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The excellent remote sensing ability of synthetic aperture radar (SAR) will be misled seriously when it encounters deceptive jamming which possesses high fidelity and fraudulence. In this paper, the dynamic synthetic aperture (DSA) scheme is used to extract the difference between the true and false targets. A simultaneous deceptive jamming suppression and target reconstruction method is proposed for a single channel SAR system to guarantee remote sensing ability. The system model is formulated as a sparse signal recovery problem with an unknown parametric dictionary to be estimated. An iterative re-weighted method is employed to jointly handle the dictionary parameter learning and target reconstruction problem in an majorization-minimization framework, where a surrogate function majorizing the Gaussian entropy in the objective function is introduced to circumvent its non-convexity. After dictionary parameter learning, the grid mismatching problem in a fixed grid based method is avoided. Therefore, the proposed method can reap a super resolution result. Besides, a simple yet effective DSA section scheme is developed for the SAR data excerpting, in which only two DSAs are required. Experimental results about location error and reconstruction power error reveal that the proposed method is able to achieve a good performance in deceptive jamming suppression.

Measuring the dust explosion characteristics of aluminum-based activated fuels was a prerequisite for developing effective prevention and control measures. In this paper, ignition sensitivity, flame propagation behaviors and explosion severity of aluminum/polytetrafluoroethylene (Al/PTFE) compositions including 2 PT (2.80 wt.% F), 4 PT (7.18 wt.% F) and 8 PT (11.90 wt.% F) were studied. When the content of F increased from 2.80 wt.% to 11.90 wt.%, the minimum explosive concentration MEC decreased from 380 g/m3 to 140 g/m3, due to the dual effects of increased internal active aluminum and enhanced reactivity. The average flame propagation velocities increased as the percentage of F increased. The maximum explosion pressure Pm of 500 g/m3 aluminum-based activated fuels increased from 247 kPa to 299 kPa. Scanning electron microscopy demonstrated that with the increase of PTFE content, the reaction was more complete. On this basis, the explosion mechanism of aluminum-based activated fuels was revealed.

One-bit quantization is a promising technique due to its performance retention and complexity reduction in a deceptive jammer against synthetic aperture radar (SAR). In this paper, the 1-bit quantization technology is utilized to agilely generate split false targets in the SAR imagery once the radar signal is intercepted, which reduces the complexity of the jammer significantly with guaranteed focusing quality. A single-frequency threshold is used to decompose harmonics incurred by the 1-bit quantization, and its parameters are adjusted through different pulse repetition intervals to provide steerable modulations. In this way, the SAR signal is split into coupled false scatterers during the 1-bit interception. By further deploying amplitude, time-delay, and Doppler frequency modulations on the 1-bit intercepted signal, the split false targets are created. The proposed approach is compared with different deceptive jamming methods to show its validity in effectiveness and cost, and numerical experiments are also presented for verification.

The study of high-energy and low-vulnerability propellants is important for the power performance and safety of solid propellant rocket motors. The modified split Hopkinson pressure bar (SHPB) tests are performed on two kinds of propellant with different crosslinking density to study the dynamic mechanical responses and damage-ignition mechanism. SHPB apparatus is equipped with a highperformance infrared camera and high-speed camera to capture the deformation, damage-ignition feature and temperature evolution images in the impact process. The results suggested that the mechanical responses and damage-ignition mechanism of the propellants were affected by the strain rates and crosslinking density. The damage-ignition degree is more intense and the reaction occurs earlier with the increase of strain rates. For propellant 1 with higher crosslinking density, the critical ignition strain rate is 4500 s-1. Two kinds of propellants show different ignition mechanism, i.e. crack generation, propagation and final fracture for propellant 1 while viscous shear flow for propellant 2. Meanwhile, the SEM images also reveal the difference of damage-ignition mechanism of the two kinds of propellants. Finally, the ignition mechanism under different strain rates and critical ignition strain rate of propellants are further explained by the theoretical calculation of temperature variations. [ABSTRACT FROM AUTHOR]

