Abstract:A big database containing molecular structures and multiple properties of 2899 hydrocarbon molecules （the number of carbon atom is from 1 to 50）， was constructed via data collection， structure optimization and quantum chemistry calculation. Seven properties were focused， including melting point （T_m）， boiling point （T_b）， density （ρ）， internal energy at 0 K （U₀）， internal energy at 298.15 K （U）， enthalpy at 298.15 K （H） and Gibbs free energy at 298.15 K （G）. Four different machine learning models were established， including Decision Tree Regressor， Lasso CV， Ridge CV and XGBoost Regressor， using coulomb matrix representing molecular structures as the input. In comparison， the XGBoost Regressor model is more suitable for regressing experimental melting point， boiling point and density of hydrocarbon molecules； Ridge CV model is more suitable for the prediction of four thermodynamic energy properties. In addition， the optimized machine learning combined model can accurately predict the properties of the hydrocarbon molecules with same carbon numbers， hydrocarbons with different types and hydrocarbon isomers. Furthermore， the densities of 34 high-density hydrocarbon fuels reported experimentally were calculated by the optimized machine learning model. The mean absolute error between the calculated values and the experimental values is only 0.0290 g cm^-3. Next， the fuel properties of 319，893 hydrocarbon molecules in GDB-13C were predicted by the machine learning model to establish a big database containing hydrocarbon structure and fuel properties. Based on high-throughput screening， 37 hydrocarbon fuel molecules with low freezing point and high density have been discovered. Through the proof-of-concept via group contribution method and DFT method， the net heat of combustion and specific impulse of the as-screened new molecules are similar to those of JP-10 and quadricyclane （QC）.

Abstract:This study conducted in-situ micro-CT characterization experiments on HTPB propellant under wide temperature range and uniaxial tension conditions. The mesoscopic dewetting damage behavior of the propellant with three environmental temperatures of -20 ℃， 20 ℃， and 50 ℃ was analyzed， and a three-dimensional mesoscopic representative volume element model based on the volume proportions of the mesoscopic components of HTPB propellant was constructed. The stress-strain relationship and dewetting proportion-strain relationship of the model for different temperatures and strain rates were analyzed. It was found that HTPB propellant had more severe dewetting at low temperatures （-20 ℃）， with the filler/matrix interface dewetting proportion of nearly 30% when the propellant specimen fractured， while the porosity was only 6%. Through numerical simulation， it was found that the propellant undergoes more severe dewetting with low temperature and high strain rate， which greatly deteriorates the mechanical properties of the propellant. By comparing experimental and simulation results， the numerical model constructed in this paper can effectively predict the dewetting damage behavior and macroscopic mechanical properties of propellants.

Abstract:In order to study the effects of different strain rates and different tensile-shear angles on the tensile-shear strength of NEPE propellant， the tensile-shear tests of the propellant for 5 tensile-shear angles （0°， 30°， 45°， 60°， 90°） and 5 strain rates （0.0012， 0.0048， 0.024， 0.12， 1 s^-1） were carried out by using tensile-shear fixtures and butterfly test specimens. The variation of tensile-shear strength with tensile-shear angle and strain rate of propellant under combined tensile-shear loading was obtained. Based on the experimental results， the tensile-shear strength limit of propellant was described by the improved circular equation， and the tensile-shear strength criterion of propellant at different strain rates was established by combining the double shear unified strength theory， and the corresponding theoretical limit surface of the unified strength of propellant was drawn. Finally， the established tensile-shear strength criterion was used to predict the tensile-shear strengths of 0.12 s^-1 and 1 s^-1 strain rates for the tensile-shear angles of 15° and 75°. The validity of the established tensile-shear strength criterion was verified by comparing the predicted results with the experimental data. The results show that the tensile-shear strength of NEPE propellant under combined tensile-shear load increases with the increase of tensile-shear angle and strain rate. By fitting and solving the material parameter values， the improved circular equation and unified strength criterion established can well describe the tensile-shear strength of NEPE propellant for different loading angles and strain rates. Based on the established strength criterion， the errors between the predicted values and the experimental values of the tensile strength limits at the strain rates of 0.12 s^-1 and 1 s^-1 for the tensile-shear angles of 15° and 75° are less than the allowable error range of the actual treatment by 15%.

