38—Creep of Wool Fibres in Water

Abstract

Under suitable loads, creep of wool fibres in distilled water was obtained with extensions varying from 2 per cent to 30 per cent, while the duration of test varied from 1 second to a few minutes. The rate of extension of single wool fibres increased rapidly with increase of load, the temperature being kept constant. Also the rate of extension increased rapidly with increase of temperature, the load being kept constant. An empirical relation 1/l_t= a/t ☎ b was found between the extension l_t at time t, and the time t, a and b being constants, when temperature and load were kept constant. The value of a has been shown experimentally to vary with load and temperature as follows: where E' is an activation energy, F is the load, and α is a quantity independent of F which relates a to F. A two state energy model proposed by Burte and Halsey has been fitted to the results obtained up to 90 per cent of the asymptotic value of the creep extension. This model also explains the variation of the value of a with temperature and load. The value of the activation energy calculated from the model agrees with the values obtained directly from the present creep tests. Further, an explanation has been suggested for the reproducibility of the mechanical properties of wool fibres for strains less than 30 per cent.