Search Results (13)

Composite solid propellants, which serve as the core energetic materials in aerospace and military propulsion systems, necessitate tailored enhancement of their mechanical properties to ensure operational safety and stability. A critical challenge involves elucidating the interfacial interactions among the multiple propellant components (≥6 components, including the polymer binder HTPB, curing agent IPDI, oxidizer particles AP/Al, bonding agents MAPO/T313, plasticizer DOS, etc.) and their influence on crosslinked network formation. In this study, we propose an integrated computational framework that combines coarse-grained simulations with reactive force fields to investigate these complex interactions at the molecular level. Our approach successfully elucidates the two-step reaction mechanism propagating along the AP interface in multicomponent propellants, comprising interfacial self-polymerization of bonding agents followed by the participation of curing agents in crosslinked network formation. Furthermore, we assess the mechanical performance through tensile simulations, systematically investigating both defect formation near the interface and the influence of key parameters, including the self-polymerization time, HTPB chain length, and IPDI content. Our results indicate that the rational selection of parameters enables the optimization of mechanical properties (e.g., ~20% synchronous improvement in tensile modulus and strength, achieved by selecting a side-chain ratio of 20%, a DOS molar ratio of 2.5%, a MAPO:T313 ratio of 1:2, a self-polymerization MAPO time of 260 ns, etc.). Overall, this study provides molecular-level insights into the structure–property relationships of composite propellants and offers a valuable computational framework for guided formulation optimization in propellant manufacturing. Full article

Fuel cells, propulsion systems, and reaction control systems (RCSs) are just a few of the space applications that depend on pressure vessels (PVs) to safely hold high-pressure fluids while enduring extreme environmental conditions both during launch and in orbit. Under these challenging circumstances, PVs must be lightweight while retaining structural integrity in order to increase the efficiency and lower the launch costs. PVs have significant challenges in space conditions, such as extreme vibrations during launch, the complete vacuum of space, and sudden temperature changes based on their location within the satellite and orbit types. Determining the operational temperature limits and endurance of PVs in space applications requires assessing the combined effects of these factors. As the main propellant for satellites and rockets, hydrogen has great promise for use in future space missions. This study aimed to assess the structural integrity and determine the thermal operating limits of different types of hydrogen pressure vessels using finite element analysis (FEA) with Ansys 2019 R3 Workbench. The impact of extreme space conditions on the performances of various kinds of hydrogen pressure vessels was analyzed numerically in this work. This study determined the safe operating temperature ranges for Type 4, Type 3, and Type 1 PVs at an operating hydrogen storage pressure of 35 MPa in an absolute vacuum. Additionally, the dynamic performance was assessed through modal and random vibration analyses. Various aspects of Ansys Workbench were explored, including the influence of the mesh element size, composite modeling methods, and their combined impact on the result accuracy. In terms of the survival temperature limits, the Type 4 PVs, which consisted of a Nylon 6 liner and a carbon fiber-reinforced epoxy (CFRE) prepreg composite shell, offered the optimal balance between the weight (56.2 kg) and a relatively narrow operating temperature range of 10–100 °C. The Type 3 PVs, which featured an Aluminum 6061-T6 liner, provided a broader operational temperature range of 0–145 °C but at a higher weight of 63.7 kg. Meanwhile, the Type 1 PVs demonstrated a superior cryogenic performance, with an operating range of −55–54 °C, though they were nearly twice as heavy as the Type 4 PVs, with a weight of 106 kg. The absolute vacuum environment had a negligible effect on the mechanical performance of all the PVs. Additionally, all the analyzed PV types maintained structural integrity and safety under launch-induced vibration loads. This study provided critical insights for selecting the most suitable pressure vessel type for space applications by considering operational temperature constraints and weight limitations, thereby ensuring an optimal mechanical–thermal performance and structural efficiency. Full article

