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Serbena, F. C. "The brittle-ductile transition of NiAl single crystals." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.294341.
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Deva, Reddy Jayadeep. "Mechanical Properties of Silicon Carbide (SiC) Thin Films." Scholar Commons, 2007. https://scholarcommons.usf.edu/etd/210.
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There is a technological need for hard thin films with high elastic modulus. Silicon Carbide (SiC) fulfills such requirements with a variety of applications in high temperature and MEMS devices. A detailed study of SiC thin films mechanical properties was performed by means of nanoindentation. The report is on the comparative studies of the mechanical properties of epitaxially grown cubic (3C) single crystalline and polycrystalline SiC thin films on Si substrates. The thickness of both the Single and polycrystalline SiC samples were around 1-2 µm. Under indentation loads below 500 µ-Newton both films exhibit Elastic contact without plastic deformation. Based on the nanoindentation results polycrystalline SiC thin films have an elastic modulus and hardness of 422 plus or minus 16 GPa and 32.69 plus or minus 3.218 GPa respectively, while single crystalline SiC films elastic modulus and hardness of 410 plus or minus 3.18 Gpa and 30 plus or minus 2.8 Gpa respectively. Fracture toughness experiments were also carried out using the nanoindentation technique and values were measured to be 1.48 plus or minus 0.6 GPa for polycrystalline SiC and 1.58 plus or minus 0.5 GPa for single crystal SiC, respectively. These results show that both polycrystalline SiC thin films and single crystal SiC more or less have similar properties. Hence both single crystal and polycrystalline SiC thin films have the capability of becoming strong contenders for MEMS applications, as well as hard and protective coatings for cutting tools and coatings for MEMS devices.
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Ozden, Seray. "The relationship between the anatomy and mechanical properties of different green wood species." Thesis, University of Manchester, 2016. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.684776.
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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.
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Alrahlah, Ali Awad. "Physical, mechanical and surface properties of dental resin-composites." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/physical-mechanical-and-surface-properties-of-dental-resincomposites(213a08bf-5791-4e1c-bce9-a45ca268d1d3).html.
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Since resin composites were first presented to dentistry more than half a century ago, the composition of resin composites has developed significantly. One major change was that the reinforcing filler particles were reduced in size to generate materials of a given filler content that display better physical and mechanical properties. Resin composites may absorb water and chemicals from the surrounding environment but at the same time, composites may release constituents to their surroundings. The physical/mechanical properties of a restorative material provide an indication of how the material will function under stress in the oral environment. The aims of this research were to examine the effects of water at 37°C on the physical and mechanical properties, and the effect of food-simulating solvents of a variety of experimental and contemporary resin composites, on the surface properties. Eight representative resin composites were selected (Exp. VT, BL, NCB, TEC, GSO, XB, VDF and CXD). Due to the recent development of bulk fill materials on the market during the course of this research, the post-cure depth of cure of new bulk fill materials was also investigated. Five representative resin composites were selected: TBF, XB, FBF, VBF and SF. Water sorption and solubility were investigated at 37°C for 150 days. Sorption and solubility are affected by the degree of hydrophilicity of the resin matrix. The bulk fill materials examined showed the lowest water sorption and solubility. Laser scan micrometer (LSM) was used to investigate hygroscopic expansion. The extent of the hygroscopic expansion positively correlated with the amount of water sorption. The effect of water on fracture toughness was also examined. A self-adhesive hydrophilic resin matrix decreased in fracture toughness after 7 days of storage at 37°C. By contrast, the least water absorbed bulk fill material increased in fracture toughness over time. The effect of food-simulating solvents (distilled water, 75% ethanol/water and MEK) on surface micro-hardness, colour stability and gloss retention were investigated. The MEK solvent resulted in the lowest micro-hardness and the greatest colour change (ΔE) for most of the examined composites, while the 75% ethanol/water solution caused the greatest loss in gloss for most of the examined composites. A highly filled nano-composite showed the best result over time, regardless of the condition of storage. Surface micro-hardness profiles were used as an indirect method to assess the depth of cure of bulk fill resin composites. The examined bulk fill resin composites can be cured to an acceptable depth (4 mm).
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Pendse, Siddhi. "Morphological properties of poly (ethylene terephthalate) (PET) nanocomposites in relation to fracture toughness." Thesis, University of North Texas, 2005. https://digital.library.unt.edu/ark:/67531/metadc4845/.
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The effect of incorporation of montmorillonite layered silicate (MLS) on poly (ethylene terephthalate) (PET) matrix was investigated. MLS was added in varying concentration of 1 to 5 weight percent in the PET matrix. DSC and polarized optical microscopy were used to determine the crystallization effects of MLS addition. Non isothermal crystallization kinetics showed that the melting temperature and crystallization temperature decrease as the MLS percent increases. This delayed crystallization along with the irregular spherulitic shape indicates hindered crystallization in the presence of MLS platelets. The influence of this morphology was related with the fracture toughness of PET nanocomposites using essential work of fracture coupled with the infra red (IR) thermography. Both the essential as well as non essential work of fracture decreased on addition of MLS with nanocomposite showing reduced toughness.
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Wang, Yanfei. "The improvement of thermal and mechanical properties of La2Zr2O7-based pyrochlores as high temperature thermal barrier coatings." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/the-improvement-of-thermal-and-mechanical-properties-of-la2zr2o7based-pyrochlores-as-high-temperature-thermal-barrier-coatings(2cb87afa-4650-4af4-a159-d1b4f2febb78).html.
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To fully exploit the strengths of La2Zr2O7 pyroclores and promote them as a next-generation thermal barrier coating (TBC), the improvements of their thermally insulating property and fracture toughness are studied in this thesis. A strong phonon scattering source, rattlers, is found in Y3+-doped La2Zr2O7 pyrochlores. Rattlers dramatically flatten k (thermal conductivity)-T curves, or even make k approach the amorphous limit. The presence of rattlers is strongly dependent on (1) oversized atomic cages that are formed in pyrochlores; and (2) the occupation of smaller guest ions in those oversized cages. To maximize the rattling effect, In3+/Sc3+ ions that are much smaller than Y3+ are introduced to the La2Zr2O7 lattice. As envisaged, the smaller ions in the oversized lattice voids make k glass-like at a much lower doping content. Nevertheless, they are still not effective in reducing the high temperature plateau kmin. Instead, oxygen vacancies are very effective in reducing kmin, because they generate an electrostatic repulsion force among cations surrounding them, resulting in stronger lattice anharmonicity and weaker bonds. The plateau kmin is reduced dramatically by the filling of the B-sites in La2Zr2O7 with a 21% larger (and 50% heavier) Ce4+ guest ion rather than a 96% heavier (but similar-sized) Hf4+ ion, suggesting that a large absolute size of substitutional atoms is more effective in reducing kmin than a heavy absolute mass. This is because: (1) kmin is proportional to (E/M)0.5 (where E is the elastic modulus and M is the average atomic mass); (2) a larger size of guest ions tends to produce a weaker ionic bond and consequently, a lower E; and (3) the changing extent of E by introducing larger guest ions is much greater than that of M induced by adding heavier ones. Lastly, the fracture toughness (KIc) has been increased by dispersing the tetragonal 3 mol% Y2O3-stabilized zirconia (t-3YSZ) particulates in the La2Zr2O7 (LZ) matrix. The tendency of the dispersive t-3YSZ second phases transforming to monoclinic (m) phases strongly depends on the volume fraction introduced. For samples made from equilibrium route, they are toughened by phase transformations within the dispersive t-3YSZ second phases and a crack shielding effect arising from the residual compressive stress within the LZ matrix. An anticipated increase of KIc from ferroelastic toughening together with the residual compressive stress toughening highlights a potential to improve coating durability by depositing t’-3YSZ/LZ composite TBCs by the non-equilibrium route.
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Findikoglu, Gulin. "An Experimental Study Of Mechanical Properties Of Non Enzymatically Glycated Bovine Femur Cortical Bone." Phd thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614536/index.pdf.
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The aim of this study is to investigate the deterioration in mechanical integrity of the collagen network in bovine bone with aging, which are related to fracture toughness. Age-related changes in collagen molecular structures formed by non-enzymatic glycation were examined and indentation fracture technique was used as a method for measuring the microstructural toughness of cortical bone. Microcrack propagation characteristics of bone for fragility were also studied.
Young and old group of bovine cortical bone specimens were grouped into 2 as ribosylated and non-ribosylated which were rested in solutions for four weeks. Series of indentations were made on bone specimen groups for each of five masses 10g, 25g, 50g, 100g and 200g for 10 sec to detect the effect of applied indentation load. The applied load was increased to 300g, 500g, 1000g and 2000g for 10 sec to be able to make microcracks. Series of indentations were made on bone specimen groups for each of five durations 5sec, 10sec, 20sec, 30sec for 100g to study the effect of indentation duration. Specimens were examined in the wet and dry state while studying the factors effecting microhardness measurement.
Microhardness values measured by 10g of load for 10sec were indifferent between the ribosylated and non-ribosylated groups in the young and old bovine bone pointing that this load is not indicative of the structural collagen changes. Loads of 25g, 50g, 100g and 200g for 10 sec were able to differ ribosylated bone from non-ribosylated bone for the young and old bovine bones. Degree of microhardness increased with increased incubation period. Microhardness of dry specimens being either ribosylated or non-ribosylated were found to be statistically higher than wet specimens in young and old bone except for 10g for 10sec.
It has been shown that the calculated fracture toughness measured by the indentation method is a function of indentation load. Additionally, effect of indentation size might have resulted in a higher toughness measurement for higher indent loads with longer cracks even if the toughness is not actually higher.Methods using indentation technique has difficulty in relating the resistance to crack growth to the Mode I fracture toughness definition.Indentation fracture toughness allows sampling only one point on the Rcurve methods and was not considered as successful for assessing materials with rising R
curve. Toughness is ranked incorrectly among riboslated and non-ribosylated bovine bone by this technique. Presence of extrinsic toughening mechanisms including crack bridging due to uncracked ligaments and collagen fibers were directly observed by scanning electron microscope. Ribosylated bone was found to have lower number of collagen bridging compared ton on-ribosylated bovine bone.As a summary, indentation fracture method by Vickers indentation in bone is a method for measuring the fracture toughness.
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Sun, Fengzhen. "Mechanical Properties and Deformation Behaviour of Polymer Materials during Nanosectioning : Characterisation and Modelling." Doctoral thesis, Uppsala universitet, Tillämpad mekanik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-328906.
