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In order to investigate the effect of the carrier's initial velocity on the jet's damage power, this paper conducted the numerical simulation of a jet penetrating thick‐walled targets at various following velocities (the carrier's initial velocity). For large stand‐off distance (D), the influence on jet formation parameters was revealed under different following velocities (ranging from 0 to 1000 m/s), and the jet's penetration performances were analyzed at various stand‐off distances (ranging from 3D to 10D). Then, taking 3D as an example, the study investigated the influence mechanism of the coupling between following velocity and impact angle (ranging from −60° to 60°) on jet penetration performance. The results show that an increase in the following velocity causes the jet to bend and break at an earlier time. The following velocity has a minimal effect on jet tip velocity. Additionally, the lateral displacement is linearly correlated with stand‐off distance. For normal penetration, the jet penetration depth decreases exponentially as the following velocity increases at the same stand‐off distance. Especially, the penetration depth decreases by over 80% when the following velocity exceeds 600 m/s, and a further increase in the following velocity has a minimal effect on jet penetration depth. A greater jet penetration depth was achieved for the climbing‐oblique penetration (COP) than the diving‐oblique penetration (DOP) due to an increase in dynamic stand‐off distance. Finally, the ratio of oblique to normal penetration depth for a jet with varying following velocities was derived based on the theory of steady‐jet and hole expansion, and its accuracy was verified. [ABSTRACT FROM AUTHOR]

In order to improve the research and development efficiency and quality of low-density liners in production and scientific research development, PLA and PLA-Cu composite liners were prepared based on 3D-printing technology. In this paper, the relationship between the shock wave velocity D and the particle velocity u of PLA and PLA-Cu materials was tested by a one-stage light gas gun experiment device, and then the Grüneisen equation of state parameters of the two materials was obtained by fitting. The forming process of the two jets was numerically simulated by using the equation of state. When combined with the pulsed X-ray shooting results of the jets, it was found that the jets of the two materials showed obvious characteristics of "expansion particle flow", and the head of the PLA jet had a gasification phenomenon. The length of the PLA jet at 20 μs in the numerical simulation was 127.2 mm, and the average length of the PLA jet at 20 μs in the pulsed X-ray shooting experiment was 100.45 mm. The length of the PLA jet gasification part accounted for about 21% of the total length of the jet. The average velocity of the head of the PLA jet is 7798.35 m/s, and the average velocity of the head of the PLA-Cu jet is 8104.25 m/s. In this paper, 3D-printing technology is used to prepare the liner for the first time, aiming to open up a new preparation technology and provide a new material selection for low-density material liners. [ABSTRACT FROM AUTHOR]

In this paper, the reaction characteristic and its application in shaped charge warhead of a novel reactive material, which introduced copper (Cu) and plumbum (Pb) into traditional polytetrafluoroethylene/aluminum (PTFE/Al), are studied. The thermal analysis and chemical reaction behavior of the PTFE/Al/Cu/Pb mixture are investigated by Differential Scanning Calorimetry (DSC),Thermo-gravimetry (TG), and X-ray Diffraction (XRD) techniques. Then, the shaped charge liners with PTFE/Al/Cu/Pb reactive materials are fabricated, and the X-ray experiments show that they could form reactive jets with excellent performance under the detonation effects of the shaped charge. Based on that, the penetration experiments of shaped charge with PTFE/Al/Cu/Pb reactive liner against steel plates are carried out, and the results demonstrate that the PTFE/Al/Cu/Pb reactive jets could produce a deeper penetration depth compared to the traditional PTFE/Al reactive jets. Meanwhile, the PTFE/Al/Cu/Pb reactive jets also show significant inner-blast effects, leading to dramatically cracking or fragmentation behavior of the penetrated steel plates. This new PTFE/Al/Cu/Pb reactive liner shaped charge presents enhanced penetration behavior for steel targets that incorporates the penetration capability of a high-density and ductility jet, and the chemical energy release of PTFE-matrix reactive materials.

