AbstractThe Iosipescu shear test, also known as asymmetric four point bending of a V-notched beam,is frequently used for measuring in-plane shear properties of composites. The ASTM standard(ASTM D-5379-05) regulates how the test is to be performed. It prescribes a notch openingangle of 90° independently of the material tested, although this has proven to produceinhomogenous strain distributions in the test region (between the notches) for orthotropicmaterials. Commonly, strain gauges are attached in the center of the test region where thedeviation from average strain is high. Thus, systematic errors in the measurement in the rangeof 10% or more may be introduced. The modified Iosipescu shear test, presented in this thesis, uses a variable notch opening angledepending on the material orthotropy and orientation to accomplish even stress- and strainfields in the test region. The variable notch opening angle accommodates both anisotropicmaterials and their orientation. Based on an elastic rescaling theory for orthotropic materials,the geometry was rescaled to recreate the same stress distribution in the test region as forisotropic materials. Specifically the notch opening angle was rescaled depending on theorthotropic ratio, the ratio of the two in-plane principal stiffnesses (Ex/Ey), to obtain theoptimal notch geometry. The rescaling procedure has been verified numerically with FEsimulationsand experimentally for several materials of different orthotropic ratio showingthat this was a very feasible method. Using a whole field optical measurement system duringtesting, significantly more homogenous strain fields were observed than for the standardspecimen geometry. Thus, there is no longer any need for correction factors, relying on FEsimulation,to obtain correct shear moduli. Constitutive shear properties and strength can thusbe more accurately measured, more completely and with fewer sources of error. Notablyhigher shear strengths at larger strains were also recorded compared to standard testing.The function of the new fixture was evaluated and compared with the standard Wyomingfixture. Combined in-situ 3D deformation measurements of both the new fixture and thespecimen showed that out of plane specimen deformation was very low and substantiallylower than the Wyoming fixture. Thus considerably lower parasitic stresses are introducedwith the new fixture. Recommendations regarding fastening of the specimen were determined based on simpleanalysis combined with FE-calculations and experiments. For both isotropic and orthotropic itwas found favorable if the clamp load used to hold the specimen and the expected net peakload and were set about equal. This reduces the risk of failure outside the test region bycrushing, brushing, splitting and etc. The same effects as shown in the FE-simulations werealso observed experimentally and of similar relative magnitude.Problems with differences in strains arising on the front and back face of the specimen duringtesting have been frequently reported in the literature. This is believed to stem from deviationsfrom nominal specimen geometry such as non-parallel and/or non-perpendicular boundingsurfaces. Three types of these combinations were evaluated numerically and the two mostsignificant were confirmed experimentally. The most critical geometrical deviation assessedwas a specimen with slightly conical cross section in the gripping region. For both isotropicand orthotropic materials, very small deviations from nominal geometry, caused unacceptablylarge errors in measurements of constitutive behavior / QC 20100827

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2018-01-15T21:40:49Z No. of bitstreams: 1 VirginiaBezerraOliveiraCampos_DISSERT.pdf: 3793113 bytes, checksum: 4435d7d3c46fc8d73615a9b23cd0e5f4 (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2018-01-17T15:55:28Z (GMT) No. of bitstreams: 1 VirginiaBezerraOliveiraCampos_DISSERT.pdf: 3793113 bytes, checksum: 4435d7d3c46fc8d73615a9b23cd0e5f4 (MD5) / Made available in DSpace on 2018-01-17T15:55:28Z (GMT). No. of bitstreams: 1 VirginiaBezerraOliveiraCampos_DISSERT.pdf: 3793113 bytes, checksum: 4435d7d3c46fc8d73615a9b23cd0e5f4 (MD5) Previous issue date: 2017-08-10 / A constante busca de materiais mais eficientes e com alto desempenho mec?nico, contribue efetivamente para a crescente demanda na utiliza??o de comp?sitos h?bridos. O processo de hibridiza??o pode propiciar melhoria significativa