This work studies the water absorption behaviour of woven glass fibre reinforced cyanate ester composites used in the plenum of the air conditioning pack of aircraft's environmental control system. For absorption tests, samples were immersed in distilled water baths at four different temperatures: 40°C, 60°C, 75°C and 90°C. In general, the composites have shown strong nonFickian behaviour. The progression of mass absorption is described analytically using a combination of Fickian diffusion and relaxation process. Thus for the temperatures of 40°C, 60°C and 75°C a dual stage model was used. At 90°C the material exhibits extreme non-Fickian behaviour due to chemical ageing procedures which cannot be accurately modeled. From the mass control analysis, lots of information is provided for the correlation between the temperature and the diffusion coefficient or the start of the moisture equilibrium. Also, the regions of physical and chemical ageing can be clearly distinguished, giving a good profile of the material behaviour at elevated temperature. The dual stage model that is proposed precisely describes the behaviour of these materials at different temperatures up to 75°C. The chemical ageing that is taking place at 90°C creates another profile that should be investigated in a more detailed level than macro-scale.

The need to develop methodologies for life prediction of glass fibre reinforced polymers (GFRPs) has rapidly increased with the use of composites in many different industries. Currently, there is very little understanding of the ageing mechanisms in composites. It is important to develop a detailed through the thickness degradation analysis due to ageing, so as to predict its effect on the lifetime of composite structures. In the first part of this study an effort has been made to model the moisture absorption, the concentration of the absorbed fluid, and the reduction of mechanical properties, especially elastic moduli and strength in the through the thickness direction of a GFRP structure. The water absorption behavior of woven glass fibre reinforced cyanate ester composites used in the plenum of the air conditioning pack of aircraft's environmental control system has been modeled. The combined models describe the diffusion procedure primarily at material level and continuously at structure level. The amount of the absorbed moisture can be crucial for the mechanical behavior of the structure. Therefore, there is a need for a better understanding of the evolution of mechanical properties during ageing. The whole procedure utilizes the results of the diffusion model for the calculation of the degradation of the moduli during the water uptake process. Predictive models have been proposed, by considering different sections throughout the thickness and provide a solid background for modeling the long term behavior of a structure under consideration exposed at different temperature and different time period. Keywords: Models for Combined Diffusion and Moduli Degradation Analysis of Glass Reinforced Cyanate Ester Composites Structures 2/15Copyright: ©2017 Kostopoulos et al. there is a need for a deeper understanding of the degradation of composite properties during given operating ageing so as to predict the mechanical properties at any given time [9].Primarily, SD Speake et al. [10] had tried to create a method in order to predict the changes of mechanical properties in laminates as a consequence of prolonged immersion in water. These changes were found to be function of the absorbed moisture [10]. In S. Kajorncheappunnganet al.[11] studied the effects of the environmental ageing on the durability of glass/ epoxy composites. He was focused on the major factors that influenced the degradation of glass/epoxy composites [11]. In JR Reeder et al. [12] had developed a prediction methodology of long-term strength degradation of thermoplastic composites using time-temperature superposition [12]. In P. Surathi et al. [13] tried to investigate the reduction of moduli and strengths according to moisture absorption measurements [13]. In G. Carra et al. [14] tried to estimate the reduction of mechanical properties of pultruded glass fibre reinforced polymer composites due to their exposure in combined environmental agents [14]. In Duncan Bruce et al. [15] were focused on measurement and modelling of permeation and d...