High-pressure Shock Waves Research Articles

Effects of different conductive ions on pore-structure evolution of medium- and high-rank coal bodies induced by electric pulses

Electric pulse fracturing technology is a new type of coal seam fracturing and permeability increasing technology based on high-pressure shock wave technology. Compared with conventional technology, electric pulse fracturing has the advantages of a higher energy efficiency, less environmental pollution, and a shorter fracturing time, but having the disadvantages of rapid energy loss and a small fracture radius. To reduce the energy loss of electric pulses and increase the fracture radius, the experimental system of high-voltage electric pulse was employed in this study. The effects of NaCl, CaCl2, and AlCl3 conductive ions on the evolution of the pore structure induced by electric pulses were examined for medium- and high-rank coal bodies. The experimental results indicated the adsorption capacity of coal for ions was positively correlated with the valence of the cations and the soaking time, and the amount of ions adsorbed was larger when the solution was more alkaline. Amounts of ions adsorbed onto the coal surface decreased in the following order Al3+ > Ca2+ > Na+. After the treatment, the conductivity of the coal was significantly improved, making the plasma channel in the coal body more fully developed in the process of high-voltage electric pulse impaction, thus reducing significantly the breakdown voltage of the coal samples. Additionally, tthe total pore volume, total specific surface area, porosity, and average pore diameter of the treated coal increased and that the percentages of macropores and mesopores increased, indicating that the pore structure of coal samples is significantly improved.

Sub-micrometer and nanoscale imprinting on large-area foils using high-pressure underwater shock waves

Laser shock imprinting (LSI) is an emerging method for creating sub-micrometer and nanoscale reliefs on thin metal foils. This report proposes using underwater shockwaves, generated by detonating an explosive charge, for high-quality imprinting as an alternative to LSI. The nanoscale relief of a polycarbonate mold with 740 nm periodic grooves was replicated on an Al foil using an underwater shockwave. Underwater detonation of a high explosive creates a shockwave with pressure ≥ 1 GPa that lasts for more than 100 ns, significantly longer than that for LSI. This provides a relief depth equal to 90% of the depth of the grooves on the mold. This mold filling efficiency is the best achieved by shock imprinting reported to date. In addition, underwater shockwaves can be used for imprinting over a large area in a single shot. Furthermore, the thickness of the Al foil can be increased in comparison to that for LSI. Using a simplified 1-D model of foil acceleration, we showed that increasing the foil thickness decreases the imprinting accuracy. This study paves new ways for large-area manufacturing of micro/nanopatterns on metals that would be especially beneficial for future applications in the fields of plasmonics and metasurfaces.

Numerical study and experimental validation of blastworthy structure using aluminum foam sandwich subjected to fragmented 8 kg TNT blast loading

A blastworthy structure is defined as a structure that has the ability to deform with a controlled force and preserve sufficient residual space around the occupants to limit bodily injury during a blast impact incident. In this research, a blastworthy aluminum foam sandwich (AFS) structure that consisted of an occupant side plate (OSP), a struck side plate (SSP), and an aluminum foam (Al-foam) core were numerically and experimentally subjected to blast-fragmented loading. The explosion with high-pressure shock waves was produced by steel-covered TNT, creating a synergistic blast and fragment loading. The interaction between the blast-fragment loading and the AFS created a unique perforation pattern due to Monroe's effect. The measured blastworthiness characteristics included structural integrity, acceleration, and reaction force. A numerical modeling strategy to analyze the blastworthiness performance of the AFS structure was developed to capture the dynamic responses and the damage mechanism. Two types of blast loading, namely load blast enhanced (LBE) and smooth particle hydrodynamic (SPH) blast loading, were utilized along with the Cockcroft-Latham damage modeling on the AFS. A blast experimental setup with a fix-clamped method was used to evaluate the blastworthy characteristics of the panel to acquire the central acceleration and reaction force histories. A two-step process of experimental validation was carried out. First, a pre-test system validation with a very low explosive blast using 60 gram of TNT was conducted on the sandwich specimen to ensure the data acquisition system's functionality and to obtain comparable data for system validation. Second, a blast impact test using 8 kg of steel-covered TNT was carried out to validate the numerical modeling results. The results of the numerical analysis showed that the LBE model had good agreement with the test data for the small deformation blast impact loading with 60 gram TNT. For the large deformation blast impact loading with 8 kg TNT, the SPH models provided excellent agreement with the damage mode and dynamic responses, where the acceleration and the reaction force performances were both within 6.1% and 6.4% of the experimental validation, respectively. As for the structural performance of the AFS construction, it was observed that the sandwich panel met the structural integrity requirements. There were no cracks or fractures in the OSP. The SSP and Al-foam absorbed more than 98.3% of the blast impact energy, providing extra protection for the OSP. This research contributes to the dynamic structural-response and damage investigation of AFS subjected to fragmented 8 kg TNT blast loading.

