Search Results (2,861)

Continuous gas leakage in thin-walled sealed spacecraft structures produces sustained broadband acoustic-emission (AE) signals from which reliable first-arrival picking is difficult. This study presents an interpretable two-stage workflow that decouples leak screening from regional localization. Experiments used a 500 × 500 × 2.5 mm 3A21 aluminum-alloy plate with eight piezoelectric AE sensors under 0.1 MPa pressure difference. Intact, circular-hole, and slit-leak conditions were each tested three times with a 0.5–1.5 s steady-state window. Leak screening employed the 20–200 kHz mean spectral amplitude (Hann window). A provisional threshold of 0.85, set from three intact records, separated all leak records from intact controls. Regional localization used relative logarithmic RMS amplitudes in an energy-decay plus maximum-likelihood-estimation (ED+MLE) cost function on a 10 mm grid. The equivalent attenuation coefficient, empirically selected as 2.3 m⁻¹ using the 1 mm central-hole calibration case, gave a 10 mm grid error for that calibration demonstration. With this coefficient fixed, the four transfer conditions yielded mean localization errors of 19.6–45.7 mm. The results provide preliminary feasibility evidence for leak detection and regional localization under the controlled laboratory conditions investigated in this study. Further validation requires independent channel calibration, larger background datasets, leak-rate measurements, parameter-sensitivity analysis, and testing on more representative structures. Full article

This study aimed to develop polymer matrix nanocomposites reinforced with Al₂O₃ nanoparticles to enhance the mechanical properties of PMMA. The composite was fabricated via friction stir processing (FSP) to ensure the homogenous dispersion of Al₂O₃ nanoparticles in the polymer. A grid of 5 holes in a 7 × 7 mm² area was made in which the hole diameter was varied from 1.77 mm to 2.28 mm to obtain different volume fractions of reinforcement ranging from 15% to 25%. The holes were made with a depth of 3 mm in a 4 mm-thick PMMA sheets. After packing the Al₂O₃ powder in the holes, a 2 mm-thick PMMA sheet was used as a cover to prevent the sputtering of nanoparticles. A number of FSP parameters were examined. The tool rotation rates ranged from 800 to 1200 rpm, traverse speeds of 25 and 50 mm/min, and tool tilts of 1 and 2° were used. A soft paraffin (Vaseline) layer was used on the top surface to prevent severe shoulder friction with the PMMA plate, which caused severe wear and thinning on the surface. For the developed PMMA/Al₂O₃ nanocomposites, the surface quality, SEM microstructure, impact energy, and transverse hardness were investigated. Good surface quality and dispersion of nanoparticles were attained by employing adequate processing conditions. The experimental results indicated that as the nanoparticle percentage increased, impact energy, hardness, and tensile strength increased, reaching 2 kJ/m², 14.7 HV, and 52.1 MPa at a nanoparticle concentration of 25%. This means that the polymer ceramic composite’s toughness, hardness, and tensile strength are higher than those of unprocessed PMMA by 66%, 33%, and 23%, respectively. Full article

The creation of new settlements on the Moon is an extraordinary opportunity for both economic and research purposes, but it is hindered by the prohibitive costs of transporting materials from Earth. In this frame, in situ resource utilization (ISRU) can significantly reduce these costs by exploiting lunar regolith, the Moon’s most abundant resource. In this work, a lunar regolith simulant is aggregated by an innovative manufacturing process based on geopolymerization. Bricks were obtained by mixing the simulant with a small amount of sodium hydroxide solution, followed by cold compaction at 20 MPa and oven drying at 500 °C for 1 h. Regolith bricks reinforced with unidirectional dry carbon fibers were manufactured by alternating the regolith-based mixture with layers of CFs. Mechanical properties were evaluated by bending and compression tests. Neat bricks were manufactured for comparison. Improvements in mechanical behavior were obtained thanks to fiber insertion, mainly in terms of resilience, even if stress at break is not improved. In compression, fibers limit brittle behavior, resulting in an average increase in toughness of 59.5%. Fast curing time and limited water consumption, compared to the traditional geopolymerization process, make this manufacturing process highly attractive to obtain lunar regolith bricks. Full article

