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Abstract:In order to realize the non-destructive evaluation of the interface bonding quality of metal-energetic material bonding structure and improve its structural safety， the non-destructive testing of debonding defect in metal ring and energetic material bonding structure is studied in this paper. A new non-contact testing method based on electromagnetic acoustic resonance is proposed for the inspection of the metal ring-energetic material structure. A special miniature electromagnetic acoustic transducer is made， and an automatic scanning system of electromagnetic acoustic testing is developed. The simulated debonding defects specimen were scanned and imaged automatically. A corresponding signal processing method was developed. The feasibility and detection ability of this technology for non-contact detection of debonding defects of metal ring-energetic materials interface were verified.

Abstract:To investigate the effect of micro-defects on the shock response， chemical decomposition， and damage evolution of pentazolate salts， ab initio molecular dynamics method is employed to simulate the dynamics evolution and initial chemical reaction mechanisms for perfect Mn（N₅）₂ crystal and the crystal with 3% vacancy defects under different shock velocities （8， 9， 10， 11 km·s^-1 and 12 km·s^-1）. The calculated Hugoniot curves indicate that the vacancy-containing system exhibits a slightly higher compression ratio under high-pressure conditions than the perfect system. The molecular dynamics results indicate that when shock velocity v_shock<10 km·s^-1， perfect and vacancy-containing system only show a slight （<10%） volume compression and neither of them exhibit chemical reactions within 5000 fs. When v_shock=10 km·s^-1， N─N starts to uniformly rupture within the space of perfect crystal at 512.8 fs， whereas the reaction of vacancy-containing system is advanced to 281.6 fs and the N─N is ruptured near the vacancy. When v_shock continually increases to 11 and 12 km·s^-1， the starting time of reaction for two systems is further advanced and the reaction process is further speeded up. The positive effects of the vacancy on shock sensitivity and chemical reaction process are weakened with the increase of v_shock. The simulated results at the atomistic scale reveal that vacancy defect is one of the early nucleation structures of hot spots. The stress near the vacancy promotes the cascade decomposition of the surrounding pentazolate anion， thereby causing the growth and propagation of damage and ignition of energetic materials.

Abstract:The finite element method （FEM） has algorithmic difficulties in describing fracture and friction， while the discrete element method （DEM） has difficulties in describing the structure response of explosives. Aiming at these problems， a three-dimensional numerical simulation combining FEM and DEM was established. The deformation of the outer metal shell of the explosive was simulated by FEM； the crack propagation and frictional heating inside the explosive were simulated by DEM； the decomposition heat release of the explosive was describe by the Arrhenius equation； and finally， a three-dimensional simulation of non-impact ignition of charge low-speed impact is realized. Taking Steven impact test as an example， the charge damage and ignition simulation of the brittle explosive PBX-2 under two impact conditions of ball head projectile and flat head projectile were carried out. The influence of the non-uniformity of the explosive was investigated. The history of load stress， crack distribution， temperature rise curve， ignition time and position， and velocity threshold of impact ignition were obtained. The random dispersion characteristics of impact ignition of ball head projectile and flat head projectile were analyzed. The simulation results based on the ignition mechanisms of explosive crack friction and self-reaction heat release are in good agreement with the reported experimental results.

Abstract:The dynamic behavior of Al/Ni energetic structural materials under shock compression loading was investigated by mesoscale simulation. The influence of material composition and manufacturing technique on microstructures were analyzed against the scanning electron micrographs （SEMs） of three typical Al/Ni materials. Two types of mesoscale models were established based on the SEMs and the uniform particle morphologies of Al/Ni material， respectively. The shock responses of Al/Ni material， including particle deformation， pressure， temperature， and propagation of shock waves， were analyzed. The results show that， as for Al/Ni powder composites， Ni particles are the main components of the matrix， and the embedded Al particles gradually reunite with its volume fraction increasing. In contrast， Al layers are the main components of the matrix of Al/Ni multi-layered composites， and Ni particles parallelly distributed in the material. The mesoscale model with the uniform particles could not be used to predict the formations of local high pressure and hot spots， since that such processes are related to the heterogeneous microstructure of Al/Ni materials.

