Small Explosive Charge Research Articles

Residual axial capacity of circular reinforced concrete columns subjected to contact explosions

The threat of terrorist bombing attacks on critical infrastructure has attracted a lot of attentions over the past decades. Contact explosion with a small explosive charge mass can cause severe damage to RC columns. Since columns are the primary load-bearing components in structures, the failure of critical columns can initiate collapse of the entire structure and result in devastating consequences associate with significant casualties and economic losses. To prevent catastrophic structural collapse, the most critical requirement of blast-damaged columns would be the residual capacity to withstand axial load. In this study, the residual axial load-carrying capacity of RC columns damaged by contact explosions was numerically investigated. A high-fidelity physics-based numerical model of RC columns under contact explosions was developed using the non-linear dynamic analysis program LS-DYNA with Arbitrary-Lagrangian–Eulerian (ALE) and Fluid-Structure Interaction (FSI) algorithms. The numerical model was comprehensively validated with existing experimental results in literature. An extensive parametric study was carried out to determine the effect of critical design parameters, including explosive charge mass, column diameter, longitudinal reinforcement ratio, and transverse reinforcement ratio on the residual axial load-carrying capacity of RC columns after contact explosions. The damage degree of the blast-damaged columns was quantitatively analyzed with a damage criterion based on the residual axial load-carrying capacity. Based on the parametric analysis results, an empirical formula was developed through multivariable regression analysis method for prediction of the damage degree and residual axial load-carrying capacity of blast-damaged RC columns under contact explosions. The proposed empirical formula can be utilized in preliminary design of RC columns against contact explosions and failure risk assessment of RC columns after contact explosions.

Shock wave characteristics in a conical water explosion shock tube under cylindrical charge condition

A conical shock tube is a kind of underwater explosive devices which uses small conical explosive charge to form high intensity shock pressure. Theoretically, the shock wave pressure in the conical shock tube is the same as that generated by a virtual spherical explosive charge in free field water. However, considering the effect of practical factors, the characteristics of shock wave in the actual device and the theoretical device are different to some extent. In order to investigate the shock wave characteristics in the conical water explosion shock tube under a cylindrical charge condition, and to obtain the variation rules of the peak pressure value, the specific impulse and the energy flux density, a series of numerical calculations with different cone angles and different quality of cylindrical charges were conducted. The reliability of the simulation methods was verified by comparing with the published experimental data. Through the analysis of the pressure data obtained by the validated simulation method, it is found that the shock wave in the tube follows the same scaling law as it is in the free field underwater explosion. The constants k and n of the empirical expressions for peak pressure, the impulse and the energy flux density for the shock wave in shock tube are obtained by data fitting. Furthermore, the relationships among the coefficient k, index n and cone angle α were deduced, and the result shows that the coefficients k have well linear relationship with constructed angle coefficient β, and the indexes n can be quantitatively expressed by cone angle α. Regarding the free field as a special case with a cone angle of 360°, it’s constants k and n also conform to the obtained relationships. It is also found that the secondary pulsation pressure period shows an anomalous change rule with explosive mass, which can be well explained by the significant increasement of the equivalent hydrostatic pressure depth. The ratio between the secondary impulse pressure peak and initial pressure peak is bigger than that in free field while the ratio between the secondary impulse pressure’s impulse to the initial pressure impulse is almost the same. These results can provide support for the application of conical shock tubes.

Numerical investigations on the large deformation behaviour of ring stiffened cylindrical shell subjected to underwater explosion

