Laser Sintering (LS) is a powder based Additive Manufacturing (AM) technology capable of producing near-net shape objects from 3D data. The benefits of LS include almost unlimited design freedom and reduced material waste, however the number of commercially available materials are limited, with materials traditionally being optimised for the process using a trial and error method and material development being led by previous research into polyamide (PA). There is a desire for greater material choice in LS, particularly high performance polymers. The EOSINT P800 by AM systems manufacturer EOS GmbH is the first commercially available high temperature laser sintering (HT-LS) system capable of working high performance polymers; a PolyEtherKetone (PEK) known by the trade name HP3 PEK is the first material offered by EOS for use with the system. This research project undertakes to characterise the EOSINT P800 and HP3 PEK material with different thermal histories. Experimental work focusses on establishing material properties such as size and shape, crystallinity and decomposition. Characterisation of coalescence behaviour and comparison with theoretical models for viscous sintering is presented as a less experimentally intensive method of understanding how a material will behave during the LS process. A map of temperatures inside the powder bed in the EOSINT P800 is created for the first time and compared with output from on-board temperature sensors in the system, demonstrating the thermal distribution within the bed during building, and explaining differences between as-received and used powder. The results demonstrate that material and process characterisation methods are useful for understanding how and why a high temperature laser sintering material behaves the way it does. The behaviour of HP3 PEK observed during experimental work indicates that guidelines based on LS of PA are too restrictive as indicators of suitability for LS and newer systematic approaches are potentially better suited for qualification of HT-LS polymers. The novel method for mapping thermal distribution inside the LS system documented here shows the limitations of current hardware to effectively process high performance polymers. Overall, the finding of this research project is that understanding of material and process cannot be considered in isolation but combined have the potential to reduce the amount of trial and error required during qualification of new materials and increase the range and variety of polymers available for LS and HT-LS.

A simulação numérica de componentes estmturais necessita de dados do material que são obtidos por ensaios mecânicos. Materiais não-lineares, como termoplásticos, podem apresentar em ensaios de tração estricção quando submetidos à deformações firútas. Este fenômeno normalmente ainda está associado a campos de deformações heterogêneos que possuem uma cinemática particular, se propagando ao longo do corpo. A formação e propagação da estricção podem mascarar o real comportamento mecârúco do material quando obtido por um ensaio de tração, levando o processo de caracterização da curva tensão-deformação real do material a um procedimento não-trivial. Através de um ensaio de tração de um termoplástico, dados experimentais de força e do campo de deslocamentos da região de estricção, obtido através de métodos ópticos, são utilizados em um procedimento numérico-experimental de otimização para a deternúnação dos parâmetros (FEMU) de alguns modelos constitutivos capazes de representar a tendência do comportamento de termoplásticos. De modo a estudar a capacidade representativa da resposta mecânica do ensaio, um modelo constitutivo multi linear e um modelo constitutivo variacional, são estudados. Uma função objetivo conveniente que utiliza dados experimentais e numéricos é usada para considerar a cinemática da estricção, responsável pela mudança geométrica que diferencia as respostas nonúnais e reais da curva tensão-deformação. Por meio dos resultados obtidos neste trabalho verificou-se que a caracterização dos modelos constitutivos utilizando somente a resposta de força, não garante uma caracterização constitutiva adequada, sendo necessária a resposta de deslocamento para garantir a representação da cinemática da região de estricção. / Numerical simulation of structural components requires material data obtained from mechanical testing. Nonlinear materials, like thermoplastics, submitted to tensile testing presents necking undergoing finite strain. This phenomenon is still typically associated to heterogeneous strain fields which possess a particular kinematic, propagating through the body. Necking and colddrawing may mask the actual mechanical behavior measured by a tensile testing machine, turning the real stress-strain curve characterization process into a non-trivial procedure. Through a thermoplastic tensile testing, force experimental data and displacement experimental data from the necking region, obtained by optical methods, are used in a numerical-experimental optimization procedure in order to determine the constitutive parameters (FEMU) from some constitutive models which are able to represent the thermoplastic behavior tendency. In order to study the representative capacity of the mechanical testing response, a multilinear constitutive model and a variational constitutive model, are studied. A suitable objective function which uses experimental and numerical data is used to consider the necking kinematics, responsible for geometric change that distinguishes the nominal and real responses of the stress-strain curve. Through the obtained results, it can be seen that the model parameters determination using, in addition to force, the displacement field in the objective function is necessary to represent the kinematic behavior in the necking region.

