Abstract:

Abstract:Molecular dynamics simulation is an important method to predict the shock sensitivity of energetic materials， yet it is computationally expensive and needs to use force fields that may be unavailable. Here， an algorithm was designed and implemented in a computer program in Python for calculating the Steric Hindrance Index （SHI）， which is a descriptor for evaluating shock sensitivity. The algorithm 1） compresses the crystal unit cell of an energetic material keeping the molecular unit rigid to simulate deformation under shock； 2） establishes a new rectangular coordinate system for the specific slip system and rotates the cell to deal with general shock directions and slip systems； 3） assigns molecular units to layers based on the coordinate of their centroid； 4） calculates the overlapped area of each two adjacent layers after projection along the slip direction； and 5） obtains SHI by normalization of overlapped areas. For PETN， BTF， RDX， and TNT at a compression ratio of 0.1， the calculated average SHI are 0.8707， 0.7940， 0.4228， and 0.0924， respectively， which is consistent with the decreasing order of impact sensitivity mentioned in references. SHI classifies the slip systems in line with those based on molecular dynamics simulations， yet with better computing efficiency and methodological applicability.

Abstract:In order to study the safety of processing explosives with femtosecond laser， a calculation model of femtsecond laser sequence machining on explosives was established， which took into account the autothermal reaction of the explosives. The processes of femtosecond laser sequence machining on three different explosives （TNT， TATB and HMX） were calculated. The safety of these processes was analyzed. Results show that the frequencies of the femtosecond laser sequence， the heat release of the autothermal reaction and the thermal diffusion coefficient of explosives will affect processing safety. Among these three explosives， the heat release of the autothermal reaction of HMX is the largest， and its thermal diffusion coefficient is the smallest， so its heat accumulation effect is the most significant. Therefore， HMX is ignited when processing with all the three femtosecond sequences with different frequencies （1×10³ Hz， 1×10⁵ Hz and 2×10⁵ Hz）. On the contrary， the heat accumulation effect of TATB is the weakest， so no ignition occurs when processing with the three femtosecond sequence with different frequencies. The heat accumulation effect of TNT is between those of HMX and TATB， so ignition only occurs when using the femtosecond laser sequence with higher frequencies. In the actual machining process， especially for the explosives with greater heat release of the autothermal reaction and smaller thermal diffusion coefficient， femtosecond laser sequence with low frequency should be selected to ensure safety.

Abstract:Hollow charges usually adopt compression molding process. Using the method of continuum mechanics， a finite element simulation of the compression process model was established. First， the relative density， displacement and equivalent stress change laws of the pressing process of the JO-9159 explosive were simulated and analyzed. Then， the influences of pressing rate， initial relative density and friction coefficient on the pressing quality of JO-9159 explosive are simulated and analyzed. Results show that the JO-9159 explosive powder flows mainly in the axial direction during the pressing process， and the explosive powder flows slowly near the female mold area； when the pressing rate is 0.5 mm·s^-1 and the friction coefficient is 0.25， the relative density of the charge after molding is more uniform and the amount of rebound is smaller.

Abstract:In order to study the damage and failure process of adhesive interface of solid rocket motor， rectangular adhesive specimen of solid rocket motor was made based on QJ2038.1A-2004 regulation standard and tensile tests was carried out. The damage and failure mode of the adhesive interface specimen was obtained. The parameter inverse identification method which is based on step inverse and Hooke-Jevees optimization algorithm was adopted. The relevant parameters of the bilinear cohesive model of mix mode at the propellant/liner/insulator interface were obtained and were applied into the numerical simulation of the damage and failure process of adhesive specimen in tensile tests. Results show that the main failure form of adhesive interface specimen is the debonding at the interface of the propellant/liner/insulator layer； the proposed parameter inverse identification method can obtain the interface parameters of solid rocket motors well. The initial modulus， maximum bonding strength and fracture energy of the propellant/liner/insulator layer of solid rocket motors are 0.86 MPa， 0.63 MPa and 3.13 kJ·m^-2 at tension speed of 2 mm·min^-1， respectively. The damage of the propellant/liner/insulation layer interface makes the increase rate of stress decrease with the tensile strain. The initiation interface crack at the tip of the artificial debonding layer and the expansion along the center of the specimen， and finally penetration of the bonded specimen is the main damage and failure mode of the adhesive specimen.

Abstract:In order to study the migration phenomenon of deterrent in double-base oblate spherical propellant during storage， micro-Roman technique was used to characterize the concentration distribution of dibutyl phthalate（DBP） and poly （neopentyl glycol adipate）（NA） in double-base oblate spherical propellant after accelerated aging； and the combustion performance of double-base oblate spherical propellant was tested by the closed bomb test. Results show that the concentration of DBP and NA changed exponentially from the surface to the inside in one-dimensional direction， which conformed to Fick"s second diffusion law. During the accelerated aging process， the migration of DBP in double-base oblate spherical propellant was bidirectional， the concentration gradient of deterrent decreased gradually， the diffusion depth increased， the peak position of concentration shifted inward， and the combustion performance of double-base oblate spherical propellant also gradually decreased. High temperature would aggravate the migration of deterrent. The progressive combustion characteristic values of double-base oblate spherical propellant samples aged at 65 ℃，75 ℃ and 85 ℃ for 10 days were 1.3351， 1.2917 and 1.1888， respectively. With the increase of temperature， the progressive combustion characteristic values of double-base oblate spherical propellant decreased. Under the same aging conditions， the anti-migration characteristics of NA was higher than that of DBP.

