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In their service life, fibre reinforced plastics (FRP) face a variety of environmental conditions resulting from natural or artificial factors. These include variable temperature and humidity conditions, energetic radiations such as ultraviolet rays from the sun, and diverse chemical reactants such as liquid in storage tanks and pipes. These factors are always combined and negatively affect the material properties over the time. Therefore, optimized utilization of FRP material requires reliable methods for quantifying, controlling, and predicting environmental effects. This allows for optimal handling of issues related to component design, economic assessment and safety considerations, as well as the technical problems relating to equipment maintenance. Efforts worldwide are devoted to the modelling of FRP environmental degradation. However, modelling efforts have been hindered by the complexity of the process. This analysis presents a comprehensive model of the environmental degradation of FRP and a prediction method. The modelling method consists of a theoretical demonstration based on material science theories. An analytical approach is proposed. It resolves the complexity of the process into only three components: the chemical degradation, the physical degradation, and the stress state modification. A method to represent the real service environment as a constant environment in laboratory is also introduced. Then, the comprehensive model is expressed as a dynamic constitutive equation resulting from the combination of the historical variation in chemical link density and cohesive forces and the stress history of the material. It is shown that: • The average of the chemical and physical degradation as well as its upper and lower limits can be determined in a laboratory, in a constant environment, as exponential functions of the degradation time. • The environmental degradation can be comprehensively measured as a stress relaxation. • Acceleration of the predictive test can be obtained from a modified time temperature shift principle.

The mechanical properties of alumina trihydrate (ATH)-filled epoxy resin at loadings of up to 100 parts by weight ATH per hundred of resin (epoxy and hardener) (pphr) have been investigated. A low peak exotherm, increased Young's modulus and increased critical strain energy release rate (G[sub]IC) and critical stress intensity factor (K[sub]IC) can be achieved by incorporating a dispersion of ATH into an epoxy resin. However, the high filler loadings required for effective fire resistance reduce tensile strength and elongation. Tensile modulus increases with filler loading in line with previous studies and theoretical equations. However, the tensile strength is higher and the ultimate elongation lower than current theories predict. The tensile and fracture process in ATH-filled epoxy follows linear elastic fracture mechanics, but can be considered in two parts. The initiation of a crack occurs from a large critical flaw, either as a large particle or agglomerations of particles. A flaw can also be formed on the application of a tensile load, when large stress concentrations cause localised microcracking of the matrix. The propagation of a flaw requires more energy and is dependent on several possible mechanisms. Shear yielding and associated crack blunting are shown to be the most important mechanisms, whilst minor contributions from matrix microcracking and debonding of ATH particles are possible. The absence of crack pinning in this study is believed to be due to the inherently weak nature of ATH particles. The presence of a 10pphr rubber dispersion in ATH-filled epoxy only increases the values of G[sub]IC and K[sub]IC at low filler loadings. Amine-terminated butadiene acrylonitrile rubber (ATBN)-modified epoxy matrix exhibits little adhesion to ATH and therefore the efficiency of stress transfer between particle and matrix is reduced, diminishing shear yielding.

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A previous study, looking at the creep-rupture behaviour of mixed reinforcement GRP when immersed in water, had discovered that low loads, behaviour became temperature sensitive. Since the recorded time to failure of a sample was reduced at elevated temperatures, from that predicted by a linear extrapolation of the short term creep-rupture results, this deviation caused problems in the accurate prediction of long-term design stresses. In order to improve the accuracy of long term design predictions, it was decided to study the mechanisms of creep in GRP that initiates time dependent failure. From this, it was hoped that accurate design criteria suitable for predicting GRP response over a 30 year design life from short term creep tests, could be developed. This thesis reports the results obtained from such a study. A series of creep tests were performed on mixed reinforcement GRP samples at several stress levels, both in air, and in room temperature distilled water, using a microcomputer based data collection system. In conjunction with this work, damage development in samples, due to combinations of water uptake and creep loading, was followed, using both scanning electron, and optical, microscopy. Moisture uptake measurements were undertaken under a series of load/temperature regimes, and fibre/matrix debonding followed using photographic techniques. In this way, water absorption, both in terms of uptake rate, and location within a sample, could be characterised. Tensile tests were also performed to determine the standard mechanical properties of the mixed reinforcement GRP used. It was found that a critical damage state was created at loads in excess of 50% of ultimate, but not below. This took the form of between 2 and 8 neighbouring filament breaks in the longitudinal woven rovings at weave crossover points, producing microcracks in the reinforcement. The creation of this multifilament fracture damage during primary creep, was considered to be necessary for time dependent failure to occur in air. Secondary greep strain was found to increase in discrete steps, both in air and water. This was attributed to the formation of transverse grasks in the longitudinal woven rovings, propogating from the above critical damage. In water, diffusion was found to be non-Fickian. Moisture uptake increased with increases in applied load and temperature. Water was seen to accumulate at weave cross-over points when immersed under load. This led to stress-enhanced fibre corrosion in these regions, weakening the reinforcement, and reducing the failure time from that expected at the same load level in air. The localised nature of moisture degradation was thought to result in the formation of critical fibre damage at loads below 50% of ultimate, when immersed in water. Two design criteria based on the observed creep mechanisms, have been developed for GRP that predict response when loaded in either air, or water. Both predict the existence of creep-rupture limits at low loads.

Fibre reinforced plastic (FRP) composites consist of two or more components combined to give a synergistic effect for a better performance in service. One of the phases comprises layers of fibrous material while the other phase comprises of a polymer matrix. In this project, carbon fibre pre-preg material was used. All materials contain imperfections. Materials constituents and manufacturing anomalies are the main causes of faults in FRP composites. The presence of voids in FRP composites is the most common defect. The aim of this project was to determine the influence of voids on the static and dynamic compressive properties of carbon fibre reinforced plastic (CFRP) composites. The influence of voids on fatigue life and failure behaviour were also investigated.

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