Orientador: Edson Cocchieri Botelho / Coorientadora: Mirabel Cerqueira Rezende / Banca: Michelle Leali Costa / Banca: Luis Rogério de Oliveira Hein / Banca: Geraldo Maurício Cândido / Banca: Antônio Carlos Ancelotti Júnior / Resumo: O grau de cristalinidade de termoplásticos semicristalinos desempenha um papel importante na determinação das propriedades finais de materiais compósitos estruturais, por exemplo: tenacidade e rigidez, e de suas resistências às intempéries climáticas. O principal objetivo deste trabalho é estudar a influência do grau de cristalinidade em compósitos de FC/PEEK e FC/PPS, processados por moldagem por compressão a quente com três diferentes taxas de resfriamento. Neste estudo, a morfologia e as propriedades térmicas e mecânicas dos laminados processados foram analisadas e comparadas. Assim como, as suas resistências à umidade, salinidade e radiação ultravioleta. Os resultados apresentaram um aumento na resistência mecânica dos compósitos processados com menores taxas de resfriamento. Evidências de melhora na interface fibra/matriz e nucleação de cristalitos na superfície da fibra também foram identificadas. Os compósitos com maior grau de cristalinidade apresentaram maior resistência à umidade e à salinidade. No entanto, aqueles com menor grau de cristalinidade apresentaram maior resistência aos efeitos da radiação ultravioleta / Abstract: The crystallization degree of semi-crystalline thermoplastics plays an important role in determining the final properties of structural composite materials, e.g. toughness and stiffness, and their weather resistance. The main purpose of this work is to study different induced crystallinity degrees in CF/PEEK and CF/PPS composites processed by hot compression molding at three different cooling rates. In this study, the morphology, thermal and mechanical properties of the processed laminates were investigated and compared. As well as their resistance to humididy, salinity and ultraviolet radiation. The results showed an increase in mechanical strength for the composites processed with lower cooling rates. Evidences of fiber/matrix interface improvement and crystallites nucleation on the fiber surface were also identified. The composites with higher crystalline degree showed to be more resistant to humidity and salinity. However, those with lower crystalline degree were more resistant to the effects of the ultraviolet radiation / Doutor

<p>In later years polymer replication techniques have become a frequently employed fabrication method for microfluidic and micro-optical devices. This thesis describes applications and further developments of microstructures replicated in polymer materials. </p><p>A novel method for homogenous amplified single-molecule detection utilizing a microfluidic readout format is presented. The method enables enumeration of single biomolecules by transforming specific molecular recognition events at nanometer dimensions to micrometer-sized DNA macromolecules. This transformation process is mediated by target specific padlock probe ligation, followed by rolling circle amplification (RCA) resulting in the creation of one rolling circle product (RCP) for each recognized target. Throughout this transformation the discrete nature of the molecular population is preserved. By hybridizing a fluorescence-labeled DNA detection oligonucleotide to each repeated sequence of the RCP, a confined cluster of fluorophores is generated, which makes optical detection and quantification possible. Spectral multiplexing is also possible since the spectral profile of each RCP can be analyzed separately. The microfluidic data acquisition process is characterized in detail and conditions that allow for quantification limited only by Poisson sampling statistics is established. The molecular characteristics of RCPs in solution are also investigated.</p><p>Furthermore a novel thermoplastic microfluidic platform is described. The platform allows for observation of the microchannels using high magnification optics and also offers the possibility of on-chip cell culture and the integration of mechanical actuators.</p><p>A novel fabrication process for the integration of polymer micro-optical elements on silicon is presented. The process is used for fabrication of a micro-optical system consisting of a laser and a movable microlens making beam steering possible. Such a micro-scanning system could potentially be used for miniaturized biochemical analysis.</p>

