Research On Mechanics-thermotics Characteristic Of Drill-lunar Regolith Interaction And Prediction Of The Temperature Field

Planetary sampling has great significance to exploring celestial bodies. Our research on autonomous sampling of planetary exploration is still in its infancy, and there are a number of key technologies require breakthroughs. The aim of the third phase of lunar exploration plan of China is autonomous sampling and return. The drilling-coring is one of the main ways of sampling. Given the deep-sampling, dry drilling process, high-vacuum environment of lunar surface, and the poor thermal properties of lunar soil, it is reasonable to expect that the drill bit may reach a very high temperature, which could result in structural damage to the drill bit. And it also will lead to unknown effect on lunar soil, which will directly affect the sampling quality. This dissertation study is supported by the National Science and Technology Major Project of the Ministry of Science and Technology of China to carry out research on mechanics-thermotics characteristic between drill and lunar soil and prediction of the temperature field to provide essential theoretical foundations that support optimization design of drill tool configuration and drilling parameters.Interaction between drill and lunar soil is the most common.Without regard to rock temporarily, this analysis, considering the interaction and flow characteristics between the cutting edge and lunar soil, based on metal cutting principles, determine the heat source and main heat transfer form. On this basis, aiming at specific configuration of cutting edge and boundary condition, according to the heat transfer model in an infinite object caused by a transient point heat source by Jaeger, this research try to establish thermal model for local heat transfer in cutting edge. The analytic solution for the three-dimensional heat transfer problem is derived. The theoretical model for relation between temperature rise and force is established. And the temperature field in cutting edge in drilling into pure soil can be predicted. Moreover, the drilling test bed with fiber Bragg grating temperature measuring system is built, and the verification test is performed.Interaction between drill and lunar rock will generate a lot of heat. Considering the possible lunar rock which is most likely responsible for high temperature in drilling process, and vacuum environment, this reaserch model the heat generation and temperature rise of a sampling drill in drilling lunar rock in a vacuum based on spatial and time discretizing idea. In order to improve the applicability, the model gradually considers the form of heat source, tool configuration and computing speed optimization. Finally, a fast, widely applicable for different tool configuration, drilling parameter-oriented and load-oriented numerical calculation method to predict the temperature of the sampling drill is proposed. Drilling experiments on a lunar rock stimulant in a vacuum environment are also conducted to improving and validating the model.Regarding lunar soil as discrete granular system, based on discrete element method(DEM), study key parameter for characterizing heat transfer in granular assemblies, effective thermal conductivity(ETC). Aiming at ETC, calibration for granular heat transfer parameters in DEM is performed. The measurement testbed is developed and ETC of simulated lunar soil in normal pressure and vacuum is tested using the steady method. ETC of granular assemblies in DEM is measured using a transient method. Then, DEM heat transfer parameter calibration was performed based on Central composite design(CCD) to provide foundations for subsequent DEM simuationsSimulation study has a natural advantage on achieving complex environment and tracing Characteristics of soli or rock particles. On the base of drill temperature calculation model and DEM heat transfer parameters calibration, by redevelopment to DEM sofrware, EDEM, the simulations for drilling processes under various conditions are performed. Comparing simulation results to previous experimental results, the reliability of studing drilling thermal characteristics and temperature field prediction using DEM is verified. On this basis, the DEM simulation analysis and study on drilling thermal characteristics, drill temperature rise prediction, temperature field in lunar soil and rock are conducted. This research provides essential theoretical foundations and reference for drilling parameters optimization of drilling sampling project on lunar.