Mrk 501 is one of the most prominent TeV-emitting blazars and belongs to the class of high synchrotron peaked (HSP) blazars. The Doppler factors derived from the jet kinematics are much too low to provide sufficient beaming for the detected high-energy emission (the so-called Lorentz factor crisis). This BL Lac object is also a prime example of a misaligned AGN with an approximately 90 ∘ difference in orientation between the inner parsec-scale jet and the kpc-scale jet structure. We have performed a detailed analysis of the pc-scale jet kinematics, based on 23 years of VLBA observations (at 15 GHz) and find, in addition to robustly consolidating the already claimed stationary jet features and a hinted absence of component ejections, a significant drift of the outer nuclear jet. The two outermost jet features move with somewhat higher but still subluminal speeds. Albeit, they move orthogonally to the inner jet, which itself does not partake in the drifting motion. The effect of this intriguing kinematics is that the jet appears strongly curved at first (1995) but then appears to straighten out (2018). To our knowledge, this is the first time that the orthogonal swing of just the outer part of a nuclear jet has been observed. We discuss the possible physical nature of this turning maneuver. In addition, we report evidence for jet emission, which most likely originates in a spine–sheath structure. [ABSTRACT FROM AUTHOR]

In order to improve the research and development efficiency and quality of low-density liners in production and scientific research development, PLA and PLA-Cu composite liners were prepared based on 3D-printing technology. In this paper, the relationship between the shock wave velocity D and the particle velocity u of PLA and PLA-Cu materials was tested by a one-stage light gas gun experiment device, and then the Grüneisen equation of state parameters of the two materials was obtained by fitting. The forming process of the two jets was numerically simulated by using the equation of state. When combined with the pulsed X-ray shooting results of the jets, it was found that the jets of the two materials showed obvious characteristics of “expansion particle flow”, and the head of the PLA jet had a gasification phenomenon. The length of the PLA jet at 20 μs in the numerical simulation was 127.2 mm, and the average length of the PLA jet at 20 μs in the pulsed X-ray shooting experiment was 100.45 mm. The length of the PLA jet gasification part accounted for about 21% of the total length of the jet. The average velocity of the head of the PLA jet is 7798.35 m/s, and the average velocity of the head of the PLA-Cu jet is 8104.25 m/s. In this paper, 3D-printing technology is used to prepare the liner for the first time, aiming to open up a new preparation technology and provide a new material selection for low-density material liners.

Mrk 501 is one of the most prominent TeV-emitting blazars and belongs to the class of high synchrotron peaked (HSP) blazars. The Doppler factors derived from the jet kinematics are much too low to provide sufficient beaming for the detected high-energy emission (the so-called Lorentz factor crisis). This BL Lac object is also a prime example of a misaligned AGN with an approximately 90∘ difference in orientation between the inner parsec-scale jet and the kpc-scale jet structure. We have performed a detailed analysis of the pc-scale jet kinematics, based on 23 years of VLBA observations (at 15 GHz) and find, in addition to robustly consolidating the already claimed stationary jet features and a hinted absence of component ejections, a significant drift of the outer nuclear jet. The two outermost jet features move with somewhat higher but still subluminal speeds. Albeit, they move orthogonally to the inner jet, which itself does not partake in the drifting motion. The effect of this intriguing kinematics is that the jet appears strongly curved at first (1995) but then appears to straighten out (2018). To our knowledge, this is the first time that the orthogonal swing of just the outer part of a nuclear jet has been observed. We discuss the possible physical nature of this turning maneuver. In addition, we report evidence for jet emission, which most likely originates in a spine–sheath structure.

The jet morphology of square and circular cross-section shaped charge with same inscribed circle diameter were observed by conducting an X-ray experiment. Depth-of-penetration tests at standoffs 80 and 160 mm were also carried out. The jet formation was studied by using AUTODYN software. The results showed that the jet of square cross-section shaped charge consists of a condensed part and a non-condensed part. The condensed part has similar characteristics to the corresponding part of circular cross-section shaped charge. And the non-condensed part is distributed at the jet tail. The non-condensed part consists of a main fluid moving along the axis and four off-axis fluids with off-axis velocity along the symmetry plane. The noncondensing of jet reduces the penetration depth of square cross-section shaped charge, the decreasing rate increased from 2.67% to 17.3% when the standoff is increased from 80 mm to 160 mm. When the inscribed circle diameter of the charge cross-section increases to 67.2 mm (1.2 times of 56 mm) and the liner structure remains the same, the square cross-section shaped charge will form a cohesive jet. [ABSTRACT FROM AUTHOR]

