Search Results (123)

Coatings based on the eutectic alloy Fe–TiB₂–CrB₂ were obtained by detonation spraying and subjected to pulsed plasma treatment. Comprehensive studies of the microstructure, phase composition, and mechanical and electrochemical properties of the coatings were carried out using SEM, TEM, and XRD methods. The initial coatings are characterized by a typical lamellar structure with interlamellar pores and defects. After pulsed plasma treatment, pronounced compaction of the surface layer, grain refinement, and sealing of interlamellar voids and cracks are observed. The thickness of the modified zone is about 15–30 μm, and the structure becomes fine-grained and more uniform. According to XRD and TEM data, the main boride phases (TiB₂, CrB₂) remain stable, while the intensity of γ-Fe decreases and weak Cr₂₃C₆ peaks appear, indicating phase stabilization and diffusion hardening. After treatment, the microhardness of the near-surface zone increases from ~14 GPa to 17–18 GPa, confirming the strengthening effect. Electrochemical tests showed an increase in corrosion resistance: the corrosion potential shifts to the positive side by approximately 0.15 V, and the corrosion current density decreases by almost two times. Thus, the use of pulsed plasma treatment significantly improves the density, phase stability, hardness, and corrosion resistance of Fe–TiB₂–CrB₂ detonation coatings, making this duplex approach promising for use in conditions of intense wear and exposure to aggressive environments. Full article

Differing from traditional isobaric combustion, a pulse detonation-based ramjet (PD-Ramjet) was proposed in this study to enhance the efficiency of traditional ramjets. By using a two-dimensional numerical simulation method, the filling process and detonation initiation process of the hydrogen/air stoichiometric mixture in channels equipped with typical flameholders were studied under the inflow condition of a ramjet combustor, and the influences of the typical flameholders on the filling process and detonation initiation process were analyzed. Single cavity, sudden expansion cavity, central cavity, and V-shaped groove were chosen as typical ramjet flameholders. The simulation and analysis results indicated that the flameholders would affect the filling effect, and the blocking ratio had a great influence on the filling process. The hydrogen volume discharged from the outlet of the channel and the time for mixed gas to reach the outlet were related to the blocking ratio and the cavity aft wall inclination angle. The detonation initiation process revealed that the flameholders promoted the generation of detonation waves. Contrastingly, the detonation wave could not be initiated in the channel without flameholders despite the better filling effect. Moreover, different flameholders would change the position of high-pressure point formation and the time for generating the stable detonation wave. On the whole, the sudden expansion cavity had a lower blockage ratio and also gave consideration to the filling effect and detonation initiation characteristic, making it the most suitable flameholder structure for PD-Ramjet in this study. Full article

In rock blasting for engineering applications—such as quarrying and tunnel construction—blasting is often detonated in carefully timed sequences to optimize rock fragmentation. This study examines Model I crack propagation in tunnel blasting sections with empty holes using circular PMMA (Polymethyl Methacrylate) samples containing pre-made initial cracks and empty holes. The distance between holes was varied from 10 mm to 30 mm. Using AUTODYN V18.0 numerical simulation software, how these holes affect crack initiation, propagation, and the surrounding stress field were analyzed. Key findings include the following: (a) Blasting stress waves diffract and reflect off empty hole edges, creating overlapping pressure zones between adjacent empty holes. Within a critical range of the empty hole distance, wider hole distance leads to slower stress wave propagation due to increased dispersion. (b) The empty holes weaken the stress concentration at crack tips, with greater distance further reducing peak strength. Proximal crack tips experience more pronounced stress field alterations than distal ones. (c) Holes hinder crack initiation, with the required stress intensity factor rising in near-linear proportion to hole separation distance. Full article

