Search Results (315)

The thermal decomposition performance of ammonium perchlorate (AP) is a key factor in regulating the combustion of composite solid propellants, and its catalytic decomposition process is considered a typical multiphase catalytic process. The exposure of catalytic centers during multiphase catalysis is a key factor affecting catalytic performance. In response to the problem of low atomic utilization efficiency of traditional metal oxide catalysts, this study successfully prepared nitrogen-doped carbon-supported single-atom cobalt catalyst (SACo-PC-X) using the “zinc volatilization pore formation and nitrogen anchoring” method with inexpensive biomass as the precursor. Aberration-corrected transmission electron microscopy, together with XPS and XRD analyses, suggests that Co species are predominantly stabilized in an atomically dispersed Co-N_x configuration. This catalyst exhibits excellent catalytic performance for the thermal decomposition of AP, significantly reducing its high-temperature decomposition temperature from 433.5 °C to 322.7 °C (The cobalt content in the system is less than 0.2%). Gas studies have shown that Co-N_x sites efficiently accelerate the oxidation process of NH₃ by promoting electron transfer, resulting in a significant increase in the proportion of N₂O gas. This work not only provides an efficient and stable new catalyst for AP decomposition, but also offers new ideas for designing energetic material decomposition catalysts at the atomic level. Full article

Understanding the curing and molding process of HTPB two-stage solid propellants and their stress and strain distributions is essential for the efficient manufacturing, long-term storage, safe transportation, and reliable operation of solid rocket motors. In this study, the residual stress and strain generated during the curing and molding of HTPB two-stage solid propellants were numerically investigated. The mechanisms responsible for residual stress and strain were analyzed, the relaxation modulus was characterized using a Prony series and the WLF time–temperature superposition equation, and the curing and cooling processes of a two-stage solid propellant grain were simulated. Furthermore, the effects of the modulus m and length-to-diameter ratio n on the residual stress and strain fields were investigated. The results show that at the end of the curing and cooling of the grains, there are high stress and strain zones on the sides close to the core mold and the shell. At the connection point between the first-stage and second-stage grains, due to the different materials, there is a sudden change in stress and strain. The curing stage accounts for 32.1% of the total residual stress and 32.6% of the total residual strain. As the modulus m increases, the overall stress and strain of the grain increase. As the length-to-diameter ratio n increases, the overall stress and strain of the grain decrease. This work provides a basis for the dimensional design of two-stage solid propellant grains and the selection of critical regions for structural safety evaluation. Full article

Graphite nozzles remain the dominant choice for small hybrid and solid rocket motors operating on laboratory and university budgets, owing to their low cost, ease of machining, and rapid turnaround during iterative design campaigns. These same programs, however, must contend with the fact that graphite erodes through coupled thermochemical and mechanical mechanisms when exposed to the oxidizing species generated by high-energy propellant combustion, and the resulting throat-area growth fundamentally alters the time histories of chamber pressure, thrust, and delivered specific impulse. This paper presents a nozzle-erosion reconstruction model that extracts the time-resolved throat area from coupled thrust and chamber-pressure measurements using the thrust coefficient relationship, scales the reconstructed area history against pre- and post-test throat measurements, identifies the onset and rate of erosion, and accounts for variable sensor lag between the thrust-stand and pressure-transducer signal chains. The model is exercised on two complementary sets of laboratory-scale GOX/ABS hybrid hot-fire data that together span roughly two orders of magnitude in total throat-area change and peak chamber pressures from 0.5 to 3.4 MPa: a controlled three-operating-point campaign conducted in support of the NASA Plume-Surface Interaction (PSI) program, and a set of higher-pressure firings from the laboratory development series in which the technique was matured. Reconstructed erosion-onset times, erosion rates, and total throat-diameter change are reported for each firing, the reconstruction accuracy is characterized as a function of erosion magnitude. A correlation of graphite erosion with chamber pressure is examined across the combined envelope. The results demonstrate the robustness of the reconstruction technique and provide a reusable framework for post-test reconstruction of transient nozzle geometry in rocket-engine ground testing. Full article

This case study investigates the ageing behaviour of hydroxyl-terminated polybutadiene (HTPB)-based solid propellants, containing 0.5% iron oxide and a bimodal ammonium perchlorate (AP) distribution (300 µm coarse AP and 40 µm fine AP). To achieve higher burning rates in large solid rocket motors, burning-rate catalysts were preferred over ultra-fine oxidiser compositions due to processing advantages. Characterisation of the iron oxide burning rate catalyst, specific to its surface area, was attempted. The role of surface characteristics in burning rate augmentation and ageing reactions was studied. Particle size and surface area estimates were obtained, and propellant burning rates, pressure exponents, and propellant ageing behaviour were evaluated to support the study. Accelerated thermal ageing of composite solid propellant samples at three different temperatures is carried out. The Arrhenius equation was used to model the dependence of the initial modulus on ageing time and temperature. An activation energy of 68.18 kJ/mole was obtained, which is approximately 4–8% lower than previously reported values for conventional propellants. The study concludes that iron oxide with a specific surface area of 10 m²/g and proportions up to 0.5% by weight can be safely used in propellant formulations without a significant reduction in the propellant’s shelf life. Full article