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Research in local fracture processes and micro-machining of polymers and polymer-based composites has attracted increasing attention, in development of composite materials and miniaturisation of polymer components. In this thesis, sectioning (machining) of a glassy polymer and a carbon nanotube based composite at the nanoscale was performed by an instrumented ultramicrotome. The yield stresses and fracture toughness of these materials were determined by analysing the sectioning forces. Fractographic analysis by atomic force microscopy was conducted to characterise the topographies and elastic properties of the sectioned surfaces to explore the deformation and fracture behaviour of the polymer during nanosectioning. The study reveals that a transition from homogenous to shear localised deformation occurred as the uncut chip thickness (depth of cut) or sectioning speed increased to a critical value. Analytical and finite element methods were used to model the nanosectioning process. The shear localised deformation was caused by thermal softening due to plastic dissipation. Although not considering sectioning, the tensile properties of a polymer nanocomposite were additionally investigated, where the degree of nanofibrillation and polyethylene glycol (PEG) content had significant effects.
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Ngo, Austin. "Effects of Build Orientation and Post Processing on the Mechanical Properties of Additively Manufactured AlSi10Mg." Case Western Reserve University School of Graduate Studies / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case1588623582368507.
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Taveri, Gianmarco. "Geopolymers Incorporating Wastes and Composites Processing." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2019. http://www.nusl.cz/ntk/nusl-403861.
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Buildings construction and realization of public infrastructures have always been a primary need in the human society, developing low cost and user-friendly materials which also encounter safety and durability requirements. Portland cement is the most used material in construction industry from the industrial revolution up to date, but the raising concerns related to the climate change are pushing the governments worldwide to replace it with more eco-friendly and greener materials. Geopolymers are considered to be best alternatives to Portland cement in construction industry, but issues related to cost and mechanical properties are still hindering the commercialization of this material. Geopolymer incorporating wastes is one of the solutions. Fly ash, a thermal power plant by-product, and borosilicate glass, a recycled glass from pharmaceutical vials, are suitable candidates in geopolymers activation. NMR and FTIR spectroscopies demonstrated that borates from borosilicate glass are active compounds in geopolymerization, substituting the alumina is its role, composing a B-Al-Si network never observed before. Various fly ash and borosilicate glass weight contents were studied in terms of mechanical properties (compression test, 3-point bending test). It was found that fly ash 55 wt.% and borosilicate 45 wt.% composition activated in 13 M NaOH solution holds the best compressive and flexural strength (45 and 4 MPa respectively), 25% stronger than similar counterparts found in literature. Cellulose fibres in different weight contents were dispersed into the geopolymeric paste to produce geopolymer composites, with the aim to render the material more suitable for structural applications. 3-point bending test showed an improvement of the flexural strength of about 165% (12 MPa), while the chevron notch method displayed a fracture toughness of 0.7 MPam1/2, in line with the results of geopolymer composites found in literature. In this thesis work, fly ash was also successfully densified in 3 M NaOH solution and distilled water through a new method based on hydraulic pressure, called hydro-pressure sintering. This innovative technology involves a drastic reduction of NaOH utilization in geopolymerization, rendering the material more eco-friendly. XRD spectroscopy conducted on produced samples revealed a higher formation of crystals, most likely induced by the application of hydraulic pressure (450 MPa).
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Hankla, Lorenzo W. "Mechanical properties of particulate-reinforced boron carbide composites." [Tampa, Fla] : University of South Florida, 2008. http://purl.fcla.edu/usf/dc/et/SFE0002749.
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Xu, Shuangyan. "Evaluating Thermal and Mechanical Properties of Electrically Conductive Adhesives for Electronic Applications." Diss., Virginia Tech, 2002. http://hdl.handle.net/10919/27112.
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The objective of this study was to evaluate and gain a better understanding of the short-term impact performance and the long-term durability of electrically conductive adhesives for electronic interconnection applications. Three model conductive adhesives, designated as ECA1, ECA2 and ECA3, supplied by Emerson & Cuming, were investigated, in conjunction with printed circuit board (PCB) substrates with metallizations of Au/Ni/Cu and Cu, manufactured by Triad Circuit Inc.
Effects of environmental aging on the durability of conductive adhesives and their joints were evaluated. All the samples for both mechanical tests and thermal tests were aged at 85%, 100%RH for periods of up to 50 days. Studies of bulk conductive adhesives suggested that both plasticization, which is reversible and further crosslinking and thermal degradation, which are irreversible, might have occurred upon exposure of ECAs to the hot/wet environment. The durability of electrically conductive adhesive joints was then investigated utilizing the double cantilever beam (DCB) test. It was observed that the conductive adhesive joint was significantly weakened following hydrothermal aging, and there was a transition from cohesive failure to interfacial failure as aging continued. A comparative study of the durability of different conductive adhesive and substrate metallization combinations suggested that the resistance of the adhesive joints to moisture attack is related to the adhesive properties, as well as the substrate metallizations. It was noted that the gold/adhesive interface had better resistance to moisture attack than the copper/adhesive interface. A reasonable explanation of this phenomenon was given based upon the concept of surface free energy and interfacial free energy. XPS analysis was performed on the fractured surfaces of DCB samples. For adhesive joints with copper metallization, copper oxide was detected on the failed surfaces upon exposure of the conductive adhesive joints following aging. XPS analysis on the fractured surfaces of adhesive joints with Au metallization suggested that diffusion of Cu to the Au surface might have happened on the Au/Ni/Cu plated PCB substrates during aging.
The impact performance of conductive adhesives was quantitatively determined using a falling wedge test. This unique impact resistance testing method could serve as a useful tool to screen conductive adhesives at the materials level for bonding purpose. Moreover, this test could also provide some useful information for conductive adhesive development. This study revealed that the viscoelastic energy, which is a result of the internal friction created by chain motions within the adhesive material, played an important role in the impact fracture behavior of the conductive adhesives. This study also demonstrated that the loss factor, evaluated at the impact environment conditions, is a good indicator of a conductive adhesive's ability to withstand impact loading.Ph. D.
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Pérez, Galmés Magdalena. "Analysis and development of experimental characterization methodologies of mode II fracture toughness on CFRP bonded joints." Doctoral thesis, Universitat de Girona, 2018. http://hdl.handle.net/10803/664508.
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Adhesives have been shown to be an excellent solution for joining fibre reinforced polymer (FRP) components thanks to their capacity to redistribute loads, reduces stress concentrations and contribute to overall weight saving in the structure. The most relevant mechanical property in adhesive bonded joints design is the shear (mode II) fracture toughness of the adhesive.
The application of the existing mode II delamination standards to adhesive joints entails some major limitations that result in severe under/over estimations of the adhesive properties and, in many cases, can even prevent results from being obtained from tests.
The main objective of the present thesis is to develop robust tools for the determination of shear (mode II) facture toughness in adhesive joints. This includes studying data reduction methods as well as the test geometriesEls adhesius han demostrat ser una magnífica solució per unir components de polímers reforçats amb fibres (FRP) gràcies a la seva capacitat per redistribuir càrregues, reduir les concentracions de tensions i contribuir a l’estalvi general de pes en l’estructura. La propietat mecànica més rellevant en el disseny d’unions adhesives és la tenacitat a la fractura a tallant (mode II) de l’adhesiu. L’aplicació dels actuals assajos estandaritzats a les unions adhesives pot derivar en estimacions errònies, per sota o per sobre, de les propietats adhesives i, en molts casos, evitar que l’assaig es pugui realitzar satisfactòriament. L’objectiu principal d’aquesta tesi és el desenvolupament d’eines robustes per a la determinació de la tenacitat a la fractura a tallant (mode II) d’unions adhesives. S’estudia l’aplicabilitat dels mètodes d’assaig de deslaminació en mode II existents a les unions adhesives estructurals. Això inclou l’estudi dels mètodes de reducció de dades i de les geometries d’assaig
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Kazem, Navid. "Soft Multifunctional Composites Using Liquid Metal." Research Showcase @ CMU, 2018. http://repository.cmu.edu/dissertations/1164.
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Progress in the fields of wearable computing, soft robotics and bio hybrid engineering depend on new classes of soft multifunctional materials that match the mechanical properties of soft biological tissue and possess high toughness, while having metal-like electrical and thermal properties.
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Al-Shehri, Abdulhadi S. "Tensile and fracture behaviour of isotropic and die-drawn polypropylene-clay nanocomposites : compounding, processing, characterization and mechanical properties of isotropic and die-drawn polypropylene/clay/polypropylene maleic anhydride composites." Thesis, University of Bradford, 2010. http://hdl.handle.net/10454/5223.
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As a preliminary starting point for the present study, physical and mechanical properties of polypropylene nanocomposites (PPNCs) for samples received from Queen's University Belfast have been evaluated. Subsequently, polymer/clay nanocomposite material has been produced at Bradford. Mixing and processing routes have been explored, and mechanical properties for the different compounded samples have been studied. Clay intercalation structure has received particular attention to support the ultimate objective of optimising tensile and fracture behaviour of isotropic and die-drawn PPNCs. Solid-state molecular orientation has been introduced to PPNCs by the die-drawing process. Tensile stress-strain measurements with video-extensometry and tensile fracture of double edge-notched tensile specimens have been used to evaluate the Young's modulus at three different strain rates and the total work of fracture toughness at three different notch lengths. The polymer composite was analyzed by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, wide angle x-ray diffraction, and transmission electron microscopy. 3% and 5% clay systems at various compatibilizer (PPMA) loadings were prepared by three different mixing routes for the isotropic sheets, produced by compression moulding, and tensile bars, produced by injection moulding process. Die-drawn oriented tensile bars were drawn to draw ratio of 2, 3 and 4. The results from the Queen's University Belfast samples showed a decrement in tensile strength at yield. This might be explained by poor bonding, which refers to poor dispersion. Voids that can be supported by intercalated PP/clay phases might be responsible for improvement of elongation at break. The use of PPMA and an intensive mixing regime with a two-step master batch process overcame the compatibility issue and achieved around 40% and 50% increase in modulus for 3% and 5% clay systems respectively. This improvement of the two systems was reduced after drawing to around 15% and 25% compared with drawn PP. The work of fracture is increased either by adding nanoclay or by drawing to low draw ratio, or both. At moderate and high draw ratios, PPNCs may undergo either an increase in the size of microvoids at low clay loading or coalescence of microvoids at high clay loading, eventually leading to an earlier failure than with neat PP. The adoption of PPMA loading using an appropriate mixing route and clay loading can create a balance between the PPMA stiffness effect and the degree of bonding between clay particles and isotropic or oriented polymer molecules. Spherulites size, d-spacing of silicate layers, and nanoparticles distribution of intercalated microtactoids with possible semi-exfoliated particles have been suggested to optimize the final PPNCs property.
