Search Results (514)

Graphite anodes are widely used as consumable electrodes in the high-temperature electrolytic production of rare earth metals within fluoride molten salts. However, their rapid and complex corrosion presents significant economic and operational challenges, including high consumption costs, process instability, greenhouse gas emissions, and product contamination. While the corrosion morphology of specific graphite types has been studied, a systematic investigation linking the intrinsic properties of diverse graphite materials to their microstructural and chemical evolution during corrosion is lacking. This study elucidates the corrosion mechanisms of three distinct graphite anodes—fine-grained, isostatically pressed graphite anodes (#1), medium-coarse-grained, extruded graphite anodes (#2), and recycled, extruded graphite anodes (#3) in industrial PrNdF₃–LiF molten salt electrolytes at 1050 °C. Through a multifaceted analytical approach encompassing SEM, EDS, XRD, Raman, and FT-IR, we investigated the macro- and microscale corrosion behaviors across multiple scales. The results revealed markedly different degradation patterns: the #1 anode exhibited intergranular corrosion with granular exfoliation; the #2 anode developed a protective but cracked resolidified salt layer; and the #3 anode suffered the most severe uniform and pitting corrosion. Postcorrosion analysis confirmed surface enrichment with fluorine, praseodymium, and neodymium, the formation of PrF₃ and NdF₃ phases, and substantial degradation of the graphitic structure. Raman spectroscopy specifically revealed a reduction in the crystallite size, introduction of in-plane point defects, and disruption of the interlayer stacking order. On the base of infrared spectroscopy analysis, all key characteristic absorption peaks of the graphite anodes undergo consistent attenuation after corrosion. This work provides critical insights for the informed selection and optimization of graphite anodes to increase the efficiency and sustainability of rare earth electrolysis. Full article

Nanofibers, with their lightweight structure and superior sound absorption, are promising materials for noise control in automotive and architectural applications. However, due to the complex porous structure of nanofibers, established acoustic models often fail to accurately quantify the microstructure’s influence on sound absorption characteristics, resulting in substantial prediction errors. To determine the sound absorption characteristics of nanofibers, an equivalent fiber network model was developed using the multiscale finite element analysis (MFEA) method based on SEM images of nanofibers. The slip boundary condition (SBC) was then applied to calculate the microstructural parameters necessary for macroscopic characterization. The sound absorption coefficients of nanofibers were characterized using three acoustic models, and the results were compared with the experimental data. The predictions of the Limp frame model agreed well with the experimental data within the 500–6400 Hz frequency range. Through use of the multiscale model developed in this study, a deterministic relationship between microstructure and acoustic properties was established, revealing that the inertial interactions between sound waves and the nanofiber skeleton, as well as the slip boundary effect at the nanofiber surfaces, are among the primary mechanisms contributing to the flow resistance and superior sound absorption performance of nanofibers. Full article

Thick steel plates in bridges exhibit mechanical property gradients along their thickness, yet the underlying micro-mechanisms remain unclear. This study investigates an 80 mm thick 420 MPa-grade HSLA steel plate, and also quantitatively investigates the mechanism of its mechanical gradient behavior in the thickness direction through layered tensile tests combined with multi-scale microstructural characterization. The unique contribution of this work lies in establishing a quantitative correlation between the gradient in the dislocation density and the transition in yielding behavior. The results show that the surface layer area of the tested steel exhibited continuous yield characteristics, while all core layers exhibited pronounced discontinuous yielding. The mechanical properties showed a gradient distribution along the thickness direction, with the yield strength and tensile strength decreasing from 512.4 MPa and 545.9 MPa at the surface to 419.5 MPa and 520.4 MPa at the center (1/2t). Microstructural analysis shows that the full-thickness structure was composed of granular bainite (GB) and polygonal ferrite (PF). With respect to increases with depth, the average grain size increased from 6.86 µm at the surface to 11.57 µm at the center. Moreover, the surface region exhibited a broader grain size distribution range and higher size dispersity. The second-phase precipitates in the full thickness were mainly of two types, namely, Fe₃C and (Nb, Ti) (C, N) composite precipitates, and the precipitates in the surface layer had smaller sizes and higher distribution densities. Crucially, the dislocation density decreased sharply from the surface to 1/8t, then stabilized. While quantitatively elucidating the contributions of various strengthening mechanisms to the strength gradient, the mechanistic analysis also reveals a dislocation microstructure synergistic mechanism underlying the yield behavior differences. Full article

