Explosion Fragments Research Articles

Classification of Hyperspectral Images of Explosive Fragments Based on Spatial–Spectral Combination

The identification and recovery of explosive fragments can provide a reference for the evaluation of explosive power and the design of explosion-proof measures. At present, fragment detection usually uses a few bands in the visible light or infrared bands for imaging, without fully utilizing multi-band spectral information. Hyperspectral imaging has high spectral resolution and can provide multidimensional reference information for the fragments to be classified. Therefore, this article proposed a spatial–spectral joint method for explosive fragment classification by combining hyperspectral imaging technology. In a laboratory environment, this article collected hyperspectral images of explosion fragments scattered in simulated scenes. In order to extract effective features from redundant spectral information and improve classification accuracy, this paper adopted a classification framework based on deep learning. This framework used a convolutional neural network–bidirectional long short-term memory network (CNN-BiLSTM) as the spectral information classification model and a U-shaped network (U-Net) as the spatial segmentation model. The experimental results showed that the overall accuracy exceeds 95.2%. The analysis results indicated that the method of spatial–spectral combination can accurately identify explosive fragment targets. It validated the feasibility of using hyperspectral imaging for explosive fragment classification in laboratory environments. Due to the complex environment of the actual explosion site, this study still needs to be validated in outdoor environments. Our next step is to use airborne hyperspectral imaging to identify explosive fragments in outdoor environments.

A design model of multi-layer modified aramid fabrics against fragment simulating projectiles and full metal jacketed bullets

Soft body armor is required to meet threats of both bullets and explosion fragments in battlefield. However, designing body armor that can protect against these two types of projectiles considering both critical velocity and back face deformation (BFD) is often based on experience and extensive ballistic experiments. This paper proposes a quick design model for determining the layers of aramid fabrics modified by polyethylene (PE) to protect against fragment simulating projectiles (FSP) and full metal jacketed bullets (FMJ). Firstly, ballistic experiments are conducted discovering the optimal concentration of PE modification against the sphere and FSP is 10 %. Secondly, finite element model is adapted to explore the protection capabilities of modified aramid fabrics against FSP and FMJ and a linear relationship between the BFD and the critical velocity has been observed. Thirdly, an analytical model is established to uncover the reason of this relationship. Finally, a design model is proposed to configure the improved outer tactical vest (IOTV) generation III based on the derived formulae of critical velocity and BFD for different layers of modified aramid fabrics against FSP and FMJ. The model indicates that the objectives of intercepting FSP or FMJ and reducing blunt trauma are usually not simultaneously attainable. 38 layers of modified aramid fabrics are sufficient to meet the protection requirements for both FSP and FMJ, regardless of critical velocity and BFD. Besides, 498 m/s is the threshold of FMJ impact velocity to determine the priority of intercepting bullets or reducing blunt trauma. The design model can serve for the development of lightweight and effective body armor.

Exploring the ultrafast and isomer-dependent photodissociation of iodothiophenes via site-selective ionization.

C-I bond extension and fission following ultraviolet (UV, 262 nm) photoexcitation of 2- and 3-iodothiophene is studied using ultrafast time-resolved extreme ultraviolet (XUV) ionization in conjunction with velocity map ion imaging. The photoexcited molecules and eventual I atom products are probed by site-selective ionization at the I 4d edge using intense XUV pulses, which induce multiple charges initially localized to the iodine atom. At C-I separations below the critical distance for charge transfer (CT), charge can redistribute around the molecule leading to Coulomb explosion and charged fragments with high kinetic energy. At greater C-I separations, beyond the critical distance, CT is no longer possible and the measured kinetic energies of the charged iodine atoms report on the neutral dissociation process. The time and momentum resolved measurements allow determination of the timescales and the respective product momentum and kinetic energy distributions for both isomers, which are interpreted in terms of rival 'direct' and 'indirect' dissociation pathways. The measurements are compared with a classical over the barrier model, which reveals that the onset of the indirect dissociation process is delayed by ∼1 ps relative to the direct process. The kinetics of the two processes show no discernible difference between the two parent isomers, but the branching between the direct and indirect dissociation channels and the respective product momentum distributions show isomer dependencies. The greater relative yield of indirect dissociation products from 262 nm photolysis of 3-iodothiophene (cf. 2-iodothiophene) is attributed to the different partial cross-sections for (ring-centred) π∗ ← π and (C-I bond localized) σ∗ ← (n/π) excitation in the respective parent isomers.

