Experimental Testing of An Off-Road Tire in Soft Soil.

UNCLASSIFIED: Distribution Statement A. Approved for public release.

The main goal of this study is to improve the understanding of the interaction between a pneumatic tire and deformable terrain. A design of experiments has been implemented, that gives insight into the effect of individual tire and soil parameters, as well as into the effect of combinations of such parameters on the tire and soil behavior. Such data is extremely relevant, providing significant information to tire manufacturers for tire design, to users for operating conditions selection, as well as providing modeling parameters for tire models. Moreover, experimental investigation of tire-soil interaction provides validation data for tire models operating under similar conditions.

In support of the validation of a soft soil tire model currently being developed at Virgina Tech under the auspices of the Automotive Research Center, experimental work has been performed on a low-speed, indoor single-wheel tester on  a terramechanics rig. The terramechanics rig provides a well-controlled environment to assure repeatable testing conditions and void vehicle component effects. The test tire for the rig is instrumented with a wireless sensory system that measures tire deflection at the contact patch; combining this system with other instruments of the rig allows accurate estimations of wheel sinkage. A methodical soil preparation procedure has rendered great data to analyze several relations, such as the drawbar pull and the sinkage dependency on slip. The data collected indicated that, when looking at the effect of individual parameters, by increasing the soil compaction, the normal load, and by decreasing the inflation pressure will result in a higher normalized drawbar pull. The combined effect of the increase in the soil compaction and the decrease in the inflation pressure yields an even higher normalized drawbar pull than for individual parameter. The sinkage has increased dramatically with the slip ratio, growing to values 3-4 times larger at high slip (70-90%) when compared to lower slip (0-5%) ratios.