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Orientador: Marcos Tadeu Tibúrcio Gonçalves / Coorientador: Manoel Cléber de Sampaio Alves / Banca: Marcos Valério Ribeiro / Banca: Ivaldo de Domenico Valarelli / Resumo: Este trabalho apresenta estudos de usinabilidade de peças de madeira de eucalipto, tendo por objetivo principal efetuar análises da resistência de juntas coladas em relação à qualidade das superfícies usinadas, a fim de se verificar a influência da rugosidade superficial sobre a adesão das superfícies coladas com adesivo à base de acetato de polivinila (PVA). Amostras da espécie de madeira Eucalyptus saligna foram preparadas para testes de resistência na lâmina de cola em ensaios de ruptura por cisalhamento e por tração normal segundo a norma NBR 7190. As superfícies de colagem foram preparadas por operação de fresamento empregando-se velocidade nominal de avanço de 11,0 m/min e posteriormente por operação de lixamento empregando-se cinco diferentes granulometrias de lixas, de granas: 80, 100, 120, 150 e 220. Depois de lixadas, as superfícies foram submetidas à medição da rugosidade com rugosímetro equipado com uma ponta apalpadora de diamante, de forma cone-esférica, com raio de ponta de 2µm, em conjunto com o programa de análise de superfícies. Dos resultados obtidos podem-se destacar os melhores desempenhos de resistência a ruptura; ao cisalhamento para superfícies lixadas por lixa de grana 220; à tração normal para superfícies lixadas por lixa de grana 120 / Abstract: This paper shows studies on machinability of eucalyptus wood battens; main goal is make analysis of resistance bonded joints in relation the quality of machined surface to determine the influence of surface roughness on the adhesion of the bonded surfaces adhesive-based polyvinyl acetate (PVA). Samples Eucalyptus saligna wood species were prepared for resistance testing in trials blade glue shear rupture and tensile normal according to NBR 7190. The bonding surfaces were prepared by milling operation employing feed speed of 11.0 m/min and then by the grinding operation using five different grain sizes of sandpaper (grands: 80, 100, 120, 150 and 220). After sanding, the surfaces were subjected to measurements of roughness with roughness equipped with a diamond probe tip of cone-spherical shape, with nose radius of 2µm, together with surface analysis program. Among the results we can point out the best performances of rupture strength, shear strength for sanded surfaces by sanding the bundles 220, the normal traction surfaces sanded by sanding to 120 cash / Mestre

Le collage structural se présente comme une alternative intéressante aux méthodes classiques d'assemblages par ajout d’éléments mécaniques pour alléger les structures aéronautiques. Cependant, l'utilisation de cette méthode soulève de nombreuses questions en termes de conception, caractérisation ou modélisation. Ce travail, à fort caractère expérimental, visent deux grands objectifs : (i) sélectionner les moyens d'instrumentation les plus adaptés pour la caractérisation du comportement jusqu'à rupture des assemblages collés et (ii) prédire le comportement des assemblages collés à partir d'une caractérisation et d'une modélisation complète sous chargements quasi-statiques bi-axiaux, en utilisant un type d’essai simple et industrialisable. Dans un premier temps, pour atteindre ces objectifs, un nouvel essai appelé Scarf modifié a été proposé, afin de caractériser le comportement mécanique du joint de colle, en minimisant les effets de bord par la présence de becs. La deuxième partie de la thèse porte sur le développement d'une stratégie de caractérisation simplifiée du comportement de joint de colle, sous certaines hypothèses (états de contraintes/déformations, continuité du champ de contraintes). Cette stratégie a permis d'obtenir le comportement intrinsèque de l’adhésif sous la forme de courbes contraintes/déformations. La dernière partie abordée dans ces travaux, s'intéresse quant à elle à l'identification et la sélection des moyens de métrologie les plus appropriés, pour accompagner la caractérisation expérimentale. / Today, structural bonding presents an interesting alternative to conventional methods of assembly, in order to reduce the weight within aeronautical structures. However, the use of this method raises many questions in terms of design, characterization or modeling. This work presents a robust experimental work, aiming two main objectives: (i) select the most suitable instrumentation for the characterization of the behavior of bonded joints up to failure and (ii) predict the behavior of bonded joints from complete characterization and modeling under quasi-static bi-axial loading, using a simple test, directly integrated to industry. In a first stage, to achieve this goal, modified Scarf test has been proposed to characterize the mechanical behavior of adhesive joints. This type of specimen allows applying multiaxial loadings without having high-stress concentrations near the edges. The second part of the thesis deals with the development of a strategy for simplifying the characterization of a bonded joint using some hypotheses (stress/strain states). This strategy allows obtaining the intrinsic behavior of the adhesive in the form of the stress/strain curves. The last part of this work deals with the identification and selection of the most appropriate instrumentation systems in the experimental characterization.

