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Abstract:To investigate the stress wave effect in semi-infinite concrete targets under penetration-implosion loadings induced by reactive jet （RJ）， two sets of RJ peneration-implosion experiments were conducted to obtain stress wave data and characteristic damage patterns of concrete targets. LS-DYNA software combined with a restart algorithm was used for staged numerical simulations of the penetration-implosion process， and to analyze the stress wave propagation characteristics in concrete under the combined action of RJ penetration and explosion. The findings demonstrate that numerical and experimental results showed good agreement in stress waves and target damage features. During the penetration stage of RJ， concrete failure occurs after successive loadings of dynamic stress wave zone and static high-pressure zone， with the latter having a faster loading rate but a shorter action duration. The concrete damage caused by RJ penetration accelerates energy dissipation， reduces peak stress during the explosion stage， but accelerates stress wave propagation. Compared with the undamaged target， the peak stress of the explosion in the target after RJ penetration decreased by up to 47%， and the growth rate of the stress wave propagation speed could reache up to 7%. However， when the depth of measuring point exceeds 335 mm， the influence of RJ penetration on the explosion stage can be ignored.

Abstract:In order to attenuate the blast shock wave in the tunnel efficiently， the design idea of setting up multiple continuous diffusion chambers in the tunnel was proposed. Based on the numerical simulation method， the influence of the structural parameters of the multi-stage diffusion chamber on the wave absorption efficiency was systematically discussed， and the propagation attenuation characteristics of the shock wave with a pressure of 2-11 MPa and a positive pressure duration of 18.25-1000 ms in the pit containing single， double/tertiary diffusion chamber were investigated. The results showed that the increase in the number of diffusion chambers can effectively improve the wave dissipation efficiency of the tunnel， and the peak pressure of the shock wave after passing through the three-stage diffusion chamber pit is 81.08% lower than the peak pressure of the straight pit without diffusion chamber with the same length， while the spacing between the diffusion chambers has a limited effect on the wave dissipation efficiency of the tunnel. Under the condition that the total length of the diffusion chamber is equal， the tertiary diffusion chamber has the best attenuation effect on the shock wave compared with a single long diffusion chamber and the secondary diffusion chamber. With the increase of shock wave pressure under the same positive pressure duration， the wave dissipation efficiency of the multi-stage diffusion chamber pit slowly increases. Under the same peak overpressure condition， the wave loss efficiency of the three-stage diffusion chamber pit decreases greatly with the increase of positive pressure time， but it can still maintain a wave loss efficiency of 43.38% when the positive pressure time is 1000 ms.

Abstract:To study the mechanisms of rock breaking and cavity formation by hole-inner layered charge blasting， the influence of hole-inner layered charges on the rock breaking and cavity formation of deep hole cutting was first investigated through theoretical analysis and model experiments. Then， numerical simulations were carried out using SPH-FEM algorithm to reveal the processes of rock breaking and throwing as well as the mechanisms of rock breaking and cavity formation. Finally， field tests were conducted to explore its application effects. The results show that the hole-inner layered charge could realize the uniform distribution and release of explosive energy， which could eliminate the large rock in the upper cavity and weaken the constraint effect of the surrounding rock in the bottom cavity， so as to achieve the cavity formation efficiency of 96.5%. The numerical simulation realized the visualization of the blasting process. The simulation results confirmed the beneficial effect of uniform energy distribution and sequential release on rock breaking and cavity formation. Compared with traditional cutting blasting technique， using the hole-inner layered charge cutting technique， cycle footage and hole utilization were increased by 0.45 m and 17.3%， respectively， the specific charge and detonator were reduced by 0.42 kg·m^-3 and 0.21 PCS·m^-3， respectively. The results demonstrated the applicability of hole-inner layered charge cutting technique in deep hole blasting.

Abstract:To address the issue of highly localized blast loads caused by limited distribution layers in shallow-buried layered fortifications， an equivalent single-degree-of-freedom （SDOF） dynamic analysis method considering the characteristics of localized loads was proposed. This method was used for evaluating the response of the roof slab of supporting structural layers. Based on the selected mode shape functions and the energy equivalence principle， dynamic coefficient calculation methods for both elastic and plastic response stages of the structure were established. The validity of the method was verified through finite element simulations. Results indicate that the static deflection curve under uniformly distributed loads can still serve as the mode shape function under localized loads， with acceptable deviations. If localized loads are simplified to uniformly distributed loads for design purposes based on equal impulse principle， the maximum displacement of the structure may be significantly underestimated， with errors potentially reaching up to 9.7 times. In the plastic response stage of the structure， the dynamic coefficient of structural resistance is negatively correlated with the degree of plastic deformation. The product of the total load duration and the structure’s natural frequency significantly influences the structural response： when this value is less than or equal to 1， the response is impulse-dominated； when it approaches 10， moderately extending the pressurization time favours structural resistance to blast loads； when the product exceeds 50， the beneficial effect of extending the pressurization tends to saturate. This method effectively characterizes the dynamic response characteristics of supporting structure layers in shallow-buried fortifications under localized blast loads， providing a theoretical support for the blast-resistant design of related protective structures.