The evolution behavior of combustion crack reaction of highly confined solid explosives after non-shock ignition is governed by multiple dynamic processes, including intrinsic combustion of explosives, crack propagation, and rapid growth of combustion surface area. Here, the pressure increase can accelerate the combustion rate of explosives, and the crack propagation can enlarge the combustion surface area. The coupling between these two effects leads to the self-enhanced combustion of explosive charge system, which is the key mechanism for the reaction development after ignition. In this study, combustion cracknetwork (CCN) model is established to describe the evolution of combustion crack reaction of highly confined solid explosives after non-shock ignition and quantify the reaction violence. The feasibility of the model is verified by comparing the computational and experimental results. The results reveal that an increase in charge structure size causes an increase in the time of crack pressurization and extension of cracks due to the high temperature-generated gas flow and surface combustion during the initial stage of explosive reaction, but when the casing is fractured, the larger the charge structure, the more violent the late reaction and the larger the charge reaction degree. The input pressure has no obvious influence on the final reaction violence. Further, a larger venting hole area leads to better pressure relief effect, which causes slower pressure growth inside casing. Larger reserved ullage volume causes longer lowpressure induction stage, which further restrains the internal pressure growth. Furthermore, the stronger the casing constraint, the more rapid the self-enhanced combustion of the high temperaturegenerated gas, which results in more violent charge reaction and larger charge reaction degree during casing break. Overall, the proposed model can clarify the effects of intrinsic combustion rate of explosives, charge structure size, input pressure, relief area, ullage volume, and constraint strength on the reaction evolution, which can provide theoretical basis for violence evaluation and safety design for ammunition under accident stimulus. [ABSTRACT FROM AUTHOR]

To investigate the shock response of cyclotetramethylene tetranitramine (HMX) single crystals at elevated temperatures (below the phase transition point), plate impact experiments at elevated temperatures were designed and conducted. The HMX/window interface particle velocities at temperatures of 300 K, 373 K, and 423 K were measured by the velocity interferometry system for any reflector (VISAR) technique. To further analyze the related mesoscale deformation mechanisms, a nonlinear thermoelastic-viscoplastic model was developed, which considers thermal activation and phonon drag dislocation slip mechanisms. The proposed model could well reproduce the measured thermal hardening behavior of Hugoniot elastic limit (HEL) of HMX single crystals. At elevated temperatures, the reduced dislocation mobility was observed, which stems from both phonon scattering and radiative damping effects. Comparatively speaking, radiative damping contributes less than phonon scattering to thermal hardening behavior. The calibrated model was further used to predict shock response of HMX single crystals with different thicknesses at different initial temperatures. Both the stress relaxation and elastic precursor decrease with thickness are mainly due to the rapid dislocation generation. These insights shed light on the interplay between dislocation motion and dislocation generation in thermal hardening behavior, stress relaxation, and elastic precursor decay, which serves to reveal the mesoscale deformation mechanisms at elevated temperatures. [ABSTRACT FROM AUTHOR]

A quasi-isentropic study on the process of driving a cylinder with aluminized explosives was carried out to examine the influence of the aluminum (Al) reaction rate on cylinder expansion and the physical parameters of the detonation products. Based on the proposed quasi-isentropic hypothesis and relevant isentropic theories, the characteristic lines of aluminized explosives driving a cylinder were analyzed, and a quasi-isentropic model was established. This model includes the variation of the cylinder wall velocity and the physical parameters of the detonation products with the Al reaction degree. Using previously reported experimental results, the quasi-isentropic model was verified to be applicative and accurate. This model was used to calculate the physical parameters for cylinder experiments with aluminized cyclotrimethylenetrinitramine explosives with 15.0 % and 30.0 % Al content. The results show that this quasi-isentropic model can be used not only to calculate the cylinder expansion rule or Al reaction degree, but also to calculate the physical parameters of the detonation products in the process of cylinder expansion. For explosives with 15.0 % and 30.0 % Al, 24.3 % and 18.5 % of the Al was found to have reacted at 33.9 ms and 34.0 ms, respectively. The difference in Al content results in different reaction intensity, occurrence time, and duration of two forms of reaction (diffusion and kinetic) between the Al powder and the detonation products; the post-detonation burning reaction between the Al powder and the detonation products prolongs the positive pressure action time, resulting in a continuous rise in temperature after detonation. [ABSTRACT FROM AUTHOR]

