Correlation of Rubber Properties between Field Aged Tires and Laboratory Aged Tires

Abstract

Abstract The kinetics of aging of key tire properties both in the field and in oven exposures at different temperatures has been interpreted by using a combination of empirical models and accelerated shift factors. Crosslink density and rubber modulus increase with aging while peel strength and elongation-to-break decrease. In the case of oven aging, the rate of property change increases from 40 °C to 70 °C and then decreases. In the case of field aging, the rate of property change is greatest in hotter climates such as Phoenix and is slower in cooler climates such as Detroit. Spare tires age at a rate that is ∼70% as fast as on-road tires. Below 70 °C, the rate data for all of the aging changes can be fit to an Arrenhius relationship with an activation energy of ∼69 kJ/mole, a value that is consistent with the aging process resulting from diffusion limited oxidation. The measured acceleration factor of oven aging at 70 °C relative to on-road aging in Phoenix is independent of the property change measured confirming that it is possible to chemically age tires in ovens. It takes 6–7 weeks of oven aging at 70 °C to produce a tire that is aged 4 years in Phoenix. Field results show that the rate of tire aging varies by over a factor of 5 for the different tire types and brands studied in this work. The implications for tire durability testing are discussed.