na combina??o global de propriedades, possibilitando assim aplica??es espec?ficas em elementos estruturais que requerem excel?ncia em suas propriedades mec?nicas e baixa massa espec?fica. Atrelado ? gradativa utiliza??o destes materiais, estudos que incidem nas previs?es de falha e, consequentemente, an?lises das cargas m?ximas que estes materiais podem suportar tornam-se essenciais para garantia da confiabilidade quanto a sua aplica??o. Neste sentido, a presente pesquisa buscou analisar o comportamento mec?nico de uma l?mina constitu?da ? base de tecido h?brido bidirecional (vidro/carbono) e resina ep?xi ?ster-vin?lica. Bem como, avaliar a representatividade de crit?rios de falhas desenvolvidos para comp?sitos unidirecionais quando aplicados em comp?sito h?brido de natureza bidirecional. A l?mina estudada foi caracterizada mecanicamente com base nos resultados obtidos pelos ensaios de tra??o e cisalhamento realizados em amostras com fibras de carbono orientadas a 0?, 30?, 45?, 60? e 90?. Observou-se a partir destes ensaios que materiais com fibras em ?ngulos fora do eixo (off-axis) de aplica??o de carga apresentam resist?ncia menor, embora apresentem maiores alongamentos, quando comparados a amostras com fibras alinhadas na dire??o principal do carregamento. Os dados experimentais referentes ?s propriedades cisalhantes, normatizados pela ASTM D3518M-13 (ensaio de cisalhamento por tra??o ?45?) e ASTM D5379-12 (ensaio de Iosipescu), apresentaram diferen?as significativas para a resist?ncia ao cisalhamento e similaridade nos valores do m?dulo de cisalhamento. O ensaio de tra??o ?45?, conforme an?lise macromec?nica, mostrou-se como o mais adequado para comp?sito com caracter?sticas similares ao analisado. Ao inserir os dados dos ensaios nas equa??es te?ricas que definem os crit?rios de falhas da M?xima Tens?o, Tsai-Hill, Tsai-Wu e Hashin e, analis?-los estatisticamente, contatou-se que estas teorias de falhas descrevem satisfatoriamente o comportamento experimental da l?mina, e, portanto, podem ser utilizados para predizer a resist?ncia mec?nica em comp?sitos como o avaliado, embora se tenha observado ?ndices de representatividade maiores quando se utiliza o ensaio de cisalhamento por tra??o ?45?. / The constant search for more efficient materials and with high mechanical performance, contributes effectively to the growing demand in the use of hybrid composites. The hybridization process can provide significant improvement in the overall combination of properties, thus enabling specific applications in structural elements that require excellence in their mechanical properties and low specific mass. Coupled with the gradual use of these materials, studies that focus on fault predictions and, consequently, analyzes of the maximum loads that these materials can withstand become essential to guarantee the reliability of their application. In this sense, the present research sought to analyze the mechanical behavior of laminae composed of two-way hybrid fabric (glass/carbon) and epoxy resin vinyl ester. As well as evaluating the representativeness of failure criteria developed for unidirectional composites when applied in hybrid composites of a bidirectional nature. The laminas studied were mechanically characterized based on the results obtained by tensile and shear tests performed on samples with carbon fibers orientated at 0?, 30?, 45?, 60? and 90?. It was observed from these tests that materials with fibers at off-axis loading angles exhibit lower strength, although they exhibit greater elongations when compared to samples with fibers aligned in the main direction of loading. Experimental data on shear properties, standardized by ASTM D3518M-13 (tensile shear test ?45?) and ASTM D5379-12 (Iosipescu's test), showed significant differences for shear strength and similarity in the modulus values of Shear. The tensile test ? 45?, according to macromechanical analysis, proved to be the most suitable for composite with characteristics similar to the one analyzed. By inserting test data into the theoretical equations defining Tsai-Hill, Tsai-Wu, and Hashin fault criteria, and statistically analyzing them, it was found that these fault theories satisfactorily describe the experimental behavior of the blade , and therefore can be used to predict mechanical strength in composites as evaluated, although higher representativity indices were observed when using the ? 45? traction shear test.

