存在衰减和真实气体效应的激波管激波速度的计算

用一般理论计算激波管参数,由于激波的衰减不可避免以及一定压力下的气体是非理想气体,故会有不小误差。本分别考虑了衰减和真实气体效应这两种对激波速度有影响的因素,对一种具有良好压力平台的激波管（驱动气体为Ｈ２,被驱动气体为ＣＯ２）中的激波速度进行了计算。首先采用考虑真实气体效应的理论,计算破膜后形成的初始激波速度;在激波沿管运行理论不能准确计算的阶段,采用由实验得出的激波衰减公式进行计算。计算结果与     

Effective temperature rise during propagation of shock wave and high-speed deformation in metals

Two theoretical models are developed for the calculations of temperature rise during high-speed deformation and shock wave propagation. In the first model the calculations of the temperature distribution in metals during high-speed deformation are based on a model where the stationary high-speed deformation is considered as a propagation of shock wave with some fixed velocity in these metals. In this model the self-consistent system of equations describing the equation of state of metals and the conservation laws for momentum, energy and flow of energy is used for the determination of the temperature profile in the front of shock wave. The numerical calculations of the temperature distribution profile in shock wave front have been performed using the microscopic Thomas–Fermi–Dirac model for such metals as Al, Cu and Fe. In the second theoretical model the process of high-speed deformation is considered as an adiabatic process where a fraction of plastic deformation is converted into heat. The results of the numerical calculations of temperature rise during high-speed deformation in the dependence of strain to fracture are presented for metals: Al, Cu, Ni and Fe. It was shown that using these models the temperature during high-speed deformation can increase in different metals up to 1000 K.     

水下钻孔爆破的爆炸冲击波测试与分析

以厦门港古雷航道水下炸礁为例,分析了水下钻孔爆破的水击波形成特征,并通过爆破区的水中冲击波压力监测,实测了不同距离处的水击波压力大小和变化规律,研究了水中冲击波压力幅值、正压作用时间等作用特性,得到了水击波传播衰减公式。研究成果对指导工程设计施工和环境安全评估具有参考意义。     

Experimental study of λ-phase transition induced by shock compression

The λ-phase transition induced by shock compression was experimentally investigated by using the superfluid shock tube facility. A compression shock wave is generated in He II by the impingement of a gas dynamic shock wave onto a He II free surface. The shock-compressed He II can be converted to He I crossing the λ-line in the case of initial He II temperature close to T_λ. The resultant temperature variation has been measured with in-house-made superconductive temperature sensors. Furthermore, the visualization photographs were taken by a digital still camera with the Schlieren optical method. It is found that the magnitude of the entropy production Δs induced by shock compression process highly depends on the temperature difference between the temperature in the shock compressed state and the lambda temperature as well as on the shock strength. In particular, Δs becomes extremely large in the case where the λ-phase transition is induced.     

Effect of shock wave treatment on luminescence of ZnS:Cu,Cl phosphors

It is shown that shock wave treatment of ZnS:Cu phosphor between synthesis and annealing steps by placing phosphor powder into preservation ampoule and subjecting to the effect of explosion has positive effect on photo- and electroluminescence brightness due to increase of activator (copper) solubility in phosphor matrix and formation of additional Cl_S–Cu_Zn and Cl_S–V_Zn luminescent centers.     

The correct analysis of shocks in a cellular material

Cellular materials have applications for impact and blast protection. Under impact/impulsive loading the response of the cellular solid can be controlled by compaction (or shock, see Tan et al. (2005) 3 and 4) waves. Different analytical and computational solutions have been produced to model this behaviour but these solutions provide conflicting predictions for the response of the material in certain loading scenarios. The different analytical approaches are discussed using two simple examples for clarity. The differences between apparently similar “models” are clarified. In particular, it is argued that mass-spring models are not capable of modelling the discontinuities that exist in a compaction wave in a cellular material.     

The birth of dislocations in shock waves and high-speed friction

Large-scale atomistic simulations by non-equilibrium molecular dynamics have revealed that shock-wave loading and high-speed friction between dry metal interfaces have surprising similarities, in that plastic deformation occurs by the violent birth of dislocations. Shock-wave deformation is initiated at the shock front, while in sliding friction, the interface produces dislocations that move first within the plane and then out of it, so as to generate a microstructure that accommodates the slippage. For both shocks and friction in perfect, or nearly perfect, crystals, there is a threshold driving force that needs to be overcome in order to induce plastic flow. Below that threshold, pre-existing extended defects are able to trigger plastic microstructure that resembles the kind seen above the threshold. This revised version was published online in July 2006 with corrections to the Cover Date.     

