No description available.

No description available.

A detailed review of moisture sorption kinetics and equilibria within polymers and fibre reinforced composites (FRC) provides an indication of the mechanisms which may affect moisture transport in FRCs. Three reviewed models are investigated for their applicability to the sorption behaviour of a FRC. The first considers only classical Fickian diffusive transport, while the other two include additional parameters to account for dual sorption phenomena or matrix relaxation respectively. An edge diffusion correction technique is developed to correct experimental 3D sorption data to equivalent 1D data for ease of modelling. The sorption data used to assess the suitability of the models is used also to examine the effects of lay-up, environmental conditions, multiple sorption cycling and long term exposure on the sorption behaviour of the a FRC. Each model is numerically assessed for its ability to represent the experimental sorption data. The more complex models provide good representation of the slightly anomalous FRC absorption data while the Fickian model is acceptable for desorption. The effect of absorbed moisture on the mechanical performance of the FRC is assessed and found to be especially detrimental to the matrix dominated properties. The glass transition temperature of the FRC is also found to be reduced by absorbed moisture. The effects of post-join (atmospheric) and pre-join (substrate) moisture on the durability and strength of bonded joints with FRC substrates are assessed using a scarf joint. One months exposure to high environmental humidites after bonding is found to reduce the strength of the joints significantly. A similar loss in performance is also observed if the FRC has a high substrate pre-join moisture content. Pre-drying of moist substrates is found to be beneficial in regaining the performance of the joint. Joint strength is found to be directly related to the quantity of moisture desorbed from the substrates during joint/adhesive cure. A model for the drying process is subsequently developed and found capable of estimating the ideal drying conditions for a given substrate moisture content.

There is great scope for problems and deficiencies in the workmanship of concreting operations namely. batching. mixing. transporting. placing. compacting. finishing and curing. These problems will adversely affect the quality of the finished concrete. Improving the knowledge and experience of the supervisory staff and workmen on construction sites is essential if these defiCiencies are to be minimized. It has been observed that specifications for concreting activities contain insufficient information regarding workmanship. This causes difficulties in controlling the concreting operations. This thesis addresses the problems associated with the transfer of knowledge from acknowledged experts in concreting operations to site practitioners. It is proposed that an appropriate tool for this information transfer is the use of computer based expert systems. Therefore, an expert system. called ESCON. has been developed to advise on concreting activities. The knowledge of this system was acquired from technical literature, site visits, self experience, and by interviewing experts in the domain. ESCON is capable of: 1) defining and diagnosing concreting problems; 2) giving expert recommendations for the solution of these problems. including the reasons behind the solution; 3) educating inexperienced staff by improving their appreciation of the domain; 4) preparing comprehensive specifications including information on the. workmanship requirements of concreting procedures; 5) calculating the expected loss in the strength of concrete when recommendations are ignored. Experimental work was undertaken at CRIB (Construction Industry Training Board), Bircham Newton, Norfolk, to assist in the verification of the model. The model was tested by undertaking five evaluation methods, including comparison of the result with an objective standard, sensitivity analysis, expert's experience, novice users, and a real life case study.

Relevant literature on plain and hybrid unidirectional fibrous composites is critically reviewed and the difficulty of assessing previous work due to insufficient data is emphasized. A systematically varied series of hybrid composites based on vinyl ester resin and unidirectional carbon and E-glass fibre reinforcements is studied and the constituent materials characterized. Particular attention is given to the effect of total and relative fibre volume fractions, geometrical arrangements and fibre surface treatments on the tensile characteristics and interlaminar shear strength of the composites. Certain hybrid tensile specimens exhibited what is termed a 'hybrid effect', their first failure strain being greater than the expected failure strain of the parent carbon composites. This is discussed in terms of the data and information obtained from the tensile and interlaminar shear strength tests and from a study of the tensile fracture surfaces. Theoretical models for the tensile failure of hybrid composites are critically examined. The tensile fracture mode and the importance of the statistical nature of fibre tensile strength are discussed. Modifications are made to existing statistical failure theory which result in two equations for the ratio of the lower bound on hybrid composite first tensile failure strain to that on the tensile failure strain of the lower elongation fibre parent composite. Comparison between the two equations enables the prediction of the composite failure mode. Where appropriate the theories are applied to the experimental results. Factors controlling the initial failure strain are shown to be the relative volume fractions and statistical characteristics of the two fibre types, the fibre ineffective length and the stress concentrations acting on fibres adjacent to a failed fibre.

This research has tackled the major problem in the field of sprayed fibre reinforced concrete composites, the lack of detailed design information. An extensive series of sprayed fibre concrete field trials and laboratory testing of hardened specimens was complemented by an investigation of flexural testing of cast specimens. Post-cracking toughness and ductility were examined in accordance with the current ASTM (1989a) proposals for toughness index determination. Some of the requirements of ASTM standard C1018 were shown to be impractical.

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Coal-tar pitch is a promising carbon matrix precursor for carbon-carbon composites. It has a suitable viscosity, high carbon yield, and it forms graphitic structures. In addition, pitch is a relatively cheap raw material. This thesis is a study on the use of coal-tar pitch as carbon matrix precursor in carbon–carbon composites.

Carbon fibre reinforced carbon (C/C) composites are advanced materials which exhibit good performance in high temperature inert environments. These materials are generally produced from carbon fibre reinforced polymers (CFRP) by carbonisation and a long series of densification treatments using chemical vapour deposition (CVD) or polymer impregnation. The carbonisation of CFRP results in a highly porous structure with low strength and stiffness so that the aim of the densification is to fill the voids to improve mechanical properties. It is however known that an understanding of void structure in the composites and its relation to raw materials, processing conditions and mechanical properties is important.

A technique is developed whereby Silicon Carbide whiskers may be incorporated uniformly into epoxy resin using an ethanol transport medium. Volume fractions up to 10% are achieved. The mechanical properties of the whisker loaded resin are studied using uniaxial tensile coupons and compact tension test methods. With increasing fraction of whisker, the tensile modulus, tensile strength and fracture toughness are all found to increase significantly. A method for producing hybrid E-glass fibre/epoxy resin/SiC whisker crossply laminates is developed from an existing frame winding technique. Scanning electron microscopy of polished sections of the resultant laminates confirm that an reasonable distribution of the whisker in the matrix is achieved. Laminates containing 0%, 2% 5% and 10% matrix volume fraction of SiC whisker are fabricated. Tensile coupons taken from the laminates were tested under quasi-static and tension-tension fatigue loading conditions. Under both static and fatigue loading, the residual stiffness and accumulation of cracks in the transverse ply are monitored. It is shown that the presence of whisker delays the onset of matrix cracking and the subsequent multiplication of transverse ply cracks under both static loading and fatigue loading conditions. A model to describe the transverse ply crack spacing-applied stress relationship for each laminate type under static loading conditions is developed. The model is based on a combination of a shear-lag stress analysis with a two parameter Weibull statistical description of the transverse ply strength variation. A computer simulation is developed which simulates the propagation of transverse ply cracks across the width of a laminate based on a fracture mechanics analysis. Using a Paris law expression to describe the growth of individual cracks modified to allow for crack interaction the model predicts the variation in residual stiffness with increasing fatigue cycling.