Fragment Velocity Research Articles

Study of the coupling characteristics of damage elements with cased charge

In this paper, the coupling characteristics of fragments, detonation products and explosive shock wave have been studied. Although a large number of studies have been conducted to discuss the damage effects of structures under the combined loading of blast and fragments impact, there is a lack of research on the coupling characteristics of damage elements and their mechanism of action. This study uses the law of conservation of energy to propose a more reasonable method to evaluate the velocity of fragment. In addition, the isentropic expansion theory of bare charge detonation products is used to explore the expansion characteristics of cased charge detonation products, and the expansion process of cased charge detonation products can be divided into three phases. The results show that the limiting expansion volume of detonation products with cased charge is smaller than that of bare charge due to the inhibiting effect of the casing. Taking into account the energy absorbed in the crushing of the casing, the shock wave produced by the explosion of the cased charge is equal to the shock wave produced by the explosion of a given amount of bare charge, and the corresponding formula is given. Then, based on the known performance parameters of each damage element, the arrival time of the damage element at the target structure is systematically analyzed, and the coupling of the damage element is divided into five phases according to the arrival time, and the range of damage effect of each coupling phase is analyzed in two cases. Finally, a numerical simulation based on Euler's method is performed, and the theoretical results agree well with the numerical simulation results.

Experimental study on the effect of water absorption level on rockburst occurrence of sandstone

To investigate the mechanism of rockburst prevention by spraying water onto the surrounding rocks, 15 experiments are performed considering different water absorption levels on a single face. High-speed photography and acoustic emission (AE) system are used to monitor the rockburst process. The effect of water on sandstone rockburst and the prevention mechanism of water on sandstone rockburst are analyzed from the perspective of energy and failure mode. The results show that the higher the absorption degree, the lower the intensity of the rockburst after absorbing water on single side of sandstone. This is reflected in the fact that with the increase in the water absorption level, the ejection velocity of rockburst fragments is smaller, the depth of the rockburst pit is shallower, and the AE energy is smaller. Under the water absorption level of 100%, the magnitude of rockburst intensity changes from medium to slight. The prevention mechanism of water on sandstone rockburst is that water reduces the capacity of sandstone to store strain energy and accelerates the expansion of shear cracks, which is not conducive to the occurrence of plate cracking before rockburst, and destroys the conditions for rockburst incubation.

Lateral enhancement effect of reactive PELE: Two-step segmented simulation and analytical modeling

Comparing with traditional PELE, the reactive PELE shows a more significant lateral enhancement effect due to the deflagration reaction of the filling by impact. Here an analytical model for thin-walled jacket fragmentation and dispersion is presented based on the wave interaction and the reaction of reactive filling. Subsequently, a two-step segmented numerical simulation for the impact deflagration of reactive PELE is developed. Based on the numerical simulation, the wave interaction process and the internal stress distribution of the filling were given firstly, then the deflagration reaction of reactive filling, jacket fragmentation and dispersion were simulated. By the theory and simulation, the experiment results of reactive PELE impacting steel plate are analyzed. In the experiment, the thickness of the front steel target is 6mm-20 mm, and the multi-layer witness aluminum plate is set behind the steel target to obtain the lateral effect of the reactive PELE. The analysis results show that the released energy of the reactive filling increases the maximum radial velocity of the jacket fragments by more than 40 %, and the perforation dispersion on the witness plate significantly depends on the filling reaction level and the front steel plate thickness, the lateral enhancement mechanism of reactive PELE impacting plate is explained.

The Effect of Dust Evolution and Traps on Inner Disk Water Enrichment

Abstract Substructures in protoplanetary disks can act as dust traps that shape the radial distribution of pebbles. By blocking the passage of pebbles, the presence of gaps in disks may have a profound effect on pebble delivery into the inner disk, crucial for the formation of inner planets via pebble accretion. This process can also affect the delivery of volatiles (such as H2O) and their abundance within the water snow line region (within a few au). In this study, we aim to understand what effect the presence of gaps in the outer gas disk may have on water vapor enrichment in the inner disk. Building on previous work, we employ a volatile-inclusive disk evolution model that considers an evolving ice-bearing drifting dust population, sensitive to dust traps, which loses its icy content to sublimation upon reaching the snow line. We find that the vapor abundance in the inner disk is strongly affected by the fragmentation velocity (v f) and turbulence, which control how intense vapor enrichment from pebble delivery is, if present, and how long it may last. Generally, for disks with low to moderate turbulence (α ≤ 1 × 10−3) and a range of v f, radial locations and gap depths (especially those of the innermost gaps) can significantly alter enrichment. Shallow inner gaps may continuously leak material from beyond it, despite the presence of additional deep outer gaps. We finally find that for realistic v f (≤10 m s−1), the presence of gaps is more important than planetesimal formation beyond the snow line in regulating pebble and volatile delivery into the inner disk.

