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Zinc xanthates are active catalysts in stereoregular polymerization of propylene oxide and markedly more stable than that of known classical stereoregular catalysts. But steric control of zinc xanthates is weaker. To find more effective catalyst systems the isopropyl xanthates of Cu, Pb, Ni, Fe, Al and Sn are investigated and only copper (Cu(isoPr)Xt) and tin (Sn(isoPr)Xt) isopropyl xanthates were appeared to be active, but Cu(isoPr)Xt yielded only low molecular weight product. Therefore Sn(isoPr)Xt system was investigated in detail in polymerization of propylene oxide (PO). Polymerization of PO with this catalyst produced two contrasting polymers / high molar mass, crystalline (K-polymer) and low molar mass (D-polymer). Formation of double bonds in D-polymer was thought to be due to as an anionic process. Polymerization reactions were studied by changing polymerization conditions and reacting catalyst with predetermined amount of water. It&amp / #8217 / s found that Sn(isoPr)Xt have considerably low efficiency than that of Zn(isoPr)Xt catalyst. The yield linearly increases by increasing catalyst concentration. The propagation is competed by termination or transfer process hence overall activation energy is negative. Some mechanistic features of this system was also discussed. The catalytical activity of carbamates in this field has also been reported, without any information about catalytical efficiency and stereoregularity of the process. Therefore zinc diethyl dithiocarbamate was also studied and found as an active catalyst in stereoregular polymerization but it showed weaker efficiency in the PO polymerization than that of Zn(isoPr)Xt catalyst (about 12 times weaker).

In the current context of oil resources rarefaction, the development of biobased polymers is of major importance. The present work focused on the development of a biobased amorphous polyphthalamide, based on furan-2,5-dicarboxylic acid. The first part of the study was devoted to the development of a molecular modelling protocol that could calculate the glass transition temperature of polyphthalamides with accuracy. In order to do this, model polyphthalamides based on isophthalic, terephthalic acid and hexamethylene diamine were synthesized and characterized as well as simulated. By comparison between simulated and measured Tg, the protocol was validated. In a second part of the study, this protocol was applied to FDCA based polyphthalamides. These PPA were also synthesized. It was found that the PA 6-F undertakes a decarboxylation, preventing it from reaching high a molar mass. It was also found that the mechanical and thermal properties decrease as the amount of FDCA in the copolymers increases.

A sinterização a laser (SL), uma das tecnologias de manufatura aditiva (MA), se mostra de grande interesse devido a uma série de características, mas, principalmente, devido a sua capacidade de processar uma ampla gama de materiais em pó, a qual amplia possibilidades de pesquisa e desenvolvimento no campo do Design. Neste trabalho, sob o prisma da MA, tem-se por objetivo realizar a sinterização a laser em um equipamento de gravação e corte a laser convencional, sem pré-aquecimento do material. No desenvolvimento do estudo, foi utilizado um equipamento galvanométrico a laser para a realização de experimentos de sinterização de poliestireno em pó (PS 200). Os ensaios de caracterização desse material polimérico amorfo, constataram o diâmetro médio dos grãos de 54,3 μm em formato irregular. Para viabilizar o processo proposto, investigaram-se os parâmetros de processo para a SL, valendo-se de um dispositivo de controle da altura da mesa de trabalho. A melhor amostra (geometria circular) foi construída com potência 20 W, velocidade de varredura de 200 m/min e distância entre linhas de varredura do feixe laser de 0,1 mm. Esse último parâmetro, é relacionado ao diâmetro do foco do feixe laser, o qual foi estimado pelos ensaios em 0,3 mm. Com isso, foi calculada a densidade de energia transferida para o material, conhecida como Número de Andrew (An), em 0,06 J/mm² Análises visuais, macroscópicas e microscópicas, antes e depois da sinterização de uma camada (2D) e de camadas empilhadas (3D), além de sua digitalização tridimensional, foram realizadas. As amostras apresentaram deformação no plano x-y (elipticidade), no eixo z (empenamento) e grande porosidade. Nos ensaios de empilhamento de camadas foi determinada, para os parâmetros utilizados, a espessura de camada de 0,15 mm. Posteriormente, foi construído um modelo 3D com 100 camadas, o qual apresentou um acabamento liso na maior parte de sua lateral, porém, foram observadas estrias verticais ao longo da sua altura, as quais foram consideradas como característica do processo (devido à inércia dos espelhos galvanométricos). Por fim, esses parâmetros foram validados em um ensaio valendo-se de uma forma orgânica (face humana) em escala 1:4. O fator crítico foi o empenamento, o qual prejudica a distribuição de novas camadas de pó, mas pôde ser contornado com espessuras de camada de alturas superiores a esse empenamento. Assim, considera-se que para a viabilização prática do processo de sinterização proposto, em equipamentos de corte e gravação a laser convencionais, torna-se importante o desenvolvimento de um dispositivo de distribuição de pó automatizado, o qual permitiria a construção de modelos 3D de maior tamanho e complexidade. / Laser sintering (SL), one of the additive manufacturing (MA) technologies, is of great interest due to a number of characteristics, but mainly due to its ability to process a wide range of powder materials, which offers possibilities for research and development in the Design’s field. In this work, under the prism of the MA, the goal is to perform laser sintering in a conventional laser engraving and cutting equipment, without preheating the material. In the development of the study, a galvanometric laser equipment was used to perform powder polystyrene (PS 200) sintering experiments. The characterization tests of this amorphous polymer material showed the average grain diameter of 54.3 μm in irregular shape. In order to make the proposed process feasible, the process parameters for the SL were investigated, using a device to control the height of the workbench. The best sample (circular geometry) was built with 20 W power, laser scan speed of 200 m/min and distance between scanned lines of 0.1 mm. This last parameter is related to the diameter of the laser beam waist, which was estimated by the tests in 0.3 mm Thus, the energy density transferred to the material, known as Andrew's Number (An), was calculated at 0.06 J/mm². Macroscopic and microscopic visual analysis, before and after the sintering of a two-dimensional layer (2D) and of stacked layers (3D), in addition to its 3D scanning, were performed. The samples displayed deformation in the x-y plane (ellipticity), at the z-axis (warpage) and high porosity. In the layer stacking tests, the layer thickness of 0.15 mm was determined for the parameters used. Next, a 3D model with 100 layers was sintered, which presented a smooth finish in most of its lateral, however, vertical streaks were observed along its height, which were considered as characteristic of the process (due to the inertia of the galvanometric mirrors). Finally, these parameters were validated in an assay using an organic form (human face) in a 1: 4 scale. The critical factor was the warpage, which impairs the distribution of new layers of powder, but could be worked around with layer thicknesses of heights higher than this warpage. Thus, it is considered that for the practical feasibility of the proposed sintering process in conventional laser cutting and engraving machine, it is important to develop an automated powder distribution device, which would allow the construction of greater size and complexity 3D models.

A sinterização a laser (SL), uma das tecnologias de manufatura aditiva (MA), se mostra de grande interesse devido a uma série de características, mas, principalmente, devido a sua capacidade de processar uma ampla gama de materiais em pó, a qual amplia possibilidades de pesquisa e desenvolvimento no campo do Design. Neste trabalho, sob o prisma da MA, tem-se por objetivo realizar a sinterização a laser em um equipamento de gravação e corte a laser convencional, sem pré-aquecimento do material. No desenvolvimento do estudo, foi utilizado um equipamento galvanométrico a laser para a realização de experimentos de sinterização de poliestireno em pó (PS 200). Os ensaios de caracterização desse material polimérico amorfo, constataram o diâmetro médio dos grãos de 54,3 μm em formato irregular. Para viabilizar