Cylindrical Explosive Charge Research Articles

Improved method for prediction of detonation velocity for C−H−N−O based pure, mixed and aluminized explosives

AbstractAn improved method is presented for the prediction of detonation velocity of C−H−NO based pure, mixed, and aluminized explosives. The new empirical relation is based on calculated values of the heat of detonation and the number of moles of gaseous detonation products. A constant of the empirical relation has been found using regression analysis of 74 data points of pure and mixed explosives as well as 22 data points of aluminized explosives. The value of the constant is found to be 1.00 with R2 value of 0.96. Proposed empirical relation has been validated by comparing predicted values of detonation velocities with measured values for TNT, HMX/RDX‐TNT‐Al and HMX‐TNT based explosives. Experimental measurement of detonation velocity has been carried out using pin‐ionization method on cylindrical explosive charges of diameter 50 mm and height 150 mm. The predicted values of detonation velocities are in good agreement with measured values with a root mean square error of 1.28 %. The validation of the new relation has also been carried by comparing calculated values of detonation velocities using present and literature methods with reported experimental values.

New approach for calculation of peak over pressure and impulse of aluminized explosive charges

ABSTRACT RDX/HMX-TNT-based aluminized explosive compositions have been investigated to find empirical relations based on heat of explosion (Q) and velocity of detonation (VOD) for calculation of peak over pressure (POP) and impulse (I). Four HMX-TNT-based aluminized compositions have been selected based on calculated values of Q and explosive power. Explosive charges of RDX/HMX-TNT-based aluminized compositions and TNT have been prepared by melt-cast technique for measurement of VOD and air blast. Cylindrical explosive charges with length to diameter ratio of ~ 1 and weight ~ 1.3 kg have been used for measurement of pressure-time profiles at standoff distance of 2–6 m. Similar measurements were also performed for the explosive charges of TNT of weight ~ 11 and 17 kg. Normalized values of Q and VOD 2 with corresponding values of TNT have been used to compute charge weight for calculation of scaled distance which is termed as normalized scaled distance. Form of empirical relations has been decided from variation of POP and I with normalized scaled distance. Values of constants used in these relations have been determined using regression analysis. Validation of empirical relations has been carried out by comparing calculated and experimental values of POP and I for explosive charges.

Applicability limits of the DAX test in plastic bonded explosives

The Disc Acceleration eXperiment (DAX) is one of the most recent experimental methods of performance characterization of new energetic materials. A cylindrical explosive charge accelerates a thin metallic disc and its velocity is measured continuously using photonic Doppler velocimetry. The detonation velocity is measured simultaneously. The DAX test can be used to obtain the Chapman-Jouguet (CJ) detonation pressure and to describe detonation products expansion using reduced amount of explosive. A series of DAX tests was performed at various charge diameters and disc thicknesses with Semtex 1 A plastic bonded explosive and sensitized nitromethane. The DAX-like evaluation was also applied to previously measured data of Semtex 1A and A-IX-1 explosives. The optimum disc thickness is determined by the disc to explosive mass ratio of 0.01–0.08. The repeatability of the Semtex 1 A detonation pressure results is about four times lower compared to the pressed and liquid explosives.

Evaluating blast wave overpressure from non‐spherical charges using time of arrival from high‐speed video

AbstractScaled distance is used to predict blast wave overpressure surrounding the detonation of a known mass of explosive under the assumption that the charge geometry is spherical. Altering charge geometry from spherical overdrives regions of the blast wave resulting in areas of higher overpressures than predicted by scaled distance calculations. Empirical data can be used to scale the blast wave overpressure to cylindrical charges, but available overpressure data for more complex geometries is not available in published literature. In the present study the time of arrival of the blast wave was measured from high‐speed video and the Rankine‐Hugoniot relationship used to measure blast wave overpressure for varied explosive geometries. The radial overpressure of prismatic charges with cross‐sectional shapes of triangle, rectangle, and 5‐point star isotropic were compared to the radially isotropic overpressure distribution produced by a cylindrical explosive charge. The rectangle produced the highest overpressure measuring 3.5 times that of the cylinder while the triangular charge had the greatest presented surface area and was only overdriven 3.0 times. From the high‐speed video the fireball of detonation products surrounding the star appears significantly overdriven from the internal angle, but this orientation was underdriven at 2.0 meters. The blast wave overpressure downstream from the outside corners of the rectangular and triangular prismatic charges were similar to that of the cylinder at 1.5 meters but trended higher at increasing distance.

