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Hybrid fabrics represent a rapidly emerging branch of reinforcements in composite materials. A justified use of these textiles requires a good understanding of their role on the failure behaviour and the mechanical performance of Intraply Woven Hybrid Composite (IWHC). This thesis presents a methodology, which helped to describe and explain the failure behaviour of IWHC using combined experimental and analytical results. In addition it has been demonstrated that Finite Element (FE) models can be used successfully to evaluate the extent of damage under impact loading. The efficiency of the models has been tested against the experimental results and other established micro-mechanical models. Tensile tests supported by non-destructive techniques such as acoustic emission, X-ray and strain field measurements have been conducted to characterise the mechanical behaviour, damage modes and the mechanisms of failure. The experimental tensile results have identified the non-linear plastic damage behaviour, while the FE results have indicated the linear elastic damage behaviour. The overall picture of the failure mechanism has been established by combining the results gathered from the FE and the experimental analyses. The results of the longitudinal tensile tests show an increase in stiffness and strength properties with the increase in the carbon content in the carbon-aramid hybrid composite. Fibre dominated elastic properties have been predicted with an acceptable accuracyb ut predictionf or matrix-dominatedb ehaviourh ash ad significante rrors. This study has identified three major damage events during the tensile loading process at different strain levels. These include a) onset of damage initiated by debonding of aramid fibres, b) formation of clusters of damaged carbon fibres c) necking of aramid fibres at the high stress concentration areas (crimp regions). Eventually, when the content of unbroken fibres is insufficient to withhold the load, abrupt failure occurs locally. Furthermore the residual compressive strengths of the hybrids have been assessed after subjecting them to low velocity impact loading. All the experimental data have been used to support and test the FE models of impact loading. X-ray and scanning electron microscopy techniques have been used to identify the extent and mechanism of damage operating during the impact loading. It has been shown that the lower stiffness property in the hybrid composite has prevailed over the high toughness property. Interesting trends have been established for the flexure energy absorption, impact energy absorption and damage tolerance in compression after impact testing for hybrid composites with different carbon contents.

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No description available.

Ionomer cements, a novel composite material, are formed at ambient temperatures by mixing an aqueous polyacid with an ion-leachable powder. The glass ionomer cement known as ASPA, a dental restorative material, produces strong and hydrolytically stable cements. Applications of this material outside of dentistry have been restricted by its rapid set, its poor mechanical performance in dry environments and its. highcost. The objective of this research have been to modify the ASPA system and develop other ionomer cements for applications outside of dentistry and to provide a further understanding of the mechanical properties of ionomer cements. The rapid set of ASPA cements was reduced by acid treatment of the ion-leachable glass. Cements prepared from this acid treated glass (ATG) were mechanically superior to the ASPA cements and retained their mechanical properties in environments of low humidity due to a greater extent of aluminium polyacrylate formation than in the ASPA cement. The rapid set of the ASPA system was also reduced by replacing the ionleachable glass with various fillers. The mechanical properties of these filled ASPA cements were dependent upon the physical characteristics of the filler and were poor in low humidity environments. Other zinc-glass ionomer cements and certain treated mineral ionomer cements showed promise as low cost alternatives to the ASPA glass. The mechanical properties of ionomer cements were dependent upon the size and packing properties of the glass particles, the volume fraction of glass in the cement and the interfacial wetting properties between the glass and the polyacid matrix. Ionomer cements were mechanically superior and more resistant to hydrothermal ageing than epoxy and polyester composites. It was proposed that this was due to a more water tolerant matrix and due to stable primary interfacial bonds being formed at the glass-polyacid interface.

The demands made of materials have resulted in the formation of complex composite structures; one such example of these is nanocomposites. This study is primarily devoted to the preparation and characterisation of nanocomposites. Reactively cast and reactively extruded nanocomposite strategies for the preparation of polyamide-6 composites were compared. The catalyst and activator system selected was based on an industrially successful combination. The extruder screw and barrel configuration used had previously been proven effective for the reactive polymerisation of polyamide-6. The principal objectives were the investigation of the influence of layered-silicates on both the microstructure and the physical properties of the composites. As well as the analysis of the mechanisms that influence the physical performance of the materials produced. The characterisation of the filler-matrix microstructure and its effect on physical properties of the composites were investigated using a range of chromatographic, microscopic, thermal and X-ray analytical techniques. Selected mechanical properties were measured using standard test procedures. Therefore results obtained and subsequent trends observed in reaction cast and reaction extruded nanocomposites could be compared and contrasted. The influence of the polymerisation conditions, residual monomer content and the nature of the composite structure produced were considered. It was observed that the nature of the matrix crystalline structure could be greatly influenced by the material composition, method of preparation and processing technique. The crystal form of the spherulites present appeared to be the key factor in influencing mechanical strength. The treatment of the silicate-layered clay successfully increased the inter-layer spacings, which was further increased by the presence of high shear forces.

This work relates to the development of a method of preparing a filled phenolic resin, for use particularly, but not exclusively, in building materials. The method includes mixing filler and micro-filler, a catalyst, resin and a hetrocyclic alcohol (i.e. furfuryl alcohol) at a stable temperature, compacting the mixture and allowing the mixture to set and cure. The condition for setting may be with heat and pressure, with heat and/or pressure, or at ambient temperature and pressure. To design a particular grading from the various numbers of filler components available, a computer program was produced permitting up to 14 components of known grading to be combined into the closest possible approximation to a defined target grading. This was compared to the grading obtained using a combination of trial and error and graphical procedures. In developing the Phenolic Concrete mixes, initially, the cold set resol phenolic systems were used which resulted in products with low strength as a result of insufficient bond development between the inert granular or powder like materials (fillers) and the resin. Consequently, modified resins were developed which resulted in the production of high strength Phenolic Concrete systems. The determination of the Phenolic Concrete properties was used in describing the indicative inter-relation between the mix constituents, mix proportioning, and criteria of both strength and economy. In addition, Phenolic Concrete mixes were designed with optimization of the mix matrix resin in developing highly fillable media and defining its macro- properties affecting the strength of the end product. Its material properties as a function of its microstructure was investigated using fracture mechanics. The maximum mix ratio devised was 9:1 weight by weight of filler to resin. Maximum compressive cylinder strength obtained was 88.3 N/mrn(^2) and maximum disc tensile strength was 8.85 N/mm(^2) with maximum flexural strength being 30.5 N/mm(^2). The unit weights ranged from 2.08 to 2.28 g/cm(^3), modulus of elasticity ranged from 14.64 X 10(^9) to 19.6 X 10(^9) N/m(^2) and flexural modulus ranged from 17.4 x 10(^9) to 32.4 X 10(^9) N/m(^2). Maximum fracture toughness obtained was 2.12 N/m(^3/2), and maximum fracture energy was 220.7 J/m(^2). The development, construction techniques and properties of various phenolic resin concretes were investigated and described. Using the modified resin systems and the techniques developed here, filled phenolic resin concrete was produced cheaply without sacrificing strength and stiffness. The use of wet or dry fibre glass laminates as primary reinforcement resulted in exceptionally strong composite systems. Alternatively, or in addition, the filled phenolic resin systems were combined with further reinforcing materials such as profiled high yield steel bars. These were then used in manufacturing box beams, bridge deck panels, (and subsequently, access floor tiles). The technique by which these components were constructed proved to be reliable and repeatable. The structural behaviour of these Phenolic Concrete components was studied and proved to be predictable applying elastic theory and ultimate load analysis.