o processo proposto, investigaram-se os parâmetros de processo para a SL, valendo-se de um dispositivo de controle da altura da mesa de trabalho. A melhor amostra (geometria circular) foi construída com potência 20 W, velocidade de varredura de 200 m/min e distância entre linhas de varredura do feixe laser de 0,1 mm. Esse último parâmetro, é relacionado ao diâmetro do foco do feixe laser, o qual foi estimado pelos ensaios em 0,3 mm. Com isso, foi calculada a densidade de energia transferida para o material, conhecida como Número de Andrew (An), em 0,06 J/mm² Análises visuais, macroscópicas e microscópicas, antes e depois da sinterização de uma camada (2D) e de camadas empilhadas (3D), além de sua digitalização tridimensional, foram realizadas. As amostras apresentaram deformação no plano x-y (elipticidade), no eixo z (empenamento) e grande porosidade. Nos ensaios de empilhamento de camadas foi determinada, para os parâmetros utilizados, a espessura de camada de 0,15 mm. Posteriormente, foi construído um modelo 3D com 100 camadas, o qual apresentou um acabamento liso na maior parte de sua lateral, porém, foram observadas estrias verticais ao longo da sua altura, as quais foram consideradas como característica do processo (devido à inércia dos espelhos galvanométricos). Por fim, esses parâmetros foram validados em um ensaio valendo-se de uma forma orgânica (face humana) em escala 1:4. O fator crítico foi o empenamento, o qual prejudica a distribuição de novas camadas de pó, mas pôde ser contornado com espessuras de camada de alturas superiores a esse empenamento. Assim, considera-se que para a viabilização prática do processo de sinterização proposto, em equipamentos de corte e gravação a laser convencionais, torna-se importante o desenvolvimento de um dispositivo de distribuição de pó automatizado, o qual permitiria a construção de modelos 3D de maior tamanho e complexidade. / Laser sintering (SL), one of the additive manufacturing (MA) technologies, is of great interest due to a number of characteristics, but mainly due to its ability to process a wide range of powder materials, which offers possibilities for research and development in the Design’s field. In this work, under the prism of the MA, the goal is to perform laser sintering in a conventional laser engraving and cutting equipment, without preheating the material. In the development of the study, a galvanometric laser equipment was used to perform powder polystyrene (PS 200) sintering experiments. The characterization tests of this amorphous polymer material showed the average grain diameter of 54.3 μm in irregular shape. In order to make the proposed process feasible, the process parameters for the SL were investigated, using a device to control the height of the workbench. The best sample (circular geometry) was built with 20 W power, laser scan speed of 200 m/min and distance between scanned lines of 0.1 mm. This last parameter is related to the diameter of the laser beam waist, which was estimated by the tests in 0.3 mm Thus, the energy density transferred to the material, known as Andrew's Number (An), was calculated at 0.06 J/mm². Macroscopic and microscopic visual analysis, before and after the sintering of a two-dimensional layer (2D) and of stacked layers (3D), in addition to its 3D scanning, were performed. The samples displayed deformation in the x-y plane (ellipticity), at the z-axis (warpage) and high porosity. In the layer stacking tests, the layer thickness of 0.15 mm was determined for the parameters used. Next, a 3D model with 100 layers was sintered, which presented a smooth finish in most of its lateral, however, vertical streaks were observed along its height, which were considered as characteristic of the process (due to the inertia of the galvanometric mirrors). Finally, these parameters were validated in an assay using an organic form (human face) in a 1: 4 scale. The critical factor was the warpage, which impairs the distribution of new layers of powder, but could be worked around with layer thicknesses of heights higher than this warpage. Thus, it is considered that for the practical feasibility of the proposed sintering process in conventional laser cutting and engraving machine, it is important to develop an automated powder distribution device, which would allow the construction of greater size and complexity 3D models.

