冲击加载下液态水的结构相变

在一级轻气炮上,利用冲击波加载技术结合光透射测量技术获得了水在1—1.6 GPa压力范围内的透射光谱.结果表明,透射光变化是由于在冲击压缩过程中,液态水结构在P=0.9 GPa左右存在的不连续引起的,与文献报道结果一致.结合热力学计算结果和水的相图表明,该变化可能是压力导致液态水由低密度到高密度态的转变所致.实验为在线研究液态水和其他分子液体的结构相变提供了新的途径和方法.     

动态加载过程中石英玻璃诱导水的快速结晶相变

在气炮加载试验中利用弹载光源原位测试技术,观测了夹于石英玻璃之间的水在动态压缩过程中的透光特性. 通过其光透射特性研究了水的冲击相变. 实验结果发现液态水在动态冲击压缩过程中, 其压力低于2 GPa 就出现透明性变差的现象,而且水的透明性下降与石英玻璃的存在有关,是一种石英诱导水的结晶相变现象.     

在石英界面处液态水的冲击结构相变

利用轻气炮加载技术和光透射测量技术, 观测了冲击加载过程中水/石英界面处的水结构变化.实验发现,冲击条件(0.5—2 GPa, 335—375 K)下水在液相区内能够发生结构改变且起始于水/石英界面,结构改变的速率和程度与石英界面的特性有关.证实在固/液相边界一定区域内的液态水,在经历高温高压状态的变化中表现出特殊的相转变现象.同时,研究表明液态水结构转变的过程区分为明显的四个动力学阶段.     

多次冲击加载-卸载路径下铁α-ε相变动力学特性研究

采用气炮作为加载手段,结合反向碰撞技术和多台阶三层组合飞片技术,通过精细的样品/窗口波剖面测量,对典型加载-卸载-再加载路径下铁的相变动力学特性进行了研究.观测到一次卸载阶段的多波结构及再加载段的双波结构.获得首次逆相变阈值约为(11.3±0.5)GPa,首次加卸载相变特征时间为30 ns;再加载相变起始压力为10—1...     

冲击压缩下金属钯的结构相变

钯作为典型高压标定材料,研究其在极端条件下的结构变化以及热力学性质具有广泛需求并充满了挑战,特别是冲击加载下钯的固-固相变过程研究仍然匮乏.本文基于嵌入原子势,使用经典分子动力学方法从原子角度揭示了冲击载荷加载下钯的结构相变路径,在0—375 GPa的压力区间观察到一系列复杂的结构转变特征,从初始的面心立方(FCC)结构,至带密排六方(HCP)结构的层错体心立方(BCC)结构,直至完全熔化.在沿<100>晶向冲击下,在70.0 GPa发现了FCC-BCC相变过程,远低于之前研究中静高压的结果.此外,还发现了冲击方向依赖的相变点,在沿着<110>及<111>晶向冲击时FCC-BCC相变压力分别增加至135.8和165.4 GPa,同时相比完美晶体,引入缺陷会使FCC-BCC相变压强值有20—30 GPa的增幅,并通过势能分布的分析予以验证.本文发现冲击加载下钯的FCC-BCC相变压力大大降低的特殊现象,为钯在高压实验等极端条件下的应用提供了新的理论认识.     

冲击加载下孔洞诱导相变形核分析

用分子动力学方法模拟了冲击加载(沿［001］向)下单晶Fe中孔洞诱导相变形核及生长过程,并分析了初始温度对这一生长过程的影响.数值模拟显示：1) 相变形核首先出现在孔洞周围的(110)和(110)面上,并分别沿［110］,［110］向和［110］,［110］向生长成片状,之后核的生长方向则变为沿〈111〉向,形成“V”形板条状新相颗粒;2) 在相同冲击压力下,初始温度为300 K时在新相晶核边缘出现许多核胚,生成的新相颗粒比60 K时明显减小.这些现象表明,孔洞诱导相变形核及生长过程沿着特定晶向进行,而初 关键词： 相变 孔洞 分子动力学     

