大颗粒岩块对月壤钻取过程的影响分析

针对月壤钻取采样过程中存在大颗粒岩块情况进行三维离散元动态仿真分析。建立考虑扭转、弯曲力矩及等效引力作用的新型三维离散元月壤模型,通过三轴仿真试验进行细观参数标定,得到黏聚力为0.90 kPa,内摩擦角为42.25°的满足真实月壤宏观力学指标的仿真模型。针对月壤内层存在大颗粒情况设计4种采样工况分别进行仿真分析,监测大颗粒运动轨迹与采样效率,发现了“旋入效应”、“纵向运移效应”与“阻塞效应”,仿真结果表明岩块粒径大小直接影响采样结果：当岩块粒径小于钻头“虚拟切削圆”时,其无论存在于任何位置对采样效率与后续样品缠绕收集均无明显影响;当岩块粒径大于“虚拟切削圆”时,阻塞现象严重,样品收集困难,极易导致采样失败。研究结论对月壤钻取采样控制设计与钻具结构设计具有重要的工程参考价值。

Effect of large granular rocks on drilling process of lunar soils

The drilling process of lunar soils with a large granular rock under the surface is simulated dynamically by 3D discrete element method. A novel 3D discrete element model considering bending and twist moments and equivalent attractive force is established firstly, and then, a triaxial simulation test is conducted to calibrate the micro-parameters. The mechanical macro-parameters of the model are calculated as follows: the cohesion is 0.90 kPa and the internal friction angle is 42.25°, meeting with those of the real lunar soils. Four working conditions are designed and simulated respectively focusing on the case that a large granular rock exists in the lunar soils. By monitoring the sampling efficiency and the motion trajectory of the rock, the "screwing-in phenomenon", "vertical migration phenomenon" and "blocking phenomenon" are discovered. The results show that the diameter of the "large particle" influences the sampling results directly: when the particle size is smaller than the diameter of the "virtual cutting round" of the drill bit, there are no obvious effects either on the sampling efficiency or on the later winding collection; and the blocking phenomenon will appear, reducing the sampling efficiency badly and probably making the sampling task a failure. The achievements of this work have vital engineering reference value to the design of sampling controller and drill structure.