No description available.

Structural energetic materials (SEM) are a class of multicomponent materials which may react under various conditions to release energy. Fragmentation and impact induced reaction are not well characterized phenomena in SEMs. The structural energetic systems under consideration here combine aluminum with one or more of the following: nickel, tantalum, tungsten, and/or zirconium. These metal+Al systems were formulated with powders and consolidated using explosive compaction or the gas dynamic cold spray process. Fragment size distributions of the indicated metal+Al systems were explored; mean fragment sizes were found to be smaller than those from homogeneous ductile metals at comparable strain rates, posing a reduced risk to innocent bystanders if used in munitions. Extensive interface failure was observed which suggested that the interface density of these systems was an important parameter in their fragmentation. Existing fragmentation models for ductile materials did not adequately capture the fragmentation behavior of the structural energetic materials in question. A correction was suggested to modify an existing fragmentation model to expand its applicability to structural energetic materials. Fragment data demonstrated that the structural energetic materials in question provided a significant mass of combustible fragments. The potential combustion enthalpy of these fragments was shown to be significant. Impact experiments were utilized to study impact induced reaction in the indicated metal+Al SEM systems. Mesoscale parametric simulations of these experiments indicated that the topology of the microstructure constituents, particularly the stronger phase(s), played a significant role in regulating impact induced reactions. Materials in which the hard phase was topologically connected were more likely to react at a lower impact velocity due to plastic deformation induced temperature increases. When a compliant matrix surrounded stronger, simply connected particles, the compliant matrix accommodated nearly all of the deformation, which limited plastic deformation induced temperature increases in the stronger particles and reduced reactivity. Decreased difference between the strength of the constituents in the material also increased reactivity. The results presented here demonstrate that the fragmentation and reaction of metal+Al structural energetic materials are influenced by composition, microstructure topology, interface density, and constituent mechanical properties.

O presente trabalho apresenta um breve apanhado do processo de forjamento, resultados da investigação experimental e da análise computacional acerca do teste de compressão do anel e ensaio do tubo cônico, ambos visando a determinação do coeficiente de atrito existente na região de contato entre as matrizes e os corpos-de-prova, para as ligas de alumínio AA6351 e de titânio Ti6Al4V. Foram realizadas curvas teóricas de calibração do coeficiente de atrito tanto para o alumínio quanto para o titânio com faixa de temperatura distinta para cada um dos materiais. Após a realização da calibração por meio das curvas foram realizados os ensaios práticos de compressão do anel e do tubo cônico, também foram realizadas as simulações computacionais dos ensaios do tubo. Estas simulações permitiram a verificação teórica do fluxo de material no interior dos corpos de prova comparando-as com o material obtido em ensaios práticos, comprovando a eficiência dos programas de simulação, visto que a geometria do tubo favorece a comparação entre a simulação e os testes experimentais. Os resultados obtidos tanto nos experimentos teóricos como os práticos, efetuou-se uma comparação com os dados das referências bibliográficas descritas neste trabalho. Em que os dois lubrificantes testados apresentaram desempenho satisfatório, devido à redução do contato interfacial da relação matriz/peça. E o ensaio do tubo cônico mostrou-se viável apenas para determinação a quente do coeficiente de atrito, neste caso o comportamento em ambos os ensaios é similar. / This paper presents a brief overview of the forging process and the results of experimental investigation and computational analysis of ring compression testing and conical tube-upsetting test, both aiming to determine the coefficient of friction in the region of contact between die and bodies-of-evidence for the AA6351 aluminum alloy and titanium Ti6Al4V. Theoretical calibration through curves were performed of the coefficient of friction were performed for both aluminum and titanium with different temperature range for each material. After completion of the calibration curves compression ring and the conical tube practical tests were performed, computer simulations of the tube-upsetting test were also performed. Continue) These simulations allowed to verify the theoretical flow of material within the samples and comparing them with the material obtained in practical tests, proving the efficiency of simulation programs, since the geometry of the tube facilitates the comparison between the simulation and testing experiments. The results in both theoretical and practical experiments, were a compared with the data from the references described herein. Two oils tested showed a satisfactory performance due to the reduced interfacial contact relationship die/workpiece. And the tube-upsetting test was feasible only to determine the hot coefficient of friction, in this case the behavior in both tests is similar.