Abstract:When polymer-bonded explosives （PBX） charges are rapidly extruded in a crack in the warhead′s case， it′s required to accurately predict unexpected ignition of cased PBX for safety reasons. Using the combined microcrack and microvoid model （CMM）， damage-ignition responses of crack-extruded PBX are investigated in three aspects： （i） interactions between crack and extruded PBX； （ii） mechanical-thermal-chemical responses of PBX at the macroscale； and （iii） underlying mechanisms of damage-ignition at the mesoscale. Meanwhile， the difference between two typical PBXs （pressed PBX-5 and casted GOFL-5） in response to crack-extruded loading is compared. The results show that， under 200 m·s^-1 extruded velocity， pressed PBX-5 exhibits brittle failure （extruded 3 mm at 60 μs） and shows a stress concentration near the crack； microcrack shows a rapid growth along the 45° angle with the extruded surface. In contrast， under the same extruded condition， casted GOFL-5 exhibits a rapid flow rate near the crack； large quantities of material are extruded （extruded 9 mm at 60 μs）. Both pressed and casted PBXs show an ignition near the crack. Shear-crack hotspot is the dominated ignition mechanism for PBX-5， while locally plastic dissipation is a possible dominated ignition mechanism for GOFL-5.

Abstract:In order to study the propagation characteristics of the flame generated by ignition charge combustion in the propellant pellet packed bed under the ignition transmission structure of the central fire tube， a porous media model was used to simulate the gun propellant pellet packed bed in the propellant chamber， the flow and propagation process of high temperature and high speed gas generated by the combustion of ignition charge in the gun propellant pellet bed is simulated by using the N-S equation， the isothermal surface propagation of the temperature field is equivalent to the flame front propagation， and the simulation results were compared with those of experimental data. The results show that in the case of a dense charge bed of propellant， the isothermal surface is equivalent to the flame front in the process of ignition flame propagation， and the simulation value of flame propagation velocity is 91 m·s^-1， which is close to 96 m·s^-1 obtained by experiment；the simulated cloud images of temperature field of high temperature flame gas propagation are consistent with those of the experimental flame propagation images； the pressure data at the three pressure measuring holes in the chamber calculated by the porous media model are in good agreement with those of experimental data.

Abstract:In order to obtain the mechanical properties of the 1，3，5-triamino-2，4，6-trinitrobenzene（TATB） granules， an in-situ micron-level mechanical loading device suitable for X-ray Micro-Computed Tomography system was designed. By using the X-ray Micro-Computed Tomography technique， the structural characteristics were non-destructively characterized. Hertz contact model was used to study the force-displacement relationship of the individual granule. Mechanical properties of granule such as Young"s modulus， yield point， contact stiffness， breakage force， and structural characteristics of granule such as particle shape， pore shape， pore distribution were determined. The results show that the quasi-static normal compression process of a single TATB granule has three stages： elastic deformation， elastic-plastic deformation， and collapse. The pores with small size and dispersed spatial structure in the granule do not change during the particle deformation process， and the large sheet-like pores inside granule paralleled to the loading direction significantly reduce the breakage strength of the particles. The difference in the internal structure of the particles has large influence on their compression mechanical properties significantly.

Abstract:Perchlorates with the strong oxidizing capability and gas generating have been widely used in energetic formulations， such as solid propellants and pyrotechnics. In order to study the effect of perchlorates on reactivity of Al-MnO₂ nanothermite， the potassium perchlorate （KClO₄） and ammonium perchlorate （NH₄ClO₄） have been used as typical additives to prepare KClO₄-Al-MnO₂ and NH₄ClO₄-Al-MnO₂ nanocomposites by electrospray method. The samples were characterized by field emission scanning electron microscope （FE-SEM）， simultaneous thermal analysis （TG-DSC）， X-ray diffraction （XRD） and combustion tests. The results showed that the Al nanoparticles and MnO₂ nanorods are distributed evenly on the surface of perchlorates substrates. All of perchlorates in nanothermite system would decompose exothermically before the thermite reaction. The mass fractions of nanothermite components has to be replaced by KClO₄ and NH₄ClO₄， which leads to the delayed thermite reaction by 21 ℃ and 31 ℃ according to the thermal analysis. The phase analysis of the collected reaction residues after TG-DSC tests indicates that the main product of KClO₄-Al-MnO₂ nanocomposite is Mn₃O₄， whereas it is MnO for NH₄ClO₄-Al-MnO₂， which means that NH₄ClO₄ can better improve the utilization of O elements in MnO₂. In the case of reaction kinetics， both perchlorates greatly reduced the activation energy of thermite reaction by more than 35%. The ignition and combustion experiments were carried out using a fast heating wire. The addition of perchlorates can significantly increase the burning rate， but they can also reduce the size and brightness of the flame. This work provides a new understanding for design and development of the additive selection for nanothermite formulations.

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