Effect of creep on the Young's modulus of aramid fibres

The effect of creep and recovery on the Young's modulus of different aramid fibres was investigated by an acoustic method. Creep leads to the growth of the Young's modulus of up to 215 GPa. Some of the difference between moduli values obtained by the acoustic and mechanical methods can be traced to fibre viscoelastic deformation. The dependence of the reciprocal Young's modulus on the creep strain is described by a straight line, the slope of which is practically independent of stress and temperature. Creep and recovery may be described as a thermoactivated transition between two energy states that have different elasticities of the polymer chain. These states are supposed to be the straightened molecule and a molecular kink.