Double Shock Research Articles

Effect of Reloading on Dynamic Recrystallization in Shock Deformed Aluminum Alloy

In order to verify influence of particle velocity non-uniformity on dynamic recrystallization (DRX), shock tests of D16 Al alloy were conducted under uniaxial strain conditions within strain-rate range of 105 ÷ 107 s-1. The particle velocity non-uniformity arises due to both initial heterogeneity and non-linearity of shock-wave process. Apart from the nature of DRX mechanism, migrational or rotational, the particle velocity non-uniformity facilitates growth of local strain, strain rate and temperature. To adjust a duration of the particle velocity non-uniformity degree, two limiting situations is provided by means of single and double shock loading (reloading). The experimental technique used allows to register both mean particle velocity profile and particle velocity variation which is the quantitative characteristic of velocity non-uniformity. Shock tests of D16 Al alloy in single and reloading regimes [ show that dynamic recrystallization takes place only in the second case. The reloading regime initiates a ten-fold increase in duration of the particle velocity non-uniformity stage, which is sufficient for fulfillment of the well-known DRX conditions: γ 3, dγ/dt 104 s1, T 0.4Tm. The regions of DRX with equal-axis grains of ~1 μm in diameter are revealed with the metallography and X-ray analysis.

Quantum molecular dynamics simulation of shock-wave experiments in aluminum

We present quantum molecular dynamics calculations of principal, porous, and double shock Hugoniots, release isentropes, and sound velocity behind the shock front for aluminum. A comprehensive analysis of available shock-wave data is performed; the agreement and discrepancies of simulation results with measurements are discussed. Special attention is paid to the melting region of aluminum along the principal Hugoniot; the boundaries of the melting zone are estimated using the self-diffusion coefficient. Also, we make a comparison with a high-quality multiphase equation of state for aluminum. Independent semiempirical and first-principle models are very close to each other in caloric variables (pressure, density, particle velocity, etc.) but the equation of state gives higher temperature on the principal Hugoniot and release isentropes than ab initio calculations. Thus, the quantum molecular dynamics method can be used for calibration of semiempirical equations of state in case of lack of experimental data.

Double shock experiments and reactive flow modeling on LX-17 to understand the reacted equation of state

Experimental data from measurements of the reacted state of an energetic material are desired to incorporate reacted states in modeling by computer codes. In a case such as LX-17 (92.5% TATB and 7.5% Kel-F by weight), where the time dependent kinetics of reaction is still not fully understood and the reacted state may evolve over time, this information becomes even more vital. Experiments were performed to measure the reacted state of LX-17 using a double shock method involving the use of two flyer materials (with known properties) mounted on the projectile that send an initial shock through the material close to or above the Chapman-Jouguet (CJ) state followed by a second shock at a higher magnitude into the detonated material. By measuring the parameters of the first and second shock waves, information on the reacted state can be obtained. The LX-17 detonation reaction zone profiles plus the arrival times and amplitudes of reflected shocks in LX-17 detonation reaction products were measured using Photonic Doppler Velocimetry (PDV) probes and an aluminum foil coated LiF window. A discussion of this work will include the experimental parameters, velocimetry profiles, data interpretation, reactive CHEETAH and Ignition and Growth modeling, as well as detail on possible future experiments.

Investigation into the behavior of a graded cellular rod under impact

Over the past few decades, functionally graded materials (FGMs) have attracted many research interests. For the cellular material, the variation of the mechanical property may significantly influence the global performance of the structure. Previously the authors have presented the basic deformation patterns in a simple case, in which only the quasi-static plateaus stress gradually decreases or increases along the rod and the density is uniform. In the current study, further investigations are carried out into the effect of the gradient in the initial density, which inherently leads to variation in the quasi-static plateau stress. A simple impact scenario is considered, in which a rigid mass strikes a stationary cellular rod with variation in the initial density of the material. Similar to the previous studies, the rigid-perfectly plastic-locking (R-PP-L) material model and the simple shock theory are employed to carry out the analysis. Current study confirms that the basic deformation modes (i.e. double shock (DS) and single shock (SS) modes) still exist in the cellular rod with density gradient. The analytical results indicate that the negative gradient weakens the capacity of energy absorption while positive gradient has little influence. Then, the effect of the initial density gradient is further investigated by considering two artificial cases with only one gradient either in the quasi-static stress or in the initial density. Finally, finite element (FE) simulations are carried out with practical metal foam in order to verify the analytical modeling.

