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A thermodynamic framework was presented for the development of powderconstitutive models. The process of powder compaction through Equal ChannelAngular Extrusion (ECAE) at room temperature was modeled using the finiteelement analysis package ABAQUS. The simulation setup was used to conduct aparametric study involving varying the process parameters of ECAE, aimed ataiding the process design.Two powder compaction models, the Gurson model and the Duva and Crowmodel, were used to test their efficacy in modeling this process. Thethermodynamic framework was applied to derive the constitutive equations of theDuva and Crow model. Modeling parameters like friction coefficients, interactionconditions were determined by comparing the simulations for solid billet and anempty can with actual experimental runs for loads, shear angle and workpiece geometry. The simulations using the two powder constitutive models showed nosignificant difference in the stress in the powder during the extrusion.The results obtained from the 3-D simulations were also compared toexperiments conducted to compact copper powder with a size distribution of 10mto 45m. It was found through experiments that the powder does not fullyconsolidate near the outer corner of the workpiece after the first ECAE pass and theresults from the simulations were used to rationalize this phenomenon.Modifications made to the process by applying a back pressure during thesimulations resulted in a uniformly compacted powder region.Further, simulations were carried out by varying the process parameters likethe crosshead velocity, the friction coefficient between the walls of the die and thecan, can dimensions and material, shape of the can cross section etc and the effectof each of these parameters was quantified by doing a sensitivity analysis.

A thermodynamic framework was presented for the development of powderconstitutive models. The process of powder compaction through Equal ChannelAngular Extrusion (ECAE) at room temperature was modeled using the finiteelement analysis package ABAQUS. The simulation setup was used to conduct aparametric study involving varying the process parameters of ECAE, aimed ataiding the process design.Two powder compaction models, the Gurson model and the Duva and Crowmodel, were used to test their efficacy in modeling this process. Thethermodynamic framework was applied to derive the constitutive equations of theDuva and Crow model. Modeling parameters like friction coefficients, interactionconditions were determined by comparing the simulations for solid billet and anempty can with actual experimental runs for loads, shear angle and workpiece geometry. The simulations using the two powder constitutive models showed nosignificant difference in the stress in the powder during the extrusion.The results obtained from the 3-D simulations were also compared toexperiments conducted to compact copper powder with a size distribution of 10mto 45m. It was found through experiments that the powder does not fullyconsolidate near the outer corner of the workpiece after the first ECAE pass and theresults from the simulations were used to rationalize this phenomenon.Modifications made to the process by applying a back pressure during thesimulations resulted in a uniformly compacted powder region.Further, simulations were carried out by varying the process parameters likethe crosshead velocity, the friction coefficient between the walls of the die and thecan, can dimensions and material, shape of the can cross section etc and the effectof each of these parameters was quantified by doing a sensitivity analysis.

The objective of this research was to design aluminum powder metallurgy (PM) alloys and processing strategies that yielded sintered products with thermal properties that rivaled those of the cast and wrought aluminum alloys traditionally employed in heat sink manufacture. Research has emphasized PM alloys within the Al-Mg-Sn system. In one sub-theme of research the general processing response of each PM alloy was investigated through a combination of sintering trials, sintered density measurements, and microstructural assessments. In a second, the thermal properties of sintered products were studied. Thermal conductivity was first determined using a calculated approach through discrete measurements of specific heat capacity, thermal diffusivity and density and subsequently verified using a transient plane source technique on larger specimens. Experimental PM alloys achieved >99% theoretical density and exhibited thermal conductivity that ranged from 179 Wm-1K-1 to 225 Wm-1K-1. Thermal performance was largely dominated by the amount of magnesium present within the aluminum grains and in turn, bulk alloy chemistry. Data confirmed that the novel PM alloys were highly competitive with even the most advanced heat sink materials such as wrought 6063 and 6061. Two methods of thermal analysis were employed in order to determine the thermal conductivity of each alloy. This first consisted of individual analysis of the specific heat capacity (Cp), thermal diffusivity (?) and density (?) as a function of temperature for each alloy. The thermal conductivity (K) was subsequently determined through the relationship: K=C_p ??. The second means of thermal analysis was a direct thermal conductivity measure using a transient plane source (TPS). The thermal diffusivity and density of samples were both found to decrease with temperature in a linear fashion. Conversely, the specific heat capacity was found to increase with temperature. The only measured thermal property that appeared to be influenced by the alloy chemistry was the thermal diffusivity (and subsequently the calculated thermal conductivity). Both means of thermal analysis showed high thermal conductivity in alloys with low concentrations of magnesium, demonstrating the significance of having alloying elements in solid solution with aluminum. Overall, several alloys were developed using a press and sinter approach that produced higher levels of thermal conductivity than conventional aluminum heat sink materials. The highest thermal conductivity was achieved by alloy Al-0.6Mg-1.5Sn with a calculated value of 225.4 Wm-1K-1. This novel aluminum PM alloy was found to exceed both wrought 6061 and 6063 (195 and 217 Wm-1K-1 respectively). Furthermore, PM alloy Al-0.6Mg-1.5Sn was found to have a significant advantage over die-cast A390 (142 Wm-1K-1).

