Abstract:To study the effect of inert sugar particles on the non-shock ignition mechanism of two kinds of single compounds octogen(HMX) and hexogen(RDX), the processes of undergoing the crushing, melting, sputtering, igniting and combustion of HMX and RDX single compound containing inert particles were captured by a drop weight impact device equipped with anoptical observation system. Results show that the ignition is easy to occur around the sugar particle in the cases of HMX fine particle and RDX powder containing sugar. The combustion will propagate outward along the periphery of the sugar particle, and intense sputtering phenomena occur before the combustion reaction. In the HMX particle with sugar, the ignition occurs in the solid phase. In the RDX powder explosive with sugar, the explosive near the sugar particle enters into the melting state firstly, then the melting region expands gradually, and the ignition points are easy to appear in the molten liquid phase of RDX at the edge of the sugar particle. The ignition frequency of HMX and RDX with one or three sugar particles respectively was compared. Results show that the cases of three sugar particles are more likely to cause the ignition of explosives, because the more fragments are produced after crushing, which interact strongly with HMX or RDX single compound, and may lead the hot spots to form in multiple locations, and the combustion reaction will be more intense than that of the cases of single sugar particle.Finally, the upper and lower limit analysis shows that the addition of sugar particles can inhibit the ignition of HMX fine particles and promote the ignition of RDX powder explosive.

Abstract:Visco-SCRAM model was applied to study on the influence of the initial crack on Octogen (HMX)-based polymer bonded explosive (PBX) ignition under low velocity impact. By means of the simulation of the standard low impact Steven test, the influence of the initial crack length and its distribution on the temperature rise and the hotspot formation was analyzed. The simulation results demonstrate that as the increment of the initial crack length, the friction work between the surfaces of the micro-cracks is strengthened, which brought in high temperature rise and further the hotspot is formed more easily. When the initial crack length is increased from 1mm to 3mm, the ignition impact threshold velocity is reduced from 45 m∙s^-1 to 38 m∙s^-1. Considering the heterogeneous initial crack, during the low velocity impact, the temperature rise region is obviously changed. Moreover, the hotspot formation is beneficial of the heterogeneous initial crack, and further it resulted in the reduction of the ignition impact threshold velocity. When the distribution of the initial crack follows the uniform distribution U(0.8, 1.2), the ignition impact threshold velocity is 36 m∙s^-1. When the distribution of the initial crack follows the normal distribution N(1, 0.115), the ignition impact threshold velocity is 31 m∙s^-1.

Abstract:In order to investigate the characteristics of crack penetration in explosive bulk driven by burning products, and deepen the mechanism understanding on the process of high intensity reaction induced by burning products entering into cracks and forming convective burning under accidental ignition. The penetration of cracks in a HMX-based PBX (with a content of 95% for HMX) under thermal initiation at the preformed gap was photographed by the high-speed camera. Experimental results reveal that, due to the strong meso-heterogeneity of polymer bonded explosive (PBX), different samples of the same kind of explosive have different meso-structures, which results in the difference of crack propagation paths (which may propagate in a straight line or deflect)., Velocities of the crack penetration are nearly the same under same confinement and same pre-load stress. The average crack penetration velocity is about 146.7 m·s^-1 in the experimental condition of this research.

Abstract:The constitutive relationship of polymer bonded explosive (PBX) including damage is one of the key fundamental issues of the safety research of PBX. To study the damage constitutive relationship of PBX explosive, it is necessary to accurately acquire and understand the dynamic mechanical response of PBX explosive.. Therefore, in allusion to the SHPB tests on PBX, it is particularly discussed that the influence of loading ways on the mechanical response of PBX. Through different shapers, loading wave length, and repeated loading, the influences of different loading ways on the mechanical response including damage of PBX have been analyzed, and a series of stress-strain curves were obtained. The ultimate damage morphology of recycled samples was observed by scanning electron microscopy, and the damage development process of PBX explosive under dynamic uniaxial compression and its performance in stress-strain relationship were analyzed.. Results show that loading with brass shaper leads to large strain acceleration and still has an impact on PBX, resulting in additional damage. The failure of specimens subjected to dynamic uniaxial compression is characterized by multiple transgranular fracture or even fragmentation of crystals. The constitutive relationship considering damage can be described by the nucleation, stable growth, and unstable propagation through crystals of micro-cracks.