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Yao, Zhao Yue. "Synthesis, structure, and mechanical properties of lead- and zinc-copper borate glasses." Thesis, Rennes 1, 2016. http://www.theses.fr/2016REN1S080.
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Le but de ce travail est d'étudier l'effet de la teneur en cuivre et de la valence des atomes de cuivre sur la structure et les propriétés mécanique du verre. Des verres de zinc- et plomb- cuivre borate ont été étudiés. Les changements structurels avec le remplacement de PbO ou ZnO par CuO sont observés par réflectance infrarouge et Raman. L'état d'oxydation, l'environnement du site et la liaison caractéristique d'ions de cuivre ont été étudiés par spectroscopie optique et de résonance de spin électronique. Les propriétés mécaniques ont été déterminées et corrélées à la structure du verre et à sa composition, en mettant l'accent sur les propriétés élastiques, le comportement d'indentation (dureté et micro-fissures), la ténacité et la dépendance à la température de l'élasticité. Le cuivre a une tendance à stabiliser le bore en coordinence trigonale et donne une structure de type métaborate plus homogène. L'ajout d'ions de cuivre au verre métaborate améliore les performances mécaniques (modules d'élasticité et dureté), et diminue la sensibilité à la température ainsi que le taux de ramollissement des verres au plomb. Toutefois, l'ajout d'ions de cuivre dans les verres au zinc a des effets opposés sur ces propriétés. Les changements chimiques à la surface des verres de borates de cuivre et de zinc après traitement thermique sont également étudiés. L'étude par nanoindentation et par rayage montre que la couche cristallisée améliore la résistance mécanique de la surface du verreThe aim of this work is to study the effect of copper content and copper valence on the structural and mechanical properties of glass. Zinc- and lead- copper borate glasses were studied. Their structural changes with the substitution of CuO for ZnO or PbO are followed by Raman and reflectance infrared. The oxidation state, site environment and bonding characteristic of copper ions are studied by optical and electron spin resonance spectroscopy. The mechanical properties were determined and correlated to the glass structure and composition, with a particular emphasis on the elastic properties, sharp indentation behavior (hardness and micro-cracking), toughness and temperature dependence of elasticity. Copper tends to stabilize trigonal boron and gives a more homogeneous metaborate structure. Adding copper ions to the metaborate glass clearly improves the mechanical performance (elastic moduli and hardness), in the meantime decreases the temperature sensitivity and soften rate of lead borate glasses. However, adding copper ions in zinc borate glasses has opposite effects on these properties. The chemistry changes at zinc-copper-borate glass surface after heat-treatment are also studied. Investigation of the nanoindentation and scratch behavior show that the crystallized layer improves the mechanical resistant of glass surface
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Lukich, Svetlana. "VIBRATIONAL AND MECHANICAL PROPERTIES OF 10 MOL % SC2O3-1 MOL % CEO2- ZRO2 ELECTROLYTE CERAMICS FOR SOLID OXIDE FUEL CELLS." Master's thesis, University of Central Florida, 2009. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4001.
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Solid Oxide Fuel Cells (SOFCs) are emerging as a potential breakthrough energy conversion technology for clean and efficient production of electricity and heat from hydrogen and hydro-carbon fuels. Sc₀.₁Ce₀.₀₁ZrO₂ electrolytes for Solid Oxide Fuel Cells are very promising materials because their high ionic conductivity in the intermediate temperature range 700°C-800°C. The vibration response of cubic and rhombohedral ([beta]) 10 mol%Sc₂O₃ - 1 mol%CeO₂ - ZrO₂ (Sc₀.₁Ce₀.₀₁ZrO₂) both at room and high-temperatures is reported. The in-situ heating experiments and ex-situ indentation experiments were performed to characterize the vibrational behavior of these important materials. A temperature and stress-assisted phase transition from cubic to rhombohedral phase was detected during in-situ Raman spectroscopy experiments. While heating and indentation experiments performed separately did not cause the transition of the cubic phase into the rhombohedral structure under the performed experimental conditions and only broadened or strained peaks of the cubic phase could be detected, the heating of the indented (strained) surface leaded to the formation of the rhombohedral Sc₀.₁Ce₀.₀₁ZrO₂. Both temperature range and strained zone were estimated by in situ heating and 2D mapping, where a formation of rhombohedral or retention of cubic phase has been promoted. The mechanical properties, such as Young’s modulus, Vickers hardness, indentation fracture resistance, room and high temperature four point bending strength and SEVNB fracture toughness along with the stress--strain deformation behavior in compression, of 10 mol% Sc₂O₃--1 mol % CeO₂ - ZrO₂ (ScCeZrO₂) ceramics have been studied. The chosen composition of the ScCeZrO₂ has very high ionic conductivity and, therefore, is very promising oxygen ion conducting electrolyte for the intermediate temperature Solid Oxide Fuel Cells.
Therefore, its mechanical behavior is of importance and is presented in this study.M.S.M.S.E.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Materials Science & Engr MSMSE
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Alkoles, Omar M. S. "Mechanical behaviour and fracture toughness of unfilled and short fibre filled polypropylene both drawn and undrawn. Experimental investigation the effect of fibre content and draw ratio on the mechanical properties of unfilled and short glass fibre filled polypropylene." Thesis, University of Bradford, 2011. http://hdl.handle.net/10454/5510.
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The goal of this research is to investigate the combined effects of glass fibre reinforcement and molecular orientation in polypropylene-short glass fibre composites. Specimens have been fabricated using the injection moulding process and drawn using a small die drawing rig. The effects of die drawing on the fibre composites are complex, with the drawing process orienting both the polymer molecules and the glass fibres. This may be accompanied by the creation of voids in the polymer matrix and their destruction in the compressive stress field thus restoring the interfacial contact area between fibre and matrix. Unfilled and short glass fibre filled polypropylene specimens, with fibre content 7% wt, 13%wt, 27%wt, and 55%wt, were injection moulded prior to the die drawing process. An experimental program of die drawing within an oven at elevated temperature was conducted for polypropylene filled to various levels and at different strain rates. The specimens drew to draw ratios in the range ¿=1.41 to ¿=5.6. Mechanical characterization of the test materials has been conducted by examining the tensile stress strain and fracture behaviour under uniaxial conditions. The influence of glass fibre content and drawing conditions (draw ratio) on the fracture toughness and crack propagation was investigated using the double edge notched fracture test. The notch lengths ranged from 1.5 to 2.5 mm for 10 mm wide specimens. The critical stress intensity factor increased as the fibre content increased up to a limiting filler level. The fracture toughness of both unfilled and fibre filled polypropylene were found to be highly dependent on draw ratio. The results were analysed to find out the optimal draw ratio and fibre content that yielded the maximum modulus, strength and fracture toughness. Data showed that, at a given draw ratio, modulus, strength and fracture toughness increased with increasing fibre content to a maximum and then decreased. The optimum material was obtained at a draw ratio of 2.5 and filler loading 13wt%.
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Loffredo, Maria de Castro Monteiro. "Resistencia mecanica e tenacidade a fratura do osso cortical bovino." [s.n.], 2006. http://repositorio.unicamp.br/jspui/handle/REPOSIP/263211.
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Orientador: Itamar FerreiraDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
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Resumo: As fraturas de ¿stress¿ são fraturas causadas pela fadiga óssea em pessoas jovens e saudáveis e que fazem treinamentos físicos rigorosos, como os chamados atletas de elite. Por essa razão, as causas para ocorrerem tais fraturas ainda são indefinidas. Sabe-se que sua fisiopatologia é caracterizada pela nucleação e propagação de micro-trincas na cortical óssea. Dessa forma, foi proposto neste estudo identificar algumas propriedades mecânicas do osso cortical que se aproximem das condições de tensão geradas nas atividades físicas. Foi, então, estudado o comportamento de uma barra retangular de osso cortical bovino no ensaio de flexão em três pontos para identificar o módulo de ruptura e o módulo de elasticidade do osso. O ensaio de tenacidade à fratura também foi conduzido por meio do ensaio de flexão em três pontos em corpos-de-prova com um entalhe usinado transversalmente ao eixo longitudinal dos espécimes. Os resultados mostraram que apesar do osso cortical ser um material mecanicamente resistente, com módulo de ruptura (MOR) médio de 227,5 MPa, ele possui níveis razoavelmente baixos de tenacidade à fratura, KIc médio de 9,6 MPa.m1/2. A análise fractográfica dos espécimes ensaiados mostrou que o osso apresenta alguns mecanismos de fratura característicos e que suas microestruturas estabelecem funções na nucleação e propagação da trinca, tornando o osso mais ou menos tenaz
Abstract: Stress fractures are caused by fatigue exercising in bones that occur in young health people who are submitted to rigorous physical training. It¿s known that its path physiology is characterized by initiation and propagation of microcracks. Thus, the purpose of this study is to identify some of the mechanical properties of cortical bone that approach to the tension conditions originated in physical activities. A rectangular beam of bovine cortical bone was then tested in three-point bending to determine the values of modulus of rupture and Young¿s modulus of bone. Fracture toughness tests were conducted in single-edge-notched specimens. Results showed that bone is a strength material, with averaged modulus of rupture of 227.5 MPa, and a low value of fracture toughness averaged in 9.6 MPa.m1/2. The fractographic analyses of tested specimens showed that bones have some characteristic fracture mechanisms during failure and its microstructures influence the initiation and propagation of cracks, making it more or less resistant to crack propagation
Mestrado
Materiais e Processos de Fabricação
Mestre em Engenharia Mecânica
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永正, 邵., and Yongzheng Shao. "Study on the effects of matrix properties on the mechanical properties of carbon fiber reinforced plastic composites." Thesis, https://doors.doshisha.ac.jp/opac/opac_link/bibid/BB12902982/?lang=0, 2015. https://doors.doshisha.ac.jp/opac/opac_link/bibid/BB12902982/?lang=0.