The goaf backfilling with the coal gangue is an effective strategy for mitigating the mining-induced surface subsidence and reducing the solid waste accumulation. However, the conventional backfilling methods often suffer from limited transport efficiency, poor material distribution, and high operational cost. The present paper proposes a novel technique using an inclined spiral propeller to propel the gangue particles into the goaf, aiming to improve both the backfill rate and spatial uniformity. A three-dimensional parametric model of the inclined screw conveyor is developed, and the discrete element method (DEM) is employed to simulate the dynamic transport and placement of the gangue particles. An L9 ($3^3$) orthogonal experimental design is implemented to systematically evaluate the effects of the rotational speed (240, 300, 360 r/min), inclination angle ($30°$, $45°$, $60°$), and screw pitch (180, 240, 300 mm) on the two critical performance indicators, namely, filling mass and spreading coverage area. The range analysis and matrix analysis are performed to determine the primary influencing factors and to identify the optimal parameter combination for the multi-objective performance. The results show that the inclination angle is the dominant factor for the filling mass, with a $60°$ angle yielding the highest throughput (38.60 kg). In contrast, the rotational speed is the dominant factor for the spreading coverage area, where an increase from 240 to 360 r/min nearly triples the covered area. The optimal compromise for the comprehensive backfilling performance is the rotational speed 360 r/min, inclination angle $60°$, and screw pitch 300 mm, which simultaneously achieves the high transport capacity (36.65 kg) and the largest spreading area (2.87 ${\mathrm{m}}^2$). The present study provides a theoretical and methodological foundation for the engineering design of efficient, low-cost goaf backfilling systems. Full article

Low combustion efficiency is a challenge of aluminum (Al) particles in solid propellants, especially in small solid rocket motors. Therefore, it is necessary to adjust the combustion performance of Al to improve the energy release of solid propellants. Here, a core–shell structured Al-based composite Al@IL/FG with high combustion efficiency has been prepared through ionic liquid (IL) and fluorinated graphene (FG) coating. It is seen that IL can form a smooth coating layer on the surface of Al particles and encapsulate fluorinated graphene inside the coating layer. Thermal analysis results show that the coating layer can lower the reaction temperature of Al in the solid propellants due to the surface activation reaction between the Al and IL/FG. After substituting Al@IL/FG with Al, the residual Al content in the condensed combustion products of solid propellants decreased by 11.37%. In addition, compared with Al-based propellant, the d (0.5) of condensed combustion products of Al@IL/FG-based solid propellant was reduced from 69.157 to 21.559 μm. These results indicate that Al@IL/FG has a higher combustion efficiency than Al in solid propellants. Full article

To address the time-consuming and labor-intensive procedures associated with traditional approaches for evaluating the integrated burning rate of wire-embedded propellants in solid rocket motors (SRMs), this study proposes an efficient and reliable prediction method. This new method is based on an improved burning-rate–initial-temperature correlation, achieved through Abaqus-Python secondary development that enables fully automated geometric modeling, transient heat-transfer analysis, and temperature-field extraction for wire-embedded propellants. The relative error between the present method and the experimental results is less than 5%. The accuracy and engineering applicability of the present method are verified. The effects of the material parameters and wire diameters on the integrated burning rate is investigated. The results indicate that wires of different materials exhibit substantial variations in burning-rate enhancement efficiency, with smaller diameters and higher thermal diffusivity producing stronger enhancement effects. When the specific heat capacity and density are held constant, the integrated burning rate increases monotonically with the wire’s thermal conductivity, though the growth trend gradually approaches saturation. In contrast, the influences of the wire’s specific heat capacity and density are comparatively weak. The integrated burning rate prediction framework developed in this study demonstrates strong versatility and scalability. It enables rapid performance evaluation of propellants embedded with wires of various sizes and thermophysical properties, providing valuable theoretical guidance and practical tools for the design and optimization of wire-embedded solid rocket motors. Full article

