Equivalent boundary model of lunar soil drilling simulation by DEM

Aiming to solve the computational cost problem in the discrete element simulation for lunar soil drilling sampling, an equivalent boundary method was proposed. A high-accuracy DEM model of lunar soil was established firstly. As the novel alterable constitutive law, the accuracy of the model was verified to meet the performance of real lunar soil very much both in shear strength indices and elastic–plastic behavior. A common drill bit in the geological exploration field for sampling soil was chosen as the simulation object. In preanalysis, it was known that with the increase of drilling depth, the stress concentration area was always near the drill bit, while the affected area of the lunar soil was a cylindrical area around the drill pipe, which extended towards the drilling direction instead of extending around it. Then a big boundary drilling simulation scene was established to investigate the flow direction of lunar soil particles. The motion law of particles and the velocity field information were obtained, and a U-shape chain was described around the drill bit. Finally an equivalent boundary was set near the U-shaped chain, and the size was determined by comparing the soil stress in the fierce collision zone and around the reference boundary. This method could be a reference for other lunar soil drilling researches with other drills of different sizes.