Two-Ply Laminate Fatigue Life of New, Field-Retrieved, and Laboratory-Aged Light-Vehicle Tires

This report is the seventh in a series of scientific reports intended to provide an understanding of the degradation of light vehicle tires during on-vehicle service. The report series was used to guide the agency’s development of a laboratory-based accelerated service life test for light-vehicle tires (i.e., “tire aging test”). The two-ply laminate fatigue test was one test used to quantify the level of degradation in tire belt package during on-vehicle service in Phoenix, Arizona, and to evaluate the effectiveness of proposed roadwheel tire aging methods. Preliminary data analysis showed that cycles to failure or log of cycles to failure at any of these strains had no statistically significant correlation to tire type, age, or mileage. However, since the test machine runs in “load control,” small differences in the amount of strain experienced by each sample per unit load can result in large differences in input energy (load x displacement) over the many tens or hundreds of thousands of cycles to failure. As a result, the test laboratory, ARDL, Inc., developed a new analytical technique to calculate the cycles to failure at an average energy input of 500 N-mm. This would allow for comparisons of test results between samples from the same tire, and samples from different tires. Of the six tire models collected from service in Phoenix, Arizona, only five had a sufficient number of tires available for advanced test methods such as two-ply laminate. Within these five tire models, three showed a relatively strong correlation of the “Cycles to Failure at 500 N-mm” variable to both the mileage and age variables, with a general reduction in the cycles to failure with increasing age and mileage. Excessive scatter resulted in no correlation for the other two tire models. New versions of the six tire models collected from Phoenix, Arizona, were subjected to the two-ply analysis following one of two laboratory roadwheel aging tests. Five of the six tire models showed a relatively strong correlation to time in both roadwheel tests for the Cycles to Failure at 500 N-mm, with cycles to failure decreasing with increasing test duration. In sharp contrast, the “Type B” BFGoodrich tire model, the smallest and lightest tire of the group, was almost completely insensitive to roadwheel aging. No explanation for this anomalous behavior was apparent. Overall, the results suggest that use of the two-ply laminate test in conjunction with the Average Input Energy method can be useful in determining tire belt package fatigue properties. In the end, due to the complexity and limitations of the test, as well as the variability of the results, the authors chose not to continue use of this test in subsequent phases of the project.