Rate-Dependent Response of Polymers to Tensile Impact

Abstract

A strain-rate-independent theory is shown to be inadequate to describe the response of polymers to tensile impact. A nylon yarn and a rubber strip were subjected to longi tudinal impact at velocities up to 100 m sec-1 and the resulting strains observed pho tographically. Rate-independent theory is used to calculate the expected results. Fundamental differences are noted between the observed and the calculated response. Particularly noted is the absence, in the observations, of shock waves that are predicted by the rate-independent theory. A technique is described for loading a sample at uniform intervals along its length, and thus increasing the strain level reached before the resulting strain wave is reflected, even though the impact velocity is limited. This technique is used to determine a critical velocity for nylon yarn. Critical velocities calculated by a method based on rate- independent theory do not agree with this determination.