The global shortage of freshwater resources and the energy crisis have propelled solar-driven interfacial evaporation (SDIE) coupled with photocatalytic technology to become a research focus in efficient and low-carbon water treatment. Graphene-based materials demonstrate unique advantages in SDIE–photocatalysis integrated systems, owing to their broadband light absorption, ultrafast thermal carrier dynamics, tunable electronic structure, and low evaporation enthalpy characteristics. This review systematically investigates the enhancement mechanisms of graphene photothermal conversion on photocatalytic processes, including (1) improving light absorption through surface morphology modulation, defect engineering, and plasmonic material compositing; (2) reducing water evaporation enthalpy via hydrophilic functional group modification and porous structure design; (3) suppressing heat loss through thermal insulation layers and 3D structural optimization; and (4) enhancing water transport efficiency via fluid channel engineering and wettability control. Furthermore, salt resistance strategies and structural optimization significantly improve system practicality and stability. In water treatment applications, graphene-based SDIE systems achieve synergistic “adsorption–catalysis–evaporation” effects, enabling efficient the degradation of organic pollutants, reduction in/fixation of heavy metal ions, and microbial inactivation. However, practical implementation still faces challenges including low steam condensation efficiency, insufficient long-term material durability, and high scaling-up costs. Future research should prioritize enhancing heat and mass transfer in condensation systems, optimizing material environmental adaptability, and developing low-cost manufacturing processes to promote widespread application of graphene-based SDIE–photocatalysis integrated systems. Full article

The azido propellant, with high energy and low signature, has been a hotpot in the field of propellants. However, the risk of low heat resistance and mechanical performance restricts their range of applications in high-energy formulations. In this study, four azido propellants based on 3,3-bis (azidomethyl) oxetane-tetrahydrofuran copolyether (BAMO-THF) have been prepared, their basic physical properties including energetic properties, internal micro-structure and true density were studied; their tensile properties, dynamic mechanical performances, were investigated, the structure-properties relationship was proposed. The results demonstrate that the obtained propellant shows an elastomeric composite material behavior, with an obvious relaxation in the initial stage and susceptibility to loading condition. The formula structure not only causes obvious difference in the second stage of relaxation, but also strongly affects the initial stage, which is quite different from the influence of testing condition. Besides, the low temperature toughness of the azido propellant is improved by using diol partly replaces diamine as a chain extender, but their stress modulus drop down obviously, leading to the notable stress relaxation behavior at high temperatures. It was found that the improvement of the ordering degree of microstructure or network integrity could restrict the stress relaxation, which was an effective approach to improve the heat resistance and mechanical performance of azido propellant at high temperatures. Full article

With the increasing demand for high-performance leisure boat propellers, this study explores the development of high-strength aluminum alloy propellers using the low-pressure die-casting (LPDC) process. In Part I of the study, we identified the optimal alloy compositions for Al-6Zn-2Mg-1.5Cu propellers and highlighted the challenges of hot tearing at the junction between the hub and blades. In this continuation, we developed a coupled thermal fluid stress analysis model using ProCAST software to optimize the LPDC process. By adjusting casting parameters such as the melt supply temperature, initial mold temperature, and curvature radius between the hub and blades, we minimized hot tearing and other casting defects. The results were validated through simulations and practical applications, showing significant improvements in the quality and structural integrity of the propellers. Non-destructive testing using X-ray CT confirmed the reduction in internal defects, demonstrating the effectiveness of the simulation-based approach for alloy design and process optimization. Full article

In a high-temperature test of the gas generator with a free-loading composite propellant, an abnormal jitter appeared in the latter part of the internal ballistic curve, whereas no such abnormality was observed in the low-temperature and normal-temperature tests. To investigate the cause, quasi-steady-state simulations of the internal flow field, as well as strength and buckling simulations of the grain, were conducted. The strength simulation revealed that the maximum stress experienced by the composite propellant during operation at 323 K is 0.7 MPa, which is lower than the ultimate stress of the grain (1.01 MPa), indicating no stress failure. The buckling simulation demonstrated that the instability arises from an imbalance of pressure on the inner and outer surfaces of the grain. In the original structure, the ventilation effect on each surface of the grain varied with the regression of the burning surface, leading to a pressure imbalance on the inner and outer surfaces of the composite propellant. Consequently, a non-ablative cladding layer was applied to ensure that the ventilation effect of each channel remains constant. The simulation demonstrated that the pressure on the surfaces of the composite propellant gradually balanced with the operation of the gas generator. Upon retesting at high temperatures, no abnormal jitter was observed in the internal ballistic curve. This indicates that maintaining a constant ventilation area for the combustion chamber and preventing changes in the ventilation effect can ensure the structural integrity of the composite propellant during operation. The working state of the composite propellant with this non-ablative cladding layer is not affected by variations in the design of the solid rocket motor. This approach enhances the adaptability and reliability of the free-loading composite propellant under different motor structures. Full article