The rapid expansion of island and reef infrastructure has intensified the demand for sustainable concrete materials, yet the scarcity of conventional aggregates and freshwater severely constrains their supply. More critically, the fundamental bonding mechanism between steel reinforcement and coral aggregate concrete (CAC) remains poorly understood due to the highly porous, ion-rich nature of coral aggregates and the complex interfacial reactions at the steel–cement–coral interface. Moreover, the synergistic effect of polyoxymethylene (POM) fibers in modifying this interfacial behavior has not yet been systematically quantified. To fill this research gap, this study develops a C40-grade POM-fiber-reinforced CAC and investigates the composition–property relationship governing its bond performance with steel bars. A comprehensive series of pull-out tests was conducted to examine the effects of POM fiber dosage (0, 0.2%, 0.4%, 0.6%, 0.8%, and 1.0%), protective layer thickness (32, 48, and 67 mm), bar type, and anchorage length (2 d, 3 d, 5 d, and 6 d) on the interfacial bond behavior. Results reveal that a 0.6% POM fiber addition optimally enhanced the peak bond stress and restrained radial cracking, indicating a strong fiber-bridging contribution at the micro-interface. A constitutive bond–slip model incorporating the effects of fiber content and c/d ratio was established and experimentally validated. The findings elucidate the multiscale coupling mechanism among coral aggregate, POM fiber, and steel reinforcement, providing theoretical and practical guidance for the design of durable, low-carbon marine concrete structures. Full article

Selenium (Se) is an essential trace element for human health, which is crucial for antioxidant defense, immune function, and disease prevention. Se deficiency affects around 40 countries worldwide, with China being one of the most severely impacted. While previous research has explored factors influencing soil Se content, such as the parent material, climate, and soil properties, the dominant controlling mechanisms across different spatial scales remain a subject of debate, especially in the Se-rich coastal regions of southeastern China. This study focuses on Fujian Province, using hotspot analysis and geographically weighted regression (GWR) to systematically examine the spatial distribution of soil Se and its key influencing factors. Hotspot analysis reveals multi-scale patterns in Se distribution: at the 1 km scale, Se hotspots are closely linked to metal minerals like sulfide and coal deposits; at the 2 km scale, Se-rich carbonate rocks and carbonaceous mudstones dominate; and, at the 10 km scale, Se accumulation is mainly controlled by organic matter and low-temperature conditions in high-altitude areas (≥1200 m). GWR analysis further clarifies the nonlinear relationships between soil Se and key environmental factors: organic matter strongly correlates with Se in coastal regions but weakly in land, indicating that this relationship is modulated by factors such as weathering intensity and clay content. The mobility of Se increases in alkaline soils (pH > 8.5), thus reducing its content; meanwhile, in acidic soils (pH < 4.5), its fixation is more complex. In acidic, low-aluminum settings, iron oxides adsorb Se effectively, whereas organic matter becomes the main carrier under alkaline conditions. Precipitation affects Se via atmospheric deposition and leaching, temperature promotes sulfide substitution through deposition but also accelerates the breakdown of organic matter, and altitude influences Se through hydrothermal variations. This study provides the first comprehensive analysis of the multi-factor mechanisms controlling soil Se in the Se-rich coastal areas of southeastern China at a regional scale, offering a scientific basis for the sustainable use of Se-enriched land resources. Full article

During the development of oil and gas fields, the plugging problem in the wellbore and near-wellbore area is a key factor affecting oil recovery efficiency and economic benefits. This paper systematically reviews the research progress on the formation mechanisms, influencing factors, and plugging removal technologies of four common types of plugging, namely wax plugging, scaling, sand plugging, and hydrate plugging. Studies show that plugging is the result of the coupling of multiple physicochemical processes, and is jointly affected by multiple factors such as fluid properties, temperature and pressure conditions, flow rate, and surface properties. Currently, the plugging removal technology has formed a synergistic system of multiple methods including chemical, physical, mechanical, and thermodynamic approaches; however, it still faces challenges such as limited treatment depth, high cost, and risk of secondary damage. In the future, efforts should be made to strengthen research on multi-scale plugging mechanisms and develop environmentally friendly and high efficiency plugging removal agents as well as intelligent monitoring technologies, so as to improve the reliability and economy of complex oil and gas resource development. This paper aims to provide theoretical support and technical directions for researchers and engineers, and promote the innovation and development of efficient oil and gas field development and flow assurance technologies. Full article

