Search Results (72)

Addressing the stability control challenges of roadways with composite roofs in the No. 34 coal seam of Donghai Mine under high-strength mining conditions, this study employed integrated methodologies including laboratory experiments, numerical modeling, and field trials. It investigated the mechanical response characteristics of the composite roof and developed a synergistic control system, validated through industrial application. Key findings indicate significant differences in mechanical behavior and failure mechanisms between individual rock specimens and composite rock masses. A theoretical “elastic-plastic-fractured” zoning model for the composite roof was established based on the theory of surrounding rock deterioration, elucidating the mechanical mechanism where the cohesive strength of hard rock governs the load-bearing capacity of the outer shell, while the cohesive strength of soft rock controls plastic flow. The influence of in situ stress and support resistance on the evolution of the surrounding rock zone radii was quantitatively determined. The FLAC^3D strain-softening model accurately simulated the post-peak behavior of the surrounding rock. Analysis demonstrated specific inherent patterns in the magnitude, ratio, and orientation of principal stresses within the composite roof under mining influence. A high differential stress zone (σ₁/σ₃ = 6–7) formed within 20 m of the working face, accompanied by a deflection of the maximum principal stress direction by 53, triggering the expansion of a butterfly-shaped plastic zone. Based on these insights, we proposed and implemented a synergistic control system integrating high-pressure grouting, pre-stressed cables, and energy-absorbing bolts. Field tests demonstrated significant improvements: roof-to-floor convergence reduced by 48.4%, rib-to-rib convergence decreased by 39.3%, microseismic events declined by 61%, and the self-stabilization period of the surrounding rock shortened by 11%. Consequently, this research establishes a holistic “theoretical modeling-evolution diagnosis-synergistic control” solution chain, providing a validated theoretical foundation and engineering paradigm for composite roof support design. Full article

Superhydrophobic coatings possess distinct wettability characteristics and hold significant potential in metal corrosion protection and underwater drag reduction. However, their practical application is often hindered by poor durability arising from the fragility of their micro/nanostructured surface roughness. In this study, a durable superhydrophobic coating featuring a hierarchical, hydrangea-like micro/nanostructure was successfully fabricated on an aluminum alloy substrate via a simple one-step cold-spraying technique. The coating consisted of hydrangea-shaped SiO₂ nanoparticles modified with 1H,1H,2H,2H-perfluorodecyltrimethoxysilane (PFDT) to produce multiscale roughness, while epoxy resin (EP) served as the binding matrix to enhance mechanical integrity. The hydrangea-like SiO₂ nanostructures were characterized by solid cores and wrinkled, petal-like outgrowths. This unique morphology not only increased the surface roughness but also provided more active sites for air entrapment, thereby enhancing the coating’s overall performance. The h-SiO₂@PFDT-EP composite coating exhibited excellent superhydrophobicity, with a WCA of 170.1° ± 0.8° and a SA of 2.7° ± 0.5°. Durability was evaluated through sandpaper abrasion, tape peeling, acid and alkali immersion, artificial weathering, and salt spray tests. The results demonstrated that the coating retained stable superhydrophobic performance under various environmental stresses. Compared with bare 6061 aluminum and EP coatings, its corrosion current density was reduced by four and three orders of magnitude, respectively. Furthermore, the coating achieved a maximum drag-reduction rate of 31.01% within a velocity range of 1.31–7.86 m/s. The coating also displayed excellent self-cleaning properties. Owing to its outstanding durability, corrosion resistance, and drag-reducing capability, this one-step fabricated superhydrophobic coating showed great promise for applications in marine engineering and defense. Full article

