Abstract 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 61.6mm, 88.0mm and 105.7mm 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.

中文翻译：

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月球土壤钻孔取样分层信息保留特性研究

摘要 地层信息的保留特性是月壤钻探过程的重要因素之一。建立了高精度月壤DEM模型，验证了其抗剪强度指标和弹塑性行为均准确。然后建立了硬管取心和软袋取心的钻井模拟模型，提出了“表面坡度法”进行分层描述。通过拟合样品层中离散颗粒的倒U形表面，可以准确地描述每层样品的分层变化，并可以通过表面的斜率来量化分层变形的程度。此外，提出了一个精确的量化指标“失效界限”，在此基础上进行了61.6mm、88.0mm和105三个深度模拟。对两种取芯方法进行了 7mm，以评估样品有效面积随钻孔深度的变化。结果表明，硬管取芯可以更好地保护样品分层，但由于压缩而丢失了更多的样品。随着钻孔深度的增加，两种取心方法各层的分层破坏越来越严重，这种现象在软袋取心中更为明显。通过对速度场的分析，中间层的分层容易被破坏，顶层的粒子运动更趋于混乱。结果表明，硬管取芯可以更好地保护样品分层，但由于压缩而丢失了更多的样品。随着钻孔深度的增加，两种取心方法各层的分层破坏越来越严重，这种现象在软袋取心中更为明显。通过对速度场的分析，中间层的分层容易被破坏，顶层的粒子运动更趋于混乱。结果表明，硬管取芯可以更好地保护样品分层，但由于压缩而丢失了更多的样品。随着钻孔深度的增加，两种取心方法各层的分层破坏越来越严重，这种现象在软袋取心中更为明显。通过对速度场的分析，中间层的分层容易被破坏，顶层的粒子运动更趋于混乱。