Modern synthetic structural adhesives are finding a place in the drive to improve the fuel efficiencyof automobiles through weight reduction of the structure. One of the most important properties ofthe adhesives used in this type of joining is the fracture energy.A literature study is carried out to gain a broader understanding of the methods used for thedetermination of the fracture energy of adhesives. One of the most common experimental methodsrelies on the use of the Double Cantilever Beam (DCB) test specimen. International standards for theDCB test are studied. Prediction of the fracture energy using Linear Elastic Fracture Mechanics andthe J-integral approach, a closed form solution and finite element methods are also seen. Differencesin these methods are attributed in part to the nonlinear behaviour of the adhesive being studied. It isdecided to use the results of a non-standard DCB test and the 40% error calculated by a theoreticalstandard method as a point of reference.A comprehensive comparison of the American Society for Testing Materials (ASTM) and BritishStandard Institution (BSI) standards for the determination of the fracture energy of adhesives isundertaken. Limitations and overlaps in the standards are identified. A DCB specimen isrecommended and an experimental procedure that satisfies elements one or both standards issuggested along with several small additions such as using a wire to assist in the application of theadhesive and the use of cameras to track the crack growth. In addition, a new fixture to allow testingof the recommended DCB specimen according to the standards is designed and manufactured.Materials for the preparation of tests specimens are ordered and, based on available laboratorytime, a single DCB test specimen is made for the purposes of testing a rubber-based automotivestructural adhesive. The specimen is tested using the recommended experimental procedure usingthe new fixture. The data produced during the test are collected and interpreted using themethodology proposed in the BSI standard for the calculation of the fracture energy of the selectedrubber-based adhesive. Several challenges found during this process are identified. The fractureenergy determined from the standard-based experiment ranges from 140 J/m2 to 1380 J/m2depending on the methodology used.The values of the fracture energy determined from the standard-based DCB experiment are thencompared to the fracture energy seen with the nonstandard-based experiment and to the standardbasednumerical test seen in the literature. It is shown that when simple beam theory method isused the difference in the results found in the standard-based experiment and nonstandard-basedexperiment can be confirmed to lie within the 40% error observed in the literature.Finally, the contributions of the project are summarized and recommendations for future work aremade. In particular, the lack of information given in the BSI standard when calculating the fractureenergy and the need for multiple test specimens are required by the standard, must be addressed inorder to support the obtained results and conclusions.

Ultra-High Performance Concrete (UHPC) is an evolving structural material that has attracted interest in the civil engineering industry recently. Currently, it is being used mainly for highway infrastructure in the US and also being explored for various other applications. The existing design guides on UHPC in countries like Japan, Australia and France are not as detailed as the concrete or steel guides. Most of the sections made of UHPC are slender due to its superior mechanical properties which are expected to simplify construction. Being an expensive material to use, making slender sections also helps to minimize the overall cost of the structure and makes it competitive with that of high strength steel and prestressed concrete. It has also been demonstrated to have very high compressive strength and considerable tensile strength. To begin with, an introduction on UHPC and its current applications around the world is presented, followed by a review of the existing design guides on UHPC. The importance as well as the methodology to measure fracture energy of concrete with factors to be considered for fiber reinforced concrete is discussed in detail. The main motive of this research is to introduce a creative modeling concept which served as the theoretical basis for the development of a computer program called Lattice 3D. The program is a modeling tool for engineers studying the behavior of UHPC, and in the future will be developed into a finite element protocol for analyzing complex structures made of UHPC. Parametric studies on lattice models of thin simply supported plates in compression and three-point bending of beams have been demonstrated in this research. Experimental tests conducted on briquette specimens under uniaxial tension are also discussed. / Master of Science

Puncture resistance is among the major mechanical properties often required for protective clothing, especially in the medical sector. However the intrinsic material parameters controlling puncture resistance of protective materials are still unknown. Therefore, the purpose of this work is to study the mechanism and mechanical behaviors of puncture resistance of protective clothing materials to various probe types. A better understanding of puncture mechanics will be helpful to develop suitable methods to evaluate the puncture resistance and to predict the failure of protective clothing materials. The thesis includes 4 articles which expose two major phases in this study. Article I and II studied the mechanics and mechanisms of puncture by conical and cylindrical probes used in the standard test methods (ASTM F1342 and ISO 13996). The results show that the punctures of rubber membranes by conical and cylindrical probes are controlled by a maximum local deformation (or puncture failure strain) that is independent of the probe geometry. The puncture strengths of elastomer membranes are much lower than their tensile and biaxial strengths. In addition, a simpler cylindrical probe can be used in the place of the costly conical probe required by the ASTM standard and still provides a quantitative characterization of puncture. Actually, since 2005, an alternative method B had been added to F1342 ASTM with 0.5 mm-diameter rounded-tip cylindrical probe. Furthermore, the puncture probes used in the ASTM F1342 are very different to the actual pointed objects (medical needle, pointed tip of knife... ) and cannot accurately characterize the puncture resistance to real objects. Therefore, in the second step, the mechanics and mechanisms of puncture by medical needles were studied. Article III shows that the puncture by sharp-pointed objects like medical needles is very different from the puncture by conical probes used in the ASTM standard test. For medical needles, the puncture resistance involves cutting and fracture energy of material. Using the fracture mechanics, based on the change in strain energy with the change in fracture surface, the fracture energy in puncture was estimated. This calculation assumes that there is no friction between the needle tip and fracture surface. However, even with the application of a lubricant on the needle surface, the effect of friction on the puncture process cannot be totally eliminated, preventing the determination of the material fracture energy. Therefore, Article IV has described a method, similar to that of Lake and Yeoh for cutting to access the precise value of fracture energy in puncture of rubbers by sharp-pointed objects. The method allows substantially eliminating the effects of friction on the evaluation of the fracture energy involved in the puncture process.

