The behaviour of paste is complex.  It has many unusual properties that do not fit with other engineering materials.  These can be linked to the volume effects that occur as the material is sheared. A multi-phase model based on a soil mechanic approach has been developed to consider the particle, liquid and gas components.  The volume is allowed to change during shearing and links these effects to the shear stress through pore fluid pressure and surface tension.  There is also a movable reference strain to allow the model the ability to simulate both cyclic and monotonic deformations in one system. Constrained pressure tests were conducted over a fixed strain amplitude cyclic deformation.  These were conducted in a series to consider the effects of strain rate, amplitude and pressure in a paste.  They were then analysed visually and statistically to find which of the variables were significant to the stress-strain response in paste. A further series of tests carried out with an increasing amplitude cyclic test.  This test was simpler but allowed a series of different pastes to be analysed without attempting to control the pore pressure in the materials.  A number of different responses were noted and a fuller picture of paste reaction was developed. Finally, the material model was matched to physical tests to evaluate the model’s ability to fit to different paste responses.  This was completed successfully with the use of an optimisation algorithm.

A small-scale propane burner test was developed to enable rapid characterization of composite systems under reproducible conditions for either hot face temperature or heat flux. The burner rig is a low cost device which enables a 100mm square specimen to be subjected to a near uniform heat flux over its surface. The small-scale tests were conducted to measure the thermal conductivities of woven roven (WR) glass fiber mats with a weight of 0.13kg and 11.8mm thickness at high temperatures up to 800°C. An empirical equation was derived for calculating the variation in thermal conductivity of the dry glass fiber mats. A series of fire resistance tests on composite laminates was carried out using a small scale furnace. During the tests the samples were that prepared and laminated using hand-lay-up techniques were exposed to fire conditions defined by a furnace temperature versus time curve. Excellent fire resistance under hydrocarbon curve test conditions was demonstrated for several matrix materials (i. e. isophthalic polyester, orthophthalic polyester, vinyl ester). This information was important for the marine sector and companies such as Devonport group (DML) and Vosper Thorneycroft (VT) to determine if materials could perform to the A60 requirements. The A60 requirements for fire resisting structural are refer to the subject the material to 60 minutes fire testing under the SOLAS temperature/time regime. This then press the material for CFRP pipe repair and metal vessels in petroleum and transportation industries. The experimental results from tests using the small scale furnace were compared with predictions of thermal responses of composite panels in fires using an existing theoretical model. The ID FD model is capable of modelling the thermal response behaviour of polyester/WR and vinyl ester/WR laminates subject to fire for small scale heat sources. Substantial savings in the cost of implementation of new applications may be achieved by modelling thermal responses. A thermal model based on a finite difference technique takes into accountt he decompositionp rocessesin the laminate. The thermal model used was an extension of a model already developed by the Composites Group at the University of Newcastle. This model can also be developed to incorporate the responses of composite structures under load.

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The study presented in this thesis investigates the relationship between the experimentally determined behaviour of Z-pinned laminates under various delamination fracture loading conditions and their mesostructure Mode I, mode II and mixed mode 1/11 delamination fracture testing was carned out on Z-Fibre reinforced unidirectional beams of IMS/924 laminates For the Double Cantilever Beam specimens (DCB) under mode I loading, the crack propagation resistance of the beam is enhanced with increased pinning density For the range of pin diameters and pmmng densities used for this study, the load carrying capability has been improved by up to 5 times and the apparent toughness has been improved by up to 20 times The most noteworthy example of the effectiveness of ZFibreTM pinning is the stabilisation of delamination crack propagation under mode II loading conditions in the intrinsically unstable 3pt-ENF configuration Although the current data analyses, based on LEFM, included in the test protocols for the calculation of delamination toughness values are invalidated by the presence of the through-the- thickness reinforcement, they are used here as the best currently available means of normalising the fracture results However, these data reduction methods do not allow direct quantification of effects of the different pinning parameters on the crack bridging capability of the through-the- thickness reinforcement In order to relate the micromechanics at the pin level with the Mesomechanics of the delamination fracture specimens, the determination of the traction laws of a single Z-Fibre, bridging a crack and deformmg under various loading conditions, have been determined successfully by single pin experiments A finite element approach, utilising these experimentally determined single pin bridging laws, is presented as a tool to cany out parametric studies of the effects of pin length, diameter and location on the behaviour of delaminating beams The good agreement between the simulated and experimental R-curves demonstrates that the mode I delamination behaviour of DCB specimens is related to the single pin pullout traction laws Finally, preliminary studies of the compression after impact behaviour of ZFibreTh reinforced laminates indicate the existence of a complex relationship between the dramatic enhancement of the delamination crack propagation resistance of a material and the much lower (up to 50%) ultimate improvement in its compression after impact performance