Establishment of a combat damage control surgery training platform for explosive combined thoraco-abdominal injuries

PurposeIt is challenging to prepare military surgeons with the skills of combat damage control surgery (CDCS). The current study aimed to establish a damage control surgery (DCS) training platform for explosive combined thoraco-abdominal injuries. MethodsThe training platform established in this study consisted of 3 main components: (1) A 50 m × 50 m square yard was constructed as the explosion site. Safety was assessed through cameras. (2) Sixteen pigs were injured by an explosion of trinitrotoluene attached with steel balls and were randomly divided into the DCS group (accepted DCS) and the control group (have not accepted DCS). The mortality rate was observed. (3) The literature was reviewed to identify the key factors for assessing CDCS, and testing standards for CDCS were then established. Expert questionnaires were employed to evaluate the scientificity and feasibility of the testing standards. Then, a 5-day training course with incorporated tests was used to test the efficacy of the established platform. In total, 30 teams attended the first training course. The scores that the trainees received before and after the training were compared. SPSS 11.0 was employed to analyze the results. ResultsThe high-speed video playback confirmed the safety of the explosion site as no explosion fragments projected beyond the wall. No pig died within 24 h when DCS was performed, while 7 pigs died in the control group. After a literature review, assessment criteria for CDCS were established that had a total score of 100 points and had 4 major parts: leadership and team cooperation, resuscitation, surgical procedure, and final outcome. Expert questionnaire results showed that the scientific score was 8.6 ± 1.25, and the feasibility score was 8.74 ± 1.19. When compared with the basic level, the trainees’ score improved significantly after training. ConclusionThe platform established in this study was useful for CDCS training.

High-hardness polyurea coated steel plates subjected to combined loadings of shock wave and fragments

To investigate the effect of polyurea on the protective performance of a steel target plate under the combination of shock wave and fragments, the failure characteristics, damage process and micro mechanism of the polyurea coated steel plates with different coating methods under the combination of explosion shock waves and fragments were analyzed through experiments and numerical simulations. The results showed that single-sided coatings aggravated the damage of target plate when the coating thickness was 2 mm. While the polyurea thickness greater than 4 mm could significantly reduce the damage degree of the steel plate. When the polyurea was coated on the double sides, it would aggravate the damage, no matter how thick the polyurea was. Through microscopic research, it was found that the front coated polyurea was severely ablated by detonation products, which greatly reduce its energy absorption efficiency. The polyurea coated on the back underwent tensile fracture under the influence of tensile stress wave. The breaking of intramolecular hydrogen bond of polyurea was the key to the energy absorption of polyurea.

Wavelength dependence of the angular distribution of the Coulomb explosion in the femtosecond ionisation of methyl iodide

The angular distribution of the ions coming from Coulomb explosion following femtosecond ionisation of methyl iodide is studied in the spectral range of 600 to 1450 nm. Under these conditions, iodine and methyl fragment ions are generated, both via dissociative ionisation and via Coulomb explosion following the double ionisation of the parent ion. However, the dependence of the angular distribution of the fragment ions on the ionisation wavelength is completely different for those two mechanisms: dissociative ionisation fragments are being ejected with high anisotropy, irrespectively of the wavelength, while the angular distribution of the Coulomb explosion fragments changes from anisotropic, for an excitation wavelength close to 600 nm, to isotropic close to 950 nm, and remain isotropic up to 1450 nm.

Analysis of causes of burst failure of a buffer tank

An explosion failure occurred in a buffer tank at an oil transfer station. The explosion fragments flew out, causing 2 deaths and 1 injury. To analyze the root cause of the failure, visual inspection, thickness measurement, mechanical test, chemical composition test, corrosion product analysis, fracture analysis, pressure-bearing capacity check, explosion analysis, and operational condition investigation were conducted. The results showed that the chemical composition and mechanical properties of the buffer tank meet the standard requirements; the metallographic structure of the steel is ferrite, pearlite, and a small amount of Widmanstatite, and the structure has not deteriorated after a long time of service; the buffer tank has local corrosion, and the pressure-bearing capacity still meets the design requirements; operational condition investigation revealed that when the buffer tank burst, the operating personnel were conducting pressure test on the newly-built pipeline outside the station. The pressure test medium used was air. The buffer tank was isolated from the pressure test equipment, and the valve connecting the pressure test pipeline and the buffer tank had internal leakage. Gas entered the buffer tank, causing an overpressure explosion of the tank, and the overpressure wave leads to the collapse of the wall and casualties. Explosion energy analysis showed that the location of casualties was within the range of overpressure wave casualties. In order to avoid such incidents, the use of gaseous media for pressure testing should be avoided.

