Duration Of Shock Wave Research Articles

Experimental study on the blast resistance of polyurea-coated aramid fabrics

This paper investigates overpressure attenuation capacity and failure mechanism of the polyurea-coated aramid fabric (PCAF) subjected to air-blast loading experimentally. The peak overpressure, arrival time and positive pressure duration of shock waves on the blast and back side of PCAFs were obtained in tests and analyzed. In addition, the failure mode and mechanism were revealed with the electron scanning microscope (SEM), meanwhile the effect of polyurea type, coating position and thickness ratio on the blast resistance were discussed. The results show that in the cases of scaled distances of 1.84 and 2.32 m/kg1/3, PCAFs, one-layer polyurea coated on three-layer aramid woven fabrics, can attenuate the peak overpressure by about 70 %, delay the arrival time by about 0.7 ms, and shorten the positive pressure duration by 10 %-50 %. This is due to the increased out-of plane stiffness and closure of interweaving apertures of the aramid fabric. Furthermore, perforation is the main failure mode of aramid fabrics, in which the tensile breakage in weft yarn and the frictional slip in warp yarn, while the failure modes of PCAF mainly include fracture and exfoliation, with both weft and warp yarns breakage and polyurea failure. It was concluded that the degree of infiltration between the polyurea and fabric affects mechanical properties of the fiber, changing the failure mode of PCAF. In terms of the extent of damage, the PCAF exhibits a superior blast resistance when the polyurea coated on the back side. The blast resistance of PCAF increases first then decreases with an increase in the thickness of the polyurea layer under the same areal density.

Research on shock wave driving technology of methane explosion

In order to improve the driving ability of the explosion wave simulation equipment, reduce the erosion effect of condensed explosives on the explosion wave simulation equipment, improve the safety of the test process, and make better use of the meteorological detonation driving method, it is necessary to optimize the source of the shock wave load in the driving section. Based on the finite volume method of FLACS, a methane detonation driving model corresponding to the test is established to explore the feasibility of using methane as an explosion source to test the structure against explosion shock wave. A methane detonation drive test was carried out to verify the accuracy of the numerical model. Finally, an engineering model for attenuation of shock wave overpressure peak value in pipeline is established by dimensional analysis, and the model coefficient is determined by numerical simulation and test data. The results show that the blast pressure is the highest when the methane volume ratio reaches 9.5 vol% in the methane-air mixture. Simply increasing oxygen content has little effect on the peak overpressure and positive pressure duration of shock wave. In the pure oxygen environment, the detonation effect can be achieved when the volume ratio of methane to oxygen is 1:2, and the incident pressure of the shock wave is proportional to the volume of the gas cloud. When the gas cloud volume is constant, a reasonable selection of methane-oxygen mixture ratio can achieve a better detonation effect, which can effectively increase the peak overpressure of the shock wave in the test section. The research results can provide technical reference for the development of new explosion wave simulation equipment.

Plane shock wave propagation in partially saturated soil

Considered that the gas content of partially saturated soil would decrease under a shock load, which would cause volumetric plastic deformation, Lyakhov's constitutive model is improved. The P-α state equation is used to describe the volume compression relationship of partially saturated soil. Numerical and experimental results are compared to validate the material model. The peak stress and duration of shock wave are crucial to study the dynamic response of underground structures. Considered the saturation of partially saturated soils under natural conditions increases with depth and both peak stress and duration change when shock waves propagate in inhomogeneous media, several partially saturated soil models with linearly decreasing air content in the depth direction are developed. The propagation law of shock waves with various peak stresses and durations in partially saturated soils is studied. The results show that the peak stress caused by the incident load in partially saturated soil first decreases and then increases under incident loads with a shorter duration, and it increases monotonically under incident loads with a longer duration. The rate of change in the incident peak stress is proportional to the air content at the top of the partially saturated soil. The peak free-field stress reaches its maximum, which is 2.2 to 5.5 times the peak stress of the incident load, in fully saturated soil. Long-duration incident loads such as nuclear explosions are more threatening to underground structures than short-duration incident loads. Underground structures buried in fully saturated soil or below fully saturated soil with higher air contents above are more at risk than underground structures buried in partially saturated soil with smaller air contents.