In the continuing quest for more efficient designs, structural adhesives are being used in place of, or with, traditional fastening methods; however designing with adhesives is refined as traditional methods. To obtain the adhesive design properties, tests are often performed on bulk tensile and bonded shear specimens. Questions remain about the relationship between properties obtained from in situ adhesive joints and bulk adhesive specimens. As a result, an experimental plan was developed which characterized both the linear and nonlinear region of bulk and in situ adhesive performance of a two-part acrylic adhesive from Dow Chemical Company. A standard uniaxial tensile test was used for the bulk normal, while an Iosipescu shear test was used to characterize the bulk shear performance. In situ testing was performed on a napkin-ring specimen loaded in both tension and torsion. Stress-strain relationships in both shear and normal were developed and bulk and in situ adhesive performance was compared. Observations from testing were: 1. Bulk shear and in situ shear tests showed similar performance in both the linear and nonlinear regions. 2. Modulus of elasticity in bulk adhesive tests was similar to the effective modulus of elasticity in in situ tests. 3. Prediction of normal yield strengths of the in situ adhesive through simple failure theory models proved to be inaccurate. Stress singularities, loading imperfections, and potentially a hydrostatic sensitivity were considered possible explanations. 4. Adhesive showed sensitivity to voiding and surface flaws when loaded in a tensile configuration, refinement of specimen fabrication minimized these effects. / Master of Science

Mechanical pulping for producing pulps from softwood suitable for printing grade papers, like news, is a highly energy-intensive process consuming around 2000 kWh/t in electrical energy. Due to increasing energy costs and environmental issues there is a high demand for decreasing this energy consumption. The mechanical treatment of wet wood pieces in a refiner, in the mechanical pulp plant, is a complex mechanical loading. This is a process occurring between rotating discs at high speed and temperatures of 140 °C - 160 °C, where by means of shear and compression forces the fibres are separated and then made flexible, fibrillated and collapsed for good bonding ability. In this process also fines are created giving the optical properties of the paper. In mechanical pulping only a fraction of the applied energy is used for the structural changes of the wood material. Thus fundamental studies of the loading modes of wood under refining conditions and in particular under combined shear and compression loading are desired to gain more information regarding the possibility of affecting the mechanical pulping in an energy efficient way. The possibilities to study the behaviour of wood under a combined shear and compression load were in this thesis investigated using two methods: the Iosipescu shear test and the Arcan shear test. In both apparatus different combinations of shear and compression load were achieved by different rotations of the shear test device itself. Measurements with the Iosipescu device on a medium density fibreboard showed good agreement between experimental results and numerical simulations. Finite element analysis on wood showed, however, that with the use of a homogeneous material in the model the level of strain reached would be ten times smaller than experimentally measured. This fact is probably due to the honeycomb structure of the wood cells that allows for different local deformations that could not be represented by a continuous material model. Thus to study the deformations on the fibre level of wood an experimental equipment that uses smaller samples was needed. With a modified Arcan shear device such deformations under combined shear and compression load and in pure compression were possible showing different deformation patterns. During pure compression the cell walls bend in a characteristic “S” shape, independently of the shape of the fibre cells and their cell wall thickness. Under combined shear and compression, however, mainly the corners of the fibre cells deform giving a “brick” shape to the cells. In a second deformation performed in compression, the fibre cells follow the same deformation pattern as given by the first deformation type whether in compression or in combined shear and compression. The interpretation is that permanent defects in the cells themselves are introduced already in the first load cycle of the wood samples. The energy used under the different loading conditions showed that the first deformation required the largest amount of energy, for all loading conditions. The deformation in compression required larger amounts of energy than the deformation in combined loads. For subsequent deformations less energy was needed for compression if a combined load had preceded it. Due to the fact that less energy is needed to start to deform wood in combined load than under compression load, the application of a combined load as a first cycle may thus be a way to permanently deform fibres using less energy. To investigate the critical parameters determining the permanent deformation of cells, a finite element model of a network of twelve cells was developed. Special care was given to the material properties to study how the variation of the fibril angle in the different layers affects the deformation pattern of the wood fibres under the different loading conditions. The model shows that whether modelled as homogeneous linear isotropic material or as an orthotropic material defined for every layer of the cells wall, no difference in the deformation of the network of the fibres was achieved. It is probable that the deformation type is more determined by the geometry of the fibres themselves than by their material properties / QC 20101005

No description available.