Continuous-Time Fast Motion of Explosion Fragments Estimated by Bundle Adjustment and Spline Representation Using HFR Cameras

This paper introduces a continuous-time fast motion estimation framework using high frame-rate cameras. To recover the high-speed motions trajectory, we inherent the bundle adjustment using a different frame-rate strategy. Based on the optimized trajectory, a cubic B-spline representation was proposed to parameter the continuous-time position, velocity and acceleration during this fast motion. We designed a high-speed visual system consisting of the high frame-rate cameras and infrared cameras, which can capture the fast scattered motion of explosion fragments and evaluate our method. The experiments show that bundle adjustment can greatly improve the accuracy and stability of the trajectory estimation, and the B-spline representation of the high frame-rate can estimate the velocity, acceleration, momentum and force of each fragments at any given time during its motion. The related estimated result can achieve under 1% error.

A fast and accurate model for the creation of explosion fragments with improved fragment shape and dimensions

Explosion models based on Finite Element Analysis (FEA) can be used to simulate how a warhead fragments. However their execution times are extensive. Active protection systems need to make very fast predictions, before a fast attacking weapon hits the target. Fast execution times are also needed in real time simulations where the impact of many different computer models is being assessed. Hence, FEA explosion models are not appropriate for these real-time systems. The research presented in this paper delivers a fast simulation model based on Mott’s equation that calculates the number and weight of fragments created by an explosion. In addition, the size and shape of fragments, unavailable in Mott’s equation, are calculated using photographic evidence and a distribution of a fragment’s length to its width. The model also identifies the origin of fragments on the warhead’s casing. The results are verified against experimental data and a fast execution time is achieved using uncomplicated simulation steps. The developed model then can be made available for real-time simulation and fast computation.

Experimental analysis on dynamic response of pre-cracked aluminum plate subjected to underwater explosion shock loadings

As the main defense component of the ship against the attack of external damage sources, the liquid cabin will inevitably suffer some damage like holes or cracks in the battle because of the explosion fragments or the penetration of high-speed projectiles. The research on the rest capacity and dynamic response of the cabin with different damage cracks due to the underwater explosions is of great significance to the improvement of the protection design of cabin structures and the development of the fluid-solid coupling theory. For the sake of simplicity, an aluminum thin-walled plate with central prefabricated crack was adopted to solve the problem on coupling loads induced by underwater explosion, and an underwater shock wave tube was used to substitute an underwater explosion load to generate the shock loading on thin-walled aluminum plate. The shock wave pressures in the underwater explosion tube and the dynamic deformation responses of aluminum thin-walled plates with central prefabricated crack were recorded by three pressure sensors and two high-speed cameras, respectively. By analyzing experimental results, the history characteristics of the dynamic increase of plastic bulge height and the crack propagation of the aluminum plates were obtained. The results show that the time of the crack growth and the bulge increasing are not synchronized in the dynamic response of thin-walled plate; in addition, the effects of the crack shape and size on the bulge and the crack growth in dynamic response of target plate can be attributed to the trade-off between the energy leakage and the bending stiffness of the target plate. Finally, according to the velocity and acceleration on the target and based on a plastic-rigid material model, we obtain that the target bending angle sine is linear with the radial distance, and the conclusion was well validated by experimental target bending angle data.

Study on the failure mode of a sandwich composite structure under the combined actions of explosion shock wave and fragments

To improve the protective performance of structures in terms of explosive shock waves and fragment penetration, a foamed aluminum/UHMWPE fiber sandwich composite structure was designed. A “explosion+fragmentation” penetration experiment was used to study the failure mode of the structure and the failure mechanisms of materials, the effects of the core material combination and explosion distance were discussed, meanwhile, numerical simulation using LS-DYNA was adopted to simulate the timing and distribution law of the shock wave and fragments. The results show that the explosion distance is the main influencing factor for the timing, and the experimental and numerical results have a good consistency. When the structure was perforated completely by fragments, the front aluminum plate was damaged mainly by shear plugging, and the rear aluminum plate was broken largely by cracking and tearing. When the fragments arrived prior to the shock wave, the tearing damage to the rear aluminum plate was more obvious. The foamed aluminum absorbed the explosive energy through its own crushing deformation, and the fiber layer absorbed the kinetic energy of the fragments through its own tensile failure. Of the composite structures prepared herein, the composite structure consisting of foamed aluminum/foamed aluminum/UHMWPE fiber had the best protection performance.

