Tip angle dependence for resistive force into dry granular materials at shallow cone penetration
In relation to the interaction of the earth's surface with machines and organisms, and its engineering applications, there has been a recent increase in interest in the penetration resistive force into granular materials at shallow depths. Previous studies have proposed various models for penetration resistive forces into dry granular materials. This study focuses on the model which has a coefficient depending on the angle of repose and the increase of resistive force in proportion to the penetration volume. In the previous studies, the model has been validated for several geometries such as cylinders, cones, and spheres. However, for cones, the model has only been validated under conditions of a tip angle close to the angle of repose. In this study, the effect of cone tip angle on penetration resistive force is investigated under several conditions with different angles of repose. This study carries out cone penetration simulations using the discrete element method. For the cone geometry, five tip angles ranging from sharp to blunt (tip angles are 15, 30, 45, 60, 75 deg) are used. The simulation results show that the penetration resistive forces for blunt cones are much higher than that computed by the model. To solve the discrepancy between the model and simulation results, this study modifies the model by assuming that the stagnant zone formed in front of the cone penetrating the granular material behaves as an effective cone. Thereby, the proposed model can calculate penetration resistive forces more accurately for cones with a wider range of tip angles than in the previous model.