Rupture of rubber. VI. Further experiments on the tear criterion

A criterion for the tearing of rubber based on an energy balance approach, proposed previously, has been critically examined experimentally. This criterion implies that the energy required to form unit area of surface by tearing should be a constant of the material, and it can be tested by finding if tearing results from test pieces of different shapes are selfconsistent. Previous work has indicated that the criterion is approximately correct for natural rubber, and the present paper gives a much more rigorous check for a noncrystallizing and therefore more convenient material (GR-S). The results from three test pieces of widely different shapes show excellent agreement. The material used exhibited an abrupt change in the mode of tearing as the tearing energy increased through 3 × 106 ergs/cm.2, the rate of tearing suddenly increasing from about 10−2 to 10 cm./sec. This correlated with a change in the appearance of the torn surfaces from rough to smooth.