Abstract:The nozzle structural constraints of solid rocket motors significantly affect the response process of propellants under cook-off stimuli. To study the influence of nozzle throat diameter on the cook-off response of GAP-based solid propellants， a thermal load loading and control system for nozzle structural test pieces was designed and constructed. Using high-speed laser schlieren imaging technology， the entire cook-off response process of GAP-based propellants under the constraints of motor nozzle structures was observed. Additionally， the temperature of test pieces and the shock wave overpressure generated upon the ignition response were measured. The results indicate that the cook-off response of GAP-based solid propellant specimens with nozzle constraints can be divided into the following stages： softening and expansion of the propellant before ignition， and flame acceleration， deflagration-to-detonation transition （DDT）， casing failure， and deflagration process after ignition. The post-ignition response lasts only 0.5-2 milliseconds. From the pressure curve， it is evident that during the flame acceleration phase， the pressure grows slowly. When the nozzle throat diameter is relatively small， flow choking is more likely to occur. Once choking occurs， pressure and burning rate rapidly increase and reinforce each other， ultimately leading to deflagration-to-detonation transition. In contrast， for test pieces with large nozzle throat diameters， the rapid pressure rise cannot occur or be sustained， reducing the likelihood of deflagration-to-detonation transition and maintaining the structural integrity of test pieces.

Abstract:The response surface methodology （RSM） along with Box-Behnken design was firstly applied to optimize the denitration process of the single-hole propellant. The effects of three main influencing factors， hydrazine hydrate concentration， reaction temperature and reaction time on the denitration rate in the denitration process of single-hole propellant were investigated. A quadratic mathematical model with the denitration rate as the response value was established. The results showed that the degree of influence of each factor on denitration rate was hydrazine hydrate concentration > reaction time > reaction temperature， and the interaction between the factors was not significant. The correlation coefficient of the established quadratic model is 0.9774. The experimental values of denitration rate and the predicted values of the model were in good agreement with the relative deviation of 1.61%， when multiple experiments were conducted within the range of the factor levels， indicating that the proposed quadratic model is highly reliable and can be used to predict the denitration rate in the denitration process of the propellant and optimize the process conditions. Through the characterization of the structure and combustion performance of the single-hole propellant before and after denitration， it is further confirmed that the gradient nitrate single-hole propellant have a gradient distribution of nitrate group concentration in the surface layer and at the edge of the hole， with excellent progressive burning performance.

Abstract:In order to study the effects of shape and size on the molecular tailoring process of single-base propellant， three gradiently denitrated single-base propellants （seven-holes， one-hole and non-hole single-base propellants） were prepared by using hydrazine hydrate as denitration agent. Based on the Avrami model， the kinetics of the molecular tailoring process of different shapes of single‐base propellants have been investigated. The results showed that the Avrami model could be used to describe the molecular tailoring process of the three single-base propellants. The Avrami index of seven-holes single-base propellant is n>1 in the range of 70-75 ℃， indicating that the molecular tailoring reaction process was controlled by the chemical reaction process. When the temperature was in the range of 75-80 ℃， n<1， it was controlled by a combination of internal diffusion and chemical reaction. The Avrami index n<1 for one-hole and non-hole single-base propellants， and the molecular tailoring process was controlled by a combination of internal diffusion and chemical reaction. According to the Fick''s law， the diffusion coefficient D of one-hole single-base propellants was 3.8×10^-13-10.2×10^-13 m²·s^-1， and that of non-hole single-base propellants was 3.7×10^-13-5.1×10^-13 m²·s^-1. Using the Arrhenius equation， the apparent activation energies of the seven-holes， one-hole and non-hole single-base propellants were calculated to be 45.84， 52.88 and 38.26 kJ·mol^-1， respectively. The study of the kinetics of molecular tailoring reaction for different shapes of single-base propellants can provide theoretical guidance for the controllable preparation of gradiently denitrated single-base propellants.

Abstract:To obtain the factors which affect the interior ballistic performance of desensitized high-energy nitramine gun propellants， the interior ballistic model was built through the closed vessel test and the 14.5 mm ballistic test. The correction coefficients were fitted by the particle swarm optimization algorithm. Then， the effects of muzzle velocity V₀ and maximum chamber pressure p_m on burning progressive factor Pr and charge mass ω were analyzed through the theoretical model calculation. It was found that， the correction coefficient of burning rate χ and the utilization coefficient of propellant force η should be considered to predict the dynamic combustion characteristics of high-energy nitramine gun propellants by the classical interior ballistic theory. Compared with the case of static combustion， the relative increase of burning rate could exceed 10% in the dynamic combustion. Meanwhile， because of the energy dissipation， only about 80% of the propellant force can be effectively converted into the kinetic energy of projectile in the theoretical calculation. In result， the interior ballistic performance of gun propellants is affected by the coupling of Pr， ω， χ and η. As the major mechanism， the interior ballistic performance is significantly affected by the static combustion characteristics and the charge mass. There is a linear positive correlation between V₀ and ω， while p_m can be expressed by an exponential function of ω， and the coefficients in different correlations are determined by Pr. Nevertheless， with the different process conditions， the fluctuations of χ and η lead to the varying of interior ballistic performance， which increases the prediction deviation of the fitting correlation.