No description available.

En microélectronique, certains dispositifs (MEMS) nécessitent une couche de protection appelée encapsulation pour assurer un fonctionnement optimal. Ce procédé met en jeu une couche structurée de polymère BCB (benzocyclobutène). Celle-ci est en contact avec unsubstrat de silicium d’un côté et une couche de nickel de l’autre. Une compréhension du comportement de ces interfaces et primordiale. L’objectif de cette thèse est la caractérisation de l’énergie d’adhérence des interfaces discontinues Ni/BCB et BCB/Si. Deux essaismécaniques (test de flexion 4-points et insertion de lame) ont été mis en œuvre. Les modèles analytiques mis au point dans le cas d’une interface continue ont servi à l’exploitation de ces essais mais ont aussi montré leur limite. La structuration de l’interface induit des effets géométriques et des effets d’échelle qui ne sont pas bien pris en compte par les modèles classiques. Pour pallier à cette difficulté, un modèle analytique modifié est proposé pour le test d’insertion de lame, ainsi que des calculs de simulation numérique. Ils mettent en avant l’influence des paramètres de la structuration : taille des motifs, espacement. / In microelectronics, some devices (MEMS) need to be encapsulated by a protective layer for optimal performances. This technique involves a patterned layer made of BCB polymer (benzocyclobutene). This layer is between a nickel film and a silicon substrate. A good understanding of those two interfaces is of first importance. The aim of this thesis is the mechanical characterization of the fracture energy of the Ni/BCB and BCB/Si patterned interfaces. Two mechanical tests (the 4-points bending test and the wedge test) have been selected in that purpose. Analytical models are well established to analyze those tests but for continuous interfaces. With patterned ones, those models are limited and do not take into account all the size effects and the geometrical effects induced by the patterning. A modified analytical model is proposed for the wedge test in order to overcome these limitations. Numerical studies are also carried out to complement the study. Patterning effects such as the size of the patterns and the space between them are enhanced.

Trees are exposed to many stresses over their lifetime and withstand them due to their woody skeleton which provides excellent mechanical support. Wood has therefore been one of the most used materials throughout the history of humanity. However, the mechanical properties of wood vary considerably depending on wood anatomy and also show significant differences between and within trees. Wood is a cellular solid, characterised by a high degree of anisotropy at all levels of organisation and is formed by cells which are oriented largely in the longitudinal and radial directions, making wood mechanics rather complicated. Therefore, there is a need for an understanding of the mechanical properties of wood in different species and in different parts of the tree and its relationship to wood anatomy. This study began with two investigations into the transverse toughness of green trunk wood in different tree species including both hardwood and conifers. Double-edge notched tensile tests were conducted on the specimens to quantify their specific fracture energies and evaluate their failure fashions. The influence of wood anatomy on the toughening mechanism of wood was observed using both electron microscopy and light microscopy. It was found that the fracture properties of woods were mainly affected by the wood density and anatomy. Hardwoods were found to have higher fracture energies than conifers due to their denser woods and higher volume fraction of rays. The results also found that the specific fracture energies of RL and RT systems were around 1.5-2 times greater than TL and TR systems. This difference was mainly explained by the presence of rays which provided toughness in the radial direction, at least in hardwoods, as breaking across rays resulted in spiral fractures of the cell walls. The mechanical properties of green branches and coppice shoots of three temperate tree species (chestnut, sycamore and ash), were then investigated at three distances from the tip. The study also investigated how bending failure was influenced by the morphology and anatomy of branches and coppice shoots. Coppice shoots were shown to be more likely to buckle in bending, whereas branches failed with a clean fracture. It was shown that ash and sycamore had greater properties in their coppice shoots than their branches, while chestnut showed better properties in their branches. It was suggested that this occurred because increasing the leaf node frequency resulted in a decrease in mechanical properties; ash and sycamore had more leaf nodes in their branches, thus lower properties in their branches, while chestnut had more leaf nodes in its coppices. The mechanical properties also decreased from base to tips of branches and coppice shoots because of falls in diameter of shoots and wood density. The results also suggested why coppice shoots can act as a useful structural material. Finally, this thesis investigated how and why the fracture properties vary around the structure of tree forks. The fracture properties of green hazel forks were examined using double-edge notched tensile tests in the RT and TR directions. The fracture surfaces were also observed using scanning electron microscopy in both fracture systems. The results showed that the central apex of forks were considerably tougher than other locations, suggesting they provide the load-bearing capacity of tree forks. It was shown that the increased toughness was related to both higher wood density and an interlocking wood grain pattern. Interestingly, the TR fracture system was found to be tougher than the RT fracture system at the central apex of forks, probably related to the orientation of the fibres. These results provide insight into the relationship between wood mechanics and anatomy, particularly showing the importance of rays. They can also help us understand how our ancestors shaped wood and designed tools and how we could design better structures.