Studies of microbial degradation of historic woods are essential to help protect and preserve these important cultural properties. The USS Cairo is a historic Civil War gunboat and one of the first steam-powered and ironclad ships used in the American Civil War. Built in 1861, the ship sank in the Yazoo River of Mississippi in 1862 after a mine detonated and tore a hole in the port bow. The ship remained on the river bottom and was gradually buried with sediments for over 98 years. After recovery of the ship, it remained exposed to the environment before the first roofed structure was completed in 1980, and it has been displayed under a tensile fabric canopy with open sides at the Vicksburg National Military Park in Vicksburg, Mississippi. Concerns over the long-term preservation of the ship initiated this investigation to document the current condition of the wooden timbers, identify the fungi that may be present, and determine the elemental composition resulting from past wood-preservative treatments. Micromorphological characteristics observed using scanning electron microscopy showed that many of the timbers were in advanced stages of degradation. Eroded secondary cell walls leaving a weak framework of middle lamella were commonly observed. Soft rot attack was prevalent, and evidence of white and brown rot degradation was found in some wood. DNA extraction and sequencing of the ITS region led to the identification of a large group of diverse fungi that were isolated from ship timbers. Soft rot fungi, including Alternaria, Chaetomium, Cladosporium, Curvularia, Xylaria and others, and white rot fungi, including Bjerkandera, Odontoefibula, Phanerodontia, Phlebiopsis, Trametes and others, were found. No brown rot fungi were isolated. Elemental analyses using induced coupled plasma spectroscopy revealed elevated levels of all elements as compared to sound modern types of wood. High concentrations of boron, copper, iron, lead, zinc and other elements were found, and viable fungi were isolated from this wood. Biodegradation issues are discussed to help long-term conservation efforts to preserve the historic ship for future generations. Full article

The dissociation of the C-NO₂ bond is the initial step in the process of the detonation of nitroaromatic explosives. The strength of the C-NO₂ bond is significantly influenced by the relative position of the nitro group with respect to the aromatic ring plane since the planar arrangement enables the delocalization of electron density, which strengthens this bond. In this study, we have combined a statistical analysis of geometrical parameters extracted from crystal structures of trinitroaromatic molecules with ab initio calculations of non-covalent index plots and Wiberg bond index values for selected trinitroaromatic molecules to elucidate the influence of nearby substituents on the relative position of nitro groups with respect to the aromatic ring plane. The results of the analysis showed that neighboring substituents have a significant impact on the geometry of nitro groups. The results also showed that this influence arises from the repulsive interaction of voluminous substituents, attractive non-covalent contacts, and the electronic effects of substituents. Full article

In this study, powders based on a high-entropy AlCoCrFeNi alloy obtained by mechanical alloying were successfully applied to a 316L stainless steel substrate by detonation spraying under various conditions. Their microstructural features, phase composition, hardness, and wear resistance were studied. A comparative analysis between the initial powder and the coatings was performed, including phase transformation modeling using Thermo-Calc under non-equilibrium conditions. The results showed that the phase composition of the powder and coatings includes body-centered cubic lattice (BCC), its ordered modification (B2), and face-centered cubic lattice FCC phases, which is consistent with the predictions of the Scheil solidification model, describing the process of non-equilibrium solidification, assuming no diffusion in the solid phase and complete mixing in the liquid phase. Rapid solidification and high-speed impact deformation of the powder led to significant grain refinement in the detonation spraying coating, which ultimately improved the mechanical properties at the micro level. The data obtained demonstrate the high efficiency of the AlCoCrFeNi coating applied by detonation spraying and confirm its potential for use in conditions of increased wear and mechanical stress. AlCoCrFeNi coatings may be promising for use as structural materials in the future. Full article

The deflagration-to-detonation transition (DDT) is a critical process for achieving reliable ignition in detonation-based propulsion systems, such as Rotating Detonation Engines (RDEs). This study experimentally investigates the effect of spatial variations in blockage ratio (BR) on flame acceleration and detonation onset within a modular pre-detonator. Three DDT device configurations (converging, constant, and diverging) were designed to have an identical average BR of 0.5 and were tested over equivalence ratios ranging from 0.64 to 1.6. High-speed imaging, pressure transducers, and schlieren visualization were employed to characterize flame propagation velocity, pressure evolution, and exit wave structures. The converging configuration consistently promoted earlier detonation onset and higher success rates, especially under fuel-rich conditions (ϕ = 1.6), while the diverging configuration failed to initiate detonation in all cases. Enhanced flame compression in the converging layout led to strong coupling between the shock and reaction fronts, facilitating robust detonation formation. These findings indicate that the spatial distribution of BR, rather than average BR alone, plays a decisive role in DDT performance. This work offers validated design insights for optimizing pre-detonator in RDE applications. Full article