This paper investigates the dynamic performance of web frame structures under the impact of a conical hammer head. Compared with existing research on flat plates and stiffened panels, web frame structures exhibit significant differences in load-bearing mechanisms and design principles. To address these limitations, a series of drop-weight impact tests under different impact conditions are conducted, and the effects of drop heights on the dynamic responses of the web frame structure are systematically analyzed. By measuring the impact force responses and damage shapes, nonlinear dynamic characteristics and damage modes of the web frame structures under conical hammer head impacts can be revealed. The results indicate that higher drop heights lead to more severe damage areas, and damage area is more concentrated in the contact area of the indenter. Meanwhile, the peak impact force increases from 429.06 MN to 606.62 MN as the drop height increases from 1 m to 2.5 m, indicating a 41.38% rise. Additionally, the maximum energy absorbed by the structure reaches 62.89 KJ, and the energy loss ratio ranges from 18.58% to 30.73%. The findings offer critical theoretical insights and technical support for the optimization of impact resistant designs in web frame structures. Full article

Directionally solidified (DS) superalloys have become a primary material choice for turbine blade applications. Due to the complex shape of the blades, certain regions inevitably experience stress axes oriented orthogonally to the crystal growth direction. Therefore, this study explores the creep characteristics of a DS superalloy in different orientations (transverse (T) versus longitudinal (L) with respect to grain growth direction) under intermediate and high temperatures (980 °C and 1070 °C), while simultaneously analyzing their respective deformation mechanisms and microstructural transformation behaviors. Experimental findings reveal pronounced orientation-dependent variations in creep performance, deformation modes, and microstructural development. Notably, the T specimen exhibits higher creep resistance at 980 °C, which can provide a basis for the design of some components that require high creep resistance and maintain small deformation. At 980 °C, L specimens primarily undergo γ′ phase shearing via antiphase boundaries (APBs) pairs, whereas T specimen exhibits APB pairs and superlattice intrinsic stacking faults (SISFs) shearing mechanisms. At 1070 °C, the L specimen exhibits dislocation shearing of γ′ alongside dislocation bypassing of tertiary γ′, while the T specimen demonstrates dislocation climbing within the γ channels. Additionally, the L specimen exhibits significant N-type rafting, while the T specimen shows significant Ostwald ripening characteristics, with an Ostwald ripening rate constant of 1.04 × 10⁻²⁰ m³/h. Full article

The marine environment is highly complex, characterized by substantial fluctuations in flow velocity. To enhance the adaptability of robotic large yellow croakers to such conditions, this study takes into account multiple factors, including shape, dimensions, and material properties, and evaluates their hydrodynamic resistance characteristics. A 2D model of large yellow croakers aged 1, 4, 7, 10, and 12 months was established as the bionic object. Based on computational fluid dynamics, the water resistance characteristics of this model were investigated in the same water environment. A 3D model of this species based on the 2D model and three skin materials, PE, PC, and ST, was added, and the effects of these materials on the water resistance of the 3D model were investigated. It was shown that in a water environment with a current speed of 0.1~1 m/s, the water resistance of large yellow croaker models at different ages ranged from 0.1006 to 6.8485 N; that of croakers with different body lengths ranged from 0.1067 to 28.5760 N; and that of croakers with different skin materials ranged from 0.0048 to 0.8672 N. The results showed that in the water environment with a current speed of 0.1–1 m/s, the 12-month-old large yellow croaker model had a lower water resistance range of 0.1006~3.6512 N in the watershed compared with other models of the same age; the large yellow croaker models with body lengths of 20, 30, and 40 cm had a smaller range of water resistance of 0.1125~12.5110 N in the watershed compared with other models of the same body length; and large yellow croaker models made of PE had a smaller range of resistance of 0.0048~0.7523 N in the watershed compared to those made of PC and ST materials. The results of this study are important for the design and fabrication of robotic fish capable of prolonged underwater operations. Full article