Experimental study of damage to ultra-high performance concrete slabs subjected to partially embedded cylindrical explosive charges

In this study, long and thin cylindrical charges were partially embedded in ultra-high-performance concrete (UHPC) and normal-strength concrete (NSC) slabs to investigate the damage characteristics of UHPC slabs subjected to explosions by conventional weaponry. The sizes of ejection and spalling craters were recorded after the experiment to compare the obtained data with the concrete slab damage characteristics predicted by current damage forecasting methods. The current damage forecasting methods were found to be unsuitable for the conditions considered in this study as they do not account for the effects of the explosive shape and depth of embedment (DOE) simultaneously. The results of the experiment using partially embedded charges indicated that the damage on the sides of the slabs decreased with decreasing slab thickness; the use of UHPC without fiber reinforcement instead of using NSC significantly increased the compressive strength but decreased the ability of the concrete structure to resist spalling damage; furthermore, a suggested estimation of the cone slope angle is 60° for theoretical analyses and the design of numerical simulation or field experiments.

Spherical equivalence of cylindrical explosives: Effect of charge shape on deflection of blast-loaded plates

Quantification of near-field blast loading is a pressing issue for defence, transport security, and structural engineering. Realistic explosion scenarios often involve the detonation of non-spherical high explosive charges, rather than the idealised spherical/hemispherical explosives assumed in commonly employed semi-empirical approaches. Additionally, near-field effects are of great importance when assessing structural damage and injury risk from such an event. There is a need, therefore, to incorporate the effects of charge shape and the resulting loading distribution in simplified engineering-level tools using adjustments based on sound physical principles. This article details the development of an energy equivalent formulation to derive spherical equivalence factors, with the methodology illustrated for the scenario of a centrally detonated cylindrical explosive charge. A validated two-part numerical model is used to generate specific impulse distributions and quantify the resulting plate deformation, for a wide range of cylindrical aspect ratios (0.20≤L/D≤5), at a range of near-field scaled distances (0.108≤Z≤0.485 m/kg1/3) for different sized structural targets. A series of verification examples are used to demonstrate the accuracy of the method, with the peak deflection under the equivalent spherical charge matching peak deflection under the cylindrical charge to within ∼4%. The method developed in this article could be extended to find equivalence between any two systems with complex distributed loading, allowing for a fast running engineering approximation in cases where detailed modelling is inappropriate or infeasible.

Shock focusing effects on silica phase production during cyclotrimethylene trinitramine/2,4,6-trinitrotoluene detonations

Detonation is an increasingly studied method for the synthesis of nanomaterials due to the rapid reaction rate producing extreme pressures and temperatures for short durations, which can result in the production of ultra-hard and high-temperature nanomaterials. The present study shows that phase formation in detonation depends on the distribution of inert additives in the explosive charge. Numerical simulations and experimental validation were conducted on silica powders that were shock loaded by detonation of a 3.8 cm diameter cylindrical explosive charge composed of cyclotrimethylene trinitramine, 2,4,6-trinitrotoluene, and paraffin wax. Silica was incorporated into the explosive in three configurations and at two different starting particle sizes in both simulation and experiments. The detonation residues were purified to concentrate the silica and characterized via x-ray diffraction with Rietveld refinement and optical microscopy. Loading conditions and silica phase morphology were not consistent between the configurations and starting size of silica incorporated into the charge. The implication of these results is that the prediction of phase production in detonation synthesis experiments cannot be based on Chapman–Jouguet steady detonation parameters of the explosive matrix but must also include analysis of shock interaction and heat transfer into the additives incorporated into the explosive.

Influence of charge shape and point of detonation of high explosive cylinders detonated on ground surface on blast-resistant design

