A novel torque analysis method for drilling deep lunar soil by DEM.

• A novel torque analysis method for drilling deep lunar soil by DEM is presented. • Drilling models for the bit and stem are built separately using the idea of equivalence. • A torque synthesis method is proposed to get the basic torque at different depths. • The prediction curve of 1.4 m drilling depth was compared with the experiment curve. • This method can save the simulation time greatly for engineers to design the torque. In order to solve the torque design problem of deep lunar soil sampling using drilling, a novel torque analysis method was presented based on discrete element model (DEM). This method includes three stages: drilling simulation of the bit and stem segment, resultant torque calculation, and predicted curve fitting. First, special drilling models were designed for a bit and stem separately. A high-density equivalent particle group, boundary vibration control, pre-drilling simulation and constant pressure surface control were designed for the bit and stem drilling modelling at different depths to ensure the rationality of the model. An example of the torque synthesis process was given, and the simulation time was analyzed. Finally, the simulation predicted torque curve was plotted and compared with the experimental curve. The experimental and simulation curves show that as the drilling depth increases, the torque increases approximately linearly first and then flattens out gradually after a depth of 1 m. The consistency between the two results indicated that the proposed method was validated. Using this method, engineers can take short time to analyze the torque and design basic parameters of the drill mechanism. The problem of high experimental cost and long simulation time in torque design is solved. [ABSTRACT FROM AUTHOR]