The article focuses on the development of the new calculation method of jet penetration into the target using ANSYS AUTODYN simulation. The jet formation and its penetration capability dependence on properties of targets are studied. Two kinds of steel armours - Armox 440T and S235JR - in standardized plates of thickness 20 mm are used as materials of the target. The paper contains an analysis of the penetration depth in the targets containing the pure material plates set, combined material plates set and sets of Armox 440T plates with gaps 10 mm and 20 mm among individual plates. The theoretical results of simulation are compared with the results of experiments. [ABSTRACT FROM AUTHOR]

The article presents the influence of the wave shaper position on the jet formation and penetration depth of a shaped charge, which uses the liner of the PG-7VM warhead by numerical method and experimental method. The results show that, when moving the plexiglass wave shaper position towards the liner apex, the jet tip velocity and the jet velocity gradient increase. In addition, the results of the study also pointed out the existence of the wave shaper position at which the penetration depth is greatest. They indicate a match between the simulation and experimental results. The differences between simulated and experimental penetration depth are less than 15%. The results of the study are the basis for the evaluation of the influence of the wave shaper position on the liner collapse and the reasonable use of the wave shaper in the structure of the shaped charge. [ABSTRACT FROM AUTHOR]

Shaped charges are used to pierce hard targets in all three versions of warfare land, air and naval. High explosives compositions fillings produce a thin high velocity metal jet which is used for target damage. Shaped charges can efficiently damage tanks possessing thick armour protection, bunkers and aircraft and are also useful for attacking ships and submarines. Shaped charges have a very long history since the Second World War Theoretical modeling started with the steady state theory of Birkhoff in 1948, which was modified by the non-steady state theory known as PER theory of shaped charges. To review the development in the shaped charges three stages are defined. In the first stage development until 1990 is presented when shaped charge theory was fully developed and penetration predictions with fairly good accuracy were possible. In the second stage, review of the work carried out in the last decade of the 20th century is discussed. During this period experimental verification of different parameters was established. The third stage deals with all the work carried out in the 21st century (2000-2010), including tools for advanced diagnostics, new fabrication and inspection, as well as new liner materials were included. The anomalies occurred were resolved by further refinements in the theoretical models.

On the basis of the RCL circuit model and Pugh–Eichelberger–Rostoker (PER) theory of jet formation and combining with Maxwell equations, the calculation method for the electromagnetic force and the collapse velocity of the liner is obtained through the infinitesimal method. The theoretical model of jet formation of a liner driven by a strong magnetic force is established. The model can calculate the collapse process and jet formation of the liner, jet and tail velocity, jet length, diameter, and other important parameters at any time. Simultaneously, the jet and tail velocity parameters and the shape of the jet under different voltages are calculated using the theoretical model established in this research. To verify the correctness of the theoretical model, a liner has been calculated and compared with the experimental results. The relative error of the jet tip velocity is found to be 3.7%. The results show that the theoretical model established in this research can accurately calculate the jet forming process and the related parameters driven by strong electromagnetic energy. [ABSTRACT FROM AUTHOR]

The process of formation, flying, penetration of explosively-formed projectiles (EFP) and the effect of water on performance of the charge for underwater applications is simulated by Ansysis Autodyn 2D-Hydro code. The main objective of an explosively formed projectile designed for underwater applications is to disintegrate the target at longer standoff distances. In this paper we have simulated the explosively formed projectile from OFHC-Copper liner for 1200 conical angle. The Affect of water on the penetration of EFP is determined by simulations from Ansysis Autodyn 2-D Hydrocode and by varying depth of water from 1CD-5CD. The depth of penetration against steel target is measured experimentally. Flash X-Ray Radiography (FXR) is used to capture EFP jet formation and its penetration against target is measured by depth of penetration experiments. Simulation results are compared with experimental results. The difference in simulated and experimental results for depth of penetration is about 7 mm, which lies within favorable range of error. The jet formation captured from FXR is quite clear and jet velocity determined from Flash X-ray radiography is the same as the ones obtained by using other high explosives. Therefore, it is indicated that Insensitive Munition (8701) can be utilized instead of Polymer Bonded Explosives (PBX) for air and underwater environments with great reliability and without any hazard.

