The Method of Constructing the Diagrams of Shear Stresses in the Contact Zone of an Slipping Wheel With Soil 2018-01-1335

The process of interaction of the driving wheels of mobile energy resources with soil is considered. A computational and experimental method is proposed for plotting the shear stresses in the contact zone of the skid wheel with a supporting surface, based on the use of normal stresses obtained for specific ground conditions. The character of the interaction of the driving wheel of the tractor with various types of supporting base has been studied in detail: a dirt road, stubble, a field prepared for sowing. It is revealed that, contrary to the generally accepted ideas, the slipping wheel has practically no adhesion zone in the contact spot. After touching the tiller of the supporting surface, it immediately begins to shift backward. Therefore, when calculating the shear stresses in the contact patch of the skid wheel with the support, it is more correct to assume that the shift of the elementary points increases as they move away from the entrance to the contact zone and depends on the amount of slippage. When rolling the drive wheel, even with a slight slippage on the deformable surface, there is practically no bonding zone at the point of contact between the two contacting bodies (the tire and the ground). On the surface of the soil, normal stresses reach their maximum, gradually decreasing with increasing depths of its layers. With a slight slipping (up to 10 %), the maximum tangential stresses occur at the back of the contact spot - in the zone of the largest shear deformations of the soil. As the traction load increases, the tangential contact stresses are shifted to the center of the contact patch - to the zone where the deformations of the soil did not exceed the optimum level characteristic for each specific soil type. Thus, the elongation of the tire contact patch is effectively up to a certain level limited by the limiting values of shear deformation of the soil above which the tangential stresses cease to grow and even begin to decline for most types of cohesive soils. It was found that an excessive increase in shear deformation of the soil at slippage leads to a decrease in the efficiency of the wheeled propulsor.