The explosive working of materials in the USSR

Abstract

The studies of the processes related to working the materials by explosive energy were initiated in the Soviet Union during the World War II. The process of armour piercing by shaped charges developed at the beginning of the twentieth century in the United States and in Germany was investigated. The investigations were carried out by a research team of Academician M. A. Lavrentiev in Kiev in 1944–1946 and several modifications of the explosive welding phenomenon were detected'. In the mid-fifties, investigation of explosive powder compaction were begun in Moscow by Professor Yu. N. Riabinin². In the early sixties, M. A. Lavrentiev undertook a large-scale research program on explosive hardening and welding in Novosibirsk¹. Later, explosive powder compaction was also included into the research program³. The first attempts to investigate the strength of the explosive chambers relate to the same period⁴.     

Force chain splitting in granular materials: A mechanism for large-scale pseudo-elastic behaviour

We investigate both numerically and analytically the effect of strong disorder on the large-scale properties of the hyperbolic equations for stresses proposed in J.-P. Bouchaud, M.E. Cates, P. Claudin, J. Phys. I 5, 639 (1995), and J.P. Wittmer, P. Claudin, M.E. Cates, J.-P. Bouchaud, Nature 382, 336 (1996); J.P. Wittmer, P. Claudin, M.E. Cates, J. Phys. I 7, 39 (1997). The physical mechanism that we model is the local splitting of the force chains (the characteristics of the hyperbolic equation) by packing defects. In analogy with the theory of light diffusion in a turbid medium, we propose a Boltzmann-like equation to describe these processes. We show that, for isotropic packings, the resulting large-scale effective equations for the stresses have exactly the same structure as those of an elastic body, despite the fact that no displacement field needs to be introduced at all. Correspondingly, the response function evolves from a two-peak structure at short scales to a broad hump at large scales. We find, however, that the Poisson ratio is anomalously large and incompatible with classical elasticity theory that requires the reference state to be thermodynamically stable. Received 13 November 2000 and Received in final form 3 January 2001     

碾压混凝土振动压实的实验研究

本文通过实验室与现场的实验,对RCC 的振动压实机理进行了研究,初步弄清RCC 层的动态特性及上层碾压对下层的作用,得到:振动压实能沿层深的衰减规律,RCC的各碾压参数之间的关系,振动碾的最佳机械参数,并阐述了RCC 的结构机理与压实过程.     

Correlation between compacity distributions in compressed Si powders and in Si sintered pellets

Resistivity measurements have been performed on silicon powder beds with different thicknesses which were submitted to uniaxial pressure (0-640 MPa). For the smallest thicknesses of the Si pellets, the pressure dependence of conductivity may be described using models based on effective medium theory or strongest stresses network. For largest Si thicknesses, it exists an inhomogeneous distribution of pressure in the granular medium as a consequence of arching effects. It is shown that the conductivity variation with Si powder thickness may be understood using a distribution of conductivity induced by the distribution of pressure. Finally, it is shown that the conductivity of the sintered Si pellets is correlated with the uniaxial compression step. Received 14 September 2001 and Received in final form 18 December 2001     

Experimental compaction of anisotropic granular media

We report on experiments to measure the temporal and spatial evolution of packing arrangements of anisotropic and weakly confined granular material, using high-resolution -ray adsorption. In these experiments, the particle configurations start from an initially disordered, low-packing-fraction state and under vertical solicitations evolve to a dense state. We find that the packing fraction evolution is slowed by the grain anisotropy but, as for spherically shaped grains, can be well fitted by a stretched exponential. For a given type of grains, the characteristic times of relaxation and of convection are found to be of the same order of magnitude. On the contrary, compaction mechanisms in the media strongly depend on the grain anisotropy.     

Testing the Edwards hypothesis in spin systems under tapping dynamics

The Edwards hypothesis of ergodicity of blocked configurations for gently tapped granular materials is tested for aaabstract models of spin systems on random graphs and spin chains with kinetic constraints. The tapping dynamics is modeled by considering two distinct mechanisms of energy injection: thermal and random tapping. We find that ergodicity depends upon the tapping procedure (i.e. the way the blocked configurations are dynamically accessed): for thermal tapping ergodicity is a good approximation, while it fails to describe the asymptotic stationary state reached by the random tapping dynamics. Received 30 November 2001     

X射线荧光光谱法测定土壤污染样品中9种重金属

采用粉末压片法制样,利用理学ZSX PrimusⅡX射线荧光光谱仪,用国家标准物质土壤(GSS系列)、沉积物(GSD系列)、环境保护部标准样品研究所研制的土壤标准样品GSB Z 50011-88(黑钙土)、GSB Z 50012-88(棕壤)、GSB Z 50013-88(红壤)、GSB Z 50014-88(褐土)、湖南污染土壤标准(GBW0732729)做标准样品,建立XRF方法测定农业地质土壤污染物样品中的Cu、Pb、Cr、Ni、Zn、Co、As、Mn、V这9种重金属元素的方法,采用经验系数法校正谱线重叠干扰和基体校正。用3个土壤考核样和环境保护部标准样品研究所研制的GSB07-3272-2015作为样品评估该方法的准确度和精密度,结果符合《全国土壤污染状况详查土壤样品分析测试方法技术规定》中上述元素的规定检测方法质量要求。     

DEM simulations of die filling during pharmaceutical tabletting

The flow behaviour of powders from a stationary shoe into a moving die, which mimics the die filling process in a rotary tablet press, was analysed using a discrete element method (DEM), in which 2D irregular shaped particles were considered. The influence of the particle shape,size and size distribution, the number of particles used in the simulation, the initial height of powder bed in the shoe, and the filling speed on the average mass flow rate and the critical filling speed (the highest speed at which the die can be completely filled) were explored. It has been found that a maximum flow rate is obtained at the critical filling speed for all systems investigated and poly-disperse systems have higher mass flow rates and higher critical filling speeds than mono-disperse systems. In addition, the powder with particles which can tessellate generally has a lower filling rate and a lower critical filling speed.     

爆炸压实过程中颗粒碰撞问题的SPH法数值模拟

 目前采用SPH无网格方法对大变形问题进行数值模拟已成为计算机仿真技术的研究热点。利用LS-DYNA程序中的SPH法对粉末爆炸压实过程中颗粒的碰撞问题进行了数值模拟。在二维及三维模型下,模拟出了微射流的产生及孔隙塌缩闭合过程,验证了粉末压实理论。另外还利用三项式状态方程及Rankine-Hugoniot关系推导得出了LS-DYNA中采用的高压下固体材料的Grüneisen状态方程。