Investigating the structural evolution of particulate gels is a very challenging task due to their vulnerability and true flow characteristics. In this work, deeper insight into the rheological properties of gel fuels filled with fumed silica (FS) and aluminum microparticles (Al MPs) was gained by changing shear procedures. Firstly, the flow curves were found to no longer follow the monotonic power law and exhibited subtle thixotropic responses. As the shear rate increased, the gel structure underwent a transition from local shear to bulk shear in the nonlinear region after yielding. This finding reveals the prevalence of nonideal local shear in industry. Secondly, the time-dependent rheological responses demonstrated that the strength spectrum of gel fuels depends on the applied shear rate, with stress relaxation more easily observed at lower shear rates. Those results involved the structural disruption, recovery, and equilibrium of particulate gels from two scales of shear rate and shear time.

Thermal-driven microstructural evolution in pressed polymer-bonded explosives (PBXs) critically impacts safety predictability. This study investigates the thermal decomposition characteristics of hexogen (RDX)-based pressed PBXs and the thermomechanical response of the binder through simultaneous thermal analysis and thermomechanical analysis. By integrating submicrometer-resolution 3D reconstructions obtained via x-ray microscopy (XRM), this study analyzes the temperature-dependent evolution of pore volume, sphericity, tortuosity, and pore-throat angles. The results reveal that pore evolution is controlled by the interplay between the softening-flow behavior of the binder and the reactivity of energetic crystals. The viscous flow of the binder at 160 °C minimizes both porosity (3.26%) and the average pore-throat angle of three-edge nodes (104.1°). At this temperature, the average pore volume is minimized with the most concentrated distribution, while sphericity peaks—microstructural features associated with enhanced safety potential based on reduced gas permeability and stress concentration mitigation. Beyond 160 °C, rising thermal stresses induce interfacial debonding, enhancing pore connectivity and degrading safety. The evolution of pore networks can be categorized into three phases: Isolated Closed-Pore Dominance Phase (T ≤ 160 °C), Pore Network Formation Phase (180 °C ≤ T ≤ 200 °C), and Structural Collapse Phase (T ≥ 210 °C). This study provides critical insights for the safety design and modeling of pressed PBXs under thermal loads, bridging microstructural dynamics to macroscopic risk assessment.

The viscoelastic cohesion of gel fuels is resistant to aerodynamic breakup, posing challenges for effective atomization in propulsion. This study investigated the breakup and atomization behaviors of aluminum-loaded gel fuels subjected to under-expanded flows. High-speed schlieren imaging revealed that effective atomization is primarily governed by the high-speed flow behind the contact surface, with shear and entrainment associated with the vortex structures promoting rapid breakup. A distinctive plume morphology was observed in high Mach number flows, providing direct evidence of the link between viscoelasticity and aerodynamic fragmentation in the non-Newtonian systems. Quantitative fitting of the cloud displacement established breakup thresholds linked to the Mach number and gel rheology, demonstrating that an increased aluminum content enhances the structural robustness but suppresses secondary atomization. These results advance the understanding of gel–fuel fragmentation dynamics and provide a physical framework for optimizing atomizer designs and gel formulations in aerospace propulsion.