Effect of thermal spikes on the structural characteristics of Kevlar fibres

The effect of upto six cumulative exposures to thermal spikes, each of 10 s duration, on Kevlar 49 fibres has been analysed. X-ray data show that expo sures to spikes corresponding to T's greater than or equal to 400 degreesC cause changes at the level of the crystal lattice. At and above 500 degrees C, severe surface damages such as introduction of longitudinal openings, pe el-offs and extraneous material are found to occur. The tensile properties of the spike-exposed fibres manifest changes which conform well with the st ructural changes. As in the case of prolonged thermal exposures, the spike induced effects are also controlled by two parameters, viz., the temperatur e and the duration of the cumulative exposure. The data from spike exposed fibres indicate that the thermally induced changes in the structural and te nsile characteristics get initiated at the very early stages of thermal exp osure viz., of the order of 10 s.