Abstract:To obtain the ignition and growth model parameters of HNS-Ⅳ based polymer bonded explosive （PBX） under shock initiation， the shock wave loading method from explosive plane wave lens was used. The shock waves were attenuated by attenuators and impacted with tested explosives， and the interface particle velocity profiles between tested explosives and LiF （lithium fluoride） windows were measured by photonic Doppler velocimetry. Several explosive pellets with varying thicknesses could be mounted to the attenuator in one shot， by adjusting the thickness of attenuator to change the input pressure， the growth process of interface particle velocity was obtained. Meanwhile， the unreacted shock adiabatic curve of tested explosive was measured by the reverse-impact method， and the cylinder expansion velocity history was acquired by 10 mm diameter cylinder test. Then， the JWL （Jones-Wilkins-Lee） equation of state （EOS） parameters of unreacted explosives and detonation products were fitted with experimental results by genetic algorithm. Finally， the interface particle velocity histories between explosives with varying thicknesses and LiF windows were fitted with the ignition and growth model. The results show that the fitting correlation coefficients of EOS parameter curves for unreacted explosives and detonation products are high enough， and the obtained ignition and growth model parameters well simulate shock initiation experimental results， which can meet the requirement of initiation train design.

Abstract:In order to investigate the influence and regularities of planar integrated transient voltage suppressor diodes （TVS） on the performance of anti-static integrated semiconductor bridge initiator transducers， capacitor discharge firing experiments were carried out to study the effect of the parallel quantity of planar integrated TVS diodes and breakdown voltage on the electrical explosion performance. Its influence on the static electrostatic reliability performance of semiconductor bridge initiator transducers were also investigated by 500 pF/500 Ω/25 kV static discharge experiments. The results indicate that when the excitation energy approaches the upper limit of the energy absorbed per unit time by a single planar integrated TVS diode， increasing the number of parallel planar integrated TVS diodes will prolong the burst time of the SCB initiator transducer element， and may even affect the normal bursting of the SCB initiator transducer element. Conversely， if the excitation energy is insufficient to bring the energy absorbed per unit time by a single planar integrated TVS diode close to its upper limit， the bursting performance of the SCB initiator transducer element will not change with the number of parallel planar integrated TVS diodes. When the excitation voltage exceeds the breakdown voltage of the planar integrated TVS diodes， the lower the breakdown voltage of the TVS diode， the longer the burst time of the SCB initiator transducers， and the greater the burst energy， and potentially affecting the normal burst of the SCB initiator transducer element. Reducing the breakdown voltage of the planar integrated TVS diodes and increasing the number of parallel diodes can enhance the electrostatic reliability of the SCB initiator transducers. When designing an antistatic integrated semiconductor bridge chip with dimensions of 350 μm（W）×100 μm（L）×2 μm（H）， it is possible to integrate two TVS diodes with breakdown voltages slightly below 14 V， or one with a breakdown voltage slightly above 7 V.

Abstract:Analytical characterization techniques are indispensable tools for scientific research and production in the chemistry field of energetic materials. Analytical characterization techniques for energetic materials mainly includes chromatography， mass spectrometry， wave spectrum， spectroscopy， thermal analysis， microscopy， scattering and diffraction， etc. Through the qualitative/quantitative analysis of characterization technology， the chemical structure， component content， microscopic morphology and other information of energetic materials can be obtained， thereby providing important data results for energetic materials in synthesis characterization， quality control， inventory maintenance， public safety， environmental monitoring and other scenarios， which greatly promotes the development of energetic materials. In recent years， analytical characterization techniques have exhibited obvious multidisciplinary cross-integration characteristics on the basis of traditional analysis metheds， and have gradually developed in the direction of automation， intelligence， in-situ online， multi-scale penetration， high temporal and spatial resolution. In order to understand the current status and trends of analytical characterization techniques for energetic materials well， this paper systematically reviews the technical connotation， functional characteristics and application status of each major analytical method， and discusses future development trends to provide support for related analytical characterization research in the field of energetic materials.