Nonstationary deformation of an elastic plate with a notch under the action of a shock wave

The behavior of a thin elastic plate with a rectilinear notch under the action a weak shock wave in air is studied experimentally. A technique is developed for this purpose. The effect of the notch on the strain state of the plate is analyzed __________ Translated from Prikladnaya Mekhanika, Vol. 43, No. 11, pp. 99–104, November 2007.     

Mach reflection of a plane shock wave passing a mountain of 45° inclination

The transition from regular reflection (RR) to Mach reflection (MR) as a plane shock wave diffracts around a triangular mountain of 45° inclination is analysed in this paper, both by optical measurement in a shock tube and by numerical simulation the numerical method developed by Li Yingfan^[1] is of the FLIC type with triangular mesh. The dependence of the critical transition point Lk ofRR→MR on shock Mach numberM _i is analyzed and the variations of the incidence angle ω _i of the impinging shock and the reflection angle ω _r with the distanceL ^* are investigated. Our experimental and numerical results agree well with the theoretical results of Iton and Italya.     

气云爆轰的一维模型

激波作用下，悬浮液谪在高温、高压和高速气流中变形、蒸发、剥离甚至破碎。雾化燃料经过一段延迟时间后点火燃烧释放出大量的能量。这些能量由局部爆炸波所携带，通过碰撞传递给引导微波，从而使气云爆轰波自持。文中提出的气云爆轰的一维模型考虑了上述基本过程，并从理论上推导了点火面和ＣＪ面的判据。通过计算，文中讨论了气云爆轰的松弛结构和影响ＣＪ爆速的因素，爆速的计算值与实验值基本相符。     

Direct initiation of detonation in cryogenic gaseous H2-O2 mixtures

Critical conditions for the direct initiation of self-sustained detonation in cryogenic hydrogen-oxygen mixtures are examined experimentally. These initial conditions are expected to depend mainly on four parameters: the equivalence ratio of the mixture, the amount of the initial energy deposition, the initial temperature and pressure of the mixture. These critical conditions are determined by fixing alternatively three of these parameters and varying the fourth one from subcritical to supercritical detonation conditions. Results are presented for initial pressuresP _o and equivalence ratios ranging from 0.3 to 1 bar and from 1 to 2 respectively, for the two initial temperaturesT _o, 123 K and 293 K. These results indicate that for the lowest values of the initial pressure, a decrease of initial temperature may favour the onset of detonation. Whatever the initial conditions, the measured detonation pressures and velocities are in reasonably good agreement with the corresponding Chapman-Jouguet values computed using the ideal-gas equation of state.     

Flows Resulting from the Incidence of a Discontinuous Wave on a Bottom Step

The solvability of the problem of the flows resulting from the incidence of a discontinuous wave on a bottom step is studied using a single-layer shallow water model. Solutions in which the total energy of the flow is conserved at the step and those in which it is lost at the step are considered. Regions of double and triple hystereses in the obtained self-similar solutions are found. An analogy is drawn with the problem of single-layer flow over a bottom obstacle. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 2, pp. 8–22, March–April, 2006.     

Thermal and mechanical analysis of material response to non-steady ramp and steady shock wave loading

Ramp wave experiments on the Sandia Z accelerator provide a new approach to study the rapid compression response of materials at pressures, temperatures and stress or strain rates not attainable in conventional shock experiments. Due to its shockless nature, the ramp wave experiment is often termed as an isentropic (or quasi-isentropic) compression experiment (ICE). However, in reality there is always some entropy produced when materials are subjected to large amplitude compression even under shockless loading. The entropy production mechanisms that cause deformation to deviate from the isentropic process can be attributed to mechanical and thermal dissipations. The former is due to inelasticity associated with various deformation mechanisms and the rate effect that is inherent in all the deformation processes and the latter is due to irreversible heat conduction. The main purpose of the current study is to gain insights into the effects of ramp and shock loading on the entropy production and thermomechanical responses of materials. Another purpose is to investigate the role of heat conduction in the material response to both the non-steady ramp wave and steady shock.Numerical simulations are used to address the aforementioned research objectives. The thermomechanical response associated with a steady shock wave is investigated first by solving a set of nonlinear ordinary differential equations. Using the steady wave solutions as the reference, the material responses under non-steady ramp waves are then studied with numerical wave propagation simulation. It is demonstrated that the material response to ramp and shock loading is essentially a manifestation of the interaction between the time scale associated with the loading and the intrinsic time scales associated with mechanical deformation and heat transfer. At lower loading rates as encountered in ramp loading, the loading path is closer to an isentrope and results in lower entropy production. The reasonable ramp rate to obtain a quasi-isentropic state depends on the intrinsic time scales of the dissipation mechanisms which are strongly material dependent. Thus shockless loading does not necessarily produce an isentropic response. Between two equilibrium states, heat conduction was shown to have significant effect on the temperature history but it contributes little to the overall temperature change if the specific heat remains constant. It also affects the history of entropy, but only the irreversible part of heat conduction contributes to the net entropy change. The various types of thermomechanical responses of materials would manifest themselves more significantly in terms of the thermal history than the mechanical history. Thus temperature measurement appears to be an important experimental tool in distinguishing the various mechanisms for the thermomechancial responses of the materials.     

装药及外界保护介质对炸药爆轰合成超微金刚石的影响

研究了不同保护介质对超微金刚石（ＵＦＤ）生成的影响，认为爆轰产物与外部介质间的传热速度对ＵＦＤ得率影响很大；外部保护介质在爆轰产物膨胀阶段的保压作用在ＵＦＤ合成过程中有重要作用。实验结果指出，要提高ＵＦＤ得率，装药应存在一个最佳直径。用水和冰作为保护介质可使ＵＦＤ得率超过１０％，比利用马赫效应装药更适用于实际生产。     

CH4-O2 混合气中爆燃爆震转捩的数值模拟

运用化学流体力学基本理论和两步燃烧反应模型原理，建立了一维封闭体系可燃气爆燃爆震转变现象的数学模型，利用拉格朗日质量坐标变换下的Ｌａｘ－Ｗｅｎｄｒｏｆ和Ｍｅｃｏｒｍｉｃ气动差分与Ａｄａｍｓ化学差分格式，求解基本方程，成功地完成了过程的数值模拟，清楚地说明了可燃气中ＤＤＴ现象由压缩波到激波达到稳态爆震的发生机制和火焰带引生爆震波的过程行为。     

爆轰合成超细金刚石机理探讨

就爆轰合成超细金刚石的机理进行探讨:１．传统的碳相图已不能作为爆轰合成过程的依据；２．由于存在等离子体－晶体的直接相变，整个过程可能有几种相变作用共存；３．爆炸容器中的介质对产物有重要的影响。最后，提出了对整个问题进行研究所应遵循的规律。