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It was found that a significant improvement of mechanical properties of CFRPs can be achieved by the adjustment of the matrix properties such as toughness and CF/matrix adhesion via the chemical modification, as well as the physical modification by a small amount of cheap and environment-friendly nano fibers. Based on investigation of fracture mechanisms at macro/micro scale, the effects of matrix properties and nano fiber on the mechanical properties of CFRP have been discussed. Subsequently, the relationship has been characterized by a numerical model to show how to modulate the parameters of the matrix properties to achieve excellent fatigue properties of CFRP.博士(工学)
Doctor of Philosophy in Engineering
同志社大学
Doshisha University
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Alkoles, Omar M. "Mechanical behaviour and fracture toughness of unfilled and short fibre filled polypropylene both drawn and undrawn : experimental investigation of the effect of fibre content and draw ratio on the mechanical properties of unfilled and short glass fibre filled polypropylene." Thesis, University of Bradford, 2011. http://hdl.handle.net/10454/5510.
Full textAbstract:
The goal of this research is to investigate the combined effects of glass fibre reinforcement and molecular orientation in polypropylene-short glass fibre composites. Specimens have been fabricated using the injection moulding process and drawn using a small die drawing rig. The effects of die drawing on the fibre composites are complex, with the drawing process orienting both the polymer molecules and the glass fibres. This may be accompanied by the creation of voids in the polymer matrix and their destruction in the compressive stress field thus restoring the interfacial contact area between fibre and matrix. Unfilled and short glass fibre filled polypropylene specimens, with fibre content 7% wt, 13%wt, 27%wt, and 55%wt, were injection moulded prior to the die drawing process. An experimental program of die drawing within an oven at elevated temperature was conducted for polypropylene filled to various levels and at different strain rates. The specimens drew to draw ratios in the range γ=1.41 to γ=5.6. Mechanical characterization of the test materials has been conducted by examining the tensile stress strain and fracture behaviour under uniaxial conditions. The influence of glass fibre content and drawing conditions (draw ratio) on the fracture toughness and crack propagation was investigated using the double edge notched fracture test. The notch lengths ranged from 1.5 to 2.5 mm for 10 mm wide specimens. The critical stress intensity factor increased as the fibre content increased up to a limiting filler level. The fracture toughness of both unfilled and fibre filled polypropylene were found to be highly dependent on draw ratio. The results were analysed to find out the optimal draw ratio and fibre content that yielded the maximum modulus, strength and fracture toughness. Data showed that, at a given draw ratio, modulus, strength and fracture toughness increased with increasing fibre content to a maximum and then decreased. The optimum material was obtained at a draw ratio of 2.5 and filler loading 13wt%.
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Sant'Anna, Pedro Carneiro. "Influencia de tratamentos termicos intercriticos na microestrutura e propriedades mecanicas do aço API 5L X65." [s.n.], 2006. http://repositorio.unicamp.br/jspui/handle/REPOSIP/263175.
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Orientador: Itamar FerreiraTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
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Resumo: Investigou-se o efeito de tratamentos térmicos intercríticos na microestrutura e propriedades mecânicas do aço API 5L X65 comumente utilizado em tubulações soldadas para transporte de óleo e gás. Vários pesquisadores demonstraram a existência de zonas frágeis na região intercrítica da zona afetada pelo calor (ZAC) de aços C-Mn e ARBL (alta resistência e baixa liga), produzidas durante o procedimento de soldagem de passe único e passes múltiplos. Além dos efeitos nocivos da martensita e da bainita superior, o microconstituinte formado por martensita-austenita retida, denominado constituinte M-A, é usualmente apontado como sendo o principal responsável pela degradação da tenacidade à fratura de alguns destes aços. Após os tratamentos térmicos de homogeneização e normalização, amostras do aço API 5L X65 foram submetidas a tratamentos térmicos intercríticos, realizados a 780 °C por 20 minutos e resfriadas com taxas equivalentes às dos insumos de calor obtidos em soldagens por arco submerso em chapas de 12 mm. As propriedades mecânicas foram avaliadas por meio dos ensaios de tração, dureza, resistência ao impacto Charpy e tenacidade à fratura CTOD. As características microestruturais foram analisadas por meio de microscopia ótica e microscopia eletrônica de varredura. O tratamento térmico de homogeneização foi eficiente para eliminar o bandeamento e a linha de segregação central da chapa. Verificou-se que o constituinte M-A está presente em todas as condições de resfriamento dos tratamentos térmicos realizados na região intercrítica, incluindo aquelas que promoveram alta tenacidade à fratura. A redução da taxa de resfriamento aumenta a quantidade do constituinte M-A até um determinado limite, pois ele se decompõe em ferrita + carbonetos. Pode-se concluir que os baixos níveis de tenacidade à fratura e ductilidade estão relacionados com a fração volumétrica da martensita obtida em altas taxas de resfriamento ou ao constituinte M-A com caráter martensítico. A condição intercrítica resfriada com taxa de 19 °C/s foi a que promoveu melhor relação resistência mecânica e tenacidade à fratura. Deve-se, portanto, selecionar procedimentos de soldagem que reduzam a fração volumétrica da martensita e do constituinte M-A
Abstract: The intercritical heat treatment effect on the microstructure and mechanical properties of the API 5L X65 steel, widely used in oil and gas pipeline, was investigated. Many researchers have suggested the existence of local brittle zones in the intercritical heat treatment zone (haz) of C-Mn and HSLA (high strenth low alloy) steels of single and multipass welding. Beyond deleterious effect of the martensite and upper bainite, the martensite and retained austenite microstructure, named MA constituent, is usualy pointed as being responsible for the toughness degradation of some of these steels. The specimens were submitted to homogenization and normalizing heat treatments, and then they were submitted to intercritical heat treatments performed at 780 oC for 20 minutes; after that the specimens were cooled using different cooling rates. The cooling rates were equivalent to the heat input obtained with 12 mm steel plate submerged arc weld. The tension, Vickers hardness, Charpy impact and CTOD tests were conducted. Microstructure characterizations were performed by using optical and scanning electron microscopy. Homogenization heat treatment was efficient to eliminate banding and the centerline segregation. It was verified that M-A constituent is present in all intercritical heat treatment conditons, including those of high fracture toughness. The cooling rate reduction increases the amount of M-A constituent until a certain limit, then it decomposes in ferrite + carbides. It was concluded that low toughness and ductility levels are closely related with the volume fraction of martensite obtained in high colling rates or with M-A constituent with a martensite character. The intercritical condition with 19°C/s cooling rate promoted the best correlation between strength and fracture toughness. To improve the intercrictical HAZ toughness of welds, it is suggested to select a welding procedure that diminishes the proportion of martensite and M-A constituent
Doutorado
Materiais e Processos de Fabricação
Doutor em Engenharia Mecânica
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Golisch, Georg Verfasser], Wolfgang [Akademischer Betreuer] [Bleck, Sebastian [Akademischer Betreuer] Münstermann, and Peter [Akademischer Betreuer] Langenberg. "Evaluation of the lower shelf toughness properties of high strength steels using fracture and damage mechanics approaches / Georg Golisch ; Wolfgang Peter Bleck, Sebastian Münstermann, Peter Langenberg." Aachen : Universitätsbibliothek der RWTH Aachen, 2018. http://d-nb.info/1181335167/34.
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Golisch, Georg [Verfasser], Wolfgang [Akademischer Betreuer] Bleck, Sebastian [Akademischer Betreuer] Münstermann, and Peter [Akademischer Betreuer] Langenberg. "Evaluation of the lower shelf toughness properties of high strength steels using fracture and damage mechanics approaches / Georg Golisch ; Wolfgang Peter Bleck, Sebastian Münstermann, Peter Langenberg." Aachen : Universitätsbibliothek der RWTH Aachen, 2018. http://d-nb.info/1181335167/34.
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Pompeu, Neto Bernardo Borges. "Efeitos do tipo, tamanho e teor de agregado graudo na resistencia e energia de fratura do concreto." [s.n.], 2004. http://repositorio.unicamp.br/jspui/handle/REPOSIP/265011.
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Orientadores: Itamar Ferreira, Vitor Antonio DucattiTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia mecanica
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Resumo: Este trabalho expõe os resultados de um estudo conduzido para avaliar os efeitos do tipo, tamanho e consumo de agregado graúdo no comportamento do concreto de moderada e de alta resistência, e as relações entre a resistência à compressão, resistência à tração, resistência à flexão e a energia de fratura. As misturas de concreto estudadas continham agregados britados de basalto e de granito com dimensões máximas características de 9,5 mm e 19 mm e fração volumétrica no traço entre 0,65 e 0,75. A relação águalaglomerantes variou de 0,35 a 0,50. Nas misturas de alta resistência foi empregado um teor fixo de sílica ativa de dez porcento da massa do cimento de alta resistência inicial e teores adequados de aditivo superplastificante. Foram feitas dezesseis (16) misturas e realizados cento e noventa e dois ensaios mecânicos para medir a resistência à compressão, a resistência à flexão, resistência à tração, módulo de elasticidade e energia de fratura. As propriedades de fratura foram determinadas de acordo com Comitê Técnico 89-FMT e FMC-50 da RILEM. A resistência à compressão do concreto de acordo com os materiais empregados foi de 40 a 60 MPa para os concretos de resistência média e de 70 a 110 MPa, para os concretos de alta resistência. Os resultados mostram que a resistência. à compressão, tração, flexão e a energia de fratura do concreto para uma dada relação águaJaglomerante depende do tipo, dimensões e teor de agregado. Para o concreto de alta resistência o comprimento característico do concreto aumenta com o tamanho do agregado graúdo
Abstract: This thesis presents the results of the experimental study carried out for considering the effects of the type, size and amount of coarse aggregate on the behavior of nonnal and high strength concretes, and on relationship among the fracture energy and typical mechanical strength of concrete. The experimental concrete mixtures were made with basalt and granite coarse aggregates having maximum size partic1e 9.5 mm e 19 mm and volumetrically fraction in the mixture ranging from 0.65 to 0.75. The water to cementation materiaIs ratio ranged from 0.35 to 0.50. The high strength concrete mixtures contained a tixed amount of 10 percent of si1ica fume in relation to the weight Portland cement used and a proper addition of superplasticizing agent. Sixteen (16) concrete batching, and one hundred and ninety two tests were carried out to measure the mechanical resistance of concrete (compressive strength, flexure strength, spittling tensile strength, modulus of elasticity) and fracture energy. The fracture properties measured in agreement of the RILEM test methods. The concrete compressive strength ranged from 40 to 60 MPa, and from 70 to 110 MPa, for moderate and hi~ strength concretes, respectively, depending on the type of coarse aggregate utilized. The results showed that the concrete resistance (compressive, flexure, spittling tensile) and fracture energy, at given water to binder ratio, depend on type, particle dimension and content of coarse aggregate. The characteristic length of Hillerborg's tictitions cracks model increases with the variation in the partic1e dimension of coarse aggregate
Doutorado
Materiais e Processos de Fabricação
Doutor em Engenharia Mecânica
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Rádsetoulal, Milan. "Hodnocení lomového chování svarových spojů používaných v energetickém průmyslu." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2021. http://www.nusl.cz/ntk/nusl-442748.
