High-intensity Shock Research Articles

Microscopic and Macroscopic Fragmentation Characteristics under Hypervelocity Impact Based on MD and SPH Method.

This work investigates the difference in the fragmentation characteristics between the microscopic and macroscopic scales under hypervelocity impact, with the simulations of Molecular Dynamics (MD) and Smoothed Particle Hydrodynamics (SPH) method. Under low shock intensity, the model at microscopic scale exhibits good penetration resistance due to the constraint of strength and surface tension. The bullet is finally embedded into the target, rather than forming a typical debris cloud at macroscopic scale. Under high shock intensity, the occurrence of unloading melting of the sample reduces the strength of the material. The material at the microscopic scale has also been completely penetrated. However, the width of the ejecta veil and external bubble of the debris cloud are narrower. In addition, the residual velocity of bullet, crater diameter and expansion angle of the debris cloud at microscopic scale are all smaller than those at macroscopic scale, especially for low-velocity conditions. The difference can be as much as two times. These characteristics indicate that the degree of conversion of kinetic energy to internal energy at the microscopic scale is much higher than that of the macroscopic results. Furthermore, the MD simulation method can further provide details of the physical characteristics at the micro-scale. As the shock intensity increases, the local melting phenomenon becomes more pronounced, accompanied by a decrease in dislocation atoms and a corresponding increase in disordered atoms. In addition, the fraction of disordered atoms is found to increase exponentially with the increasing incident kinetic energy.

Shock wave characteristics in a conical water explosion shock tube under cylindrical charge condition

A conical shock tube is a kind of underwater explosive devices which uses small conical explosive charge to form high intensity shock pressure. Theoretically, the shock wave pressure in the conical shock tube is the same as that generated by a virtual spherical explosive charge in free field water. However, considering the effect of practical factors, the characteristics of shock wave in the actual device and the theoretical device are different to some extent. In order to investigate the shock wave characteristics in the conical water explosion shock tube under a cylindrical charge condition, and to obtain the variation rules of the peak pressure value, the specific impulse and the energy flux density, a series of numerical calculations with different cone angles and different quality of cylindrical charges were conducted. The reliability of the simulation methods was verified by comparing with the published experimental data. Through the analysis of the pressure data obtained by the validated simulation method, it is found that the shock wave in the tube follows the same scaling law as it is in the free field underwater explosion. The constants k and n of the empirical expressions for peak pressure, the impulse and the energy flux density for the shock wave in shock tube are obtained by data fitting. Furthermore, the relationships among the coefficient k, index n and cone angle α were deduced, and the result shows that the coefficients k have well linear relationship with constructed angle coefficient β, and the indexes n can be quantitatively expressed by cone angle α. Regarding the free field as a special case with a cone angle of 360°, it’s constants k and n also conform to the obtained relationships. It is also found that the secondary pulsation pressure period shows an anomalous change rule with explosive mass, which can be well explained by the significant increasement of the equivalent hydrostatic pressure depth. The ratio between the secondary impulse pressure peak and initial pressure peak is bigger than that in free field while the ratio between the secondary impulse pressure’s impulse to the initial pressure impulse is almost the same. These results can provide support for the application of conical shock tubes.

Sensitization and desensitization of PBXs stemming from microcrack and microvoid in responses to pressure-time loading

Comprehensively understanding the main differences exhibited in the ignition stage of high-intensity shock and low-intensity impact initiation processes of polymer bonded explosives (PBXs), including defect-related hotspot formation, ignition threshold, and sensitization or desensitization, is necessary for the safety evaluation of PBXs. The roles of shear-crack and void-collapse hotspots in the ignition for single-impacted PBXs are first studied using a physically based thermomechanical model. The variations of sensitivity for pre-impacted PBXs are further reported. Results show that a crack hotspot dominates in a low pressure range (90–200 MPa) with a relatively long ramp time (∼1.0 μs). High pressure will cause a friction-locked crack, while low pressure will lead to the insufficient frictional heating, thus resulting in a slight increase in hotspot temperature. Moreover, a long duration (∼10.0 μs) is required for satisfying the hotspot temperature-size criterion of ignition. The void hotspot dominates in high pressure (≥350 MPa) with a short ramp time (<0.1 μs). The dominant range of crack hotspots is extended (70–240 MPa) after a pre-impact load, while that of the void hotspot reduces (≥550 MPa). If the secondary loading is high-intensity shock, the explosives are desensitized due to the pre-elimination of voids. In contrast, if the secondary loading is low-intensity impact, the explosives are sensitized due to the pre-increase in crack-related damage.

