Rupture of rubber. VIII. Comparisons of tear and tensile rupture measurements

Abstract

The energy to initiate tearing at an incision with a tip of semicircular form was shown in a previous paper to be approximately equal to Ed, E being the work to break/unit volume as measured in a tensile rupture test and d the diameter of the tip of the incision. In the present paper this relation is used to compare the effects of the speed of test on tear and tensile rupture measurements. It is shown that the variation of the work to break/unit volume with the speed of test adequately accounts for the effect of the speed of test on the energy to initiate tearing at incisions with tips of semi-circular form. It is assumed that the relation applies also in continuous tearing, d being in this case the effective diameter of the tip of the tear, and it is shown that the variation of the tearing energy with the rate of tear propagation, at low and moderate rates of propagation, may be plausibly accounted for in terms of the variation of the work to break/unit volume with the speed of test and variation of the effective diameter of the tip of the tear, d. Values of d of a few tenths of a millimeter were generally required to fit the tear and tensile rupture measurements, the values being, as expected, comparable in magnitude with the irregularities in the torn surfaces. It is shown that in certain instances the values assumed for d may be confirmed by direct measurement of the diameter of the tip of the tear.