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This thesis is focused on assessment of fracture behaviour of heterogeneous welded joint. The goal is to determine fracture behaviour at the interface of ferritic base metal and austenitic weld metal at temperature of 255°C. This kind of weld is widely used at energy industry. Fracture toughness was evaluated using CT specimens with size 0,5T in order to determine the initiation values of stable crack propagation. Fracture behaviour of the weld is correlated with results of metallography and fractography analysis. Both light and scanning electron microscopy is used for fractography analysis. An assessment of fracture behaviour of the interface of the weld joint is first of all connected with a need of suitable location of cycled crack to the interface of metals. In the case of well-prepared crack the lowest values of J-integral are observed. In other cases of slight crack deviation from the notch plane fracture values increase. Due to a large scatter of mechanical properties of heterogeneous weld joints an increased number of test specimens is needed to obtain relevant and conservative fracture toughness values. Correlation of fracture toughness with the results of fractography analysis leads to clarification of the crack trajectory and to description of fracture mechanism.
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Sieurin, Henrik. "Fracture toughness properties of duplex stainless steels." Doctoral thesis, Stockholm, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3964.
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Staudinger, Ulrike. "Morphologie und Bruchverhalten von Block- und Multipfropfcopolymeren." Doctoral thesis, [S.l. : s.n.], 2007. http://nbn-resolving.de/urn:nbn:de:swb:14-1187261828675-34703.
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Nogueira, Fabiano da Cruz. "Influência do raio de ponta do entalhe, do tipo de carregamento e da microestrutura no processo à fratura do aço estrutural ABNT-4340 /." Ilha Solteira : [s.n.], 2006. http://hdl.handle.net/11449/94491.
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Orientador: Ruis Camargo TokimatsuBanca: Wyser Jose Yamakami
Banca: André Luis Moreira de Carvalho
Resumo: O ensaio de impacto Charpy convencional é um ensaio mecânico consagrado no meio científico e industrial. Sua função é determinar a energia total absorvida para causar a fratura completa de um corpo-de-prova entalhado, padronizado segundo a norma ASTM E?23. Entretanto, a energia global absorvida possui um valor de uso muito limitado. Ela normalmente não é aceita como um indicador quantitativo da resistência à fratura do material. Assim, através da instrumentação adequada, pode-se aumentar a quantidade de informações obtidas a partir do ensaio de impacto Charpy clássico. No presente trabalho, estudou-se a influência do raio de ponta do entalhe, do tipo de carregamento e da microestrutura dos corpos-de-prova no processo à fratura dinâmica do aço ABNT-4340 a partir do ensaio Charpy Instrumentado. As diferentes condições microestruturais foram resultantes de diferentes condições de tratamentos térmicos: como-recebido, como-temperado e revenido nas seguintes temperaturas: 473K, 573K, 673K e 773K. Para cada microestrutura foram confeccionados corpos-de-prova com dois tipos de raio de ponta - pré-trincado e entalhe arredondado (0,25mm). Os corpos-de-prova assim preparados foram submetidos ao ensaio Charpy Instrumentado e tiveram seus sinais digitalizados. O sinal capturado com tal cadeia de medição foi utilizado na determinação dos valores de tenacidade à fratura dinâmica. Os resultados experimentais foram obtidos através dos ensaios de dureza, monotônicos (em três pontos), dinâmicos (Ensaio de Impacto Charpy). Os ensaios de dureza foram realizados com objetivo de ratificar a qualidade dos tratamentos térmicos. Os ensaios monotônicos servirão como referências para auxiliar o entendimento dos dados obtidos com os ensaios dinâmicos.
Abstract: The proof of conventional impact Charpy is a mechanic proof consecrated in scientific in industry. Its function is determinate the absorb total energy in order to the complete fracture in a indented proof body, standardized according to the ASTM E- 23 pattern. Therefore, the absorb global energy has a very limited value. It is not accepted a quantities indicator of resistance to the matter fracture. Thus, though adequate instrumentation, it can increase the quantity of information obtained from the proof of the classic impact Charpy. In this paper, we intend to study the influence of the ray of intende tip, of the loading type and of the microstructure of proof bodies in process the fracture of the structural steel ABNT-4340 from the instrumented proof Charpy. The different microstructure conditions are resulted of different conditions of thermal treatments: drawgeting, draw tempering, drawing in following temperatures: 473 K, 573 K, 673 K and 773 K. For each microstructures prepared proof body with two types of tip ray - sharp rack and rounding indented (0,25 mm). Proof bodies prepared this way are submitted the instrumented proof Charpy and have your signal digitalized. The signal capturing with such ranger of measurement will de used in determination of values of toughness to dynamic fracture. The experimental result were obtained through the rehearsals of hardness, almost-static (in three points), dynamic (instrumented proof Charpy). The rehearsals of hardness were accomplished with objective of ratifying the quality of the thermal treatments. The rehearsals almost-static will serve as references for to aid the understanding of the data obtained with the dynamic rehearsals.
Mestre
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Manaâ, Rabah. "Étude de la ténacité des assemblages bois-colle résorcine-phénol-formol." Vandoeuvre-les-Nancy, INPL, 1995. http://www.theses.fr/1995INPL028N.
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La méthode de détermination de l'énergie de rupture GIC d'une éprouvette DCB (Double Cantilever Beam) en bois collée à la résorcine-phénol-formol, considère un bras de l'éprouvette comme une poutre élastique sur fondations viscoélastiques dont les constantes de la loi de comportement sont déterminées en réalisant des essais au viscoanalyseur. La méthode de la complaisance expérimentale établie par Sassaki a été adoptée pour déterminer l'énergie de rupture GIC. La solution du problème est d'assimiler le matériau de l'éprouvette DCB à un modèle de Zener ou le bois est considéré comme un matériau élastique et représente par un ressort, alors que la colle est considérée comme un matériau viscoélastique et représente par un modèle de Voigt (un ressort et un amortisseur en parallèle). L’énergie de rupture du modèle est déterminée par la relation (P-d). Les résultats sont satisfaisants dans la mesure où la différence des énergies entre les valeurs expérimentales et celles du modèle est très minime
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Dhansay, Nur Mohamed. "Fracture mechanics based fatigue and fracture toughness evaluation of SLM Ti-6Al-4V." Master's thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/24326.
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The focus of this research project was to determine experimentally the fatigue and fracture toughness characteristic, from a fracture mechanics perspective, of Ti-6Al-4V titanium alloy manufactured by Selective Laser Melting (SLM). Three build orientations are considered where a fatigue crack is grown parallel and two are grown perpendicular to the build orientation. The project then endeavours to generate a fracture mechanics based Paris equation from the fatigue crack growth rate results and together with the fracture toughness, fatigue life predictions may be determined based on crack propagation lifetimes. SLM is an Additive Manufacturing (AM) technique whereby an object is fabricated in a layerwise manner via the use of lasers, directly from a 3D CAD model. This process allows for the manufacture of complex designs in its net or near net shape form, which is not possible with conventional manufacturing techniques. There are minimal amounts of material wastage and it potentially eliminates post manufacture machining and processing costs. Ti- 6Al-4V is used in many applications where high strength at low density is required at moderate temperatures. Corrosion resistance qualities of the alloy are also considered for many applications. Some of the applications where this alloy is used include turbine engine components, aircraft structural components, aerospace fasteners, high-performance automotive parts, marine applications, medical implant devices and sports equipment. Due to the large use of the alloy in industry and with the potential benefits of manufacturing by SLM, there is a great need for investigating SLM Ti-6Al-4V as a viable alternative to conventional casting, forging and machining. There is limited literature covering the fatigue crack growth rate and fracture toughness of SLM Ti-6Al-4V and the effect of build orientation on these characteristics. However, it is clear, from the limited available literature that fatigue crack growth rate behaviour is affected by build orientation, and so this project investigates the effect of these orientations, and aims to contribute to understanding why these orientation effects occur. Since there is even less literature available on the fracture toughness of SLM Ti-6Al-4V with respect to build orientation, this project also endeavours to characterise orientation effects on fracture toughness, if any, and compares these with those of conventionally manufacture Ti-6Al-4V.
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Yang, Kao Z. "MENs Doped Adhesive and Influence on Fracture Toughness." FIU Digital Commons, 2016. http://digitalcommons.fiu.edu/etd/2487.
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Composites are in high demand; however, fasteners are often required for joining process and can reduce their advantages. One solution is adhesive bonding, but uncertainty exists regarding long term durability and the ability to interrogate bonds noninvasively. One potential solution to qualify bond integrity over its service life is to dope an adhesive with magneto-electric nanoparticles (MENs). MENs can yield output magnetic signatures that are influenced by bond quality and damage state. In this study, adhesives have been doped with MENs prior to bonding at 1% volume concentration. For optimum implementation, this health monitoring system should be evaluated for effects of the MENs on the mechanical properties. Lap-shear testing was conducted to assess changes in the bond strength from addition of the nanoparticles. End-notched flexure (ENF) tests were also conducted for fracture mechanism evaluation. Results showed an increase of 12% in shear strength as a function of MENs loading concentration. In addition, a feasibility study of output magnetic signature as a function of elevated temperature and humidity were evaluated for MENs doped and un-doped adhesives. Results gave an order of magnitude change in magnetic signal as a function of exposure time.
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Rider, Andrew Chemistry Faculty of Science UNSW. "Surface Properties Influencing the Fracture Toughness of Aluminium-Epoxy Joints." Awarded by:University of New South Wales. School of Chemistry, 1998. http://handle.unsw.edu.au/1959.4/17804.
