NHTSA Tire Aging Test Development Project Phase 2-Evaluation of Laboratory Tire Aging Methods.

摘要

As a result of the TREAD Act of 2000, NHTSA initiated an effort to develop a laboratory-based accelerated service life test for light vehicle tires (often referred to as a tire aging test). It is believed that if such a test method was successful, then light vehicle tires could eventually be required to meet standards that would make them more resistant to operational degradation and possibly reduce their failure rate during normal highway service. The first phase of test development examined how six tire models changed during service by measuring their roadwheel performance levels and material properties after varying lengths of service and accumulated mileages in Phoenix, Arizona. This report documents the second phase of test development in which new tires of the models collected from service in Phoenix were subjected to one of three laboratory aging test methods and compared to the results of the service-aged tires. Two of the laboratory tire aging methods evaluated were combined roadwheel aging and durability tests that were fully developed when provided by tire manufacturers for evaluation. The third was a tire oven aging method undergoing development by a vehicle manufacturer that would significantly accelerate the degradation of the tire materials prior to a structural evaluation, such as a post-oven roadwheel durability test. Canonical correlation showed that the properties of the tire components tended to change in the same direction with both increased time in service in Phoenix and increased time in each of the laboratory aging methods. All of these changes are consistent with the proposed mechanism of thermo-oxidative aging. In general, the longest roadwheel test times showed the same level of change in properties as tires with 1 to 3 years of service in Phoenix. Oven aging at the most severe conditions tended to show the same level of change in properties as tires with 3 to over 6 years of service in Phoenix. However, oven aging alone could not reproduce the modulus properties in the belt-packages of certain tire models without a pre-oven roadwheel-break-in of the tire. Also, after 6 weeks of oven aging, the oxygen-enriched tire inflation gas had decreased from an initial average of approximately 45% O2 to approximately 35% O2, resulting in the onset of oxygen-deprived aging (i.e., not representative of service aging). Therefore, future oven aging test development will include periodic venting and re-inflation of the tires with fresh oxygen-enriched gas.