月壤双轴试验的剪切带离散元数值分析

土体的破坏问题一般都是从其剪切带入手进行研究的。针对真实月壤所处的环境（无水、低重力场、低气压等）和内摩擦角较大的特点,采用最近提出的1种考虑粒间抗转动作用与粒间范德华力2个因素的月壤散粒体力学接触模型,用离散单元法模拟了柔性边界条件下月球环境（含范德华力）与地球环境（不含范德华力）2种试样的双轴压缩试验,通过试样局部变形、速度场、孔隙比及转动场的变化情况研究了2种试样剪切带形成与发展。研究结果表明,剪切带的形成是试样内部应变局部化的结果,同时也伴随着试样内部颗粒相对转动的局部化,月面环境对试样的破坏形式与性状（剪切带的倾角及厚度）有显著的影响,探月工程中必须考虑到月面环境对月壤力学性质的影响。     

用于月面车辆力学试验的模拟月壤研究

研究月面环境下的车辆地面力学,对保证月球探测车辆的正常工作具有重要意义,而用于月面车辆力学试验的模拟月壤则影响其结果的准确度与可信度。用于月面车辆力学试验的模拟月壤,以月壤样本与JSC-1模拟月壤为参考标准,以吉林辉南县火山灰为主要原料、赤铁矿砂为辅料,通过调整试样的粒径分布与赤铁矿砂含量,使模拟月壤的比重、内摩擦角、凝聚力、承压特性、粒径分布、颗粒形态、矿物组成等参数接近JSC-1模拟月壤,并在月壤样本的参数变化范围之内,表明该模拟月壤可用于月面车辆力学试验研究。     

月壤及模拟月壤微观结构的研究

为了对比研究月壤与模拟月壤的微观结构,介绍了月壤的形成作用过程和5种基本颗粒类型;通过真实月壤照片,对月壤微观结构进行了分析;利用火山灰为模拟月壤主体材料,对其成分进行了检测;对模拟月壤的火山灰颗粒进行了显微图像分析试验。结果表明,月壤存在胶结物微观颗粒,胶结物颗粒具有分支的组织形态和封闭的气泡,并且有金属铁珠存在;火山灰所含的主要成分及含量与月壤相似,经过粉碎的火山灰试样棱角较为明显,其纵横比峰值略小,稍显长条状,但与月壤比较相近,而复杂度因子则略有欠缺,说明颗粒还不够粗糙和多棱     

模拟月壤抗剪强度试验研究及离散元分析

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。     

制备TJ-1模拟月壤空心圆柱试样的新方法

针对TJ-1模拟月壤颗粒级配跨度大、粒径〉2mm．的颗粒含量多,采用常规方法制备空心圆柱试样容易出现粗细颗粒分离、试样整体不均匀的特点,提出改良型制备方法．首先采用分层欠压法与冰冻法相结合制备出孔隙比e=1．0的实心圆柱试样,并对实心样的均匀性进行评价,得到分层制备相同孔隙比的TJ-1模拟月壤均匀试样时每层试样的高度;...     

月壤水平开挖推剪阻力影响因素离散元数值分析

通过引入考虑范德华力和抗转动作用的月壤微观接触模型,采用离散单元法模拟月壤水平推剪试验(简化的土-开挖设备间相互作用模型),对月壤推剪破坏机制进行研究,分析了推剪深度、倾角和速率的影响,为真实月面环境下开挖提供参考。结果表明:推剪过程中推剪阻力首先随推剪位移增加至峰值,而后下降并趋于稳定;随推剪位移的进一步发展,推墙前方土体堆积,推剪阻力缓慢回升,推墙前土体受扰动区范围逐渐增大;当推剪面竖直时,随着推剪深度增加,推剪阻力和能量消耗增大,前方受扰动土体范围增大,破坏面为直平面;相同推剪深度下,推剪倾角越大,推剪阻力和能量消耗越小,前方扰动土体范围越小,破坏面为直平面;推剪速率越大,推剪阻力和能量消耗增大,前方扰动土体范围越大。由于月面开挖时推剪反力由机械与月面摩擦提供,考虑到开挖机械重量受空间运输能力限制,建议采用对推力(机械重量)要求低的浅层、倾斜、慢速开挖,适用于月面早期建设活动。     