Microjet formation from the grooved surface of aluminum under shock waves with different pulse durations

The shock-induced microjet phenomenon has attracted much attention due to its importance in shock compression science and technology. The existing researches have shown that shockwave profile has a significant effect on the microjet formation. This work investigates the influence of shock pulse duration on the microjet systematically based on smoothed particle hydrodynamics simulations and theoretical analysis. In fact, when the pulse duration of shock wave is more than 7.31 times the time of shock front passing through groove, the microjet mass and its time-space evolution will be consistent with the case under supported shock. It is shown that there is a critical value for the shock pulse duration (about 4.21 times the time of shock front passing through groove), below which the effect of shock pulse duration is distinct. With decreasing the shock pulse duration, the mass from spike to bubble experiences a rapid increase due to the increase of the velocity gradient behind the free surface, while the mass from spike to the theoretical free surface experiences a gradual reduction because the shock energy reduces. As a result, the spike becomes very thinner and the bubble amplitude is lengthened. The damage will be localized around the groove region. Besides, with the interaction between the release stage of incident waves and the release waves from the groove, the cavities and different low-density fragments are observed.

Vibrational Response of Initially Deformed Bistable Microbeams Under the Combined Effect of Mechanical Shock Loads and Electrostatic Forces

This paper focuses on the influence of sudden drop tests on the nonlinear structural behavior of electrically actuated bi-table shallow microelectromechanical system (MEMS) arches. The assumed structure consists of an initially bell-shaped doubly clamped microbeam with a rectangular cross section. The Euler–Bernoulli beam theory is assumed to model the nonlinear structural behavior of the bistable system under the combined effect of both the direct current (DC) actuating load and the shaking waves. Moreover, the structural model takes into account both geometric midplane stretching and electric actuation nonlinear terms. A multimode Galerkin-based decomposition is used to discretize the beam equations to extract a reduced-order model (ROM). The convergence of the ROM simulations are first verified and furthermore compared to published experimental data. A thorough ROM parametric study showed that the effect of increasing the shallow arch initial rise alter drastically the system behavior from undergoing a uninterrupted snap-through motion to a sudden snap-through instability. Moreover, the arch rise relationship with its shock spectrum response (SSR) is investigated and it was concluded that as increasing the rise value can cause the system to collapse under the combined DC and shock wave loadings if the shock wave duration is lower or near the system fundamental natural period. All the presented graphs in this investigation represent some robust numerical approaches and design tools to help MEMS designers in improving both the reliability and efficiency of these bistable-based microdevices under shaking dynamic environments.

A Compact Blast-Induced Traumatic Brain Injury Model in Mice.

Blast-induced traumatic brain injury (bTBI) is a common injury on the battlefield and often results in permanent cognitive and neurological abnormalities. We report a novel compact device that creates graded bTBI in mice. The injury severity can be controlled by precise pressures that mimic Friedlander shockwave curves. The mouse head was stabilized with a head fixator, and the body was protected with a metal shield; shockwave durations were 3 to 4 milliseconds. Reflective shockwave peak readings at the position of the mouse head were 12 6 2.6 psi, 50 6 20.3 psi, and 100 6 33.1 psi at 100, 200, and 250 psi predetermined driver chamber pressures, respectively. The bTBIs of 250 psi caused 80% mortality, which decreased to 27% with the metal shield. Brain and lung damage depended on the shockwave duration and amplitude. Cognitive deficits were assessed using the Morris water maze, Y-maze, and open-field tests. Pathological changes in the brain included disruption of the blood-brain barrier, multifocal neuronal and axonal degeneration, and reactive gliosis assessed by Evans Blue dye extravasation, silver and Fluoro-Jade B staining, and glial fibrillary acidic protein immunohistochemistry, respectively. Behavioral and pathological changes were injury severity-dependent. This mouse bTBI model may be useful for investigating injury mechanisms and therapeutic strategies associated with bTBI.