Effects of repeated anodal transcranial direct current stimulation on auditory fear extinction in C57BL/6J mice

BackgroundTrauma-based psychotherapy is a first line treatment for post-traumatic stress disorder (PTSD) but not all patients achieve long-term remission. Transcranial direct current stimulation (tDCS) received considerable attention as a neuromodulation method that may improve trauma-based psychotherapy. ObjectiveWe explored the effects of repeated anodal tDCS over the prefrontal cortex (PFC) on fear extinction in mice as a preclinical model for trauma-based psychotherapy. MethodsWe performed auditory fear conditioning with moderate or high shock intensity on C57BL6/J mice. Next, mice received anodal tDCS (0.2 mA, 20 min) or sham stimulation over the PFC twice daily for five consecutive days. Extinction training was performed by repeatedly exposing mice to the auditory cue the day after the last stimulation session. Early and late retention of extinction were evaluated one day and three weeks after extinction training respectively. ResultsWe observed no significant effect of tDCS on the acquisition or retention of fear extinction in mice subjected to fear conditioning with moderate intensity. However, when the intensity of fear conditioning was high, tDCS significantly lowered freezing during the acquisition of extinction, regardless of the extinction protocol. Moreover, when tDCS was combined with a strong extinction protocol, we also observed a significant improvement of early extinction recall. Finally, we found that tDCS reduced generalized fear induced by contextual cues when the intensity of conditioning is high and extinction training limited. ConclusionsOur data provide a rationale to further explore anodal tDCS over the PFC as potential support for trauma-based psychotherapy for PTSD.

АДАПТИВНИЙ МЕХАНІЧНИЙ ФІЛЬТР ДЛЯ ПꞌЄЗОЕЛЕКТРИЧНОГО АКСЕЛЕРОМЕТРА

When conducting dynamic tests, when simulating shock effects, the measurement system - from the sensor to the data acquisition unit is subject to significant overloads. In this circuit, the accelerometer is the most vulnerable link. Therefore, piezoelectric accelerometers have become widely used in measuring shocks as more reliable and durable, but they also have a number of disadvantages. Thus, under broadband vibration effects, excitation in the region of mechanical resonance is observed. That is, the material of the sensor crystal may not have an excessive mechanical load, but generate a large amount of output charge due to the resonance of the sensor. This increases the electrical signal and can lead to saturation or, in many cases, damage to the signal shapers and amplifiers following the sensor. The result of such modes of operation is the loss of data due to the displacement of direct current over time. There is often a shift of the zero level of the output signal. When piezoelectric elements are in resonance, there may be a relative displacement of the sensing element. This state of overload leads to the appearance of parasitic output charges, which leads to a change in the generated charge in a short period of time. Due to mechanical overload, under the action of high-intensity shocks, physical destruction of the sensor is also possible. In many cases, the use of mechanical filters made of viscoelastic materials, which are placed between the object of measurement and the piezoelectric accelerometer (sensor), prevents the undesirable consequences of these shortcomings and improves the process of measuring shocks. The use of mechanical filters made of viscoelastic materials makes it possible to significantly reduce the amplitude of oscillations of the piezoelectric accelerometer (over -12 dB) and shift its resonant frequency towards higher frequencies. That is, the use of mechanical filters significantly reduces the mechanical load on the sensor, which makes the process of measuring vibration (especially shock) more predictable.

High-intensity Interval Training Shock Microcycle Improves Running Performance but not Economy in Female Soccer Players.