冲击加载下孔洞诱导相变形核分析

用分子动力学方法模拟了冲击加载(沿［001］向)下单晶Fe中孔洞诱导相变形核及生长过程，并分析了初始温度对这一生长过程的影响.数值模拟显示：1) 相变形核首先出现在孔洞周围的(110)和(110)面上,并分别沿［110］，［110］向和［110］，［110］向生长成片状，之后核的生长方向则变为沿〈111〉向，形成“V”形板条状新相颗粒；2) 在相同冲击压力下，初始温度为300 K时在新相晶核边缘出现许多核胚，生成的新相颗粒比60 K时明显减小.这些现象表明，孔洞诱导相变形核及生长过程沿着特定晶向进行，而初     

冲击加载下硅烷流体的导电特性研究

采用二级轻气炮加载技术,结合低温靶和光电监测技术,研究了在多次冲击压缩状态下液态硅烷的导电特性。本文在7—56GPa压力区间获得了一组新的电阻率数据点,并结合在高压区(65—108GPa)已发表的电阻率数据,在更宽压缩区间(7—108GPa)给出了硅烷流体电阻率随压力的变化规律。结果表明,硅烷流体在7—41GPa之间具有较好电绝缘性,但在41—52GPa之间电阻率从约150Ωcm迅速下降到约1Ωcm,其降幅达到两个数量级。当压力从52GPa进一步升高到108GPa,硅烷流体的电阻率再降低了近5倍,但与低压段相比电阻率随压力变化的速率明显减小。分析lnρ~P图中数据点分布特征发现在52GPa附近出现明显拐折点。据此推测硅烷流体在该压力附近可能发生了结构相变。     

给定压力下纯铁材料的冲击相变与层裂特性研究

采用VISAR测量样品自由面速度剖面和回收样品观测分析联合技术,开展等厚对称碰撞实验,结合文献中的实验结果,研究了冲击加载压力大于纯铁材料冲击相变阈值约2~5 GPa和大于冲击相变阈值约10 GPa两种压力状态下纯铁材料的加卸载历程及各相区的变化,并从应力波相互作用的角度,指出了冲击加载压力略大于纯铁材料相变阈值约2 GPa时,等厚对称碰撞样品反常二次层裂与冲击相变及逆相变的关联机制。     

冲击加载下 FeMnNi合金相变和层裂特性实验研究

采用激光速度干涉仪(VISAR)、X射线衍射(XRD)和扫描电镜(SEM)联合测试技术,利用等厚对称加载和逆向加载实验,研究了Fe MnNi合金的冲击相变和层裂行为。结果发现:加载压力大于6.5 GPa时,Fe MnNi合金样品发生α→ε相变;中心稀疏波的卸载作用使内压力降至4~5 GPa时,Fe MnNi合金样品发生ε→α逆相变,并伴有卸载稀疏冲击波形成。分析Fe MnNi合金样品中塑性波、相变波、稀疏波和稀疏冲击波的传播作用过程,发现加载压力大于其相变应力时,等厚对称加载下Fe MnNi合金存在产生层裂行为的物理机制。     

钒的高压声速测量

采用反向碰撞方法进行了钒冲击实验,利用激光干涉测速技术对V/LiF窗口界面粒子速度剖面进行测量.通过对粒子速度剖面的分析获得了32—88 GPa压力范围内钒的高压声速.实验获得的声速-冲击压力关系在约60 GPa存在间断,表明钒发生了冲击相变.相变压力与静高压实验结果及第一性原理计算结果基本一致.     

部分道路关闭引起的交通激波特性研究

本文根据实际交通中经常遇到的交通事故或部分道路施工等情况, 建立了部分道路关闭的交通流模型. 采用平均场理论分析和确定性NS元胞自动机规则分别对模型进行解析和数值模拟, 结果表明, 系统存在三种稳定的物理状态:低密度相、激波相和高密度相, 并找到了系统发生相变的临界密度. 理论分析和数值模拟能很好地符合.     

Atomistic investigation of phase transition in solid argon induced by shock wave transmission

A molecular dynamics (MD) simulation is employed to study the phase transition process in argon induced by shock wave transmission. Deriving the relation between the shock and piston velocities, the theoretical equation of state for argon is presented. Also, argon equation of state is obtained by measuring the quantities directly from simulations to be able to detect the phase transitions. The phase transition is also detected by using argon phase diagram and free energy calculations. A comparison shows good agreement between the theoretical and MD results for the phase transitions. Based on these simulations, it is concluded that under a shock wave transmission with suitable energy, the solid argon experiences a phase transition from solid to liquid and another from liquid to supercritical fluid. By reflecting the shock wave back at the end of its passage, the whole argon may reach the supercritical state.     