Lattice materials demonstrate exceptional advantages in lightweight design applications due to their low mass density, high specific strength, and customizable topology. Inspired by the hollow vascular bundle structure of bamboo, this study develops four bio-inspired lattice configurations through two key modifications to conventional body-centered cubic (BCC) structures: Z-axis (loading direction) strut reinforcement and strut hollowing. The specimens were fabricated using AlSi10Mg powder via selective laser melting (SLM) technology, followed by the systematic evaluation of the compressive properties and the energy absorption characteristics. The experimental results reveal that the synergistic combination of Z-strut reinforcement and hollow design significantly enhances both the compressive resistance and the energy absorption capacity. The optimized BCC-5ZH configuration (5 Z-struts with full hollowing) achieves remarkable performance metrics at 0.5 g/cm³ density: yield strength (16.78 MPa), compressive strength (27.91 MPa), and volumetric energy absorption (10.4 MJ/m³). These values represent 236.9%, 283.4%, and 239.3% enhancements, respectively, compared to the reference BCC lattices with an equivalent density. Z-strut integration induces homogeneous stiffness distribution throughout the lattice architecture, while strut hollowing increases the effective moment of inertia. This structural evolution induces a failure mode transition from single shear band deformation to dual X-shaped shear band propagation, resulting in enhanced deformation sequence regulation within the lattice system. Full article

This paper investigates the repeated disturbance of weakly cemented overburden rock caused by closely spaced coal seam mining, focusing on the effect of water infiltration on the strength degradation of weakly cemented mudstone. The study compares the fissure and fissure distribution characteristics of the overburden rock under seepage conditions. It also examines the dynamic evolution of seepage parameters during repeated mining and their impact on the overburden rock’s bearing capacity and structural stability. The findings are as follows: (1) After water infiltration, the clay mineral content in weakly cemented mudstone decreases, leading to a significant reduction in strength, increased microcrack development, and a moisture content increase from 0% to 3.27%. Uniaxial compressive strength decreases by 59.83%. (2) In the absence of seepage effects, the fissure development zone in the overburden rock changes from a positive trapezoidal shape to an inverted trapezoidal one, with a water-conducting channel forming first on the setup entry side. When seepage is considered, the fissure development in the weakly cemented overburden rock significantly increases, and the location of large-scale fissure initiation and expansion is advanced by 80 m. (3) During coal seam mining, excavation of the upper seam reduces the pore water pressure in the roof, causing the region of reduced pore pressure to shift from a trapezoidal to an “M” shape. As mining progresses to the lower seam, a seepage channel forms near the setup entry and expands. (4) Under repeated mining conditions, seepage field evolution in the overburden rock triggers the migration and transmission of formation water and pore pressure. The sustained influence of fissure water infiltration and seepage pressure accelerates the development of the water flowing fracture zone. As the overburden rock experiences renewed fracturing and caving, secondary fissure formation intensifies the movement of formation water. Consequently, the bearing capacity and water-resistance properties of the overburden rock are gradually degraded, significantly increasing the extent of structural damage within weakly cemented mining overburden rock. Full article

Frequency multipliers are essential components in communication systems, and graphene’s exceptional electrical properties make it highly promising for flexible electronics. This paper addresses the technical challenges of multi-frequency multipliers based on graphene field-effect transistors (GFETs) and introduces a novel fabrication method using graphene as the channel material and metals with different work functions as the top gate. By employing Ti and Pd with distinct work functions, we develop a dual-gate GFET device that exhibits stable M-shaped resistance characteristics on a flexible polyethylene naphthalate (PEN) substrate. We demonstrate frequency doubler, tripler, and quadrupler on the flexible substrate. The results show that the GFET-based frequency multiplier offers advantages such as low operating voltage (<1 V), high voltage conversion efficiency (up to 8.4% for tripler and 6% for quadrupler), and high spectral purity (up to 88% for tripler and 76% for quadrupler). The intrinsic maximum operating frequency of the frequency quadrupler reaches 54 GHz. The use of a monolayer graphene channel, dual-metal gate control enabling an M-shaped transfer curve, and flexible characteristics all contribute to its superior performance compared to conventional devices. Full article

