Track-soil interaction for maximum tractive effort☆

Abstract This paper deals with the problem of evaluation of the tractive effort of tracked agricultural vehicles. Two alternative solutions by Bekker and by Cho et al. , applicable to the case of long pitch multi-wheeled vehicles, are analysed. It is shown that the “integration” solution by Bekker actually implies a smooth (no grousers) track-terrain interaction and constitutes a limiting approximation of the “summation” solution by Cho et al. The “summation” solution is consistent with the discrete character of the soil shear by the track grousers. In contrast to the “integration” approach, the “summation” traction is a function of the number of grousers along the track-terrain contact length. It is shown, however, that the numerical discrepancy between the two solutions is acceptable for tracks with a practical number of grousers. The question of the existence of an optimum vehicle slip was analysed with reference to the “integration” solution. It is shown that an optimum slip exists only in the case of “humped” shear stress-displacement curves. A criterion for the existence of an optimum slip corresponding to maximum traction is established. It is shown that both the optimum slip and the maximum traction can be evaluated by a geometric method which uses the soil shear stress-displacement curves directly.