MECHANICS OF TILLAGE TOOLS

Tillage tools are mechanical devices that are used to apply forces to the soil to cause some desired effect such as pulverization, cutting, inversion, or movement of the soil. Tillage tools usually produce several effects simultaneously. The ultimate aim of tillage is to manipulate a soil from a known condition into a different desired condition by mechanical means. The objective of a mechanics of tillage tools is to provide a method for describing the application of forces to the soil and for describing the soil’s reaction to the forces. An accurate mechanics would provide a method by which the effects could be predicted and controlled by the design of a tillage tool or by the use of a sequence of tillage tools. Furthermore, the efficiency and economy of the tillage operation could be evaluated from the mechanics. A thorough knowledge of the basic forces and reactions is required to develop the mechanics. Such knowledge is not available at present, and soil reactions cannot even be predicted, let alone controlled. As a result, an operation is performed, the conditions are arbitrarily evaluated, and additional operations are performed in sequence until the conditions are adjudged to be adequate. Thus, today, tillage is more an art than a science. Progress has been made, however, in developing mechanics where simple tools or simple actions are involved and where forces and reactions can be described. This chapter presents several approaches that have been used to develop simple forms of soil-tillage tool mechanics. Only homogeneous soil conditions are considered. Although this approach is completely unrealistic, it does not negate the results of the studies. Complete knowledge of reactions for a homogeneous soil will provide a basis for solving problems dealing with layered soils. Interactions of importance will probably occur, but they should not present unsurmountable obstacles. The approaches discussed in this chapter do not represent any final solution of the problems that are posed. The approaches, however, do represent those that have been utilized and those that may contribute to the development of a successful mechanics of tillage tools.