Antioxidant capacity of spray-dried plant extracts: Experiments and simulations

The effects of different inlet air temperatures (70–150 °C) have been studied on the antioxidant retention and yields of a spray-dried bioactive solution (Hibiscus sabdariffa L.) from a Buchi B-290 spray dryer and compared with plug-flow spray drying simulations. Antioxidant retention has been tested using the Oxygen Reducing Antioxidant Capacity assay (ORAC). Experimentally, a peak yield of between 65% and 70% of the solids fed to the dryer has been found at an outlet gas temperature of 60–65 °C and an inlet air temperature of 110 °C, regardless of the batch of material or the liquid feed rate. The varying outlet gas temperatures did not significantly affect the antioxidant retention of the sample, and the simulations demonstrate that this result is due to the competing effects of increasing air temperature and decreasing water activity (at higher inlet air temperatures) on the degradation kinetics. These results suggest that it is more important to obtain greater product yields rather than minimising the degradation amount in this spray-drying situation.     

Synthesis and modification of materials by shock waves: real-time measurements and mechanisms of reaction

The formation of AB-type compounds under isothermal conditions is accompanied by a volume decrease. However, as a result of the heat release, there is a net increase in volume, when the reaction exothermicity is high. Exothermic reactions under high pressure lead to a volume increase of approximately 80% (alkali halogenides) to 20% (other compounds). The kinematic measurements allow the determination of the volume changes for the latter cases if the conversion degree is more than 30% because the experimental error of the volume measurements is usually 3–6%. In this article, a review of the kinematic (shock and particle velocities) shock-wave measurements of reactions in the condensed state is presented. The temperature measurements have an accuracy and time resolution of one order better than the kinematic ones. The mechanism of superfast diffusion based on a difference of the particle velocities of compounds is discussed and it is suggested that the penetration of particles through each other follows their crushing. Taking into consideration that spalling in shock waves leads to domains of 10 nm in size and assuming that chemical reactions occur on surfaces of such domains, a degree of conversion is obtained that correlates well with the experiment.     

Re-examination of the shock wave’s peak pressure attenuation in soils

The paper investigates the problem of a charge exploding in soil and focuses on the characteristics of the shock wave’s peak pressure attenuation. Analysis of existing empirical data observes different attenuation factors for apparently similar certain types of soils whereas for other types of soils there is no significant difference. It was also observed that prediction of the shock wave’s peak pressure with existing power law empirical formulas yields a large discrepancy in comparison to test data. The discrepancy is significant even in case where the specific tested soil parameters are used. These observations among others motivated this study. The power law relationship has been investigated through numerical simulations of the shock wave propagation in different soils. The soil is modeled as a bulk irreversible compressible elastic plastic medium, including full bulk locking and dependence of the current deviatoric yield stress on the pressure. The Lagrange approach and the modified variational difference methods are used to simulate the process. The study shows that the shock wave’s peak pressure attenuation for certain types of soils may be well presented by a power law with a constant exponent, whereas other types of soils may be presented by a power law for a limited distance range and their behavior for a wide distance range is poorly described by a linear relationship on a logarithmic scale but is well represented by a bi-linear or a tri-linear realtionship. These findings explain some of the above mentioned observations.     

Damage prediction of concrete gravity dams subjected to underwater explosion shock loading

The damage prediction of concrete gravity dams under blast loads has gained importance in recent years due to the great number of accidental events and terrorist bombing attacks that affected engineering safety. It has long been known that an underwater explosion can cause significantly more damage to the targets in water than the same amount of explosive in air. While the physical processes during an underwater explosion and the subsequent response of structures are extremely complex, which involve lots of complex issues such as the explosion, shock wave propagation, shock wave-structure interaction and structural response. Hence a sophisticated numerical model for the loading and material responses would be required to enable more realistic reproduction of the underlying physical processes. In this paper, a fully coupled numerical approach with combined Lagrangian and Eulerian methods, incorporating the explosion processes, is performed. The RHT (Riedel–Hiermaier–Thoma) model including the strain rate effect is employed to model the concrete material behavior subjected to blast loading. Detailed numerical simulation and analysis of a typical concrete gravity dam subjected to underwater explosion are presented in this study. In terms of different TNT charge weights, the structural response and damage characteristics of the dam at different standoff distances are investigated. Based on the numerical results, critical curves related to different damage levels are derived.     