Abstract:In order to understand the constant volume combustion performance of single charge and the mixed charge（MC+B） of 37-hole nitroguanidine propellant， a lace-shaped 37-hole triguanidine-15 propellant is used as the main charge （MC）， and the lace-shaped 19-hole triguanidine-15 coated propellant is used as the auxiliary charge（B）. The packing density is 0.20 g·cm^-3， under 50 ℃， 20 ℃， -40 ℃， the effect of arc thickness on the combustion performance of single main charge and the effect of the mixing mass ratios on the combustion performance of the mixed charge （MC+B） were studied through constant volume closed-bomb test. The results show that the lower the temperature， the more obvious the erosion and combustion phenomenon of the 37-hole single main charge. At the same temperature， the greater the arc thickness of the main charge， the less obvious the erosion and combustion phenomenon， the stronger the progressive combustion， and the better the combustion performance. The higher the temperature， the greater the value of ΔL， L_m/L₀ of the mixed charge of the same mixing ratio， the better the progressive combustion； At the same temperature， the progressive combustion of the mixed charge is stronger than that of the single main charge， and as the ratio of the coated propellant increases， the erosion combustion peak gradually decreases， indicating that the addition of the coated propellant significantly improves the progressive combustion and reduces the erosion combustion peak of the mixed charge， and at 50 ℃， 20 ℃， -40 ℃， the mixing ratio of the mixed charge to obtain better progressive combustion is 7∶3.

Abstract:To gain insights into the stability of nano TATB in different storage environments， aging conditions at 90 ℃， 10%RH， 50%RH， 90%RH and 200 Pa low atmospheric pressure were considered. The microstructure evolution of nano TATB was characterized by small angel neutron scattering （SANS）， scanning electron microscope （SEM）， X-ray diffraction （XRD）， Raman spectroscopy （Raman） and infrared spectroscopy （IR）. Results show that the specific surface area of nano TATB decreases obviously after the thermal aging at 45 ℃， 60 ℃ and 71 ℃， and the higher the aging temperature， the more obvious the specific surface area decreases， accompanied by the growth of some crystal particles. The long-term stability of nano TATB crystal particles is significantly affected by the extreme humidity and heat environment （90 ℃， 90% RH）. After short-term storage （5 days）， the nano TATB particles grow up with the size of about 1-3 μm. The nano TATB particles also grow and form a micro flake structure after aging in a low pressure （200 Pa） environment at 90 ℃. Based on the experiment results， the growth and aging mechanism of nano TATB were discussed. The high surface energy of nano TATB facilitates TATB molecules overcoming the energy barrier， which results in the TATB molecules diffusion and rearrangement on the crystal surface and correspondingly leads to the grow-up of particles.

Abstract:In order to improve the anti-electromagnetic interference capability of the electronic equipment on blast field， the characteristics of electromagnetic radiation generated by high explosive were studied. An electromagnetic radiation measurement device based on ultra-wideband omnidirectional antenna and shortwave omnidirectional antenna was designed while 8 test points were set up for electromagnetic radiation measurement of 60 kg TNT explosion. The experimental results showthat the electromagnetic radiation signals generated by TNT explosion last up to 600 ms after the explosion， the most intense period of electromagnetic radiation signal produced by TNT explosion is from 80 ms to 110 ms after the explosion. The frequency of the electromagnetic radiation signals generated by the explosion is mainly concentrated below 100 MHz， where the energy distribution in the low frequency band which below 50 MHz is the most obvious. The distance of the center of explosion hasa significant effect on the spectrum distribution of electromagnetic signals， and the frequency distribution of electromagnetic radiation in different directions was inconsistent. The electromagnetic radiation intensity generated by TNT explosion mainly ranges from 64.33 V·m^-1 to 348.25 V·m^-1， and the electromagnetic radiation intensity decreased largely with the increase of detonation distance. The electromagnetic radiation intensity measured by test points in different directions also hasa certain gap， and the difference ranges from 11.1% to 17.7%.

Abstract:The oxidation reaction of micro and nano aluminum powder is an important way of energy release and aging inactivation. Molecular dynamics and reaction kinetics provide necessary means for elucidating the microscopic mechanism of oxidation reaction of aluminum powder and quantitatively describing the oxidation process. According to the type of reaction system， the oxidation of aluminum powder can be divided into aluminum-oxygen （Al-O₂）， aluminum-water （Al-H₂O） and aluminum-other oxides （Al-other oxides） reaction systems. The recent progress of molecular dynamics and reaction kinetics in the above reaction systems is reviewed. The mechanism of oxidation kinetics of aluminum powder and its key influencing factors， including the oxide layer， particle size， atomic diffusion rate， temperature and oxygen concentration， were discussed， which proved the flexibility and effectiveness of molecular dynamics and reaction kinetics. On this basis， the important problems in different oxidation reaction systems were analyzed and prospected. It is pointed out that the oxidation kinetics of aluminum powder under multiple factors， the kinetics of Al-water vapor reaction， and the intrinsic mechanism of Al-other oxides reaction are the key problems to be solved in the future.