The process modelling of autoclave composites has received much attention over the years. This thesis concentrates on two types of processes namely the prepreg processing method and the resin infusion processing method. The work focuses on the modelling and simulation of the resin flow, heat transfer and cure processes of the composites during processing. The Hercules 3501-6/AS4 composite was chosen for the simulation and the data for its thermal properties was obtained from Loos and Springer [12]. The composite is considered as a multilayered system consisting of prepregs or dry fibre layers with alternate layers of resin. A similarity analysis for the prepreg process was carried out allowing the velocity field, in both the prepreg and the resin, to be analytically determined. This then permitted the temperature and the degree of cure to be computed numerically. A similar, but different analysis was then carried out for the resin film infusion process, allowing the temperature and rate of cure to be computed directly. The simulation results of the prepreg case of Hercules 3501-6/AS4 were compared to known experimental results and good agreement has been found. Experimental work was performed on the flow dynamics of the resin infusion case and good agreement has also been observed.

The present study has been performed on β'-sialon matrix reinforced with either carbon fiber, metals or TiN components. The study describes the optimum methods of fabrication of these composites and also investigates their mechanical and electrical properties. In carbon fiber/sialon system, reaction between the fiber and the matrix has been identified and overcomed by applying high densification rate and low temperature sintering. Samples containing 10-20V% fiber was hot pressed to almost theoretical density at temperatures 1500-1550°C. In metal reinforced sialon matrix composites there is always a reaction between the metal and the sialon to form metal silicide liquid at relatively low temperatures, which is found to be helpfull in decreasing the maximum densification temperature. Sialon reinforced by 15V% Ni powder is pressureless sintered to over 95 % of the theoretical density at temperature of 1450°C. Reaction in such composites can be controlled by increasing the sintering heating rate and the amount of silicon metal dissolveed into the metal particles (which strongly influences the composites mechanical properties) can be controlled by a two stage heat treatment sintering particularly in the stainless steel/sialon system. The addition of TiN to sialon matrix resulted in processing with no troubles of chemical incompatibility and composites with attractive mechanical properties. Density of almost theoretical was achieved in the addition of 10-30V%TiN to sialon. The crack type investigations on sialon and sialon matrix composites shows that the cracks are of Palmqvist type. The indentation fracture toughness of the composites mentioned above is dependant on the reinforced phase type, volume fraction and sintering temperature. In fiber/sialon composites fracture toughness of 4 7.9 MNm⁻³/² was achived by hot pressing 15V% carbon fiber/sialon composites. In metal/sialon composites, however, fracture toughness of 13 MNm⁻³/² is achieved, whilst the indentation fracture toughness of 30V%TiN reinforced sialon composites is 8.9 MNm⁻³/². The electrical conductivity of these composites is strongly dependant on the reinforced phase volume fraction and most importantly on the particles size of the conductive phase. However, resistivity of 0.5 Ω. cm is achieved in the addition of 20V% carbon to the sialon matrix. In metal/sialon systems resistivity of 3.37 Ω. cm is achieved in 20V% Ni/sialon composite whilst 30V%TiN is required to create a resistivity of 443 Ω. cm in such composites.

A wide ranging study of the effects of low velocity impact on the performance of a quasi-isotropic, woven CFRP laminate has been conducted. The study considered the response of the laminate to constant velocity impact up to an incident energy of approximately 9J. The resulting damage, a complex network of delaminations, matrix cracking and fibre failure, was related to the incident energy and also to the residual static tensile and compressive strength of the material. The growth of matrix cracking and delamination and also the reductions in tensile stiffness, measured locally over the impact damage site, were followed under constant amplitude zero-tension fatigue on specimens impacted at approximately 3J and 7J, representative of two characteristic damage states. The growth of matrix micro-cracking was found to be very rapid with numbers of cycles and was related to increases in tensile strength of plain, notched and impacted specimens, but substantial decreases in tensile stiffness. This type of fatigue related damage was observed to act as a 'pseudo-plastic' zone providing stress relieving around stress concentrations. No growth of this type of damage was noted in impacted specimens when the ratio of maximum fatigue stress to residual static strength was reduced to approximately 20%. Growth of delamination was found to be related to the original impact damage and was only rapid towards the end of specimen life. The propagation of this type of damage under zero-tension fatigue was also apparently related to reduction in tensile stiffness. The applicability of available 'equivalent flaw' models to the residual tensile and compressive strengths was investigated. In order to widen the applicability of the equivalent flaw approaches, a model has been suggested which predicts the fatigue strength of CFRP subjected to low velocity impact and subsequent zero-tension fatigue loading.