In later years polymer replication techniques have become a frequently employed fabrication method for microfluidic and micro-optical devices. This thesis describes applications and further developments of microstructures replicated in polymer materials. A novel method for homogenous amplified single-molecule detection utilizing a microfluidic readout format is presented. The method enables enumeration of single biomolecules by transforming specific molecular recognition events at nanometer dimensions to micrometer-sized DNA macromolecules. This transformation process is mediated by target specific padlock probe ligation, followed by rolling circle amplification (RCA) resulting in the creation of one rolling circle product (RCP) for each recognized target. Throughout this transformation the discrete nature of the molecular population is preserved. By hybridizing a fluorescence-labeled DNA detection oligonucleotide to each repeated sequence of the RCP, a confined cluster of fluorophores is generated, which makes optical detection and quantification possible. Spectral multiplexing is also possible since the spectral profile of each RCP can be analyzed separately. The microfluidic data acquisition process is characterized in detail and conditions that allow for quantification limited only by Poisson sampling statistics is established. The molecular characteristics of RCPs in solution are also investigated. Furthermore a novel thermoplastic microfluidic platform is described. The platform allows for observation of the microchannels using high magnification optics and also offers the possibility of on-chip cell culture and the integration of mechanical actuators. A novel fabrication process for the integration of polymer micro-optical elements on silicon is presented. The process is used for fabrication of a micro-optical system consisting of a laser and a movable microlens making beam steering possible. Such a micro-scanning system could potentially be used for miniaturized biochemical analysis.

No description available.

This thesis presents a comprehensive study on the thermal modelling aspects of laser transmission welding of thermoplastics (LTW), a technology for joining of plastic parts. In the LTW technique, a laser beam passes through the laser-transmitting part and is absorbed within a thin layer in the laser-absorbing part. The heat generated at the interface of the two parts melts a thin layer of the plastic and, with applying appropriate clamping pressure, joining occurs. Transient thermal models for the LTW process were developed and solved by the finite element method (FEM). Input to the models included temperature-dependent thermo-physical properties that were adopted from well-known sources, material suppliers, or obtained by conducting experiments. In addition, experimental and theoretical studies were conducted to estimate the optical properties of the materials such as the absorption coefficient of the laser-absorbing part and light scattering by the laser-transmitting part. Lap-joint geometry was modelled for semi crystalline (polyamide - PA6) and amorphous (polycarbonate - PC) materials. The thermal models addressed the heating and cooling stages in a laser welding process with a stationary and moving laser beam. An automated ANSYS® script and MATLAB® codes made it possible to input a three-dimensional (3D), time-varying volumetric heat-generation term to model the absorption of a moving diode-laser beam. The result was a 3D time-transient, model of the laser transmission welding process implemented in the ANSYS® FEM environment. In the thermal imaging experiments, a stationary or moving laser beam was located in the proximity of the side surface of the two parts being joined in a lap-joint configuration. The side surface was then observed by the thermal imaging camera. For the case of the stationary beam, the laser was activated for 10 s while operating at a low power setting. For the case of the moving beam, the beam was translated parallel to the surface observed by the camera. The temperature distribution of a lap joint geometry exposed to a stationary and moving diode-laser beam, obtained from 3D thermal modelling was then compared with the thermal imaging observations. The predicted temperature distribution on the surface of the laser-absorbing part observed by the thermal camera agreed within 3C with that of the experimental results. Predicted temperatures on the laser-transmitting part surface were generally higher by 15C to 20C. This was attributed to absorption coefficient being set too high in the model for this part. Thermal imaging of the soot-coated laser-transmitting part surface indicated that significantly more scattering and less absorption takes place in this part than originally assumed. For the moving laser beam, good model match with the experiments (peak temperatures predicted within 1C) was obtained for some of the process conditions modelled for PA6 parts. In addition, a novel methodology was developed to extract the scattered laser beam power distribution from the thermal imaging observations of the moving laser beam. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2008-10-08 10:39:30.952

One-, two- and three-dimensional transient heat transfer finite element models are developed to simulate the resistance welding process of pre-consolidated unidirectional AS4 carbon fibre reinforced Poly-ether-ether-ketone (APC-2/AS4) laminates with a metal mesh heating element, in a lap-shear configuration. The finite element models are used to investigate the effect of process and material parameters on the thermal behaviour of the coupon size welds, yielding to a better understanding of the process. The 1-D model determines: (a) the importance of including the latent heat of PEEK, and (b) the through-thickness temperature gradient away from the edges, for different tooling plate materials. The 2-D model simulates the cross-section of the process, considering the convective and irradiative heat losses from the areas of the heating element exposed to air. The 3-D model includes the heat conduction along the length of the laminates, to fully depict the thermal behaviour of the welds. Finally, the models are compared with experimental data.

