The basis of tractor performance theory: Part 1—General laws of soil strength and deformationLes théories de base relatives aux performances d'un tracteurDie Grundlage einer theorie für das Zugkraftverhalten von traktoren

The deformation and strength characteristics of soils play an important part in the prediction of the tractive performance of tractors. The paper shows that the usual exponential laws describing stress deformation of soils can be replaced by hyperbolic functions. The hyperbolic equation derived for compressive pressure sinkage has two soil dependent parameters and the corresponding shear stress deformation equation contains three such parameters. All these parameters have a definite physical significance. These laws are used in the second part of the paper to derive expressions for the tractive effort and rolling resistance of crawler tractors.