The traditional polytetrafluoroethylene (PTFE)/Al reactive material liner shaped charge generally produces insufficient penetration depth, although it enlarges the penetration hole diameter by chemical energy release inside the penetration crater. As such, a novel high-density reactive material liner based on the PTFE matrix was fabricated, and the corresponding penetration performance was investigated. Firstly, the PTFE/W/Cu/Pb high-density reactive material liner was fabricated via a cold pressing/sintering process. Then, jet formation and penetration behaviors at different standoffs were studied by pulse X-ray and static experiments, respectively. The X-ray results showed that the PTFE/W/Cu/Pb high-density reactive material liner forms an excellent reactive jet penetrator, and the static experimental results demonstrated that the penetration depth of this high-density reactive jet increased firstly and then decreased by increasing the standoff. When the standoff was 1.5 CD (charge diameter), the penetration depth of this reactive jet reached 2.82 CD, which was significantly higher than that of the traditional PTFE/Al reactive jet. Moreover, compared with the conventional metal copper jet penetrating steel plates, the entrance hole diameter caused by this high-density reactive jet improved 29.2% at the same standoff. Lastly, the chemical reaction characteristics of PTFE/W/Cu/Pb reactive materials were analyzed, and a semi-empirical penetration model of the high-density reactive jet was established based on the quasi-steady ideal incompressible fluid dynamics theory.

• The jet formation of shaped charges with six different liner materials, i.e. copper, Cu-Zn alloy, steel1006, high nitrogen steel, and two titanium alloys were examined using both experimental and numerical method. • Under the same charge structure, the cohesiveness of the six material jets is different. Among them, copper, Cu-Zn alloy and steel1006 formed cohesive jets, while the other three materials formed non-cohesive jets. The straightness and dispersion of the jet have a significant impact on its penetration ability, and the jet with too large dispersion can hardly cause significant damage to the steel target. • Under the Euler algorithm and the Johnson-Cook model, the shape of the jet head obtained from the simulation can predict the discreteness of the actual jet. Arrowheads or oval heads usually represent cohesive jets, while blunt heads indicate a certain discreteness of jets. The degree of blunting of the jet head may also characterize the degree of dispersion. • Compared with Shock EOS, copper and Cu-Zn alloy are suitable for adopting Linear EOS to ensure the calculation accuracy of speed in simulation. Shock EOS can guarantee the calculation accuracy of steel1006, high nitrogen steel, TC21 and TB6 jets. Both Shock and Linear EOS can guarantee the calculation accuracy such as jet length, while there is a large error in diameter, especially for scattered jets. • Materials with higher strength, stronger strain effects, and lower shear modulus are more prone to form scatter jets. The threshold related to these three material parameters is proposed as a reference for predicting the discreteness of the jet, which provides convenience for judging the cohesion of the jet when the collapse angle is difficult to obtain under the traditional sound speed criterion. • The viewpoint of predicting the jet cohesion by using the macroscopic parameters of the material is put forward, which provides a preliminary reference for the design of shaped charge and the selection of the material of the liner. The Zr-based amorphous alloy material verifies the relevant conclusions, which also provides a reference for its application as a shaped charge liner. A comparative study of the shaped jets of six liner materials, namely, copper, Cu–Zn alloy, Steel1006, high nitrogen steel, and two titanium alloys, was conducted to investigate the influence of the macroscopic mechanical properties of the materials on the jet's performance. The X-ray experiment of the jet was performed, and the numerical calculation of the jet formation was carried out by means of simulation based on the Johnson–Cook model. Copper, Cu–Zn alloy, and Steel1006 formed cohesive jets, whereas the jets of the three other materials had different degrees of radial dispersion. The penetration depth of the jet has a significant negative correlation with its radial dispersion degree. In the numerical calculation, the head shape of the jet under the Euler algorithm can be used to judge its cohesion. Arrowheads or rounded oval heads symbolize cohesive jets, whereas blunt or even mouth-forward "bowl-shaped" heads indicate jets with radial dispersion. The degree of dispersion is positively correlated with the degree of dullness of the jet head. Simulation results show that the influence of material melting temperature and thermal softening effect on jet velocity, length, and diameter is particularly evident, whereas the influence ability of yield strength and strain rate effect is always at a very low level. Materials with small shear modulus, high yield strength, and significant strain effects are more prone to forming non-cohesive jets, which was verified by the jet forming experiments of amorphous alloy with these material characteristics. [ABSTRACT FROM AUTHOR]