Simultaneous Use of Two Defibrillators for the Conversion of Refractory Ventricular Fibrillation

T?>HE SIMULTANEOUS use of two defibrillators to deliver higher energy levels for the treatment of refractory arrhythmias is currently not a component of standard advanced cardiac life support (ACLS) guidelines. 1 Field J.M. Hazinski M.F. Sayre M.R. et al. Part 1: Executive summary: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2010; 122: S640-S656 Crossref PubMed Scopus (773) Google Scholar As a result, it is an underappreciated and underutilized therapy, despite case reports and series demonstrating its efficacy and safety in refractory atrial and ventricular arrhythmias. 2 Bjerregaard P. El-Shafei A. Janosik D.L. et al. Double external direct-current shocks for refractory atrial fibrillation. Am J Cardiol. 1999; 83 (A10): 972-974 Abstract Full Text Full Text PDF PubMed Scopus (34) Google Scholar , 3 Chang A.K. Lent G.S. Grinberg D. Double-dose external cardioversion for refractory unstable atrial fibrillation in the ED. Am J Emerg Med. 2008; 26 (e1-e3): 385 Abstract Full Text Full Text PDF PubMed Scopus (6) Google Scholar , 4 Hoch D.H. Batsford W.P. Greenberg S.M. et al. Double sequential external shocks for refractory ventricular fibrillation. J Am Coll Cardiol. 1994; 23: 1141-1145 Abstract Full Text PDF PubMed Scopus (59) Google Scholar , 5 Kabukcu M. Demircioglu F. Yanik E. et al. Simultaneous double external DC shock technique for refractory atrial fibrillation in concomitant heart disease. Jpn Heart J. 2004; 45: 929-936 Crossref PubMed Scopus (18) Google Scholar , 6 Marrouche N.F. Bardy G.H. Frielitz H.J. et al. Quadruple pads approach for external cardioversion of atrial fibrillation. Pacing Clin Electrophysiol. 2001; 24: 1321-1324 Crossref PubMed Scopus (25) Google Scholar , 7 Saliba W. Juratli N. Chung M.K. et al. Higher energy synchronized external direct current cardioversion for refractory atrial fibrillation. J Am Coll Cardiol. 1999; 34: 2031-2034 Abstract Full Text Full Text PDF PubMed Scopus (60) Google Scholar This brief report describes the utility of double-dose defibrillation in refractory ventricular fibrillation (VF) and further publicizes its efficacy. Erratum to “Simultaneous Use of Two Defibrillators for the Conversion of Refractory Ventricular Fibrillation” J Cardiothorac Vasc Anesth 29(2015):369-378Journal of Cardiothoracic and Vascular AnesthesiaVol. 29Issue 4PreviewIt was discovered that the original online version of the above article contained errors that were not the fault of the author(s). The Publisher decided to ‘resupply’ (repost and replace) the XML and online PDF of the article. Unfortunately the discovery of the errors was too late to correct the printed issue. Full-Text PDF

Experimental study on of dynamics of particles in the flow filed with intensive gradients

The dynamic response of particles in hyper/supersonic flow is one of the key points of techniques using tracer particles, such as particle image velocimetry (PIV). In the literature, it is validated by the single oblique shock response testing. However, particles suffer intensive variation of velocity, density and viscosity, when used to trace and measure the complex flow field in the high speed vehicle engine. To test and validate the dynamics of particles in such a flow field with intensive gradient, in this paper we conduct a series experiments dealing with this issue. The study includes the measurements on the velocity field at the exit of the wind tunnel nozzle to testify the performance of PIV system, the measurements on the oblique shock response of particles in Mach 4.2 and Mach 3.0 supersonic flows over a 10° wedge and a 15° wedge respectively, and measurements on the double oblique shock response of particles in the flow field which is designed to simulate the flow field inside the vehicle engine with gradients and without the influence of expansion wave. Based on the particle dynamic models, the relaxation time, relaxation distance, Stokes numbers of different cases can be gained. And the influence of unstable shock oscillation is analyzed and revised based on image method and statistic analysis. It can be found that the relaxation time and distance increase with the Mach number, given the same wedge degree. However, with the same incoming Mach number, the relaxation time and distance drop when the wedge degree increases. Due to the intensive variation of Reynolds number and viscosity, the results show that in a certain extent particles lose their following ability by 5.7%, while its Stokes number increases by 1%. In the flow condition herein, the Stokes number still meets the requirement of supersonic flow. However the decrease of particle following ability is worth being concerned, especially when using particles in the complex flow field with more intensive gradients.

