Chapter 2. Traction Mechanics. Part III. Traction Device-Soil Interface Behavior

Abstract [First paragraphs]: The tractive and turning performance of a wheel or track can be completely determined if the distributions of normal, longitudinal, and lateral stresses in the contact area are known. Moreover, pressure distributions within the soil are largely a function of the pattern of pressures on the soil surface, and only to a minor extent of the soil physical characteristics (Chancellor, 1977). Stress distributions at rigid wheel-soil interfaces are determined by soil deformation only since the effect of wheel deformation is not present, and is of particular interest as rims of cage wheels are often used under paddy soil conditions and also with hybrid systems that use tires, rollers, and wheels in some seedbed preparations. Radial and tangential interface stresses may be measured using transducers mounted on the device. Interface stresses normal to the soil surface may be measured inexpensively using transducers placed flush with the soil surface. The directions as well as magnitudes of stresses are required to completely analyze equilibrium conditions of a traction system. An additional complication when measuring tire interfacial stresses on flexible rubber tires is tracking the exact locations and orientations of the transducers once they contact the soil. This information combined with knowledge of soil deformation at the interface also offers promise for predicting soil compaction more accurately. Even if the dynamic load, travel reduction, and inflation pressure are known for a vehicle on a given soil surface, if the deformation is unknown, the stress distribution imposed by the vehicle and stresses within the soil may not be predicted accurately (Koolen and Kuipers, 1989; Wulfsohn and Upadhyaya, 1992b).