Omega phase of zirconium: Formation under shock wave compressin and stability at atmospheric pressure

Abstract

The structure of Zr after shock compression in the 8–32 GPa range at initial tempertures 290 K and 90 K has been investigated by X-ray diffraction and transmission electron microscopy. ω-phase fraction vs. peak pressure and crystallographic relationship between α- and ω-phases have been obtained. A dilatometric study of Zr samples containing ω-phase has been performed.     

Liquid xenon study under shock and quasi-isentropic compression

Abstract

The shock adiabat for liquid xenon in the density range of 5.2–7.9 g/cm³ and pressure range of 8–70 GPa was investigated. The brightness temperature of a shock wave front from 5000 K to ?15,000 K, as well as the electrical conductivity behind the front from 4·10³ to 1.2·10⁵ 1/Ohm m, were measured. X-ray technique was used to measure quasi-isentropic compression of liquid xenon up to ～13 g/cm³.

The equations of state for liquid and solid phases of xenon were found. Anomalous behavior of xenon at p=8.37 g/cm³ was revealed, that is due to a structural transition.     

Synthesis of CsCl-type single-phase RuSi under shock compression

Shock recovery experiments were performed on ruthenium–silicon powder mixtures by a flyer plate impact technique. The flyer velocities were in the range of 0.46–2.73 km/s, and the incident shock pressures were calculated to be ～2.9–～40.4 GPa by the impedance matching method. The recovered samples were characterized by X-ray diffraction and scanning electron microscopy. Results indicate that shock could induce a reaction between ruthenium and silicon. The shock pressure was found to affect reaction kinetics and microstructure of the recovered sample significantly. The dynamic reaction has a threshold pressure, and the samples loaded above threshold pressure almost completely reacted to a single-phase intermetallic compound of CsCl-type RuSi. These results indicate that shock compression could be an effective way to synthesize RuSi.     

Evolution of electric response of Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 and Pb0.99[(Zr0.90Sn0.10)0.96Ti0.04]0.98Nb0.02O3 ferroelectric ceramics under shock wave compression

The objective of this work is to investigate the dependence of the electric behavior on shock pressure in Pb_0.99(Zr_0.95Ti_0.05)_0.98Nb_0.02O₃ (PZT 95/5-2Nb) and Pb_0.99[(Zr_0.90Sn_0.10)_0.96Ti_0.04]_0.98Nb_0.02O₃ (PZST) ferroelectric ceramics under shock wave compression. PZT 95/5-2Nb and PZST ceramics were subjected to high dynamic pressure generated by plate impacts. The output currents were measured under the short-circuit condition in the pressure range from 0.23 to 4.50 GPa. The evolution of the electric response exhibits three distinct regions: (1) Below the critical phase transition pressure (σ_C), alternate negative and positive piezoelectric currents are observed and the corresponding piezoelectric constant is e ₃₁. (2) Above σ_C and below the complete phase transition pressure (σ_H), released charge increases with increasing shock pressure, illustrating the transition of ferroelectric to antiferroelectric phase. (3) Above σ_H, the output current is insensitive to the shock pressure. A similar evolutionary process is also observed in hydrostatic and uniaxial stress experiments.     

Study on the propagation of coupling shock waves with phase transition under combined tension-torsion impact loading

Phase transition can strongly change the stress wave propagation features. In this paper, the characteristic wave propagation under combined tension and torsion impact loading was studied with a simplified constitutive model of phase transition considering both pressure and shear stress. The results showed that for loading from the austenitic phase to the mixed phase, the wave propagation was similar to that in the elasto-plastic materials. However, for an instantaneous loading from the austenitic phase or mixed phase directly to the martensitic phase, a coupling shock wave (CSHW) with phase transition was predicted due to the second phase strengthening effect, which has barely been studied before. Through analysis of the constitutive equations with phase transition and the discontinuity conditions of shock waves, the control equations of the generalized Hugoniot curve was obtained and the CSHW problem with phase transition was solved analytically. An independent numerical simulation of step loading along a NiTi thin walled tube suffering a combined tension-torsion impact loading was given to prove the existence of CSHW. The simulation discloses the formation mechanism of CSHW and the adjusting process of the stress state ahead of CSHW, which reflects the intrinsic characteristic of materials with strong nonlinear constitutive behavior.