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Laser welding has great potential as a fast, non-contact joining method for thermoplastic parts. In the laser transmission welding of thermoplastics, light passes through a semi-transparent part to reach the weld interface. There, it is absorbed as heat, which causes melting and subsequent welding. The distribution and quantity of light reaching the interface are important for predicting the quality of a weld, but are experimentally difficult to estimate. A model for simulating the path of this laser light through these light-scattering plastic parts has been developed. The technique uses a Monte-Carlo approach to generate photon paths through the material, accounting for absorption, scattering and reflection between boundaries in the transparent polymer. It was assumed that any light escaping the bottom surface contributed to welding. The photon paths are then scaled according to the input beam profile in order to simulate non-Gaussian beam profiles. A method for determining the 3 independent optical parameters to accurately predict transmission and beam power distribution at the interface was established using experimental data for polycarbonate at 4 different glass fibre concentrations and polyamide-6 reinforced with 20% long glass fibres. Exit beam profiles and transmissions predicted by the simulation were found to be in generally good agreement (R2>0.90) with experimental measurements. The simulations allowed the prediction of transmission and power distributions at other thicknesses as well as information on reflection, energy absorption and power distributions at other thicknesses for these materials. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2013-09-27 10:41:08.997

Relatively few studies have been carried out on polymers at high rates of deformation compared to more traditional materials such as metals, and it is therefore important to develop constitutive models to help predict how materials will behave under specified conditions. The stress-strain behaviour of polymers shows a very marked dependence on time (or rate) and temperature. Polymers (including polyethylene, polypropylene, nylon 66, polyetherketone, polyetheretherketone, a liquid crystal polymer, polyethersulphone and polycarbonate) have been compressed at strain rates of -10-3 to 1O-1s-1 (using an "Instron" which measures deformation versus time at constant rates of compression) and _103s-1 (using a novel drop-weight impact machine) to strains of up to -100%. This drop-weight system is different from commercially available machines in that it operates in compression rather than fracturing specimens and provides stress-strain data directly. The initial crystallinity and orientation of specimens were examined using x-ray diffraction, and kinetic decomposition parameters were obtained using differential scanning calorimetry. Also thermocouples were inserted into some specimens compressed at high strain rates in order to measure any rises in temperature. Several important results have emerged so far: I) sufficiently high bulk temperature rises occ;ur during high rate deformation to considerably alter the stress-strain curve from isothermal conditions; 2) localised deformation in the form of cracking or shear banding in tough polymers appears to lead to temperature rises sufficiently high for significant thermal decomposition to occur; 3) data obtained at lower rates could be approximately fitted to the Eyring Theory unlike that obtained at the highest rate; 4) initial investigations suggest that Poisson's ratio varies with strain and strain rate and is not a constant of 0.5 as generally assumed.

The processing characteristics of PVC compounds play a major role on the ability of the equipment to control the final properties of the product. Therefore, information on the effect of processing conditions on such characteristics. and its influence on the final properties can lead to an optimization of the extrusion process. In this work. a statistically based experimental design was used in order to investigate the role of the operating conditions on the extrusion of a simple lead based PVC formulation. Both a single and a twin screw extruder were used - they were instrumented, and data collected by computer. A die was designed for the formulation used. with both shear and extensional flows being taken into account. These experiments produced both core samples along the screw(s) and final products with varying states of fusion. The fusion mechanism on processing was monitored with the help of electron and light microscopy techniques. thermal analysis and density measurements. In both types of extruders the primary particles were found to fuse well before the grains, but the overall mechanism differs for each type of machine. An experimental technique was developed for the study of the Residence Time (RT) and Residence Time Distribution (RTD) of the material in the processing equipment. These functions were related to the operating conditions and compared with the available models for extrusion. The degree of fusion of the processed products was assessed by rheology and thermal analysis. A range of mechanical properties, relevant to the general end - use of rigid PVC formulations. was analysed: flexural. tensile and impact properties were found to be directly related with fusion level. Hardness, measured using a newly developed apparatus. proved to be a potential technique for the degree of gelation of PVC formulations.

This study was designed to provide information concerning polyester resin as a material for jewelry making. The secondary purpose was to develop processes which create an artistic form for jewelry sustained by a poetic tone based on the fluid and translucent qualities of the material.

Since the civilization, population and living standards of the peoples of the world have increased in such gigantic proportions, especially in the last fifty years; and since the supply of natural resources cannot meet the demand, we have of necessity had to find new materials to take their place. These new materials must fulfill two purposes; namely, to take the place of the natural resources so wantonly destroyed and to meet requirements that the natural materials are not able to meet. Foremost among these new materials are the synthetic resinous materials known as plastics. Plastics are one way of getting around the fact that Nature has not thought of everything. The ability of man to imagine things that he does not see and to fashion these things from what he finds around him is responsible for what we call progress -- and for plastics.

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