Sustainable rural development seeks to balance social, economic, and environmental needs in rural areas, improving the quality of life of communities and the long-term protection of natural resources. Indigenous local solutions give place to grassroots entrepreneurial initiatives, which together with associative and economic integration are key factors for agricultural production, transformation of products, self-consumption, and commercialization. This study was done in Hñähñu communities with the aim to test if participative workshops based on detonating questions are an effective approach for developing entrepreneurship agriculture initiatives of self-managed social enterprises. The initiatives were proposed by the communities to solve local problems. Three initiatives arose: (1) a community seed bank of local species associated with the Milpa including agave; (2) reforestation with agave to produce agave shoots, leaves, and sap; and (3) a company to produce agave-sap syrup. The participants, based on their traditional knowledge, developed the projects, including economic evaluation, risk analysis, and environmental aspects. Some impacts are the conservation of soil and endangered landraces, accessibility to quality seeds not commercially available, building of local organizational and entrepreneurial capacities, strengthening the community, improving the family’s income, recovery of traditional agroecological techniques, and conservation of agrobiodiversity. In conclusion, the methodology is effective for the Indigenous communities to develop initiatives for sustainable self-managed social enterprises. Full article

Here, a pure and systematic numerical study is conducted to investigate the detonation propagation in a curvature bend by focusing on the combined effect of curvature and cross-section area with a simple two-step chemical reaction model. In a channel with a small radius of curvature R/λ < 10, the detonation wave presents a periodical failure-reinitiation mode. The detonation wave near the inner wall cannot sustain itself due to the strong curvature effect. In contrast, the compression of the outer wall strengthens the front and can form a transverse detonation wave to re-initiate the failed detonation near the inner wall. In a channel with a large radius of curvature R/λ > 10, the inner wall’s weak rarefaction effect is not strong enough to completely quench the detonation wave. In the same way, the numerical results also show that a large area expansion rate inevitably produces a strong rarefaction effect near the inner wall, causing wave front decoupling and even failure. According to the radius of the curvature and the area increase rate, there are three different modes of detonation propagation: stable, critical, and unstable. By defining a new parameter κ to characterize different detonation modes and by considering both the curvature and area expansion effect, we found that the threshold κ = 0.33 can be used to distinguish the unstable and critical modes. Full article

Combustion caused by hydrogen-dominated combustible gas mixtures presents critical threats to nuclear safety during severe accidents in nuclear power plants, primarily due to their propensity for flame acceleration, deflagration, and subsequent detonation. Although the direct initiation of detonation from localized hydrogen accumulation at critical concentrations remains challenging, flame acceleration can induce rapid pressure escalation and lead to deflagration-to-detonation transition under suitable conditions. The ultra-high-pressure loads generated almost instantaneously will pose serious risks to containment integrity and equipment or instrument functionality within nuclear facilities. This paper investigates the flame acceleration mechanism and criterion, which is crucial for precise hydrogen risk assessment. A hydrogen combustion flame acceleration model is developed, integrating both laminar and turbulent flame propagation across multiple control volumes. Validated against the RUT test, the model demonstrates high fidelity with a maximum 3.17% deviation in flame propagation velocity and successfully captures the pressure discontinuity. The developed model enables comprehensive simulation with improved predictive accuracy of the flame acceleration process, making it an essential tool for advancing fundamental understanding of hydrogen behavior and severe accident analysis. This model’s development marks a paradigm in nuclear safety research by providing an analytical instrument for integrated severe accident programs in nuclear power plants, contributing to improving the potential hydrogen risks assessment and management in next-generation reactor safety. Full article

