Accelerated Aging of Tires, Part III

Abstract

Abstract The purpose of this research is to determine the conditions whereby a new tire can be artificially aged in an accelerated manner, in order to duplicate the actual mechanism of chemical aging observed in field-aged tires. The ultimate goal of the study is to age tires to a desired level, say equivalent to 4 years old, and then test the tires in durability, high speed, and performance tests. The previous paper described various oven aging methodologies and the data analysis techniques used. This paper will build on the previously described data analysis techniques developed for elongation at break measurements and apply them to swelling ratio data and peel strength data. By utilizing the method initially developed by Gillen and modified by this laboratory for use with tires, it has been shown that the skim rubber of tires oxidatively ages at oven temperatures between 40 °C and 70 °C when mounted and inflated with either air or a blend of 50/50 N2/O2. The methodology has been successfully extended from elongation at break data to peel strength and swelling ratio data. The calculation of the Arrhenius activation energy for diffusion of oxygen through new and aged rubber was also determined. The effect of aging on permeability is to reduce the permeability of oxygen and increase the activation energy. These results have important implications when attempting to model the diffusional aging characteristics of inflated tires. The effect of changing the partial pressure of oxygen and its concomitant effect on the acceleration of aging was also investigated. The results indicate that by doubling the partial pressure of oxygen, the rate of oxidation is increased by approximately 1.5 times. This result is entirely consistent with the theory of diffusion limited oxidation.