Molecular dynamics simulations have been employed to study the ε-CL-20-based PBXs under COMPASS force field. ε-CL-20 was chosen as the base explosive due to its higher energy, density and detonation performance than conventional explosives. Four polymers, GAP, GAP-NH₂, GAP-NO₂ and GAP-NH₂-NO₂ were added into the ε-CL-20(001) crystalline surface to build the PBX models. The cohesive energy densities (CEDs), elastic coefficients, isotropic mechanical properties (Young's moduli, bulk moduli, shear moduli, Poisson's ratio, Cauchy pressure and K/G) and initiation bond length distribution were studied. It turned out that the CEDs order was A1 < A4 < A3 < A2 < A. The mechanical properties of pure ε-CL-20(001) were effectively improved by building PBX models. System A3 showed better comprehensive mechanical properties than the other three PBXs. A study on the initiation bond length distribution showed that the L_max and L_ave of N–NO₂ increased with increasing temperature and they were related to the sensitivity of the explosives. The order of L_max was A3 < A4 < A2 < A1 < A, which indicated that the PBXs owned lower sensitivity than system A. These studies are thought to provide guidance for further research on the application of GAP and its derivative polymers. Meanwhile, they are meaningful for the studies on ε-CL-20-based PBXs.

To study the mechanical properties of highly filled hydroxy-terminated polybutadiene (HTPB) propellant with 90 wt% solid fillers, the stress–strain curves of the propellant under different temperatures (−50 to 70 °C) and strain rates (0.000476 to 0.119048 s⁻¹) were obtained by uniaxial tensile test. Moreover, to obtain the glass transition temperature and understand the effect of low temperatures on the mechanical properties of the propellant, DMA experiments were carried out. On this basis, the mechanical response laws of the propellant were analyzed, and the master curves of mechanical properties were established. Furthermore, the fracture features of the propellant under typical loading conditions were obtained by SEM, and the corresponding failure mechanisms were analyzed. The results show that the maximum strength decreases with increasing temperature, while the maximum elongation increases with increasing temperature at the same strain rate. The maximum tensile strength increases with increasing strain rate, while the maximum elongation decreases with increasing strain rate at the same temperature. The maximum tensile strength is lowest with a value of 0.35 MPa when the temperature is 343.15 K and the strain rate is 0.000476 s⁻¹, at which time the maximum elongation reaches the highest with a value of 44%. In terms of failure mechanisms, the propellant shows no particle fracture, and the failure modes of the propellant are mainly matrix tearing and dewetting.

To further explore the quasi-static mechanical characteristics of composite solid propellants at low strain rates, an investigation was conducted on the mechanical behavior and damage mechanisms of a four-component hydroxy-terminated polybutadiene (HTPB) propellant by means of experiments and numerical simulation. A uniaxial tensile test and scanning electron microscope (SEM) characterization experiment were carried out. A microstructural model, which accurately represents the mesoscopic structure, was developed via the integration of micro-CT scanning and image-processing techniques. The constructed microstructural model was utilized to conduct a numerical simulation of the mechanical behavior. The experimental results demonstrated that the maximum tensile strength increases with increasing strain rate, and the primary cause of propellant failure at low strain rates is the dewetting phenomenon occurring at the interface between the larger particles and the matrix. The maximum tensile strength is 0.48 MPa when the strain rate is 0.00119 s⁻¹, and the maximum tensile strength is 0.37 MPa when the strain rate is 0.000119 s⁻¹. The simulation results indicated a consistent trend in variation when comparing the simulation and experimental curves. This suggested that the established model exhibits a high level of reliability, and provides a promising approach for carrying out microstructural simulations of heterogeneous propellants in future. The mechanical behavior of the propellant can be effectively described by utilizing a mesoscopic finite element model that incorporates the superelastic constitutive model of the matrix and the bilinear cohesive model. This framework facilitates the representation of mesoscopic damage evolution, which consequently provides insights into the damage mechanism. Additionally, the utilization of such models assists in compensating for the limitations of damage evolution characterization experiments.

Powder ramjets are a kind of vehicle propulsion system with high specific impulse and efficiency. They provide significant benefits in terms of extended propulsion and thrust adjustment. The pursuit of a highly reactive fuel appropriate for powder ramjets is likely to stimulate advancements in innovative propulsion systems, which are crucial for deep space exploration and long-term space missions. This work presents experimental studies on the thermal oxidation and laser ignition performance of aluminum–magnesium–lithium powders at atmospheric pressure. TG-DSC curves of powders in three heating rates were obtained. The ignition processes and ignition delay times were recorded by a CO₂ laser ignition experiment system at a laser power of 10~60 W. The results show that at a lower heating rate of 10 K/min, the powder’s thermal hysteresis is less, and the powder energy released in stage I is more concentrated. However, the degree of heat release concentration approached a similar level at heating rates of 30 K and 50 K. The ignition delay time decreased as the laser flux density increased. When the laser flux density exceeds 80 W/cm², the effect of laser power on the ignition delay time decreases. At atmospheric pressure, the mathematical relationship between ignition delay time and laser flux density is given. Finally, the powder ignition processes at different laser powers are represented graphically.

In solid propellants, the combustion of aluminum particles often occurs in a hydrocarbon combustion atmosphere. In order to study the combustion energy release process of aluminum particles during propellant combustion, we carried out a study of the combustion behavior of aluminum particles in the combustion atmosphere of hydrocarbon fuels and conducted experiments using a plane flame burner to observe the combustion process of aluminum particles in a methane plane flame combustion atmosphere. High-speed microscopy revealed a new special combustion phenomenon: ejection combustion with the release of internal components from a point on the particle at high speed, in addition to the already observed particle microexplosions. Both phenomena show faster-than-normal combustion with short combustion energy release times. The experiments also showed that the combustion behavior of aluminum particles changes with the combustion environment. As the ambient effective oxidizer mole fraction increases from 13% to 29%, the basic combustion behavior of aluminum particles changes from vapor evaporation combustion to multiphase surface combustion. In addition, the percentage of aluminum particles burned by ejection increases from 18.2% to 49.2%, which becomes the dominant mechanism in the special combustion phenomenon of aluminum particles. This paper argues that the multiphase surface combustion provides higher heating rates due to the heat production collected on the particles and the diffusion combustion in the air around the aluminum particles, compared with the evaporation combustion. Therefore, the rate of temperature rise within the particle is affected by the ambient oxidant concentration, leading to a transformation from microexplosion to ejection combustion. The effect of the temperature of the combustion environment on this phenomenon has also been investigated through experiments conducted under different conditions.