黄土与其矿物颗粒表面水膜类型及其定量表征

黏性土中细粒表面水膜是影响其物理力学性质的内在因素。经典土力学一般将土粒表面水膜分为强结合水和弱结合水,即所谓双电层模型,弱结合水的存在是土具有可塑性的原因,强弱结合水的界限含水率为塑限,该模型很好地解释了黏性土的稠度变化及其有关的物理力学行为。然而,通过等温吸附试验发现,土粒表面还存在吸附水膜,对非饱和土高吸力段的物理力学特性有重要影响。为此,本文将黄土颗粒表面水膜分为单层吸附水、多层吸附水、强结合水、弱结合水和自由水5种类型。取甘肃正宁Q₂最顶层的L₂黄土试样,采用等温吸附和液限、塑限测试,对该黄土样和其中的单矿物颗粒各水膜之间的界限含水率进行了定量表征,并测试黄土试样的土水特征曲线（SWCC）,在SWCC上界定了这些界限含水率与基质吸力的关系。当水汽压很低时,土粒表面的吸力来自水的偶极分子与颗粒表面离子间的静电引力,形成单层吸附水,水膜厚度为1个水分子直径;离颗粒表面超出水分子直径的地方,吸力来自范德华力,水的偶极子相互靠拢呈定向排列,形成了多层吸附水;当土粒周围水分增加,颗粒表面未平衡掉的分子引力又可吸引更多的极化水分子,此时在吸附水的周围形成结合水,结合水又分为强结合水和弱结合水;吸附水和结合水膜以外的水为自由水。     

模拟月壤的抗剪强度特性试验

对火山玄武岩破碎后形成的6个粒组区间的试样依规范进行直剪试验,得出不同相对密度下的内聚力和内摩擦角试验数据;根据抗剪强度参数的统计结果,按Chauvenet法剔除粗差数据,并评价变异性,以提高数据的准确性和可靠度。对试样在不同的相对密度下和不同粒组区间的力学规律进行对比、研究分析后得出:模拟月壤的内聚力为0.33~5.5kPa,内摩擦角为29.1°~35.65°;抗剪强度参数与颗粒粒径、密度具有较好的线性关系;颗粒粒径决定了密度的变化范围,这导致了抗剪强度参数在密度的一定的范围内随之变化,而总的变化趋势却是由粒径来控制的。根据以上结论,按一定颗粒级配研制模拟月壤混合样,其内聚力为0.16~1.59kPa,内摩擦角为34.8°~45.5°,符合真实月壤的实际情况。可为后续的模拟月壤研制和性能评估提供参考。     

月壤中的氦-3

除了极少数非常陡峭的山脉与撞击坑和火山通道的峭壁外，整个月球表面几乎都被一层厚度不等的月尘、岩屑和岩块的混合堆积物即月壤所覆盖。由于月球无大气层等特殊环境，太阳光长驱直入，太阳风粒子直接注入到月壤细小颗粒上使月壤中富含稀有气体等太阳风粒子组分。本文在系统阐述月壤的形成过程与形成机制的基础上，分析了月壤中稀有气体的来源及其浓度与月壤的成熟度、月壤颗粒大小、月壤矿物组成和化学成分的相关关系，进而利用已有的探测数据和分析结果，对月壤中氦-3资源的开发利用前景进行了初步评估。     

嫦娥五号返回月壤微观形貌特征及其对太空风化的指示意义

研究识别嫦娥五号返回月壤样品颗粒的类型、含量、形貌、结构和成分特征,可为嫦娥五号着陆区月壤的成因与月球表面演化过程提供关键科学依据.利用扫描电镜-能谱仪、矿物自动定量分析系统和显微激光拉曼光谱仪对嫦娥五号表取月壤样品CE5C0400（YJFM00403）进行了系统研究,发现月壤颗粒组成多样,包括斜长石、单斜辉石和橄榄石等矿物、玄武岩碎屑、黏结物和玻璃球.颗粒表面和内部微观结构复杂,呈现各种破碎、表面附着堆积、微撞击坑、溅射物等形式的微米-纳米级的形貌特征.嫦娥五号月壤的微形貌特征记录了以微陨石撞击为主导的复杂太空风化过程:一方面反复的撞击作用使月壤颗粒破碎、粒度变细,另一方面撞击引发的局部熔融又使颗粒发生胶结,同时伴随含铁矿物分解形成微-纳米级单质铁颗粒.上述过程反复进行,导致月壤颗粒大小和物相组成复杂多变.      