Nanoscopic fuel-rich thermobaric formulations: Chemical composition optimization and sustained secondary combustion shock wave modulation

Advanced thermobaric explosives have become one of the urgent requirements when targeting caves, fortified structures, and bunkers. Highly metal-based systems are designed to exploit the secondary combustion resulted from active metal particles; thus sustained overpressure and additional thermal loadings can be achieved. This study, reports on a novel approach for chemical composition optimization using thermochemical calculations in an attempt to achieve the highest explosion power. Shock wave resulted from thermobaric explosives (TBX) was simulated using ANSYS® AUTODYN® 2D hydrocode. Nanoscopic fuel-rich thermobaric charge was prepared by pressing technique; static field test was conducted. Comparative studies of modeled pressure–time histories to practical measurements were conducted. Good agreement between numerical modeling and experimental measurements was observed, particularly in terms of the prediction of wider overpressure profile which is the main characteristics of TBX. The TBX wider overpressure profile was ascribed to the secondary shock wave resulted from fuel combustion. The shock wave duration time and its decay pattern were acceptably predicted. Effective lethal fire-ball duration up to 50ms was achieved and evaluated using image analysis technique. The extended fire-ball duration was correlated to the additional thermal loading due to active metal fuel combustion. The tailored thermobaric charge exhibited an increase in the total impulse by 40–45% compared with reference charge.

Mechanism of membrane poration by shock wave induced nanobubble collapse: a molecular dynamics study.

We performed coarse-grained molecular dynamics simulations in order to understand the mechanism of membrane poration by shock wave induced nanobubble collapse. Pressure profiles obtained from the simulations show that the shock wave initially hits the membrane and is followed by a nanojet produced by the nanobubble collapse. While in the absence of the nanobubble, the shock wave with an impulse of up to 18 mPa s does not create a pore in the membrane, in the presence of a nanobubble even a smaller impulse leads to the poration of the membrane. Two-dimensional pressure maps depicting the pressure distributed over the lateral area of the membrane reveal the differences between these two cases. In the absence of a nanobubble, shock pressure is evenly distributed along the lateral area of the membrane, while in the presence of a nanobubble an unequal distribution of pressure on the membrane is created, leading to the membrane poration. The size of the pore formed depends on both shock wave velocity and shock wave duration. The results obtained here show that these two properties can be tuned to make pores of various sizes.

Effect of shock wave duration on dynamic failure of tungsten heavy alloy

It has been well established that dynamic fracture or spall is a complex process strongly influenced by both microstructure and the loading profile imparted to the specimen. Having previously considered ductile materials with damage and deformation kinetics that are volume additive and therefore relative slow, here we consider a brittle material with damage and deformation kinetics that are fast. The present study elucidates the effect of loading profile on the fundamental mechanisms of brittle fracture in brittle tungsten heavy alloy (WHA) specimens. Spall experiments are performed with two significantly distinct shock pulse durations and accompanying unloading rates. For both profiles, it is observed that the failure in WHA is by brittle trans-particle crack growth with additional energy dissipation through crack branching in the more brittle tungsten particles. We also observe that for the 15.4 GPa peak shock stress, the wave profile does not influence the spall strength significantly. This is believed to be directly linked to the relative insensitivity of WHA to time dependent processes.

Shock wave emission from a hemispherical cloud of bubbles in non-Newtonian fluids