Shock Solutions for High Concentration Particle-Laden Thin Films

We study the shock dynamics for a recently proposed system of conservation laws (Murisic et al. [J. Fluid Mech., 17 (2013), pp. 203--231]) describing gravity-driven thin-film flow of a suspension of negatively buoyant particles down an incline. When the particle concentration is above a critical value, singular shock solutions can occur. We analyze the Hugoniot topology associated with the Riemann problem for this system, describing in detail how the transition from a double shock to a singular shock happens. We also derive the singular shock speed based on a key observation that the particles pile up at the maximum packing fraction near the contact line.

Double shock front formation in cylindrical radiative blast waves produced by laser irradiation of krypton gas

Radiative blast waves were created by irradiating a krypton cluster source from a supersonic jet with a high intensity femtosecond laser pulse. It was found that the radiation from the shock surface is absorbed in the optically thick upstream medium creating a radiative heat wave that travels supersonically ahead of the main shock. As the blast wave propagates into the heated medium, it slows and loses energy, and the radiative heat wave also slows down. When the radiative heat wave slows down to the transonic regime, a secondary shock in the ionization precursor is produced. This paper presents experimental data characterizing both the initial and secondary shocks and numerical simulations to analyze the double-shock dynamics.

Cellular Rod with Varying Cross-Section Under Impact

The aim of this paper is to investigate the effect of the gradient on the cross-section on the dynamic behavior of the graded cellular rods under impact loading. A graded cellular rod, whose cross-section varies along the axial direction, is supposed to impinged by a rigid mass G with initial velocity . The shock theory proposed by Reid and Peng [1] is employed to establish the analytical model. Similar to the previous work [2], the analytical results show that only one shock front appears when the gradient is positive while two shock fronts exist in the rod with negative gradient. Closed form solution is found for the single shock (SS) mode, while finite difference method is employed to obtain solutions for the double shock (DS) mode.

Double Tube Shock Absorber Model for Noise and Vibration Analysis

ABSTRACTThe “structure-borne” noise of the shock absorber is often responsible for undesirable noise in the car interior cabin.These vibrations are attributed to friction, opening/closing of the valves, fluid cavitation or other complex phenomena.Early numerical prediction of the level of these vibrations in the car development process saves time and money. Mostof the shock absorber models existing in the literature are limited to analysis of vehicle ride and handling. For noise andvibration analysis, the published works do not explicitly describe any model with its associated assumptions and a clearcorrelation with the experiments for high frequencies. Moreover there is no interpretation of the physical meaning of thehigh-frequency content of the response.The objective of the present work is to build a double tube shock absorber model correlated up to 700 Hz. Experimentaltesting results are presented in this paper in order to put in evidence the non-linear phenomena localized on the pistonshock absorber. The model includes the fluid compressible behavior, non-linear flow-rate pressure relationship and springvalve dynamics. Unknown parameters like bulk modulus are identified with experimental data.The numerical results are compared to the experiments, showing that the shock absorber model is able to reproducevery well the local non-linear phenomena. This confirms our hypothesis and improves our knowledge of the potential noisesources in the shock absorber.CITATION: Benaziz, M., Nacivet, S., Deak, J. and Thouverez, F., Double Tube Shock Absorber Model for Noise andVibration Analysis, SAE Int. J. Passeng. Cars - Mech. Syst. 6(2):2013, doi:10.4271/2013-01-1912.____________________________________

Illiquidity shocks and the comovement between stocks: New evidence using smooth transition

This paper extends the smooth transition conditional correlation model by studying for the first time the impact that illiquidity shocks have on stock market return comovement. We show that firms that experience shocks that increase illiquidity are less liquid than firms that experience shocks that decrease illiquidity. Shocks that increase illiquidity have no statistical impact on comovement. However, shocks that reduce illiquidity lead to a fall in comovement, a pattern that becomes stronger as the illiquidity of the firm increases. This discovery is consistent with increased transparency and an improvement in price efficiency. We find that a small number of firms experience a double illiquidity shock. For these firms, at the first shock, a rise in illiquidity reduces comovement while a fall in illiquidity raises comovement. The second shock partly reverses these changes as a rise in illiquidity is associated with a rise in comovement and a fall in illiquidity is associated with a fall in comovement. These results have important implications for portfolio construction and also for the measurement and evolution of market beta and the cost of capital as it suggests that investors can achieve higher returns for the same amount of market risk because of the greater diversification benefits that exist. We also find that illiquidity, friction, firm size and the pre-shock correlation are all associated with the magnitude of the correlation change.