O presente trabalho apresenta um breve apanhado do processo de forjamento, resultados da investigação experimental e da análise computacional acerca do teste de compressão do anel e ensaio do tubo cônico, ambos visando a determinação do coeficiente de atrito existente na região de contato entre as matrizes e os corpos-de-prova, para as ligas de alumínio AA6351 e de titânio Ti6Al4V. Foram realizadas curvas teóricas de calibração do coeficiente de atrito tanto para o alumínio quanto para o titânio com faixa de temperatura distinta para cada um dos materiais. Após a realização da calibração por meio das curvas foram realizados os ensaios práticos de compressão do anel e do tubo cônico, também foram realizadas as simulações computacionais dos ensaios do tubo. Estas simulações permitiram a verificação teórica do fluxo de material no interior dos corpos de prova comparando-as com o material obtido em ensaios práticos, comprovando a eficiência dos programas de simulação, visto que a geometria do tubo favorece a comparação entre a simulação e os testes experimentais. Os resultados obtidos tanto nos experimentos teóricos como os práticos, efetuou-se uma comparação com os dados das referências bibliográficas descritas neste trabalho. Em que os dois lubrificantes testados apresentaram desempenho satisfatório, devido à redução do contato interfacial da relação matriz/peça. E o ensaio do tubo cônico mostrou-se viável apenas para determinação a quente do coeficiente de atrito, neste caso o comportamento em ambos os ensaios é similar. / This paper presents a brief overview of the forging process and the results of experimental investigation and computational analysis of ring compression testing and conical tube-upsetting test, both aiming to determine the coefficient of friction in the region of contact between die and bodies-of-evidence for the AA6351 aluminum alloy and titanium Ti6Al4V. Theoretical calibration through curves were performed of the coefficient of friction were performed for both aluminum and titanium with different temperature range for each material. After completion of the calibration curves compression ring and the conical tube practical tests were performed, computer simulations of the tube-upsetting test were also performed. Continue) These simulations allowed to verify the theoretical flow of material within the samples and comparing them with the material obtained in practical tests, proving the efficiency of simulation programs, since the geometry of the tube facilitates the comparison between the simulation and testing experiments. The results in both theoretical and practical experiments, were a compared with the data from the references described herein. Two oils tested showed a satisfactory performance due to the reduced interfacial contact relationship die/workpiece. And the tube-upsetting test was feasible only to determine the hot coefficient of friction, in this case the behavior in both tests is similar.

O presente trabalho apresenta um breve apanhado do processo de forjamento, resultados da investigação experimental e da análise computacional acerca do teste de compressão do anel e ensaio do tubo cônico, ambos visando a determinação do coeficiente de atrito existente na região de contato entre as matrizes e os corpos-de-prova, para as ligas de alumínio AA6351 e de titânio Ti6Al4V. Foram realizadas curvas teóricas de calibração do coeficiente de atrito tanto para o alumínio quanto para o titânio com faixa de temperatura distinta para cada um dos materiais. Após a realização da calibração por meio das curvas foram realizados os ensaios práticos de compressão do anel e do tubo cônico, também foram realizadas as simulações computacionais dos ensaios do tubo. Estas simulações permitiram a verificação teórica do fluxo de material no interior dos corpos de prova comparando-as com o material obtido em ensaios práticos, comprovando a eficiência dos programas de simulação, visto que a geometria do tubo favorece a comparação entre a simulação e os testes experimentais. Os resultados obtidos tanto nos experimentos teóricos como os práticos, efetuou-se uma comparação com os dados das referências bibliográficas descritas neste trabalho. Em que os dois lubrificantes testados apresentaram desempenho satisfatório, devido à redução do contato interfacial da relação matriz/peça. E o ensaio do tubo cônico mostrou-se viável apenas para determinação a quente do coeficiente de atrito, neste caso o comportamento em ambos os ensaios é similar. / This paper presents a brief overview of the forging process and the results of experimental investigation and computational analysis of ring compression testing and conical tube-upsetting test, both aiming to determine the coefficient of friction in the region of contact between die and bodies-of-evidence for the AA6351 aluminum alloy and titanium Ti6Al4V. Theoretical calibration through curves were performed of the coefficient of friction were performed for both aluminum and titanium with different temperature range for each material. After completion of the calibration curves compression ring and the conical tube practical tests were performed, computer simulations of the tube-upsetting test were also performed. Continue) These simulations allowed to verify the theoretical flow of material within the samples and comparing them with the material obtained in practical tests, proving the efficiency of simulation programs, since the geometry of the tube facilitates the comparison between the simulation and testing experiments. The results in both theoretical and practical experiments, were a compared with the data from the references described herein. Two oils tested showed a satisfactory performance due to the reduced interfacial contact relationship die/workpiece. And the tube-upsetting test was feasible only to determine the hot coefficient of friction, in this case the behavior in both tests is similar.