Ring stiffened cylindrical shells find wide applications in marine vehicles such as submersibles, submarine, autonomous underwater vehicles (AUV) and torpedoes. The structures used for military applications are susceptible to shock loadings from an underwater explosion. It is imperative to understand the shock damage mechanism of such structures to design for survivability. The problem is quite complex involving explosive-fluid interaction, fluid-structure interaction, material, geometric nonlinearity and strain rate effects. In this paper, an attempt has been made to study the shock response of a ring stiffened cylindrical shell of length 1000 mm, diameter 600 mm and thickness 6 mm shock tested using small explosive charge of 70 gm PEK I. The numerical study is performed using LS-DYNA finite element code considering the fluid-structure interaction, strain rate effects, geometric and material nonlinearity. The stiffened cylinder under consideration is modelled using Belytschko-Tsay shell element and the fluid and explosive using Eulerian solid element. The explosive is modelled using JWL equation of state, the fluid using Gruneisen equation of state and the stiffened cylinder fluid interaction using ALE coupling. The permanent deformation obtained from the numerical study compares well with experimental results within 5% accuracy. Subsequently, parametric investigation has been carried out for various charge weights with different cylindrical shell thickness and the results of permanent deformation, effective plastic strain are presented.

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.

Inversion of seabed acoustic parameters in shallow water using the warping transform

In this paper, a method is described for inverting geoacoustic parameters of the seabed from short range field data recorded by single hydrophone. The original data in time domain are processed by a warping operator at first, and then, the dispersion curve and the mode amplitude ratios are extracted separately from the warped data. The velocity and the density in the bottom are inverted from the dispersion curve, and the attenuation from the mode amplitude ratios, respectively. The performance of the method is examined using simulated data and then experimental data from the North Sea of China. The source used in the experiment was a small explosive charge that provided good signal to noise ratio over the frequency band from 200 Hz to 1 kHz. The depth of the water was about 30 m, and the water sound speed was nearly constant with depth. The seabed geoacoustic parameters are inverted from the data received at different ranges from 2 to 14 km. The results from the different ranges are consistent with a simple half space model of the bottom. The seabed velocity is about 1600 m/s.

Considering the Influence of Chemical Reactions between Detonation Products on Specific Heat Ratio Calculating of the TNT Explosive with Small Explosive Charge Volume Ratio

The formula and calculating method of specific heat ratio in confined explosion with small explosive charge volume ratios under considering chemical reactions of the detonation products was researched. Taking the TNT explosive as an example, a numerical calculating program was written, and the specific heat ratio of the confined explosion either considering the influence of the chemical reactions or not were calculated by the program.

Ballistic and physical properties of highly fractured alumina

It is known that ceramic materials in armour are often shattered by a penetrating projectile and the resistance to penetration is therefore dependent upon the properties of this failed material. A small explosive charge was used to shatter a confined 95% alumina tile by passing the stress wave from an explosive detonation through a steel cover plate and into the ceramic. This fractured material was shown to have an elastic modulus of 130 GPa compared to 330 GPa for the monolithic alumina. Impact indentation tests and ballistic depth of penetration tests were performed on the intact ceramic, shattered ceramic and a pressed ceramic powder compact. It was found that the fractured material had a ballistic efficiency approximately 70% of that of the monolithic alumina and was also able to cause significant erosion to the projectile.

Blast phenomena associated with high-speed impact

An experimental, analytical, and numerical investigation was conducted in order to measure air pressure at the target surface near the point of normal impact into semi-infinite rolled homogeneous armor (RHA) of a high-speed, 10 mm diameter tungsten carbide sphere. Impact speeds varied from 0.9 to 3.8 km/s. Numerical simulations of the impact were conducted in which the crater lip and ejecta motion were successfully coupled with the surrounding air. An analytical model of the air blast field resulting from the impact has been developed employing the blast generated by a small explosive charge initiated at the time and point of impact. This is a one-dimensional solution in which all characteristics of the blast field are a function only of the radius from the charge center and the energy released by the charge. Thus, a single empirically derived parameter—the equivalent explosive charge energy—completely defines the blast field. For each test, this parameter was obtained from a least squares fit to the peak pressures measured as a function of distance from the impact (explosion) center. The model predicts the data well at all test speeds. The tests, analytical modeling, and numerical simulations resulted in the following conclusions: The air blast field contains about 0.7% of the kinetic energy of the impacting projectile and results from three sources: (1) the air entrained by the projectile which impinges upon the target plate; (2) the air accelerated by the radially expanding crater lip; and (3) the air entrained by the impact induced ejecta.

