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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Influence of fabric weave on the consolidation of thermoplastic composites

Ogunribido, Abiodun Oludare January 2010 (has links)
An investigation into the influence of fabric weaves on the consolidation of commingled thermoplastic composites was undertaken. The study was carried out to investigate the influence of fabric weaves on the fibre volume fraction of composites and the resultant effect on the mechanical properties of the composites. Furthermore the correlation between changes in composite void content with changes in the consolidation parameters and the changes in composite thicknesses was also investigated. Four samples representing some of the common preform weave styles used in the production of thermoplastic composites were selected for experimental and theoretical investigations. The sample weaves were, Plain, 2x2 twill, 4x4 twill and unidirectional plain weave. In order to study the influence of preform weaves on the melt impregnation of commingled fabrics, dry preform modelling was carried out to develop a method for predicting nesting in multilayer stacking of plain and nonplain woven preforms. This allows for the prediction of the fibre volume fraction of the dry preform before the onset of melt impregnation. Experimental measurements using the samples show a good correlation between the models and experimental data. Void fraction measurements were carried out using optical microscopic methods. The consolidated samples were subjected to tensile, shear and flexural tests to assess their mechanical properties. Results indicated that preform weaves strongly influenced the consolidation quality measured as a function of the void content and the mechanical properties of the composites. Fabrics with fewer interlacements generally consolidated into composites with void contents lower than fabrics with higher number of interlacements at lower consolidation temperature and pressure. This is due to lower fibre volume fraction and larger inter-tow pore spaces, which is due to very low inter-layer nesting. However, at higher temperatures, void contents of composites consolidated from fabrics with higher interlacements were lower than those consolidated from fabrics with fewer interlacements. This is attributed to nesting within the preform leading to reduction in the pore size of the inter-tow spaces coupled with the reduction in matrix viscosity. The changes in composite thickness as the processing parameters were varied were found to correlate closely with changes in the void content of the corresponding composite. This led to the conclusion that changes in composite thickness can be used as a measure of consolidation quality. This is important as it allows for quick measurements to be taken without the need for tedious void content measurements. Mechanical properties of the composites indicate that preforms with longer float length had better tensile, interlaminar shear and flexural properties. However, unidirectional preforms with little or no transverse bridging fibres tend to be pushed apart during matrix impregnation resulting in resin rich areas. This ultimately results in poorer interlaminar bond strength.

A study of fatigue failure in vulcanized rubber

James, A. G. January 1970 (has links)
Some aspects of fatigue failure in rubbers have been examined. Scanning electron micrographs of the surface exposed by the failure confirm the incremental, crack-propagation nature, of the fatigue process. Many other features of the failure surface have been identified and related to this process. The complicating effect of a reinforcing filler has also been investigated. The fatigue resistance of rubber test-pieces deformed in simple tension was measured as a function of frequency and temperature. This showed that an increase in frequency was equivalent to a decrease in temperature; for an amorphous unfilled rubber the time and temperature effects of crystallisation and fillers on the validity of this transformation is considered. This transformation indicates that hysteresis plays an important part in the fatigue process. Torsional pendulum measurements were used to demonstrate the dependence of the fatigue life on the mechanical damping. An apparatus was developed to measure the hysteresial energy loss directly at deformations, rates of deformation and temperatures consistent with a typical fatigue test. Measurements made with this apparatus are compared with fatigue values and a quantitative relationship is suggested describing fatigue, in terms of the energy lost per unit energy input in a cycle of a fatigue test.

Rubber-like elasticity in the body : a study of elastin and its synthetic analogue poly (2-hydroxyethyl methacrylate)

Dorrington, Keith L. January 1977 (has links)
No description available.

The development of more environmentally friendly replacements for synthetic rubber

Auden, Leigh Adams January 1994 (has links)
The target of this work is to modify natural rubber by an environmentally friendly process, in order to obtain materials with properties analogous to, or extending those of synthetic rubber. On this basis the route chosen towards the modification of natural rubber was by direct enzyme action. The enzyme chosen for this work was cytochrome P-450 (, which is an iron-porphyrin-containing monooxygenase. It was obtained for this work from hepatic microsomes. Various incubation procedures for the oxidation of several simple liquid hydrocarbons have been examined, and the conditions optimised. Product yields in excess of 90 % have been obtained using cytochrome P-450 from liver homogenates obtained from rats stimulated by the use of phenobarbital. The highest yields were obtained when NADPH, the natural reducing agent of the enzyme was used. After the incubation conditions had been optimised for the enzymic oxidation of these simple liquid hydrocarbons such as cyclohexane and decane, steps were made towards achieving the enzymic oxidation of liquid hydrocarbons of more similar unit structure to the cis-polyisoprene unit, such as 1-methyl-l-cyclohexene. The successful oxidation of these species has led to progressive oxidation attempts upon larger substrates such as dihydromyrcene, squalene, polybutadiene and natural rubber itself. Although the oxidation of natural rubber by cytochrome P-450 has not yet been achieved, proton-n.m.r. analysis of the products extracted from incubations upon a synthetic liquid cis-polyisoprene sample (m.wt. 30000), has shown that the enzyme has oxidised this species to a small extent @ 0.5 %.

Natural rubber : network changes with vulcanization temperature

Loo, Cheng Teik January 1974 (has links)
The influence of cure temperature in the range 140–200°C on the network structures of pure gum NR vulcanized with sulphenamide-accelerated sulphur systems is established. Cure systems investigated include three proportions of CBS*/sulphur and variation of the type of sulphenamide at a fixed molar concentration.

The accelerated sulphuration of natural rubber, CIS-1, 4-polybutadiene and their blends

Skinner, T. D. January 1971 (has links)
No description available.

Kinetics of thiazole-accelerated sulphur vulcanisation of natural rubbers at high curing temperatures

Redding, R. B. January 1969 (has links)
No description available.

Modification and improvement of polymeric materials by exposure to ionising radiations reinforcement of silicone rubber

Morris, J. January 1967 (has links)
No description available.

Prevention of roll breakage on two-roll mills for rubber and plastics

Brichta, A. M. January 1969 (has links)
No description available.

Ultrasonic non-destructive evaluation of natural rubber latex suspensions

Jaafar, Rosly January 1996 (has links)
This thesis describes the development of wide bandwidth ultrasonic pulse transmission and pulse echo comparison spectrometer methods to measure the ultrasonic phase velocity and absorption in natural rubber latex. Details of the quantitative design and construction of simple prototype test rigs include the mechanism of: variable path length pulse transmission, variable path length reflected pulse echo, and dual transducers reflected pulse echo. Special signal processing of experimental data, including transducer impulse response correction routines to calculate the acoustical parameters, are outlined. Measurements made using the constructed prototype test rigs are compared with each other and with data available in the pulished literature. A selection of methods to suit varying requirements for acoustical measurements in natural rubber latex samples is made. Calibration curves relating the measured ultrasonic absorption and phase velocity with the dry rubber content (d.r.c.) at temperatures of 20 to 30°C were constructed. Experiments to test the usefulness of these calibration curves were undertaken to determine if there was any deviation from the Standard Laboratory Method. A comparison between the experimental results obtained using the dual transducer reflected pulse method and the simulation of the Allegra and Hawley model with multiple scattering is presented. Good agreement was obtained between the experimental and the theoritical approaches up to 40% d.r.c. The feasibility of the detection of adulterant materials in natural rubber latex concentrates by using an ultrasonic method is discussed. Finally, the dual transducers reflected pulse echo technique is found be an alternative method to determine d.r.c. in natural rubber latex and could be used as a real time monitoring system for liquids and suspensions in a production environment.

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