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This thesis systematically investigates the properties of the aluminium adherend which influence the fracture toughness of aluminium-epoxy adhesive joints in humid environments. The fracture energy of the adhesive joint exposed to a humid environment in comparison with the fracture energy in a dry environment provides a measure of the joint durability. A 500C and 95% relative humidity environment is used to simulate aging of an adhesive joint over several years under normal service conditions. Initially, surface roughness is found to have a significant influence on the fracture toughness of the adhesive joint in humid conditions. A direct correlation between the bond durability and the angle of deliberately machined micro-roughness in the aluminium surface is determined. Consequently a model is developed which initially has the capacity to describe the bond durability performance. The preparation of aluminium surfaces involves the use of a novel ultramilling tool to produce well defined and controlled surface topography. This work represents the first time surface angles of features in the 1????m to 10????m range have been systematically varied and a direct relationship with bond durability has been determined. The use of surface analytical tools aids in elucidating mechanisms involved in the failure of the adhesive joint and contributes to the development of the stress based diffusion model. Examination of the aluminium oxide hydration level reveals this property has a negligible effect on the fracture toughness of the aluminium-epoxy joints exposed to humid environments. This information confirms the dominant role of the physical properties of the aluminium surface in determining the adhesive joint durability. This is the first occasion that planer oxide films grown in an RF plasma have had their hydration state adjusted in a controlled manner and their properties subsequently assessed in terms of bond durability properties. Further alteration of the aluminium surface chemistry is achieved through the application of an organo-silane coupling agent and a series of novel organo-phosphonate compounds. This work further develops the stress based diffusion model developed in conjunction with the micro-machining studies. The components of surface roughness and the ability of interfacial bonds to co-operatively share load are essential for the maintenance of fracture toughness of adhesive joints exposed to humid conditions. The ability of the silane coupling agent to share load through a chemically cross-linked film is a significant property which provides the superior fracture toughness in comparison with the phosphonate treated joints. Although the organo-phosphonate treated aluminium provides hydrolytically more stable bonds than the silane coupling agent, the film is not cross-linked via primary chemical bonds and the reduced load sharing capacity of interfacial bonds increases the bond degradation rate. The stress based diffusion model evolving from the initial work in the thesis can be used to predict the performance of more complex systems based on a thorough characterisation of the aluminium surface chemistry and topography. The stress based diffusion model essentially describes the concept of the production of micro-cavities at the epoxy-aluminium interface under mode 1 load, as a result of the distribution of strong and weak adhesive bonds. Alternatively, micro-cavities may result from an inhomogeneous stress distribution. In areas where the adhesive bonds are weak, or the local stresses are high, the interfacial load produces larger micro-cavities which provide a path of low resistance for water to diffuse along the bond-line. The water then degrades the adhesive bond either through the displacement of interfacial epoxy bonds or the hydration of the oxide to form a weak barrier layer through which fracture can occur. Alternatively, the water can hydrolyse the adhesive in the interfacial region, leading to cohesive failure of the epoxy resin. The bond durability performance of a series of complex hydrated oxide films used to pre-treat the aluminium adherend provides support for the stress based diffusion model. Whilst surface area is an important property of the aluminium adherend in producing durable bonding, the best durability achievable, between an epoxy adhesive and aluminium substrate, requires a component of surface roughness which enhances the load sharing capability in the interfacial bonding region. This component of durability performance is predicted by the model. In more specific terms, a boiling water treatment of the aluminium adherend indicates a direct correlation between bond durability, surface area and topography. The characterisation of film properties indicates that the film chemistry does not change as a function of treatment conditions, however, the film topography and surface area does. The overall bond durability performance is linked to both of these properties. The detailed examination of the hydrated oxide film, produced by the boiling water treatment of aluminium, is the first time the bond durability performance has been related to the film topography. It is also the first occasion that the mechanism of film growth has been examined over such a large treatment time. The combination of surface analysis and bond durability measurements is invaluable in confirming the properties, predicted by the stress based diffusion model, which are responsible in forming fracture resistant adhesive bonds in humid conditions. The bond durability of high surface area and low surface area hydrated oxide films indicates that surface area is an important property. However, this study confirms that the absence of the preferred surface topography limits the ultimate bond durability performance attainable. The fracture toughness measurements performed on aluminium adherends pre-treated with a low surface area film also supports the mechanism of load sharing of interfacial adhesive bonds and its contribution to the overall bond durability. The role performed by the individual molecules and particles in an oxide film is similar to the load sharing performed by the silane coupling agent molecules. Further support for the stress based diffusion model is provided by films produced on aluminium immersed in nickel salt solutions. The topography of these film alters as a function of treatment time and this is directly related to fracture toughness in humid environments. This work provides the first instance where such films have been characterised in detail and their properties related to bond durability performance. The study is also the first time that the growth mechanism of the film produced on the aluminium substrate has been examined in detail. The film growth mechanism supports the film growth model proposed for the hydrated oxide film produced by the boiling water treatment. The major findings presented in this thesis are summarised as the direct correlation between surface profile angle, the importance of co-operative load sharing of interfacial adhesive bonds and the relative insignificance of surface oxide hydration in the formation of durable aluminium-epoxy adhesion. This information is used to develop a stress based diffusion model which has the capacity to describe the fracture toughness of a range of aluminium-epoxy adhesive joint systems in humid environments. The stress based diffusion model is also capable of predicting the relative performance of the bond systems examined in the final chapters of the thesis, where complex interfacial oxide films are involved in the formation of adhesive bonds.
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Nogueira, Fabiano da Cruz [UNESP]. "Influência do raio de ponta do entalhe, do tipo de carregamento e da microestrutura no processo à fratura do aço estrutural ABNT-4340." Universidade Estadual Paulista (UNESP), 2006. http://hdl.handle.net/11449/94491.
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O ensaio de impacto Charpy convencional é um ensaio mecânico consagrado no meio científico e industrial. Sua função é determinar a energia total absorvida para causar a fratura completa de um corpo-de-prova entalhado, padronizado segundo a norma ASTM E?23. Entretanto, a energia global absorvida possui um valor de uso muito limitado. Ela normalmente não é aceita como um indicador quantitativo da resistência à fratura do material. Assim, através da instrumentação adequada, pode-se aumentar a quantidade de informações obtidas a partir do ensaio de impacto Charpy clássico. No presente trabalho, estudou-se a influência do raio de ponta do entalhe, do tipo de carregamento e da microestrutura dos corpos-de-prova no processo à fratura dinâmica do aço ABNT-4340 a partir do ensaio Charpy Instrumentado. As diferentes condições microestruturais foram resultantes de diferentes condições de tratamentos térmicos: como-recebido, como-temperado e revenido nas seguintes temperaturas: 473K, 573K, 673K e 773K. Para cada microestrutura foram confeccionados corpos-de-prova com dois tipos de raio de ponta - pré-trincado e entalhe arredondado (0,25mm). Os corpos-de-prova assim preparados foram submetidos ao ensaio Charpy Instrumentado e tiveram seus sinais digitalizados. O sinal capturado com tal cadeia de medição foi utilizado na determinação dos valores de tenacidade à fratura dinâmica. Os resultados experimentais foram obtidos através dos ensaios de dureza, monotônicos (em três pontos), dinâmicos (Ensaio de Impacto Charpy). Os ensaios de dureza foram realizados com objetivo de ratificar a qualidade dos tratamentos térmicos. Os ensaios monotônicos servirão como referências para auxiliar o entendimento dos dados obtidos com os ensaios dinâmicos.
The proof of conventional impact Charpy is a mechanic proof consecrated in scientific in industry. Its function is determinate the absorb total energy in order to the complete fracture in a indented proof body, standardized according to the ASTM E- 23 pattern. Therefore, the absorb global energy has a very limited value. It is not accepted a quantities indicator of resistance to the matter fracture. Thus, though adequate instrumentation, it can increase the quantity of information obtained from the proof of the classic impact Charpy. In this paper, we intend to study the influence of the ray of intende tip, of the loading type and of the microstructure of proof bodies in process the fracture of the structural steel ABNT-4340 from the instrumented proof Charpy. The different microstructure conditions are resulted of different conditions of thermal treatments: drawgeting, draw tempering, drawing in following temperatures: 473 K, 573 K, 673 K and 773 K. For each microstructures prepared proof body with two types of tip ray - sharp rack and rounding indented (0,25 mm). Proof bodies prepared this way are submitted the instrumented proof Charpy and have your signal digitalized. The signal capturing with such ranger of measurement will de used in determination of values of toughness to dynamic fracture. The experimental result were obtained through the rehearsals of hardness, almost-static (in three points), dynamic (instrumented proof Charpy). The rehearsals of hardness were accomplished with objective of ratifying the quality of the thermal treatments. The rehearsals almost-static will serve as references for to aid the understanding of the data obtained with the dynamic rehearsals.
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Mirjalili, Vahid. "Aspects of the fracture toughness of carbon nanotube modified epoxy polymer composites." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=103601.