This study aimed to evaluate the effect of high-intensity interval training shock microcycles (HIITSM) on endurance, running economy and change of direction economy in female soccer players. Nineteen sub-elite female soccer players were randomised to two groups: HIITSM (10 HIIT sessions over 13 days) or HIITTRAD (4 HIIT sessions over 13 days) interventions. Endurance performance was evaluated through the 30-15 intermittent fitness test (30-15IFT); running economy over a 5-min treadmill run; and change of direction economy over two conditions: (1) 5-min 20m shuttle run, and (2) 5-min 10m shuttle run. HIITSM significantly improved 30-15IFT scores compared to baseline (+4.4%, p=0.009; d=0.96) and 30-15IFT scores relative to HIITTRAD (p=0.002; d=2.01). There was no significant interaction (group×time) for running economy and change of direction economy. Pre- to post- intervention there was a significant main time effect for blood lactate over 20m and 10m shuttle runs (p<0.001 and p=0.037, respectively), with large (d=0.93) and moderate (d=0.53) changes observed for the HIITSM over the two distances, respectively. HIITSM may be more effective than HIITTRAD to improve 30-15IFT over shorter training periods but may not affect running economy and change of direction economy.

Construction of simulation models for analyzing high-intensity shock effects in a spacecraft

In this paper, we consider the procedure for constructing stochastic models (based on processing of experimental data). These models allow to assess the propagation of high-intensity shock effects on the performance of unpressurized spacecrafts. The developed models are recommended for simulation of the load and the model of the system under study. Show the histograms of the distribution of total values of the impact reduction coefficient for typical structural joints, trusses, and shock isolators. The developed method allows to obtain an acceptable estimate of the propagation of high-intensity shock effects in the SC design.

Effects of a 14-Day High-Intensity Shock Microcycle in High-Level Ice Hockey Players' Fitness.

Brocherie, F, Perez, J, and Guilhem, G. Effects of a 14-day high-intensity shock microcycle in high-level ice hockey players' fitness. J Strength Cond Res 36(8): 2247-2252, 2022-Elite athletes face congested schedules with increased competition frequency and restricted time for training periods. Therefore, time is lacking to design long-term sport-specific block periodization. This study aimed to investigate the effects of adding a 14-day off-ice high-intensity training (HIT) shock microcycle to the usual training content of the pre-season preparation of high-level male ice hockey players' fitness. Fourteen players were randomly assigned to off-ice HIT ( n = 7) or usual pre-season training (control, n = 7). For the HIT group, additional off-ice training content included 2 sessions of repeated-maximal resistance training, 2 sessions of repeated-sprint training, and 2 sessions of high-intensity intermittent training. Control group performed equal number of off-ice sessions using traditional strength and conditioning training. Off-ice Yo-Yo intermittent recovery test level 2 (YYIR2) and on-ice repeated-sprint ability test (RSA) were conducted before (pre-test) and 3 days after the intervention (post-test). Statistical significance was set at p < 0.05. Significant group × time interactions were found for off-ice YYIR2 performance ( p < 0.05) and on-ice RSA-cumulated skating time (RSA TT ; p < 0.05). Compared with pre-test, off-ice YYIR2 distance covered significantly increased (from 708.6 ± 97.2 to 885.7 ± 118.7 m, p < 0.01; +25.8 ± 16.9%, p < 0.05) and on-ice RSA TT significantly decreased (from 28.35 ± 0.87 to 28.14 ± 0.84 seconds; -1.7 ± 2.1%, both p < 0.05)] for HIT group. No significant pre-test to post-test changes were found for the control group (+2.7 ± 20.0% for YYIR2 and +0.9 ± 2.2% for RSA TT ). The implementation of a 14-day shock microcycle (including 6 HIT sessions) significantly improved fitness performance in high-level male ice hockey players. Such HIT block periodization offers a promising way to deal with congested schedules.

Shock-induced plasticity and damage in single-crystalline Cu at elevated temperatures by molecular dynamics simulations

Initial temperature effects on shock responses, including shock-induced plasticity and spalling damage behaviors of single-crystalline Cu are investigated by molecular dynamics simulations. Firstly, initial temperature effects on stress wave profiles are investigated. The simulations show that shock Hugoniot stress deceases as initial temperature increases, which can be explained by the Rakine-Hugoniot conservation theory. Initial temperature effects on dislocation density are studied. It is found that the dislocation density decreases as initial temperature increases. Shock-induced spalling is dominated by cavitation, i.e., void nucleation, growth and coalescence. Initial temperature effects on cavitation are discussed. In cases of relatively low shock intensity, the total number of voids increases as initial temperature rises; for strong shock intensities that induce melting and micro-spalling, initial temperature effects on the total number of voids are not obvious. Furthermore, initial temperature effects on spall strength are found to be dependent on shock intensity. For relatively weak shock intensity, the simulations show that spall strength starts to drop when initial temperature exceeds 900 K, far below the melting temperature, this result is well consistent with previous experimental measurements; however, for high shock intensity, our simulations predict that spall strength decreases monotonically as initial temperature increases.