Shock wave emission from a hemispherical cloud of bubbles, situated in non-Newtonian fluids, is investigated by high-speed photography, with up to 20million frames/s and an exposure time of 5ns, and acoustic measurements. The non-Newtonian fluids consist of a 0.5% polyacrylamide (PAM) aqueous solution, with a strong elastic component, and a 0.5% carboxymethylcellulose (CMC) aqueous solution, with a weak elastic component. In the relatively inelastic CMC solution, the maximum amplitude and the duration of the shock wave emitted during bubble cloud rebound are almost identical to the case of water. A significant reduction of the shock wave pressure was found in the elastic PAM solution. This difference ranges from a factor of 2, for a maximum radius of the bubble cloud Rmax≈800μm, up to a factor of 3, at Rmax≈270μm. A decrease of the shock wave duration was also observed in the elastic PAM solution. The observed reduction is attributed to an increased resistance to extensional flow which is conferred upon the liquid by the polymer additive and to an increase of the cavitation threshold of the liquid. At a maximum radius of about 400μm, the shock pressure for a bubble cloud, situated in water and 0.5% CMC solution, is with a factor of six larger than the value measured in the case of individual cavitation bubbles. This difference is smaller in the case of a 0.5% PAM solution where the shock pressure for a bubble cloud is only three times larger than for a single bubble. The results are discussed with respect to cavitation erosion in polymer solutions and collateral effects in pulsed high-intensity focused ultrasound surgery, such as histotripsy used for the destruction of blood clots.

Impulsive loading on reinforced concrete wall

This paper deals with the air blast and ground shock parameters for reinforced concrete wall panels. In this investigation peak pressure, pressure wave front arrival time, rising time, decreasing time and duration of the positive pressure phase of air blast time history parameters, and peak particle acceleration, arrival time, shock wave duration and time lag between ground shock and air blast pressure arrival at structures of ground shock owing to air blast were determined experimentally. Empirical relationships have been developed between different parameters. Typical values measured due to various charge weights have been compared with results of previous researchers and Conwep. The SAP2000 was used for stress analysis of wall panels using experimental results. The methodology outlined can be used to estimate the blast response of reinforced concrete walls. It is concluded that an accurate analysis of structure response and damage of structures caused by a nearby surface explosion requires simultaneous consideration of ground shock and air blast pressure.

Collapse of micrometer-sized cavitation bubbles near a rigid boundary

The interaction of cavitation bubbles with a rigid boundary and its dependence on the distance between bubble and boundary is investigated experimentally. Individual cavitation bubbles, with a maximum radius of 150 μm, are generated by using pulsed high-intensity focused ultrasound. Observations are made with high-speed photography with framing rates of up to 200 million frames per second and exposure time of 5 ns, and the spatial resolution is in the order of a few micrometers. The significant parameter of this study is the non-dimensional stand-off parameter, γ, defined as the distance between the ultrasound focus and the rigid boundary scaled by the maximum bubble radius. Both the velocity of the liquid jet developed during bubble collapse and the maximum pressure of the shock wave emitted during bubble rebound show a minimum for γ ≈ 1 and a constant value for γ > 3. The maximum jet velocity is slightly smaller than the corresponding values obtained in the case of millimeter-sized bubbles and ranges from 80 m/s (at γ ≈ 1) to 130 m/s (for γ > 3). No jet formation was observed for γ > 3. The shock wave pressure, measured at a distance of 5 mm from the emission center, ranges from 0.2 MPa (at γ ≈ 1) to 0.65 MPa (for γ > 3). These values are an order of magnitude smaller than those obtained in the case of millimeter-sized bubbles. The shock wave duration is almost independent of γ at a value of about 75 ns. For large γ values (γ > 3), a large percentage of the bubble energy (up to 60 %) is transformed into the mechanical energy of the shock wave emitted during bubble rebound but, for γ ≈ 1, the conversion efficiency decreases to 30 %. Independent of the relative distance between bubble and rigid boundary, the shock pressure decays proportionally to r−1 with increasing distance r from the emission center. The results are discussed with respect to cavitation damage and collateral effects in pulsed high-intensity focused ultrasound surgery.

The Basic Research for Pulverization of Rice Using Underwater Shock Wave by Electric Discharge