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Epoxy resins used in fibre reinforced composites exhibit a brittle fracture behaviour, because they show no sign of damage prior to a catastrophic failure. Rubbery materials and micro-particles have been added to epoxy resins to improve their fracture toughness, which reduces strength and elastic properties. In this research, carbon nanotubes (CNTs) are investigated as a potential toughening agent for epoxy resins and carbon fibre reinforced composites, which can also enhance strength and elastic properties. More specifically, the toughening mechanisms of CNTs are investigated theoretically and experimentally. The effect of aligned and randomly oriented carbon nanotubes (CNTs) on the fracture toughness of polymers was modelled using Elastic Plastic Fracture Mechanics. Toughening from CNT pull-out and rupture were considered, depending on the CNTs critical length. The model was used to identify the effect of CNTs geometrical and mechanical properties on the fracture toughness of CNT-modified epoxies. The modelling results showed that a uniform dispersion and alignment of a high volume fraction of CNTs normal to the crack growth plane would lead to the maximum fracture toughness enhancement. To achieve a uniform dispersion, the effect of processing on the dispersion of single walled and multi walled CNTs in epoxy resins was investigated. An instrumented optical microscope with a hot stage was used to quantify the evolution of the CNT dispersion during cure. The results showed that the reduction of the resin viscosity at temperatures greater than 100 °C caused an irreversible re-agglomeration of the CNTs in the matrix. The dispersion quality was then directly correlated to the fracture toughness of the modified resin. It was shown that the fine tuning of the ratio of epoxy resin, curing agent and CNT content was paramount to the improvement of the base resin fracture toughness. For the epoxy resin (MY0510 from Hexcel), an improvement of 38% was achieved with 0.3 wt.% of Single Walled CNT (SWNT). Finally, the CNT-modified epoxy resin was used to manufacture carbon fibre laminates by resin film infusion and prepreg technologies. The Mode I and Mode II delamination properties of the CNT-modified composite increased by 140% and 127%, respectively. In contrast, this improvement was not observed for the base CNT-modified polymers, used to manufacture the composite laminates. A qualitative analysis of the fractured surface using a Scanning Electron Microscope revealed a good dispersion in the composites samples, confirming the importance of processing to harness the full potential of carbon nanotubes for toughening polymer composites.Les résines époxy utilisées dans des composites à renforts fibreux ont en général un comportement à rupture fragile qui peut conduire à une rupture catastrophique des composites. Afin d'améliorer leur ténacité à la rupture, des matériaux caoutchouteux et des microparticules sont ajoutés, au dépend de leurs propriétés mécaniques. Dans cette recherche, des nanotubes de carbone (CNTs) ont été ajoutés à la résine époxy pour améliorer sa ténacité. Plus spécifiquement, les mécanismes de résistance à la rupture des nanotubes de carbone ont été étudiés de façon expérimentale et numérique. Tout d'abord, l'effet de l'alignement des nanotubes de carbone (aligné ou aléatoire) sur la résistance à la rupture a été modélisé en utilisant les lois de mécanique de la rupture élastique et plastique. L'influence de la longueur critique des CNT sur les conditions de rupture et sur les mécanismes de résistance à la rupture par arrachement des nanotubes à été considérée. Le modèle développé a été ensuite utilisé pour identifier l'effet des propriétés géométriques et mécaniques des nanotubes de carbone sur la ténacité à la rupture des résines époxy modifiées. Les résultats montrent qu'une dispersion uniforme ainsi qu'une orientation des nanotubes de carbone perpendiculairement à la direction de propagation de la fissure conduisent à une amélioration de la ténacité de la résine. L'effet du procédé de fabrication sur la dispersion des nanotubes de carbone à paroi simple et à parois multiples a été également étudié expérimentalement. Une plaque chauffante instrumentée avec un microscope optique a été utilisée pour quantifier la dispersion des CNT pendant la polymérisation de la résine. Les résultats montrent qu'une réduction de la viscosité de la résine à des températures supérieures à 100ºC cause une ré-agglomération irréversible des CNT dans la matrice. La qualité de la dispersion a été ensuite corrélée à la ténacité de la résine modifiée. La détermination d'un ratio optimum entre la résine époxy, le catalyseur et la concentration de CNT est primordiale pour améliorer la ténacité de base de la résine. Pour la résine époxy étudiée (MY0510 de Hexcel), une amélioration de 38% a été obtenue avec 0.3% de CNT à paroi simple. Finalement, la résine modifiée avec les CNT a été utilisée pour fabriquer des laminés avec des renforts de fibres de carbone par les procédés d'infusion de résine et de préimprégnés. Les propriétés de délamination du composite ont été augmentées d'un maximum de 140% (mode I) et 127% (mode II) par rapport aux propriétés de base du composite. Cette amélioration n'a pas été observée pour les échantillons de résine modifiée sans renfort. Une analyse qualitative de la surface de cassure par microscope électronique à balayage (SEM) révèle une bonne dispersion des CNT dans le composite. Ceci reconfirme l'importance du procédé de fabrication et de la dispersion afin d'utiliser les nanotubes de carbone au maximum de leur potentiel pour renforcer les composites à matrice polymère.
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Kuntz, Joshua D. "Processing and properties of ceramic nanocomposites designed for improved fracture toughness /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2005. http://uclibs.org/PID/11984.
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Rothwell, Glynn. "Fracture toughness determination using constraint enhanced sub-sized specimens." Thesis, Liverpool John Moores University, 2003. http://researchonline.ljmu.ac.uk/4971/.
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Prakash, Sunil. "Modeling the Constraint Effects on Fracture Toughness of Materials." University of Akron / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=akron1259271280.
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Achon, Philippe. "Comportement et ténacité d'alliages d'aluminium à haute résistance." Paris, ENMP, 1994. http://www.theses.fr/1994ENMP0546.
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La modélisation des phénomènes de rupture ductile des alliages d'aluminium a haute résistance, est abordée ici a l'aide de l'approche locale. Dans cette approche, on établit des relations quantitatives entre les propriétés mécaniques globales de rupture (la ductilité) ou de ténacité (K#I#C ou J#I#C), les lois de comportement du matériau dépendantes des traitements thermomécaniques qu'il a subi, et les paramètres métallurgiques contrôlant la rupture ductile (nature, forme et répartition des composes intermétalliques). L’étude a été entreprise sur une famille d'alliages (série 7000) se présentant sous forme de tôles fortes, laminées a chaud, avec des niveaux de pureté différents (7075-7475) et ayant subi plusieurs traitements thermiques (t3, t6, t73). Nous décrivons les microstructures puis l'étude de métallographie quantitative effectuée sur les composes intermétalliques. Les premiers essais de caractérisation mécanique nous ont révélé une anisotropie du comportement plastique des alliages que nous décrivons à l'aide des coefficients de Lankford. La modélisation de cette anisotropie est ensuite effectuée a partir du modèle phénoménologique de Hill, puis a l'aide d'un modèle micromécanique tenant compte de la texture cristallographique. L’étude expérimentale entreprise, nous permet d'observer les mécanismes physiques et de quantifier les paramètres métallurgiques de chacune des étapes de la rupture ductile. Une modélisation a partir de la mécanique des milieux poreux, ou la porosité est décrite a partir des regroupements des composes intermétalliques sous forme d'amas, nous permet d'obtenir une adéquation satisfaisante avec l'expérience. Les essais de ténacité sont réalisés sur des éprouvettes de mécanique de la rupture, selon différents sens de prélèvement. Les examens microfractographiques effectues sur les surfaces de rupture nous indiquent que la répartition spatiale des composes intermétalliques gouverne la propagation de la fissure. Les trois modèles proposes, tenant compte de cette répartition, présentent un degré croissant de sophistication, et offrent des résultats en bon accord avec les données expérimentales.
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ALBUQUERQUE, Siderley Fernandes. "Avaliação microestrutural e das propriedades mecânicas em juntas soldadas de aços API 5L X80 utilizados para transporte de petróleo e gás usando processo de soldagem robotizado." Universidade Federal de Campina Grande, 2015. http://dspace.sti.ufcg.edu.br:8080/jspui/handle/riufcg/1041.
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No Brasil, a soldagem de tubulações ainda emprega processos manuais com eletrodo revestido, porém, tem crescido as pesquisas com o objetivo de implementar processos mais produtivos, e que atendam às exigências requeridas por normas específicas. Processos de soldagem robotizados estão sendo largamente utilizados em vários países, com ganho considerável na produtividade, como também na qualidade superficial. A utilização de processos de soldagem automatizados possibilita, além da maior produtividade, um maior controle dos parâmetros de soldagem, podendo favorecer positivamente as transformações microestruturais, e consequentemente, em melhores propriedades mecânicas da junta soldada. O objetivo deste trabalho foi avaliar a tenacidade à fratura de juntas soldadas em chapas aço API 5L X80 com 19 mm de espessura, utilizados para transporte de petróleo e gás, quando submetidos à soldagem robotizada nas posições plana e vertical ascendente, utilizando processo de soldagem a arco elétrico com arame maciço para o passe de raiz (ER 120S-G), e processos de soldagem com arame tubular para os passes de enchimento e acabamento, utilizando arame do tipo flux-cored e proteção de gás externa (E101T-1), e arame do tipo autoprotegido (E91T8-G); o gás de proteção utilizado foi Ar+25%CO2. Foram realizadas análises de microdureza e microestrutural na ZTA das juntas soldadas, utilizando microscopia óptica e microscopia eletrônica de varredura; para avaliação da tenacidade na ZTA das juntas soldadas, foram usinados corpos de prova do tipo SE(B) para ensaio CTOD. A análise microestrutural na ZTA para todos os procedimentos indicam a presença de bainita e ferrita acicular, com exceção do procedimento de soldagem na posição plana utilizando arrame autoprotegido que apresentou ferrita primária. Os resultados de tenacidade a fratura obtidos indicam que os procedimentos de soldagem robotizados na posição plana apresentaram a maioria dos valores de CTOD superiores aos procedimentos de soldagem na posição vertical ascendente. Os procedimentos de soldagem robotizados na posição plana usando arame autoprotegido apresentaram o melhor resultado em termos de crescimento da pré-trinca de fadiga, com perfil na região central de forma arredondada, diferente do procedimento de soldagem na posição plana com RP- G que apresentou a forma plana.
In Brazil, the welding pipes still uses manual processes with coated electrodes, however, research has grown to implementing more productive processes, and complying with the requirements of specific rules. Robotic welding processes are in use in Sweden, USA, Canada, Russia and China, with a considerable increase in productivity, and higher quality welds surface. The use of automated welding processes increase the productivity, and promote better control of the welding parameters, and microstructural changes, and consequently, better mechanical properties of the welded joint. The objective of this study was to evaluate the fracture toughness of API 5L X80 steel welded joints with thickness for 19 mm, used for oil and gas transmission, when subjected to robotic welding in the flat and vertical upward positions using arc electric welding process with solid wire for the root pass (ER 120S-G), and tubular wire for the filler passes and finishing, using flux- cored wire (E101T-1) and Ar + 25% CO2 as shielding gas and self-protected wire (E91T8-G). For this, CTOD specimens with all notched located in HAZ were prepared and submitted to metalographic and microhardness test were also done to observe the resulting microstructure and hardness value in the region of the crack, using optical and scanning microscopy analysis. The microstructural analysis in the ZTA of the specimen for all procedures indicated the presence of Bainite and Acicular Ferrite, except those obtained in flat position using the Flux-Cored Self-Shielded welding process which also presented Primary Ferrite. The results of fracture toughness test indicated that the welding in a flat position presented the most superior CTOD values. The robotic welding procedures in the flat position using Flux-Cored SelfShielded welding process showed the best result in terms of the fatigue pre-crack growth, with profile in the central region of rounded shape, unlike flat shape in the robotic welding procedures in the flat position using Flux-Cored and Ar + 25% CO2 as shielding gas.
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Morsi, Khaled M. B. E. "Mechanical properties of particle reinforced alumina." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320644.
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Watring, Dillon S. "Development of Novel, Microscale Fracture Toughness Testing for Adhesives." FIU Digital Commons, 2017. http://digitalcommons.fiu.edu/etd/3474.