In the present study, thermal hazards of TNT and DNAN used as the molten binder in TKX-50-based meltcast explosives were comparatively studied through accelerating rate calorimeter (ARC) and Cook-off experiments. Two kinds of ARC operation modes were performed to investigate the thermal safety performance under adiabatic conditions (HWS mode) and constant heating (CHR mode). The obtained results demonstrated that at both heating modes, DNAN/TKX-50 outperformed TNT/TKX-50 from the thermal safety point of view. However, the sensitivity to heat of the samples was reverse because of the different heating modes. In addition, the results of thermal hazard assessment obtained from the cookoff experiment complied with ARC analysis which indicated the molten binder TNT replaced by DNAN would reduce the hazard of the TKX-50 melt cast explosive. Furthermore, the results of cook-off experiments also showed that DNAN/TKX-50 outperformed TNT/TKX-50 from the aspect of thermal stability, which was consistent with the result of CHR mode because of the similar heating process. [ABSTRACT FROM AUTHOR]

A melt-cast Duan-Zhang-Kim (DZK) mesoscopic reaction rate model is developed for the shock initiation of melt-cast explosives based on the pore collapse hot-spot ignition mechanism. A series of shock initiation experiments was performed for the Comp B melt-cast explosive to estimate effects of the loading pressure and the particle size of granular explosive component, and the mesoscopic model is validated against the experimental data. Further numerical simulations indicate that the initial density and formula proportion greatly affect the hot-spot ignition of melt-cast explosives. [ABSTRACT FROM AUTHOR]

This study investigates and quantifies some possible sources affecting the position of impact points of small caliber spin-stabilized projectiles (such as 12.7 mm bullets). A comparative experiment utilizing the control variable method was designed to figure out the influence of tiny eccentric centroids on the projectiles. The study critically analyzes data obtained from characteristic parameter measurements and precision trials. It also combines Sobol's algorithm with an artificial intelligence algorithmdAdaptive Neuro-Fuzzy Inference Systems (ANFIS) - in order to conduct global sensitivity analysis and determine which parameters were most influential. The results indicate that the impact points of projectiles with an entry angle of 0- deflected to the left to that of projectiles with an entry angle of 90°. The difference of the mean coordinates of impact points was about 12.61 cm at a target range of 200 m. Variance analysis indicated that the entry angle - i.e. the initial position of mass eccentricity - had a notable influence. After global sensitivity analysis, the significance of the effect of mass eccentricity was confirmed again and the most influential factors were determined to be the axial moment and transverse moment of inertia (Izz Iyy), the mass of a projectile (m), the distance between nose and center of mass along the symmetry axis for a projectile (Lm), and the eccentric distance of the centroid (Lr). The results imply that the control scheme by means of modifying mass center (moving mass or mass eccentricity) is promising for designing small-caliber spin-stabilized projectiles. [ABSTRACT FROM AUTHOR]

A perforation model is developed to predict the attitude deflection in the oblique perforation of concrete targets by a rigid projectile, in which the inertial moment of the projectile is introduced, together with taking the attitude deflection during the shear plugging sub-stage into account, and the shape of the plug formed on the rear surface of target is also re-investigated. Moreover, a new classification of concrete targets is proposed based on the target thickness, with which the attitude deflections in different kinds of concrete targets are analyzed. It is found that the numerical results by using the new perforation model are in good agreement with the previous experimental data and simulated results. Furthermore, the variations of the attitude deflection with the initial conditions (the initial attitude angle and the initial impact velocity) are investigated. [ABSTRACT FROM AUTHOR]

The cartridge case headspace is the axial clearance between the cartridge and bolt of an automatic weapon, and influences the reliability and security of the weapon. Accordingly, theoretical and numerical studies were conducted to analyze the dynamic response of cartridge cases during internal impact considering the initial radial clearances between the cartridge case and chamber. A theoretical model was proposed to predict the cartridge case headspace considering both the deformation and movement of the cartridge case and confirmed by the results of nonlinear finite element simulations. The differences between the results of the conventional static model and the dynamic model were then comprehensively evaluated. The effects of the angle between the cartridge and chamber, the cartridge case material, and the internal impact pressure on the predicted headspace value were also analyzed. The dynamic response of the cartridge case predicted by the dynamic model was more accurate than that predicted by the conventional static model. The internal impact pressure, pressure change rate, and cartridge material were all found to affect the predicted headspace. [ABSTRACT FROM AUTHOR]