In this paper a novel laser impact spot welding (LISW) method is described, in which a hump was formed on the flyer plate on the intended welding spot location by local pre-forming. When the flyer and base plates were placed together to perform welding, the two plates kept in contact over their entire surfaces except at the hump, where a local air gap was enough to guarantee the impact velocity and collision angle to achieve spot welding using laser pulse energy. The presented approach was implemented to join thin titanium foils to copper foils under low laser energy system. Joints with regular shapes were obtained. The microstructure in the weld interface was studied with scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). It was found that the jetting occurred at the central region of the weld spots due to oblique impact. Wave features were observed in the weld interfaces. The impact energy was found to have significant influence on the wave's characteristics. Moreover, SEM images and EDS analysis did not show apparent element diffusion across the weld interface. Besides, the lap shearing test was used to characterize the mechanical properties of the spot welded joints. [ABSTRACT FROM AUTHOR]

Jet flows have been applied in numerous fields to control flow separation. Over the last decade, several studies on the production of synthetic jets have been performed. However, little information is available about a number of aspects concerning synthetic jets, including details of the structure and the formation mechanism of such jets. The present study attempts to clarify some of the fundamental flow characteristics of free synthetic jets on the basis of experiments and numerical simulations. Experimental velocity measurements and flow visualizations are performed using the hot-wire anemometer and the smoke wire method, respectively. It is found that both the temporal change in the flow pattern and the time-averaged velocity distribution at the centerline depend on K = ReU/S2 (the ratio of the Reynolds number to the square of the Stokes number). The unsteady downstream flow characteristics are discussed in addition to the relation between the formative point of the synthetic jet and the value of K. Furthermore, the flow pattern and the unsteady flow characteristics of the synthetic jet are compared with those of a continuous jet.

Nonlinear shallow water equations and the method of matched asymptotic expansions are used to solve the problem of the impact of a box-type body with a flat bottom on a thin elastic liquid layer at a small angle in the plane formulation. It is established that, at certain values of the input parameters of the problem, the liquid pressure near the body edges becomes less than atmospheric pressure, and the liquid separates from the bottom of the box. Calculations demonstrating the influence of elastic bottom and liquid separation on the body motion are performed. It is shown that the presence of an elastic bottom significantly changes the hydrodynamic pressure distribution and can cause loads higher than in the case of a rigid body. [ABSTRACT FROM AUTHOR]

Abstract: A computational study based on a front tracking method was conducted by solving an unsteady, axisymmetric Navier–Stokes equation to investigate the mixing efficiency between two colliding droplets subsequent to their merging. Results show that, for droplets of sufficiently dissimilar sizes, the smaller droplet would transform into a mushroom-shaped jet that penetrates into the interior of the larger droplet, and hence greatly facilitates mixing. The jet acquires its energy from the surface energy of the colliding interfaces that are eliminated upon merging. For droplets of similar sizes, jet formation is not favored due to symmetry, and the eliminated surface energy is rapidly dissipated through viscous action of the droplet internal motion. The results qualitatively agree well with previous experimental observations. [Copyright &y& Elsevier]

Results of numerical and experimental modeling of jet formation during a high-velocity oblique impact of metal plates accelerated by an explosion are presented. Numerical simulations are performed by the method of molecular dynamics. The impact of metal plates is directly studied in experiments with flash radiography of phenomena ahead of and behind the impact point. A metallographic study of the samples is performed. It is demonstrated that numerical simulations by the method of molecular dynamics ensure a qualitatively and quantitatively adequate description of jet formation and evolution. [ABSTRACT FROM AUTHOR]

n analysis for liner collapsing and jet/slug formation of a double-layer shaped charge (DLSC) is presented. Variations of the collapse angle, collapse velocity, and jet velocity of the DLSC are discussed. Numerical simulations based on the Lee-Tarver model are performed to have an insight into the jet formation. Ballistic tests are conducted using a conical (60°) metal liner 56 mm in diameter to have a contrast with an ordinary shaped charge jet. It is shown that the collapse angle and velocity are both increased by the convergent detonation wave in the DLSC. The jet velocity, kinetic energy, and ballistic capability are significantly increased by using the DLSC, and the DLSC is an efficient way to improve shaped charge performance. [ABSTRACT FROM AUTHOR]