Investigation of the Fracture and Fragmentation of Implosively Driven Thin-Walled Cylindrical Shell: From Thermodynamic Analysis to CDEM Simulation.

The scattering of fragments is a notable characteristic of the explosive detonation of a shelled charge. This study examines the fracture and fragmentation of the shell and the process by which natural fragments form under the strains of implosion. The analysis takes into account both the explosive's energy output and the casing's dynamic response. For this purpose, utilizing a thermochemical code as an alternative to the conventionally employed cylinder test, the Jones-Wilkins-Lee equation of state (JWL EOS) was calibrated within a range of relative specific volume up to 13. The detonation of the shelled charge was subsequently analyzed using the continuum-discontinuum element method (CDEM). Following this, the formation mechanisms and scattering characteristics of natural fragments were scrutinized. The analysis found that the shell predominantly experiences shear failure with uniform evolution, displaying a "hysteresis effect" and two mutation stages in the evolution of tensile failure. Within the JWL EOS's calibrated range, the representation of fragment displacement and velocity improved by 47.97% and 5.30%, respectively. This study provides valuable guidance for designing the power field of warheads and assessing their destructive power.

Study on evaluation method for driving fragment ability of explosives

The present study proposes an evaluation method for the driving fragment ability of explosives, which aims to provide theoretical and technical support for the selection of explosives used in warheads. The evaluation method is proposed in the light of the dimensional method and the similarity principle, and it uses TNT equivalent as the evaluation indicator. To acquire the evaluation indicator, a test system for driving fragment ability of explosives is constructed, which includes a dynamite gun type driven device, a spherical fragment, and a multi-zone fragment velocity measurement system. TNT and thermobaric explosive were used to carry out the verification experiments of the evaluation method. On the basis of the evaluation method, the basic evaluation model for the driving fragment ability of explosives was established by the TNT mass and the corresponding fragment maximum velocity. Using the basic evaluation model, the TNT equivalent of the thermobaric explosive in driving fragment ability was calculated to be 1.29, which was 3.2% different from the ratio (1.25) of both explosives’ Gurney-specific energy. The relative error of 3.2% falls within the allowable range of engineering error, confirming the feasibility of the proposed evaluation method. The result shows that the proposed evaluation method is effective and accurate in evaluating the driving fragment ability of explosives.

Velocity and Isotope Distributions of Projectile-Like Fragments in Reaction $${}^{40}$$Ar (36.5 A MeV)/$${}^{9}$$Be

Velocity and Isotope Distributions of Projectile-Like Fragments in Reaction $${}^{40}$$Ar (36.5 A MeV)/$${}^{9}$$Be

Coagulation–Fragmentation Equilibrium for Charged Dust: Abundance of Submicron Grains Increases Dramatically in Protoplanetary Disks

Dust coagulation in protoplanetary disks is not straightforward and is subject to several slowdown mechanisms, such as bouncing, fragmentation, and radial drift to the star. Furthermore, dust grains in UV-shielded disk regions are negatively charged due to collisions with the surrounding electrons and ions, which leads to their electrostatic repulsion. For typical disk conditions, the relative velocities between micron-sized grains are small, and their collisions are strongly affected by the repulsion. On the other hand, collisions between pebble-sized grains can be too energetic, leading to grain fragmentation. The aim of the present paper is to study the combined effect of the electrostatic and fragmentation barriers on dust evolution. We numerically solve the Smoluchowski coagulation–fragmentation equation for grains whose charging occurs under conditions typical for the inner disk regions, where thermal ionization operates. We find that dust fragmentation efficiently resupplies the population of small grains under the electrostatic barrier. As a result, the equilibrium abundance of submicron grains is enhanced by several orders of magnitude compared to the case of neutral dust. For some conditions with fragmentation velocities of ∼1 m s−1, macroscopic grains are completely destroyed.