Currently shock effects on surface ships can be determined by full scale shock trials, Finite Element Analysis or semi empirical methods that reduce the analytical problem to a limited number of degrees of freedom and include hull configurations, construction methods and materials in an empirical way to determine any debilitating effects that an explosion may have on the ship. This research has been undertaken to better understand the effect of hull shape on surface ships' shock response to external underwater explosions (UNDEX). The study is within the semi empirical method category of computations. A set of simple closed-form equations has been developed that accurately predicts the magnitude of dynamic excitation of different 2- D rigid-hull shapes subject to far-field UNDEX events. This research was primarily focused on the affects of 2-D rigid hull shapes and their contribution to global ship motions. A section of the thesis,

Adhesively bonded joints have been investigated for several decades. In most analytical studies, the Bernoulli-Euler beam theory is employed to describe the behaviour of adherends. In the current work, three analytical models are developed for adhesively bonded joints using the Timoshenko beam theory for elastic material and a Bernoulli-Euler beam model for viscoelastic materials. One model is for the peeling test of an adhesively bonded joint, which is described using a Timoshenko beam on an elastic foundation. The adherend is considered as a Timoshenko beam, while the adhesive is taken to be a linearly elastic foundation. Three cases are considered: (1) only the normal stress is acting (mode I); (2) only the transverse shear stress is present (mode II); and (3) the normal and shear stresses co-exist (mode III) in the adhesive. The governing equations are derived in terms of the displacement and rotational angle of the adherend in each case. Analytical solutions are obtained for the displacements, rotational angle, and stresses. Numerical results are presented to show the trends of the displacements and rotational angle changing with geometrical and loading conditions. In the second model, the peeling test of an adhesively bonded joint is represented using a viscoelastic Bernoulli-Euler beam on an elastic foundation. The adherend is considered as a viscoelastic Bernoulli-Euler beam, while the adhesive is taken to be a linearly elastic foundation. Two cases under different stress history are considered: (1) only the normal stress is acting (mode I); and (2) only the transverse shear stress is present (mode II). The governing equations are derived in terms of the displacements. Analytical solutions are obtained for the displacements. The numerical results show that the deflection increases as time and temperature increase. The third model is developed using a symmetric composite adhesively bonded joint. The constitutive and kinematic relations of the adherends are derived based on the Timoshenko beam theory, and the governing equations are obtained for the normal and shear stresses in the adhesive layer. The numerical results are presented to reveal the normal and shear stresses in the adhesive.

The effects of high loading rates (HLR), and nano reinforcement on the mechanical response of adhesively-bonded SLJs with composite adherends, subjected to different loading (strain) rates are systematically investigated. The results are then compared to those of neat thermoset resin and thermo-plastic adhesive. More specifically, nano-reinforced and neat resin bonded joints mating carbon/epoxy and glass/epoxy adherends were subjected to tensile loadings under 1.5 and 3 mm/min and tensile impacts at a loading rate of 2.04E+5 mm/min. In some cases, additional tests were conducted under 15, 150, and 1500 mm/min to obtain additional properties gained using the nano-reinforcements for use in the further numerical investigations. The HLR tests were conducted, using a modified instrumented pendulum equipped with a specially designed impact load transfer apparatus. The dispersion of nanoparticles was facilitated using a mechanical stirrer and a three-roll mill machine. The failure mechanisms were studied with a scanning electron microscope.

