Abstract:To systemly investigate the influence of the mesostructure and the shock loadings on the shock initiation and detonation of polymer bonded explosives (PBXs), a modified Duan-Zhang-Kim（DZK）mesoscopic reaction rate model is proposed. A burn-up and a porosity factors are introduced to describe effects of the outer burning on the surfaces of grains of the explosive at the low-pressure slow reactive stage and the initial charge density, respectively. The calculated pressure-time histories inside the HMX-based PBXC03 explosive samples using the modified model with one set of parameters are in good agreement with the experimental data, which indicates that this model can be used to well predicate the influence of the particle size, the porosity and the shock loading on the shock initiation (i.e., ignition and detonation growth) processes of PBXs. Moreover, it is also observed that the detonation grows fastest in the explosive with a moderate porosity. And the smaller the particle size of the explosive is, the more difficult the explosive can be ignited, in which the detonation grows fastest once the explosive is ignited.

Abstract:To investigate the effect of crystal defects on properties of HMX-based polymer bonded explosive (PBX), two defect-free models and four defective models were established. Using molecular dynamics (MD) method, different models were simulated and the sensitivity, binding energy, detonation performance and mechanical properties of different models were calculated and compared. Results show that the crystal defects cause the interaction energy of trigger bond and cohesive energy density to decrease by 2.46-5.72 kJ·mol^-1 and 0.0251-0.0544 kJ·cm^-3, respectively, indicating that the sensitivity of defective models is increased and safety is decreased. The binding energy of defective models is decreased by 106.89-231.65 kJ·mol^-1, meaning that their stability is deteriorated. The density, detonation velocity and detonation pressure of defective models are decreased by 0.01-0.05 g·cm^-3, 36.35-185.69 m·s^-1 and 0.36-1.79 GPa, respectively. However, the variation of oxygen balance and detonation heat can be negligible. The variation of detonation parameter indicates that the damage power of defective models is weakened. Tensile modulus, bulk modulus, shear modulus of defective models are decreased by 0.062-1.772, 0.261-1.188 GPa and 0.012-0.685 GPa, respectively. The ratio of bulk modulus to shear modulus is increased by 0.002-0.366. The Cauchy pressure of dislocation and vacancy defective models is decreased by 0.822 GPa and 0.479 GPa, while it is increased by 0.114 GPa and 0.491 GPa in doping and twin defective models respectively, indicating that the deformation resistance of the defective models is decreased and the flexibility is enhanced.

Abstract:Interfacial interactions of polymers with 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105) directly influence the surface boating effects of LLM-105. The analyses of interactional models and strength at the atomic and molecular level will help to reveal the micro-mechanism of the interfacial interactions. In this work, molecular dynamics (MD) method was used to simulate the interfacial interactions of fluoropolymers (F₂₃₁₁, F₂₃₁₃, F₂₃₁₄, F₂₄₆₂) and polyurethane (Estane 5703) with LLM-105 at different crystal faces. Interactional mode and strength between the polymers and LLM-105 at different crystal faces were analyzed, and the screening principle of the polymer binders was preliminarily proposed. According to the principle, nitrifying bacterial cellulose (NBC, a new polymer) was selected and the interactions between NBC and LLM-105 were simulated. The effect of six polymers on the mechanical properties of LLM-105 was discussed using static elastic constant analysis. The simulation results show that the bonding energies of all polymers with LLM-105 at various crystal faces are positive and the increasing order of bonding strength is LLM-105/NBC≈LLM-105/Estane 5703>LLM-105/F₂₃₁₃≈LLM-105/F₂₃₁₄≈LLM-105/F₂₃₁₁>LLM-105/F₂₄₆₂. The (1 0 1) crystal face with the largest binding energy has the smallest exposed surface in the crystal(0.39%), while the(0 2 0) and (0 1 1) crystal faces with smaller binding energies have the larger exposed surface (>60% in total). The Van der Waals force is dominant in the interfacial interactions and is much higher than the electrostatic interactions. The polymers possessing strong interactions with LLM-105 simultaneously have good hydrogen-bonding donors and acceptors. The effective isotropic modulus and the Cauchy pressure values show that NBC, Estane 5703, and F₂₄₆₂ can slightly improve, F₂₃₁₁ and F₂₃₁₃ has no influence, and F₂₃₁₄ reduce the mechanical properties of LLM-105.

