Calculation, Validation and Simulation of Soil Reactions on Concave Agricultural Discs

Abstract

Abstract There are several recently developed mathematical models which quantify the geometry of the contact surfaces of agricultural discs and the soil reactions which act on them. The paper illustrates the application of these models by means of a detailed worked example which sets out a systematic calculation procedure for estimating soil reactions generated by a Mohr-Coulomb soil on a concave spherical agricultural disc of specified curvature and size. The tilted disc in this example is set with a disc angle which brings the convex disc surface into contact with the furrow wall. From a practical standpoint, this worked example incorporates the basic steps in a general computer solution for predicting the quasi-static behaviour of disc cutting elements. The predictions of the mathematical models have been evaluated against measured orthogonal force components acting on a vertical disc and a disc with three tilt angle settings. These investigations were carried out under carefully controlled laboratory conditions with the discs working loam soils. The disc angles were varied from around 10° to 80°. The model was found to predict the performance of these discs with reasonable accuracy. The best agreement between experiment and theory was found to occur at disc angle settings around 30°, this being particularly so for the draught and suction force components. The mathematical models are also used to examine the nature of the theoretical soil reaction characteristics of concave agricultural discs when operating in typical light and heavy soils. A selection of simulated performance curves are presented and these illustrate the general trends in the variation of the soil forces acting on concave discs as their angular orientation and depth of cut are varied over a comprehensive range of settings. Some unambiguous conclusions for optimising disc performance can be drawn from these simulations.