Cementitious materials are multiscale and multiphase composites whose frost resistance at the macroscale is closely governed by microstructural characteristics. However, the interfacial transition zone (ITZ) between clinker and hydrates, recognized as the weakest solid phase, plays a decisive role in the initiation and propagation of microcracks under freezing conditions. Understanding the frost damage mechanism of ITZ is therefore essential for improving the durability of concrete in cold regions. The motivation of this study lies in revealing how freezing affects the mechanical integrity and microstructure of ITZ in its early ages, which remains insufficiently understood in existing research. To address this, a nanoscratch technique was employed for its ability to quantify local fracture properties and interfacial adhesion at the submicronscale, providing a direct and high-resolution assessment of ITZ behavior under freeze–thaw action. The ITZ thickness and fracture properties were characterized in unfrozen cement paste and in cement paste frozen at 1 and 7 days of age to elucidate the microscale frost damage mechanism. Moreover, the enhancement effect of nano-silica modification on frozen ITZ was investigated through the combined use of nanoscratch and mercury intrusion porosimetry (MIP). The correlations among clinker particle size, ITZ thickness, and ITZ fracture properties were further established using nanoscratch coupled with scanning electron microscopy (SEM). This study provides a novel micromechanical insight into the frost deterioration of ITZ and demonstrates the innovative application of nanoscratch technology in characterizing freeze-induced damage in cementitious materials, offering theoretical guidance for designing durable concrete for cold environments. Full article

Reinforced concrete walls (RC walls) are widely used in transportation, building structures, and civil air defence engineering. RC walls are vulnerable to low-velocity impact, such as the fall of components caused by earthquakes or explosions, for example, and the impact from road objects, such as vehicles, during their service life. When subjected to instantaneous high-energy impact, RC walls at key positions are prone to severe damage, which can further lead to structural collapse. Therefore, it is necessary to consider improving the impact resistance of key RC walls in a structure. Using a porous honeycomb structure with excellent energy absorption performance to provide impact protection for key RC walls is an effective way to reduce the damage of RC walls and thereby enhance the impact resistance of a structure. Therefore, based on the author’s previous series of experimental and numerical studies on the impact resistance of RC walls, as well as the high-mass pendulum impact experimental study on the honeycomb sandwich panel composite RC wall (HSP-RC wall), this paper adopts a multi-scale modelling method in micro-mechanics and macro-mechanics to establish a pendulum impact finite element model (FEM) for the HSP-RC wall. The representative volume element (RVE) and periodic boundary condition (PBC) are used to calculate the elastic property parameters of the honeycomb, which guide the establishment of the FEMs for the HSP-RC wall. The FEMs can avoid the computational difficulty caused by refined simulation, analyse the impact damage of the HSP-RC walls more accurately, quantify the impact protection effect of the honeycomb sandwich panel, and thus facilitate the parametric analysis of the impact resistance of HSP-RC walls with different honeycomb panel structural parameters in subsequent studies. Full article

Dental enamel exhibits a unique combination of high hardness and high toughness. This outstanding mechanical property is closely tied to its multi-scale hierarchical structure. In this study, rat tooth enamel was selected as the research object, the different structural layers and mechanical properties of tooth enamel were investigated and characterized experimentally. The multi-scale mechanical models with different structural layers were developed and analyzed using numerical simulations. The research results indicate that, regarding the load-bearing mechanism, the outer layer of tooth enamel consists of hydroxyapatite crystal bundles arranged in parallel and inclined orientations, and this structural feature enables it to exhibit excellent elastic modulus and resistance to deformation, while the inner layer with cross-arranged crystal bundles shows different mechanical response characteristics. In terms of crack propagation behavior, the outer layer is more prone to crack initiation due to the consistency of crystal orientation, and the cracks tend to extend in a straight line, while the unique cross arrangement of crystals in the inner layer can effectively inhibit crack propagation by inducing crack deflection and branching mechanisms, thus demonstrating more excellent fracture toughness. This “outer hard and inner flexible” gradient structure design elucidates the synergistic mechanism between crystal orientation and crack propagation behavior in tooth enamel, offering significant design insights for biomimetic composite materials. Full article

During natural gas extraction, understanding multiphase flow in fractured reservoirs remains a critical challenge due to the heterogeneous distribution of pores and fractures and the multi-scale nature of seepage mechanisms. These complexities introduce randomness in fluid distribution and tortuosity in seepage channels, limiting accurate characterization of gas-water flow. To address this issue, a dual-medium gas-water two-phase relative permeability model is developed by incorporating the fractal dimension of fracture surfaces, the tortuosity of the rock matrix, and the stress sensitivity of fracture networks. The model integrates essential microstructural parameters to capture the nonlinear flow behavior in dual-porosity systems. A systematic sensitivity analysis is conducted to evaluate the effects of fracture and matrix properties on the relative permeability curve. Results indicate that the fracture surface fractal dimension exerts a dominant influence in the two-phase flow region (fracture fractal dimensions in the range of 1.6–2.8), while near single-phase flow, fracture fractal dimensions in the range of 2.4–2.8 strongly affect flow behavior. Overall, the findings demonstrate that fracture-related parameters play a greater role than matrix properties in governing permeability evolution. This study provides predictive capability for two-phase flow in stress-sensitive fractured carbonates. Full article