Study on anti-penetration performance of Kevlar reinforced honeycomb liquid-filled cabin on warship: Experimental verification and numerical analysis

The water hammer effect produced when fragments penetrate the liquid tank on warship will cause integral expansion and damage to the structure of the liquid tank. In this paper, a kind of liquid-filled honeycomb structure reinforced by Kevlar fiber tube is designed, and the mechanism of Kevlar fiber tube reinforced honeycomb liquid-filled structure against fragmentation is analyzed. The numerical model of Kevlar reinforced honeycomb liquid-filled structure is established, and the process of high-speed fragments penetrating the defense structure is analyzed by ALE calculation method, and the armor-piercing test of liquid-filled structure is carried out, which verifies the reliability of simulation calculation. The influence of honeycomb core layer and Kevlar fiber tube on the defense of liquid-filled structure against high-speed fragment is further discussed. In addition, an air compartment is arranged in the honeycomb liquid-filled structure to weaken the water hammer effect. It is found that the air compartment has a slight decrease in the ability to weaken the fragment velocity, but it greatly reduces the damage degree of the structure caused by fragment penetration.

Research on rotational angular velocity of preformed fragments

The rotational angular velocity of fragments under the driver of explosive products makes the fragments constantly flip during the trajectory, which has a huge effect on the velocity decay of the fragments. In order to more accurately calculate the residual velocity of the fragments during flight, it is necessary to study the rotational angular velocity of the fragments. Based on the paper target system, an experimental method for measuring the angular velocity of fragments is proposed. By using ANSYS/LSDYNA finite element software, the rotational angular velocity of preformed fragments under explosion is studied. A new meshing method is proposed to simulate the driven process of the explosive products on the fragments more accurately. The experimental results and the numerical simulation results are considered to be consistent within the margin of error. And at last, the distribution of fragment is studied base on numerical simulation. The research results provide a foundation for studying the trajectory of preformed fragments after explosive driven.

Study on Radial Distribution of Fragments Velocity of D-shaped Fragmentation Warhead

For the asymmetric D-shaped fragmentation warhead with high charging coefficient and space efficiency, we simulate the driving process of fragments under typical eccentric initiation by using the fluid-structure interaction algorithm, and obtained the change rule of the fragment velocity radial distribution with the central angel, the thickness and material of the upper end cap. The results of numerical simulation show that the fragment velocity of D-shaped warhead increases gradually from the reverse to the forward direction, the velocity of fragment in forward direction increases by about 10% under single-point eccentric initiation compared with the cylindrical casing under center initiation, and the fragment velocity under double-point eccentric initiations is higher than single-point eccentric initiation; The initial velocity of the fragment has a positive correlation with the thickness and density parameters of the upper end cap; the mass of the warhead and the total kinetic energy of the fragments in the forward area increase with the increase of the central angle, but their ratio increases first and then decreases with the increase of the central angle. The results can be applied to structural optimization design and power evaluation of the warhead.

Ballistic performance of spherical fragments penetrating PCrNi3MoV target plates

PCrNi3MoV steel is a medium-carbon, low-alloy quenched and tempered steel that finds its applications in military gun barrels due to the high wear resistance and ablation resistance. To study the penetration and failure modes of PCrNi3MoV plates impacted by tungsten spheres, tungsten spheres of various diameters (5 mm, 8 mm, and 10 mm) were used to impact PCrNi3MoV steel plates with thicknesses of 6 mm, 9 mm, and 14 mm. The penetration performance of the spheres was analyzed for different velocities, and the ultimate penetration velocity of the plate was obtained. It was found that the primary failure modes of the PCrNi3MoV plate were compression pitting failure and shear failure. Using the dimensional analysis method, a relationship between the bulge height of the steel plate and the fragment velocity, an equation for the ultimate penetration velocity, and a relationship between the target penetration energy and the fragment velocity were obtained. Then, a projectile–target action index was proposed to describe the process of tungsten spheres with different velocities impacting target plates. The results suggested that under the same thickness of the target plate, a larger-diameter fragment required more kinetic energy to obtain the same ultimate penetration effect as a smaller-diameter fragment. The equations obtained through dimensional analysis predicted values that agreed well with experimental values, indicating that these equations can be applied to engineering applications.

