Elastic Recovery and Plastic Flow in Raw Rubber

Abstract

Abstract In considering existing information on the mechanical properties of raw rubber, it is not generally possible to distinguish between the effects of elastic and of plastic deformation. In the experiments described great care was taken to secure the complete removal of elastic strain, after stretching to various extensions at different temperatures. The plastic flow increased to a maximum with increasing elongation and fell again at higher elongations, an effect attributed to the increase of crystallization with increasing extension. For rubber held extended for one hour at 25° C the flow was never greater than 2% of the original extension, and for extensions greater than 440% or less than 130% it was negligibly small. Curves showing the decay of tension at constant extension, and the recovery of length after stretching, in conjunction with the observations on plastic flow, are interpreted in terms of a theory proposed by Busse, according to which the rubber molecules are held together at certain points by cohesional linkages of low energy, some of which are broken down during stretching.