月壤临界尺度颗粒运移特性对钻采阻力影响研究

Influences of critical fragment migration characteristics of lunar soil on drilling resistance

临界尺度颗粒是指平均直径大于或等于钻头取芯孔直径的月球土壤颗粒,其广泛分布于月球次表层土壤中。在钻进过程中受到钻削作用,一部分临界尺度颗粒被从孔底置出,并被嵌入钻孔壁产生孔壁置入现象,从而增大了切削负载功耗;另一部分跟随钻具回转无法被取芯孔采集,从而增加了钻进失败的风险。通过建立月壤临界尺度颗粒切削模型,考虑临界尺度颗粒粒径及其与切削刃相互作用位置,对切削阻力的影响进行敏感度分析,得到位置的变化对切削阻力影响最明显。提出法向重叠率的概念,用以研究位置变化对临界尺度颗粒运移特性及切削阻力的影响关系。将切削刃的回转运动等效为直线运动,采用离散元方法验证法向重叠率对切削阻力的影响,得到法向重叠率与临界尺度颗粒孔底置出和孔壁置入现象之间的关系,以及对应的切削阻力时域变化曲线的特征。通过临界尺度颗粒运移特性模拟试验,得到法向重叠率与切削阻力呈同方向的线性关系,当临界尺度颗粒分别产生孔底置出和孔壁置入现象时,对应的切削阻力时域曲线特征分别为连续峰值和仅有一个峰值点。研究可为月球采样任务中的钻进工况参数识别提供理论依据。

The critical fragment refers to the lunar soil particles with average diameter greater than or equal to the diameter of coring bit hole,which is widely distributed in lunar subsurface soil.On one hand,due to the drilling effect in the drilling process,some of the critical fragments are placed from the bottom of the hole and embedded into the borehole wall to produce the hole wall insertion phenomenon,thus increasing consumption of the cutting load power.On the other hand,the others cannot be collected by the coring hole following the rotation of the drilling tool,thus increasing the risk of drilling failure.Firstly,the critical fragment cutting model for lunar soil is established,the particle size of the critical fragment and its interaction position with cutting edge are considered,the sensitivity of cutting resistance is analyzed,and it is obtained that the change of position has the most obvious influences on cutting resistance.Then,the concept of normal overlap ratio is put forward to study the influences of position change on the migration characteristics and cutting resistance of the critical fragment.The rotary motion of cutting edge is equivalent to the linear one,and the influences of normal overlap ratio on the cutting resistance are verified by the discrete element method,so as to obtain the relationship between the normal overlap ratio and the phenomenon of being placed from the bottom of the hole and embedded into the borehole wall to produce the hole wall insertion,as well as the characteristics of the corresponding time-domain change curve of cutting resistance.Finally,through the simulation tests on the migration characteristics of the critical fragment,it is found that the normal overlap ratio and cutting resistance have a linear relationship in the same direction.When the critical fragment produces the process of being placed from the bottom of the hole and embedded into the wall,the time-domain curve features of the corresponding cutting resistances are continuous peak points and only one peak point respectively.The above results may provide the theoretical basis for the parameter identification of drilling conditions in lunar sampling mission.