Functionally graded materials (FGM) are composite materials with microstructure gradation optimized for the functioning of engineering components. For the case of fibrous composites, the fibre density is varied spatially, leading to variable material properties tailored to specific optimization requirements. There is an increasing demand for the use of such intelligent materials in space and aircraft industries. The current preferred methods to study engineering components made of FGM are mainly modelling particularly those that are finite element (FE) based as experimental methods have not yet sufficiently matured. Hence this thesis reports the development of a new Mindlin-type element and new Reissner-type element for the FE modelling of functionally graded composite (FGC) structures subjected to various loadings such as tensile loading, in-plane bending and out-of-plane bending, buckling and free vibration. The Mindlin-type element formulation is based on averaging of transverse shear distribution over plate thickness using Lagrangian interpolation. Two types of Mindlintype element were developed in this report. The properties of the first Mindlin-type element (i.e. Average Mindlin-type element) are computed by using an average fibre distribution technique which averages the macro-mechanical properties over each element. The properties of the second Mindlin-type element (i.e. Smooth Mindlin-type element) are computed by using a smooth fibre distribution technique, which directly uses the macro-mechanical properties at Gaussian quadrature points of each element. The Reissner-type element formulation is based on parabolic transverse shear distribution over plate thickness using Lagrangian and Hermitian interpolation. Two types of Reissner-type element were developed in this report, which include the Average and Smooth Reissner-type elements. There were two types of non-linearity considered in the modelling of the composite structures, which include finite strain and material degradation. The composite structures considered in this paper are functionally graded in a single direction only, but the FE code developed is capable of analysing composite structures with multidirectional functional gradation. This study was able to show that the structural integrity enhancement and strength maximisation of composite structures are achievable through functional gradation of material properties over the composite structures.

In this thesis a long period grating (LPG) based sensor is investigated as a possible alternative to current process monitoring sensors used in the manufacture of composites to monitor cure. An LPG is demonstrated as a means of monitoring the cure of a UVcured epoxy resin. The wavelength shift of the attenuation bands were measured during the cure of the resin and compared with measurements made using a fibre optic Fresnel based refractometer. The results showed a good correlation (6 x 10 -3 rius) and illustrate the potential of the techniques for non-invasive composite material cure monitoring. Alternative fibre grating methods; a chirped LPG sensor, an in-fire Mach-Zehnder interferometer and a tilted fibre Bragg grating sensor, are also presented to demonstrate the versatility of grating based sensors for flow, high sensitivity refractive index and multi-parameter sensing, respectively. Demonstrations of LPG sensors in industrial applications are also presented and highlight the technical issues of integrating such devices in composite components and composite manufacturing processes.

Composite materials have been increasingly used in the past two decades since they offer significant potential weight reduction, part design flexibility and improved specific mechanical performance compared to traditional metals. For specific applications, braid reinforced composites offer better near net shape part and manufacturing flexibility than conventional unidirectional laminates, albeit at the expense of slightly lower in-plane stiffness and strength. Furthermore, for impact and crash applications, which is the emphasis of this thesis, their tow waviness and interlocking can offer excellent damage tolerance and energy absorption. In this work, heavy tow (24k) biaxial carbon and glass braided preforms were used to manufacture coupons and beam structures to undertake an extensive testing campaign to characterise different damage and failure mechanisms occurring in braided composites. Due to large shear deformation and surface degradation, non conventional measurement techniques based on marker tracking and Digital Image Correlation were successfully used to measure strains in the damaging material. The modelling of braided composites was conducted using the meso-scale damage approach first proposed by P. Ladevèze for unidirectional composites. The calibration of an equivalent braid unidirectional ply was achieved using the experimental results obtained for different braided coupons. Furthermore, failure mechanisms observed experimentally, such as tow stretching and fibre re-orientation occurring during loading history, were integrated into the model. A new unidirectional ply formulation was subsequently implemented into the explicit finite element code PAM-CRASHTM. Validation of the new model using single element, coupons and beams were conducted that provided a satisfying correlation between experimental tests and numerical predictions.

