No description available.

No description available.

No description available.

The overall aim of this work was to relate the molecular structure of injection-moulded PMMA with the levels of residual stress and processing conditions with levels of residual stress for extruded sheet. Experimental work was conducted on an experimental copolymer, supplied by ICI Plc, containing both methyl methacrylate and ethyl acrylate. Injection-moulded samples were manufactured varying in terms of molecular weight and percentage of ethyl acrylate. The influence of roll temperature and line speed during extrusion on levels of residual stresses and orientation were also studied in samples extracted from both the longitudinal and transverse directions of the extruded sheet. Residual stress distributions were calculated using the layer removal technique, birefringence measurements and in extruded samples, initial curvature measurements. Shrinkage measurements were also taken to identify the relative degree of orientation in the materials. Properties such as tensile and flexural modulus, together with tensile strength were measured. Overall, injection mouldings exhibited a parabolic residual stress distribution, with compressive stresses on the surface and tensile stresses in the core. Increasing molecular weight and decreasing levels of ethyl acrylate led to greater residual stresses being present in the material. Extruded material, however, contained tensile stresses on the surface and a less symmetrical distribution overall. The magnitudes of residual stress were lower than found in injection mouldings and lower in the transverse direction of the extruded sheet. Overall, lower roll temperatures and faster line speeds led to increased residual stresses, shown by initial curvature, layer removal and birefringence measurements. However, higher roll temperatures and slower line speeds led to increased orientation in the sheet as shown by shrinkage measurements. Thus, processing conditions during extrusion had opposite effects on residual stresses and orientation.

The first part of the thesis covers the development of a high-end GA, with arguements being made for and against a variety of evolutionary principles adopted in this field, as well as some innovations. A gradient based optimiser is also discussed which is used for comparison purposes thoughout the thesis. The GA is benchmarked against a variety of difficult, highly non-linear functions to ascertain its effectiveness, and then applied to the optimisation of 2D & 3D trusses under static and free vibration conditions. The aim of this is to provide a test-bed of benchmark examples and allow for experimentation of the more innovative features of the GA. Fairly basic sizing optimisation of trusses is first considered, moving on to more involved multi-load case, combined size & shape optimisation problems. After covering various splines typically used for shape definition, a mesh generation preprocessor algorithm, and allocation of size/shape design information for prismatic structures, the benefits of using Fourier series for the solution of simply supported beams is clarified. Extending from this 1D method to 2D curved Mindlin-Reissner finite strips, a variety of static prismatic structural problems are compared against known solutions to verify the formulation. The final chapter in this field reviews and compares the higher precision and rate of convergence of GAs against more traditional SQP based optimisation algorithms when applied to prismatic structures. Subsequently the work has progressed to the simulation of slit dies for the extrusion of polymer sheets. An in-depth investigation of the methodologies used for modelling flow and die deflection are made, including the significance of die body deflection on flowrate. The final section of this thesis considers the optimisation of exit flowrate uniformity employing the coupled flow simulation and deflection analyses mentioned in earlier chapters. Two optimisation methods are employed to determine the best possible exit flow uniformity within the movement capabilities of the choker bar. Three materials with differing shear thinning properties are selected, and simulated under high & low pressure conditions. The effect of shear thinning on the effectiveness of the choker bar optimisation is also discussed.

ABS (arcylonitrile-butadiene-styrene) is one of the most common polymers in electrical and electronic equipment. In this thesis, ABS plastics from computer equipment housings have been investigated to find the effect of reprocessing upon chemical and physical properties. A torque rheometer was used to simulate the recycling process. Two ABS plastics were reprocessed at different temperatures and rotational speeds; the other one was multiply reprocessing for different number of cycles. After reprocessing, degradation levels of the reprocessed materials were investigated by FTIR (Fourier transform infrared spectrometry), GPC (gel permeation chromatography) and DMTA (dynamic mechanical thermal analysis); the change of additives was studied by GC/MS (gas chromatography/mass spectrometry); impact testing and tensile testing of reprocessed materials were carried out, and the fracture surfaces were examined using SEM (scanning electron microscopy). It was found that cross-linking of the rubber phase occurred at high reprocessing temperature. During multiple reprocessing, cross-linking of rubber might be accompanied by a slight increased thermo-oxidative degradation of ABS. Some additives were lost during processing. The impact strength of ABS plastic reduced after reprocessing, particularly at high temperature. During multiple reprocessing, impact strength of ABS plastic reduced continuously. Failure strain reduced after reprocessing. By SEM, the heterogeneity of reprocessed materials and the breakdown of microstructure of ABS polymer could be observed from the fracture surfaces of ‘after reprocessing’ samples. In this study, it was found that defects were possibly an important reason for the reduction of impact strength and failure strain after reprocessing at low temperature; at high reprocessing temperature, the reduction of impact strength was perhaps related to cross-linking of the rubber phase; the lack of adherence along SAN/rubber particles interface, which might be promoted by degradation of rubber, was an important reason for the reduction of impact strength of ABS plastic.