The electrokinetic properties and flotation behaviour of apatite and calcite in the presence of dodecylamine chloride

Electrokinetic and flotation studies on apatites and calcite show that under certain conditions these minerals are floatable with dodecylamine chloride (DDACl) and the possible mode of DDACl adsorption is due to Coulombic and Van der Waals forces. The results indicate hemi-micelle formation of dodecylamine ions and suggest involvement of neutral molecular amine in the hemi-micelle structure, the critical hemi-micelle concentration being influenced by the nature of charge at the mineral surface.     

湿度影响下莫高窟壁画地仗层吸附水及吸力变化特征研究

莫高窟气候干燥,窟内壁画地仗层常处于低含水率、高吸力的状态,受到洞窟环境湿度波动的影响较大。为了进一步了解湿度影响下地仗层土体中吸附水以及吸力变化特征,本文通过蒸汽吸附法测试莫高窟不同地仗层高吸力段内的土水特征曲线,并且根据测试结果分析土体中由于范德华力与毛细凝聚作用产生的不同吸力的变化特征;同时进一步利用蒸汽吸附法测试了含NaCl地仗层土水特征曲线并探讨水汽吸附过程中渗透吸力特征;此外利用热重分析方法测试地仗层土体中在范德华力与毛细凝聚作用下所吸附水分的特征。结果表明:地仗层水汽吸附过程中土体内大部分基质吸力来自于毛细凝聚作用,土颗粒分子间范德华力仅在含水率极低的情况下为土体提供比较明显的吸力,湿度影响下地仗层水汽吸附过程中土体内渗透吸力仅在外界环境湿度大于地仗层中盐分的潮解临界湿度时才比较明显;地仗层土体所吸附的水分大部分以弱结合水形式存在,并且地仗层中澄板土含量越高,弱结合水临界含水率越大。结论可以为湿度影响下的壁画病害机理以及地仗层中水汽运移等问题的研究提供理论基础。     

Rock deformations caused by crystal growth in counter-diffusion of reagents

Experiments performed by the author indicate the possibility of vein formation in rock blocks at atmospheric pressure. The diffusing reagents may cause intensive mechanical deformation, producing cavities and fissures. The formation of fissures is the result of combined crystallization pressure, hydraulic fracturing, and wedging pressure created by thin liquid films due to Van der Waals and electrostatic forces. -- E. A. Alexandrov.     

范氏气体准静态开放式系统与气枪子波模拟

在范氏气枪模型中,理想气体准静态开放式系统方程通常被直接应用在范氏气体条件下,从而引起模拟结果的偏差。这里详细推导了范氏气体条件下准静态开放式热力学系统方程,并结合气泡振荡方程,应用四阶Runge-Kutta方法进行子波模拟。经过与实际数据对比分析,得到比原范氏气枪模型更接近实测子波的结果。     

Study on the mechanism of isotope fractionation in soil water during the evaporation process under equilibrium condition

In this study, with the method of vacuum extraction, two evaporative processes of soil water and free water under equilibrium condition were simulated. For each sample, water vapor was condensed by liquid nitrogen and was collected in four time intervals. From the analysis of hydrogen and oxygen isotopic compositions of the water collected at different times, it was discovered that the isotope fractionation of soil water also follows the mode, which is just the same as the evaporative process of free water. The relationship between the stable hydrogen and oxygen isotopes in residual water showed that the simulative evaporation line was close to the global meteoric water line (GMWL) under the equilibrium condition at about 20°C. Comparison of the two types of evaporative processes indicated that the isotope fractionation and evaporation velocity of soil water were only slightly modified by the Van der Waals force.     