Abstract:In order to improve the safety and ignition ability of Ni-Cr thin film igniter, a new Ni-Cr@Al/CuO insensitive energetic element was fabricated by combining Al/CuO energetic thin film with Ni-Cr thin film bridge by magnetron sputtering. The Ni-Cr@Al/CuO insensitive energetic element can be used both as the energy transducer element and as the simplest electrical ignition elements. It simplified the point fire transmission sequence and adapt to the development needs of ammunition miniaturization. The safety of Ni-Cr@Al/CuO was tested at the loading condition of 1A1W5min, and its electric ignition sensitivity and ignition capability were tested. The results show that the 50 ms critical ignition current of the insensitive nucleus Ni-Cr igniter is 3.08 A, 99.9% firing current is 3.18 A, 0.1% firing current is 2.98 A. Under the same conditions, Ni-Cr@Al/CuO insensitive energetic element can ignite B/KNO₃, besides, it can achieve 1mm gap ignition, while Ni-Cr thin film igniter can not successfully ignite B/KNO_3.

Abstract:To investigate the parameter optimization problem of the transient voltage suppression diode (TVS) device used in the anti-electrostatics design of semiconductor bridge (SCB) initiator, a capacitor discharge ignition equivalent circuit and a SCB initiator model were established in the PSpice software. In the PSpice circuit simulation software, the influence law of TVS parameter variation on the electro-explosive performance of the SCB initiator was studied. The results show that for 22 μF/16 V capacitor discharge ignition circuit, the simulation circuit was in good agreement when the wire inductance was 40 nH, while the loop resistance is 3.3 mΩ, and the equivalent series resistance and inductance of tantalum capacitor is 288 mΩ and 0.68 μH, respectively. By comparing the electro-explosive curve and data, the SCB initiator model created by the impedance-energy list exhibited higher accuracy. There were two thresholds for the effect of TVS on the electro-explosive performance of SCB. The SCB failed to burst when the TVS breakdown voltage was less than 6 V. When the breakdown voltage of TVS was between 8-12 V, the SCB could burst normally even if the TVS breakdown voltage was lower than the voltage for the ignition of the semiconductor bridge. But the shunting effect caused by the breakdown of TVS caused the delay of burst time, and the delay time increased as the TVS breakdown voltage decreased.

Abstract:To further understand the structural evolution law of internal and external groups of ε-phase 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (ε-CL-20) molecule skeleton during the heating process, the temperature response law of internal and external groups of ε-CL-20 skeleton was quantitatively compared and analyzed by in-situ Fourier transform infrared spectroscopy (in-situ FT-IR) and differential scanning calorimetry (DSC). Results show that the infrared absorption peak intensity of external groups (—NO₂, C—H) of ε-CL-20 skeleton undergoes three change stages as temperature increases: linear decrease (Z_Ⅰ), accelerated decrease (Z_Ⅱ), and second accelerated decrease (Z_Ⅲ), which correspond to the thermal expansion, thermally induced phase-transition and thermal decomposition process of CL-20 crystal, respectively. The C—N stretching vibration inside the molecular skeleton also undergoes the above-mentioned three stages,but the initial temperature of Z_Ⅱ and Z_Ⅲ regions are significantly higher than that of the external group, indicating that the external groups are more sensitive to temperature than internal groups, whether thermally induced phase-transition or thermal decomposition, while the internal groups of the skeleton respond to temperature only at higher temperature. The temperature response characteristics of C—C stretching vibration inside molecular skeleton are even more complex. As temperature increases, the peak intensity of C—C stretching only undergoes an accelerated reduction process, and a new characteristic peak of C—C stretching vibration is observed, which is closely related to ε-γ phase transition, illustrating that the phase transition process makes the vibration mode of C—C bond inside the molecular skeleton change significantly. After further heating, the relative proportion of the new characteristic peak area is continuously increasing, showing that the change of the vibration mode inside the skeleton is still ongoing until the end of thermal decomposition.

Abstract:To explore the influence of cold-pressed forming pressure on the microstructure of polymer bonded explosive (PBX), the small angle neutron scattering (SANS) signals of different pressure-formed octogen (HMX)-based PBX were measured by contrast variation SANS technique. The evolution of interfacial surface area between explosive crystal, binder and void in sample with the forming pressure was obtained by Porod’s theorem. Results show that when the forming pressure increases from 64MPa to 178 MPa, the density of sample increases from 1.55g·cm^-3 to 1.72 g·cm^-3 , and the interfacial binding rate between HMX and binder increases from 23.7% to 26.7%, and the total internal interfacial surface area per unit mass PBX, S_total decreases by 6.1% (the error of experiment is 3%), and the interfacial surface area between HMX and binder (S_HB) increases by 15.2%, and the interfacial surface area between HMX and void (S_HV) basically remains unchanged, while the interfacial surface area between binder and void (S_BV) decreases by 38.0%, indicating that the modeling powder and binder are gradually compacted during the process. When the forming pressure increases from 178 MPa to 382 MPa, the density of sample increases to 1.79 g·cm^-3, and the interfacial binding rate between HMX and binder increases to 42.3%, and S_total decreases by 11.2%, and S_HB increases by 49.0%, and S_HV decreases by 25.8%, and S_BV decreases by 45.5%, indicating that in this process, except the compaction of modeling powder and binder, a great amount of binder flows to the surface of HMX crystal. In addition, when the forming pressure increases from 64 MPa to 382 MPa, the sum of S_HB and S_HV (i.e. total internal interfacial surface area per unit mass PBX sample) remains basically unchanged, indicating that the cold-pressed process does not lead to a large number of transcrystalline breakage of HMX crystal, which is consistent with the optical microscopic results.

