模拟月壤抗剪强度试验研究及离散元分析

Experimental research and discrete element analysis of shear strength of lunar soil simulants

模拟月壤作为探月工程模型试验的基床材料,其力学特性将直接影响到月球探测器、着陆器等机构的设计,而抗剪强度是其主要力学特性之一。针对软着陆模型试验所用的TJ-1模拟月壤,采用标准应力路径三轴仪对其进行静三轴试验,得到了不同相对密度、剪切速率和围压条件下模拟月壤的应力-应变关系曲线、弹性模量和抗剪强度指标值等,试验结果表明:模拟月壤具有应变软化特征并存在一定大小的表观黏聚力,峰值内摩擦角的值介于43°~51°之间;相对密度越大,应变软化特征越明显,黏聚力和内摩擦角的值都越大:在密实状态时,剪切速率越大,模拟月壤的抗剪强度指标值呈整体下降的趋势。利用PFC^(3D)软件建立三轴试验数值模型,研究了颗粒间摩擦系数、初始孔隙率以及颗粒刚度这3个细观参数对模拟月壤抗剪强度的影响,模拟结果表明:颗粒间摩擦系数是影响抗剪强度指标内摩擦角的主要因素,而初始孔隙率及颗粒刚度的影响则相对不明显;在一定数值范围内,颗粒间摩擦系数越大,内摩擦角的值越大,两者近似呈线性关系。

The mechanical properties of lunar soil simulant which is used as the bed material of the model test for the lunar exploration,directly affect the design of structures like lunar probe and lander,and the shear strength is one of the main mechanical properties.To determine the mechanical properties of TJ-1 lunar soil simulant used in soft-landing model tests,a series of triaxial tests with triaxial apparatus under standard stress path is carried out to obtain its stress-strain relationship curves for different relative densities,shear rates and confining pressures.The result shows that,TJ-1 lunar soil simulant possesses the characteristics of strain softening and an apparent cohesive force of certain values,the peak inner frictional angle lies in the range of 43°-51°.With the increase of relative density of lunar soil simulant,the characteristics of strain softening grows more obvious and the values of cohesive force and angle of internal friction become greater;meanwhile,the values of shear strength indices decrease generally when the loading rates becomes faster.A numerical model of triaxial test using PFC^（3D） is established to study the effect of meso parameters,such as inter-particle frictional coefficient,initial porosity and particle stiffness on the shear strength indices of lunar soil simulant.The simulation turns out that the inter-particle frictional coefficient is the primary factor affecting the angle of internal friction,while the other two have less effect.Within a certain limit value,the inter-particle frictional coefficient increases approximately linearly with the angle of internal friction.