Определение скорости гиперзвуковых компактных элементов в наземной испытательной установке

Protection of spacecraft from high-speed impact when encountering meteorite particles and man-made debris is currently a pressing issue. This article presents methods for determining the reaction of complex structures to the impact of particles with cosmic velocities. To determine the anti-meteorite resistance of materials and structures and to study the reaction of materials under high-intensity shock loading, schemes are developed for the production and registration of high-speed metal compact elements moving at hypersonic speeds using cumulative explosive throwing devices based on high-power condensed explosives. The use of the ‘hemisphere-cylinder’ shaped lining made it possible to test a shaped charge, consistently forming a steel compact element with a velocity of 6 km/s. The paper presents the results of numerical calculations and experimental testing of such a booster. Using this device, a method for determining the speed of the hypersonic striker pin is developed based on visualization of the head shock wave at the entrance of the striker into water.

Atomistic simulations of shock compression of single crystal and core-shell Cu@Ni nanoporous metals

We have performed systematic molecular dynamics simulations to study the deformation behavior of a single crystal structure and a core-shell Cu@Ni nanoporous (NP) structure under shock loading for a wide range of shock intensities. Our results suggest that the core-shell structure exhibits less volume compression than the single crystal NP structure by virtue of its enhanced mechanical strength and associated interfacial strain-hardening under shock loading. The core-shell NP structure also demonstrates an increased shock-energy absorption efficiency of around 10.5% larger than the single crystal NP structure because of its additional Cu/Ni interface. The mechanisms of shock-induced deformation are observed to vary greatly with shock intensity. Pores are observed to collapse partially in both NP structures at very low shock intensity, up≤0.15 km/s. Complete collapsing of the pores through plastic deformation followed by direct crushing and formation of internal jetting and hot-spot have been observed at higher shock intensities. The evolution of microstructure and the underlying mechanisms operating at different shock intensity regimes have been investigated in this article. At a shock pressure of ∼6.05 GPa, i.e., up=0.75 km/s, the shock-induced deformed microstructure of both NP structures recovered through dynamic recrystallization. The postshock dynamic recrystallization has been observed to be mediated through rapid relaxation of shear stress followed by atomic rearrangements.

Emotional enhancement of memory for neutral information: The complex interplay between arousal, attention, and anticipation

It can be challenging to explain why certain mundane details circumstantial to an emotional event are nonetheless remembered long after the experience. Here, we examined how attention selectively shapes memory for neutral objects that happen to coincide with either an unexpected or anticipated emotional event. Pictures of neutral objects were presented for 2 s and terminated with either a high-intensity shock, a low-intensity shock, or no shock. Recognition memory was tested 24 -hs later in a surprise test. Results showed no effect of shock intensity on memory for attended objects when shocks were unpredictable (Experiment 1). Similarly, there was no effect of shock intensity for attended objects when shock delivery was signaled before the object appeared (Experiment 2). There was a reduction in memory for unattended objects paired with an anticipated high-intensity shock (Experiment 3). Finally, subjects recognized slightly more attended objects paired with a high-intensity shock if shock intensity was signaled one second after the object was encoded (Experiment 4). We conclude that simply pairing objects with high-intensity shocks is insufficient to drive episodic memory enhancements for neutral information. But anticipation of an impending source of arousal can induce bidirectional effects: attending to an impending emotional event interferes with encoding of neutral information, but encoding an object just prior to anticipation of an emotional event can sometimes benefit memory. Overall, these results highlight a complex interplay between arousal, attention, and anticipation on emotion-induced memory for neutral information.