Abstract:The fast-running method based on engineering experience is an important tool to assess the explosion damage inside the building structure. To provide the reference for the selection and subsequent improvement of relevant calculation methods， the full-scale confined explosion tests on three-story masonry-concrete building were carried out under two scenarios. The five fast-running methods developed in recent years （i.e. FIST method， charge weight-standoff graphs method， equivalent dynamic load method， energy method， equivalent method） were used to calculate the damage of the buildings. The evaluation indicator and scoring criteria of 5-dimensional calculation ability were put forward. The characteristics of each fast-running method were compared and analyzed. The reasons for the difference in the ability of each method are discussed. Some suggestions for improvement are given. The results show that the charge weight-standoff graphs method is not suitable for the damage assessment of building structure subjected to confined explosions. The FIST method and equivalent method have high accuracy in calculating the masonry wall. The energy method has high accuracy in calculating the RC slabs， but the computational efficiency is low. The calculation efficiency of equivalent dynamic load method is high， but the calculation accuracy is low. In addition， considering the propagation law of the shock wave in complex building structure， improving the scale of numerical simulation are the main way to improve the computing ability of FIST-like and equivalent-like method.

Abstract:Reinforced concrete structures are frequently subjected to impact loads during their service life， leading to complex dynamic responses that are often difficult to predict. To systematically investigate the influence of concrete heterogeneity on the impact response and scaling effect of geometrically similar RC beams. Using a comparative analytical approach， three numerical models were established： a homogeneous RC beam （Homogeneity） and two heterogeneous RC beams （Heterogeneity-I and Heterogeneity-II）. The displacement， impact force， and reaction force were compared. Furthermore， damage modes， deflection curves， and energy absorption characteristics were analyzed to explore the intrinsic mechanisms of scaling effect. The results indicate that the concrete heterogeneity is one of the factors contributing to the scaling effect in the displacement of geometrically similar RC beams， while its influence on impact force and reaction force is relatively minor. The intrinsic mechanism of the above-mentioned phenomenon may be the difference in damage modes due to heterogeneity， which enhances the local response of the RC beams with analysis of deflection curves and energy absorption. Additionally， within the scope of this study， higher impact velocities lead to more pronounced scaling effect in the displacement. These findings provide theoretical insights for impact-resistant design of concrete structures and for similitude analysis in scaled experimental studies.

Abstract:The pressure of underwater near-field explosion is high and damping rapidly， which is difficult to test accurately. To investigate the near-field explosion shock wave loading and driving characteristics of aluminized explosives， a model was established to calculate the incident shock wave pressure according to the theory of strong shock wave driving air-backed metal plate. Finally， tests of underwater explosion driving 3 mm-thick air-backed steel plate at 5 R₀ were conducted on TNT and five different aluminized explosives， which verified the accuracy of the shock wave pressure calculation model. The free-field shock wave pressure at 2 R₀-6 R₀ （charge radius） distance of spherical TNT charges and driving law of 3 mm-thick air-backed steel plate were calculated by numerical simulation. Then the shock wave pressure before cavitation was calculated based on the velocity-time history data. Results also show that for every 5% increase in the content of 2 μm aluminum， the acceleration time of plates increases by 4.4%. With larger particle size of aluminum powder， the acceleration time of plate is longer， but the maximum velocity is smaller. 20 μm and 2 μm aluminum powder absorbs energy in the detonation reaction zone， resulting in a decrease in the detonation velocity and pressure of TNT. While 200 nm aluminum powder may partially participate in the detonation reaction zone and release energy， which positively supports the propagation of detonation waves.

Abstract:In recent years， the frequent occurrence of terrorist attacks and industrial accidental explosions has triggered in-depth research and extensive application of blast wall structures in the field of protective engineering. According to the development sequence， structural characteristics， and explosion-resistant mechanisms of blast walls， this paper classifies and reviews blast walls into traditional blast walls and innovative blast walls. Traditional blast walls mainly use conventional building materials to resist shock waves through the inherent properties of the walls. In contrast， innovative blast walls further enhance their explosion resistance through material and structural innovations. Material innovations mainly involve the use of high-strength materials， fiber-reinforced composites， etc.， which are used to construct the walls， incorporated into the raw materials （such as concrete） of the walls， or attached to the wall surfaces to improve the overall strength and stability of the walls. Structural innovations involve designs such as multi-layer wall structures and sandwich fillings， aiming to enhance the overall explosion-resistant effect by leveraging the performance advantages of different materials. This paper summarizes and generalizes the blast-resistant performance evaluation， application scenarios， experimental and numerical simulation methods， as well as related research results， covering key factors such as material selection， dimension design， shape optimization， and reinforcement methods of blast walls， providing a reference basis for future blast wall designs.