The work reported herein concerns the production and characterisation of ordered microporous and nanoporous polymer films. High speed microphotographic (HSMP) studies of the formation process reveal that near the surface of a suitable polymer solution, vapour condensation produces near monodisperse water droplets which form a close-packed monolayer (or ‘breath figure’. Following solvent evaporation, characterisation of the residual solid form by Atomic Force Microscopy and Scanning Electron Microscopy reveals that its surface has extensive regions of hexagonally close-packed microscopic pores, whose spatial arrangement replicates that of the initial droplet monolayer. Atomic Force Microscopy shows that the surficial pores represent open sections of sub-surficial spheroidal cavities formed by encapsulation of the water droplets within the polymer solution. An interesting feature is the occurrence of nano-scale pores at the film surface and within the walls of the sub-surficial pores. This is the first physical evidence report of such features in porous polymer films produced by a process involving breath-figures. Moreover the work reported herein reveals, for the first time, that the structural template represented by the water droplet array is directly transferred into the resulting solid polymer film and, in doing so, maintains the features present in the water droplet array. This work provides the first direct (i.e. non-circumstantial) association between the droplet template and pore structure in breath figure work. Previous reports of this process have merely been able to report that the pores are not formed in the absence of moisture. The mechanism whereby substantial regions of the water droplet ‘raft’ (or array) are transferred en masse into the rapidly evaporating polymer solution is essentially that envisaged by Srinivasarao <i>et al</i> (2001), and the present work provides the first experimental confirmation of their ideas.

A study into the process of in-mould decoration (IMD) has been undertaken. The properties of the two components of printed IMD film; namely the ink and the film have been studied. The work has focussed on the heat absorption, visual and mechanical properties of printed IMD film and the changes than occur during the forming stage of the process. The films used in IMD possess mechanical properties typical of plastics. Their mechanical properties are tailored by blending polyesters with polycarbonate. The blended films possess a higher natural draw ratio and elongation before fracture and have lower softening temperatures. Infrared heat absorption by IMD film is dependent on the film type, the ink coating and whether the film is heated from the print or non-printed (first) surface. Heat absorption characteristics affect the temperature of the film and therefore its mechanical strength during forming. Several techniques were used to characterise the appearance of IMD films. The methods are based on measuring the reflected or transmitted light; with each having advantages and disadvantages. The films tested have a surface texture that diffuses incident light, giving a matt appearance to second surface print. Upon heating the texture deteriorates in all films and discoloration occurs in blended films. The ink systems used in IMD had different mechanical and optical characteristics. Solvent-based inks become more ductile with heating but residual solvents make them prone to a "pinhole" effect and weaken the film. UV curable inks become more brittle with heating. Finite element simulations of forming processes have been developed, using material models derived from tensile test data. The simulations predict the geometry and strain distribution in a formed part, which differs depending on the forming method, the temperature and the film. This can then be used to predict the visual changes in the formed part.

An application of the finite element method to a class of thermally coupled non-Newtonian viscous incompressible flow problems is attempted in the present work. We implement the reduced integration penalty function method and the balancing dissipation technique in the numerical computations. The results of theoretical numerical analysis for these approximations are briefly summarized and a few possible modifications to improve the numerical performance are suggested. A class of first order hyperbolics related to the deformation of fluid particles are also treated numerically using finite elements with the balancing dissipation. Several numerical examples are included to indicate the applicability of the present numerical solution to the flow and heat transfer in polymer melts.

The present work is concerned with the automated optimization of the design of PVC profile extrusion dies. The aspects of the research are the parameterization techniques, the development of suitable optimization strategies, and the determination of material parameters from experimental studies. Due to the aim of this work, namely to apply automatic optimization techniques to industrially relevant PVC profile dies, the necessary tools have to be developed such, that these are capable of dealing with profile dies with a comparatively complex shape while being still efficient. The starting point of this work is a collection of CFD tools based on an FE flow analysis performed on so-called 2d die-slices, which represent 2d cross-sectional cycle is set-up, in which shape optimization is applied to each die-slice geometry. As objective function the flow rate fraction distribution is used leading to a flow balancing. Parameterization tools are developed that deal with the required automatic geometry modification within the optimization cycle. For this purpose a number of design variable (DV) types are pre-defined, which enable to prescribe DVs on the die-slice geometry before entering the optimization cycle. Due to the comparatively high number of DVs and the intended industrial application, an efficient optimization strategy is necessary. Several methods are looked at and a suitable strategy is developed. This strategy performs well regarding the required manual time to set-up and the required computational time. A comparison with a manual die design process confirms that the resulting geometry is acceptable.