This thesis discusses how to test the mechanical properties of openlattice truss structures and hybrids being a tube containing a latticetruss structure. By properties we mean strength, stiffness, thermalconductivity and so forth.Mechanical testing was done on two different structures to betterunderstand how the load-bearing properties change when these structuresare subjected to tensile, compressive and bending forces. The structuresinvestigated were Diamond and Octagon built at 45° and 90°. Acousticemission was also used to evaluate and analyze the different behaviour ofthe structures. The test results were used to produce design criteria forproperties in different cell structures manufactured of Hastelloy X™. Amap with design criteria containing stiffness and weight per cubiccentimetre was produced for parts that would be subjected to compressiveforces.

No description available.

The failure behavior of composite laminates is modeled numerically using the Generalized Layerwise Plate Theory (GLPT) of Reddy and a progressive failure algorithm. The Layerwise Theory of Reddy assumes a piecewise continuous displacement field through the thickness of the laminate and therefore has the ability to capture the interlaminar stress fields near the free edges and cut outs more accurately. The progressive failure algorithm is based on the assumption that the material behaves like a stable progressively fracturing solid. A three-dimensional stiffness reduction scheme is developed and implemented to study progressive failures in composite laminates. The effect of various parameters such as out-of-plane material properties, boundary conditions, and stiffness reduction methods on the failure stresses and strains of a quasi-isotropic composite laminate with free edges subjected to tensile loading is studied. The ultimate stresses and strains predicted by the Generalized Layerwise Plate Theory (GLPT) and the more widely used First Order Shear Deformation Theory (FSDT) are compared with experimental results. The predictions of the GLPT are found to be in good agreement with the experimental results both qualitatively and quantitatively, while the predictions of FSDT are found to be different from experimental results both qualitatively and quantitatively. The predictive ability of various phenomenological failure criteria is evaluated with reference to the experimental results available in the literature. The effect of geometry of the test specimen and the displacement boundary conditions at the grips on the ultimate stresses and strains of a composite laminate under compressive loading is studied. The ultimate stresses and strains are found to be quite sensitive to the geometry of the test specimen and the displacement boundary conditions at the grips. The degree of sensitivity is observed to depend strongly on the lamination sequence. The predictions of the progressive failure algorithm are in agreement with the experimental trends. Finally, the effect of geometric nonlinearity on the first-ply and ultimate failure loads of a composite laminate subjected to bending load is studied. The geometric nonlinearity is taken in to account in the von Kármán sense. It is demonstrated that the nonlinear failure loads are quite different from the linear failure loads, depending on the lamination sequence, boundary conditions, and span-to-depth ratio of the test specimen. Further, it is shown that the First order Shear Deformation Theory (FSDT) and the Generalized Layerwise Plate Theory (GLPT) predict qualitatively different results. / Ph. D.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Nesta dissertação de Mestrado do programa de Pós-Graduação em Ciência e Tecnologia dos Materiais é apresentado um estudo para a caracterização do concreto reforçado com fibras de polipropileno e de aço pela análise das imagens de microtomografia computadorizada por transmissão de raios X (μCT). Foram produzidos corpos de prova de concreto para determinar a sua resistência mecânica à compressão. As imagens foram obtidas no sistema Skyscan, modelo 1174, reconstruídas e analisadas. Foi possível observar na análise das imagens a estrutura da fibra de aço dispersa na matriz do concreto e quantificá-las pelo programa de análise de imagens Ctan e perceber um ganho na resistência mecânica em relação ao concreto sem fibras. Não foi feito a quantificação das amostras de fibras de polipropileno dispersas na matriz de concreto, mas foi observada a presença de aglomerados dessa fibra que resultaram na perda da resistência mecânica em relação ao concreto sem fibras. / In this dissertation Masters Program Graduate in Science and Technology of Materials is presented a study for characterization of concrete reinforced with polypropylene fibers and steel by image analysis of computed microtomography X ray transmission (μCT). Concrete samples were produced to determine their mechanical resistance to compression. The images were obtained in the SkyScan model 1174, reconstructed and analyzed. It was possible, in image analysis, to observe the structure of steel fiber dispersed in the concrete matrix and quantify them by image analysis program Ctan and observed a gain in strength compared to concrete fiber less. The quantification was not did to samples of polypropylene fibers dispersed in the matrix of concrete, but we observed the presence of clusters fibers resulting in the loss of mechanical strength compared to concrete fiber less.