Large concrete structures are being built for the production, storage and transportation of oil. The effects of crude oil on the properties of concrete are not well known and little data is available in the published literature. The present investigation is divided into three parts: 1) A study of the mechanical properties of oil saturated hardened cement paste, mortar and concrete. 2) A study of the effect of absorbed oil on the average bond stress, and the bond stress distribution between reinforcing bar and concrete. 3) A study of the changes in the dynamic modulus and logarithmic decrement of concrete soaked in oil for different periods. All the specimens were oven dried to increase the permeability of concrete to oil and to increase the degree of oil saturation. The results were compared with those of similar specimens soaked in water or sealed in polythene bags as control specimens. The mechanical properties. of HCPs, mortar, and concrete studied here were adversely affected by oil saturation. The compressive strength and elastic modulus were reduced by amounts depending on the amount of oil absorbed. The tensile strength was also reduced due to soaking in oil but the reduction was less than that of the companion specimens sealed as a reference. It appears that the oil mainly affects the aggregate-cement bond strength. - i - The average bond strength between steel and concrete, for both plain and deformed bars, decreases with an increase in the amount of absorbed oil. The reduction. for the plain bar was between 1.8-2.3 times greater than that for the deformed bar. The study of the bond stress distribution showed that at the maximum applied-load, the local bond stress at the embedded end of the oil saturated specimens was about six times greater than that at the loaded end. The dynamic modulus of elasticity increased by 12-14% after soaking the concrete in oil for 580 days compared to the oven dried specimens. The increase w~s about 37% less than that of similar water soaked specimens. The studies of logarithmic decrement indicate that the loss of moisture is the most important factor influencing damping capacity.

This thesis presents a detailed investigation on the engineering properties and microstructural characteristics of concrete containing a high volume of fly ash (HVF A). The purpose of the project is to evaluate the concept of using relatively large volumes of fly ash in normal portland cement concrete, and hence enhance the beneficial use of fly ash in value-added products and construction. A total of eight concrete mixtures with and without fly ash was investigated. The proportion of fly ash in all the HVF A concrete mixtures varied from 50 to 80 % by weight of the cementitious materials, with a constant water-to-cementitious ratio of 0.40 for all the mixtures. A high degree of workability was maintained by the use of a superplasticizer. To optimize the pozzolanic activity in the HVF A concrete, silica fume was used in some of the mixes. The total cementitious materials content was kept constant at 350 kg/m3 and 450 kg/m3 respectively. The influence of the different replacement materials and two curing regimes was studied. The study consisted of two parts. The first part is an extensive study of the engineering properties such as strength development, modulus of elasticity, ultrasonic pulse velocity, swelling, and drying shrinkage at various ages up to 18 months. The depth of carbonation of HVF A concrete under different curing regimes was also investigated. A study of the microstructure of HVF A concretes forms the second part of the investigation. Pore structure, air permeability and water absorption of HVF A concretes with different replacement mixtures were studied. A detailed discussion dealing with the change of the morphological phase under different curing regimes is also presented. The results show that HVF A concretes exhibit excellent mechanical properties with good long-term strength development. Compressive strength in the range of 40 to 60 MPa "as achieved for all the HVF A concretes at the age of 90 days. The dynamic modulus of elasticity reached values of the order of 55 GPa at 90 days. Under similar conditions, concretes made with both fly ash and silica fume had engineering properties which were as good as those made with cement replaced by fly ash alone. The use of fly ash to replace both cement and sand has the advantage of mobilizing and combining the benefits and effects of both separate replacements. The HVF A concretes also have low permeability and exhibit good potential characteristics to resist water penetration. Reduction in the volume of large pores was observed with the progress of the pozzolanic reaction. Higher HVF A concrete strength was generally associated with a lower volume of large pores in the concrete. A decrease in the levels of calcium hydroxide was seen with progressive water curing and age in all the HVF A concretes, providing evidence of continued pozzolanic reactivity of the fly ashes. Various empirical relationships and design equations are presented and conclusions are drawn at the end of each part. It is recommended that further research is required to determine the influence on HVF A concretes of extreme curing conditions such as high or low temperature and low moisture availability, and to improve the early strength properties of the HVF A concretes.