Abstract:To explore the design method of sealing structure which can meet the slow release requirements of warhead charge under slow cook-off condition，a small-sized cook-off bomb with adjustable connection strength and prefabricated area of pressure relief hole was designed. For octogen (HMX)-based aluminized explosive charge, the conditions of no more intense reaction occurs than combustion were obtained by experiments, including the strength threshold of shell and area threshold of pressure relief channel of cook-off bomb, etc. parameters. Based on this, a design method of two-stage sealing slow-release structure, which can satisfy the requirement of high connection strength and reliable pressure relief of the end cap, was proposed and the method was tested and verified in the cook-off bombs with kilogram charge. The results show that when two-stage sealing design for cook-off bomb is adopted, if the ratio of the area of the pressure relief channel to the charge cross section is not less than 30%, and the pressure of the gas product does not reach 96.5 MPa in the slow cook-off process, the pressure relief passage can be opened, which avoids the further growth of charge reaction, makes the combustion occur only and keeps the integrity of shell structure.

Abstract:To enhance the catalytic effect of nano-sized metals for the thermal decomposition of ammonium perchlorate (AP), Ni@C nanorods were prepared by combining solvothermal method and high-temperature calcining process using nickel-based metal-organic frameworks (Ni-MOFs) as precursor. The morphology, structure and composition of Ni@C nanorods were characterized by X-ray diffractometer (XRD), field-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectrometer (XPS), Raman spectrometer, full-automatic physical adsorption analyzer and so on. The catalytic effect of Ni@C nanorods on the thermal decomposition of AP at different calcination temperatures was studied by differential scanning calorimeter (DSC). Results show that Ni@C nanorods are porous core-shell structures with metal Ni as core and graphitized C layer as shell, and highly graphitized C layer effectively prevents the oxidation of nano-Ni particles. Ni@C nanorods possess more superior catalytic performances on the thermal decomposition of AP than single Ni nanoparticles and C nanorods. In particular, Ni@C nanorods calcined at 1000 ℃ make the peak temperature of high-temperature decomposition of AP reduce from 423.4 ℃ to 323.8 ℃, the apparent heat of decomposition increase from 825.4 J·g^-1 to 1423.8 J·g^-1, and the activation energy of reaction decrease from 172.50 kJ·mol^-1 to 130.04 kJ·mol^-1.

Abstract:In order to effectively improve the reliability level of the explosive logic circuit system and identify the weakness of the system, the reliability analysis method of the explosive logic circuit system was established based on the GO theory (goal oriented methodology). According to the working principle of the single output explosive logic circuit system, the GO model was established, and the state combination method was used for quantitative calculation and qualitative analysis. Results show that the reliability of the single output explosive logic circuit system is 0.977, while the minimum cut set is the detonator I₁，detonator I₂, detonator I₃, null gate N₁ and null gate N₃. The reliability block diagram of the single-output explosive logic circuit system was also established, and the system reliability was calculated. The result is consistent with the GO state combination method, which verifies the feasibility of the GO method applied to the reliability analysis of single-output explosive logic circuit system.

Abstract:Octogen(HMX) is one of the most widely used energetic materials. Research progress in the two molecular conformation structures, electronic structure properties and molecular thermal stability of HMX and the stacking structure and thermal stability of HMX-based crystals were reviewed. The essential difference between the conformational stability of HMX and the thermal stability of HMX-based crystals were analyzed from the molecular angle and crystal packing structure. The kinetic and thermodynamic data of different decomposition mechanisms were compared. It is considered that the future research should focus on exploring the transformation mechanism and thermodynamic properties of each crystal form of HMX, preparing new HMX cocrystals and understanding the formation mechanism,and establishing more accurate simulation calculation method for HMX.

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