Abstract: This theoretical and computational study provides insight into the behaviour of large bubbles generated by underwater explosions near the seabed and airguns close to supporting structures when at least two opposing forces influence bubble behaviour. A null final Kelvin impulse occurs when these forces are in balance over a pulsation. Likewise for smaller bubbles such as occur in levitation phenomena for bubbles in a sound field, an ‘equilibrium’ bubble position is achieved. In both cases, energy dissipation mechanisms near minimum volume are important in determining subsequent bubble behaviour. Two cases typify the jetting behaviour near the null final Kelvin impulse state: (i) formation of an inward-flowing circular radial jet leading to bubble splitting, and (ii) formation of two opposite high-speed axial jets directed towards the bubble centre. The complex behaviour is attributed to a slight difference between the strength of the opposing forces acting on the bubble during growth and collapse. The present results indicate that the jetting behaviour in the neighbourhood of the neutral bubble collapse can be adequately described by the Kelvin impulse itself, but evaluated during the collapse phase of the bubble. Its direction determines the position of the radial jet in the initial phase of the collapse while its magnitude indicates the degree of asymmetry of the bubble-split and the intensity of the radial jet. Both factors are essential in estimating the final fate of the bubble at the neutral collapse state. Away from this null-state, the final Kelvin impulse is a valuable tool in predicting the migratory characteristics of the bubble and the direction of the axial jet developed during bubble collapse. [Copyright &y& Elsevier]

Here we derive a closed form analytical solution for an unsteady inviscid jet caused by the asymmetric collapse of a 2-d ring using linearized, small disturbance, velocity potential theory and classical analytical methods. Use is made of both the Laplace transformation and elementary eigenfunction expansions to solve the associated governing equations. The streamwise diffusion term, e.g. φrr is shown to be second order and is neglected. Jet shape that was computed using the analytical model is compared with CTH (hydrocode) simulations and limited experimental data and shown to provide reasonable agreement. Jet spreading is shown to be consistent with classical turbulent jet scaling in accordance with known shaped charge jet hydrodynamic assumptions. With confidence that the analytical solution is a viable tool we consider the numerical issues associated with rotational symmetry, the effect of boundary loading disturbance to the jet and the effect of finite arrival time detonation wave conditions. Thus we conclude that this model provides a simple, but useful supplement to conventional hydrocode simulation jetting phenomenon due to asymmetric loading of 2-d circular rings. [Copyright &y& Elsevier]

This paper addresses waterjet systems at pressures up to 700 MPa that is beyond the current commercially available systems. It is expected that increasing and localising the energy of the waterjet allows to cut deeper, narrower and faster. It also expands the possibilities of the waterjet since it makes it possible to cut thin sheet of metal, glass and composite. Main issues are addressed. Guidelines for designing an upstream tube are presented. Pressure and power measurements were conducted with pure waterjet. The theoretical results are in good agreement with the measurements. Defects were observed at the orifice at the end of the tests. [Copyright &y& Elsevier]

Jet formation was studied in the region of two‐dimensional and three‐dimensional waves in a heated liquid film flowing down a vertical surface. Jet‐to‐jet spacings were measured versus the film Reynolds number and the heat flow density. Three‐dimensional waves on the film surface were formed naturally or by artificial perturbations. In addition to the thermocapillary mechanism of jet formation, a thermocapillary–wavy mechanism was found to exist. [ABSTRACT FROM AUTHOR]

• A scaling law for jet velocity, revealing capillary-driven mechanism, is proposed. • The physical arguments predict the jet velocity to scale as V jet ~ (HW)1/4. • A phase diagram (Bo b , Oh b) for jet breakup and no breakup is established. • A linear relationship between the drop Oh d and jet Ca numbers is demonstrated. • The effects of bubble collapse and jet dynamics on drop size have been decoupled. Bubble deformation and its outcome play a central role in natural and industrial processes. In this paper, we investigate experimentally the formation and breakup of an inertial jet arising from the relaxation of a highly deformed bubble produced by coaxial coalescence. It is found that various jets can emerge inside the bubbles with given shapes and velocities. We develop a robust scaling law to describe the jet velocity and unravel its dependence on initial bubble shape, capillary, gravity, viscosity and liquid properties. With such a model, we demonstrate a capillary-driven mechanism for the jet formation. Then, the evolution of the jet-pinching process is analyzed in detail, and we confirm two different mechanisms at play in jet breakup, namely end-pinching and root-pinching. It appears that jet breakup can be predicted well by considering the bubble Ohnesorge and Bond numbers. Moreover, in this parameter space, a phase diagram for jet breakup and no breakup is established. Following jet breakup, an interesting "Liquid in Gas" structure: one or multiple droplets encapsulated in a large bubble, is observed. We establish two different scaling laws for top jet drop radius from the perspective of bubble collapse and jet dynamics, respectively. These scaling behaviors corresponding to different parameter spaces shed light on the effects of viscous, capillary and gravitational forces on drop detachment clearly. Especially, a simple linear relationship between the drop Ohnesorge and jet Capillary numbers is demonstrated. Furthermore, we systematically establish a complete functional relationship from bubble collapse to jet formation to droplet detachment, which is helpful to control the bubble-collapsing jet. [ABSTRACT FROM AUTHOR]

