Viscoelastic factors in the strength of elastomers under complex stress by a puncture method

Abstract Investigations of the viscoelastic aspects of the mechanical behavior of polymers have been limited almost exclusively to relatively simple conditions of homogeneous stress, that is, to tension or shear loadings. In the present work a study has been made from the viscoelastic standpoint of the response of several elastomers to a much more complex type of stress distribution arising from penetration up to failure by a cylindrical indentor for a range of temperatures and rates of penetration. The failure or “puncture point” was determined by a dip in the recorded curve of load versus depth of penetration. The puncture strength values were reduced to 25°C. by applying the ratio of absolute temperatures and plotted against the logarithm of the reciprocal of the rate of penetration. These curves were then shifted on the time scale to give a master curve after the manner of Tobolsky and of Ferry. The logarithms of the shift factors thus obtained were related to the reciprocal of the absolute temperature over the range studied. The results indicate a broader generality for the viscoelastic principle of time–temperature equivalence than has usually been supposed.