Understanding the characteristics of downburst wind fields is crucial for studying structural resistance to downbursts. Based on measured data from the 325 m meteorological tower in Beijing, this paper investigates the spatiotemporal evolution of mean and fluctuating winds during a non-stationary downburst. Key wind field parameters such as the mean wind speed, turbulence intensity, turbulence integral length scale, probability density function, power spectral density, evolutionary power spectral density, and gust factor are statistically analyzed. The results show that the wind speed of downburst undergoes rapid changes, with wind direction significantly influenced by outflow vortices at low altitudes and relatively stable at higher altitudes. When the event happens, the temperature decreases sharply. The mean wind speeds and turbulence integral length scale of the downburst exhibit pronounced “nose-shaped” profile characteristics at the moment when peak wind speed occurs. The turbulence intensity at lower altitudes predominantly exceeds that at higher altitudes. The probability density distribution function of the reduced fluctuating wind speed matches the standard Gaussian distribution curve. The fluctuating wind speeds of the downburst exhibit significant non-stationary characteristics, with their energy mainly distributing in the period of rapid change of wind speed in the time domain and concentrating in the vicinity of 0–0.1 Hz in the frequency domain. The gust factor reaches its maximum at the moment when the peak wind speed occurs. Full article

This paper presents research on the effects of the addition of various contents of graphene oxide and sintering temperature on the mechanical, tribological, and electrical characteristics of WC-ZrO₂ composites. Wet processing and spark plasma sintering provided dense samples with simultaneous reduction of graphene oxide (rGO) during sintering. The obtained results showed that the best mechanical properties were observed at a sintering temperature of 1700 °C in samples with 0.5 vol.% rGO content; namely, indentation fracture toughness (5.8 ± 0.4 MPa·m^1/2) and flexural strength (872 ± 43 MPa) increased by 9% and 24.3% compared with the sample without rGO. In addition to improved mechanical performance, rGO-reinforced composites exhibited lower wear rates and friction coefficients than non-rGO composites, due to the formation of a graphitic lubricating tribolayer on worn surfaces and counterbodies in a friction pair, which provided sufficient lubrication to reduce the coefficient of friction and wear rate. The resulting composites also showed low electrical resistivity, suggesting the possibility of using electrical discharge machining to manufacture ceramic products of complex shapes from them. Full article

This study explored how post-casting heat treatment and forging affected the tribological and microstructural characteristics of 0.20% beryllium (Be)-added CuAl₁₀Ni₅Fe₄ alloys. The heat-treated CuAl₁₀Ni₅Fe₄ microstructure exhibits a copper-rich α (alpha)-solid-solution phase, a martensitic β (beta)-phase, and diverse intermetallic κ (kappa)-phases, such as leaf-shaped κ_I, thin κ_III, and black globs. Adding 0.20% beryllium to CuAl₁₀Ni₅Fe₄ alloys enhanced the dendritic arm thickness, needle-like shape, and κ-phase quantities. Significant κ_IV- and κ_II-phase precipitation was observed in the tempered β-phase. Beryllium improves the aluminum matrix’s microstructure. Forging greatly reduced the microstructural thickness of CuAl₁₀Ni₅Fe₄ and CuAl₁₀Ni₅Fe₄-0.20% Be alloys. The forging process also developed new κ_IV-phases. Wear resistance and hardness improved with beryllium. The CuAl₁₀Ni₅Fe₄-0.20% Be alloy had the highest hardness values (235.29 and 255.08 HB) after solution treatment (ST) and tempering (T) after casting and forging (F). The CuAl₁₀Ni₅Fe₄-0.20% alloy with Be added had the best wear after solution treatment, tempering, and forging. The CuAl₁₀Ni₅Fe₄-0.20% Be alloy demonstrated a 0.00272 g weight loss, a 1.36 × 10⁻⁸ g/N*m wear rate, and a 0.059 friction coefficient at 10,000 m after forging (F). Full article

