Simulation of Icy Lunar Regolith and Experiment on its Shear Strength
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摘要:为获得月球永久阴影区中冻土的剪切强度特性，分析了月球冻土的矿物成分、粒径分布、干密度、含水率、赋存温度等物理特性，提出了月球冻土的模拟物制备与参数检测方法。基于变角剪切试验（VAST）方法，开展了斜长质和玄武质原料混配、干密度1.71 g/cm 3（相对密实度100%）、含水率3.7～9.5 wt%、温度低于–180℃的模拟月球冻土剪切强度测试。实验结果表明：模拟月球冻土在低围压下的剪切破坏模式以剪断面上的脆性断裂为主，随围压升高，模拟月球冻土的脆性降低、延性增加，破坏模式转变为整体压剪破坏，表观剪切强度下降；按直线型莫尔–库伦准则对模拟月球冻土在低围压下的剪切强度参数计算，结果显示其内聚力随含水率增加而近似线性增加，内摩擦角基本不随含水率变化，取值在50°～53°。
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关键词:
- 月球冻土（ILR）/
- 模拟月壤（LRS）/
- 变角剪切试验（VAST）/
- 剪切强度/
- 莫尔-库伦理论
Abstract:In order to obtain the shear strength of icy lunar regolith (ILR) in the permanently shadowed region (PSR) of the Moon, the physical properties of ILR such as mineral composition, particle size distribution, dry density, water content, and deposition temperature are analyzed, and a method for ILR simulant preparing and parameters testing is proposed. Based on the variable angle shear test (VAST) method, shear strength tests of ILR simulant were conducted with a mixed raw material made of anorthosite and basalt, dry density of 1.71g/cm 3(i.e. 100% relative density), water content from 3.7wt% to 9.5wt%, and temperature below –180°C. The result shows that the shear damage mode of the ILR simulant under low confining pressure is dominated by brittle fracture on the shear surface, but with the increase of the confining pressure, the brittleness of the ILR decreases and the ductility increases. In this case, its damage mode changes to compression-shear damage, and the shear strength decreases. the shear strength parameters of the ILR simulant under low confining pressure are calculated according to the linear Mohr-Coulomb criterion. The results show that the cohesion increases linearly with the increase of the water content, but the internal friction angle hardly varies with water content, taking values between 50° and 53°. -
图 6陪样传感预置与温升标定
Fig. 6Sensor preset and temperature rise calibration by companion samples
图 7试样温升–时间曲线标定结果
Fig. 7Calibration results of the temperature rise of the companion samples
图 11模拟月球冻土变角剪切试验载荷–位移曲线
Fig. 11Load-displacement curve of ILR simulant in variable-angle shear test
图 12模拟月球冻土变角剪切试验破坏应力
Fig. 12Damage stress of ILR simulant in variable-angle shear test
图 14低正应力下模拟月球冻土剪切强度参数与含水率关系
Fig. 14The relationship between shear strength parameters and water content of the ILR simulant under low normal pressure
表 1混配模拟月壤与Apollo 16样品化学成分对比
Table 1Comparison on chemical composition of mixed LRS and Apollo 16 sample
成分 Apollo 16 JLU-H CUG-1A 7∶3混配 SiO2 45.10 65.15 48.32 60.10 Al2O3 26.80 19.28 16.01 18.30 CaO 15.60 6.45 7.39 6.73 FeO 5.40 — 12.50 3.75 Fe2O3 — 1.31 — 0.92 MgO 0.60 0.06 6.95 2.13 TiO2 0.60 0.04 2.38 0.74 MnO 0.22 0.01 0.15 0.05 Na2O 0.43 4.95 0.19 3.52 K2O 0.14 2.74 2.12 2.55 P2O5 0.10 0.01 0.54 0.17 LOI 0.00 0.77 0.19 0.60 
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表 2模拟月壤原料及混配后颗粒比重
Table 2Specific gravity of LRS raw materials and mixed LRS
参数 值 斜长质颗粒比重/（g·cm–3） 2.69 玄武质颗粒比重/（g·cm–3） 2.89 混配后斜长质月壤含量 70wt%（71.5 vol%） 混配后平均颗粒比重/（g·cm–3） 2.75 下载:
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表 3月壤与模拟月壤的相对密实度定义参数
Table 3Parameters for definingDrof lunar regolith and LRS
参数 原位月壤
估计值模拟原料
实测值模拟月壤
定义值颗粒比重ρs/（g·cm–3） 3.10 2.75 2.75 最小干密度ρmin/（g·cm–3） 1.30 1.28 1.15 最大孔隙比emax 1.38 1.15 1.38 最大干密度ρmax/（g·cm–3） 1.92 1.88 1.71 最小孔隙比emin 0.61 0.46 0.61 下载:
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表 4试验参数设定值及实测值
Table 4Set value and measured value of test parameters
参数 名义数值 实测数值 试样尺寸/mm 40×40×40 平均边长40.7 含水率/wt% 4，6，8.5，10 3.85±0.26，5.73±0.19，
8.07±0.17，9.47±0.25干密度/（g·cm–3） 1.71 1.714±0.016 破坏温度/℃ 低于–160 –186~–180 模具倾角/° 20，25，30，40 — 加载速率/（mm·min–1） 10 — 下载:
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表 5破坏载荷与试样参数的相关系数表
Table 5Correlation coefficients between axial load and sample parameters
参数 名义含水率 4 wt% 6 wt% 8.5 wt% 10 wt% 模具倾角 0.887 1* 0.937 2* 0.967 2* 0.902 7* 含水率 0.403 3 0.354 5 0.078 4 0.449 9 干密度 0.107 3 0.273 8 0.156 9 0.141 0 破坏温度 0.624 8 –0.019 4 0.390 6 0.346 4 下载:
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表 6解释相关系数大小的经验法则
Table 6Rule for interpreting the size of correlation coefficient
相关系数|r| 解释 0.9~1.0 极高相关性 0.7~0.9 高相关性 0.5~0.7 中等相关性 0.3~0.5 低相关性 0.0~0.3 几乎不相关 下载:
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表 7模拟月球冻土剪切强度拟合结果
Table 7Shear strength fitting results of ILR simulant
含水率/wt% 内聚力/MPa 内摩擦角/（°） 3.9 1.40±0.10 51.2±1.2 5.7 2.81±0.24 50.5±1.5 8.1 3.92±0.30 52.7±1.1 9.5 5.24±0.44 52.9±1.1 下载:
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