No description available.

The demand for road making materials continues to pressurise the supply of traditional good quality aggregates. Over the years, therefore, consideration has been given to alternative materials including industrial wastes. This thesis is concerned with potential use of Minestone, the by-product of coal mining, for the lower structural layers of pavement construction. Because of their clay like nature, Minestones do not merit consideration for such applications in an unbound state and, therefore, some form of stabilisation is necessary. Previous research has demonstrated that certain cement bound minestones, containing between 5 and 10 per cent cement, satisfy current Department of Transport requirements for use in pavement construction and, furthermore, they are not frost susceptible. However, doubts concerning the durability of cement bound minestones still remain. The thesis includes a review of both the cement and lime stabilisation techniques and also traces the origin and development of the methods used to assess the quality and durability of stabilised materials. An experimental study is described in which cement bound minestone specimens were subjected to a programme of tests which examined compressive strength, resistance to immersion, and resistance to freezing and thawing. The results of the tests were related to the properties of the raw materials. It was discovered that the response to cement stabilisation was governed mainly by the source of the minestone and, to a lesser degree, the cement content. It was also found that resistance in the durability tests was generally improved when the initial moisture content was raised above the optimum value. The result suggest that current methods for assessing cement stabilised materials are not appropriate to cement bound minestones. Alternative methods and criteria, based on volume change and retained strength following immersion and freeze-thaw tests, have been proposed. It is believed that these methods and criteria should also apply to other cement bound materials.

In Part I of the thesis the effect oif sulphonated melamine formaldehyde (SMF) superplasticizer on the hydration, microstructure and internal chemistry of ordinary Portland cement, as well as on individual pure cement clinker components such as tricalcium aluminate (C3A) was investigated. Conduction calorimetry, thermal analysis, X-ray diffractometry, scanning electron microscopy and pore fluid extraction techniques were used. In order to determine SMF content of the cement pore fluids, it was necessary to develop a new analytical method for SMF. Because of high pH of cement pore fluids the conventional U.V. method was found to be inapplicable. Therefore a new method based on spectrofluorometry was developed; it can be used up to a. pH of about 10, and neutralization can be made using HN03 solution. The role of SMF during cement hydration was further assessed using the method. The results showed that C3A phase of Portland cement adsorbed large amounts of SMF superplasticizers from the aqueous phase of C3A-gypsum mixes in the first few minutes of hydration. In Part II of the thesis, chemical interactions between alkali-resistant (AR) glass fibres and cement matrices was studied. The effect of silica fume additions on the interactions were also investigated. The results of the present work suggest that there are a number of points to be clarified, concerning the use of superplasticizers and AR-glass fibres in cement. The future work to be carried out on superplasticizers may be divided into several groups such as alkali-silica reaction, corrosion of reinforcing steel and durability aspects. Superplasticizers are normally employed as sodium salts. It is evident that addition of superplasticizers into ordinary Portland cement increases the Na+ content of pore solution as well as its pH. Therefore, the rate of alkali-silica reaction may be enhanced due to the increasing pH of cement matrices. Superplasticizers are currently used for the placement of concrete in heavily steel-reinforced structures. The alkaline nature of concrete matrices provides excellent protection for steel reinforcement. However, carbonation of the concrete lowers the pH of the matrix. On the other hand, penetration of aggressive species such as Cl- ions from the sea or other sources accelerates the corrosion of steel reinforcement. There is as yet no detailed study on the chemical behaviour of superplasticizers in chloride- bearing concretes, especially, in relation to their effect on steel reinforcement corrosion kinetics. Superplasticizers greatly influence the morphology of cement hydration products, mainly calcium hydroxide. There is controversy as to whether calcium hydroxide crystals formed in cement paste make a positive or negative contribution to the strength development of cement pastes. In addition, the effect of the presence of thin calcium hydroxide crystals on the durability and long-term properties of cement pastes is not yet known. Zr02-containing commercial AR-glass fibres show poor durability characteristics in a Portland cement matrix, cured in a humid environment, although the deterioration of zirconia glass is much slower than that of ordinary glass. Attack on the fibres is attributed to both the high alkalinity of Portland cement matrices and the growth of hydration products, mainly calcium hydroxide. One solution to these problems seems to be to reduce both the alkalinity and the calcium hydroxide content of cement pastes. Pozzolanic materials such as silica fume, fly ash, slag etc. are very effective in reducing both the pH and the calcium hydroxide content of cement pastes. From the results presented in this thesis, the highly brittle nature of cement pastes with silica fume leads to a decrease in flexural strengths of AR-GFRC composites, although it improves the durability of composites to some extent. The use of other pozzolans, for example, fly ash and slag have not received much attention. Another possibility is the use of less alkaline cement matrices to decrease the chemical attack on AR-glass fibres. In addition to changing composition of cement matrices, the covering of the surface of original glass fibres by alkali- resistant organic or inorganic materials may protect the glass from chemical attack and slow down the corrosion process. Investigations on more alkali-resistant glass compositions may,- also result in the manufacturing of new types of glass fibres.