Pulse detonation engines (PDEs) have become a transformative technology in the field of aerospace propulsion due to the high thermal efficiency of detonation combustion. However, initiating detonation waves within a limited space and time is key to their engineering application. Direct initiation, though theoretically feasible, requires very high critical energy, making it almost impossible to achieve in engineering applications. Therefore, indirect initiation methods are more practical for triggering detonation waves that produce a deflagration wave through a low-energy ignition source and realizing deflagration to detonation transition (DDT) through flame acceleration and the interaction between flames and shock waves. This review systematically summarizes recent advancements in DDT methods in pulse detonation engines, focusing on the basic principles, influencing factors, technical bottlenecks, and optimization paths of the following: hot jet ignition initiation, obstacle-induced detonation, shock wave focusing initiation, and plasma ignition initiation. The results indicate that hot jet ignition enhances turbulent mixing and energy deposition by injecting energy through high-energy jets using high temperature and high pressure; this can reduce the DDT distance of hydrocarbon fuels by 30–50%. However, this approach faces challenges such as significant jet energy dissipation, flow field instability, and the complexity of the energy supply system. Solid obstacle-induced detonation passively generates turbulence and shock wave reflection through geometric structures to accelerate flame propagation, which has the advantages of having a simple structure and high reliability. However, the problem of large pressure loss and thermal fatigue restricts its long-term application. Fluidic obstacle-induced detonation enhances mixing uniformity through dynamic disturbance to reduce pressure loss. However, its engineering application is constrained by high energy consumption requirements and jet–mainstream coupling instability. Shock wave focusing utilizes concave cavities or annular structures to concentrate shock wave energy, which directly triggers detonation under high ignition efficiency and controllability. However, it is extremely sensitive to geometric parameters and incident shock wave conditions, and the structural thermal load issue is prominent. Plasma ignition generates active particles and instantaneous high temperatures through high-energy discharge, which chemically activates fuel and precisely controls the initiation sequence, especially for low-reactivity fuels. However, critical challenges, such as high energy consumption, electrode ablation, and decreased discharge efficiency under high-pressure environments, need to be addressed urgently. In order to overcome the bottlenecks in energy efficiency, thermal management, and dynamic stability, future research should focus on multi-modal synergistic initiation strategies, the development of high-temperature-resistant materials, and intelligent dynamic control technologies. Additionally, establishing a standardized testing system to quantify DDT distance, energy thresholds, and dynamic stability indicators is essential to promote its transition to engineering applications. Furthermore, exploring the DDT mechanisms of low-carbon fuels is imperative to advance carbon neutrality goals. By summarizing the existing DDT methods and technical bottlenecks, this paper provides theoretical support for the engineering design and application of PDEs, contributing to breakthroughs in the fields of hypersonic propulsion, airspace shuttle systems, and other fields. Full article

Hydrogen is a promising candidate for addressing environmental challenges in aviation, yet its use in structural validation tests for Wing Structure-Integrated high-pressure Hydrogen Tanks (SWITHs) remains underexplored. To the best of the authors’ knowledge, this study represents the first attempt to assess the feasibility of conducting such tests with hydrogen at aircraft scales. It first introduces hydrogen’s general properties, followed by a detailed exploration of the potential hazards associated with its use, substantiated by experimental and simulation results. Key factors triggering risks, such as ignition and detonation, are identified, and methods to mitigate these risks are presented. While the findings affirm that hydrogen can be used safely in aviation if responsibly managed, they caution against immediate large-scale experimental testing of SWITHs due to current knowledge and technology limitations. To address this, a roadmap with two long-term objectives is outlined as follows: first, enabling structural validation tests at scales equivalent to large aircraft for certification; second, advancing simulation techniques to complement and eventually reduce reliance on costly experiments while ensuring sufficient accuracy for SWITH certification. This roadmap begins with smaller-scale experimental and numerical studies as an initial step. Full article

