Modeling And Modification Of Interaction Between Drilling Tools And Lunar Soil Based On Ground Test Data

The main task of the lunar exploration project after the third stage is to obtain the lunar soil samples from the moon through drilling and successfully bring back to the Earth.Drilling pressure and torque are important indicators that reflect the working state of the drilling process.In the process of drilling,the abnormal drilling pressure or the abnormal torque value can cause the sampling effect is not good or even the task fails.Therefore,in order to solve the problem of estimating drilling pressure and torque in drilling process,this paper establishes the model of interaction between drilling tool and lunar soil in the deep drilling process,through which drilling pressure and torque at different depths can be calculated according to the ratio of rotary speed and drilling speed,and gives the influence of drilling ratio on drilling pressure and torque.This model is instructive for the prediction of mechanical loading and the selection of drilling strategy.The geometrical parameters and material parameters of lunar soil particles are taken as the basic parameters,and a three-dimensional discrete element model of lunar soil particles was established.Based on the correlation properties of real lunar soil,a set of mesoscopic parameters was chosen to make that the cohesion of the model is 0.90 kPa,and the internal friction angle is 42.25?,which satisfies the real macroscopic mechanical properties.Using the calibrated discrete element model to simulate the drilling process and observing the movement of lunar particles,it can be found that,in the stable drilling stage,the lateral lunar particles do not move after a certain distance from the drilling tool.Similarly the lunar particles below the drill a certain distance will not move down with drill movement.The moon particles at the junction area of the drill bit and drill pipe will do circular motion.Therefore,it is assumed that the area of motion of the lunar soil is fixed and the state of the lunar soil at the junction area of the drill bit and drill pipe is constant.The moving lunar soil near the drill bit is divided into three areas: the density region of interaction between the driller and the lunar soil,the density region of the bit inlet and the density region of the junction of the drill bit and drill pipe.The lunar soil of the nonmoving area is natural density.According to the law of conservation of mass,the model of the density of interaction between the driller and the lunar soil is obtained,then the drilling pressure model and the torque model are obtained.The density correction coefficients were calculated according to the ground test data under the four different drilling rules,simultaneously the fitting relationship between boundary radius or the drilling pressure and the torque conversion coefficient and the drilling ratio were calculated.Finally,the model is validated by other test data.The results show that the drilling pressure and torque calculated by models are close to the experimental value,and the error is within 10%.At the same time,the model reflects the change of drilling pressure and torque in the stable drilling stage.The increase of drilling pressure showed a tendency to accelerate with the increase of depth,and torque is basically showing a uniform increase trend.At the same depth,the drilling pressure and the torque are related to the drilling ratio,the greater the drilling ratio,the smaller the drilling pressure,the greater the torque.