A sinterização a laser (SL), uma das tecnologias de manufatura aditiva (MA), se mostra de grande interesse devido a uma série de características, mas, principalmente, devido a sua capacidade de processar uma ampla gama de materiais em pó, a qual amplia possibilidades de pesquisa e desenvolvimento no campo do Design. Neste trabalho, sob o prisma da MA, tem-se por objetivo realizar a sinterização a laser em um equipamento de gravação e corte a laser convencional, sem pré-aquecimento do material. No desenvolvimento do estudo, foi utilizado um equipamento galvanométrico a laser para a realização de experimentos de sinterização de poliestireno em pó (PS 200). Os ensaios de caracterização desse material polimérico amorfo, constataram o diâmetro médio dos grãos de 54,3 μm em formato irregular. Para viabilizar o processo proposto, investigaram-se os parâmetros de processo para a SL, valendo-se de um dispositivo de controle da altura da mesa de trabalho. A melhor amostra (geometria circular) foi construída com potência 20 W, velocidade de varredura de 200 m/min e distância entre linhas de varredura do feixe laser de 0,1 mm. Esse último parâmetro, é relacionado ao diâmetro do foco do feixe laser, o qual foi estimado pelos ensaios em 0,3 mm. Com isso, foi calculada a densidade de energia transferida para o material, conhecida como Número de Andrew (An), em 0,06 J/mm² Análises visuais, macroscópicas e microscópicas, antes e depois da sinterização de uma camada (2D) e de camadas empilhadas (3D), além de sua digitalização tridimensional, foram realizadas. As amostras apresentaram deformação no plano x-y (elipticidade), no eixo z (empenamento) e grande porosidade. Nos ensaios de empilhamento de camadas foi determinada, para os parâmetros utilizados, a espessura de camada de 0,15 mm. Posteriormente, foi construído um modelo 3D com 100 camadas, o qual apresentou um acabamento liso na maior parte de sua lateral, porém, foram observadas estrias verticais ao longo da sua altura, as quais foram consideradas como característica do processo (devido à inércia dos espelhos galvanométricos). Por fim, esses parâmetros foram validados em um ensaio valendo-se de uma forma orgânica (face humana) em escala 1:4. O fator crítico foi o empenamento, o qual prejudica a distribuição de novas camadas de pó, mas pôde ser contornado com espessuras de camada de alturas superiores a esse empenamento. Assim, considera-se que para a viabilização prática do processo de sinterização proposto, em equipamentos de corte e gravação a laser convencionais, torna-se importante o desenvolvimento de um dispositivo de distribuição de pó automatizado, o qual permitiria a construção de modelos 3D de maior tamanho e complexidade. / Laser sintering (SL), one of the additive manufacturing (MA) technologies, is of great interest due to a number of characteristics, but mainly due to its ability to process a wide range of powder materials, which offers possibilities for research and development in the Design’s field. In this work, under the prism of the MA, the goal is to perform laser sintering in a conventional laser engraving and cutting equipment, without preheating the material. In the development of the study, a galvanometric laser equipment was used to perform powder polystyrene (PS 200) sintering experiments. The characterization tests of this amorphous polymer material showed the average grain diameter of 54.3 μm in irregular shape. In order to make the proposed process feasible, the process parameters for the SL were investigated, using a device to control the height of the workbench. The best sample (circular geometry) was built with 20 W power, laser scan speed of 200 m/min and distance between scanned lines of 0.1 mm. This last parameter is related to the diameter of the laser beam waist, which was estimated by the tests in 0.3 mm Thus, the energy density transferred to the material, known as Andrew's Number (An), was calculated at 0.06 J/mm². Macroscopic and microscopic visual analysis, before and after the sintering of a two-dimensional layer (2D) and of stacked layers (3D), in addition to its 3D scanning, were performed. The samples displayed deformation in the x-y plane (ellipticity), at the z-axis (warpage) and high porosity. In the layer stacking tests, the layer thickness of 0.15 mm was determined for the parameters used. Next, a 3D model with 100 layers was sintered, which presented a smooth finish in most of its lateral, however, vertical streaks were observed along its height, which were considered as characteristic of the process (due to the inertia of the galvanometric mirrors). Finally, these parameters were validated in an assay using an organic form (human face) in a 1: 4 scale. The critical factor was the warpage, which impairs the distribution of new layers of powder, but could be worked around with layer thicknesses of heights higher than this warpage. Thus, it is considered that for the practical feasibility of the proposed sintering process in conventional laser cutting and engraving machine, it is important to develop an automated powder distribution device, which would allow the construction of greater size and complexity 3D models.

