Stress induced twinning of polydiacetylene single crystal fibres in composites

Scanning electron microscopy has been used to show that twins induced by compression of DCHD-polydiacetylene fibres occur on a single crystallographic plane. Other twinning modes appear to be prohibited by the nature of the sidegroup packing. Under the optical microscope identical twinning patterns have been observed on fibres in composite specimens where matrix shrinkage had been induced by post-curing the epoxy at 100°C. Resonance Raman spectroscopy has been used to monitor the strain in a single fibre embedded in an epoxy matrix which was subjected to uniaxial compressive stress. The initiation of twinning was found to occur when the axial strain in the fibre was approximately 0.2%.