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An experimental technique was developed to measure the energy release rate for delaminations in composite materials. The method can be used in cases where conventional methods may not be applicable, such as problems involving multidirectional laminates or arbitrary specimen geometry. The work involved the experimental and computational enhancement of the optical technique of moirâe interferometry, including alternative grating technology, image processing of fringe patterns, the implementation of phase shifting and the automation of the data reduction process. The improvements provided a practical experimental means for determining full-field displacement fields surrounding delaminations, together with a convenient method for using these displacement fields to calculate energy release rates via the J-integral. Three types of experiments were performed on carbon-fibre/epoxy unidirectional laminates to validate the new approach. The results compared favourably to those obtained by conventional methods. Several experiments were also performed on multidirectional laminates to demonstrate the extended capabilities of the new method. It was concluded that the new method is not particularly well suited to the measurement of critical energy release rates, but it should be a valuable tool in the validation of computational methods.

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.