NHTSA Tire Aging Test Development Project Phase 4: Oven Aging of Tires Followed By Testing to Failure on a Roadwheel

There were two parts to this work: (1) tire aging testing of 10 tire models using oven aging plus a stepped-up-load test, and (2) tire aging testing of 20 tire models using oven aging plus the Federal Motor Vehicle Safety Standards (FMVSS) No.139 endurance and low pressure tests During the first part of this research, 10 tire models were subjected to a 2-hour break-in on a 1.707 m roadwheel at 80 km/h, then inflated with a mixture of 50% nitrogen (N2) gas and 50% oxygen (O2) gas and aged in a circulating air oven for 3 or 5 weeks at 65°C. The fill gas was vented and refreshed weekly to maintain a sufficient supply of oxygen gas in the tire cavity to support oxidative aging. Physical properties of the critical belt edge region of the aged tires were measured and the percentage change from the new tire properties was compared to the percentage change seen in tires retrieved from service in Phoenix. All of the measured physical properties changed in the same direction as the tires from Phoenix service. Oven aging from 3 to 5 weeks at 65°C produced percentage changes in properties similar to those found in tires with 3 to 6 years of service in Phoenix. After oven aging, these 10 tire models were tested using the stepped-up-load to structural failure (SUL) roadwheel test. The running time of tires aged for 5 weeks at 65°C were similar to those of tires that had been in Phoenix service for 3 to 6 years. Five of the tire models showed failures prior to 34 hours while the load on the tires did not exceed their maximum design load. Nearly all of these failures in the passenger tires were in the critical belt edge and shoulder area. Light-truck tire failures were predominantly separations between the carcass compounds or between the innerliner and ply of the tire. During the second part of this research, oven aging followed by the FMVSS 139 endurance and low pressure test was used to evaluate the structural durability of new tires. Twenty tire models were aged and tested to determine if this was a valid test of the durability of aged tires. Tires were oven aged for 3, 4, or 5 weeks at 65°C while inflated with the 50% N2/50% O2 mixture and then tested according to the FMVSS 139 endurance and low pressure tests. All new tires completed the endurance and low pressure tests. Six of 13 passenger tire models and 3 of 7 models of light-truck tires exhibited no failures after oven aging up to 5 weeks at 65°C. Approximately 70% of the failures for passenger tires took place in the critical belt edge and shoulder region of the tire. The light-truck tire failures were predominantly separations between components in the innerliner and sidewall region, including two tires that separated in the oven during aging.