In metal powder compaction, density non-uniformity due to friction can be a source of flaws. Currently in industry, uniform density distribution is achieved by the optimization of punch motions through trial and error. This method is both costly and time consuming. Over the last decade, the finite element (FE) method has received significant attention as an alternative to the trial and error method; however, there is still lack of an accurate and robust material model for the simulation of metal powder compaction. In this study, Cam-clay and Drucker-Prager cap (DPC) material models were implemented into the commercial FE software ABAQUS/Explicit using the user-subroutine VUMAT. The Cam-clay model was shown to be appropriate for simple geometries. The DPC model is a pressure-dependent, non-smooth, multi-yield surface material model with a high curvature in the cap yield surface. This high curvature tends to result in instability issues; a sub-increment technique was implemented to address this instability problem. The DPC model also shows instability problems at the intersection of the yield surfaces; this problem was solved using the corner region in DPC material models for soils. The computational efficiency of the DPC material model was improved using a novel technique to solve the constitutive equations. In a case study it was shown that the numerical technique leads to a 30% decrease in computational cost, while degrading the accuracy of the analysis by only 0.4%. The forward Euler method was shown to be accurate in the integration of the constitutive equations using an error control scheme. Experimental tests were conducted where cylindrical-shaped parts were compacted from Distaloy AE iron based powder to a final density of 7.0 g/cm3. To measure local density, metallography and image processing was used. The FE results were compared to experimental results and it was shown that the FE analysis predicted local relative density within 2% of the actual experimental density. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2010-09-23 12:15:27.371

Concrete, as primary building material, is widely used in most construction project. For this reason, large amounts of concrete waste were generated from construction and demolition. One way to reuse concrete waste is to use it as backfill material for landfilling and road bases. While the demand for backfill material is decreasing as the basic infrastructure construction gradually completes. Another way to reuse concrete waste is to grind it and use it as aggregate in casting new concrete. However, the reuse as aggregate for casting concrete requires large amount of cement. It is unsustainable because the production of cement causes significant amounts of carbon dioxide emission. How to deal with the concrete waste in a sustainable way is presently an urgent issue. Powder compaction is a new approach to completely recycle concrete waste in an environmentally friendly way. This new method was studied in the Sakai lab of the Institute of Industrial Science, The University of Tokyo. The process consists of crushing and milling concrete waste into a fine powder, filling the powder into moulds and compacting it under high pressure. By this process concrete waste powder can be turned into a solid concrete with mechanical properties so that it has potentials to be used again as a building material. Data from previous studies show that the compacted concrete waste can reach strength for construction but the required compaction pressure is quite high. Wood flour can be added in compaction for improving tensile strength and reducing compaction pressure. Lignin is a wood substance that melts under high temperature, fills gaps and improves bonding between particles. Cellulose from the wood substance functions as fibres which improves tensile strength. Wood waste from production of timber building materials, furniture and other wooden products also forms a larger quantities. Recycling of concrete waste with wooden waste through heating compaction is a potentially sustainable method. This Master thesis presents research on the effect from different production conditions on the bending strength of recycled concrete waste with wood waste through heating compaction. The condition factors studied were compaction duration, compaction pressure, concrete proportion, mixture percentage, temperature and particle size of wood flour. To enhance the water resistance of this recycled product, different water resistance treatments were discussed theoretically. The independence of production condition factors was analysed using a statistic method. Results indicated that within a certain range, an increase in compaction duration, compaction pressure, the percentage of wood waste and temperature improves the bending strength of the recycled products. Using smaller particle size of wood flour cannot improve compaction but contribute to give higher bending strength. The mechanical properties of these recycled products suggest application as non-bearing building material, such as decoration tiles and bricks for partition walls. The application as a structural material is expected in the future as improvement treatments are discovered.