This study investigated the ultrasound-assisted extraction (UAE) of gelatin from the swim bladder (SB) of Asian sea bass (Lates calcarifer) and evaluated its physicochemical and film-forming properties in comparison to commercial bovine and fish skin gelatins. UAE significantly enhanced the extraction efficiency, achieving a yield of 85.26–91.62% (dry weight) within 1–2 h, compared to 78.81% obtained through a 6 h conventional hot-water method. The SB gelatin optimally extracted via UAE for 1 h showed the presence of high-molecular-weight protein cross-links ($\beta$- and $\gamma$-chains). Consequently, it exhibited a gel strength of 258.64 g, which was higher than that of commercial fish skin gelatin (233.35 g), despite possessing a lower hydroxyproline content (47.30 mg/g). Furthermore, the SB gelatin demonstrated viable film-forming capabilities when incorporated with 25% (w/w) of hydrophilic plasticizers (glycerol, PEG-400 and a 1:1 mixture). The resultant SB films displayed higher tensile strength (60.93–71.56 MPa) and lower elongation at break compared to films derived from both commercial marine and bovine gelatins (p < 0.05). Among the evaluated plasticizers, glycerol yielded films with higher initial mechanical flexibility (indicated by the lowest elastic modulus), while the binary mixture of glycerol and PEG-400 provided the most effective water vapor barrier for the SB gelatin films. Overall, UAE-extracted Asian sea bass swim bladder represents a potential alternative source of gelatin that exhibits preliminary potential for bio-based packaging applications. Full article

The increasing polypropylene (PP) plastic cup waste requires sustainable utilization. This study examines the effect of adding 45 mm PP waste fibers on concrete flexural strength and its compliance with the 2018 Bina Marga Specification. Using an experimental method, beam specimens (15 × 15 × 60 cm) and cylinders (15 × 30 cm) with fc’ 25 MPa were tested. Variations included normal concrete, concrete with 1% PP fibers, and nylon fibers. At 28 days, flexural strengths were 4.27 MPa (normal), 3.56 MPa (PP), and 3.89 MPa (nylon), all below the 4.7 MPa requirement. However, fiber addition enhanced beam ductility, supporting PP waste as a potential eco-friendly material for rigid pavement. Full article

The trade-off between flowability and anti-dispersion properties of alkali-activated slag slurry in underwater environments represents a key technical bottleneck limiting their application in marine underwater engineering. In this study, granulated blast furnace slag (GGBS) was used as the raw material, with the modulus of liquid sodium silicate adjusted by NaOH serving as the alkali activator, and hydroxypropyl methylcellulose (HPMC) and polyacrylamide (PAM) selected as anti-dispersion agents. This study systematically investigates the synergistic regulation mechanisms of the anti-dispersion agents’ type, dosage, and activator on the anti-dispersion properties and rheological behavior of alkali-activated slag slurry, and revealed the evolution mechanisms of the microstructure of the hardened slurry through X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) analysis. The results indicate that the activator is the key factor in regulating the various properties of the slurry, and the combination of PAM and HPMC produces a significant synergistic effect. At the optimal formulation (modulus of 1.0, total blended anti-dispersion agent content of 1%, and a mass ratio of PAM to HPMC of 1:1), the slurry exhibited a wet loss rate of 38.45%, a solid retention rate of 89.98%, a flow value of 195 mm, and a 28-day compressive strength of 41.62 MPa, achieving an optimal balance between anti-dispersion performance and workability. Full article