Effect of electrical breakdown modes on shock wave intensity in water

Shock waves generated by underwater pulsed discharge have been applied to industrial and bio-medical treatments, and the key technology is to induce high intensity shock waves. Based on the underwater pulsed discharge platform, the effect of the electrical breakdown modes on the shock wave intensity in water is discussed in the positive pin-to-plane configuration. Experimental results demonstrate that the amplitude of applied voltage have a significant influence on the breakdown modes as well as the shock wave intensity. Based on the analysis of discharge images captured by a high-speed camera, it can be concluded that the breakdown modes are classified as subsonic bush-like streamers or supersonic filamentary streamers. The mechanism of subsonic streamer in lower applied voltage is more likely an electro thermal process. The micro-bubbles are firstly generated, and then discharge occurs in the bubble cluster. The bubble volume grows until a breakdown of the underwater gap, and the shock wave is the generated. The time to breakdown of subsonic streamers is commonly within hundreds of microseconds at the experimental condition. In higher applied voltage, the energy loss in the pre-breakdown process is reduced significantly as well. In our experiment, a threshold value of 22.5 kV is necessary for the subsonic streamer mode transition into supersonic streamer mode. The energy conversion efficiency, the time to breakdown and the influence of the applied voltage are discussed at different breakdown modes. The shock wave intensity differs 2–4 times in different breakdown modes even in the same applied voltage, thus increasing the applied voltage may be a remarkable way to enhance the shock wave intensity.

Uncertain is worse: modulation of anxiety on pain anticipation by intensity uncertainty: evidence from the ERP study.

To investigate the effect of uncertain information in the anticipation phase, this study used four cues to inform participants that they would face four kinds of subsequent electrical shocks: low-intensity shock, high-intensity shock, 50-50% chance of low-intensity or high-intensity shock, and no shock. Subjective evaluation on the anxiety elicited by different cues showed that uncertain cues aroused higher anxiety than certain cues, but the effect was observed only at low-intensity shock. The electroencephalogram data revealed that uncertain-shock cue elicited significantly larger stimulus-preceding negativity than certain-high-shock cue at the frontal site. The uncertain-shock cue and certain-high-shock cue both elicited significantly larger stimulus-preceding negativity than the cues of certain-low-shock and nonshock, respectively. Uncertain cues elicited significantly larger pain-evoked P2 than certain cues. The results implied that uncertainty of information regarding shock intensity captured more motivational engagement, aroused higher anxiety on anticipating for the electrical shock, and elicited higher perceived pain of shock stimulation.

Collective Projection and Recording of Compact Elements Formed by Implosion of Combined Hemisphere–Cylinder Liners

A method for obtaining and recording high-velocity compact metal elements moving with hypersonic velocities under high-intensity shock loading is developed. A light-gas ballistic device and shadow photography are used for this purpose. Application of a hemisphere–cylinder liner makes it possible to test a shaped charge that steadily forms a compact steel element moving with a velocity approximately equal to 6 km/s. The results of numerical and experimental testing of this projector are given.

Atomic-level deformation of CuxZr100-x metallic glasses under shock loading

Plastic deformation mechanisms in CuxZr100-x bulk metallic glasses (MGs) subjected to shock are investigated using molecular dynamics simulations. MGs with Cu compositions between 30 and 70 at. % subjected to shock waves generated via piston velocities that range from 0.125 to 2.0 km/s are considered. In agreement with prior studies, plastic deformation is initiated via formation of localized regions of high von Mises shear strain, known as shear transformation zones (STZs). At low impact velocities, but above the Hugoniot elastic limit, STZ nucleation is dispersed behind the shock front. As impact velocity is increased, STZ nucleation becomes more homogeneous, eventually leading to shock-induced melting, which is identified in this work via high atomic diffusivity. The shear stress necessary to initiate plastic deformation within the shock front is independent of composition at shock intensities near the elastic limit but increases with increasing Cu content at high shock intensities. By contrast, both the flow stress in the plastically deformed MG and the critical shock pressure associated with melting behind the shock front are found to increase with increasing Cu content over the entire range of impact velocities. The evolution of the short-range order in the MG samples during shock wave propagation is analyzed using a polydisperse Voronoi tessellation method. Cu-centered polyhedra with full icosahedral symmetry are found to be most resistant to change under shock loading independent of the MG composition. A saturation is observed in the involvement of select Cu-centered polyhedra in the plastic deformation processes at a piston velocity around 0.75 km/s.