Strength and Failure Modes of Hoop Wound CFRP Tubes Under Compressive High Rates of Loading

A study was undertaken to investigate the response of hoop wound carbon fibre reinforced plastic (CFRP) tubes to dynamic compressive loading at strain rates in the range of 5–200/sec. An experimental rig was designed and built to test short tubular specimens under external radial pressure with minimum end constraints. The load was applied by detonating a small explosive charge inside a water filled, steel, cylindrical chamber enclosing the test specimen. For each test the external pressure and the strains, in both circumferential and longitudinal directions, were recorded on suitable digital processing equipment. Two distinct modes of failure were identified; material and structural (buckling). The mode of failure was dependent on the rate of loading and the tube diameter/thickness ratio. For 100 mm diameter tubes with diameter/thickness=40, buckling failure dominated at strain rates below 10/s. However, at higher strain rates, material failure and a considerable enhancement in burst strength was observed. For 100 mm diameter tubes, with diameter/thickness=80, a buckling mode of failure was in evidence in all the tests, irrespective of the rate of loading.

An implosive seismoacoustic source for seismic experiments on the ocean floor

Bottom shots have been used for a number of years in seismic studies on the ocean floor. Most experiments utilized explosives as the energy source, though researchers have recognized the usefulness of collapsing water voids to produce seismoacoustic signals. Implosive sources, however, suffered generally from a lack of control of source depth. We present a new experimental tool, called SEEBOSEIS, to carry out seismic experiments on the seafloor utilizing hollow glass spheres as controlled implosive sources. The source is a 10-inch BENTHOS float with penetrator. Inside the sphere we place a small explosive charge (two detonators) to destabilize the glass wall. The time of detonation is controlled by an external shooting device. Test measurements on the Ninetyeast Ridge, Indian Ocean, show that the implosive sources can be used in seismic refraction experiments to image the subbottom P-wave velocity structure in detail beyond that possible with traditional marine seismic techniques. Additionally, the implosions permit the efficient generation of dispersed Scholte waves, revealing upper crustal S-wave velocities. The frequency band of seismic energy ranges from less than 1 Hz for Scholte modes up to 1000 Hz for diving P-waves. Therefore, broadband recording units with sampling rates >2000 Hz are recommended to sample the entire wave field radiated by implosive sources.

A facile pressing technique for the preparation of small calibre dual role explosive charge

AbstractSmall calibre shaped charges are prepared by the pressing method. The shaped charge performance is considerably influenced by the density gradient which is an inherent drawback associated with the pressing method. A new method, double action pressing technique has been developed which overcomes this problem and is amenable for large scale production. Properties of the charges prepared by the different methods especially with respect to the den sity gradient and performance against targets are presented and discussed.

The utilization of explosive loading as a nondestructive evaluation tool in geologic materials

This paper describes the use of a small explosive charge to evaluate geologic material in a non-destructive manner. One-dimensional computations have been performed using the Lagrangian finite difference code WONDY to investigate the effects that open joints and weak layers of unconsolidated material have on the propagation of stress waves resulting from the detonation of an explosive charge. Data from testing conducted by others in models or in full scale in a number of different materials have been collected and examined. Several findings of importance were noted. The computational results indicate that the characteristics of a stress pulse after passing through an open joint are significantly different from those of a stress pulse that has passed through a weak layer. The examination of data from various explosive tests in different media has yielded a way of determining the type of material that the stress pulse has passed through. These preliminary results indicate that it is theoretically possible to excite a geologic medium with a small explosive pulse and determine the type of rock and the extent to which it contains either open joints or weak layers of unconsolidated material.

