Penetration Effect of Penetrator Geometry and Interface Friction on Rotational Penetration Resistance

A previous study by the authors showed that the rotational movement of a cylindrical cone penetrator could significantly reduce penetration resistance. The effects of penetrator geometry and penetrator-particle interface friction are studied to shed light on the design of a self-burrowing robot in this study. The penetrator-granular media interactions were investigated at different scales by using the discrete element method. Generally, the penetration force on the cone increases with the penetration depth but decreases with the relative slip velocity (the ratio between the rotational velocity and the vertical velocity, v_r/v). The penetration force on the cone increases in the sequence of square, decagon, and flat-end penetrators under the same conditions due to the cross section areas. Besides, the penetration force on the cone also increases with the interface friction. Force chain network and particle trajectory visualize the rotational effect at particle-scale with different penetrator geometries. Overall, the normalized penetration force on the cone decreases dramatically at first and then gradually with the increase of the relative slip velocity. The normalized penetration force on the cone for flat-end penetrator is higher than that for square and decagon penetrators under same relative slip velocity. The normalized penetration force on the cone decreases further with the increase of the interface friction under the same relative slip velocity.