斜波压缩下锡的相变动力学特性

利用磁驱动加载装置(CQ-4)和高精度速度测试装置(DPV),开展了斜波加载下锡的动态压缩实验。实验结果表明:锡在加载阶段经历了弹塑性转变和相变等物理过程,相变压力约为7.5 GPa。β–γ相变对应的特征速度随着锡厚度的增加,从676.3 m/s减小到636.8 m/s,对应的压力从7.62 GPa降低到7.11 GPa。结合Hayes多相状态方程和非平衡相变动力学模型,对锡的斜波压缩实验过程进行了模拟,数值计算结果可以较好地描述锡在加载阶段的弹塑性转变和相变等物理过程。讨论了体模量在不同热力学过程中的物理形式,计算结果显示,斜波压缩过程需考虑压力对体模量的修正。分析了相变弛豫时间、体模量等典型物理参数对速度波形的影响,结果表明,相变弛豫时间和各相初始自由能主要影响混合区部分速度波形,γ相的体模量参数只影响相变后的速度波形,β相的体模量参数会影响整体速度波形。     

Laser anemometry measurements in a gas-solid suspension flow

A laser anemometer has been used to measure local solid particle velocities and turbulence intensities, mean particle velocity and particle wall velocity for a fully developed gas-solid suspension flowing in a vertical pipe. The technique, which does not disturb the flow and requires no calibration, can be used successfully for internal pipe flow measurements where the solids to air mass loading ratio is below about two.     

α铁冲击相变的离散元方法

利用离散元方法结合基于无扩散相变的两相模型、热力学相容的自由能函数与有限速率相变动力学方程,模拟α铁的冲击相变过程.得到铁的相边界、冲击Hugoniot关系及自由面速度剖面,并对不同冲击压力下加卸载过程的波系传播和相互作用过程进行分析,获得了加卸载波速特征.     

Nonequilibrium processes in condensed media: Part 1. Experimental studies in light of nonlocal transport theory

Based on experimental research in shock loading of solid-state materials it is shown that among the important dynamic characteristics of the process, like spatial-temporal mass velocity profiles of shock waves, are the mass velocity variation, velocity defect, and structural instability threshold recorded in real time. Analysis of these characteristics depending on the strain rate, target thickness, and structural state of material demonstrates that conventional approaches of continuum mechanics fail to provide their adequate interpretation and simulation of shock wave processes. A new concept of shock wave processes in condensed media is proposed. The concept, being based on nonlocal nonequilibrium transport theory, allows describing the transition from elastic to hydrodynamic response of a medium depending on the loading rate and time. A nonstationary elastoplastic wave model is proposed for describing the relaxation of an elastic precursor and formation of a retarded plastic front during the wave propagation in a medium with regard to structural evolution. Analysis of the experimental data shows that the division of stresses and strains into elastic and plastic components is incorrect for shock loading.     

The incubation time criterion and the acoustic strength of sea water

The approach based on the incubation time concept is used to analyze experimental data on acoustic cavitation in degassed water and in sea water. Earlier, a similar approach proved to be effective in analyzing the cavitation due to pulse loading and in studying the dynamic strength of solids. The proposed criterion takes into account the existence of the static cavitation threshold for low-frequency loading and makes it possible to explain the growth of the cavitation threshold for high-frequency loading, as well as the appreciable spread in experimental data.     

FeMnNi合金高压加卸载历程测量和相变层裂分析

 采用VISAR和X光联合测试技术,利用等厚对称和逆向碰撞法测量了FeMnNi合金高压加卸载历程和相变层裂信息。加载过程中,FeMnNi合金样品发生α→ε相转变,相变波速大于塑性波速,在撞击面上相变波与塑性波合并成单一相变波;卸载过程中,FeMnNi合金样品可能发生了逆相变,形成了除合并相变波在自由面反射中心稀疏波R以外的两道卸载波S1和S2。等厚对称高压加载下,FeMnNi合金样品发生了二次层裂。分析中心稀疏波R、卸载波S1和S2在样品中的传播作用过程,发现样品发生冲击相变和卸载逆转变是导致其等厚对称高压加载下发生二次层裂行为的主要原因。     