Effects of Increasing Acoustic Power at a Small-Diameter Ultrasonic Horn Tip on the Synthesis and Characteristics of MnO2 Nanoparticles

In this research, we measured the chemical and the physical parameters of increasing ultrasonic power amplitude at a small-diameter ultrasonic horn tip in a volume of 50 ml. This work was done using KI dosimeter, a calorimetric method, electrical power measurements, and photographs of the bubble cloud. Then, the effects of increasing ultrasonic amplitude on the synthesis and the characteristics of MnO2 nanoparticles was studied. The different MnO2 nanoparticles were characterized by using UV-Vis spectroscopy, powder X-ray diffraction (XRD), and field-emission scaning electron microscopy (FESEM). The results showed that when the acoustic power was increased, the crystallite size and the adhesion between nanoparticles increased. However, the synthesis rate of the nanoparticles was not significantly increased. The comparability of the measured data is discussed by considering cavitation dynamics, bubble collapse, high-pressure shock waves, and cavitation shielding.

Investigation on the effect of EDM process variables and environments on acoustic emission signals

The performance of electrical discharge machining (EDM) primarily depends on the spark quality generated in the inter-electrode gap (IEG) between the tool and workpiece. A method for obtaining accurate information about the spark gap is required to effectively monitor the EDM process. The rise and fall of thermal energy in the discharge zone at a rapid rate during the dielectric breakdown produces high-pressure shock waves. This work explores the suitability of using acoustic emission (AE) generated from these shock waves and the elastic AE waves released on the workpiece due to the induced stress to monitor the performance and spark gap in EDM. The information content of the AE signals acquired at various machining conditions was extracted using AE RMS, spectral energy and peak amplitude. These features were able to well discriminate the machining condition, tool material, workpiece material, flushing pressure, current density, the initial surface roughness of the tool. Additionally, the AE signal features had a good and consistent correlation with the performance parameters, including material removal rate, surface roughness (Ra and Rq) and tool wear. The findings lay the groundwork to develop an effective, non-intrusive in-situ AE-monitoring system for performance and IEG condition in EDM.

The Dynamic Evolution of Cavitation Vacuolar Cloud with High-Speed Camera

The dynamic model of a single cavitation bubble in the submerged cavitation water jet was established and solved by MATLAB to obtain its motion characteristics and pressure pulse change rules. Numerical simulation based on FLUENT to closer wall, empty bubble breaking form then influences the law of mechanics effect, with the increase in empty bubble, and the breaking time is reduced, but the maximum jet velocity and pressure increase gradually, on the mechanism of action of the solid wall by the fact that the combination of microfluidic and shock wave gradually plays a leading role, while plastic deformation and basic cavitation erosion are avoided. The maximum pressure and maximum jet velocity increase little, and the collapse time of cavitation is reduced. By comparing the grayscale images of the two combinations of jets, it can be found that the brightness of the vacuolar clouds in diameter (d) = 1.6 mm and pressure (P) = 15 MPa is slightly less than that in d = 1.2 mm and P = 30 MPa, indicating that the density of the vacuolar clouds and the dispersion is relatively high, while the increase in nozzle diameter leads to the increase in flow rate, which increases the shear layer of high-speed submerged jet in a static water. The pressure pulse generated by cavitating water jet hollow bubble failure is far greater than the linear superposition value of a single cavitation bubble. But the high-pressure shock wave value on the fixed wall and water hammer pressure are generated by microjet. The conclusion is also corresponding to the simulation results.

Experimental study on the optimum matching of CW-nanosecond combined pulse laser drilling.

