Study Of Drilling Load And Heat Generation Mechanisms In Icy Lunar Soil

One of the goals of the Chang’e 7 lunar exploration project is to drill into the icy lunar soil in the polar region of moon and sample it.Influenced by the extremely low temperature environment and ice,the icy lunar soil exhibits properties such as high mechanical strength and sensitivity to temperature rise.How to reasonably regulate the temperature rise of the icy lunar soil and drilling tools under the limited loading capacity,retrieve the high-fidelity icy lunar soil is a key plaguing the implementation of the project.This paper investigates the drilling load and temperature rise characteristics of icy lunar soil by conducting simulation of drilling and sampling of icy lunar soil.Based on test data,this paper analyzes the drilling force load,temperature field,distribution of heat sources and the proportional relationship between the energy distribution of cutting heat generation.In this paper,the following research work is conducted on icy lunar soil.(1)Based on the mechanical and thermal properties of icy lunar soil,a discrete element model of icy lunar soil is built.(2)This paper matches the discrete meta-mechanical parameters of icy lunar soil.(3)Based on the single tooth cutting model,this paper studies the cutting force loading and heat generation mechanism.(4)In this paper,the temperature rise simulation is verified experimentally and the sampling temperature under various drilling protocols is predicted.The tests of physical and thermal properties of the icy simulated lunar soil and its discrete element simulations were carried out.For the microscopic bonding characteristics of icy lunar soil,a secondary bonding model of icy lunar soil is innovatively proposed.The model of icy lunar soil was developed on the secondary development platform of the discrete element software EDEM.In this study,the simulated lunar soil with 5.0wt% water and temperature-180°C was studied,which was blended from basaltic and plagioclase materials.With the help of the stacking angle test and the direct shear test,the discrete element parameters of the quadratic bonding model were matched.Based on the stacking angle test,the regression equation between the discrete element parameter bonded surface energy γ and the stacking angle was established.Refer to the multi-factor analysis design process,this paper matches and optimizes the parameters in the discrete element model by using the response surface analysis method PB and CCD experimental design with the sample shear strength as the macroscopic response value.This paper proposes a simplified method for single tooth cutting of icy lunar soil,and compares the experimental and simulation results under this model.Based on the metal cutting heat distribution model,this paper proposes an evaluation index for cutting heat distribution of icy lunar soil and studies the simulation of single tooth cutting at different depths of cut and different cutting speeds.Based on the hypothesis of equivalent heat generation by mechanical energy loss of particle inelastic collision,the ratio of heat distribution of cutting of icy lunar soil is obtained.Based on the heat distribution relationship of lunar soil cutting,a simulation model of heat generation from drilling samples of icy lunar soil was established,and conducted comparative verification between simulation and experimental data.This paper studies the effects of model thermal parameters on the temperature of icy lunar soil sample in the deep spiral groove and drill bit during drilling and sampling.In addition,This paper predicts the temperature range of lunar soil samples under different thermal parameters,which could guide the implementation of the project.