Submitted by Johnny Rodrigues (johnnyrodrigues@ufcg.edu.br) on 2018-04-26T21:10:23Z No. of bitstreams: 1 JOÃO VITOR DE QUEIROZ MARQUES - DISSERTAÇÃO PPGEM 2015..pdf: 10546995 bytes, checksum: acf6dba421165a1333cc0862541902b2 (MD5) / Made available in DSpace on 2018-04-26T21:10:23Z (GMT). No. of bitstreams: 1 JOÃO VITOR DE QUEIROZ MARQUES - DISSERTAÇÃO PPGEM 2015..pdf: 10546995 bytes, checksum: acf6dba421165a1333cc0862541902b2 (MD5) Previous issue date: 2015-08-28 / Os compósitos poliméricos costumam ter uma elevada resistência mecânica em relação à sua densidade. Uma característica fundamental para que os materiais possam ser utilizados na engenharia é a previsibilidade de seu comportamento quanto ao carregamento. Devido à natureza heterogênea da estrutura dos compósitos e devido a interação entre suas fases constituintes as características deste material dependem das propriedades das fases constituintes, da fração volumétrica de cada fase constituinte, da iteração entre suas fases e do método de fabricação. Este trabalho trata do desenvolvimento de garras para ensaio mecânico, para materiais compósitos, que possibilitem obter o valor do cisalhamento interlaminar de compósitos poliméricos. O cisalhamento interlaminar permite avaliar, entre outras coisas, a influência do método de fabricação na resistência do compósito. Foram desenvolvidos dois tipos de garras: o tipo Iosipescu e o tipo V-notched Rail Shear. Para o desenvolvimento das garras de ensaio foi utilizada a metodologia seguinte: Projeto Informacional, Projeto conceitual, Projeto Preliminar, Projeto Detalhado, Fabricação e Testes. Além da montagem de um sistema de Instrumentação para avaliar a deformação localizada no centro dos corpos de prova. Os resultados obtidos com a garra Iosipescu apresentaram uma variação de 13,6% em relação a literatura, enquanto naquelas obtidas com a garra V-notched Rail Shear obtiveram uma variação de 3,9 % em relação a literatura.

[ES] La evolución de la tendencia del pensamiento de la gente en los últimos años ha cambiado, llevándonos a adquirir nuevos valores enfocados en la sostenibilidad de los recursos naturales y el respeto hacia el medio ambiente. Con ello, la perspectiva de producto se ha visto afectada en todos los sectores, incluido el sector de la automoción. La aparición de nuevas normas medioambientales han establecido obligaciones sobre los fabricantes de vehículos respecto a la reducción de consumo y emisiones contaminantes por lo que cada vez es más habitual identificar materiales ligeros en vehículos de uso cotidiano con la finalidad de mejorar la eficiencia energética a partir de la reducción de masa. El presente estudio pretende avanzar un paso más en la utilización de materiales compuestos centrando su temática en el desarrollo de nuevos materiales para la fabricación de componentes estructurales de vehículos que permitan la reducción de consumos desde un punto de vista sostenible. Para ello se plantea la aplicación de nuevos materiales compuestos basados en la utilización de fibras naturales, que sustituyan a los materiales utilizados tradicionalmente. En el estudio se plantea la utilización de una única matriz (epoxi) común a todos los tejidos naturales ensayados que permita realizar un estudio comparativo centrado en los tejidos, para obtener un material compuesto eficiente en su fabricación, uso y reciclaje buscando el equilibrio entre densidad, coste, resistencia y reciclabilidad. El estudio ha consistido en la realización de ensayos de tracción, compresión, flexión, impacto, dureza, cortadura y fatiga, a partir de los cuales se han podido extraer las propiedades mecánicas necesarias para realizar un modelo MEF uniaxial en el software ANSYS ACP, comparando resultados con distintas orientaciones de fibras. Tras esto, se ha dimensionado un componente utilizando el modelo MEF uniaxial para un estudio multiaxial. Este componente ha sido fabricado y posteriormente ensayado en un banco de fatiga con la finalidad de contrastar los resultados del software con los obtenidos empíricamente, y a su vez validar la aplicación. / [CA] L'evolució