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The purpose of this thesis was to develop microscale fracture toughness tests to be performed in situ based off previously used macroscale fracture toughness tests. The thesis also was to use these tests to perform in situ analysis and imaging of reinforced adhesives during crack propagation. Two different fracture toughness tests were developed for this thesis through developing fixtures and sample geometry. A microscale double cantilever beam (DCB) test was developed for mode I fracture (opening mode). A microscale end notch flexure (ENF) test was developed for mode II fracture (sliding mode).
Three different types of materials were used as a reinforcing agent and tested using the micro-DCB and micro-ENF tests. Magnetoelectric nanoparticles (MENs) doped adhesive showed a 12% increase in mode II toughness and 33% increase in total fracture energy for micro-DCB. Similarly, the graphene foam (GrF) doped adhesive showed an approximate 34% increase in mode II toughness and a 71% increase in total fracture energy for mode I. In situ imaging provided real time imaging of crack propagation for all three reinforcing agents that allowed for a novel analysis of the crack propagation and general fracture.
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Chyad, Fadhil Attiya. "The effects of metastable zirconia on the properties of ordinary Portland cement." Thesis, University of Bradford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.276103.
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Boothby, Peter James. "The structure and properties of mechanized pipeline girth welds." Thesis, University of Leeds, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328951.
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Spain, Darin R. (Darin Rodney) 1975. "Fracture toughness measurements of thin film silicone polymers using the modified edge lift-off test." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/88865.
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Kwon, Ojin. "Morphology Development and Fracture Properties of Toughened Epoxy Thermosets." Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/30660.
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The phase separation process of a rubber modified epoxy system during cure was analyzed by a model developed on the basis of a thermodynamic description of binary mixture and constitutive equations for nucleation and growth rates. As epoxy resins are cured, rubber molecules are precipitated from the epoxy matrix to a non-equilibrium composition due to the decrease in the configurational entropy and the increase in the viscosity with conversion. If phase separation takes place in a metastable region, this model can monitor the changes of rubber compositions in both phases as well as the changes in the number and size of rubber particles upon conversion of polymerization. The particle size distribution at the completion of phase separation was also calculated. The effect of cure temperature on the final morphologies of a rubber modified epoxy system was discussed.
The computed particle size distributions for piperidine and diaminodiphenyl sulfone cured systems showed good agreements with experimentally measured values. Depending on the activation energy for viscous flow of the epoxy matrix relative to that for the polymerization, the particle size distribution may show bimodal or unimodal distribution. The size of rubber rich phase increases to a maximum and then decreases with an increase in cure temperature. However, due to limitations of temperature range to probe in an actual experiment, one may observe only either decreasing or increasing particle size as cure temperature increases. The number of rubber particles per unit volume increases for the DGEBA/DDS/ETBN system as cure temperature increases in the temperature range of 30 °C to 220 °C.
Fracture toughness of cured DGEBA/DDS/ETBN system was analyzed in terms of morphologies generated by the temperature variation. Since the volume fraction of rubber particles did not change with cure temperature, the critical stress intensity factor did not vary significantly with cure temperature as expected. However, increases in cure temperature produced smaller but more numerous particles. The critical stress intensity factor normalized by the number density of particles exhibited dependence on the radius of particles to the third power. On the other hand, the critical stress intensity factor normalized by the radius of particles showed a linear dependence with respect to the number density of particles.Ph. D.
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Horschel, Jeffery D. "Mode I Fracture Toughness Testing of Friction Stir Processed HSLA-65." BYU ScholarsArchive, 2008. https://scholarsarchive.byu.edu/etd/1495.
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In order to investigate the viability of friction stir welding for use in Naval construction, mode one elastic-plastic fracture toughness of friction stir processed HSLA-65 was determined using current ASTM 1820 and BS 7448 standards. Double-sided welds were used to achieve 12.7 mm thick samples. A constant feed rate of 100 mm/min was used for all welds. To explore the effect of weld parameters on toughness, welds were produced using two rotational speeds: 340 RPM and 490 RPM. The weld centerline, advancing side hardened region (ASHR), and TMAZ/HAZ regions were sampled, in addition to un-welded parent material. All elastic-plastic fracture toughness values were thickness dependent. For welds produced at 340 RPM, toughness ranged from 33% to 75% below parent material. By increasing the rotational speed to 490 RPM, weld toughness was likewise less than the parent material, but increased 12% to 50% relative to welds produced at 340 RPM. The lowest measured toughness was in the ASHR samples for both parameters. This region of the weld exhibited mixed mode stress-strain conditions and toughness 75% and 62% less than parent material. Toughness values for all samples failed to meet qualification requirements of both ASTM 1820 and BS 7448 due to non-uniform crack extension. Irregular crack extension was caused by the through thickness change in tensile properties due to welding and the affect this had on the plastic zone size compared to the thickness. Increased weld toughness from 340 RPM to 490 RPM was attributed to microstructural differences as a result of increased rotational speed. In addition, higher crack extensions were observed in the second weld pass relative to the first for both rotational speeds. This was attributed to weld tempering of the first pass by the second. The ASHR samples exhibited the highest crack extensions. In this location, the weld microstructure consisted of Widmanstatten ferrite, a microstructure known to be detrimental to toughness.
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O'Leary, Emma-Jane. "The mechanical and fracture properties of bird bones." Thesis, University of Reading, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312569.
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Tribe, Allan M. "Study on the Fracture Toughness of Friction Stir Welded API X80." BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3740.
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High strength low alloy (HSLA) steels have been developed to simultaneously have high yield strength and high fracture toughness. However, in practical applications steel must be welded. Traditional arc welding has proven detrimental to the fracture toughness of HSLA steels. Friction stir welding has recently shown mixed results in welding HSLA steels. The range of welding parameters used in these recent studies however has been very limited. With only a few welding parameters tested, the effect of spindle speed, travel speed, and heat input on the fracture toughness of friction stir welded HSLA steel remains unknown. To understand how the friction stir welding process parameters affect fracture toughness, double sided welds in API X80 were performed and analyzed. Results show that at room temperature friction stir welded API X80 exceeded industry minimum fracture toughness requirements in both the API Standard 1104 and DNV-OS-F101 by 143% and 62%, respectively. The process parameters of spindle speed and HI have been shown to effectively control the fracture toughness of the stir zone. Relationships have been established that show that fracture toughness increased by 85% when spindle speed decreased by 59% and heat input decreased by 46%.
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Hurlston, Robert George. "Development of advanced methods for quantifying fracture toughness properties in the presence of residual stresses." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/development-of-advanced-methods-for-quantifying-fracture-toughness-properties-in-the-presence-of-residual-stresses(d5b6ce24-2135-4139-99f2-97377e43c712).html.
Full textAbstract:
Welding is an essential process in many industries for both the production and repair of engineering plant, notably pressure vessels and piping. However, welding processes cause large magnitudes of residual stress to be induced within the structure. Residual stress can be defined as a stress that exists in a material when it is under no primary loading. Whilst residual stresses can be reduced by post weld heat treatment, such treatments are not always possible, and so high residual stresses can remain in serviceThe current methodology for evaluating fracture toughness from specimens, particularly if these contain weld residual stresses is presented in BS7448-1997. This method relies on the assumption that the effect of residual stress on fracture toughness measurements can be negated by the application of a local compression, to the ligament ahead of the pre-crack in the test specimen. Recent research has investigated the validity of this assumption. The results suggest that, far from being removed, the residual stresses are modified or even enhanced via local compression. This can reduce the value of measured fracture toughness below its true value. In order to ensure the validity of fracture toughness measurements in materials that contain residual stress, a more robust method for its quantification is developed.The aim of this project was to extend current understanding regarding the magnitude and distribution of residual stresses retained in standard fracture mechanics specimens removed from welds and the consequent effects of these stresses on measured fracture toughness, both in terms of the crack driving force and crack-tip constraint. Furthermore, the project aimed to derive improved methods for the quantification of valid values of fracture toughness from laboratory specimens containing residual stresses. This was achieved via a combination of analytical and experimental work.The effect of specimen extraction on the level of retained residual stress in specimens extracted from non stress-relieved welds was investigated using parametric finite element analyses. Simplified methods to quantify the levels of residual stresses in fracture mechanics specimens removed from welds and their significance, in terms of contribution to crack driving force, are proposed.The influence of residual stresses on the measured fracture toughness properties of ferritic pressure vessel steel, tested in the cleavage fracture regime, has also been studied. A refined method of out-of-plane compression was devised and used to generate significant residual stresses in three-point bend specimens. This method was then used experimentally, alongside supporting elastic-plastic analyses, to quantify the effects of the residual stresses on fracture toughness in terms of both crack driving force and crack-tip constraint in geometrically high and low constraint specimens. A method whereby fracture toughness data, obtained from specimens containing residual stresses, can be corrected to provide valid fracture toughness properties using constraint based fracture mechanics alongside a simple fracture model has been proposed. The main conclusions from the work are as follows. Significant weld residual stresses have been shown to be retained in certain laboratory specimens post extraction from non stress-relieved welds. The magnitude and distribution of retained residual stress has been shown to be dependant on: • Material yield and flow properties • Specimen size; where larger specimens are more likely to retain significant levels of residual stress than smaller specimens • Specimen type; either compact tension (CT) or single edge notched bend (SENB), where there is a tendency for specimens to retain higher relative levels of residual stress in the directions of their largest dimensions; i.e. bend specimens retain more residual stress along their length than CT specimens and CT specimens retain more residual stress across their width than bend specimens • Extraction location, e.g. full thickness, near surface, mid-thickness etc. The stress partitioning method has been shown to provide a useful estimating approach for assessing the levels of residual stress retained in fracture mechanics specimens extracted from non stress-relieved welds in certain orientations.Retained residual stresses have been shown to affect both crack driving force and crack-tip constraint in both low and high geometrically constrained 50mm bend specimens manufactured from A533B ferritic steel. The residual stress has been shown to dominate the level of crack-tip constraint condition over and above the geometric and loading factors during the early stages of loading. The effects of residual stress on crack driving force and crack-tip constraint have been shown to result in fracture loads and, therefore, measured fracture toughness values that vary widely from those to be expected in the material under small-scale yielding conditions; i.e. if a standard specimen were to be tested containing no residual stress. Two-parameter (J-Q) fracture mechanics has been shown to provide a valid approach for quantifying fracture toughness properties from high and low constraint specimens, with and without residual stresses, with all data being shown to be consistent with a J-Q failure locus for a given level of cleavage probability.