Quantifying drying performance of a filter dryer: Experiments and simulations

Drying is one of the most commonly used unit operations in the preparation of dry granules by thermally removing volatile solvent from the wet solid. The study focuses on the quantitative investigation of heat transfer in a filter dryer in the quest to determine the optimum drying conditions. Consequently, contact drying kinetics of glassbeads–ethanol and lactose–ethanol system is investigated using an agitated filter dryer (Charles Thompson). Discrete element method is employed to simulate granular flow, mixing and heat transport in the vessel. Typical system with glass beads is numerically simulated using appropriate material properties and validated by the experimental findings. A parametric study for both simulations and experiments is performed to assess the effect of various conditions of wall temperature, fill level and impeller speed on the drying performance in the filter dryer. A high wall temperature showed an increase in the drying rate and a sharp rise in the average bed temperature, thereby decreasing the total time for drying operation. An increase in fill volume (bed depth) at constant wall temperature and speed resulted in a decline in the drying rate. The rotational speed had a nominal impact on drying of glass beads. Hence low rotational speeds seemed optimal for contact drying.     

Attenuation or enhancement—a one-dimensional analysis on shock transmission in the solid phase of a cellular material

The characteristics of compressive shock wave propagation in the solid phase of a cellular material are studied in the present paper using a one-dimensional mass-spring model. The unique compressive stress–strain relation of a cellular material leads to several interesting observations on the characteristic of one-dimensional stress wave transmission in a cellular material, which are important for understanding the blast and impact mitigation and attenuation through a cellular material. Generally, cellular material attenuates impact- or blast-induced loads by cell collapse mechanism at low impact velocities or low pulse pressure intensities when the stress transmission in a cellular material is limited by the plateau stress before the densification stage starts. This feature leads to wide applications of cellular materials in structural crashworthiness design where low speed impact is considered as potential survivable scenarios. However, scattered information has shown that stress enhancement in cellular material may occur when an intensive loading is applied, which, in contrast to the stress attenuation function of a cellular material, could produce more severe damage on the protected structures. This phenomenon is studied qualitatively in the present paper using a one-dimensional spring-mass model.     

弹性胶泥阻尼器的冲击实验研究及建模分析

通过实验与理论分析相互结合的方法,以纯硅油和不同体积比例的固体颗粒为介质的弹性胶泥阻尼器为研究对象,对各阻尼器分别进行不同高度下的冲击实验,分析在固液耦合作用下弹性胶泥阻尼器的冲击性能变化。并且在冲击实验的基础上建立阻尼器的动力学模型,通过数值方法辨识模型中方程的各参数并与实测数值进行对比。研究工作对含固体颗粒的弹性胶泥阻尼器的冲击实验分析与动力学建模以及该类阻尼器的工程应用有着理论指导意义。     

Dynamic crushing of honeycombs and features of shock fronts

The in-plane dynamic crushing of 2D hexagonal-cell honeycombs has been simulated using finite elements to explore the dynamic response of cellular materials and to investigate the features of the crushing front and to examine the assumptions employed in a one-dimensional shock theory [Reid SR, Peng C. Dynamic uniaxial crushing of wood. Int J Impact Eng 1997;19:531–70; Tan PJ, Reid SR, Harrigan JJ, Zou Z, Li S. Dynamic compressive strength properties of aluminium foams. Part II – shock theory and comparison with experimental data and numerical models. J Mech Phys Solids 2005;53:2206–30]. It has been demonstrated that progressive cell crushing is observed to propagate through the material in a ‘shock’ like manner when the crushing velocity exceeds a critical value. The simulations show that there exists a zone at the shock front across which there are essentially discontinuities in the material ‘particle velocity’, ‘stress’ and ‘strain’ as defined herein. At supercritical crushing velocities the thickness of this zone remains about one cell size, which varies little with the crushing velocity and the relative density. Densification strain increases as crushing velocity increases and asymptotes to a limit once a shock front forms. It has also been shown that the one-dimensional shock theory [Reid SR, Peng C. Dynamic uniaxial crushing of wood. Int J Impact Eng 1997;19:531–70; Tan PJ, Reid SR, Harrigan JJ, Zou Z, Li S. Dynamic compressive strength properties of aluminium foams. Part II – shock theory and comparison with experimental data and numerical models. J Mech Phys Solids 2005;53:2206–30], which was based on an equivalent rigid-perfectly plastic-locking stress–strain curve, tends to overestimate slightly the crushing stress and energy absorbed.     

Fatigue growth of short cracks in Ti-17: Experiments and simulations

The fatigue behaviour of through thickness short cracks was investigated in Ti-17. Experiments were performed on a symmetric four-point bend set-up. An initial through thickness crack was produced by cyclic compressive load on a sharp notch. The notch and part of the crack were removed leaving an approximately 50 μm short crack. The short crack was subjected to fatigue loading in tension. The experiments were conducted in load control with constant force amplitude and mean values. Fatigue growth of the short cracks was monitored with direct current potential drop measurements. Fatigue growth continued at constant R-ratio into the long crack regime. It was found that linear elastic fracture mechanics (LEFM) was applicable if closure-free long crack growth data from constant K_Imax test were used. Then, the standard Paris’ relation provided an upper bound for the growth rates of both short and long crack.The short crack experiments were numerically reproduced in two ways by finite element computations. The first analysis type comprised all three phases of the experimental procedure: precracking, notch removal and fatigue growth. The second analysis type only reproduced the growth of short cracks during fatigue loading in tension. In both cases the material model was elastic-plastic with combined isotropic and kinematic hardening. The agreement between crack tip opening displacement range, cyclic J-integral and cyclic plastic zone at the crack tip with ΔK_I verified that LEFM could be extended to the present short cracks in Ti-17. Also, the crack size limits described in the literature for LEFM with regards to plastic zone size hold for the present short cracks and cyclic softening material.     