Carbon nanotube (CNT) forests are an important class of nanomaterials with many potential applications due to their unique properties such as mechanical compliance, thermal and electrical conductance, etc. Their deformation and failure in compression loading is critical in any application involving contact because the deformation changes the nature of the contact and thus impacts the transfer of load, heat, and charge carriers across the interface. The micro- and nano-structure of the CNT forest can vary along their height and from sample to sample due to different growth parameters. The morphology of CNTs and their interaction contribute to their mechanical behavior with change of load distribution in the CNT forest. However, the relationship is complicated due to involvement of many factors such as density, orientation, and entanglement of CNTs. None of these effects, however, are well understood. This dissertation aims to advance the knowledge of the structure-property relation in CNT forests and find methodologies for tuning their mechanical behavior. The mechanical behavior of CNT forests grown with different methodologies is studied. Furthermore, the effects of coating and wetting of CNT forests are investigated as methods to tailor the degree of interaction between CNTs. In situ micro-indentation of uncoated CNT forests with distinct growth-induced structures are performed to elucidate the effects of change of morphology along the height of CNT forests on their deformation mechanism. CNT aerial density and tortuosity are found to dictate the location of incipient deformation along height of CNT forests. Macro-compression testing of uncoated CNT forests reveals mechanical failure of CNT forests by delamination at the CNT-growth substrate. Tensile loading of CNT roots due to post-buckling bending of CNTs is proposed to be the cause of this failure and simple bending theory is shown to estimate the failure load to be on the same order of magnitude as experimental measurements. Furthermore, delamination is observed to occur in the in situ micro-indentation of CNT forests coated with aluminum on the top surface, which demonstrates the role of the mechanical constraints within the CNT forest in the occurrence of delamination at the CNT-substrate interface. In addition, this dissertation explores the mechanical behavior of CNT forests coated conformally (from top to bottom) with alumina by atomic layer deposition. In situ micro-indentation testing demonstrates that the deformation mechanism of CNT forests does not change with a thin coating (2 nm) but does change with a sufficiently thick coating (10 nm) that causes fracturing of the hybrid nanotubes. Ex situ flat punch and Berkovich indentations reveal an increase in stiffness of the CNT forests that are in range with those predicted by compression and bending theories. An increase in the recoverability of the CNTs is also detected. Finally, solvent infiltration is proposed as a method of decreasing stiffness of CNT forests and changing the deformation mechanism from local to global deformations (i.e., buckling in the entire height). Presence of solvents between CNTs decreases the van der Waals forces between them and produces CNT forests with lower stiffness. The results demonstrate the effect of interaction between CNTs on the mechanical behavior. This dissertation reveals important information on the mechanical behavior of CNT forests as it relates to CNT morphology and tube-to-tube interactions. In addition, it provides a framework for future systematic experimental and theoretical investigations of the structure-property relationship in CNT forests, as well as a framework for tuning the properties of CNT forests for diverse applications.