• A strength model of jet formation under electromagnetics force which considers the strength of liner material was carried out. • The experiments of jet formation and penetration of three liners with different thickness were carried out. • The penetration of theoretical calculation and simulation were good with the experiment results. • The liner thickness has a great influence on formation and power of electromagnetic jet. • The critical yield current of a liner element was put forward. The ratio value of peak current to critical yield current is studied to judge the formation state of the liner element under electromagnetic loading theoretically. Jet formation driven by strong magnetic field adopts the electromagnetic force to collapse the liner and breaks through the traditional jet forming mode of shaped charge, which relies on explosive. The influence of material strength on the liner deformation under low current is considered in this work to study the formation characteristics of the jet. Combined with the loading circuit, the jet formation and critical yield current (CYC) models are established. Subsequently, the CQ-4 device with 0.115 MJ energy is used to carry out electromagnetic loading experiments on the conical liners with a diameter of 10 mm and thickness of 1, 1.5, and 2 mm. The static penetration test method was used to test the jet power. The liners were all collapsed, and effective jets were formed by liners with 1 mm and 1.5 mm thickness. The depth of penetration (DOP) to the aluminum and steel targets were 30 mm and 12.5 mm, respectively. However, the 2 mm-thick liner almost did not have the ability to penetrate the steel target. The formation, movement, stretching, and penetration of the jets were calculation by theory and simulation. Results are in good agreement with the experiments. In the scope of this paper, the velocity and power of the jet increase with the decrease in liner thickness. The jet formation under theoretical calculation with and without material strength are compared and analyzed. The results indicated that the material strength cannot be ignored when the loading current is small. The formation characteristics of the liners under different loading currents are also calculated theoretically. The formation of the different liner elements under various currents are also calculated theoretically, and the peak current to CYC ratio is proposed to judge the formation state of the jet. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The prediction of the penetration of three-dimensional (3D) shaped charge into steel plates is a challenging task. In this paper, the smoothed particle hydrodynamics (SPH) method is applied to simulate the jet formation generated by the shaped charge detonation and its damage to steel plates. The Jones–Wilkins–Lee (JWL) equation of state (EOS), Tillotson EOS, and elastic–perfectly plastic constitutive model were incorporated into SPH for the modeling of explosive detonation and dynamic behavior of metal material. The compute unified device architecture (CUDA) parallel programming interface has been employed in SPH to improve the computational efficiency of SPH. Firstly, the constitutive models and EOSs are validated by 3D TNT slab detonation and aluminum–aluminum (Al–Al) high velocity impact. Then the jet formation of the shaped charge detonation and its penetration into the steel plates are investigated using the graphics processing unit (GPU)-accelerated SPH methodology. The numerical results of these test cases are compared against the published experimental data or analytical result, which shows that the GPU-accelerated SPH methodology is capable of tackling the 3D shaped charge detonation and penetration involving millions of particles with high computational efficiency. [ABSTRACT FROM AUTHOR]

Bubble bursting at the liquid surface can generate the jet drops and satellite bubbles, which is widely encountered in boiling, ocean engineering, bioengineering etc. This process is affected by quite a few parameters, such as surface capillarity, gravity, temperature, density, viscosity and bubble size. In this paper, the axisymmetric numerical model with level set method is built up to study the bubble bursting process. It is found that the bubble bursting process can be analyzed through the capillary wave propagation in terms of the tangential angle along the gas-liquid interface. The capillary wave propagation method can describe well the effect of Ohnesorge number, Marangoni number, density and viscosity ratios of gas over liquid on the bubble bursting. The critical Ohnesorge number for jet drop formation during bubble bursting with negligible gravity, gas inertia and viscosity is around 0.045, and it will decrease dramatically with increasing ratios of gas density or viscosity over liquid. The jet formation during bubble bursting can be suppressed by applying the negative temperature gradient across the bubble, or by increasing density and viscosity ratio of gas over liquid, mainly because they can damp the capillary waves. These findings may help get insight in the bubble bursting when the gas properties are transiting towards the liquid under pressurized atmosphere. Image 1 • Satellite jet drop and bubble are generated due to capillary wave. • The capillary wave propagation is characterized with tangential angle. • The mechanism during bubble bursting is revealed through wave propagation. • Critical Oh is 0.045 with negligible gravity, gas density and viscosity. [ABSTRACT FROM AUTHOR]