No / In tensile stretching, many polymers undergo strain localization. The geometrical form of the localization can take the form of either a shear band or an approximately symmetric neck. We present a constitutive model of the early stages of deformation that predicts which form the localization will take. The model consists of an Eyring process acting with a Gaussian network that is implemented numerically. A Levy-Mises flow rule associated with the Eyring process has a tendency to produce shear bands. A relatively stiff Gaussian network is used in a model of polycarbonate that ensures that most of the strain is taken up by the Eyring process, resulting in shear banding. In contrast, a relatively soft Gaussian network is used in a model of polyethylene, which takes up the greater part of the strain, resulting in a neck. The predictions are compared with experiments. For polyethylene, a two-Eyring-process model is introduced for better accuracy.

Indentation hardness, H, has been widely used to characterize the mechanical properties of materials for more than a century because of the following advantages of this technique; (1) it requires small sample and (2) the test is non destructive in nature. Recent technological advances helped in the development of instrumented indentation machines which can record the load, P, vs. displacement, h, data continuously during indentation with excellent load and displacement resolutions. From these, H and the elastic modulus, E, of the indented material can be obtained on the basis of the ‘contact area’ of the indentation at the maximum load. The estimation of true contact area becomes difficult during ‘pile-up’ and ‘sink-in’, commonly observed phenomena while indentation of a low and high strain hardened materials. In order for the better understanding of these phenomena it is important to understand the plastic flow distribution under indenters. It is also important for the prediction of elastic-plastic properties from the P-h data. Recently, there have been considerable theoretical and simulation efforts on this front with a combination of dimensional analysis and finite element simulations. One of the important input parameter for the dimensional analysis is the ‘representative strain’ under the indenter, which is a strong function of the indenter geometry. However there is no comprehensive understanding of the representative strain under the indenter despite several studies till date. One objective of the present thesis is to conduct an experimental analysis of the plastic flow during the sharp indentation. The plastic zone size and shape under conical indenters of different apex angles in a pure and annealed copper were examined by employing the subsurface indentation technique to generate the hardness map. From these isostrain contours are constructed joining the data having similar strain values. The following are the key observations. (1) The plastic strain contours are elliptical in nature, spreading more along the direction of the indenter axis than the lateral direction. (2) The magnitude of the plastic strain in the contact region decreases with increasing the indenter angle. (3) The strain decay in the indentation direction follow a power-law relation with the distance. The estimated representative strains under the indenters, computed as the volume average strain within the elastic-plastic boundary, decreases with increasing indenter angle. We also performed finite element simulations to generate plastic flow distribution under the indenter geometries and compared with the experimental results. The results suggest that the experimental and computed average strains match well. However, the plastic strain contours do not, suggesting that further detailed understanding of the elasto-plastic deformation underneath the sharp indenter is essential before reliable estimates of plastic properties from the P-h curves can be made routinely. The second objective of this thesis is to understand plastic flow in amorphous alloys. It is now well established that plastic deformation in metallic glasses is pressure sensitive, owing to the fundamentally different mechanisms vis-à-vis the dislocation mediated plastic flow in crystalline metals alloys. Early work has shown that the pressure sensitivity of amorphous alloys gets reflected as high constraint factor, C (hardness to yield stress ratio), which sometimes exceed 3.0. In this thesis, we study the temperature dependence of pressure sensitive plastic flow in bulk metallic glasses (BMGs) using C as the proxy for the pressure sensitivity. Experiments on three different BMGs show that C increases with temperature hence the pressure sensitivity. In addition we have carried out finite element simulations to generate P-h curves for different levels of pressure sensitivities and match them with the experimental curves that are obtained at different temperatures. Simulations predict that higher pressure sensitivity index values are required to match the experimental curves at high temperatures confirming that the pressure sensitivity increases with increasing temperature. The fundamental mechanisms responsible for the increase in pressure sensitivity are discussed in detail. Finally we pose a question, is the increase in pressure sensitivity with temperature is common to other amorphous materials such as strong amorphous polymers? In order to answer this question we have chosen PMMA, a strong amorphous polymer. In this study also we have taken C as a proxy to index the pressure sensitivity. Indentation stress-strain curves are constructed at different temperature using spherical indentation experiments. The C values corresponding to different temperatures are determined and plotted as a function of temperature. It is found that C increases with temperature implying that the pressure sensitivity of amorphous polymers also increases with temperature. The micro-mechanisms responsible for the increase in pressure sensitivity are sought.