Activated carbons can be applied in various areas of our daily life depending on their properties. This study was conducted to investigate the effect of thermal treatment of activated carbon on its properties, considering its future use. The characteristics of activated carbon heat-treated at temperatures of 1500, 1800, and 2100 °C based on its future use are presented. The significant effect of the treatment temperature on morphological, adsorption, electrochemical, and corrosion properties was proved. Increasing the temperature above 1800 °C resulted in a significant decrease in the specific surface area (from 969 to 8 m²·g⁻¹) and material porosity—the formation of mesopores (20–100 nm diameter) was observed. Simultaneously, adsorption capability, double layer capacity, and electrochemically active surface area also decreased, which helped to explain the shape of cyclic voltammograms recorded in 2,4-dichlorophenoxyacetic acid and in supporting electrolytes. However, a significant increase in corrosion resistance was found for the carbon material treated at a temperature of 2100 °C (corrosion current decreased by 23 times). Comparison of morphological, adsorption, corrosion, and electrochemical characteristics of the tested activated carbon, its applicability as an electrode material in electrical energy storage devices, and materials for adsorptive removal of organic compounds from wastewater or as a sensor in electrochemical determination of organic compounds was discussed. Full article

No matter where we reside, the issue of greenhouse gas emissions impacts us all. Their influence has a disastrous effect on the earth’s climate, producing global warming and many other irreversible environmental impacts, even though it is occasionally invisible to the independent eye. Phase change materials (PCMs) can store and release heat when it is abundant during the day (e.g., from solar radiation), for use at night, or on chilly days when buildings need to be heated. As a consequence, buildings use less energy to heat and cool, which lowers greenhouse gas emissions. Consequently, research on thermally active medium-density fiberboard (MDF) with PCMs is presented in this work. MDF is useful for interior design and furniture manufacturing. The boards were created using pine (Pinus sylvestris L.) and spruce (Picea abies L.) fibers, urea–formaldehyde resin, and PCM powder, with a phase transition temperature of 22 °C, a density of 785 kg m⁻³, a latent heat capacity of 160 kJ kg⁻¹, a volumetric heat capacity of 126 MJ m⁻³, a specific heat capacity of 2.2 kJ kgK⁻¹, a thermal conductivity of 0.18 W mK⁻¹, and a maximum operating temperature of 200 °C. Before resination, the wood fibers were divided into two outer layers (16%) and an interior layer (68% by weight). Throughout the resination process, the PCM particles were solely integrated into the inner layer fibers. The mats were created by hand. A hydraulic press (AKE, Mariannelund, Sweden) was used to press the boards, and its operating parameters were 180 °C, 20 s/mm of nominal thickness, and 2.5 MPa for the maximum unit pressing pressure. Five variants of MDF with a PCM additive were developed: 0%, 5%, 10%, 30%, and 50%. According to the study, scores at the MOR, MOE, IB, and screw withdrawal resistance (SWR) tests decreased when PCM content was added, for example, MOE from 3176 to 1057 N mm⁻², MOR from 41.2 to 11.5 N mm⁻², and IB from 0.78 to 0.27 N mm⁻². However, the results of the thickness swelling and water absorption tests indicate that the PCM particles do not exhibit a substantial capacity to absorb water, retaining the dimensional stability of the MDF boards. The thickness swelling positively decreased with the PCM content increase from 15.1 to 7.38% after 24 h of soaking. The panel’s thermal characteristics improved with the increasing PCM concentration, according to the data. The density profiles of all the variations under consideration had a somewhat U-shaped appearance; however, the version with a 50% PCM content had a flatter form and no obvious layer compaction on the panel surface. Therefore, certain mechanical and physical characteristics of the manufactured panels can be enhanced by a well-chosen PCM addition. Full article