In this study, a test technique, referred to as the probe test, has been developed as a quantitative tool for measuring the adhesion in thin adhesive films and coatings. The technique was initially developed as a qualitative test by the Hewlett-Packard Company for measuring adhesion of thin film microelectronic coatings. In the probe test method, an inclined needle-like probe with a conical tip is advanced underneath the free edge of a thin polymeric coating bonded to a substrate, causing the edge to lift-up from the surface of the substrate. A debond is thus initiated at the loading point and propagates as a semi-circular crack at the interface as the probe slides under the coating. A standard test procedure has been developed for testing thin adhesive coating/substrate systems. The sample system used is a thin film epoxy polymer coated silicon system. The interfacial fracture energy (Gc) (or critical strain energy release rate) has been used as a quantitative measure of adhesion for the given adhesive coating/substrate system. The probe test experiments were conducted using an optical microscope and a WYKO optical profiler. Using the optical microscope, the debond radius was measured for different debond sizes. Using the WYKO optical profiler, the three-dimensional surface topography of the debonded coating around the crack front was measured for different debond sizes. Using the experimental data from the probe test, analytical and numerical (finite element-based) techniques have been developed to determine the interfacial fracture energy (Gc) for the given adhesive coating/substrate system. The analytical techniques were developed based on different plate theory formulations (thin/thick plate - small/large deflection) of the probe test geometry and local curvature measurement at the crack tip. The finite element based techniques were developed using a hybrid numerical-experimental approach and surface-based contact interaction analysis in ABAQUS. The results obtained using thick plate-large deflection formulation correlated with finite element contact interaction analysis results. The probe test can be used with transparent or opaque coatings and thus offers a promising alternative to indentation and other tests methods for characterizing thin film and coating adhesion. / Master of Science

This thesis deals with numerical simulation of a peel test with an Aluminium foil and Low Density Poly-Ethylene (LDPE) laminate. This work investigates the effects of the substrate thickness and studies the influences of interfacial strength and fracture energy of the cohesive zone between the Aluminium and LDPE. This study evaluates the proper guidelines for defining cohesive properties. A numerical cohesive zone model was created in ABAQUS. Continuum tensile tests were performed to extract LDPE material properties. The aluminium properties were found in literature. After acquiring material parameters, the simulation continued with studying the effects of changing interfacial strength, geometric parameters and fracture energy. The results were obtained in the form of root rotations and the force displacement response was studied carefully. It was validated by comparison to the traction separation curve.

