COMPRESSIVE PROPERTIES OF ARAMID FIBERS

A four-point bending beam method has been employed in order to study t he compressive properties of a number of well-characterized aromatic p olyamide (aramid) fibres using a combination of Raman spectroscopy and optical microscopy. Raman spectroscopy has been used to follow the mo lecular deformation of the aramid fibres in both tension and compressi on, from which the stress/strain data have been derived. The Raman tec hnique has also been used to map the variation of stress along aramid fibres in compression in order to define the regions of localized comp ressive failure indicated by the formation of visible kink bands. Usin g a combination of Raman spectroscopy and optical microscopy it is fou nd that the compressive kink band failure occurs through a process of yielding of the highly-oriented fibres in compression. The values of i nitial compressive failure strain are found to depend upon the orienta tion parameter of the molecules in the fibres and agree well with thos e predicted by a modified series model for fibre yielding. Possible me thods of improving the compressive behaviour of aramid fibres are disc ussed. (C) 1997 Elsevier Science Ltd.