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Braided and filament wound CFRP were fabricated with varied fiber orientations. These composites exhibited not only similar trends in their experimental strength and stiffness properties but also good correlations with predictions made by CLT. [ABSTRACT FROM PUBLISHER]

Studies were conducted on the degradation of short beam shear (SBS) and impact strength (Izod) properties of glass epoxy composite specimens with sequential ar rangements of woven roving (WR) and chopped strand mat (CSM) reinforcements, (Figure 1 of Part A) immersed in water at two different temperatures (298 K, 323 K).It was found that composites with higher fibre content, though possessed of a higher ini tial shear strength, degraded faster than those with low fibre content. This was attributed to a thin resin layer separating the glass layers and a consequential increased surface area around the fibres for the moisture absorption. Further, it was noted that while the impact strength too degraded with exposure period, the degradation patterns are almost identical in all types of laminates within the limits of fibre resin ratio chosen. [ABSTRACT FROM PUBLISHER]

Diffusion of water in epoxy composites with different sequential arrange ments of woven roving (WR) and chopped strand mat (CSM) reinforcements was studied on immersion in water at 298 K and 323 K. Laminates with CSM as skin layers showed higher diffusivity and equilibrium moisture content than WR as skin layers. The diffusion parameters obtained from the experiment conducted up to saturation limits of 323 K showed good correlation with the data computed using a moisture absorption programme written on lines suggested by G. S. Springer. Hence data at lower temperatures are also generated by using the above programme, thus shortening the time to reach saturation levels. [ABSTRACT FROM PUBLISHER]

A comparative study was made between the moisture absorption behaviours of sisal and jute fibre composites in an epoxy matrix under immersion conditions. Sisal fibres, in spite of possessing more compact structure than jute fibres, exhibited higher moisture absorp tion levels in their composite form, contrary to expectations. This tendency was attributed to the high cellulose content and a possible interfacial effect in the former. [ABSTRACT FROM PUBLISHER]

The moisture diffusion characteristics of simple (E-glass, Graphite and Kevlar) and hybrid (E-Glass-Graphite, Graphite-Kevlar and Kevlar-E-Glass) unidirectional com posites have been studied at 296 K and 343 K under water immersion conditions. The equilibrium moisture content (Mm) and diffusion coefficient (Dx) of Kevlar fibre com posites are respectively as high as 5 and 10 times those of E-glass/Graphite fibre com posites. The hybridization of impermeable fibres (E-Glass and Graphite) in a com posite does not cause significant changes in the Mm and D x values of their simple com posites. Hybridization of impermeable fibres with permeable fibres (Kevlar), however, has a significant effect on the diffusion characteristics of their simple composites. The experimental data for simple and hybrid composites comprising both impermeable and/or permeable fibre composites show good correlations with the analytical Fickian Diffusion plot. The effect of edge coating on the moisture absorption is quite signifi cant in the impermeable fibre composites. [ABSTRACT FROM PUBLISHER]

The influence of internal factors like the fibre volume fraction and its orientation to the diffusion path on the moisture absorption trends of both the permeable (Jute-Epoxy) and the impermeable types (glass-epoxy) of composites were studied. The equilibrium moisture level (Mm) and the diffusion coefficient (DJ of the glass-epoxy composite decreased as expected, with an increase of the glass fibre fraction (V f) and its orientation («), while those of the Jute-epoxy composite (ie Mm and D/) were found to increase with an increase in the resin impregnated jute fibre fraction (V/) and remain practically uninfluenced by the variations in the fibre orientation angle. These observed trends were explained in terms of typical fibre permeabilities and the diffusion paths preferred by the moisture in these composites. A term called "dif- fusivity index (DI)" was introduced to quantify the relative permeabilities of polymer composites to moisture. [ABSTRACT FROM PUBLISHER]

The influence of external factors like relative humidity (0) and ambient temperature (T) on the moisture absorption behaviour of permeable (Jute-Epoxy) and impermeable (Glass-Epoxy and Graphite-Epoxy) types of composites were reported. The respective equilibrium moisture contents (Mm and Mm) increased exponentially with relative humidity. The diffusion coefficients of both type of composites (D~'and D,) increased with ambient temperature and could be represented by an Arrhenius relationship. The permeable composite showed a higher exponential power on the relative humidity term than the impermeable composite (2.64 for Jute composite as compared to 2.0 reported by Shen and Springer for a graphite composite) and a lower activation energy for diffusion (0.9 x 101 cal. mole-' for the jute composite as compared to 4.429 x 103 cal. mole-1 obtained for a glass composite). These trends were attributed to the fibre permeability leading to different diffusion barriers in such composites. [ABSTRACT FROM PUBLISHER]

A brief description of the Fickian diffusion behaviour in polymer composites, con taining impermeable fibres (glass and graphite) is presented. The applicability of such a model to composites based on a permeable fibre phase (jute) is verified, both under the influence of varied internal (fibre volume fraction) and external (ambient temperature) factors. Very good correlations are found between the experimental data and a modified Fickian diffusion plot. The significance of a resin impregnated fibre volume fraction in such a composite is highlighted. [ABSTRACT FROM PUBLISHER]