The traditional polytetrafluoroethylene (PTFE)/Al reactive material liner shaped charge generally produces insufficient penetration depth, although it enlarges the penetration hole diameter by chemical energy release inside the penetration crater. As such, a novel high-density reactive material liner based on the PTFE matrix was fabricated, and the corresponding penetration performance was investigated. Firstly, the PTFE/W/Cu/Pb high-density reactive material liner was fabricated via a cold pressing/sintering process. Then, jet formation and penetration behaviors at different standoffs were studied by pulse X-ray and static experiments, respectively. The X-ray results showed that the PTFE/W/Cu/Pb high-density reactive material liner forms an excellent reactive jet penetrator, and the static experimental results demonstrated that the penetration depth of this high-density reactive jet increased firstly and then decreased by increasing the standoff. When the standoff was 1.5 CD (charge diameter), the penetration depth of this reactive jet reached 2.82 CD, which was significantly higher than that of the traditional PTFE/Al reactive jet. Moreover, compared with the conventional metal copper jet penetrating steel plates, the entrance hole diameter caused by this high-density reactive jet improved 29.2% at the same standoff. Lastly, the chemical reaction characteristics of PTFE/W/Cu/Pb reactive materials were analyzed, and a semi-empirical penetration model of the high-density reactive jet was established based on the quasi-steady ideal incompressible fluid dynamics theory. [ABSTRACT FROM AUTHOR]

• The jet formation and penetration capacity of hypervelocity shaped charges (HSCs) with five different disc materials, i.e. silicon carbide, steel 45#, steel 4340, copper and tungsten, against steel targets was examined using both experimental and numerical method. • The length and head velocity of the projectiles formed by HSCs with a tungsten disc are larger than those with other disc materials, and more importantly, they are even larger by 23.9% and 36.6% compared with that formed by the conical shaped charges (CSCs). • The HSC with a tungsten disc, based on a limited number of experimental firings, yields a deeper penetration depth by 6.1% compared to a CSC, while other disc materials cannot compete with CSCs. The jet formation and penetration capacity of hypervelocity shaped charges (HSCs) against three steel targets was carefully examined using both experimental and numerical method. The HSCs with five different disc materials, i.e. silicon carbide, steel 45#, steel 4340, copper and tungsten, were manufactured to explore their penetration capability and compare with a classical conical shaped charge (CSC). The jet formation and penetration of both HSCs and a CSC was simulated using a numerical model that reproduces the results of experiments. It is found that the length and head velocity of the projectiles formed by HSCs with a tungsten disc are larger than those with other disc materials, and more importantly, they are even larger by 23.9% and 36.6% compared with that formed by the CSCs. However, the corresponding diameter of the entrance in the first steel target is much smaller than that of the CSC and HSCs with other disc materials. Overall, it is encouraging that the HSC with a tungsten disc yields a deeper penetration depth by 6.1% compared to a CSC, while other materials cannot compete with CSCs. [ABSTRACT FROM AUTHOR]

Abstract In this study, using a combination of several experimental and computational methods, an attempt to improve the understanding of some important phenomena accompanying the process of explosive welding is made. The high-speed shooting was used to observe the formation of a re-entrant jet. Various methods of the materials characterization were used to estimate the morphology of the interface, the distribution of the liquid phase and analyze the evolution of the structure in the process of high-velocity oblique collision. Simulating the process of high-velocity collision using the smoothed particles hydrodynamics (SPH) method allowed us to accurately reproduce formation of the wave boundary, vortex zones, as well as the formation of a jet moving ahead of the collision point. Based on the simulation results, several significant modifications of the Bahrani-Black-Crossland model of the waves formation were done, and a new explanation for the vortex zones formation was proposed. Numerical simulation of the cooling process showed that the solidification of the liquid phase occurs under conditions of the rapid solidification during melt spinning. Combining several numerical-based approaches, a welding window for the steel-steel system was built. The results obtained show a good agreement with currently existing concepts of welding during the high-velocity collisions. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]