Dans le contexte actuel de raréfaction des ressources fossiles, le développement des polymères biosourcés est d'une grande importance. Le travail de cette thèse consiste donc en la synthèse et le développement d'un polyphtalamide amorphe à base d'acide furan-2,5-oique. Dans un premier temps, un protocole de modélisation moléculaire permettant de calculer la Tg de polyphthalamides a été développé. Pour cela, des PPA modèles (basés sur un mélange d'acides isophtaliques et téréphtaliques ainsi que l'hexaméthylène diamine) ont été synthétisés et caractérisés. En comparant les Tg obtenues par modélisation et par mesure en DSC, le protocole de modélisation a été validé. Dans un deuxième temps, ce protocole a été appliqué à des PPA à base de FDCA. Ces polymères ont également été synthétisés et caractérisés. Il en ressort que le PA 6-F subit une importante décarboxylation durant sa synthèse, l’empêchant d'atteindre une masse molaire importante. Il a aussi été montré que l'ajout de FDCA dans des copolyphthalamides diminuait leurs propriétés thermiques et mécaniques. / In the current context of oil resources rarefaction, the development of biobased polymers is of major importance. The present work focused on the development of a biobased amorphous polyphthalamide, based on furan-2,5-dicarboxylic acid. The first part of the study was devoted to the development of a molecular modelling protocol that could calculate the glass transition temperature of polyphthalamides with accuracy. In order to do this, model polyphthalamides based on isophthalic, terephthalic acid and hexamethylene diamine were synthesized and characterized as well as simulated. By comparison between simulated and measured Tg, the protocol was validated. In a second part of the study, this protocol was applied to FDCA based polyphthalamides. These PPA were also synthesized. It was found that the PA 6-F undertakes a decarboxylation, preventing it from reaching high a molar mass. It was also found that the mechanical and thermal properties decrease as the amount of FDCA in the copolymers increases.

Le sujet concerne l’influence des effets tridimensionnelles sur les champs de déformation et de contrainte au voisinage d’une éprouvette chargée en mode I. La loi de comportement caractéristique des polymères amorphes avec un seuil d’écoulement viscoplastique suivi d’un adoucissement et d’un durcissement à mesure que la déformation augmente est prise en compte. La loi est implantée dans une UMAT abaqus. Les champs au voisinage de l’entaille sont analysés et les résultats 3D comparés à ceux correspondant à un calcul 2D sous l’hypothèse de déformation plane. L’influence de l’épaisseur de l’échantillon est étudiée et nous montrons qu’au-delà d’un rapport épaisseur t sur rayon d’entaille rt, t/rt>20, les champs de déformation plastique sont qualitativement similaires entre les calculs 3D et 2D. En revanche, nous montrons que la répartition des contraintes et notamment celle de la contrainte moyenne est sur-estimée avec un calcul 2D en comparaison à une simulation 3D. Nous prenons en compte par la suite la rupture par craquelage, modélisée avec un modèle cohésif. Une étude paramétrique est menée afin de définir une procédure d’identification des paramètres caractéristiques du modèle cohésif. Par ailleurs les simulations montrent qu’au-delà d’un rapport t/rt supérieur à 20, une ténacité minimum peut être estimée : ceci constitue un résultat important pour la détermination expérimentale de la ténacité des polymères ductiles. / We investigate 3D effect of crack tip palsticity and the influence of the thickness on 3D glassy polymer fracture. The characteristuc constitutive law with a viscoplastic yield stress followed by softening and progressive hardening is accoutne for and implemented in a UMAt routine, in abaqus. The crack tip fields are investigated and 2D plasne strain versus 3D calculations compared. Qualitatively, the palstic distribution are comparableas soon as the ratio thickness over crack tip radius is larger than 20. However, the 2D calculations over estimate the stress distribution compared to the 3D cases. We have accounted for failure by crazing that is described with a cohesive models. A parametric study sheds light on the methodology to use for the calibration of the cohesive parameters. The simulations show that for a ratio thickness over craci tip radius larger than 20, a minimum tuoghness can be observed. This results has implication on the definition of a thickness larger enough experimentally.