Pneumatic soft actuators have been drawing considerable attention in the field of soft robotics, thanks to their inherent flexibility, high power density, and safe interaction. However, the strong, intricate coupling between the material’s hyperelastic behavior and the reinforcement of anisotropic fibers creates significant challenges for both analytical modeling and numerical characterization of these actuators. In this paper, we design and fabricate a fiber-reinforced pneumatic soft actuator using Ecoflex 00-30 silicone rubber as the base material and helically wound fibers as the reinforcing layer. We set up a theoretical framework that combines the Neo-Hookean model for isotropic silicone rubber with a strain energy-based formulation for anisotropic wound fibers. This framework describes how the actuator is stretched, expanded, twisted, and bent. Finite element simulations are then carried out, focusing on three key design parameters: winding fiber density (three levels: high, medium, low), air cavity offset distance from the central axis (1, 2, 3, and 4 mm), and air cavity cross-sectional geometry (cube vs. cylindrical). The simulations reveal that a higher winding fiber density promotes more uniform stress distribution across both the strain and confinement layers. In contrast, a low fiber density can lead to local bulging and large stress variations, which ultimately compromises the bending performance. The offset distance of the air cavity from the neutral axis is directly linked to the bending curvature: a larger offset produces greater air cavity deformation and higher actuation efficiency. Furthermore, the cuboid air cavity yields a larger bending angle (experimentally validated up to 90° at 0.045 MPa) and better efficiency, while the cylindrical air cavity distributes stress more evenly across the outer surface of the strain layer and reduces stress concentration at the edges. These findings provide useful quantitative guidance for optimizing the structure of fiber-reinforced soft actuators and establish a framework for hybrid analytical–numerical prediction of their mechanical behavior. Full article

Confronted with severe global challenges, including water scarcity, excessive use of chemical fertilizers and pesticides, and heavy metal contamination in soils, conventional agricultural technologies exhibit marked limitations in integrated water–fertilizer management and non-point source pollution control. Leveraging their excellent water retention capacity, intelligent sustained-release properties, and environmental responsiveness, hydrogels offer innovative solutions to advance sustainable agricultural development. This review comprehensively outlines the fundamental types, crosslinking mechanisms, and key functional properties of hydrogels, with a focused discussion on their agricultural deployment as high-efficiency soil conditioners, fertilizer vectors, and pesticide carriers; it deciphers the microscopic water-holding mechanisms under the tristate water model, delineates the divergent water-uptake and retention behaviors between ionic and non-ionic hydrogels, and clarifies the cyclic water-holding and release mechanisms of hydrogels during soil amelioration. Thise paper further synthesizes hydrogel-enabled environmental remediation applications, in which heavy metals and pesticide residues in soils and aquatic systems are removed via functional-group coordination adsorption or photocatalytic degradation; concurrently, hydrogels have been shown to activate plant systemic immunity through calcium-signaling pathways, thereby inducing broad-spectrum antiviral defense responses. Moreover, hydrogels can be integrated into precision agriculture frameworks to enable real-time monitoring of crop physiological status and to support targeted irrigation and fertilization management. This work also evaluates the role of hydrogels in promoting seed germination, root system development, crop metabolic regulation, and stress resilience, while introducing tailored application strategies across distinct plant growth stages. Their documented economic advantages include water conservation, enhanced crop yields, reduced dependence on synthetic fertilizers, and lower labor costs. Nevertheless, the large-scale implementation of hydrogels continues to face multifaceted challenges—particularly poor degradability and latent ecological risks, as conventional polyacrylamide (PAM)-based gels resist soil mineralization and retain potentially neurotoxic monomers, leaving a critical gap in multi-annual field data concerning their non-target interference with native soil aggregate evolution, pore distribution, and rhizospheric carbon–nitrogen footprints. Mechanistically, many hydrogels with tensile strengths below 1 MPa are highly susceptible to three-dimensional network collapse under high-salinity osmotic shock and tillage mechanical stress, exhibiting a precipitous drop in water retention after more than three wet–dry cycles due to deficient long-term structural stability. Compounding these technical gaps are elevated production costs and low farmer adoption, driven by the absence of texture-specific performance thresholds—such as an available water increment ≥ 40% for sandy soils—and the lack of established life-cycle cost models and farmer incentive mechanisms for bio-based hydrogels. Moving forward, hydrogel technology should pivot toward materials innovation and cost-reduction engineering to broaden its applicability, employ ≥3-year, multi-habitat regional trials to delineate ecological benefit–risk boundaries, and ultimately position hydrogels as pivotal enablers of sustainable, green agricultural paradigms. Full article

