Measurement of three-dimensional soil-tire contact area and its application to the prediction of traction and soil compaction

Both the tractive performance of a pneumatic tire and the resulting soil compaction depend on the geometry of the contact surface developed at the soil-tire interface and the magnitude and distribution of stresses over this interface. The deformation of a pneumatic tire operating on a rigid surface is affected by the dimensions of the tire, carcass stiffness, lug design, inflation pressure and axle load. When the same tire is operated on a deformable soil, the tire deformation is determined to some extent by the strength of the soil.;The use of the measured contact surface in predicting both traction and compaction in the soil profile was demonstrated based upon the 2- scD and 3- scD contact regions and an assumed pressure distribution over the profile. Several soil models were investigated including models based on linear elasticity, a logarithmic pressure-sinkage model, and a semi-logarithmic porosity-stress relationship to obtain the pressure distribution. Procedures for obtaining values of the soil coefficients used in these models were also proposed. Traction predictions based upon the three-dimensional surface were better than those based upon the two-dimensional surface. Compaction predictions based upon both contact surface configurations were similar except for immediately below the soil surface.;A technique for measuring the dynamic three-dimensional contact profile between a tire and deformable soil was developed. The method involves measuring incremental lateral arc lengths of the profile at discrete locations along the contact length and fitting the coefficients of a model of soil deformation at the soil-tire interface to the experimental data using a nonlinear constrained optimization algorithm (scSUMT). Two representations of the measured contact area were compared: (i) The 2- scD surface which is the union of all points on the original undeformed soil surface which undergo deformation by the tire. (ii) The 3- scD final deformed surface. Contact area measurements were made for two different sized tires at two levels of inflation pressure, dynamic load and slip in two different soil conditions.