A combined pulse laser (CPL) drilling method that consisted of a continuous wave (CW) laser and an assisted nanosecond laser was used for drilling the Q235B steel. The influence of the repetition rate of the nanosecond laser on the CPL drilling efficiency was analyzed. The results show that the plasma screening threshold during the CPL drilling was about ${1.40} \times {{10}^9}\,\,{\rm W}/{{\rm cm}^2}$1.40×109W/cm2. When the peak power density of the nanosecond laser exceeded the plasma screening threshold, it still could not compensate for the energy loss caused by the plasma screening, even though the high-pressure shock wave introduced by the plasma could improve the drilling efficiency. On the other hand, when the peak power density of the nanosecond laser was lower than the plasma screening threshold, it was shown that the optimum matching between the CW laser and nanosecond laser could be obtained when the repetition rate of the nanosecond laser was between 10 and 25 kHz. Finally, the results show that the CPL drilling method had a better drilling efficiency and quality than conventional millisecond laser drilling.

Adsorption characteristics of chloramphenicol onto powdered activated carbon and its desorption performance by ultrasound

ABSTRACT In this work, the adsorption characteristics, including adsorption kinetic, isotherm and thermodynamics of chloramphenicol (CAP) onto powdered activated carbon (PAC), were carried out, and the feasibility of using ultrasound to regenerate saturated PAC in aqueous solution was evaluated. The adsorption results demonstrated that the adsorption mechanism was a complex process including surface adsorption, external liquid membrane diffusion and intraparticle diffusion as well, and the adsorption process was endothermic and non-spontaneous. The optimal conditions for PAC regeneration were as follows: acoustic density of 0.36 W/mL, saturated carbon dosage of 1.0 g/L and pH value of 10.36. The analysis of thermogravimetric analysis (TGA), Fourier transform infrared spectrometry (FTIR), Brunauer–Emmett–Teller (BET) surface area, pore size distribution and scanning electron microscopy (SEM) of PAC samples revealed that ultrasound mainly acted on surface functionalities, meso-pores and macro-pores of PAC through hydroxyl radical oxidization, high-pressure shock waves and high-speed microjets due to cavitation effect. This study highlighted that ultrasound could be efficiently desorbing CAP from saturated PAC. Practical applications of this method for PAC regeneration with complex natural matrices under environmentally realistic conditions were conducted and the adsorption capacity of the regenerated PAC decreased.

Effect of Laser Shock Peening on Fatigue life of Austenitic stainless steels

.Laser shock peening (LSP) is an innovative surface treatment technique for strengthening metallic materials. The treatment improves fatigue performance and is achieved by introducing compressive residual stresses into the material surface layer. The compressive stresses are created over a significant surface area by means of high pressure shock waves, which are generated by confining the laser-induced plasma. In the present study, the LSP effect on fatigue life of austenitic stainless steels was investigated by changing the laser parameters. The tested material was austenitic stainless steel 08CH18N10T. The influence of LSP treatment on the fatigue life was examined through the three-point bend fatigue test.

Evaluation of formability enhancement of aluminum alloy sheet in electrohydraulic forming process with free-bulge die

Electrohydraulic forming (EHF), a high-speed forming process, deforms a material by using high-pressure shockwaves in a fluid-filled chamber. When a material is deformed at speeds higher than 100 m/s, its formability can be improved due to the high-strain rate effect. This allows for the production of complex shapes, such as sharp edges. Therefore, in the present study, we confirm improvement in the formability of aluminum alloy 6061-T6 under high-strain rate condition by conducting EHF experiments. The strains of the deformed specimen are measured using a strain measurement apparatus, and they are compared with the values obtained from a quasi-static forming limit diagram. The comparison verified the improvement in formability, in that the material did not fracture even though the strain distribution of the material at high speeds was located higher than the quasi-static forming limit curve. In addition, we perform finite element analysis to observe the deformed material in detail. Finally, we compare the strain distributions obtained in the numerical simulation and the experiment to verify the reliability of the numerical model proposed herein.

Graphene-Like Nanoflakes for Shock Absorption Applications

The effects of high-pressure shock waves generated by the detonation of explosives are of major interest to the strategic sector. We report interaction of transonic shock waves (1.1 Mach speed; pea...