In recent years, the food self-support rate of Japan is 40%, and this value is the lowest level in major developed countries. This reason includes decreasing of diverting rice consumption in Japan and increasing abandonment of cultivation. Therefore, these problems are solved by using rice powder instead of expensive flour, and we manage to increase the food selfsupport rate. Previously, the rice powder is manufactured by two methods. One is dry type, and the other is wet type. The former is the method getting rice powder by running dried rice to rotating metal, and has a problem which that starch is damaged by heat when processing was performed. The latter is performed same method against wet rice, and has a problem which a large quantity of water is used. As a method to solve these problems, an underwater shock wave is used. Shock wave is the pressure wave which is over speed of sound by discharging high energy in short time. Propagating shock wave in water is underwater shock wave. The characters of underwater shock wave are long duration of shock wave because water density is uniform, water is low price and easy to get and not heat processing. Thinking of industrialization, the electric discharge is used as the generating source of underwater shock wave in the experiment. As the results, the efficiency of obtaining enough grain size, 100ìm, of rice powder was too bad only using the simple processing using underwater shock wave. Therefore, in Okinawa National College of Technology collaborating with us, obtaining rice powder with higher efficiency by using converged underwater shock wave is the goal of this research. In this research, the underwater shock wave with equal energy of the experimental device of underwater shock wave is measured by the optical observation. In addition, the appearance converging underwater shock wave is simulated by numerical analysis, and the pressure appreciation rate between the first wave and converged underwater shock wave is calculated by using the pressure history of 2nd focal point.

G211 超高温パルスによるN_2Oの直接分解に関する研究(一般講演)

We investigated on direct decomposition of a gas containing N_2O by shock tube and ignition device of imploding detonation type in the present study. Our purpose is to show the treatment temperature as nitrous oxide was decomposed and the effect of H20 as additive. In the single shock wave experiment, one is experiment of using differential pressure by driving gas He, the other is experiment of ignition by fuel CsHs. As a result, the highest decomposition 99 % was obtained in the single shock wave experiment and 54 % was obtained in continuous experiment. We found that treatment temperature and duration of shock wave are important parameters in N_2O decomposition.

The Heterogeneous Multiscale Method for Dynamics of Solids with Applications to Brittle Cracks

AbstractWe present a multiscale method for the modeling of dynamics of crystalline solids. The method employs the continuum elastodynamics model to introduce loading conditions and capture elastic waves, and near isolated defects, molecular dynamics (MD) model is used to resolve the local structure at the atomic scale. The coupling of the two models is achieved based on the framework of the heterogeneous multiscale method (HMM) and a consistent coupling condition with special treatment of the MD boundary condition. Application to the dynamics of a brittle crack under various loading conditions is presented. Elastic waves are observed to pass through the interface from atomistic region to the continuum region and reversely. Thresholds of strength and duration of shock waves to launch the crack opening are quantitatively studied and related to the inertia effect of crack tips.

Dynamic Compacting of Powders of Some Amorphous Alloys

AbstractAt present amorphous metallic alloys have the broad expansion in various fields of science&engineering as a result of their unique properties. In particular, soft magnetic amorphous alloys are extensively used in electrical engineering. However the production of considerable-size nonporous wares based on the powders (or tapes) of these alloys is heavy problem owing to high hardness of the particles. Therefore shock wave’s compacting or Dynamic Compacting (DC) method is promising one to produce the wares on the base of powders of amorphous alloys because it can provides high strength and near zero porosity of the wares. The experimental D-U diagrams of soft magnetic amorphous alloys were obtained to realize this method of compacting. The calculations of the amplitude and duration of shock wave were carried out. The several versions of explosive devices using shock plane wave generator to produce circular magnetic conductors were developed and were tested. These magnetic conductors are based on amorphous alloys of 5BDSR, GM414, 10NSR trademarks (Fe with Cu, Nb, Si, B additives). XRD analysis proved that amorphous state of the alloys remains the same up to 20 GPa shock wave’s pressures. The mechanical, structural, electrical and magnetic properties both initial amorphous alloys and compacted one were obtained and compared as a result of the implemented works. It was stated that DC leads to increase of magnetic conductivity by factor ∼15 with respect to initial amorphous alloys powder. Besides the specific losses decrease in ∼4 times.

