Modeling of tire-to-soil interaction on soft artificial soil

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Jjagwe, Pius
Major Professor
Tekeste, Mehari
Eisenmann, David
Mba-Wright, Mark
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Agricultural and Biosystems Engineering
Considerable progress has been made to understand the tire soil interaction process for the prediction of tractive performance using empirical, semi-empirical, and analytical method. The empirical and semi-empirical traction models utilize soil parameters estimated from measured soil penetration using ASABE cone and flat plate soil sinkage. The similitude technique was deployed in designing the plate shape and size, and their relationships to tire-soil contact characteristics for predicting Bekker’s model and Reece’s model soil parameters for prediction of motion resistance. Plate sinkage tests were used to investigate the effects of three scaled plates (size and shape) and two soil bulk density conditions (1.21 Mg/m3 and 1.41 Mg/m3) on pressure-sinkage relationships in artificial soil using a rectangular estimated tire soil shape from vertical loading of an LT235/75R15 tire (179 kPa inflation pressure and 8 kN vertical load). Pressure sinkage data showed an increase in pressure with an increase in depth but coefficients differed for the two initial soil bulk densities with the shape of the plates having no effect on the soil model parameters. A soil tool measurement system to estimate soil model parameters for Bekker and Reece semi-empirical traction models was developed. Plate size and bulk density had a significant effect (P > 0.05) on Bekker and Reece soil parameters. However, plate shape had no significant effect on the soil model parameters. Reece model provided better estimation where the magnitude of the soil model parameter (soil sinkage exponent, frictional and cohesive modulus of soil) differed for the two bulk densities. Applying Bekker and Reece models with the estimated soil model parameters and tire parameters for the single tire (LT235/75R15) vertically loaded at 6 kN and three tire inflation pressure settings (179 kPa, 227 kPa, and 283 kPa), predicted the motion resistance (relative percent error of 23%) and sinkage (relative percent error of 15%).
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