The transition of large-scale cryogenic propellant tanks from metal to composite materials is the main trend in the global aerospace industry. Aiming to address the challenges of achieving the manufacturing of integrated and cost-effective manufacturing of aerospace cryogenic composite tanks that cannot be realized through the conventional autoclave process, and those of existing out-of-autoclave processes that are unable to effectively suppress defects under low-pressure conditions, a vibration pretreatment was innovatively introduced into the microwave curing process of composite materials in this study. Based on a systematic analysis of the inhibitory mechanisms of vibration pretreatment on void formation and the uniform heating mechanisms of microwaves in composite materials, the experimental results showed that the compound curing process enabled the production of components with complex structural features under low-pressure conditions while achieving equivalent surface precision and comprehensive properties, including porosity, interlaminar shear strength, and cryogenic permeation resistance, as those obtained through the standard 0.6 MPa autoclave process. This holds great promise for the application of out-of-autoclave processes in the manufacturing of large-scale aerospace cryogenic composite tanks. Full article

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. Full article

Additive manufacturing (AM) has experienced exponential growth over the past two decades and now stands on the cusp of a transformative paradigm shift into the realm of multi-functional component manufacturing, known as multi-material AM (MMAM). While progress in MMAM has been more gradual compared to single-material AM, significant strides have been made in exploring the scientific and technological possibilities of this emerging field. Researchers have conducted feasibility studies and investigated various processes for multi-material deposition, encompassing polymeric, metallic, and bio-materials. To facilitate further advancements, this review paper addresses the pressing need for a consolidated document on MMAM that can serve as a comprehensive guide to the state of the art. Previous reviews have tended to focus on specific processes or materials, overlooking the overall picture of MMAM. Thus, this pioneering review endeavors to synthesize the collective knowledge and provide a holistic understanding of the multiplicity of materials and multiscale processes employed in MMAM. The review commences with an analysis of the implications of multiplicity, delving into its advantages, applications, challenges, and issues. Subsequently, it offers a detailed examination of MMAM with respect to processes, materials, capabilities, scales, and structural aspects. Seven standard AM processes and hybrid AM processes are thoroughly scrutinized in the context of their adaptation for MMAM, accompanied by specific examples, merits, and demerits. The scope of the review encompasses material combinations in polymers, composites, metals-ceramics, metal alloys, and biomaterials. Furthermore, it explores MMAM’s capabilities in fabricating bi-metallic structures and functionally/compositionally graded materials, providing insights into various scale and structural aspects. The review culminates by outlining future research directions in MMAM and offering an overall outlook on the vast potential of multiplicity in this field. By presenting a comprehensive and integrated perspective, this paper aims to catalyze further breakthroughs in MMAM, thus propelling the next generation of multi-functional component manufacturing to new heights by capitalizing on the unprecedented possibilities of MMAM. Full article