Cellular Rod with Varying Cross-Section under Impact

The aim of this paper is to investigate the effect of the gradient on the cross-section on the dynamic behavior of the graded cellular rods under impact loading. A graded cellular rod, whose cross-section varies along the axial direction, is supposed to impinged by a rigid mass G with initial velocity . The shock theory proposed by Reid and Peng [1] is employed to establish the analytical model. Similar to the previous work [2], the analytical results show that only one shock front appears when the gradient is positive while two shock fronts exist in the rod with negative gradient. Closed form solution is found for the single shock (SS) mode, while finite difference method is employed to obtain solutions for the double shock (DS) mode.

Double shock mode in graded cellular rod under impact

This paper presents an analytical study of the effect of the gradient in quasi-static plateau stress on the dynamic behavior of graded cellular rods under impact loading. Finite element (FE) simulations of graded hexagonal and circular cells’ chains under uniaxial impact loading are first carried out by using ABAQUS/EXPLICIT to observe their dynamic deformation modes. To build an analytical model, a graded cellular rod, whose quasi-static plateau stress varies along the axial direction, is supposed to be impinged by a rigid mass G with initial velocity V0. Only one shock front appears when the gradient is positive, while two shock fronts appear in the rod with negative gradient. Analytical expressions of the dynamic response parameters for the graded cellular rod are theoretically derived by using the one-dimensional shock theory originally proposed by Reid and Peng (1997). Closed form solution is found for the single shock (SS) mode, while finite difference method is employed to obtain solutions for the double shock (DS) mode. Densification velocity, at which the graded rod is just fully crushed at the end of its dynamic response, is determined; and accordingly, the maximum energy-absorbing capacity of the graded cellular rod is determined. The weakest part of the graded rod is suggested to be placed at the impact end to achieve higher energy absorption. The theoretical models are then extended to the second scenario in which the graded cellular rod together with attached mass G impinges onto a rigid target. Similar to Scenario I, the gradient significantly influences the capacity of the graded cellular rod when the ratio of mass G to the mass of the rod is relatively small. The comparison between the FE simulation results and analytical predictions shows good agreement, which validates the theoretical model.

Double shock dynamics induced by the saturation of defocusing nonlinearities

We show that the saturation of defocusing nonlinearities leads to qualitative changes in the onset of wave breaking, determining double shock formation whose regularization occurs in terms of antidark solitons. In a given material, the crossover between different regimes can be controlled by changing the input intensity.

Motion Simulation and Stress Analysis of a Vehicle Shock Absorber

The shock absorber plays an important role in the properties of stability and riding comfort of the vehicle. A virtual model of a double cylinder hydraulic vehicle shock absorber is developed for motion simulation and stress analysis by SolidWorks software. The kinematic character of the shock absorber was simulated by using the virtual model. And the stress analysis result showed that the shock absorber had high liability. All the results can also be helpful to design the double cylinder hydraulic vehicle shock absorber.

A model for the two component γ-ray spectra observed from the γ-ray binaries

ABSTRACT Observations of two well-known binary systems (LS 5039 and LS I +61 303) with the satellite and Cherenkov telescopes revealed the broad-band γ-ray spectra which seems to show two components, the first at GeV energies, showing exponential cut-off at a few GeV, and the second at TeV energies which does not fit well to the extrapolation of spectrum from the GeV energy range. We propose that such two component spectrum is produced by two populations of electrons which appear within the binary system as a result of acceleration on a double shock structure separated by a contact discontinuity. Such structure is created within the binary system as a result of the interaction of the pulsar and massive star winds. The shocks from the side of the pulsar and the massive star have different proprieties which allow acceleration of electrons to different maximum energies. These two populations of electrons produce two component γ-ray spectra caused by the Inverse Compton (IC) scattering of stellar radiation. The example calculations, performed in terms of the anisotropic IC e± pair cascade model, for the location of the pulsar at the periastron and apastron passages confirm the high-energy emission features observed from LS I +61 303.