This paper studies how the properties of cylindrical explosive charges influence their generated blast loads (peak overpressure and maximum impulse) for surface burst scenarios, focusing on the aspect ratio (or length-to-diameter ratio) of the cylinder and the point of detonation of the charge. Specifically, the following three points of detonation are considered: the cylindrical charge is detonated at its bottom, middle or top centre, respectively. Numerical models are developed for both hemispherical and cylindrical charges, and are validated against experimental data available in the open literature. Important conclusions regarding the blast-resistant design are drawn from the parametric studies conducted using the validated models. Neglecting the effect of the cylindrical charge shape can result in underestimating the peak overpressure (maximum impulse) in the near field by a factor as high 6.6 (2.9). Therefore, the shape of the charge should be represented appropriately in the numerical simulations used for the blast-resistant design of protective structures subjected to near-field detonations. The generated shock front is known to smoothen out as the scaled distance increases, “healing” into a hemispherical one in the far field. However, cylindrical charges generate about 1.2 times higher blast loads in the far field than hemispherical ones do. The significance of the cylindrical charge shape effect on the peak overpressure (maximum impulse) resulting from the three considered points of detonation can be sorted in descending order as follows: bottom-centre-detonated > middle-centre-detonated > top-centre-detonated (top-centre-detonated > middle-centre-detonated = bottom-centre-detonated). The influence range is characterized by a scaled distance, above which the maximum value of the ratio of the peak overpressure (maximum impulse) of cylindrical charges and that of hemispherical charges converges to a constant value (1.2). The influence range for the overpressure is more or less the same (4.0 m/kg1/3) for the three different points of detonation, whereas the cylinder detonated at the bottom centre has a larger influence range for the impulse (8.0 m/kg1/3) than the cylinders detonated at the middle (4.2 m/kg1/3) and top centre (2.5 m/kg1/3).

Creation and Verification of Numerical Model of Explosive Charge Blast in The Ansys Software System, for the Purpose of Substantiating the Optimal Parameters of Drilling and Blasting Operations

The purpose of this paper was to create a numerical model of explosive destruction of a rock slab by exploding a cylindrical explosive charge. The paper considers the features of solving the problem of explosive charge using the finite element method in a three-dimensional setting. The equations of state of materials used for calculations are given. The results of the laboratory experiment carried out on the basis of the laboratory: “Physical and technological processes of rock destruction” and “Physics of rock destruction by explosive energy” of the Department of Blasting works of the Mining University are presented. The comparison of the results of the laboratory experiment and the numerical modeling performed using the ANSYS software system is presented. Experimental research has shown that having clarified the constants in the polynomial equation of state of the material and the Johnson–Holmquist strength model, the results of numerical modeling, in general, are similar to the experimental ones. The obtained and verified numerical model of the cylindrical explosive charge blast is considered as the basis for choosing the optimal parameters of drilling and blasting works.

Effect of Shell Material on the Detonation of an Explosive Charge

The effect of shell material (copper and silicon carbide) on the detonation of a cylindrical explosive charge was analyzed. The wave patterns in the detonation products and the shells are substantially different, which is due to different sound velocities and the rapid destruction of the ceramic under explosive loading. The wave pattern at the explosive/ceramic interface was found to be affected by desensitization of the explosive due to its loading by an advancing wave from the shell side, resulting in a decrease in pressure, blurring of the detonation front, and an increase in particle velocity. Throughout the process, there is a continuous increase in the time of explosive decomposition near the interface between the explosive and the ceramic shell. An extended region with a constant pressure close to the Chapman–Jouguet pressure was observed on the axis of symmetry behind the detonation front of the explosive charge in the ceramic shell.

Deformation and Thermal Processes That Occur during the High-Speed Collapse of a Bulky Copper Cylindrical Shell

A bulky copper cylindrical shell with an internal diameter of 118 mm and a wall thickness of 5.9 mm has been exposed to an explosion of a cylindrical explosive charge uniformly distributed around it. A cylinder with a diameter of 57–58 mm has been obtained as a result of high-speed deformation caused by the explosion. A metallographic analysis of the cylinder structure shows that the shell collapses under the influence of axially symmetric radial deformation, which is accomplished by both twinning and sliding mechanisms. It is determined that axial deformation occurs along with the radial deformation. The microstructure of the cross-section consists of three zones. A wide annular deformation zone is formed on the outside, an annular recrystallization zone is formed closer to the center, and a circular region with a dendritic structure is formed at the center. The presence of dendrites indicates that the temperature at the boundary of this region reaches the melting point of copper. The temperature change along the radius of the cylinder has been calculated.