Carbon composite reinforcement fabrics aimed at flight critical aircraft structure application were designed and the capability of the process used to manufacture them examined. Studies of the LIBA multiaxial non-crimp fabric manufacturing process focused on the effect of changes to four manufacturing parameters using an experimental design process to design the fabrics and analyse the results. The composite properties measured included microstructural features of the fibre tows and resin distribution, and mechanical performance both in-plane and their damage resistance and tolerance characteristics. Nine pairs of Toray T300 carbon based LIBA multiaxial non-crimp fabrics were manufactured and converted to composite laminates. Processing was accomplished using the interleaved Resin Film Infusion processing route with commercial Fiberdux 914 matrix resin. All the fabrics were of the same reinforcement type, consisting of 816 g/m2 of fibre; 376 g/m2 oriented along the fabric length (0°) and 220 g/m2 oriented in each of the ±45° directions. Differences between the nine pairs of fabrics were restricted to the settings of four manufacturing parameters; stitch course (needle penetrations/cm); stitch tension, 00 tension and 0° coverage (amount of constraint on the 0° material provided by the stitch). Three settings were used for each of the parameters; each representing the upper and lower limits, and standard setting. Microstructural characterisation of the laminates indicated large differences in both resin distribution and levels of 0° fibre crimp caused by the changes in manufacturing parameter settings. In-plane and damage resistance and tolerance tests on their composites allowed relationships between manufacturing settings, microstructure and engineering properties to be deduced. It was found that selected in-plane properties could be increased by as much as 17% relative to standard production materials, although a wide range of influence was observed. For damage resistance and tolerance characteristics, reductions in impact damage area (C-scan) of between 13-50% are expected across a range of energies. Manufacturing settings to maximise the impact force for delamination initiation were found to minimise the impact damage areas. Similarly the same settings maximised both the Mode I propagation strain energy release rate and the Compression After Impact strength of the materials. It was found that polyester knitting yarn was largely responsible for the control of the damage resistance and tolerance characteristics together with the mean size of the resin areas and layers within the composite. The manufacturing/microstructure/property relationships identified provide those wishing to exploit these materials with design guidelines to tailor fabric structure and performance characteristics for the intended application. Above all else the results highlight the need for precision in specifying and controlling the manufacturing process in order to repeatably produce the desired performance. Further work on the same materials could be used to provide a link to processing characteristics such as permeability for liquid resin moulding processes and ability to conform to complex curved surfaces.

This work draws some early baselines on the in-plane/out-of-plane properties balance in a 5HS woven carbon fabric/epoxy composite reinforced by tufting and resin injected by resin transfer moulding technique. Details of the manufacturing processes involved in the preparation of such through-the-thickness reinforced composites are presented together with analysis of the mesostructure of tufted specimens. Preforms were reinforced locally with a commercial glass or carbon fibre thread. The tufts were inserted in square arrangement with a KSL tufting tool interfaced to a 6 axis computer controlled robot arm from Kawasaki. The presence of tufts improved significantly the delamination resistance, assessed by testing double cantilever beam coupons in mode I loading configuration. In-plane tension and compression after im¬pact (CAI) tests revealed that the reinforcement resulted in a considerable increase in the post-impact residual strength value, with an accompanying drop down in static tensile modulus and strength of less than 10%. In addition to the standard coupons for the determination of the quasi-static mechanical properties, some cured miniature specimens containing a limited number of tufts were also prepared. These were tested in both uniaxial pull-out and in a mode II configuration in order to measure the bridg¬ing actions of the tufts and to determine the micromechanical failure mechanisms. The obtained crack bridging laws were used for calibrating a simple analytical model of the mechanical behaviour of a single tuft within the composite. The tufting technology was applied to an innovative concept that aims to adopt the tufting threads as a carrier for resin modifiers. For this purpose a single-filament and a multi-filament thermoplastic prototype threads were used. These threads are not intended to modify the composite fibre architecture but are expected to dissolve into and react with the host matrix upon cure. The outcome of mode I delamination and CAI tests conducted on woven preforms reinforced with such 'soluble' threads are presented and discussed.

Temperature profiles of and combined thermal-mechanical induced strains for Carbon Fibre Reinforced Plastic (CFRP)-Aluminium multi-fastener double lap joints in a wingbox structure are examined. Two dimensional (2D) FE analyses for cases of full, empty, and half-full fuel tank scenarios are used to develop temperature profiles. The influence of conduction, convection, and radiation on temperature profiles is examined. Results show that the empty tank scenario produces the highest temperatures, with the joint region having the peak temperatures, and that convection and radiation must both be modelled in order to accurately estimate wingbox temperatures for the empty, and halffull tank scenarios. Analytical temperature prediction models, both at and away from the joint region, are developed for combined convection and radiation boundary conditions at both external surfaces of this unique finite geometry. For transient analyses, single and multiple layer models are designed using integral transforms and separation of variables, respectively. To show the joint region is critical in terms of induced strains, sequentially coupled thermal-stress analysis is performed using the resulting temperature profiles. Based on these results, and on the results of the temperature profiling, an experimental model is designed to study the effects of thermal and mechanical 1 oading on a threefastener double lap joint with CFRP'skin and aluminium laps. To fully explore the joint region, three dimensional (3D) FE results are compared with experimental data. Mechanical tensile stress in the elastic range is applied at room temperature (295K) and at an elevated temperature (373K). Increasing temperature alters the strain patterns among the fasteners and generally decreases' the peak radial strains at individual fasteners, but increases tangential strains. The effect of torque on the strain distribution in these multi-fastener double lap joints is examined by comparing finger-tight and operationally-tight (35Nm) torques at both temperatures. Increasing torque significantly reduces peak strains on individual fasteners and evens the strain distribution across the joint