Laser sintering (LS) is an additive manufacturing process which uses laser surface heating to induce consolidation of powdered materials. This work investigates some of the process-structure-property relationships for LS of viscoelastic polymers. A one-dimensional closed-form analytical solution for heating of a semi-infinite body, with a convective boundary condition, by a moving surface heat flux was developed. This solution approximates the shape of the Gaussian energy distribution of the laser beam more accurately than previous solutions in the literature. A sintering model that combines the effects of viscoelastic deformation driven by attractive surface forces and viscous flow driven by curvature-based forces was developed. The powder-bed temperature was approximated using the thermal model developed herein. The effect of the enthalpy of melting for semi-crystalline polymers was accounted for using a temperature recovery approach. Time-temperature superposition was used to account for the temperature dependence of the tensile creep compliance. The results of the combined-mechanism sintering model will be compared to the classic Mackenzie-Shuttleworth sintering model. A lab-scale LS unit was constructed to fabricate test specimens for model validation and to test the applicability of materials to LS. In this work, sintering four materials, polycarbonate (PC) and three molecular weights of polyethylene-oxide (PEO) was predicted using the aforementioned thermal and sintering models. Samples were fabricated using the lab-scale LS unit and the sintered microstructures were investigated using scanning electron microscopy. The rheologic, thermal and physical properties of the materials were characterized using standard methods and the relevant properties were used in the models. The choice of an amorphous polymer, PC, and a semi-crystalline polymer, PEO, affords comparison of the effects of the two material forms on contact growth during LS. The three molecular weights of PEO exhibit significantly different tensile creep compliances, however, the thermal and physical properties are essentially the same, and therefore the effect of molecular weight and subsequently the rheologic characteristics on contact growth during LS will be investigated. The effects of particle size, laser power, and bed temperature were also investigated. / Ph. D.

The content of the diploma thesis deals with the study of the flexibility and adhesion of cement tile adhesives, which are modified by a polymeric additive. The effects of the quantity and type of redispersible polymer powder used on the properties of the adhesives, in particular on the deformability of adhesives and their adhesion, are monitored. The theoretical part summarizes the basic data concerning classification of the ceramic tiles, information about the adhesives, the processed part concerning the polymer modified adhesives and the effects of the polymeric additives on their properties. The practical part deals primarily with the study of adhesion and flexibility of polymer modified adhesives and study of microstructure of selected materials.

This diploma thesis deals with study of the moisture-transport properties of polymer cementious ETICS mortars at different doses of redispersible polymer powder. The effect of aerate on these screeds is also investigated. The thesis also evaluates the effect of use various external surface treatments due to risk of cumulate moisture in the perimeter structure.

The objective of this research was to develop high performing polymer modified calcium sulfoaluminate (CSA) cement materials for use in applications requiring superior adhesion characteristics. Little information is available describing interactions of CSA cement containing minor phase tri-calcium aluminate (C3A) with commonly used admixtures. Given the scarcity of information, a basic approach for developing cementitious materials was followed. The basic approach consisted of four tasks: cement design, admixture design, polymer design and testing developed materials. The iterative, time consuming process is necessary for understanding the influence of specific constituent components on overall system behavior. Results from the cement design task suggest calcium sulfate type influences microstructural characteristics and strength development for materials based upon the experimental CSA cement. Results from the admixture design task suggest lithium carbonate and tartaric acid are effective accelerating and retarding admixtures for hydration reactions including reactants yeelimite, calcium sulfate and water. Results from the polymer design task suggest vinyl acetate / ethylene (VAE) dispersible polymer powders (DPP) are compatible with systems containing the experimental CSA cement and other commonly used admixtures. Additionally, results from the polymer design task highlight a method for specifying the ductile behavior of materials containing the experimental CSA cement as majority hydraulic binding agent. Finally, results from the testing of developed materials task suggests adhesion performance for materials containing the experimental CSA cement can be influenced by adjusting the ratio of polymer to hydraulic binding agent in material formulations. Polymer modified CSA cement mortars demonstrated bond strength resulting in substrate failure when cast over porous concrete substrates. Developed mortars demonstrated consistent bonding performance when applied to non-porous substrate materials, metal and glass. Select polymer modified mortars displayed adhesion bond performance such that the glass substrate materials fractured during pull off testing.