Magnesium alloys are attractive for temporary orthopaedic applications because of their biodegradability and favourable mechanical properties; however, their relatively rapid degradation under physiological conditions remains a challenge. In this study, the microstructural evolution, residual stress and electrochemical corrosion behaviour of WE43, a rare earth-containing magnesium alloy with yttrium, neodymium and zirconium as alloying elements, coated with titanium, were investigated as functions of deposition time using direct-current magnetron sputtering. Titanium coatings were deposited for 1, 1.5, 2 and 3 h, producing coating thicknesses of approximately 500, 650, 1000 and 1400 nm, respectively. Field-emission scanning electron microscopy, atomic force microscopy and grazing-incidence X-ray diffraction revealed progressive changes from fine-grained to dense and, subsequently, coarse-grained morphologies with increasing deposition time. The 2 h coating exhibited the largest crystallite size (27.17 ± 3.42 nm) and a moderate compressive residual stress of 605.3 ± 15.11 MPa. Potentiodynamic polarisation measurements showed that the 2 h coating produced the lowest corrosion current density (0.133 ± 0.026 mA/cm²) and calculated corrosion rate (2.93 ± 0.57 mm/year), representing a 67% reduction relative to independently measured, uncoated WE43 (8.87 ± 1.11 mm/year). The 3 h coating exhibited a higher compressive residual stress of 992.4 ± 21.7 MPa and a higher corrosion rate of 4.81 ± 0.74 mm/year, accompanied by localised microcracking after corrosion testing. Contact-angle measurements performed on the uncoated alloy and the 2 h coating showed an increase from 75.0 ± 2.1° to 83.0 ± 1.8°. Overall, the results indicated that corrosion performance was governed by the combined effects of coating morphology, crystallographic development and residual stress, with the 2 h deposition condition providing the most favourable balance under the present experimental conditions. Full article

This study presents a physics-informed, climate-responsive model for predicting carbonation depth and compressive strength degradation in conventional and sustainable cementitious composites under real environmental exposure. The Semi-Theoretical Predictive Degradation (STPD) model couples hourly temperature, relative humidity, and CO₂ concentration data with two-dimensional diffusion–reaction equations implemented in FEniCS. The model accounts for humidity-sensitive diffusivity, temperature-activated carbonation kinetics, and CO₂ consumption via Langmuir decay. Experimental validation was performed on ordinary Portland cement (OPC) concrete specimens exposed for 30 days to climate profiles representative of Portugal (average 14.2 °C, RH 74%, CO₂ ~417 ppm) and Slovakia (average 4.7 °C, RH 80%, CO₂ ~414 ppm). Carbonation depth increased from 0 to 0.30 mm in Portugal and up to 0.15 mm in Slovakia, with corresponding predicted reductions in compressive strength relative to the corresponding uncarbonated reference of up to 25% and 14%, respectively. The STPD model accurately reproduced these trends, achieving RMSE values of 0.008 mm for carbonation depth and 1.55 MPa for compressive strength in OPC concrete. To assess the broader applicability of the framework, simulations were extended to fly ash/slag-blended, geopolymer, and biochar-containing concretes using material-specific parameters. Among the simulated systems, geopolymer concrete showed the highest predicted durability, with carbonation depths below 1 mm and strength loss below 10%. A degradation index combining carbonation depth and strength loss mapped high-risk zones near the exposed surface, particularly under warm and fluctuating climatic conditions. The model provides a transferable framework for climate-informed durability assessment, material selection, and the design of sustainable cementitious composites. Full article