A comparison of broadband and narrow‐band transmission loss in shallow water

Calibrated acoustic measurements were made at the Hudson Canyon Experiment site [L. Maiocco and W. Carey, J. Acoust. Soc. Am. Suppl. 1 86, S8 (1989)] during area characterization test II(ACT II) conducted in September 1993. This site was chosen because it is a surveyed area with known geophysical and geoacoustic properties. Transmission loss was measured along the previously run radials from bore hole 6010 using calibrated small broadband explosive charge sources and a narrow‐band continuous wave (cw) towed acoustic projector. These sources were, for the purposes considered here, co‐located in range because of low test ship speed (under 5 kn). The receiving sensor was a 25 element stationary vertical line array spanning the majority of the water column (73 m), with 19 elements extending off the bottom (60 m) and 6 elements along the bottom (30 m). Using the principle of reciprocity, the hydrophone elements at each of the source depths enabled comparisons of the transmission loss measurements for broadband and cw sources to be made over a range interval from 4–22 km at two frequencies (200 and 900 Hz). The comparisons were performed by means of linear regression of the data from the two sources. The results of the comparison will be presented and will include a detailed discussion of the precision of the results and of possible sources of experimental error. Finally, the cw transmission loss from ACT II will be compared with the previous measurements of Maiocco and Carey.

Nonlinear wave propagation in a water-filled, conical shock tube

A conical shock tube is being developed for evaluating hull-mounted sonar transducers and related components for their vulnerability to exploding ordnance [J. F. Zalesak and L. B. Poché, Jr., Proc. 60th Shock and Vib. Symp. III, 73–76 (1989)]. A small explosive charge at the breech end generates a robust shock wave that travels down the tube and strikes the transducer at the muzzle end. Proper design of the water-filled shock tube requires an understanding of the nonlinear propagation of shock waves in a conical waveguide with nonrigid walls. This understanding is obtained by use of a numerical solution to the generalized Burgers’ equation [D. H. Trivett and A. L. Van Buren, J. Acoust. Soc. Am. 69, 943–949 (1981)]. Here the combined effects of nonlinearity, absorption, and dispersion are included in a stepwise calculation of the propagation. Results show that the effect of dispersion must be minimized to provide an acceptable shock waveform at the muzzle. Shock waves measured in a prototype shock tube are in good agreement with the theoretical predictions. [Work supported by ONR.]

Reflection Seismic Sources for Defining Coal Seam Structure

The prime objective of the investigations described in this paper is to improve the reliability of structural information in advance of underground mining. Kembla Coal and Coke extracts high-grade coking coal by longwall mining methods. In 1984 major disruption to mining was caused by an unexpected fault which crossed the longwall panels. The costly consequences of this faulting provided the Company with a strong incentive to obtain accurate structural data in advance of mining.Seismic reflection work carried out in the 1970s using large explosive charges, produced poor data of very low resolution. In 1987, the Mini Sosie technique was used to obtain seismic data. Fair data were obtained with moderate resolution. Work carried out in 1988 established that a small explosive charge at the base of weathering produced still better data. The weathering depth was determined by a continuous seismic refraction survey.In order to reduce the costs of obtaining seismic data, as well as seeking further improvements in data quality and resolution, experiments were carried out in 1990 and 1991 using alternative sources. Data from a Bolt LSS-3B air gun, a Mertz M26 vibrator and 1.5 m deep explosive charges were compared with data from explosives at the base of weathering. Experiments were also carried out using shaped charges and high velocity of detonation explosives (up to 8600 m/s).The results from the various experiments and production work have demonstrated that all the surface and near-surface sources used, generated substantial ground roll, which reduced the dynamic range of the recording instruments and degraded the signal-to-noise ratio. Weathered near-surface layers also significantly attenuated the high frequencies, resulting in lower temporal resolution.A 240-g conventional explosive with 6800 m/s velocity of detonation, placed below the base of weathering, proved to be the best available source for obtaining good quality high-resolution data. Substantial improvements in data quality and resolution were achieved. Further work is still required in other areas of data acquisition, processing and modelling to improve confidence in the interpretation of very small faults.