Os concretos refratários são materiais que apresentam estrutura complexa contendo uma fração de partículas finas (D < 100?m) chamada de matriz e outra mais grosseira da ordem de até centímetros compostas por agregados. Dentre as propriedades importantes durante a aplicação dos concretos refratários, este trabalho aborda principalmente a energia de fratura e a resistência à erosão. Para a avaliação dessas propriedades vários estudos vêm sendo desenvolvidos nos últimos anos. A introdução do método da cunha para propagação estável da trinca é um exemplo, pois este método é utilizado para materiais com estrutura grosseira, como é o caso dos concretos. Já em se tratando de resistência a erosão, pouco se encontra na literatura a respeito desse assunto para concretos refratários. Tendo em vista a aplicação destes materiais, foi avaliado o comportamento da energia de fratura e resistência à erosão de concretos refratário aluminoso convencional antierosivo utilizado na indústria petroquímica com o objetivo de correlacionar os resultados de energia de fratura e a resistência à erosão. Para o desenvolvimento do trabalho foram usados dois concretos a com mesma composição química, variando somente o tamanho de agregado. Foram avaliadas além da energia de fratura e da resistência à erosão outras propriedades foram avaliadas como: os módulos elástico e de ruptura, porosidade aparente, fases cristalinas e microestrutura, e ainda foi realizado um estudo da matriz do concreto. Os resultados mostraram que a energia de fratura aumenta com o aumento do tamanho de agregado para o concreto estudado e a resistência a erosão aumenta com a temperatura de tratamento térmico devido a ceramização da matriz, conforme análise das imagens. Em função dos resultados, pode-se concluir que não foi observada uma boa correlação entre energia de fratura e resistência à erosão. Mas esta correlação de energia de fratura e de resistência à erosão pode ter o mesmo comportamento que a correlação entre comprimento característico e resistência á erosão para faixas específicas de tamanho de agregado. / Castables materials are known to be formed by a complex microstructure containing a fine fraction known as matrix (D<100?m) and another one known as aggregate containing thicker particles up to centimeters in size. Among its most notable properties regarding application, this research primarily addresses to the fracture energy and its erosion resistance. In recent years, some studies have been performed concerning such assessments. As an example, the wedge splitting procedure has been applied in the stable crack propagation method used for some thicker structured materials evaluation such the castables ones. On the other hand, a few data have been gathered concerning castable\'s erosion resistance. Facing such applications the main goal was the study of conventional aluminous anti erosive castables once it has been used in the petrochemical industry in order to correlate fracture energy and erosion resistance results. On this research, two castables samples with the same chemical composition were tested differing only its aggregate particle grain sizes. Besides fracture energy and erosion resistance, other important properties were evaluated as following: elastic modulus, rupture modulus, apparent porosity, crystalline phases and a castable matrix study was also carried out. The results demonstrate an increase on fracture energy as the studied castable aggregate size also increases and according to images studied, the erosion resistance suffers another increment regarding the thermal treatment temperature increase due matrix ceramization. Based on the obtained results, it can be concluded that no observation was made regarding the fracture energy and erosion resistance but it may exist an energy correlation between them once there is some observed between the characteristic length and the erosion resistance concerning the aggregate size range.

Made available in DSpace on 2017-07-21T20:42:40Z (GMT). No. of bitstreams: 1 JULIANO Swiech Ciesielski.pdf: 2201955 bytes, checksum: acf9e0e88f80e1076d0bd050b2d0f0a7 (MD5) Previous issue date: 2012-07-31 / Many of the compounds multilayers are manufactured from advanced ceramic compositions, which seeks higher mechanical performance, the manufacture of these compositions based materials, ceramic structural has been little studied. Aiming to increase the fracture energy in ceramics traditional was investigated in this study the mechanical behavior of a multilayer system formed by stacking mullite and monoporosa. The mullite is an important raw material used in the manufacture of refractory ceramic for structural, because the physical and mechanical properties at high temperatures as high melting point, low expansion, fracture toughness and thermal shock that, high resistance fluency and low dielectric constant. The monoporosa has a high resistance which gives excellent mechanical and chemical properties and is widely used as coating mass on floors and re-investments outer. The increase in fracture energy was determined by comparing the curves of three point bending of the multilayer system with its monolithic references. The fractures were characterized by optical microscopy and MEV for microstructure analysis was carried out X-ray diffraction. Samples developed were evaluated multilayer reference to the materials employed in the formation of each layer in relation to these reference strains were obtained averages to 2.58 times larger and fracture energies of up to 7 times larger. / Muitos dos compostos multicamadas são fabricados a partir de composições de cerâmica avançada, em que se busca elevado desempenho mecânico, a fabricação destes materiais a base de composições de cerâmicas estruturais tem sido muito pouco estudado. Com o objetivo de aumentar a energia de fratura em cerâmicas tradicionais, foi pesquisado nesse trabalho o comportamento mecânico de um sistema multicamadas formado pelo empilhamento de mulita e monoporosa. A mulita é uma importante matéria-prima utilizada na fabricação de refratário para cerâmicas estruturais, devido as propriedades físicas e mecânicas a altas temperaturas como alto ponto de fusão, baixa expansão, resistência a fratura e ao choque térmico, alta resistência a fluência e baixa constante dielétrica. A monoporosa possui uma alta resistência o que confere excelentes propriedades mecânicas e químicas, sendo muito utilizado como massa de revestimento em pavimentos e revestimentos exteriores. O aumento na energia de fratura foi determinado comparando as de curvas de flexão em três pontos do sistema multicamadas com as de suas referências monolíticas. As fraturas foram caracterizadas por microscopia óptica e MEV, para análise da microestrutura realizou-se difração de raios X. As amostras multicamadas desenvolvidas foram avaliadas tomando como referência os materiais empregados na constituição de cada camada, em relação a estas referencias foram conseguidas deformações médias de até 2,58 vezes maiores e energias de fratura de até 7 vezes maiores.