低应力水平下CAS–1模拟月壤力学特性试验研究

"月壤采样"工程中的关键问题是,月面特殊环境条件下钻取机具与月壤之间的相互作用机制。针对CAS–1模拟月壤在低应力水平下的力学特性,开展直剪、压缩、三轴试验。研究表明:(1)低应力水平下,当孔隙比e=0.8~1.1时,黏聚力c=2.8~5.0 k Pa,内摩擦角?=39.84°~41.09°,压缩曲线表现出先上凹、再下凹的变化特征;当e=0.9~1.1时,初始压缩模量E0=12.647~3.923 MPa,应力–应变曲线分为硬化和软化阶段,软化下降速率较快,残余强度持续时间较长,应力比曲线分布集中。(2)低应力水平下,e越小,峰值偏应力/应力比越大,峰值轴向应变越小,但均在2%~5%范围,残余强度/应力比越大,持续时间越长。(3)初始切线斜率?、峰值应力比?f、残余应力比?r均与围压P0成一定对数线性关系,但在低应力水平下,?下降较慢,初始切线模量Gi(1/?)变化幅度较小,而?f与?r均下降较快。

EXPERIMENTAL STUDY OF MECHANICAL PROPERTIES OF LUNAR SOIL SIMULANT CAS–1 UNDER LOW STRESS

The interaction between the drilling machine and the lunar soil in the special environments on lunar surface has been the key issue of sampling in lunar regolith. Direct shear tests，compression tests and triaxial tests were carried out to investigate the mechanical property of lunar regolith simulant CAS–1 under the low levels of stress. The simulant was found to have the cohesion of 2.8 to 5.0 kPa and the angle of internal friction 39.84°to 41.09°when the porosity e = 0.8–1.1 at the low stress level. The compression curve was found to have a shape of concave upward firstly and then a shape of concave downward at the low stress levels. The initial compression moduli were from 12.647 to 3.923 MPa when e = 0.9–1.1. The stress-strain curve can be divided into a harden and a soften stage. The decreasing rate of the soften stage is rather fast and the duration of the residual strength is long. When the void ratio is smaller，the ratio of peak deviator stress/stress is larger，the peak axial strain is smaller and the values of peak axial strain are between 2% and 5%，the ratio of residual strength/stress is larger and the duration is longer. The initial tangent of the stress-strain curve，the peak stress ratio and the residual stress ratio vary with the compression stress logarithmically. The initial tangent decreases slowly， the initial tangent modulus changes little but the peak stress ratio and the residual stress ratio decrease rapidly.