John M. Baldwin

Accelerated aging of tires, Part II

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 agi...

Correlation of rubber properties between field aged tires and laboratory aged tires

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.

Numerical Simulation of Thermal Oxidation in Automotive Tires

Abstract A finite element kinetic model has been developed to interpret issues related to accelerated aging of tires. The model is based on the Basic Autoxidation Scheme and incorporates mass transport limitations related to diffusion of oxygen into the layered elastomer system. The extent of oxidation is calculated at different locations within the tire as a function of time and temperature. Results for aging rates due to thermal oxidation predicted by the model are compared to experimentally derived data such as crosslink density, elongation-to-break and modulus variation. Comparative results for aging rates in different regions of the tire suggest that a reasonable accelerated oven testing temperature range is 60 °C to 70 °C. Additionally, initial results for predicted aging rates for a rolling tire are presenting indicating the thermal oxidation plays a large role in tire aging.

A Finite Element Model for Oven Aged Tires

Abstract A finite element kinetic model has been developed to interpret issues related to accelerated aging of tires. The model is based on the Basic Autoxidation Scheme and incorporates mass trans...

Effect of Tire Wear on Tire Force and Moment Characteristics

Abstract In repeated physical testing of vehicles at or near their handling limit, shoulder wear occurs that is not typical of normal customer use. It has been observed for decades that this type of severe cornering induced tire wear can have a significant effect on the force and moment characteristics of tires. In this study, this shoulder wear effect was isolated by testing tires in a controlled environment and objectively assessed for a number of tires of various brands and sizes. This testing shows how a tire’s lateral force and overturning moment capacities increase significantly as the number of runs on a tire accumulates. Additionally, one particular tire make and model was placed on a vehicle to acquire 1000 miles of normal customer driving and then evaluated under the same simulated load conditions. The results confirmed that, irrespective of a tire break-in procedure, the increases in lateral forces of the tire in repeated limit handling maneuvers were a product of the test induced atypical shou...

Correlation of Laboratory Tire Endurance and Rubber Aging

Abstract Tire endurance as measured by performance on the National Highway Traffic Safety Administration (NHTSA) Stepped Up Load (SUL) test is shown to be a function of both tire construction and the extent of oxidation in the skim and wedge rubber regions of the tire, as measured by peel strength or elongation to break retention. Tire constructions can be distinguished by speed rating. Tires with higher speed ratings (> S) tend to have relatively high times-to-failure (TTF) in the SUL test and are relatively insensitive to rubber oxidation. SUL TTFs for tires with speed rating of S and lower tend to be much more sensitive to rubber oxidation. For these tires, the SUL TTF decreases linearly with aging time in the field. The rate of loss of SUL performance is proportional to the rate of loss of rubber properties. The large variability observed in the SUL results from field aged tires can be explained by the natural variability in oxidation aging rates observed for these tires. For oven aged tires, the corr...

Numerical Model for Nitrogen Tire Inflation5

Abstract The scope of this study was twofold: (1) to quantify the contribution nitrogen inflation would have on oxidative aging of tires and (2) measure the improvement nitrogen tire inflation may have on inflation pressure retention. A previously developed tool for diffusion-limited oxidation was used to simulate aging behavior at 25 and 60 °C. Oven-accelerated tire aging (60 °C) data for different inflation media was used for successful validation of the model, and it was shown that aging rates for higher oxygen concentrations tend toward a constant value. For lower temperatures, the use of nitrogen was shown to produce lower oxygen concentration in the wedge and bead regions of the tire geometry considered when compared to air inflation. By using 95% pure nitrogen (that is, the actual nitrogen concentration in the tire cavity), a 25% reduction in aging rate (for the tire wedge) and a 35% reduction in the initial flux of mass out of the tire (a measure of inflation pressure retention) were calculated.