No description available.

Research work on metal matrix-fibre composites has concentrated in the past on aligned fibre composites. The poor transverse strength of these composites is seen as a major hindrance to their practical use in the majority of engineering applications because stresses exist in more than one direction. Materials with isotropic properties are preferred and consequently reinforcement of composites in three dimensions will be necessary. With this objective, an investigation was conducted to assess the method of fabrication and properties of A1-a110y reinforced with short fibres (SiC and A1 203) randomly oriented in three dimensions. Two composite systems were examined: Al-4.S Cu alloy reinforced with SiC fibre; and Al-3.7S Mg alloy reinforced with A1 203 fibre. The general approach was to establish a satisfactory manufacturing method for the composites before evaluating their mechanical properties. The vortex technique was used to introduce the fibres into the molten alloy. Pre-treatment of the fibres, to induce wetting, and the use of a specially designed device for fibre separation and introduction to the molten A1-ai10ys was found to be necessary so that a uniform distribution of fibres oriented in three dimensions could be achieved. The composites were squeeze cast, under conditions which were experimentally determined, to ensure the production of pore-free castings with fine equiaxed structures. The improvement in tensile strength and ductility of the cast metal, provided by squeeze casting, would be beneficial to composite properties. Composite castings, with up to 10% volume fibre, were produced with a sound structure and with fibres that were uniformly distributed and randomly oriented in three dimensions. It was found that the reaction between the fibres and the respective molten alloy must be closely controlled so that fibre reinforcement can be realised. In this respect the optimum time of contact between the fibres and the molten alloy was experimentally defined for both composite systems. The tensile properties (UTS, 0.1% proof stress, and ductility) of the fibre-free alloys were substantially improved by squeeze casting. The addition of fibre produced further substantial improvement in the tensile properties of the squeeze cast composites, in particular elastic modulus and 0.1% proof stress. Furthermore, composite properties were isotropic. The improvement in the tensile properties of composite castings (as a result of the addition of fibre) was maintained at elevated temperatures. At 250oC, castings of both composite systems with 10% (volume) fibre had 0.1% proof stress and elastic modulus values similar to those for the fibre-free castings at room temperature. The tensile properties of the composite castings were not affected by thermal cycling (at experimental conditions). The fatigue life of the squeeze cast composite was substantially improved over and above the initial improvement in fatigue life of the fibre-free castings produced by squeeze casting. Wear of cutting tools was adversely affected by the presence of fibres.