Thesis (M.Tech.: Mechanical Engineering)-Dept. of Mechanical Engineering, Durban University of Technology, 2007 xiii, 101 leaves / Polymer nanocomposites may be defined as structures that are formed by infusing layered-silicate clay into a thermosetting orthermoplastic polymer matrix. The nanocomposites are normally particle-filled polymers for which at least one dimension of the dispersed particles is in nanoscale. These clay-polymer nanocomposites have thus attracted great interest in industry and academia due to their exhibition of remarkable enhancements in material properties when compared to the virgin polymer or conventional micro and macro-composites. The present work describes the synthesis, mechanical properties and morphology of nano-phased polypropylene structures. The structures were manufactured by melt- blending low weight percentages of montmorillonite (MMT) nanoclays (0.5, 1, 2, 3, 5 wt. %) and polypropylene (PP) thermoplastic. Both virgin and infused polypropylene structures were then subjected to quasi-static tensile tests, flexural tests, micro-hardness tests, impact testing, compression testing, fracture toughness analysis, dynamic mechanical analysis, tribological testing. Scanning electron microscopy studies were then conducted to analyse the fracture surfaces of pristine PP and PP nanocomposite. X-ray diffraction studies were performed on closite 15A clay and polypropylene composites containing 0.5, 1, 2, 3 and 5 wt. % closite 15A nanoclay to confirm the formation of nanocomposites on the addition of organo clays. Transmission electron miscopy studies were then performed on the PP nanocomposites to determine the formation of intercalated, exfoliated or agglomerated nanoclay structures. Analysis of test data show that the mechanical properties increase with an increase in nanoclay loading up to a threshold of 2 wt. %, thereafter the material properties degrade. At low weight nanoclay loadings the enhancement of properties is attributed to the lower percolation points created by the high aspect ratio nanoclays. The increase in properties may also be attributed to the formation of intercalated and exfoliated nanocomposite structures formed at these loadings of clay. At higher weight loading, degradation in mechanical properties may be attributed to the formation of agglomerated clay tactoids. Results of XRD, transmission electron microscopy studies and scanning electron microscopy studies of the fractured surface of tensile specimens verify these hypotheses.

The UK Health & Safety Executive are responsible for advising on ways to ensure the safety of employees within the workplace. One of the main areas of concern is the potential problem of unwanted fire, and it has been identified that within the area of large-scale storage in warehouses, there is an uncertainty posed by large quantities of thermoplastic. Some forms of thermoplastic exhibit melt-flow behaviour when heated, and a large vertical array exposed to a fire may melt and ignite forming a pool fire in addition to a wall fire. This project is largely experimental, and aimed at quantifying the effect of a growing pool fire fuelled by a melting wall on overall fire growth rate. The pool fire has been found to increase melting and burning rates, producing a much faster growing fire. It has also been found that - 80% of flowing and burning material will enter a potential pool fire, with only 20 - 25% of total mass loss actually burning from the original array. During the project 400+ small-scale tests and several medium-scale experiments have been undertaken at both Edinburgh University and the HSE's Fire & Explosion Laboratory, Buxton. The experiments have confirmed the main parameters governing pool fire development are molecular weight degradation rate and mechanism, which control flow viscosity. There have also been investigations into other influences, the most significant of which was found to be flooring substrate. These parameters then form the basis of a simple 1-D model. A semi-infinite heat transfer approximation is used to determine temperature profile through a thermoplastic exposed to its own flame flux, with extrapolated temperature dependant material properties. The derived profile is then inserted into a gravity driven flow model, to produce estimates of flow rate and quantity for plastics undergoing either random or end chain scission thermal degradation processes. The model identifies property data which are required to permit its use as a hazard assessment tool.