Estimation of the thermal diffusivity of solids based on ‘instantaneous velocimetry’ using an interferometer

A conceptually new approach is proposed to estimate the thermal diffusivity of optically transparent solids at ambient temperature based on the ‘position-dependent instantaneous velocity’ of isothermal surfaces using a self-reference interferometer. A new analytical model is proposed using the exact solution to relate the instantaneous velocity of isothermal surfaces with the thermal diffusivity of solids. The experiment involves setting up a one-dimensional non-stationary heat flow inside the solid via step-temperature excitation to launch a spectrum of dissimilar ‘moving isothermal surfaces’ at the origin. Moving isothermal surfaces exhibit macroscale ‘rectilinear translatory motion’; the instantaneous velocity of any isothermal surface at any location in the heat-affected region is unique and governed by the thermal diffusivity of the solids. The intensity pattern produced by the self-reference interferometer encodes the moving isothermal surfaces into the corresponding moving intensity points. The instantaneous velocities of the intensity points are measured. For a given thermo-optic coefficient, the corresponding values of the isothermal surfaces are predicted to estimate the thermal diffusivity of the solids using BK7 glass as an example. Another improved method is proposed in which thermal diffusivity is estimated without measuring thermo-optic coefficient and quartz glass is utilized as a specimen. The results obtained using the proposed approaches closely match with the literature value.     

Wave velocities in shock-compressed cubic and hexagonal single crystals above the elastic limit

When solids are subjected to high-pressure shock-wave loading, multiple stress waves propagate with velocities dependent upon the elastic and inelastic compressibilities of the solid. The present paper shows that the inelastic or plastic waves in cubic and hexagonal single crystals do not necessarily propagate with the bulk sound speed as they do in isotropic elastic-plastic solids. This result is a consequence of anisotropy in the plastic deformation which depends on the slip plane orientation in the crystal and has important consequences with regard to the determination of compressibilities from shock-wave data. In particular, for wave propagation in the <110> directions of cubic crystals the departure from the bulk velocity can be significant (5–25 per cent). For wave propagation normal to the c-axis in hexagonal crystals, the plastic wave velocity also differs from the bulk sound speed (10–25 per cent). Plastic wave velocities are tabulated for a number of cubic crystals on the basis of the various slip systems common to these materials. The calculated velocities are then compared with experimental data on shock-loaded single-crystal aluminum and sodium chloride.     

弱点火条件下炸药燃烧转爆轰的数值模拟

考察颗粒炸药从传导燃烧到对流燃烧再到爆轰的过程.对装填密度为85%的HMX颗粒炸药的燃烧转爆轰过程进行数值模拟,分析传导燃烧、对流燃烧和爆轰的发展过程.点火早期燃烧速度很低,火焰面在8.16 ms之内只前进了不到0.2 mm;形成对流燃烧之后燃烧速度快速增加,只用了0.1 ms就形成了速度为8 165 m·s^-1的稳定爆轰.当炸药颗粒直径或点火压力减小时,形成稳定爆轰所需的时间增加.     

Characteristics of the relaxation to steady-state deformation in solids

The characteristics of the transient process of relaxation to steady-state deformation in solids are investigated theoretically. Various loading regimes are modeled by the method of mobile cellular automata. It is shown that the stressed state in a material is highly inhomogeneous in the relaxation stage; this property, in turn, can produce stable structures in the velocity field of the material particles and influence the evolution of deformation in later stages. Zh. Tekh. Fiz. 67, 34–37 (September 1997)     

Phase segregation in driven diffusive systems

Driven diffusive models describe an array of atoms in an external periodic potential, when the motion is damped due to energy exchange with the substrate. The systems of this class have wide application in modeling of charge and mass transport in solids. Recently, the driven diffusive models have been used in tribology, where the driving force emerges due to motion of one of two substrates, which are separated by a thin atomic layer. When a dc force is applied to the atoms, the system exhibits the locked-to-sliding transition. During the transition the system may split in domains of two kinds, the running domains where the atoms move with almost maximum velocity, and the immobile domains (“traffic jams”). We discuss a new model for a 1D chain, where the particles have a complex structure treated in a mean-field fashion: particle collisions are inelastic and also each particle is considered as having its own thermostat. This model exhibits a hysteresis and the “traffic jams” state even at high temperatures due to the clustering of atoms with the same velocity.     