Confined particulate systems, particularly powder compacts, are widely used in various applications in industries such as pharmaceutical, automotive, agriculture, and energy production. Due to their extensive applications, characterization of these materials is of great importance for optimizing their performance and manufacturing processes. Modeling approaches capable of capturing the heterogeneity and complex behavior are effective at predicting the macroscopic behavior of granular systems. These modeling approaches utilize information about the microstructure evolution of these materials during compaction processes at the mesoscale (particle-scale). Using these types of modeling depend on accurate contact formulation between inter-particle contacts. The challenge comes in formulating these contact models that accurately predict force-area-deformation relationships. In this work, contact laws are presented for elastic-ideally plastic particles and plastic particles with power-law hardening under unconfined (simple compression) and confined (die and hydrostatic compaction) compression. First, material properties for a set of finite element simulations are obtained using space-filling design. The finite element simulations are used for verification and building an analytical framework of the contact radius and contact pressure which allows for efficient determination of the contact force. Semi-mechanistic contact laws are built for elastic-ideally plastic spherical particles that depend on material properties and loading configuration. Then, rigid-plastic assumption is used to modify the contact laws to consider power-law hardening effects while keeping loading configuration dependency. Finally, after building and verifying the contact laws, they are used to estimate hardening properties, contact radius evolution, and stress response of micro-crystalline cellulose particles under different loading configurations using experimental data from simple compression.

Este trabalho apresenta um estudo dos processos de prensagem e sinterização do politetrafluoretileno (PTFE) com o objetivo principal de investigar a influência dos parâmetros desses processos na microestrutura e nas propriedades mecânicas do material após sinterização. O PTFE faz parte do grupo dos termoplásticos, mas assim como outros polímeros de alto peso molecular, apresenta elevada viscosidade no estado fundido que impede sua utilização em moldagem por injeção, e seu processamento é realizado por compactação a frio do pó polimérico seguida de sinterização. No processo de sinterização é aplicado um tratamento térmico acima da temperatura de fusão do material que é responsável por grandes deformações anisotrópicas que, por sua vez, são dependentes do histórico de carregamentos induzidos na fase de compactação. Com o objetivo de desenvolver modelos de comportamento termomecânicos para realizar simulações computacionais dessas etapas de fabricação, ensaios experimentais foram realizados para se investigar os diferentes mecanismos de evolução microestrutural e de deformações nas etapas de compactação e sinterização. O estudo experimental do processo de compactação compreendeu a realização de ensaios de compactação uniaxial (oedométrico), de compactação hidrostática em prensa isostática e ensaios triaxiais verdadeiros em um dispositivo original acoplado numa prensa triaxial com seis atuadores eletrohidráulicos. Através dos resultados obtidos dos ensaios de compactação foi possível identificar os parâmetros do modelo de Drucker-Prager/cap, disponível na biblioteca de leis de comportamento do programa de cálculo pelo método dos elementos finitos ABAQUSTM, que permitiu de simular numericamente alguns casos simples. O estudo experimental do processo de sinterização foi realizado com o auxílio de ensaios de termogravimetria (TGA), calorimetria exploratória diferencial (DSC) e ensaios de dilatometria em corpos-de-prova isótropos e anisótropos com diferentes índices de vazios. Através dos resultados obtidos destes ensaios foi possível identificar que a deformação global de sinterização é composta por uma deformação térmica reversível, uma deformação devido à mudança de fase cristalina em fase amorfa -ou vice-versa-, uma deformação devido ao fechamento dos vazios e uma deformação de recuperação. Este estudo foi realizado em dois tipos de materiais, sendo o PTFE puro e o PTFE reforçado com 5wt% de EkonolTM e 5wt% de fibras de carbono, respectivamente comercializados pelos nomes de TeflonTM 6407 e TeflonTM 6507. / The main objective of this work is to study the influence the process parameters on the microstructure and the mechanical properties of components manufactured by compaction at room temperature and sintering of polytetrafluorethylene (PTFE). Similary to other High Molecular Weight Polymers and although it belongs to the group of thermoplastic polymers, since it cannot be processed in the melt state because its very high viscosity, PTFE, is powder processed -that consists in sintering compacted powder-. Sintering corresponds to a heat treatment up to temperatures higher than the melting temprature, inducing finite deformations that are generally anistropic and dependent on the mechanical loading the material has been submitted to during the pre-compaction at room temperature. In order to develop thermo-mechanical constitutive equations that could be used during predictive numerical simulations of the whole process, different tests have been performed to study the different mechanisms that are responsible for microstructural evolutions and deformations during compaction and sintering. The experimental study of the compaction has been performed via uniaxial (oedometric) compaction tests, hydrostatic compaction tests that were made with an isostatic hydraulic press and triaxial tests that were made with and original device installed on an electrohydraulic testing machine six actuators. A \"Drucker-Prager/cap\" type elasto-plastic model -as available in the constitutiveequations library of ABAQUSTM industrial finite element software- has been identified from the results of these tests, so that a few simple cases have been numerically simulated. The experimental study of the sintering process has been performed via Thermo-Gravimetric Analyses (TGA), Differential Scanning Calorimetric analyses (DSC) and dilatometry tests that were performed on isotropic or anisotropic specimens with different values of the porosity From the results of these tests it has been possible to decompose the sintering deformation into different mechanisms, viz. a reversible thermal expansion, a strain that is linked to the transition from the crystalline phase to the amorphous phase -or vice versa-, a pore closure strain and a recovery strain. This study has been performed on a powder made of pure PTFE and a powder of PTFE filed with 5wt% EkonolTM and 5wt% of carbon fibres, respectively available as TeflonTM 6407 and TeflonTM 6507.

