Adrian Gilbert

The mechanical role of the fibre/matrix transcrystalline interphase in carbon fibre reinforced j-polymer microcomposites

Abstract Microcomposites of single-pitch-based carbon fibre reinforced J-Polymer are employed to investigate the mechanical role of the fibre matrix transcrystalline interphase. The transcrystalline interphase in this semicrystalline thermoplastic system is varied by changing the crystallization kinetics, as determined by the thermal history. The kinetics of transcrystallization under isothermal conditions are presented as an example, and are used to form different transcrystalline interphase thickness. These affect the fibre fragmentation process that occurs while the specimens are cooled from the crystallization temperature to room temperature. This fragmentation process is attributed to residual thermal stresses, which can be calculated by assuming that it is controlled by Weibull statistics. Tensile loading of either longitudinal or transverse microcomposite specimens results in additional fragmentation, the extent of which is determined jointly by the thickness of the transcrystalline layer and by the yield strain of the matrix.

The rate-dependence of flexural shear fatigue and uniaxial compression of carbon- and aramid-fibre composites and hybrids

Abstract The purpose of this work is to provide important insight into the factors that determine the unique flexural-fatigue performance of aramid-fibre/carbon-fibre (ACA) sandwich hybrid composites and its dependence on strain rate. The understanding of the response to strain rate of the single components under compression and shear conditions is the focus of this paper. Axial-compression strength, static-shear, and shear-fatigue results as a function of strain rate are analysed independently and compared in an attempt to explain the flexural behaviour of the ACA hybrid. The possibilities that the rate-dependence of the flexural-fatigue behaviour of the ACA hybrid result from contributions of those components are eliminated. The likely source of this behaviour may be related to the strain-rate gradient for the ACA beam under flexural loading, which follows the plastic yielding in compression of the aramid skin.

Transverse loading of monofilament reinforced microcomposites : a novel fragmentation technique for measuring the fibre compressive strength

Carbon/J-polymer single fibre composite samples were tested under tensile conditions with the fibre direction perpendicular to the tensile loading axis. The Poisson ratio effect induced a compression strain field in the fibre, resulting in a fragmentation phenomenon similar to that observed in a fibre subjected to tensile loading. This observation introduces a novel technique for the measurement of the compressive strength of single fibres, calculated either from the stress at first break, or from the Weibull scale parameter obtained from the fragmentation data produced at various stress levels. The special sample loading configuration used here also provides the first measurement of the effect of the length of the fibre on its compressive strength value.