Direct observation of the alpha-epsilon transition in shock-compressed iron via nanosecond x-ray diffraction

In situ x-ray diffraction studies of iron under shock conditions confirm unambiguously a phase change from the bcc (alpha) to hcp (epsilon) structure. Previous identification of this transition in shock-loaded iron has been inferred from the correlation between shock-wave-profile analyses and static high-pressure x-ray measurements. This correlation is intrinsically limited because dynamic loading can markedly affect the structural modifications of solids. The in situ measurements are consistent with a uniaxial collapse along the [001] direction and shuffling of alternate (110) planes of atoms, and are in good agreement with large-scale nonequilibrium molecular dynamics simulations.     

Shock wave chemistry

Abstract

Shock wave chemistry, a new scientific trend, deals with investigations of chemical aspects of the substance state under this new type of effect. Indeed, shock wave effect is not a greater imposition than pressure and temperature actions. Characteristic features of the effect are the tremendous rates of substance loading and subsequent unloading. The effects result in a substance in a strongly non- equilibrium state. The lifetime of the state is governed by the relaxation process of those phenomena which are provoked by shock waves in the substance. For instance, in the case of substance consisting of complex molecules with a large number of internal degrees of freedom, differing strongly in excitation times, all kinetic parts of the shock energy are at first absorbed by the translational degrees of freedom inside the shock wave front. Then, the energy is redistributed to the vibrational degrees of freedom. The non-equilibrium state time is not longer than the excitation time of the most slowly excited vibrational degrees of freedom (10¹⁰-10^?9 s). The same order of magnitude is the relaxation time of liquid substance polarization caused by dipolar molecules mechanically turning under the shock discontinuity zone effect. In polymers the zone turns some separate groups of polymer molecule atoms. In such a case the relaxation period, on the contrary, may last as long as it can. As far as “hot are concerned, their lifetime is determined by thermal relaxation regularities and it depends on their size. The hot spots in solids appear during the shock compression process at the sites of an imperfect substance structure. In liquids the hot spots can orighate when a shock wave front passes through negative density fluctuations. It transforms the fluctuations of very small size and of high probability into some positive temperature regions of large size and extremely low probability at equilibrium state behind the wave front. The hot spots in perfect solids (possibly in liquids too) appear due to the effect of shear stresses in shock front. Pointed and lengthy defects of solid structure occur under the effect. The lengthy defects appear in the shock wave front due to the transition from one-dimensional to volume compression. The transition takes place if the wave intensity is larger than the dynamic elastic limit of the solid under investigation. In brittle materials the transition results in their grinding into fragments and in the relative displacement of the fragments. Some liquid melted layers of substance appear between the fragments in the process of displacement. Their lifetime is also determined by the thermal relaxation regularities and probably is small. Nevertheless, the layers obviously govern the spall strength of brittle solids and promote solid-phase shock reactions. The defects created in solids by the shock effect can exist for a very long time if the solid substance residual temperature is lower than its recrystallization temperature. Therefore, solid substance treatment by shocks of proper intensity can increase their chemical reactivity.     

玻璃形成体系中的β弛豫

一定压强下对液体进行冷却,若避免晶化,则冷却中液体不可避免地转变为典型非晶态固体——玻璃.这种现象称为玻璃转变,是一种普遍存在的自然现象,涉及多体相互关联体系中众多基础理论问题.近几十年以来,玻璃转变问题的探索过程中,弛豫存在的普适性、其机理/物理图像及其对液体和玻璃性能认知的影响等一直是争论的热点.在梳理β弛豫研究进展的同时,本文尝试对未来β弛豫研究方向进行展望.     

Solids flow measurement by correlation methods

The flow velocity of the solids content in pneumatic conveyors is determined from the transit time between two fixed points. Transducers located at these points generate random signals due to the naturally occurring random flow patterns. A special correlator is used for cross-correlating the transducer output signals and for automatically tracking the transit time. The correlating device is simple enough so that a rugged, reliable and yet precise field instrument can be built. Using optical or capacitive transducers, the average velocity of the solid content is measured without obstructing the flow profile. Under certain restrictions, the mean loading and thus the volume flow can be determined from the same sensor signals also. The effect of sensor geometry on bandwidth and the choice of optimal sensor distance is discussed. Optical and capacitive sensors are compared. Illustrative experimental results are given.     

