Research on the retention characteristics of the stratification information of lunar soil drilling sampling

The retention characteristics of the stratification information is one of the important factors of lunar soil drilling process. A high-accuracy DEM model of lunar soil was established and verified to be accurate both in shear strength indices and elastic-plastic behavior. Then the drilling simulation models of hard tube coring and soft bag coring were established and a “surface slope method” was proposed for stratification description. By fitting the inverted U-shaped surface of the discrete particles in the sample layer, the stratification variation of the samples in each layer can be accurately described, and the degree of stratification deformation can be quantified by the slope of the surface. Furthermore, a precise quantitative index “failure bound” was proposed, based on which, three depth simulations of 61.6 mm, 88.0 mm and 105.7 mm were carried out for the two coring methods to evaluate the variation of the effective area of the sample with drilling depth. The results showed that the hard tube coring could a bit better protect the sample stratification but more samples were lost because of compression. With the increase of drilling depth, the stratification of each layer is damaged more and more seriously in both of the two coring methods, and this phenomenon is more obvious in soft bag coring. By analyzing the velocity field, the stratification of middle layers tends to be easily damaged and the particles in top layers tend to move more chaotically.