Experimental measurements are described of the conditions necessary for crack growth in an atmosphere containing ozone. It is proposed that a characteristic value of the tensile stress at the tip of an initial cut or surface flaw is required for growth to occur. This criterion is shown to predict the observed dependence of the applied stress required for crack growth on the length of an initial cut and on the surface smoothness of uncut test pieces. The number of cracks formed in an exposed edge is also shown to be in accordance with the proposed criterion. For vulcanizates of differing stiffness, the appropriate criterion is found to be the stored elastic energy. The critical value is shown to be similar for a number of different polymers, and largely unchanged by plasticization, a change in temperature from 20°C. to 50°C., and alteration in the concentration of ozone. For initial flaws consisting of sharp razor cuts, the energy required for cut propagation is found to be about 60 ergs/cm.2 of newly formed surface.
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Braden et al. (1960) studied this question.