Abstract
The mechanical anisotropy of an aromatic polyamide fibre, Kevlar 49, was studied in tension, compression and torsion. A new technique involved applying small and defined compressive strains to filaments by bonding them to one side of a beam which is subsequently bent to compress the fibres. Using scanning electron and optical microscopy, fibres were shown to form regularly-spaced helical kink bands at 50 to 60° to the fibre axis after the application of small axial compressive strains. Tensile tests of previously-compressed fibres revealed only a 10% loss in tensile strength, after application of as much as 3% compressive strain. A torsion pendulum apparatus was used to measure the shear modulus and an apparent shear strength of fibres. A loss of tensile strength after the application of large (> 10%) torsional shear strains coincided with a loss in recoverable shear strain due to longitudinal fibre splitting. Ratios of tensile-to-compressive strength, tensile-to-shear strength and tensile-to-shear moduli of 5∶1, 17∶1, and 70∶1, respectively, were measured for Kevlar 49.
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Deteresa, S.J., Allen, S.R., Farris, R.J. et al. Compressive and torsional behaviour of Kevlar 49 fibre. J Mater Sci 19, 57–72 (1984). https://doi.org/10.1007/BF02403111
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DOI: https://doi.org/10.1007/BF02403111