In this paper, first, the meso-debonding process of a GAP/CL20/AP composite solid propellant under uniaxial tension was analyzed using the advantages of the material point method (MPM) and the finite element method (FEM) for the first time; then, the numerical simulation results were compared with the experiments. Based on the basic principle of modeling with the material point method, grains of different sizes were generated quickly and efficiently. Next, the grains were dispersed into particles, and the position information of the particles was mapped onto the background grid, so the background grids were used to determine the position of the grains. After that, the generated AP and CL20 grains were imported into the commercial software Abaqus through python scripting codes for numerical calculation. Based on macro-mechanical tests and a micro-numerical simulation, this paper studies the micro-internal mechanism that affects the macro-mechanical properties of composite solid propellants. Three interface parameters needed to be determined by parameter inversion, and the value of the objective interpolation function $\min R$ was 0.05078%. From a comparison, it was found that the numerical simulation results are in good agreement with the experimental results in the aspects of micro-crack cracking characteristics and the nominal stress–strain curve of propellants. After that, the influence of interface parameters on the stress–strain curve are discussed. The research in this paper has high scientific value and engineering application value and can provide important reference and guidance for the design of composite solid propellants and its mechanical property analyses, so as to solve the structural integrity problem of solid rocket motor charges. Full article

With the increasing use of electric propulsion ships, the emergence of the shaftless rim-driven thruster (RDT) as a revolutionary integrated motor thruster is gradually becoming an important development direction for green ships. The shaftless structure of RDTs leads to their dependence on position sensorless control techniques. In this study, a novel control algorithm using a composite sliding mode observer (SMO) with a modified feed-forward phase-locked loop (PLL) is presented for achieving high accuracy position and speed control of shaftless RDT motors. The deviation between the observed and actual currents is exploited to develop a current SMO to extract back electromotive force (back-EMF) errors. On this basis, a back-EMF observer is established to achieve accurate estimation of the back-EMF. The basic structure of the PLL was modified and incorporates a speed feedforward mechanism, which enhances the performance of rotor position estimation and facilitates bidirectional rotation. The stability of the algorithm has been verified in Matlab/Simulink for a range of steady-state, dynamic, and ship propeller loading conditions. Remarkably, the control algorithm boasts an impressive adjustment time of approximately 0.006 s and its position estimation error may be as low as 0.03 rad. Simulation results highlight the performance of the algorithm to achieve bidirectional rotation, while exhibiting fast convergence, minimal vibration, exceptional control accuracy, and robustness. Full article

Aluminum (Al) has been widely used in micro-electromechanical systems (MEMS), polymer bonded explosives (PBXs) and solid propellants. Its typical core-shell structure (the inside active Al core and the external alumina (Al₂O₃) shell) determines its oxidation process, which is mainly influenced by oxidant diffusion, Al₂O₃ crystal transformation and melt-dispersion of the inside active Al. Consequently, the properties of Al can be controlled by changing these factors. Metastable intermixed composites (MICs), flake Al and nano Al can improve the properties of Al by increasing the diffusion efficiency of the oxidant. Fluorine, Titanium carbide (TiC), and alloy can crack the Al₂O₃ shell to improve the properties of Al. Furthermore, those materials with good thermal conductivity can increase the heat transferred to the internal active Al, which can also improve the reactivity of Al. Now, the integration of different modification methods is employed to further improve the properties of Al. With the ever-increasing demands on the performance of MEMS, PBXs and solid propellants, Al-based composite materials with high stability during storage and transportation, and high reactivity for usage will become a new research focus in the future. Full article

The composite bucket foundation (CBF) for offshore wind turbines is the basis for a one-step integrated transportation and installation technique, which can be adapted to the construction and development needs of offshore wind farms due to its special structural form. To transport and install bucket foundations together with the upper portion of offshore wind turbines, a non-self-propelled integrated transportation and installation vessel was designed. In this paper, as the first stage of applying the proposed one-step integrated construction technique, the floating behavior during the transportation of CBF with a wind turbine tower for the Xiangshui wind farm in the Jiangsu province was monitored. The influences of speed, wave height, and wind on the floating behavior of the structure were studied. The results show that the roll and pitch angles remain close to level during the process of lifting and towing the wind turbine structure. In addition, the safety of the aircushion structure of the CBF was verified by analyzing the measurement results for the interaction force and the depth of the liquid within the bucket. The results of the three-DOF (degree of freedom) acceleration monitoring on the top of the test tower indicate that the wind turbine could meet the specified acceleration value limits during towing. Full article