La fabrication additive est l’un des secteurs industriels les plus en développent ces dernières années. L’une de ces technologies de fabrication les plus prometteuses est la fusion laser sélective (SLS), et relève d’un intérêt croissant aussi bien industriel qu’académique. Néanmoins, beaucoup de phénomène mis en jeu par ce procédé demeure non encore bien compris, entravant ainsi son développement pour la production de pièces de bonne qualité pour des applications industrielles. L’objectif de cette thèse est de développer un cadre de simulation numérique permettant la simulation du procédé SLS pour des poudres de polymère afin de comprendre les multiples et complexes phénomènes physiques qui se produise lors du frittage laser et d’étudier l’influence des paramètres du procédé sur la qualité du produit final. Contrairement aux approches classiques de modélisation numérique, basées sur la définition de matériaux homogène équivalents pour la résolution des équations de bilan, nous proposons une simulation globale du procédé du frittage laser de poudres, en utilisant la méthode des Eléments Discrets (DEM). Cela consiste en un couplage entre quatre sous-modèles : transferts radiatif dans le milieu granulaire semi-transparent, conduction thermique dans les milieux discrets, coalescence puis densification. Le modèle de transferts par rayonnement concerne l’interaction du faisceau laser avec le lit de poudre. Plusieurs phénomènes sont ainsi pris en compte, notamment la réflexion, la transmission, l’absorption et la réfraction. De plus, une méthode de Monte-Carlo couplée à la méthode du Lancer de rayons est développée afin d’étudier l’influence de la réfraction sur la distribution de l’énergie du laser dans le lit de poudre. Le modèle de conduction dans des milieux discrets décrit la diffusion thermique inter-particules. Finalement, le modèle de frittage décrit les cinétiques de coalescence et de diffusion de l’air dans le polymère et densification du milieu. Cela permet de décrire les cinétiques de fusion des grains, dont l’énergie de surface et la diffusons de l’air sont les deux moteurs principaux. Le couplage entre les différents modèles nous a permis de proposer un modèle numérique global, validé grâce à des comparaisons à des résultats de simulations théoriques et expérimentales, trouvés dans la littérature. Une analyse paramétrique est alors proposée pour la validation du modèle et l’étude du procédé. L’influence de différents paramètres aussi bien du procédé que du matériau sur le champ de température, la densité relative du matériau sa structure, etc , est ainsi investiguée. Les résultats montrent une bonne précision dans la modélisation des différents phénomènes complexes inhérents à ce procédé, et ce travail constitue un potentiel réel pour la modélisation et l’optimisation des procédés de fabrication additive par matériaux granulaires. / Many industrial and academic interests concerning the additive manufacturing processes are developed in the last decades. As one of the most promising technique of additive manufacturing, the Selective Laser Sintering (SLS) has been valued by both industry and academic. However, it remains that several phenomena are still not well understood in order to properly model the process and propose quality improvement of parts made. The goal of this Ph.D. project is to develop a framework of numerical simulation in order to model the SLS process in polymer powder bed, meanwhile understanding multiple physical phenomena occurring during the process and studying the influence of process parameters on the quality of final product. In contrast to traditional approach, based on the equivalent homogeneous material in numerical modeling of partial differential equations derived from conservation laws, we propose a global model to simulate powder-based additive manufacturing by using the Discrete Element method (DEM). It consists in a coupling between four different physical models: radiative heat transfer, discrete heat conduction, sintering and granular dynamics models. Firstly, the submodel of radiative heat transfer concerns the interaction between the laser beam and powder bed. Several phenomena are considered, including the reflection, transmission, absorption and scattering. Besides, a modified Monte Carlo ray-tracing method is developed in order to study the influence of scattering on the distribution of the deposited laser energy inside the powder bed Furthermore, the submodel of discrete heat conduction describes the inter-particles heat diffusion. Moreover, the sintering submodel concerns the phenomena of coalescence and air diffusion. It describes the melting kinetics of grains, driven by surface tension and the release of entrapped gases inside powder bed. Finally, the granular dynamics submodel concerns the motions and contacts between particles when depositing a new layer of powders. The coupling between these submodels leads to propose a global numerical framework, validated by comparing the results to both simulated and experimental ones from literatures. A parametric study is then proposed for model validation and process analysis. The Influence of different material and process parameters on the evolution of temperature, relative density and materials structure and characteristics are investigated. The results exhibit accurate modeling of the complex phenomena occurring during the SLS process, and the work constitute a great potential in modeling and optimization of additive processes.