Experimental Research On The Drilling Tool's Thermal Characteristics During Lunar Surface's Drilling And Sampling

Lunar soil drilling is one of the most important tasks of the lunar surfaceexploration in our country. It is vitally important to ensure the thermal safety duringthe drilling. Regarding the adverse environment on the moon, such as high vacuum,high and low temperature, etc., the thermal characteristics of drilling tool in drillingprocedure were studied in this paper, as well as the simulation on temperature riseof drilling tool itself and its heat transfer to the lunar soil simulant, which wasaimed at ensuring the thermal safety and reliability of the drilling tool.The lunar soil thermal conductivity model was established and its mechanismwas analyzed based on the thermal resistance theory at first. The relation betweenthe lunar soil thermal conductance and the particle surface roughness that based onthe Hertz's theory was verified by the discrete element method. For theself-similarity of the rough lunar soil surface, the fractal dimension which can beproperly described the contact outline of the lunar soil were estimated according tothe roughness of the lunar soil surface on the basis of the fractal theory. The relationcurve of lunar soil thermal contact conductance and surface roughness was drawnunder the reasonable characteristic parameter assuming that the contact deformationwas elastic.Secondly, heat conductivity coefficient measuring equipment applied heat flowmeter method was developed on the basis of the Fourier's one-dimensional heatconduction model, which could measure the heat conductivity coefficient in theenvironment of vacuum and high heat. With this equipment, the heat conductivitycoefficient of lunar soil simulant with different temperatures and vacuum degreeswere obtained, and the effects of the two factors mentioned above were analyzedthrough the results.Thirdly, the simulation on the heat conduction of drilling tool on the process ofsampling at the surface of lunar soil were carried out using discrete elementsoftware. The models with four morphologies of lunar soil were established. Thereasonable physical parameters were set according to the lunar soil the character.Additionally, the heat of lunar soil transmitting from drill tool was measured by thesimulation result of heat transfer form in the lunar soil and the further summary ofthe temperature distribution regularity.Finally, the thermal properties of drilling tool were studied by the experimentemploying the all-parameter drill sampling experiment table. The drilling test wascarried out using sampling drilling tool, and the different cases of temperature rise on the different position of drill end and side face were monitored in real time byfiber grating sensors. The changes of temperature rise with the rotate speed anddepth speed of the drilling tool were summarized, which reveal the temperature risecharacteristics of the drilling tool during the drilling process.