Este trabalho apresenta um estudo dos processos de prensagem e sinterização do politetrafluoretileno (PTFE) com o objetivo principal de investigar a influência dos parâmetros desses processos na microestrutura e nas propriedades mecânicas do material após sinterização. O PTFE faz parte do grupo dos termoplásticos, mas assim como outros polímeros de alto peso molecular, apresenta elevada viscosidade no estado fundido que impede sua utilização em moldagem por injeção, e seu processamento é realizado por compactação a frio do pó polimérico seguida de sinterização. No processo de sinterização é aplicado um tratamento térmico acima da temperatura de fusão do material que é responsável por grandes deformações anisotrópicas que, por sua vez, são dependentes do histórico de carregamentos induzidos na fase de compactação. Com o objetivo de desenvolver modelos de comportamento termomecânicos para realizar simulações computacionais dessas etapas de fabricação, ensaios experimentais foram realizados para se investigar os diferentes mecanismos de evolução microestrutural e de deformações nas etapas de compactação e sinterização. O estudo experimental do processo de compactação compreendeu a realização de ensaios de compactação uniaxial (oedométrico), de compactação hidrostática em prensa isostática e ensaios triaxiais verdadeiros em um dispositivo original acoplado numa prensa triaxial com seis atuadores eletrohidráulicos. Através dos resultados obtidos dos ensaios de compactação foi possível identificar os parâmetros do modelo de Drucker-Prager/cap, disponível na biblioteca de leis de comportamento do programa de cálculo pelo método dos elementos finitos ABAQUSTM, que permitiu de simular numericamente alguns casos simples. O estudo experimental do processo de sinterização foi realizado com o auxílio de ensaios de termogravimetria (TGA), calorimetria exploratória diferencial (DSC) e ensaios de dilatometria em corpos-de-prova isótropos e anisótropos com diferentes índices de vazios. Através dos resultados obtidos destes ensaios foi possível identificar que a deformação global de sinterização é composta por uma deformação térmica reversível, uma deformação devido à mudança de fase cristalina em fase amorfa -ou vice-versa-, uma deformação devido ao fechamento dos vazios e uma deformação de recuperação. Este estudo foi realizado em dois tipos de materiais, sendo o PTFE puro e o PTFE reforçado com 5wt% de EkonolTM e 5wt% de fibras de carbono, respectivamente comercializados pelos nomes de TeflonTM 6407 e TeflonTM 6507. / The main objective of this work is to study the influence the process parameters on the microstructure and the mechanical properties of components manufactured by compaction at room temperature and sintering of polytetrafluorethylene (PTFE). Similary to other High Molecular Weight Polymers and although it belongs to the group of thermoplastic polymers, since it cannot be processed in the melt state because its very high viscosity, PTFE, is powder processed -that consists in sintering compacted powder-. Sintering corresponds to a heat treatment up to temperatures higher than the melting temprature, inducing finite deformations that are generally anistropic and dependent on the mechanical loading the material has been submitted to during the pre-compaction at room temperature. In order to develop thermo-mechanical constitutive equations that could be used during predictive numerical simulations of the whole process, different tests have been performed to study the different mechanisms that are responsible for microstructural evolutions and deformations during compaction and sintering. The experimental study of the compaction has been performed via uniaxial (oedometric) compaction tests, hydrostatic compaction tests that were made with an isostatic hydraulic press and triaxial tests that were made with and original device installed on an electrohydraulic testing machine six actuators. A \"Drucker-Prager/cap\" type elasto-plastic model -as available in the constitutiveequations library of ABAQUSTM industrial finite element software- has been identified from the results of these tests, so that a few simple cases have been numerically simulated. The experimental study of the sintering process has been performed via Thermo-Gravimetric Analyses (TGA), Differential Scanning Calorimetric analyses (DSC) and dilatometry tests that were performed on isotropic or anisotropic specimens with different values of the porosity From the results of these tests it has been possible to decompose the sintering deformation into different mechanisms, viz. a reversible thermal expansion, a strain that is linked to the transition from the crystalline phase to the amorphous phase -or vice versa-, a pore closure strain and a recovery strain. This study has been performed on a powder made of pure PTFE and a powder of PTFE filed with 5wt% EkonolTM and 5wt% of carbon fibres, respectively available as TeflonTM 6407 and TeflonTM 6507.