Short-term Effect of Intelsat-29e Explosion on GEO Environment

Geosynchronous Orbit (GEO) space environment model of the orbital targets with a size above 10 cm was established according to the amended data and space density. The situation of satellite explosion on GEO is simulated, including the number of fragments generated by the explosion, the size distribution as well as the corresponding mass distribution of the fragments. Under the conditions of selecting fragments of different size for analyzing, the area to mass ratio, discrete velocity, and apogee-perigee distribution can be obtained. By simulating the collisions of targets in different size and mass, and the evolution of the space environment when different size thresholds are selected, the necessity of establishing the GEO space environment and evolution model with the threshold size of 10 cm is demonstrated. The feedback collision caused by the fragments generated by the GEO satellite explosion is simulated under the conditions of different collision probability thresholds. The results show that the explosion fragments would cause a high collision risk environment for other GEO orbital targets, and the risky circumstance would last for hours. The impact of explosive debris on the security of the future space environment is analyzed

Initial velocity and influence factors of tank explosion fragments

Initial velocity and influence factors of tank explosion fragments

Real-time calculation of fragment velocity for cylindrical warheads

Abstract To simulate explosion fragments, it is necessary to predict many variables such as fragment velocity, size distribution and projection angle. For active protection systems these predictions need to be made very quickly, before the weapon hits the target. Fast predictions also need to be made in real time simulations when the impact of many different computer models need to be assessed. The research presented in this paper focuses on creating a fast and accurate estimate of one of these variables - the initial fragment velocity. The Gurney equation was the first equation to calculate initial fragment velocity. This equation, sometimes with modifications, is still used today where finite element analysis or complex mathematical approaches are considered too computationally expensive. This paper enhances and improves Breech’s two-dimensional Gurney equation using available empirical data and the principals of conservation of momentum and energy. The results are computationally quick, providing improved accuracy for estimating initial fragment velocity. This will allow the developed model to be available for real-time simulation and fast computation, with improved accuracy when compared to existing approaches.

Optimization of collision avoidance maneuver planning for cluster satellites in space debris explosion situation

In this study, the conjunction situation when a number of explosion fragments approach four cluster satellites was simulated, and an optimum avoidance maneuver plan that mitigates this risk was established. The orbits of four deputy satellites around a virtual chief satellite were defined using the Hill–Clohessy–Wiltshire equation, and NASA’s breakup model was applied to similar altitude rocket body to simulate explosions situation. The distribution of 230 explosion fragments after an explosion was simulated, and the size and direction of the Delta-V were applied to each fragment. In this situation, the collision avoidance maneuver planning strategy that uses heuristic algorithm was proposed to establish efficient avoidance maneuver plan for approaching fragments after the explosion. Avoidance maneuver plans using four heuristic algorithms were established to minimize the fuel consumption of the four cluster satellites within several constraints including conjunction risk, ground track and formation between cluster satellites. Eight simulations were performed with different combinations of the four heuristic algorithms and different generations and populations. As a result, all avoidance maneuver plan satisfied conjunction risk constraint as well as the other complex constraints. In particular, particle swarm optimization–gravitational search algorithm established the most efficient maneuver plan with the least fuel consumption and fastest convergence speed.

Explosion severity of micro-sized aluminum dust and its flame propagation properties in 20 L spherical vessel

Using 20L explosion vessel, the present research work reports some experimental results which elucidate the effects of dust concentration, particle size and specific surface areas on aluminum dust explosion severity. Dust flame propagation property and explosion products were analyzed systemically. Six kinds of aluminum powders with different size distributions were selected and specially prepared for explosion tests. Results show that explosion parameters present an increasing and then decreasing trend with dust concentrations. The optimum explosion concentrations for all the selected aluminum dusts are similarly equal to 500g/m3. Maximum explosion pressures would be quadratic correlated with the decreasing of particle size. However, (dP/dt)max would be exponentially increasing with particle size decreasing. Aluminum dust flame propagation speed would be increased and the combustion mechanism would be transited from diffusion-controlled mode to kinetically controlled mode with particles diameter decreasing. For the finer dust cloud (dS less than 10μm), dust flame propagation speed would be exponential increased with dust concentration. However, there is a power function relation between flame propagation speeds and dust concentration for the coarse aluminum dust cloud (dS larger than 10μm). At the experimental condition, flame propagation speed presents an exponentially decreased trend with the increasing of particle size. Explosion products obtained at different conditions present different apparent morphology. The higher explosion pressure, the finer explosion fragments and nano-scale spherical structure would be produced. For coarse aluminum particles, explosion products present fluffy flocculent structure. Furthermore, alumina produced under lower explosion pressure conditions are mainly γ-Al2O3 components. Under high explosion pressure condition (such as 0.56MPa), there are notable bulges corresponding to α-Al2O3 are produced. Present research results may have important significance for understanding the explosion mechanism of aluminum-air dust/air cloud.