To investigate the energy transfer mechanisms during the micro-explosive initiator-driven flyer process and to guide the performance evaluation of micro-sized charges and the structural design of micro-initiators, a combined approach of numerical simulations and experimental tests was employed to study the detonation process of copper-based azide micro-charges driving a flyer. The output pressure and detonation velocity of the copper-based azide micro-charge were measured using the manganese–copper piezoresistive method and electrical probe technique, and the corresponding JWL equation of the state parameters was subsequently fitted. A simulation model for the micro-charge-driven flyer was established and validated using Photonic Doppler Velocimetry (PDV), and the influence of charge conditions, structural parameters, and other factors on the flyer velocity and morphology was investigated. The results indicate that the flyer velocity decreases as its thickness increases, whereas the specific kinetic energy of the flyer initially increases and then decreases with increasing thickness. The optimal flyer thickness was found to be in the range of 30 to 70 μm. The flyer velocity increases with the density and height of the micro-charge; however, when the micro-charge density exceeds a certain threshold, the flyer velocity decreases. The flyer velocity exhibits an exponential decline as the diameter of the acceleration chamber increases, whereas it shows a slight increase with the increase in the length of the acceleration chamber. The diameter of the acceleration chamber should not exceed the charge diameter and must be no smaller than the critical diameter required for detonation initiation of the underlying charge. The use of a multi-layer accelerating chamber structure leads to a slight reduction in flyer velocity and further increases in the transmission hole diameter while having no significant impact on the flyer velocity. Full article

In the maritime industry, hydrogen fuel cell ships demonstrate significant potential for development due to their environmental friendliness and high efficiency. However, the risks of fire and explosion caused by hydrogen leakage pose severe challenges to their safety. To enhance the safety of hydrogen fuel cell ships and mitigate the explosion hazards caused by leakage, this study employs the XiFoam solver in the OpenFOAM v9 to establish an explosion model for a full-scale hydrogen fuel cell compartment within a hydrogen fuel cell ship. The model simulates the transient explosion process following high-pressure hydrogen leakage under varying initial hydrogen concentrations and premixed fuel conditions. By analyzing the temporary evolution of temperature distribution, flame front propagation, and explosion pressure, the study provides a comprehensive understanding of the safety implications of hydrogen leakage at different locations within the fuel cell. Specifically, increasing the hydrogen concentration from ΦH₂ = 0.10 to ΦH₂ = 0.18 and ΦH₂ = 0.20 significantly elevates the overpressure peak and accelerates the flame speed from 250 m/s to 370 m/s, with local pressure gradients approaching the deflagration to detonation transition threshold. The simulation results contribute valuable insights into optimizing hydrogen fuel cell design, formulating effective fire safety strategies, and improving overall ship safety. Full article

Shock-to-detonation transition (SDT) is the detonation of explosive charge triggered by the shock pressure from a nearby detonated explosive or an impact at high speed. A good prediction of SDT is a key in the design of explosives’ use, storage, and transportation. Typically, SDT simulation must use designated commercial software; therefore, a high license cost is necessary. This paper presents a simulation of SDT by a cost-effective hydrodynamic code developed on an open-source code framework, OpenFOAM. The code adopted the multi-material Eulerian method, Ignition and Growth reaction rate model, and Riemann solver to solve the shock-induced detonation phenomenon. The code was verified by a Pop plot calculation and a sympathetic detonation simulation. In the Pop plot calculation, the distance-of-run to the detonation of Composition B depending on the initial shock pressure was simulated. The reactant and product phases of Composition B were modeled by the Jone–Wilkins–Lee (JWL) equation of state (EOS). The aluminum plate used to create the initial shock pressure was modeled by shock Mie–Gruneisen (MG) EOS. The predicted distance-of-run against the initial shock pressure was in good agreement with an empirical correlation and experimental data. In the sympathetic detonation simulation, the charge explosive and nearby explosive were Composition B and were modeled by JWL EOS as in the Pop plot calculation and the plexiglass gap was modeled by MG EOS. The simulated critical gap for the sympathetic detonation was well predicted as in the other published data. This implies that the code is valid for SDT simulation. In addition, it is a cost-effective simulation, since the code was developed on open-source code, so massive computation can then be run without license costs. Full article