泵油饱和砂岩黏弹行为的实验研究

通过Metravib热机械分析仪, 用固定静载为100 N、 正弦波动载荷为60 N的应力-应变实验方法, 在温度为-50---175 ℃, 升温速率为1 ℃/min, 频率为1---1000 Hz的条件下, 对泵油饱和长石砂岩、 彭山砂岩样品进行单轴循环加载实验, 研究了饱和多孔岩石在弹性范围内的衰减、 耗散角、 杨氏模量和弹性波波速随温度和频率的变化规律. 取得了随频率增高饱和多孔岩石的衰减峰和耗散角峰的峰位向高温方向移动的热激活弛豫规律, 并求得弛豫峰的激活能和跃迁频率, 以饱和砂岩的特点对此作出了解释. 发现岩石中矿物离子置换时的相变内耗峰, 并用动态观点解释了该相变峰. 还获得杨氏模量和弹性波波速随温度升高而下降、 随频率增高而增大的频散效应, 随温度升高频散效应有减弱的趋势. 该研究结果对理论模型研究具有指导意义, 对地震资料的解释具有实用价值.     

Features of transition and Cherenkov radiations and the correlation between them

It is shown that transition radiation arising at the boundary of two media is being emitted as a Cherenkov one, if the phase velocity of transition radiation waves in the medium of transition radiation propagation becomes equal to the velocity of the moving radiating particle (the necessary condition for the Cherenkov radiation). The proof of this statement is based on the analysis of the transition radiation formation zone, which may become large enough and provide interference between the field of transition radiation and the own Coulomb field of the moving particle, in case when the Cherenkov radiation condition is fulfilled. As a result, the transition radiation field transforms into the Cherenkov field. The problem is considered for cases of both a waveguide and free space.     

铝的动态屈服强度测量及再加载弹性前驱波的形成机理分析

利用激光干涉测速技术(VISAR)测量LY12铝合金在20—34 GPa冲击压力下经历加载-卸载和加载-再加载过程的样品/窗口界面粒子速度剖面,采用AC方法确定了具有较高精度的动态屈服强度值.实验结果和文献发表的数据具有较好的一致性.通过以平面焊接方式制作组合飞片,克服了组合飞片在气炮发射过程中可能发生分离的技术困难,使铝的动态屈服强度测量压力范围从22 GPa扩展到了34 GPa.同时,根据对不同实验条件下的加载-再加载过程的比较,对再加载弹性前驱波的形成机理进行了讨论,认为位错是形成该现象的主要原因. 关键词： 动态屈服强度 AC方法 弹性前驱波 VISAR     

Auger electron spectroscopy - a local probe for solid surfaces

The Auger electron transition in solids is discussed under the aspect of a local excitation due to the strongly localized primary hole in an inner atomic core level. In first approximation the solid is represented by a cluster model, consisting of the excited atom and its neighbors. Using this simple model it is possible to describe the Auger electron energies, intensities and line shapes of transitions in solids in a satisfactory way. Only for the angular dependent Auger emission, characteristic long-range crystalline order has to be taken into account. It is the aim of this introductory review to point out that Auger spectra bear more information about the solid surface and particularly on its chemical bonds as has yet been exploited by surface spectroscopists.     

铝的动态屈服强度测量及再加载弹性前驱波的形成机理分析

利用激光干涉测速技术(VISAR)测量LY12铝合金在20—34 GPa冲击压力下经历加载-卸载和加载-再加载过程的样品/窗口界面粒子速度剖面，采用AC方法确定了具有较高精度的动态屈服强度值.实验结果和文献发表的数据具有较好的一致性.通过以平面焊接方式制作组合飞片，克服了组合飞片在气炮发射过程中可能发生分离的技术困难，使铝的动态屈服强度测量压力范围从22 GPa扩展到了34 GPa.同时，根据对不同实验条件下的加载-再加载过程的比较，对再加载弹性前驱波的形成机理进行了讨论，认为位错是形成该现象的主要原因.