microscope (SEM). Besides, Cl- would promote the growth of pittings and accelerate the generation of cracks. The cracks of Mg-5wt.%Sn alloy would appeared with immersion in 7wt.%,3.5wt.% and 1wt.% NaCl solution for 3 hours,5hours and more than 8 hours, respectively. This outcome expressed that the incubation period of crack initiation with immersion in higher Cl- concentration could be sooner than that with immersion in lower Cl- concentration. Furthermore, the propagation rate of cracks under higher Cl- concentration was faster than that under lower Cl- concentration. It could be concluded that the number and depth of pittings, the incubation time of cracks and the propagation rate of cracks were highly sensitive to the concentration of Cl-. These results confirmed the influence of Cl- concentration on the surface passive film which was mainly composed of MgO and Mg(OH)2.