This study compares low-parameter fractional viscoelastic models for the unified characterization and extrapolation of creep and stress relaxation behaviors in polymer-based energetic materials, including polymer-bonded explosives (PBXs) and solid propellants. Fourteen candidate models composed of springs and spring-pot elements were considered under controlled parameter complexity. Their creep compliance and relaxation modulus were evaluated through Laplace-domain formulations, and the parameters were identified using a combined Talbot inverse Laplace transform and Gray Wolf Optimizer. Published creep and stress relaxation datasets were used to assess both fitting performance and early-stage data extrapolation behavior. The results show that the fractional Zener model and Model 13 can each describe both creep compliance and relaxation modulus within compact six-parameter rheological forms. Both models generally achieved coefficients of determination above 0.99. When the first 10% of the time span was used for calibration, the selected fractional models showed extrapolation capability over an approximately one-order-of-magnitude longer time window, with rRMSE values below 8.5% in reported cases and below 2% under suitable conditions. Compared with Prony series and power-law models, these fractional models offer compact alternatives for broad viscoelastic response characterization. These results provide guidance for selecting compact viscoelastic models for long-term response analysis of polymer-based energetic materials. Full article

Predictive modeling of thermal aging in solid propellants is challenging because HTPB-based propellants are highly filled particle-reinforced polymer systems with sparse experimental data, nonlinear parameter coupling, and partially unclear aging mechanisms. This study proposes a Physics-Informed Manifold Neural Operator (PIMANO) framework for multi-parameter prediction of polymer aging in HTPB solid propellants. Accelerated thermal aging, stress relaxation, and swelling experiments were used to obtain aging temperature, aging time, crosslinking density, and viscoelastic Prony-series parameters. A continuous aging-state field was first reconstructed over the temperature–time domain by radial basis function interpolation. Crosslinking density was then introduced as a physically interpretable bridge-state variable linking aging conditions with viscoelastic responses. Among three candidate kinetic models, the modified Arrhenius–Avrami model gave the best fitting performance for crosslinking-density evolution, with R² = 0.988 and MRE = 0.0199. By combining local multi-scale neighborhood features, manifold latent representations, and DeepONet-based operator learning, PIMANO established a unified mapping from aging conditions to multi-parameter viscoelastic responses while incorporating bridge-state consistency, parameter non-negativity, and evolution-direction constraints. Under the RBF-augmented validation setting, PIMANO-ae achieved RMSE = 0.7847, MAE = 0.3366, R² = 0.9995, and MRE = 0.0027. Compared with the traditional model, RMSE, MAE, and MRE were reduced by 94.93%, 96.47%, and 96.85%, respectively. Temperature leave-one-out validation further yielded average R² values of 0.9469–0.9647 and MRE values of 4.98–6.21% at unseen aging temperatures. These results demonstrate that PIMANO provides an accurate, stable, and physically interpretable framework for multi-parameter aging prediction and life-assessment modeling of polymer-based energetic materials. Full article

High-pressure liquid CO₂ jets possess the characteristics of low-temperature cooling and dry, residue-free impact, which makes this technology particularly suitable for removing hydroxyl-terminated polybutadiene (HTPB) propellant from decommissioned solid rocket motors. However, existing studies lack multi-objective optimization of impact efficiency and CO₂ consumption, which limits their engineering applications and further promotion. In this study, a high-accuracy quadratic Response Surface Methodology (RSM) relating process parameters to damaged volume was established using a Box–Behnken design (BBD) combined with three-dimensional topography scanning. A theoretical model for CO₂ consumption was developed based on the Homogeneous Equilibrium Model (HEM). On this basis, the Non-dominated Sorting Genetic Algorithm II (NSGA-II) was used to obtain the Pareto-optimal set for maximizing propellant damaged volume and minimizing CO₂ consumption. The results indicate that nozzle diameter has the most significant effect on damaged volume and exhibits a strong interaction with jet pressure. The knee-point solution gives a jet pressure of 15.35 MPa, a stand-off distance of 5 mm, and a nozzle diameter of 1.8 mm. Compared with the initial condition, this compromise condition increases the damaged volume by 72% while increasing CO₂ consumption by only 4.9%. Furthermore, the temperature in the impact zone was reduced to a minimum of −92.4 °C, with no thermal accumulation observed. These findings reveal the influence of liquid CO₂ jet process parameters on impact efficiency and CO₂ consumption, providing a theoretical basis and parameter references for its engineering application in the safe removal of propellants from decommissioned solid rocket motors. Full article

Nickel–aluminum bronze (NAB) propellers can be severely damaged by the synergistic action of chloride corrosion and solid–liquid erosion in marine environments. However, the direct application of micro-arc oxidation (MAO) to NAB is fundamentally hindered because NAB is a non-valve metal. Herein, this limitation is circumvented via a novel hybrid strategy integrating friction stir welding (FSW) and MAO. A defect-free aluminum transition layer is first fabricated onto NAB by FSW and thinned to ~30 μm for MAO. An Al₂O₃-based composite ceramic coating is synthesized, exhibiting a duplex structure with α/γ-Al₂O₃ and an amorphous Si-O network. The coating demonstrates a nano-hardness of 16.2 ± 2.0 GPa and an elastic modulus of 251.3 ± 31.1 GPa, underpinned by a robust interfacial tensile strength of 72.7 MPa. In 3.5 wt.% NaCl, the corrosion current density is suppressed to 1.335 ± 0.151 × 10⁻⁷ A/cm², while the charge transfer resistance reaches 3.072 × 10⁵ Ω·cm². Mass loss after 30-day immersion is reduced to ~1/11 of NAB, and erosion loss at 400 rpm is ~1/8 of that of the substrate. Electrochemical results indicate that the Al transition layer provides an initial beneficial contribution, while the MAO ceramic coating further delivers the dominant barrier protection, together leading to the best overall corrosion resistance of the hybrid-treated sample. Full article