FURTHER DEVELOPMENT OF A HIGH‐FREQUENCY SEISMIC SOURCE FOR USE IN BOREHOLES1

AbstractA borehole sparker seismic source enclosed in a semi‐flexible tube has been developed to produce a short compressional seismic pulse with a frequency content in the range 250 Hz to 3.5 kHz with a peak power at 570 Hz. The pulse shape and frequency content are shown to be a function of the input power, the diameter of the spark chamber, the salinity of the electrolyte, the material of the spark chamber and the electrode configuration. When in a borehole, the source produces a vertically polarized shear wave but, being similar to a small explosive charge does not allow phase reversal as a means of identifying the shear wave in the received pulse train. The source is shown to be ideal for tomographic imaging surveys because of its repetitive nature, high frequency content and reliability. Very high resolution seismic reflection surveys are also shown to be possible under favourable circumstances.

HETERODYNE HOLOGRAPHY FOR VISUALIZATION OF SURFACE ACOUSTIC WAVES

Abstract A technique for recording and visualizing acoustic wavefronts over a finite field of view and with a resolution on the order of Angstroms has been developed. Multiple exposure holograms of an aluminum test block were used to record the surface displacements resulting from the detonation of a small explosive charge placed on the object surface. The primary wavefronts resulting from the explosive charge were sufficiently large as to be visible upon reconstruction of the holographic interferograms. In addition, details of the surface wavefronts which could not be deduced using conventional holographic interferometry were measured and displayed by modifying the pulsed recording geometry and subsequently applying heterodyne interferometric analysis to the holograms to interpolate between the observed interferometric fringes. Although theory predicts that still greater resolution is possible, fringe interpolation to 1/ 900 of a fringe ( about 3A displacement) was demonstrated.

Effect of finite ground impedance on the propagation of acoustic pulses

The propagation of an acoustic transient in the vicinity of a finite impedance ground plane has been numerically simulated. A waveform characteristic of a small explosive charge was selected for analysis. Pulse waveforms and amplitudes were computed for propagation distances from 3 to 3000 m, for microphone heights from 0 to 30 m, and for flow resistances from 10 to 1000 g cm−3 s−1. Typical values of atmospheric variables were assumed. Nonlinear propagation effects, atmospheric refraction, and turbulence were excluded from the analysis. This study indicates that finite ground impedance can significantly affect acoustic pulses from explosives. The need to consider ground effects when relating the results of small‐scale explosive tests to larger scale explosions is demonstrated. Finite impedance effects are small (<2 dB) for the pulse shape studied if the numerical distance of the fundamental frequency is less than 0.1. The surface wave term as formulated by Donato [J. Acoust. Soc. Am. 60, 34–39 (1976)] pro...

The reaction zone structure of cylindrical detonations in monodisperse sprays

Schlieren framing and streak photographs, and pressure transducer traces describing thedetailed structure of detonations propagating through low and high vapor pressure sprays are presented. The experiments were performed using a pie shaped test chamber with an included angle of 20°, a length of 140 cm and a width of 5.2 cm. Detonations were initiated with a small explosive charge at the vertex of the tube and propagated through a monodisperse spray of 400 μm decane and heptane droplets generated by 322 hypodermic needles fed by an oscillating pressure supply. The structure of low vapor pressure decane sprays in oxygen is driven by droplet shatteringand by the sudden explosion of fuel entrapped in the droplet wake after a certain ignition delay period t ig . The blast waves generated by these wake explosions are clearly shown in both the framing and streak photographs. Superposition of a pressure trace and streak photograph indicates the source of the pressure oscillations usually observed in the reaction zone of spray detonations. Values of ignition delay time and wake blast wave parameters derived from the streak photographs are presented. Different results are obtained for high vapor pressure heptane sprays in oxygen. A gaseous detonation propagates through the already vaporized fuel with properties determined by the vapor. Droplet breakup, shattering, and explosion follows at a considerable distance behind this front and does not appear to affect the detonation velocity. The structure of such “Hybrid” detonations is clearly illustrated by schlieren framing photographs.

Diver-operated Device for Immobilizing Fish with a Small Explosive Charge

Diver-operated Device for Immobilizing Fish with a Small Explosive Charge