Boron carbide (B₄C) ceramics suffer from poor sinterability and inherent brittleness, which severely limit their engineering applications. In this work, B₄C–graphene nanoplatelet (GNP) composites were fabricated by hot pressing using heterogeneously co-precipitated powder mixtures, with cetyltrimethyl ammonium bromide (CTAB) as a surfactant for achieving uniform dispersion of GNPs within the B₄C matrix. The formation mechanisms of B₄C–GNP hybrids were systematically elucidated. The results show that CTAB endows GNPs with positive charges, enabling electrostatic co-precipitation with negatively charged B₄C particles to construct layered hybrid architectures. The GNP content has a significant modulation effect on the microstructure and mechanical properties of B₄C composites. A maximum relative density of 99.65%, Vickers hardness of 33.5 GPa, and flexural strength of 488 MPa were obtained at 1 wt% GNPs, while the fracture toughness reached a peak value of 4.89 MPa·m^1/2 at 2 wt% GNPs, representing a 63.5% improvement over monolithic B₄C. The enhanced fracture toughness is attributed to multiple toughening mechanisms, including crack deflection, crack bridging, GNP pull-out, step-like fracture, and zigzag crack propagation. This study provides a feasible strategy for preparing uniformly dispersed ceramic–graphene composites with balanced mechanical properties. Full article

With the continuous advancement of deep and ultra-deep well drilling technologies, formations with complex pressure windows are becoming increasingly common. During casing running operations, it is necessary to ensure both leak prevention in loss-prone formations and pressure stabilization in high-pressure formations, demanding increasingly higher accuracy in wellbore pressure calculation. This study establishes a wellbore pressure calculation model for managed pressure casing (MPC) running in deep wells, specifically addressing the scenario where a multi-density gradient drilling fluid column exists in the annulus after tripping out. The model’s novelty lies in integrating transient surge pressure calculation with a dynamic fluid column structure model that tracks the displacement of multi-density drilling fluid layers during casing running. The governing equations based on one-dimensional unsteady flow theory are solved using the method of characteristics with adaptive time stepping and a grid independence study confirming the discretization scheme. Quantitative analysis reveals that casing running speed is the dominant factor affecting surge pressure; when the speed increases from 0.5 m/s to 1.5 m/s, the surge pressure increases from approximately 1.2 MPa to 3.5 MPa at a 2000 m depth. Drilling fluid properties also significantly influence surge pressure: increasing the density from 2.0 g/cm³ to 2.22 g/cm³ results in a surge pressure increase of approximately 0.6 MPa; increasing the yield value from 2.85 Pa to 15 Pa leads to an increase of about 1.1 MPa; the surge pressure shows a clear increasing trend with both the consistency coefficient and flow behavior index. Casing running depth affects the buffering effect of the bottomhole flow channel; when the casing is run to 7000 m, the surge pressure is approximately 0.5 MPa higher than at 2000 m. Taking a typical deep well (8578 m) with a negative pressure window of −0.008 g/cm³ as an example, three casing running speed plans were designed and evaluated. Plan 1 was selected with running speeds ranging from 0.16 m/s in the upper section to 0.115 m/s in the lower section, maintaining the equivalent circulating density (ECD) within the safe density window throughout the entire operation. Field application of this plan proceeded smoothly without any occurrences of lost circulation or overflow. This provides a practical basis for MPC running technology in deep wells with narrow or negative pressure windows. Full article

Finely dispersed Al–Ca–Ti composite alloys with a set of remarkable properties can be considered as new promising structural materials. For wider use of these alloys, data on their fatigue behavior are needed. In this work the comparative study of the low-cycle fatigue strength of hot-rolled Al–xCa–0.2Ti alloys with different eutectic fractions determined by different calcium contents was conducted. The fatigue tests were carried out according to a single-plane bending scheme using a dynamic mechanical analyzer. A symmetrical loading cycle (asymmetry coefficient R = −1) with a constant stress amplitude was used. The maximum number of cycles was 20,000. It was found that increasing the eutectic fraction from 40% to 80% led to a 75% increase in the fatigue limit—from 80 to 140 MPa—which directly correlated with the alloy’s yield strength. The fatigue crack propagation occurred with the formation of a scaly fracture surface, whereas final static rupture was associated with a ductile dimple fracture. The microstructural mechanisms of alloy fatigue failure were discussed. It was found that increasing the total length of the eutectic particles/aluminum matrix interphase boundaries changed the failure mechanism to a more brittle one. Full article

