Compressive properties of aramid fibres

A four-point bending beam method has been employed in order to study the compressive properties of a number of well-characterized aromatic polyamide (aramid) fibres using a combination of Raman spectroscopy and optical microscopy. Raman spectroscopy has been used to follow the molecular deformation of the aramid fibres in both tension and compression, from which the stress/strain data have been derived. The Raman technique has also been used to map the variation of stress along aramid fibres in compression in order to define the regions of localized compressive failure indicated by the formation of visible kink bands. Using a combination of Raman spectroscopy and optical microscopy it is found that the compressive kink band failure occurs through a process of yielding of the highly-oriented fibres in compression. The values of initial compressive failure strain are found to depend upon the orientation parameter of the molecules in the fibres and agree well with those predicted by a modified series model for fibre yielding. Possible methods of improving the compressive behaviour of aramid fibres are discussed. (C) 1997 Elsevier Science Ltd.