A novel steam ejector with pressure regulation to optimize the entrained flow passage for performance improvement in MED-TVC desalination system

Steam ejector plays a critical role in MED-TVC desalination system that can achieve a good balance between freshwater production and energy savings. In this study, a pressure regulation technology is proposed to optimize the entrained flow passage and thus improve the ejector performance. The theoretical basis is that there have some existing low-pressure potentials inside the ejector that can be used to alleviate the high-pressure effect and shock wave at the mixing chamber end. Then the feasibility verification and performance comparison of different pressure regulation schemes is implemented systematically. Analysis and research mainly pay attention to the influences of pressure regulations on the mass flow rate, the entrainment ratio and internal flow field. The results reveal that there is an optimum combination of pressure regulation schemes, by which a most considerable entrainment ratio improvement could be achieved, as large as 11.77% within the simulated conditions, and with 3.94% even under the design condition. More specifically, for the given steam ejector, TMCE pressure regulation could be used if the ejector operates under the design condition. For the off-design conditions, CMCE pressure regulation is the best choice if the back pressure is larger than 34 kPa, otherwise DMCE pressure regulation should be chosen.

Application of massive laser shock processing for improvement of mechanical and tribological properties

The present paper aims to investigate topographical, microstructural, mechanical and tribological behaviour of precipitation hardened Al alloy subjected to massive laser shock processing (LSP) without protective coating at 2500 pulses/cm2, using three beam diameters. Wear tests under dry sliding conditions resulted in severe wear, whereas the main wear mechanisms were adhesion accompanied by abrasive wear. Nevertheless, LSP with optimal processing parameters reduce the friction coefficient and wear rate with lower degrees of adhesion and abrasion inside the wear track in comparison to the untreated sample. The enhanced tribological performance is attributed to the positive influence of LSP induced surface topography, surface compressive residual stresses (RS) and dense dislocation arrangements, as the result of high-pressure shock waves. Nonetheless, due to the narrow window of optimal parameters reduced wear resistance as a consequence of undesired thermal/softening effect due to laser ablation and melting was detected with non-optimal processing parameters.

Experimental research on the effect of shock wave on the evolution of high-pressure diesel spray

With the increase in the diesel injection pressure in modern diesel engines, the velocity of the diesel spray increases accordingly, and shock waves are induced when the spray is supersonic. To better understand the effect of shock waves on the spray development, the evolution of the high-pressure diesel spray and shock wave under different diesel injection pressures and ambient pressure has been investigated using the Schlieren imaging method. The results show that the shock wave affects the development of the spray and the mixing effect between the spray and surrounding air. The shock wave promotes development of the spray tip penetration and enhances the gas entrainment effect. However, the shock wave has an inhibitory effect on the spray development in the radial direction. In addition, the shock wave angle determines the range of influence on the ambient air, which affects atomization of the spray. The shock wave angle increases with the decrease in the spray front Mach number. An empirical correlation of the shock wave angle and spray front Mach number was proposed in this paper. The calculated results are in good agreement with the experimental data. In addition, a diagram of the shock wave generation and classification in a diesel engine is proposed.

X-ray absorption radiography for high pressure shock wave studies

The study of laser compressed matter, both warm dense matter (WDM) and hot dense matter (HDM), is relevant to several research areas, including materials science, astrophysics, inertial confinement fusion. X-ray absorption radiography is a unique tool to diagnose compressed WDM and HDM. The application of radiography to shock-wave studies is presented and discussed. In addition to the standard Abel inversion to recover a density map from a transmission map, a procedure has been developed to generate synthetic radiographs using density maps produced by the hydrodynamics code DUED. This procedure takes into account both source-target geometry and source size (which plays a non negligible role in the interpretation of the data), and allows to reproduce transmission data with a good degree of accuracy.

Experimental validation of numerical modeling of electrohydraulic forming using an al 5052-H34 sheet

Electrohydraulic forming (EHF) is a high strain rate process that uses an electric discharge in fluid. When electrical energy stored in a capacitor is discharged, two electrodes that are submerged in a fluid create a high-pressure shock wave that deforms a blank to a forming die. This study presents numerical results of EHF conducted in advance using LS-DYNA commercial software. The arbitrary Lagrange–Eulerian method was employed to create elements in the fluid region, and lagrangian mesh was used for the structural region. Numerical results showed that a pressure wave was created from the electrical energy in the capacitor, which led to the deformation of an aluminum alloy sheet kept in contact with the fluid surface into a die. It was also found that the maximum strain rate of the blank was approximately 3200 s−1. An EHF apparatus was also developed and a forming test carried out as a function of the amplitude of the input voltage using a capacitor with 32 kJ stored energy. A comparison between the bulge height of the blank from the experiment and that obtained via numerical simulation showed good agreement.