Effect of shock wave hardening and cold working on mechanical properties of a new high nitrogen steel

Nitrogen alloyed austenitic steels are rather novel alloys and are still under development. They can suffer a very high deformation without the austenite becoming unstable. A very high strength can be achieved by work-hardening due to this property. In recently developed alloys, Mn-contents are reduced to about 12% with a nitrogen content of about 1%. The aim of this work is to investigate a newly developed high nitrogen steel called PANACEA. Both shock wave hardening and cold rolling were used to work-harden the alloy. The plates were shock loaded up to 600 kbar at shock wave duration from 0.5 ps to 4 μs and cold rolled with a reduction of 80%. Quasi-static and dynamic compression (SHPB) tests were performed to determine the mechanical behaviour prior and after work hardening. The microstructure was studied by optical and scanning electron microscopy.

Shock waves from a water-confined laser-generated plasma

Generation of a high amplitude shock wave by laser plasma in a water confinement regime has been investigated for an incident 25–30 ns/40 J/λ=1.064 μm pulsed laser beam. Experimental measurements of temporal and spatial profiles of induced shock waves for this regime of laser shock processing of materials were performed using a velocimetry interferometer system for any reflector system. Above a 10 GW/cm2 laser intensity threshold, a saturation of the peak pressure is shown to occur while the pressure pulse duration is reduced by parasitic plasma occurring in the confining water. The observation of the interaction zone with a fast camera system shows that this breakdown plasma, which mainly occurs at the very surface of the water rather than within the water volume, limits the efficiency of the process. This plasma absorbs the incident laser energy, and the power density reaching the target gradually decreases with increasing power densities while the shock-wave duration is correspondingly reduced. Both pressure measurements and plasma observations allow explaining the current limit of high amplitude shock-waves generation by laser plasma in the water-confinement mode and open new research areas for the understanding of breakdown plasma effects at the surface of the confining water.

Shock wave emission and cavitation bubble generation by picosecond and nanosecond optical breakdown in water

Shock wave emission and cavitation bubble expansion after optical breakdown in water with Nd:YAG laser pulses of 30-ps and 6-ns duration is investigated for energies between 50 μJ and 10 mJ which are often used for intraocular laser surgery. Time-resolved photography is applied to measure the position of the shock front and the bubble wall as a function of time. The photographs are used to determine the shock front and bubble wall velocity as well as the shock wave pressure as a function of time or position. Calculations of the bubble formation and shock wave emission are performed using the Gilmore model of cavitation bubble dynamics and the Kirkwood–Bethe hypothesis. The calculations are based on the laser pulse duration, the size of the plasma, and the maximally expanded cavitation bubble, i.e., on easily measurable parameters. They yield the dynamics of the bubble wall, the pressure evolution inside the bubble, and pressure profiles in the surrounding liquid at fixed times after the start of the laser pulse. The results of the calculations agree well with the experimental data. A large percentage of the laser pulse energy (up to 72%) is transformed into the mechanical energy ES and EB of the shock wave and cavitation bubble, whereby the partitioning between ES and EB is approximately equal. 65%–85% of ES is dissipated during the first 10 mm of shock wave propagation. The pressure at the plasma rim ranges from 1300 MPa (50 μJ, 30 ps) to 7150 MPa (10 mJ, 6 ns). The calculated initial shock wave duration has values between 20 and 58 ns, the duration measured 10 mm away from the plasma is between 43 and 148 ns. A formation phase of the shock front occurs after the ns pulses, but not after the ps pulses where the shock front exists already 100 ps after the start of the laser pulse. After shock front formation, the pressure decays approximately proportional to r−2, and at pressure values below 100 MPa proportional to r−1.06. The maximum bubble wall velocity ranges from 390 to 2450 m/s. The calculations of bubble and shock wave dynamics can cover a large parameter range and may thus serve as a tool for the optimization of laser parameters in medical laser applications.

Formation of the cubic phase of zirconium dioxide with a low concentration of stabilizing addition in a shock wave with subsequent heating

The possibility of obtaining solid solutions based on cubic ZrO2 with a low concentration of Y2O3 by detonation treatment (DT) with a shock wave duration <10−9 sec was studied. Phase formation and the defect structure of powders and sintered products after various heat treatments, including prolonged annealing at 1250°C, were studied by the methods of x-ray diffractometry and positron spectroscopy.