Abstract:To investigate the effect of post-combustion on the energy addition at tail of base bleed projectile in the transient depressurization process, a mathematical and physical model of the chemical non-equilibrium flow at tail in the transient depressurization process for base bleed equipment was established. Two-dimensional axial symmetric Navier-Stokes equations were solved by idea programming of uniform algorithm using the improved format of convective upwind vector flux splitting format（AUSM+）, the shear stress transport turbulence model SST k-ω and the H₂─CO reaction kinetic mechanism of 12-step reaction of 8 components. The numerical simulation of tail flow field was performed, the change rule of pressure in base bleed combustion chamber in the transient depressurization process with time was obtained. The simulated results were basically in agreement with the experimental ones in the literature. Base this basis, the tail flow field under the condition of with and without post-combustion in the transient depressurization process were numerically predicted, and the change rule of characteristic parameters for the tail flow field of base bleed equipment with time in the transient depressurization process were analyzed. The results show that the post-combustion has a little effect on the tail flow field in the early stage of transient depressurization process, while in the middle and late stage, the post-combustion has a great effect on the tail flow field. At this time, the characteristic parameters of tail flow field more quickly tend to be stable, and the post-combustion makes the temperature of tail flow field increase and the energy addition effect remarkable, the bottom pressure increase, the bottom drag of base bleed projectile decrease significantly and the drag reduction rate increases by 75% compared with that without post-combustion.

Abstract:To study the influence rule of afterburning effect on the parameters of explosion field, a numerical calculation method for the explosion field in a closed space considering the afterburning effects was proposed. The simplified reaction rate model was coupled with three-dimensional two components compressible Euler equations to approximately consider afterburning effects. Transient temperature was obtained by establishing the relationship between gas internal energy and heat capacity. The calculation formula of specific heat ratio was established according to thermodynamic relation. Based on FORTRAN platform, the fifth-order WENO finite difference scheme was adopted to develop an in-house 3D numerical calculation code, which can simulate the explosion field in closed space considering afterburning effects. The evolution process of internal explosion field and the influence of afterburning effects on the calculated explosion field parameters were numerically discussed based on the developed code. Results show that （1）the numerical solutions of quasi-static temperature, specific heat ratio and overpressure are in good agreement with theoretical solutions considering afterburning effects, and the relative error is less than 5%. The reliability of the developed code is preliminarily verified. （2）the afterburning effects should be paid enough attention in numerical simulation of internal explosion field. Under the same internal explosion condition, the relative errors between the numerical solutions of quasi-static temperature, specific heat ratio and overpressure and theoretical solutions without considering afterburning effects are as high as 25%, 6% and 31%, respectively, This research method can be applied to the numerical calculation of internal explosion of other types of explosives, and provide some reference and guidance for the evaluation of internal explosion damage

Abstract:To obtain a nitrocellulose membrane with enhanced mechanical properties, cellulose nanofibrils(CNFs) with nanometer-diameter and micron-length were obtained by 2,2,6,6-tetramethylpiperidine-1-oxyl(TEMPO) oxidation-sonication treatment of bamboo pulp. The N,N-dimethylformamide(DMF) and DMF/H₂O mixed solvent were used as dispersing agent. And the nitrocellulose was thoroughly mixed with the acidified or unacidified CNFs. CNFs-enhanced nitrocellulose membranes were prepared under different dispersion conditions. In addition, the morphological dimensions of CNFs and the change rule of mechanical properties of CNFs-enhanced nitrocellulose membranes were characterized by transmission electron microscope(TEM), thermogravimetric Analysis(TG), mechanical tensile test and dynamic mechanical thermal analysis(DMTA). Results shows that the diameter and length of CNFs are 5-10 nm and 500-3000 nm, respectively. The acidified and unacidified CNFs have better dispersity in DMF than in acetone. The agglomeration of CNFs occurs when the volume fraction of water in DMF/H₂O reaches 20%. Using DMF as a dispersant, the tensile strength and tensile elongation of the composite membrane prepared by adding acidified CNFs are 52.0 MPa and 10.4% respectively, significantly higher than those of the blank sample (36.6 MPa, 8.4%).

Abstract:To study the detonation performance of 2,4-dinitroanisole (DNAN) based aluminized explosives,the detonating explosive / LiF interface particle velocity and free surface velocity imparted to thin metal plates for aluminized explosives RBOL-2 (DNAN/HMX/Al/additives) and RMOE-2 (DNAN/HMX/NTO/Al/additives) were measured by a laser displacement interferometer system for any reflector (DISAR). The detonation wave parameters were obtained for these two explosives according to the interfacial particle velocity histories. The reaction zone lengths are (1.073±0.111) mm and (1.559±0.094) mm, the CJ pressures are (25.42±0.44) GPa and (20.99±0.15) GPa, and the Von-Neumann pressures are 27.69 GPa and 41.27 GPa for RBOL-2 and RMOE-2, respectively. The velocity histories of the metal plate show that the work capacity of RBOL-2 is better than that of RMOE-2. In addition, under the experimental conditions, the steady detonation status obtained by aluminized explosive is related to the initiation loading conditions and the loading pressure affects the work capacity of aluminized explosives. The greater the loading pressure, the stronger the work capacity. Under high loading pressure (21 GPa), the higher the loading pressure, the more aluminum particles react in the detonation reaction zone, and the stronger the detonation state of the aluminized explosive.