Impact testing Facility: BHISM for Performance Based Design of Reinforced Concrete (RC) Structures

This research deals with the design and development of Blast and Heavy Impact Simulation mechanism (BHISM) for generating high fidelity data for impact resistant design, testing and validation of reinforced concrete structures experimentally. A commercial finite element software LS-DYNA is used to solve the governing equations, Altair-Hypermesh for meshing and LS-Prepost for pre and post processing. The basic principle used to generate high pressure shock wave is same as the shock tube. The propulsion of shock wave will achieve due to rupture of the diaphragm by accumulation of pressure in high pressure zone (driver section) of BHISM. A missile is placed after diaphragm i.e. low pressure zone (driven section) of BHISM. The Missile is restrained in five degrees of freedom except in the forward surge direction of translation. When the pressure is transferred on to the missile, it will move with a velocity. Analysing the RC members subjected to impact loading due to missile is future target. This research will be useful to find out the necessary parameters required for better construction of RC structures due to impact loading and to modify the existing codes on impact resistant RC structures.

Protective role of chitosan oligosaccharide on blast brain injury in rats

Objective To investigate the protective role of chitosan oligosaccharide on blast brain injury (BBI) in rats. Methods Ninety male SD rats were divided into control group, BBI group and chitosan oligosaccharide group according to the random number table, with 30 rats per group. A model of BBI was induced by high pressure shock wave. Rats in chitosan oligosaccharide group received chitosan oligosaccharide (20 mg/kg body weight) intraperitoneally once a day for 5 days after the induction of BBI. For control and BBI groups, an equal amount of normal saline was given. Rat neurological severity score (NSS) was evaluated using the maze test, pole test and reflection test. Brain tissue pathological changes were observed using HE staining. Activity of catalase (CAT) and contents of malondialdehyde (MDA) and reactive oxygen species (ROS) in brain tissues were determined using the ELISA method. Protein expressions of tumor necrosis factor α (TNF-α) and nuclear factor-κB (NF-κB) in brain tissues were tested using the Western blot and immunefluorescence method . Expressions of TNF-α and NF-κB mRNA in brain tissues were determined using the Real time PCR. Results Mean NSS was 0 point in control group, 5.52 points in BBI group, and 3.56 points in chitosan oligosaccharide group (P 0.05). Conclusion Chitosan oligosaccharide can protect rats against BBI by down-regulating expressions of TNF-α and NF-κB and reducing oxidative damage. Key words: Brain injuries; Blast injuries; Chitosan; Inflammation; Oxidative stress

Graphics-Processing-Unit-Accelerated Multiphase Computational Tool for Asteroid Fragmentation/Pulverization Simulation

The simulation of asteroid target fragmentation or pulverization is a challenging task that demands efficient and accurate numerical methods with large computational power. To this end, the high-order spectral difference method is implemented with graphics-processing-unit computing. Hypervelocity kinetic-energy impactors are of practical interest, which generate high-pressure deformational shock waves in the target bodies upon impact. Due to the extremely short deformation time associated with hypervelocity impact, the material behaves in a similar manner to a compressible fluid, and the compressible Euler equations can be applied. To model the multiple material interactions, an -phase equation model is adopted into the spectral difference method. All simulations presented are solved with graphics processing units, producing solutions orders of magnitude faster than the central-processing-unit counterpart. Several impact cases are compared, including a heavy impactor and multiple impactor system, against an asteroid target. Orbital dispersion effectiveness is evaluated, and results indicate that the multiple impactor system outperforms the single heavy impactor.

Spatio-temporal filter bank for visualizing audible sound field by Schlieren method

Visualization of sound field using optical techniques is a powerful tool for understanding acoustical behaviors. It uses light waves to examine the acoustical quantities without disturbing the sound information of the field under investigation. Schlieren imaging is an optical method that uses a camera to visualize the density of transparent media. As it uses a single shot to capture the information without scanning, it can observe both reproducible and non-reproducible sound field. Conventionally, the Schlieren system is applied to high-pressure ultrasound and shock waves. However, since the density variation of air caused by the audible sound field is very small, this method was not applicable for visualizing these fields. In this paper, a spatio-temporal filter bank is proposed to overcome this problem. As the sound is a very specific signal, the spatio-temporal spectrum (in two-dimensional space and time) of the audible sound is concentrated in a specific region. The spatio-temporal filter bank is designed for extracting the sound field information in the specific region and removing noise. The results indicate that the visibility of the sound fields is enhanced by using the proposed method.