The influence of charge geometry on the response of partially confined right circular stainless steel cylinders subjected to blast loading

This article presents an experimental and numerical investigation into the effect of charge geometry on the structural response of right circular cylinders. Thin-walled, seamless 304 stainless steel cylinders were subjected to internal blast loads that were generated by detonating bare cylindrical plastic explosive charges. Charge diameter, charge mass and aspect ratio were varied. Partial confinement was created by closing one end of the cylinder and leaving the other end free to vent to air. The axial impulse, maximum diametric deflection and axial shortening increased with increasing aspect ratio when the charge diameter was kept constant. When the charge mass was kept constant, the long charges caused larger diametric deflections than their mass equivalent shorter charges. The shorter charges transferred more axial impulse to the ballistic pendulum than their mass equivalent longer charges. The concept of effective charge mass (axial and lateral) was used to interpret the results and developed to provide an empirical equation relating deflection to the charge dimensions. Numerical simulations were performed which gave good agreement with the experimental data and predicted similar trends. The model revealed that the longer charges produced more diametric deflections than their mass equivalent shorter charges because a high pressure (above 50MPa) zone, that covered a larger area and had a longer duration, developed at the cylinder wall in the case of longer charges. The insights from the model are in good agreement with the simple concept of lateral effective charge mass developed herein. When compared to spherical charge detonations in similar steel cylinders, the cylindrical charge detonations produced pressure waves which are more directional, have lower peak pressures and dissipate more gradually. The cylinders exhibited a more pronounced secondary bulge at the clamped boundary for cylindrical charge detonations.

Simulating sympathetic detonation using the hydrodynamic models and constitutive equations

A Sympathetic detonation (SD) is a detonation of an explosive charge by a nearby explosion. Most of times it is unintended while the impact of blast fragments or strong shock waves from the initiating donor explosive is the cause of SD. We investigate the SD of a cylindrical explosive charge (64 % RDX, 20 % Al, 16 % HTPB) contained in a steel casing. The constitutive relations for high explosive are obtained from a thermo-chemical code that provides the size effect data without the rate stick data typically used for building the rate law and equation of state. A full size SD test of eight pallet-packaged artillery shells is performed that provides the pressure data while the hydrodynamic model with proper constitutive relations for reactive materials and the fragmentation model for steel casing is conducted to replicate the experimental findings. The work presents a novel effort to accurately model and reproduce the sympathetic detonation event with a reduced experimental effort.

Characteristics and mechanisms of strain waves generated in rock by cylindrical explosive charges

A superposing principle, by suitably adding the strain waves from a number of concentrated explosive charges to approximate the waves generated by a cylindrical charge based on the strain wave of a point or small spherical explosive charge generated in rock, is used to further study the triggering time of strain gauges installed in radial direction at same distances but different positions surrounding a cylindrical explosive charge in rock. The duration of the first compression phase and peak value of strain wave, and furthermore, their differences are analyzed and some explanations are given. Besides that, the gauge orientation in which the maximum peak value occurs is also discussed. At last, the effect of velocity of detonation (V.O.D.) of a cylindrical explosive charge on the strain waves generated in the surrounding rock is taken as key research and the pattern of peak amplitude of a strain wave varies with the V.O.D. is likely to have been found.

Analysis of Shell Material Influence on Detonation Process in High Explosive Charge

The influence of the shell material (copper and silicon carbide) on the detonation process in cylindrical high explosive charge is experimentally and numerically investigated. We observed the significant differences of wave pictures in the detonation products and in the shells, which were due to differences in the sound velocities in the shells and rapid destruction of the ceramic shell under explosion loading. The specific features of a wave picture at the interface HE/ceramics due to desensitization of explosive under loading by an advanced wave in the shell were detected. Those features lead to decreasing of detonation pressure, blurring of the detonation front, and to increasing of mass velocity behind detonation front that is typical for under-compressed detonation. On the symmetry axis of HE charge in the ceramic shell behind the detonation front the long zone with practically constant pressure was observed. We have identified the mechanism of transmission of disturbances from the periphery to the symmetry axis of the HE charge. The source of the emergence of this zone is identified as transverse waves propagating directly behind the detonation front from the periphery to the symmetry axis of the HE charge.

Theoretical and Experimental Study on Detonation Wave Propagation in Cylindrical High Explosive Charges with a Wave-shaper

The use of a cylindrical high-explosive charge with a wave-shaper is an efficient way to obtain an ultra-high pressure and a convergent detonation wave. An analysis of flow fields corresponding to the regular and Mach reflection of detonation waves in a cylindrical high-explosive charge with a wave-shaper is presented in this paper. The pressure, flow velocity and triple point growth angle of the Mach stem were calculated. The Mach stem height was also determined by using the modified Whitham method. The results show that the Mach stem height rises from zero at the critical angle of Mach reflection and changes to the Chapman-Jouguet detonation state with the propagation of the detonation waves. Shock indentation experiments were conducted, in which a wave-shaper was used in a cylindrical high-explosive charge to form Mach reflection detonation waves. The results showed that the discrepancy between the experimental results and the theoretical calculations was less than 15%, which proves the validity of the proposed theoretical model.