Abstract:To study the thermal decomposition of dihydroxylammonium 5,5′-bistetrazole-1,1"-diolate (TKX-50), thermal decomposition experiments such as thermogravimetry and differential scanning calorimetry were carried out, respectively. Meanwhile, MATLAB software was employed to decouple the overlapping parts and the Málek method was used to study the kinetics of the thermal decomposition of TKX-50. The results show that the thermal decomposition process of TKX-50 is divided into two stages. The complete thermal decomposition curves of the two stages are obtained by MATLAB software, and the basic parameters such as T_onset, T_p, and ΔH are acquired at different heating rates. The thermal decomposition of TKX-50 follows the autocatalytic reaction model, and the kinetic parameters including activation energy, pre-exponential factor and kinetic model are obtained, respectively. For the first stage,E_a=174.99 kJ∙mol^-1,lnA=40.75,f(α)=α^0.917(1-α)^0.509， for the second stage,E_a=149.60 kJ∙mol^-1,lnA=31.84,f(α)=α^0.357(1-α)^0.117.

Abstract:To study the shock energy release characteristics of new ZrNiAlCuAg metastable alloy material, the shock overpressure experiments of energetic fragments were processed with quasi-sealed chamber test system. The change rule of overpressure time history curves, the overpressure peak value and growth rates of overpressure peak value of materials under different shock velocities were studied. The specific energy per unit mass and specific energy per volume of new ZrNiAlCuAg metastable alloy materials and multifunctional energetic structural materials were compared. The results show that the overpressure time history curves of materials show the characteristic of rapid rise first and slow decline later. The overpressure peak value and growth rate of overpressure peak value have positive correlations with the impact velocities. The reaction efficiency is close to 40% when the shock velocity is greater than 1400 m·s^-1. The energetic density of material was closed to other type of energetic fragments under lower shock velocities. The energetic density increases rapidly when the shock velocity reaches 1100 m·s^-1, which surpasses the other kinds of energetic fragments. The specific energy per unit mass of ZrNiAlCuAg metastable alloy material reaches 3.83 kJ·g^-1 and its specific energy per unit volume reaches 0.026 kJ·mm^-3 when the shock velocity is 1485 m·s^-1.

Abstract:The internal blast load in spherical vessels is simplified as a triangle pulse with subsequent quasi-static pressure. Based on the single degree of freedom model, the analytical model of elastic dynamic response of the spherical shell is established and the solution of radial displacement response is obtained. The analytical results and LS-DYNA numerical simulation are in good agreement, and the reliability of the analytical solution is verified. By analyzing the radial displacement response formula, effects of quasi-static pressure on the dynamic response can be studied. It is found that the duration time of the first pulse and the quasi-static pressure have their own critical values, which have decisive influence on the time when maximum displacement occurs. The critical duration time of first pulse is related to the fundamental frequency, and the critical quasi-static pressure is related to multi-factors such as the duration time and the peak overpressure of the first pulse, the fundamental frequency, the thickness of the shell, Young′s modulus and Poisson′s ratio, etc. The maximum displacement increases with the increase of the quasi-static pressure if it occurs in duration of the quasi-static pressure, and it is not affected by the quasi-static pressure if it occurs in the first pulse. The minimum displacement increases with the increase of quasi-static pressure, and the amplitude of subsequent vibration decreases with the increase of quasi-static pressure. The research results show that when using multiple-use explosion containment vessels to make the evaluation of the explosive effect in confined space, not only the specific details of the first pulse and subsequent quasi-static pressure of the blast load should be taken into consideration, but also the structural dynamic response history and structural parameters analysis must be closely integrated.

Abstract:Cage-like structure has become an ideal skeleton of energetic compounds due to its high symmetry, high ring tension and dense bulk density, which is a hot spot in the research field of energetic materials. In this paper, the reported cage-like skeleton energetic compounds were reviewed by classifying elementary energetic compounds and metal complex-type energetic compounds. Among them, the elementary energetic compounds of cage-like skeleton are mainly summarized as cubane-like, wurtzitane-like, adamantine-like structures and other systems, typical compounds as octanitrocycloalkane and hexanitrohexaazaisowurtzitane have become the elementary energetic compound with the highest energy level. Metal complex type energetic compounds with cage-like skeletons focus on structures with three-dimensional network cage-like spaces. These compounds form dense network structures by compact arrangement way, and the other components are incorporated into the cage-like structure by wrapping way. It is pointed out that the further research direction of elementary energetic compounds with cage-like skeleton should focus on solving the problems of long preparation routes and high cost, providing a basis for application research. The research on the metal complex-type energetic compounds with cage-like skeletons is still in the initial stage and the limited species have become the major problem, but these compounds are generally simple to prepare, low in cost and higher in energy level, which should be the key direction for the future development of cage-like skeleton energetic compounds.

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