Performance of narrow tillage tools with inertial and strain rate effects

Abstract

Conservation tillage practices have replaced traditional plowing and conventional seedbed tillage in some dry areas in Western Canada and the USA. The planter or seed drill is an important piece of equipment used in crop production systems. Because of time constraints and large cropped areas, high-speed seeding operations are desirable. However, the increased draft and power requirements associated with high operating speeds are major factors limiting the speeds at which it is feasible to use tillage tools. Dynamic effects on soil-tool cutting forces are important when operating at elevated speeds. The rate-dependent behaviour of narrow tillage tools was investigated in this study. A 9-m long linear monorail system was developed to carry narrow tools through a linear soil bin at high speeds. Steady-state speeds from 0.5 to 10.0 m/s over 1 to 3 m were attained using this system. The performance of tools with rectangular, triangular and elliptical cross sections were studied. Experimental measurements showed a linear increase of draft with increasing operating speed, for all tool shapes. Power input per operating depth and soil pulverization also increased with an increase in tool speed. Elliptical, triangular and flat tool shapes presented the lowest to highest draft requirements, respectively. A hypoelastic soil constitutive relationship with variable Young's modulus and Poisson's ratio was developed to describe the dynamic soil-tool cutting problem. Inertial effects were initially included in the stiffness matrix; however, doing this introduced numerical oscillations, even for small tool displacements ($