In this study, the blast performance of steel reinforced concrete (RC) beams was experimentally and analytically investigated. The experiment consists of a total of 10 one-half-scale beams subjected to different levels of blast loading using live explosives. The reflected pressure-time histories were recorded and different damage levels and modes were observed. The blast resilience of the damaged beams was quantified by measuring the time-dependent displacements. Experiment results show that the damage in steel reinforced concrete beams with higher explosive mass is enhanced compared with that of the beams with smaller explosive mass at the same scaled distance. Based on the experiment data, an empirical expression is developed via dimensional analysis to correct the relationship between the midspan displacement and scaled distance. Besides, a complex single degree of freedom model (SDOF) incorporating complex features of the material behavior, high strain-rate effect and the column geometry was proposed and validated by test results. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental investigation on explosive breaching of p-section concrete beams. Twenty three p-section concrete beams with a 100 cm length were tested. TNT charges were placed at three positions: contact detonation in the center, contact detonation above the web and close-in detonation in the center. The external and internal breach parameters of the panels were evaluated by measuring the diameter of the ejection crater, spalling crater and breach hole created by the charge detonation. The experimental results were compared to predict values obtained by the analytical models proposed by McVay, Morishita and Remennikov. A modified breach with crater limit line and breach without crater limit line were put forward based on the experimental results. The maximum cross-sectional destruction area ratio (MCDAR) values were used to evaluate the damage degree. The maximum value of MCDAR reached 0.331 corresponding to the C5 experimental condition, of which explosion occurred above the web. [ABSTRACT FROM AUTHOR]

The evolution behavior of combustion crack reaction of highly confined solid explosives after non-shock ignition is governed by multiple dynamic processes, including intrinsic combustion of explosives, crack propagation, and rapid growth of combustion surface area. Here, the pressure increase can accelerate the combustion rate of explosives, and the crack propagation can enlarge the combustion surface area. The coupling between these two effects leads to the self-enhanced combustion of explosive charge system, which is the key mechanism for the reaction development after ignition. In this study, combustion crack-network (CCN) model is established to describe the evolution of combustion crack reaction of highly confined solid explosives after non-shock ignition and quantify the reaction violence. The feasibility of the model is verified by comparing the computational and experimental results. The results reveal that an increase in charge structure size causes an increase in the time of crack pressurization and extension of cracks due to the high temperature-generated gas flow and surface combustion during the initial stage of explosive reaction, but when the casing is fractured, the larger the charge structure, the more violent the late reaction and the larger the charge reaction degree. The input pressure has no obvious influence on the final reaction violence. Further, a larger venting hole area leads to better pressure relief effect, which causes slower pressure growth inside casing. Larger reserved ullage volume causes longer low-pressure induction stage, which further restrains the internal pressure growth. Furthermore, the stronger the casing constraint, the more rapid the self-enhanced combustion of the high temperature-generated gas, which results in more violent charge reaction and larger charge reaction degree during casing break. Overall, the proposed model can clarify the effects of intrinsic combustion rate of explosives, charge structure size, input pressure, relief area, ullage volume, and constraint strength on the reaction evolution, which can provide theoretical basis for violence evaluation and safety design for ammunition under accident stimulus.

This study investigates and quantifies some possible sources affecting the position of impact points of small caliber spin-stabilized projectiles (such as 12.7 mm bullets). A comparative experiment utilizing the control variable method was designed to figure out the influence of tiny eccentric centroids on the projectiles. The study critically analyzes data obtained from characteristic parameter measurements and precision trials. It also combines Sobol’s algorithm with an artificial intelligence algorithm—Adaptive Neuro-Fuzzy Inference Systems (ANFIS) – in order to conduct global sensitivity analysis and determine which parameters were most influential. The results indicate that the impact points of projectiles with an entry angle of 0° deflected to the left to that of projectiles with an entry angle of 90°. The difference of the mean coordinates of impact points was about 12.61 cm at a target range of 200 m. Variance analysis indicated that the entry angle – i.e. the initial position of mass eccentricity – had a notable influence. After global sensitivity analysis, the significance of the effect of mass eccentricity was confirmed again and the most influential factors were determined to be the axial moment and transverse moment of inertia (Izz Iyy), the mass of a projectile (m), the distance between nose and center of mass along the symmetry axis for a projectile (Lm), and the eccentric distance of the centroid (Lr). The results imply that the control scheme by means of modifying mass center (moving mass or mass eccentricity) is promising for designing small-caliber spin-stabilized projectiles.