Oxytocin receptor antagonist atosiban impairs consolidation, but not reconsolidation of contextual fear memory in rats

There is increasing evidence that oxytocin is involved in learning and memory process. This study investigated the effects of blockade of oxytocin receptors using the selective oxytocin receptor antagonist atosiban (ATO) on contextual fear memory consolidation and reconsolidation in male rats. Post-training injections of different doses of ATO (1, 10, 100 or 1000 µg/kg) impaired the 48 h retention performance in a dose-dependent manner. The same doses of ATO following memory reactivation did not impair subsequent expression of contextual fear memories which formed under low or high shock intensities and tested 24 h or one week following memory reactivation. Also, no effect was found when ATO was administrated in the absence of memory reactivation. Our finding is the first report that indicates endogenous oxytocin released during training play an important role in the consolidation, but not reconsolidation of contextual fear memory in rats.

Shock response of nanoporous magnesium by molecular dynamics simulations

Shock response of nanoporous magnesium (np-Mg) is investigated by using nonequilibrium molecular dynamics simulations. Hugoniot curves of Mg are obtained and agreed well with experimental data. Two typical mechanisms of void collapse under c-axis loading are revealed: the plasticity mechanism and the internal jetting mechanism. The plasticity mechanism, which dominates under weak shock intensity, leads to transverse collapse of voids; while the internal jetting mechanism, which plays important role under higher shock intensity, leads to longitudinal filling of voids. In plasticity induced void collapse, dislocations activities on void surface are found to concentrate at positions with the incident angles being 60° and 120°. This is closely related to the basal slip system {0001}<1¯21¯0> and can be well explained from a perspective of continuum mechanics. The thermodynamic characteristics during void collapse are discussed. The energy dissipation in np-Mg is correlated to local temperature risen and stress attenuation during void collapse, which are resulted from a series of plastic activities at microcosmic (including dislocation, shear ring and fault movement, etc.). In addition, our results also discover that spall strength of np-Mg under shock loading is influenced by shock intensity and void size. In general, it will decrease with the increase of shock intensity, and large size void has a significant weakening effect while small size void has a slight enhancing effect.

Simulation Study on the Deflection Response of the 921A Steel thin plate under Explosive Impact Load

The Ship cabin would be subject to high-intensity shock wave load when it is attacked by anti-ship weapons, causing its side board damaged. The time course of the deflection of the thin plate made of 921A steel in different initial conditions under the impact load is researched by theoretical analysis and numerical simulation. According to the theory of elastic-plastic deformation of the thin plate, the dynamic response equation of the thin plate under the explosion impact load is established with the method of energy, and the theoretical calculation value is compared with the result from the simulation method. It proved that the theoretical calculation method has better reliability and accuracy in different boundary size.

Planar impacts on nanocrystalline SiC: a comparison of different potentials

Silicon carbide ceramics under shock loading is an important aspect in studying their physical and mechanical properties. Molecular dynamics simulations have been carried out using Tersoff-1989, Tersoff-1994, Tersoff-2005 and Vashishta potentials, respectively. The Hugoniot states including compression stress, shear stress, temperature and shock wave velocity are calculated, as well as shock-induced plasticity and the shock wave fronts. A comprehensive comparison among different potentials, as well as comparison to current available experiments, has been made. Tersoff-1989, Tersoff-1994 and Tersoff-2005 potentials are easily to overestimate the shock stress, shear stress and temperature, as well as shock wave velocity, while Vashishta potential shows excellent agreement with experimental data. The Hugoniot elastic limit is ~ 14.5 GPa and the maximum shear stress is ~ 6 GPa using Vashishta potential which are in good agreement with experiments, while Tersoff-like potentials yield much higher values. Due to differences in radial distribution function among these potentials, Vashishta potential is prone to produce plasticity and structural phase transformation basing on the statistics of the coordination numbers of atoms. Besides, the shock wave fronts show little difference among these potentials under elastic shock compression at low particle velocity. However, when it comes to high shock intensity resulting in plasticity or phase transition, the Tersoff-1989 and Tersoff-1994 produce the widest shock wave fronts, followed by Tersoff-2005, while Vashishta potential has the narrowest wave front. By comprehensive comparisons, the Vashishta potential is demonstrated to be the most suitable one to describe the silicon carbides ceramics under shock loadings. Our work provides useful information to select a suitable potential to study the shock response of silicon carbides ceramics using molecular dynamics simulations.