Loess is highly water-sensitive and collapsible, and its conventional use as backfill in road and railway infrastructure may lead to settlement and deformation after wetting. Converting excavated loess into controlled low-strength material (CLSM) provides an alternative for backfilling; however, its engineering performance is strongly dependent on the water-to-solids ratio (W). In field construction, variations in the natural moisture content of loess cause the actual W to deviate from its design value, whereas conventional CLSM mix designs generally assume a fixed W, which may result in insufficient flowability or strength under actual field conditions. A Box–Behnken design was first employed to investigate the effects of the cement-to-soil ratio (C), water-to-solids ratio (W), and polycarboxylate superplasticizer content (P) on flowability (f), bleeding rate (Bᵥ), wet density (ρ), and 28-day compressive strength (qᵤ), based on which regression-based predictive models were developed. The sequential least squares programming (SLSQP) algorithm was then used to optimize mix proportions for backfilling behind abutments, culverts, and retaining walls and for subgrade backfilling. The optimization minimized the material cost per unit volume while requiring all performance indicators to satisfy the specified criteria under variations in W (ΔW = 0%, ±1%, ±2%, and ±3%). The results show that W is the dominant factor governing f, Bᵥ, and ρ, whereas C has the greatest influence on qᵤ. Increasing P markedly improves f but also increases Bᵥ. For backfilling behind abutments, culverts, and retaining walls, when the mean field soil moisture content is overestimated and the actual W is consequently lower than its design value, the mix optimized for ΔW = −3% satisfies the flowability criterion even when the measured flowability is up to 21.3 mm below the design value because of the lower actual soil moisture content. Conversely, when the mean field soil moisture content is underestimated and the actual W exceeds its design value, the mix optimized for ΔW = +3% satisfies the compressive-strength criterion even when the measured strength is up to 0.09 MPa below the design value because of the higher actual soil moisture content. Accounting for possible variations of up to ±3% in the water-to-solids ratio under field conditions, the optimal mix proportions are C13.14W37.64P0.069 for backfilling behind abutments, culverts, and retaining walls and C15.00W34.28P0.097 for subgrade backfilling. These findings provide a basis for the performance control and mix design of loess-based CLSM subjected to variations in the water-to-solids ratio. Full article

High-performance alkali-free accelerators require a mechanistic understanding of interactions between inorganic accelerants and organic modifiers. Although aluminum sulfate (AS) promotes rapid ettringite (AFt) formation, uncontrolled crystallization leads to coarse microstructures and instability from AFt-to-AFm conversion. Here, a molecular-scale synergistic mechanism is identified in which an amide regulates AS-driven hydration. The amide controls nucleation and growth of AFt and C–S–H via chemisorption on C₃A/C₃S and complexation with Ca²⁺. Within the tested mixing proportions, the high-aluminum-sulfate and moderate-amide combination achieves the highest early strength (17.05 MPa at 1 day) via constructing an interlocked AFt/C–S–H skeleton, whereas excessive amide suppresses crystallization and low AS accelerates AFt-to-AFm conversion, reducing long-term performance. In-situ XRD, thermal analysis, and microscopy confirm a denser, more stable microstructure (27.37 MPa at 10 days) with minimal 28-day strength loss (17.38 MPa). Density functional theory shows an adsorption hierarchy of amide > AS species > H₂O, explaining its dominant surface-modifying role. This study provides a framework for designing cement accelerators with balanced early strength and durability. Full article