Made available in DSpace on 2014-06-11T19:27:11Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-02-15Bitstream added on 2014-06-13T19:14:24Z : No. of bitstreams: 1 alves_prg_me_guara.pdf: 1144534 bytes, checksum: c564c6fdb34127fdaaba0cd2ec9f184d (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Este trabalho apresenta estudos de usinabilidade de peças de madeira de eucalipto, tendo por objetivo principal efetuar análises da resistência de juntas coladas em relação à qualidade das superfícies usinadas, a fim de se verificar a influência da rugosidade superficial sobre a adesão das superfícies coladas com adesivo à base de acetato de polivinila (PVA). Amostras da espécie de madeira Eucalyptus saligna foram preparadas para testes de resistência na lâmina de cola em ensaios de ruptura por cisalhamento e por tração normal segundo a norma NBR 7190. As superfícies de colagem foram preparadas por operação de fresamento empregando-se velocidade nominal de avanço de 11,0 m/min e posteriormente por operação de lixamento empregando-se cinco diferentes granulometrias de lixas, de granas: 80, 100, 120, 150 e 220. Depois de lixadas, as superfícies foram submetidas à medição da rugosidade com rugosímetro equipado com uma ponta apalpadora de diamante, de forma cone-esférica, com raio de ponta de 2µm, em conjunto com o programa de análise de superfícies. Dos resultados obtidos podem-se destacar os melhores desempenhos de resistência a ruptura; ao cisalhamento para superfícies lixadas por lixa de grana 220; à tração normal para superfícies lixadas por lixa de grana 120 / This paper shows studies on machinability of eucalyptus wood battens; main goal is make analysis of resistance bonded joints in relation the quality of machined surface to determine the influence of surface roughness on the adhesion of the bonded surfaces adhesive-based polyvinyl acetate (PVA). Samples Eucalyptus saligna wood species were prepared for resistance testing in trials blade glue shear rupture and tensile normal according to NBR 7190. The bonding surfaces were prepared by milling operation employing feed speed of 11.0 m/min and then by the grinding operation using five different grain sizes of sandpaper (grands: 80, 100, 120, 150 and 220). After sanding, the surfaces were subjected to measurements of roughness with roughness equipped with a diamond probe tip of cone-spherical shape, with nose radius of 2µm, together with surface analysis program. Among the results we can point out the best performances of rupture strength, shear strength for sanded surfaces by sanding the bundles 220, the normal traction surfaces sanded by sanding to 120 cash

No description available.

Using experimental data obtained from standard fracture test configurations, theoretical and numerical tools are developed to mathematically describe non-self-similar progression of cracks without specifying an initial crack. A cohesive-decohesive zone model, similar to the cohesive zone model known in the fracture mechanics literature as the Dugdale-Barenblatt model, is adopted to represent the degradation of the material ahead of the crack tip. This model unifies strength-based crack initiation and fracture-mechanics-based crack progression. The cohesive-decohesive zone model is implemented with an interfacial surface material that consists of an upper and a lower surface that are connected by a continuous distribution of normal and tangential nonlinear elastic springs that act to resist either Mode I opening, Mode II sliding, Mode III sliding, or a mixed mode. The initiation of fracture is determined by the interfacial strength and the progression of the crack is determined by the critical energy release rate. The adhesive is idealized with an interfacial surface material to predict interfacial fracture. The interfacial surface material is positioned within the bulk material to predict discrete cohesive cracks. The interfacial surface material is implemented through an interface element, which is incorporated in ABAQUS using the user defined element (UEL) option. A procedure is established to formulate a rate dependent model based on experiments carried out on compact tension test specimens. The rate dependent model is incorporated into the interface element approach to capture the unstable crack growth observed in experiments under quasi-static loading conditions. The compact tension test gives the variation of the fracture toughness with the rate of loading, this information is processed and a relationship between the fracture toughness and the rate of the opening displacement is established. The cohesive-decohesive zone model is implemented through a material model to be used in an explicit code (LS-DYNA). Dynamic simulations of the standard test configurations for Mode I (Double Cantilever Beam) and Mode II (End Load Split) are carried out using the explicit code. Verification of these coupon tests leads to the crash analysis of realistic structures like the square composite tube. Analyses of bonded and unbonded square tubes are presented. These tubes shows a very uncharacteristic failure mode: the composite material disintegrates on impact, and this has been captured in the analysis. Disadvantages of the interface element approach are well documented in the literature. An alternative method, known as the Extended Finite Element Method (XFEM), is implemented here through an eight-noded quadrilateral plane strain element. The method, based on the partition-of-unity, is used to study simple test configuration like the three-point bend problem and a double cantilever beam. Functionally graded materials are also simulated and the results are compared to the experimental results available in the literature. / Ph. D.