Modeling study of the effects of the coagulation kernel with van der Waals forces and turbulence on the particle size distribution

In this study, variations in the size distributions due to different assumptions for the coagulation kernel are investigated. In order to evaluate how the coagulation kernel influences the form of the particle size distribution and to describe the process of the Brownian coagulation, the Brownian coagulation kernel, including the van der Waals forces, is compared with the most frequently used coagulation coefficients. Retardation should be considered for interparticle interactions for particles larger than 1μm radius. However, for particle sizes larger than 0.1 μm, the Brownian kernel is not dominant, so the retardation effect can be ignored. The inclusion of the van der Waals forces in the Brownian coagulation kernel caused a faster coagulation process in the small particle size range. Taking account of the turbulent coagulation kernel, the turbulent coagulation kernel becomes more important when the turbulent intensity is higher. The turbulent coagulation kernel affects the large particle size range and ignoring the turbulent coagulation kernel will lead to overestimation of particle number concentration in model simulation. The results of this study indicate that the inclusion of van der Waals forces or the turbulent coagulation kernel in the total coagulation kernel impacts on the modeled particle size distributions and total particle number concentration.     

Structure of sediments of kaolinite

In an assembly of clay particles placed in a fluid, each particle is typically subjected to: (1) double-layer repulsive forces; (2) van der Waals attractive forces; and (3) contact mechanical forces. The study presented here concerns an approximate, quantitative analysis of clay suspensions, with considerations to the first two - the physico-chemical forces. Using recent theories to calculate the physico-chemical forces between two clay particles in an approximate model of an assembly, the equilibrium void ratio of a clay suspension is computed. The mechanical forces are ignored in the analysis. The results serve to verify the validity of physico-chemical theories employed and help interpret experimental data more fundamentally in terms of the system variables.     

A simple model for the prediction of the deflation threshold shear velocity of dry loose particles

A very important parameter in aeolian equations is the deflation threshold shear velocity, which quantifies the instant of particle motion. In this paper, a simple model is presented for the prediction of the threshold shear velocity of dry loose particles. It has the same functional form as the widely used models of Bagnold (1941) and Greeley & Iversen (1985), but differs in its treatment of the so‐called threshold parameter. As the new expression was based on the moment balance equation used by Greeley & Iversen, it includes a function for the aerodynamic forces, including the drag force, the lift force and the aerodynamic moment force, and a function for the interparticle forces. The effect of gravitation is incorporated in both functions. However, rather than using an implicit function for the effect of the aerodynamic forces as in the Greeley & Iversen model, a constant aerodynamic coefficient was introduced. From consideration of the van der Waals' force between two particles, it was also shown that the function for the interparticle cohesion force is inversely proportional to the particle diameter squared. The model was calibrated on data reported by Iversen & White (1982). The new expression compared, at least for terrestrial conditions, very well with the Greeley & Iversen model, although it is much simpler. It was finally validated with data from wind‐tunnel experiments on different fractions of dune sand and sandy loam soil aggregates. The soil aggregates were treated as individual particles with a density equal to their bulk density. The good agreement between observations and predictions means that, when predicting mass transport of particles above a given soil, minimally dispersed particle‐size distributions should be considered rather than the granulometric composition of the soil.     

Quantification of the chemical composition of lunar soil in terms of its reflectance spectra by PCA and SVM

In the second phase of the Chang’E Program an unmanned lunar rover will be launched onto the Moon. When ground scientists get a full understanding of the chemical composition of lunar soil around the rover, they can make more detailed survey plans for the rover and various payloads onboard so as to satisfy their scientific objectives. There is an obvious relationship between the reflectance of lunar soil and its chemical characteristics. Both principal component analysis (PCA) and support vector machine (SVM) models were applied to establishing the relationship between the reflectance spectra and chemical compositions of lunar highland and mare soil samples sent back by Apollo missions 11, 12, 14, 15, 16 and 17 and measured by Lunar Soil Characterization Consortium (LSCC). PCA was used to reduce and select the features of the reflectance spectra of lunar soil samples. Then, these features were put into SVM to estimate the abundances of various chemical components in lunar soil. We also compared the results of our measurement with those obtained by the SVM model [partial least squares (PLS)] and the principal component regression (PCR) model reported in literature. Our studies showed that with the exception of TiO₂, the results of prediction of the abundances of chemical compounds in lunar soil by our model are much more reliable than those reported in literature. The reflectance spectra of lunar soil are closely related to the materials from which it was derived.