The mechanical properties of thermoplastics strengthened by short discontinuous fibres

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Abstract
The tensile mechanical properties of a commercial glass-fibre-reinforced nylon containing short glass fibres has been compared with experimental batches of nylon and polypropylene containing glass and carbon fibres of controlled lengths. It has been shown that longer fibres are more effective in improving strength than are equivalent fractions of short fibres, especially at higher values of strain. The stiffer carbon fibres are more effective than glass for reinforcing nylon. A critical length effect has been proposed where the minimum fibre length for effective reinforcement is shown to be related to the strain in the composite and to the strength of the fibre/matrix interface. Subcritical glass fibres in nylon appear to continue to support some load, but subcritical carbon fibres do not. Failure in nylon-based composites reinforced with carbon or glass appears to be initiated by fibre fracture, while in the polypropylene/glass system matrix failure occurs.