Numerical study of velocity distribution of fragments caused by explosion of a cylindrical cased charge

This paper presents a study of the velocity distribution of fragments caused by explosion of a cased charge. Available formulas usually predict a uniform fragments velocity at the middle part of the cylinder and only few sources recommend evaluation of a non-uniform velocity distribution. According to few, yet available, experimental results, the latter distribution is more realistic. Three numerical simulation techniques were used in the work described here, to simulate the velocity distribution of a cased cylindrical explosive charge: 2D simulations, 3D simulations and 3D simulations using the SPH method. Additional simulation of a pre-formed fragmentation was also investigated. The failure and erosion criteria of the casing material have been examined in the numerical analyses. The results of the numerical simulations have been verified against reported experimental data, which indicated a non-uniform velocity distribution along the cylinder axis. Overall, there was a good agreement between the 2D, 3D, 3D-SPH methods and the experimental measurements, including the distribution of the lower velocity values near the cylinder edges. Conclusions of this study include characteristics of the velocity distribution and observations regarding advantages and disadvantages of the techniques that were used. It is shown that the velocity distribution can be described by a normalized ‘shape function’, which depends on the casing length-to-diameter ratio. Finally, it is noted that the mass distribution, which has been out of the scope of this study, should be investigated as well.

Masonry infill walls under blast loading using confined underwater blast wave generators (WBWG)

The vulnerability of the masonry envelop under blast loading is considered critical due to the risk of loss of lives. The behaviour of masonry infill walls subjected to dynamic out-of-plane loading was experimentally investigated in this work. Using confined underwater blast wave generators (WBWG), applying the extremely high rate conversion of the explosive detonation energy into the kinetic energy of a thick water confinement, allowed a surface area distribution avoiding also the generation of high velocity fragments and reducing atmospheric sound wave. In the present study, water plastic containers, having in its centre a detonator inside a cylindrical explosive charge, were used in unreinforced masonry infills panels with 1.7m by 3.5m. Besides the usage of pressure and displacement transducers, pictures with high-speed video cameras were recorded to enable processing of the deflections and identification of failure modes. Additional numerical studies were performed in both unreinforced and reinforced walls. Bed joint reinforcement and grid reinforcement were used to strengthen the infill walls, and the results are presented and compared, allowing to obtain pressure–impulse diagrams for design of masonry infill walls.

Study of simple plane wave generator with an air-metal barrier

Plane wave generators (PWGs) are used to accelerate flyer plates to high velocities with their generated plane waves, which are widely used in the test of dynamic properties of materials. The traditional PWG is composed of two explosives with different detonation velocities. It is difficult to implement the related fabrication processes and control the generated waves due to its complicated structures. A simple plane wave generator is presented in this paper, which is composed of two identical cylindrical high explosive (HE) charges and an air-metal barrier. A theoretical model was established based on two different paths of the propagation of detonation waves, based on which the size of air-metal barrier was calculated for a given charge. The corresponding numerical simulations were also carried out by AUTODYN-2D ® based on the calculated results, which were used to compare with the theoretical calculations. A detonation wave with a flatness of 0.039 ms within the range of 70-percent diameter of the main charge was obtained through the simulations. Copyright © 2014, China Ordnance Society. Production and hosting by Elsevier B.V. All rights reserved.

Rear-surface collapse perforation of concrete targets under buried explosion

Experimental research on collapse and perforation failure at the rear surface of a concrete target induced by buried explosion of a cylindrical explosive charge was performed. The aim is to develop an available approach to predict the critical collapse thickness under explosion loading. It is found that both the diameter and the length-to-diameter ratio of the cylindrical explosive charges have remarkable influence on the critical collapse thickness. Based on the experimental data for the plain concrete with the compressive strength of 35MPa, an analytical expression for the relation between the dimensionless critical collapse thickness on concrete target and the length-to-diameter ratio of explosive charge is developed via dimensional analysis. Moreover, it is also found that there exists an incomplete similarity of the critical collapse thickness in the diameter of explosive charge, although the complete similarity in the length-to-diameter ratio alone cannot be established.