Experimental Study on the Effect of Buffer Layer on the Explosive Drive of Reactive Fragment

In order to study the influence of the buffer layer on the explosive drive of the reactive fragment, for the reactive fragment warhead of the same structure, the warhead static explosion test and the break-through target test method were used to test the fragment integrity and the fragment integrity of the reactive fragment warhead of the reactive fragment warhead with several different thickness silicone rubber buffer layers. The initial velocity of the fragment was measured, and its integrity and the variation law of the initial velocity were analyzed. The results show that with the increase of the thickness of the buffer layer, the integrity of the reactive fragments increases. When the thickness of the buffer layer is 2 mm, the fragment integrity rate is zero, and when the thickness of the buffer layer is greater than 8 mm, the integrity rate is greater than 0.85. The difference in the initial velocity of the warhead of the same reactive fragment is small, mainly because with the increase of the thickness of the buffer layer, the initial velocity of the fragment decreases mainly because the loading ratio of the warhead decreases; the buffer layer has a significant effect on reducing the initial velocity of the reactive fragment, and k=0.83 can be used The modified Gurney formula was used to estimate the initial velocity of the reactive fragments of the silicone rubber buffer layer.

The velocity distribution of fragment from air part of cylindrical casing

In some cylindrical casings, the non-explosive material or structure exists. The explosive charge is axially discontinuous, the propagation of detonation wave is also discontinuous, and the driving process of metal casing is diverse from continuous charge. If the non-explosive material or structure in the middle is regarded as air, it is called the cylindrical casing with air part in the middle. Due to the combined effects of rarefaction waves and the detonation wave generated by explosive charges on both sides, existing formulas of fragment velocities from cylindrical casing can neither accurately predict that from explosive charge part, nor predict that from the air part since the mass ratio of the explosive charge to the metal casing in the air part is 0. Adopt the method of simulation analysis, the cylindrical casing with air part in the middle was analyzed. A new formula was established to predict the fragment velocity of air part from cylindrical casing in the middle, which showed good agreement with the simulation results.

Numerical simulation research on fragments formation of cylindrical cased charge based on SPH method

In order to obtain the fracture and fragmentation of a cased charge under blast loading, the JWL equation of state of HMX-based PBX was fitted based on a cylinder test firstly, then the smooth particle hydrodynamics (SPH) method was used to perform a simulation of cased charge under interior blast loading, in the meantime, an blast test of cased charge was conducted. The results show that the parameters of JWL equation of state and the simulation method were reasonably. The simulated fragments velocities and calculated results from empirical formula agreed well with each other, the maximum error did not exceed 9.5%. Under the direct loading of the detonation wave, the fragments velocities increased to more than 1000m/s immediately within 5us, and then the fragments were continuously accelerated by detonation products and shock wave until the fragments reached the maximum velocities in the later 250us. Eventually, the shape of expansion contour of the casing tended to be ellipsoid. The method and results can provide references for the power design of the fragment warhead, as well as the protection design against the fragments.

Simulation study on penetration depth of spherical fragments into concrete

In order to study the influence of different spherical fragments on the penetration depth of concrete targets, AUTODYN-2D software is used to model and simulate the penetration of fragments with different diameters, materials and velocities. Through the analysis of penetration depth data, it is found that the penetration depth of tungsten alloy fragments will not continue to increase at higher speeds (when v > 1400 m / s, the penetration depth of tungsten alloy fragments begins to decrease). The process of spherical fragment penetrating concrete is analyzed, and the relationship between the penetration depth and the velocity, diameter, material parameters and concrete strength of spherical fragment is clarified. The simulation results show that the penetration depth curve parameters of different materials are quite different, due to the high utilization rate of tungsten alloy fragments, the calculation formula of penetration depth of tungsten alloy spherical fragments with respect to fragment parameters is obtained by fitting the penetration data. The penetration depth of tungsten alloy spherical fragments under different diameters and velocities can be predicted accurately by this formula.

SHAMPOO: A stochastic model for tracking dust particles under the influence of non-local disk processes