Fiber Cement Composites with Failure Detection Function

The article presents results of the research focused on multifunctional advanced materials with special properties. The aim of the research activity is to develop an electrically conductive cement-based composite which enables detection of failures in material structures caused by explosions, bullets or explosion fragments. The piezoresistive material should react to changes in the state of stress in building structures by changing its electrical properties. The paper closely describes mechanical, electrical and piezoresistive properties of the tested materials. The influence of different carbon and metal components on the conductivity of the concrete composite, its piezoresistivity and failure detection function under high-speed ballistic loading were tested. Electromagnetic shielding efficiency was additionally measured on the test detection composites. The test results did not confirm the need for the exclusive use of carbon ingredients but rather they confirmed their suitability for reducing the impedance where electrically conductive reinforcement is not used. It was proved that better conductivity does not automatically mean better detection sensitivity. Too low initial impedance of the composite adversely increases the demands on the sensitivity measuring tool. The detection composites are pressure-sensitive, they changed the impedance not only during the mechanical pressing but also during the mechanical clamping of samples for ballistic testing. Differently conductive cementitious composites enable the detection of failures in material structures caused by fast dynamic load. They change the impedance not only the failure of the matrix by projectile but also after projectile impact without breaking the matrix.

Identifying isomers of carbon-dioxide clusters by laser-driven Coulomb explosion

Clusters usually exhibit unique structures as an intermediate form of matter. However, their structures are still difficult to be determined with available experimental techniques. There are many structure distinct isomers for carbon-dioxide clusters. Here we report an experimental and theoretical joint study to determine the structures of the lowest-energy isomers. In the experiment, we exploded carbon-dioxide clusters by laser-driven multiple ionization and obtained precise momentum vectors of explosion fragments for each explosion channel. In the theory, we calculated low-energy structures of carbon-dioxide clusters and simulated their explosion dynamics. In comparison with the momentum vectors of explosion fragments, the lowest-energy isomers were identified for carbon-dioxide dimers, trimers, and tetramers.

Particle orientation from distribution of explosion fragments in XFEL experiment

In many XFEL experiments small objects with unknown orientations are introduced into the x-ray beam. However, understanding the measured quantities it would be desirable to know their orientations. This is the situation in the case of single-molecule imaging one of the main target areas of X-ray free-electron lasers. Here, the solution to the orientation problem is based on the possibility of orienting the large number of low-counting-statistics 2D diffraction patterns taken at random orientations of identical replicas of the sample. This is a difficult process and the low statistics limits the usability of these methods and ultimately it could prevent single-molecule imaging. We suggest a new approach, which avoids the use of the diffraction patterns. We propose to determine the sample orientation through identifying the direction of ejection fragments. The orientation of the sample is measured together with the diffraction pattern by detecting some fragments of the Coulomb explosion. We show by molecular-dynamics simulations that from the angular distribution of the fragments one can obtain the orientation of the samples [1].The figure shows the distribution of heavy atoms coming from different depth of the sample ( upper panel homogeneous, lower panel inhomogeneous model samples, and left to right is heavy atom at the outer boundary, halfway to center and at the center).

An investigation of potential risks of nuclear system from hydrogen production

Nuclear hydrogen production systems as a next generation energy resource are under development, which are faced with a new nuclear safety issue that takes place in the interface between a nuclear system and a hydrogen production system. Potential risks of a nuclear system from hydrogen production have been investigated according to a two-step probabilistic safety assessment (PSA) approach, i.e., (1) an identification of the potential factors of a hydrogen production system threatening the nuclear system and (2) an assessment of the impacts on the nuclear system from the identified factors. In the first step, a large scale hydrogen leakage from the hydrogen storage system and its explosion has been identified as a key potential factor. The second step has investigated the related impacts on the nuclear system by a PSA approach. From this investigation, the potential risks of the nuclear system from the hydrogen production system have been identified as (1) an impact of hydrogen explosion and (2) an impact from explosion fragments. As a result of the present study, the obtained insights provide useful information to resolve the new safety issue, which will address the interface between the nuclear system and hydrogen production system.