The effect of orientation on the shock response of a carbon fibre–epoxy composite

The effect of fibre orientation on the shock response of a two-dimensional carbon fibre–epoxy composite has been studied using the technique of plate impact. In the through-thickness orientation, it appears that the material behaves as though it is a simple polymer. When one of the fibre directions is orientated parallel to the loading axis, very different behaviour is observed. The stress pulse has a pronounced ramp, before at sufficiently high stresses, a much faster rising shock occurs above it. Examination of the wave velocities suggests that the start of the ramp travels at a near constant velocity of ca. 7.0 mm μs⁻¹, whilst the shock velocity in this orientation converges with that of the shock velocity of the through-thickness orientation. Therefore, we believe that the stress pulse is separated into a fast component that travels down the fibres, with the rest travelling at the shock velocity in the matrix between the 0° fibres (epoxy plus fibres normal to the loading axis). Finally, from the Hugoniot, we observed that at low shock intensities, the 0° orientation was significantly stiffer than the through-thickness orientation. As the severity of the shock increased, the Hugoniots of the two orientations converged. Therefore, it would appear that orientation only effects the shock equation of state at lower shock stresses.     

Experiments and simulations of directionally annealed ODS MA 754

Both directional and isothermal annealing experiments have been performed on the hot-rolled ODS nickel-based superalloy MA 754. Directional annealing of MA 754 produced an elongated, coarse grain structure with a {1 1 0}1 0 0 texture for all hot-zone velocities examined, with the grain aspect ratio and twin boundary density decreasing with increasing hot-zone velocity. Isothermal annealing also produced elongated structures, but with larger grain aspect ratios and a stronger {1 1 0}1 0 0 texture. In order to elucidate the results of the experimental studies, a front-tracking computer-based model [H.J. Frost, C.V. Thompson, C.L. Howe, J.H. Whang, Scripta Metall. 22 (1988) 65–70] was modified to simulate the directional/isothermal annealing processes for materials with particles. Simulations of directional annealing with particles aligned in the direction of hot-zone movement could produce (at the appropriate hot-zone velocities) columnar grain structures with some finer grains clustered around the particles. Contrary to experimental observations, simulations of isothermal annealing in similar particle-containing material did not produce columnar grain structures, but equi-axed grains whose size was defined by the spacing between the lines of particles. Thus, the simulation results suggest that it is the texture, and not the particles, of the hot-rolled MA 754 that leads to a columnar grain structure.     

Reliability and error estimations of mechanical shock recorders and impact indicators

There have been significant developments in the electronics industry over the past decade which have led to the development of a variety of electronic measuring devices that can be placed in packages to both record and save shock and vibration data related to shipment. Most of the earlier devices were purely mechanical in nature and used a paper graph or a visual indicator to quantify shock levels. There are many of these types of mechanical devices that are still being used today because of their low cost. This study was performed to determine the reliability and error for various types of commercial mechanical shock recorders and impact indicators. The results are presented in the form of mean per cent errors in measuring shock values. The study concluded that the Impact-O-Graph recorder measured shock values more accurately than the Impact Register and that the Omni-G, Mag 2000 and Shockranger were similar in accuracy and were better than the Shockwatch when used in a variety of packages judged to be typical for instrumented shipment.     

Punch indentation of polyurea at different loading velocities: Experiments and numerical simulations

Punch indentation experiments are performed on 10 mm thick polyurea layers on a steel substrate. A total of six different combinations of punch velocity, punch size and the lateral constraint conditions are considered. Furthermore, the time integration scheme for a newly-developed rate-dependent constitutive material model is presented and used to predict the force-displacement response for all experimental loading conditions. The comparison of the simulations and the experimental results reveals that the model is capable to predict the loading behavior with good accuracy for all experiments which is seen as a partial validation of the model assumptions regarding the pressure and rate sensitivity. As far as the unloading behavior is concerned, the model predicts the characteristic stiff and soft phases of unloading. However, the comparison of simulations and experiments also indicates that the overall model response is too stiff. The results from cyclic compression experiments suggest that the pronounced Mullins effect needs to be taken into account in future models for polyurea to improve the quantitative predictions during unloading.