Context. The abundances of carbon, hydrogen, nitrogen, oxygen, and sulfur (CHNOS) are crucial for understanding the initial composition of planetesimals and, by extension, planets. At the onset of planet formation, large amounts of these elements are stored in ices on dust grains in planet-forming disks. The evolution of the ice in dust, however, is affected by disk processes, including dynamical transport, collisional growth and fragmentation, and the formation and sublimation of ice. These processes can be highly coupled and non-local. Aims. In this work, we aim to constrain the disk regions where dynamical, collisional, and ice processing are fully coupled. Subsequently, we aim to develop a flexible modelling approach that is able to predict the effects of these processes acting simultaneously on the CHNOS budgets of planetesimal-forming material in these regions. Methods. We compared the timescales associated with these disk processes to constrain the disk regions where such an approach is necessary, and subsequently developed the SHAMPOO (StocHAstic Monomer PrOcessOr) code, which tracks the CHNOS abundances in the ice mantle of a single ‘monomer’ dust particle of bare mass mm, embedded in a larger ‘home aggregate’. The monomer inside its home aggregate is affected by aerodynamic drag, turbulent stirring, collision processes, and ice adsorption and desorption simultaneously. The efficiency of adsorption onto and the photodesorption of the monomer here depends on the depth zm at which the monomer is embedded in the home aggregate. We used SHAMPOO to investigate the effect of thefragmentation velocity υfrag and home aggregate filling factor ϕ on the amount of CHNOS-bearing ices for monomers residing at r = 10 AU. Results. The timescale analysis shows that the locations where disk processes are fully coupled depend on both grain size and ice species. We find that monomers released at 10 AU embedded in smaller, more fragile, aggregates with fragmentation velocities of 1 m s−1 are able to undergo adsorption and photodesorption more often than monomers in aggregates with fragmentation velocities of 5 and 10 m s−1. Furthermore, we find that at 10 AU in the midplane, aggregates with a filling factor of ϕ = 10−3 are able to accumulate ice 22 times faster on average than aggregates with ϕ = 1 under the same conditions. Conclusions. Since different grain sizes are coupled through collisional processes and the grain ice mantle typically consists of multiple ice species, it is difficult to isolate the locations where disk processes are fully coupled, necessitating the development of the SHAMPOO code. Furthermore, the processing of ice may not be spatially limited to dust aggregate surfaces for either fragile or porous aggregates.

Influence and its Mechanism of Non-reactive Fillers on the Dispersion Characteristics of the Fragments from Charge Structures

With the diversified development of innovative warheads and the increasing threat of improvised explosive devices (IEDs), the charge structure filled with both explosives and non-reactive materials has attracted the attention of researchers, which is few studied. In order to obtain the fragmentation of the charge structure with part of the non-reactive filler, the X-ray radiography explosion experiment was carried out for an axisymmetric charge structure partially filled with nylon that serves as a typical non-reactive filler. The fragmentation and fragment dispersion characteristics of the charge structure were observed. Based on the results of X-ray experiments, the influence mechanism of shell breakage and fragment dispersion characteristics of the charge structure filled with non-reactive filler are analysed by using SPH numerical calculation method. The results show that the non-reactive filler will significantly affect the fragmentation of the shell and considerably reduce the fragment velocity of the fragments in the filling direction. However, the fragment dispersion direction of the charge structure is not affected by the non-reactive filler. The conclusions could be a foundation and reference for further research on new charge structures.

Influence of the Fragment Velocity Gradient on the Hit Density under the Dynamic Condition

The influence of the fragment velocity gradient on the hit density under the dynamic missile-target meeting condition is discussed using theoretical analysis, and the analytical relationship is obtained. The results show that under static explosion conditions, the fragment hit density is independent of the velocity gradient of the fragment group. Under dynamic conditions, the distribution bandwidth of the fragments on the target becomes wider with the increase of the velocity of the missile-target meeting and the velocity gradient of the fragment group, and the increase of the fragment bandwidth decreases the fragment hit density.

Study on Axial Dispersion Characteristics of Double-Layer Prefabricated Fragments.

The axial distribution of initial velocity and direction angle of double-layer prefabricated fragments after an explosion were investigated via an explosion detonation test. A three-stage detonation driving model of double-layer prefabricated fragments was proposed. In the three-stage driving model, the acceleration process of double-layer prefabricated fragments is divided into three stages: "detonation wave acceleration stage", "metal-medium interaction stage" and "detonation products acceleration stage". The initial parameters of each layer of prefabricated fragments calculated by the three-stage detonation driving model of double-layer prefabricated fragments fit well with the test results. It was shown that the energy utilization rate of detonation products acting on the inner-layer and outer-layer fragments were 69% and 56%, respectively. The deceleration effect of sparse waves on the outer layer of fragments was weaker than that on the inner layer. The maximum initial velocity of fragments was located near the center of the warhead where the sparse waves intersected, located at around 0.66 times of the full length of warhead. This model can provide theoretical support and a design scheme for the initial parameter design of double-layer prefabricated fragment warheads.