Distributed optimal design brings significant solutions for experiment optimization in complex engineering design problems. A Kriging-based augmented Lagrangian Method is proposed with the help of the Multi-fidelity Hamiltonian Kriging (MHK) surrogate model. The Multi-fidelity Hamiltonian Kriging-based Augmented Lagrangian Method (MHK-ALM) uses subsystem surrogate models constructed from multi-fidelity data to speed up the inner loop solution of ALM, while also reducing the iterations of the outer loop of ALM. The MHK-ALM is illustrated with one numerical simulation of a multi-fidelity constrained NASA speed reducer problem, demonstrated with a multidisciplinary design optimization of a solid-propellant ballistic missile. The engineering application of the multidisciplinary design optimization (MDO) problem shows that the proposed method can perform precisely over certain advanced surrogate-based optimization frameworks. The MHK-ALM can be applied for any other distributed optimal design problems where one need complex subsystem decomposition. Full article

To clarify the evolution of dewetting during the aging of NEPE propellant during long-term storage and more intuitively reveal the impact of aging on dewetting behavior, we used micro-CT to scan NEPE propellant samples subjected to 20% constant strain at different points during aging. After image processing, the internal pores of the samples were extracted, porosity was calculated, and the law of the variation in dewetting behavior at the matrix/filler interface during aging was analyzed. Additionally, we used SEM technology to scan the tensile fracture surfaces of the NEPE propellant samples, observing the aging evolution of the matrix and matrix/filler interface on the fracture surfaces. Along with conducting a micro-CT test, we further explored the changes in bonding performance at the matrix/filler interface during aging. The micro-CT scanning results indicated that dewetting was evident in unaged samples under constant-strain loading, resulting in numerous petal-shaped pores with a significant volume. As aging progressed, the number of petal-shaped pores gradually decreased, and porosity dropped significantly. The SEM scanning results show that the matrix gradually softened during aging, encapsulating solid particles more tightly. Based on all the experimental results, debonding in the NEPE propellants became progressively less pronounced with aging, and interfacial adhesion between the matrix and filler improved. These results provide support for enhancing NEPE propellants’ matrix/filler interfacial bonding strength and, consequently, improving their mechanical properties. Full article

To investigate the micro-scale combustion characteristics of composite propellants, a two-dimensional BDP micro-scale model for ammonium perchlorate/hydroxyl-terminated polybutadiene (AP/HTPB) was developed. Numerical simulations were conducted to evaluate how AP particle size and mass fraction influence the diffusion behavior, flame structure, and gas-phase temperature distribution. The results indicate that increasing the AP particle size significantly enhances the overall diffusion characteristics, which gradually become the dominant factor in the combustion process. Specifically, the flame exhibits more pronounced diffusion features, and the temperature distribution near the burning surface becomes increasingly non-uniform. Furthermore, as AP particle size increases, each gaseous component demonstrates greater diffusion tendencies, requiring a thicker mixing layer to achieve complete homogenization. Regarding the AP mass fraction, its increase strengthens the thermal feedback from the gas phase to the solid phase, leading to a slight rise in the burning surface temperature. While the diffusion characteristics of AP-derived macromolecules remain relatively stable, the concentration of residual oxygen increases with higher AP mass fractions. Full article

Solid rocket propellants based on hydroxyl-terminated polybutadiene (HTPB), in which HTPB acts as the polymeric binder and fuel matrix, are widely used in aerospace propulsion. During storage, transport, and service, these composite energetic materials are exposed to sustained mechanical loads as well as environmental variations, which may induce time-dependent inelastic deformation. Such creep deformation can alter the grain geometry, affect combustion stability, and reduce the structural reliability of rocket motors. In this work, room-temperature tensile creep tests were conducted on an HTPB-based solid propellant under different stress levels. Several viscoelastic and power-law constitutive models were compared, and a composite time-hardening creep model was established to describe the experimental strain–time response. The model was further implemented in Abaqus through a Fortran user subroutine for finite element simulation. The results provide a useful basis for creep deformation assessment, formulation optimization, and structural reliability analysis of HTPB-based propellants. Full article