Abstract:To address the issue of reduced output reliability of boron/potassium nitrate igniters caused by KNO₃ hygroscopicity， a dual coating modification strategy based on an in-situ reaction and a solvent-antisolvent method was proposed. Firstly， a copper stearate （CuSt₂） coating layer was constructed on the KNO₃ surface via in-situ reaction between stearic acid and copper acetate. Secondly， the trifluoroethylene-vinylidene fluoride copolymer （F₂₃₁₄） was coated on KNO₃@CuSt₂ using the solvent-antisolvent method to prepare CuSt₂/F₂₃₁₄ double-coated KNO₃. Finally， the double-coated KNO₃ was uniformly mixed with boron at a mass ratio of 3∶1 to obtain the formula-optimized B/KNO₃@CuSt₂@F₂₃₁₄ igniter， aiming to synergistically regulate the hydrophobic properties and reaction activity of the igniter. Scanning electron microscopy （SEM）， Fourier transform infrared spectroscopy （FT-IR）， X-ray photoelectron spectroscopy （XPS）， and inductively coupled plasma spectroscopy （ICP） were employed to confirm the sequential coating of CuSt₂ and F₂₃₁₄ on KNO₃ particles. The hydrophobicity of the samples was characterized using a contact angle measurements. The effects of modified KNO₃ on the thermal reaction and combustion performance of the igniter were evaluated by thermal analysis and laser ignition experiments. The results demonstrated that the hydrophobic performance of CuSt₂@F₂₃₁₄ double-coated KNO₃ was superior to that of single-coated KNO₃with CuSt₂ or F₂₃₁₄ （the water contact angle of uncoated KNO₃ was 0°）. When the proportions of CuSt₂ and F₂₃₁₄ dual coating layers were 6% and 2%， respectively， the comprehensive performance of KNO₃@6%CuSt₂@2%F₂₃₁₄ and its boron-based igniter was optimal. The water contact angle of KNO₃@6%CuSt₂@2%F₂₃₁₄ increased to 95.8°， and the heat release of B/KNO₃@6%CuSt₂@2%F₂₃₁₄ reached 3200.67 J·g^-1， which was 23% higher than that of B/KNO₃ igniter （2601.69 J·g^-1）， while the onset temperature of the thermal reaction decreased by approximately 23 ℃. Laser ignition tests showed that compared with the unmodified B/KNO₃ igniter， the B/KNO₃@6%CuSt₂@2%F₂₃₁₄ igniter exhibited a shorter ignition delay time， stable flame propagation， and reliable laser ignition performance. This study realizes the synergistic enhancement of hydrophobicity and reaction activity in the B/KNO₃@6%CuSt₂@2%F₂₃₁₄ igniter by constructing a dual coating layer on the surface of KNO₃， providing a new approach for improving the performance of high-reliability boron/potassium nitrate igniters.

Abstract:Tetraazabicyclo molecules have attracted extensive attention from synthetic energetic materials researchers due to their high density and detonation performance. To expand the types of skeletal structures of tetraazabicyclo molecules and explore the intrinsic relationships between different skeletal structures， in this study， nitroguanidine， glyoxal and urea were used as raw materials to construct a tetraazabicyclo framework by two-step cyclization reaction， and then nitration was carried out to obtain 2-nitro-3-keto-7-nitroimino-2，4，6，8-tetraazabicyclo［3.3.0］octane（4）. This compound is a novel tetraazabicyclic molecule incorporating both glycoluril and nitroguanidine structural motifs. The structure of the intermediates and target compounds was confirmed through fourier transform infrared spectroscopy， nuclear magnetic resonance， elemental analysis， and X-ray single crystal diffraction. The intermediate crystal 3·0.5H₂O and the target compound crystal 4 were obtained. Among them， the crystal of compound 4 belongs to the triclinic crystal system， P-1 space group， with a density of 1.881 g·cm^-3 （150 K）， and with unit cell parameters of a=6.5172（3） Å， b=9.4087（4） Å， c=13.6334（5） Å， α=γ=90°， β=102.542（2）°. Compound 4 was tested by TG-DSC simultaneous thermal analysis， and its enthalpy of formation and detonation properties were calculated using atomization method and EXPLO5 software， and its mechanical sensitivity was tested by BAM method. The results showed that the thermal decomposition temperature of compound 4 reached 243 ℃， the theoretical detonation velocity and detonation pressure were 8538 m·s^-1， 30.17 GPa， and the impact sensitivity and friction sensitivity were 10 J and 120 N， respectively. It has good detonation performance and thermal stability.