In this study, a new polyionic polymer inhibitor, TIL-NH₂, was developed to address the instability of shale gas horizontal wells caused by water-based drilling fluids. The structural characteristics and inhibition effects of TIL-NH₂ on mud shale were comprehensively analyzed using infrared spectroscopy, NMR spectroscopy, contact angle measurements, particle size distribution, zeta potential, X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy. The results demonstrated that TIL-NH₂ significantly enhances the thermal stability of shale, with a decomposition temperature exceeding 300 °C, indicating excellent high-temperature resistance. At a concentration of 0.9%, TIL-NH₂ increased the median particle size of shale powder from 5.2871 μm to over 320 μm, effectively inhibiting hydration expansion and dispersion. The zeta potential measurements showed a reduction in the absolute value of illite’s zeta potential from −38.2 mV to 22.1 mV at 0.6% concentration, highlighting a significant decrease in surface charge density. Infrared spectroscopy and X-ray diffraction confirmed the formation of a close adsorption layer between TIL-NH₂ and the illite surface through electrostatic and hydrogen bonding, which reduced the weakly bound water content to 0.0951% and maintained layer spacing of 1.032 nm and 1.354 nm in dry and wet states, respectively. Thermogravimetric analysis indicated a marked reduction in heat loss, particularly in the strongly bound water content. Scanning electron microscopy revealed that shale powder treated with TIL-NH₂ exhibited an irregular bulk shape with strong inter-particle bonding and low hydration degree. These findings suggest that TIL-NH₂ effectively inhibits hydration swelling and dispersion of shale through the synergistic effects of cationic imidazole rings and primary amine groups, offering excellent temperature and salt resistance. This provides a technical foundation for the low-cost and efficient extraction of shale gas in horizontal wells. Full article

A tremendous increase in the green synthesis of metallic nanoparticles has been noticed in the last decades, which is due to their unique properties at the nano dimension. The present research work deals with synthesis mediated by the actinomycete Streptomyces tendae of silver nanoparticles (AgNPs), isolated from Little and Greater Rann of Kutch, India. The confirmation of the formation of AgNPs by the actinomycetes was carried out by using a UV-Vis spectrophotometer where an absorbance peak was obtained at 420 nm. The X-ray diffraction pattern demonstrated five characteristic diffraction peaks indexed at the lattice plane (111), (200), (231), (222), and (220). Fourier transform infrared showed typical bands at 531 to 1635, 2111, and 3328 cm⁻¹. Scanning electron microscopy shows that the spherical-shaped AgNPs particles have diameters in the range of 40 to 90 nm. The particle size analysis displayed the mean particle size of AgNPs in aqueous medium, which was about 55 nm (±27 nm), bearing a negative charge on their surfaces. The potential of the S. tendae-mediated synthesized AgNPs was evaluated for their antimicrobial, anti-methicillin-resistant Staphylococcus aureus (MRSA), anti-biofilm, and anti-oxidant activity. The maximum inhibitory effect was observed against Pseudomonas aeruginosa at (8 µg/mL), followed by Escherichia coli and Aspergillus niger at (32 µg/mL), and against Candida albicans (64 µg/mL), whereas Bacillus subtilis (128 µg/mL) and Staphylococcus aureus (256 µg/mL) were much less sensitive to AgNPs. The biosynthesized AgNPs displayed activity against MRSA, and the free radical scavenging activity was observed with an increase in the dosage of AgNPs from 25 to 200 µg/mL. AgNPs in combination with ampicillin displayed inhibition of the development of biofilm in Pseudomonas aeruginosa and Streptococcus pneumoniae at 98% and 83%, respectively. AgNPs were also successfully coated on the surface of cotton to prepare antimicrobial surgical cotton, which demonstrated inhibitory action against Bacillus subtilis (15 mm) and Escherichia coli (12 mm). The present research integrates microbiology, nanotechnology, and biomedical science to formulate environmentally friendly antimicrobial materials using halotolerant actinomycetes, evolving green nanotechnology in the biomedical field. Moreover, this study broadens the understanding of halotolerant actinomycetes and their potential and opens possibilities for formulating new antimicrobial products and therapies. Full article