de la tendència del pensament de la gent als últims anys ha canviat, portant-nos a adquirir nous valors enfocats a la sostenibilitat dels recursos naturals i al respecte cap al medi ambient. A causa d'això, la perspectiva de producte s'ha vist afectada en tots els sectors, inclòs al sector de l'automoció. L'aparició de noves normes mediambientals han establit obligacions sobre els fabricants de vehicles respecte a la reducció de consum i emissions contaminants pel que cada vegada és més habitual identificar materials lleugers en vehicles d'ús quotidià amb la finalitat de millorar l'eficiència energètica a partir de la reducció de massa. El present estudi pretén avançar un pas més en la utilització de materials compostos centrant la seua temàtica en el desenvolupament de nous materials per a la fabricació de components de vehicles que permeten la reducció de consums des d'un punt de vista sostenible. Per a això es planteja l'aplicabilitat de nous materials compostos basats en la utilització de fibres naturals, que substituïsquen els materials emprats tradicionalment. En l'estudi es planteja la utilització d'una única matriu (epoxi) comú a tots els teixits naturals assajats que permeta realitzar un estudi comparatiu centrat en els teixits per obtindre un material compost eficient en la seua fabricació, ús i reciclatge, buscant l'equilibri entre densitat, cost, resistència i reciclabilitat. L'estudi ha consistit en la realització d'assajos de tracció, compressió, flexió, impacte, duresa, tallant i fatiga, a partir dels quals s'han pogut extraure les propietats mecàniques necessàries per a realitzar un model MEF uniaxial al programa ANSYS ACP, comparant resultats amb diferents orientacions de fibres. Després d'això, s'ha dimensionat un component utilitzant el model MEF uniaxial per a un estudi multiaxial. Aquest component s'ha fabricat i posteriorment s'ha assajat en un banc de fatiga amb la finalitat de contrastar els resultats del programa amb els obtinguts empíricament, i alhora ha servit per validar l'aplicació. / [EN] The evolution of the trend of people's thinking in recent years has changed, leading us to acquire new values focused on the sustainability of natural resources and respect for the environment. As a result, the product outlook has been affected in all sectors, including the automotive. The imposition of new environmental regulations has established obligations for vehicle manufacturers in terms of fuel consumption and polluting emissions, which is why it is increasingly common to identify lightweight materials in everyday vehicles, in order to improve energy efficiency through from mass reduction. This study seeks to advance the use of composite materials, focusing its theme on the development of new materials for the manufacture of structural vehicle components. For this, it is proposed the development of new composite materials based on the use of natural fibers is proposed to replace the materials traditionally used. In the work is proposed a comparative study focused on fabrics, using a single matrix (epoxy) common to all the test specimens, to obtain an efficient composite material in its manufacture, use and recycling, seeking the balance between density, cost, resistance and recyclability. During the development of the research, it has been necessary to perform tensile, compression, bending, impact, hardness, shear and fatigue tests to extract the mechanical properties necessary to make a uniaxial MEF model in the ANSYS ACP software, comparing results with different orientations fibers. After this, a component has been dimensioned using the uniaxial FEM model for a multiaxial study. This component has been manufactured and subsequently tested in a fatigue bench in order to compare the results of the software with those obtained empirically, and in turn validate the application. / Oliver Borrachero, BA. (2021). Estudio de la utilización de fibras naturales en materiales compuestos laminados para fabricación de componentes de automoción [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/165809 / TESIS