Calculation of Shock Adiabats for Materials Undergoes a Phase Transition

We propose a model that allows a single velocity and temperature approximation, and assuming the same pressure for all phases, to calculate the behavior of porous powder mixtures during shockwave loading taking into account the phase transition. Numerical results are compared with available experimental results of different authors to solid and porous media(shock adiabat, double compression shock waves). It is shown that the calculation gives good agreement with experiment for graphite and titanium

The X-ray and radio-emitting plasma lobes of 4C23.56: further evidence of recurrent jet activity and high acceleration energies

New Chandra observations of the giant (∼0.5 Mpc) radio galaxy 4C23.56 at z= 2.5 show X-rays in a linear structure aligned with its radio emission, but seemingly anticorrelated with the detailed radio structure. Consistent with the powerful, high-z giant radio galaxies we have studied previously, X-rays seem to be invariably found where the lobe plasma is oldest even where the radio emission has long since faded. The hotspot complexes seem to show structures resembling the double shock structure exhibited by the largest radio quasar 4C74.26, with the X-ray shock again being offset closer to the nucleus than the radio synchrotron shock. In the current paper, the offsets between these shocks are even larger, at ∼35 kpc. Unusually for a classical double (FR II) radio source, there is smooth low surface-brightness radio emission associated with the regions beyond the hotspots (i.e. further away from the nucleus than the hotspots themselves), which seems to be symmetric for the ends of both jets. We consider possible explanations for this phenomenon, and reach the conclusion that it arises from high-energy electrons, recently accelerated in the nearby radio hotspots that are leaking into a pre-existing weakly magnetized plasma that are symmetric relic lobes fed from a previous episode of jet activity. This contrasts with other manifestations of previous epochs of jet ejection in various examples of classical double radio sources namely (i) double–double radio galaxies by e.g. Schoenmakers et al., (ii) the double–double X-ray/radio galaxies by Laskar et al. and (iii) the presence of a relic X-ray counter-jet in the prototypical classical double radio galaxy, Cygnus A by Steenbrugge et al. The occurrence, still more the prevalence, of multi-episodic jet activity in powerful radio galaxies and quasars indicates that they may have a longer lasting influence on the ongoing structure formation processes in their environs than previously presumed.

Clostridium difficile from healthy food animals: optimized isolation and prevalence.

Two isolation methods were compared for isolation of Clostridium difficile from food animal feces. The single alcohol shock method (SS) used selective enrichment in cycloserine-cefoxitin fructose broth supplemented with 0.1% sodium taurocholate, followed by alcohol shock and isolation on tryptic soy agar supplemented with 5% sheep blood, and cycloserine-cefoxitin fructose agar. The double alcohol shock method (DS) used alcohol shock prior to and after selective enrichment in cycloserine-cefoxitin fructose broth supplemented with 0.1% sodium taurocholate, followed by isolation on tryptic soy agar supplemented with 5% sheep blood and cycloserine-cefoxitin fructose agar. A total of 55 (15.9%, n = 345) swine fecal samples, 32 (2.4%, n = 1,325) dairy cattle fecal samples, and 188 (6.3%, n = 2,965) beef cattle fecal samples were positive for C. difficile by either method. However, the DS was significantly better than the SS for the recovery of C. difficile from swine feces, while the SS was significantly better than the DS for the recovery of C. difficile from beef cattle feces. There was no significant difference between methods for the recovery of C. difficile from dairy cattle feces. This study suggests that food animals might harbor C. difficile and it provides critical information that isolation methods might not have universal application across animal species.

A New Shock Tube Facility for Tunnel Safety

In this paper, a new double diaphragm shock tube facility for studying the structural response of a circular plate resting on soil, when subjected to a shock wave, is described. The present shock tube has been designed in the framework of a more extensive research program aimed at the investigation of underground tunnel lining under blast and fire conditions. The innovative features of the facility are an end-chamber conceived to investigate soil-structure interaction and a burner equipment to heat the specimen in order to study to what extent thermal damage can affect the transmitted and reflected pressure wave as well as the structural response. Details of the shock tube design, construction and test procedure operations are discussed in the paper. Particular emphasis is placed on the principles that have driven the experimental equipment design choices. Numerical simulations have been performed to assess the ideal shock tube performance in terms of reflected pressure and test time duration as well as to evaluate how far the fire testing situation actually is from that normally used in tunnel design.