The line contact behavior of multiscale meshing interfaces necessitates synergistic investigation spanning nano-to centimeter-scale ranges. When nominally smooth gear teeth surfaces come into contact, the mechanical–thermal coupling effect at the meshing interface actually occurs over a collection of microscale asperities (roughness peaks) exhibiting hierarchical distribution characteristics. The emergent deformation phenomena across multiple asperity scales govern the self-organized evolution of interface conformity, thereby regulating both the load transfer efficiency and thermal transport properties within the contact zone. The fractal nature of the roughness topography on actual meshing interfaces calls for the development of a cross-scale theoretical framework that integrates micro-texture optimization with multi-physics coupling contact behavior. Conventional roughness characterization methods based on statistical parameters suffer from inherent limitations: their parameter values are highly dependent on measurement scale, lacking uniqueness under varying sampling intervals and instrument resolutions, and failing to capture the scale-invariant nature of meshing interface topography. A scale-independent parameter system grounded in fractal geometry theory enables essential feature extraction and quantitative characterization of three-dimensional interface morphology. This study establishes a progressive deformation theory for gear line contact interfaces with fractal geometric characteristics, encompassing elastic, elastoplastic transition, and perfectly plastic stages. By systematically investigating the force–thermal coupling mechanisms in textured meshing interfaces under multiscale conditions, the research provides a theoretical foundation and numerical implementation pathways for high-precision multiscale thermo-mechanical analysis of meshing interfaces. Full article

In response to the issues of microcrack susceptibility, high brittleness, and unstable mechanical properties of desert sand recycled aggregate concrete (DSRAC), this study experimentally investigated the mechanical performance of DSRAC reinforced with hybrid steel–FERRO fibers. By testing macroscopic properties (compressive, splitting tensile, and flexural strengths) under different desert sand replacement ratios and fiber dosages, combined with microscopic analysis, the fiber-matrix interfacial behavior and toughening mechanism were clarified. The results showed that (1) DSRAC achieved optimal compressive strength when desert sand replaced 30% natural sand, with an obvious early strength enhancement; (2) both steel fibers and FERRO fibers independently improved DSRAC’s mechanical properties, while their hybrid combination (especially F0.15-S0.5 group) exhibited a superior synergistic strengthening effect, significantly outperforming single-fiber groups; (3) the established constitutive model accurately described the stress–strain response of hybrid fiber-reinforced DSRAC; (4) microscopic observations confirmed fibers inhibited crack propagation via bridging and stress dispersion, with hybrid fibers exerting multi-scale synergistic effects. This study provided theoretical–technical support for resource utilization of desert sand and recycled aggregates, and offered practical references for localized infrastructure materials (e.g., rural road subgrades and small-span culverts) in desert-rich regions and high-value reuse of construction waste in prefabricated components, advancing eco-friendly concrete in sustainable construction. Full article

Autoclaved lightweight concrete (ALC) exhibits considerable potential as a wall material in prefabricated structures, but its high water absorption and limited mechanical properties limit its widespread application. Ultra-high-performance concrete (UHPC), which possesses superior mechanical strength and durability, presents a promising reinforcement strategy. This study proposes the development of a UHPC-ALC composite wall material to enhance structural performance. The effects of shrinkage-reducing agent (SRA) content and expansive agent (EA) dosage on UHPC properties were systematically investigated. Results indicate that increasing SRA content improves the fluidity of UHPC and significantly reduces early autogenous shrinkage while the optimal EA dosage enhances both its mechanical properties and volume stability. Furthermore, an interfacial agent was employed to enhance the bonding performance between UHPC and ALC resulting in an average bonding strength of 0.93 MPa which represents a 675% increase compared with the untreated group. Finite element simulations and mechanical tests revealed that the composite material demonstrates a compressive strength of 11.2 MPa and a flexural strength of 6.8 MPa which corresponds to increases of 111.3% and 325%, respectively, relative to monolithic ALC. The composite demonstrated ductile failure and the experimental damage modes were consistent with those of the simulation results. This study offers guidance for optimizing UHPC-based composite wall materials via the multi-scale regulation of shrinkage behavior, interfacial properties, and structural design. Full article

Needled ceramic composites have great application prospects for high-temperature structural components. However, due to the manufacturing defects, the properties of the composite show significant dispersion, which poses great challenges for predicting the service life. Firstly, X-ray computed tomography was used to determine the pores in the composites, and multiscale models considering the pores were established. Combined with the multiscale method, the elastic modulus was predicted, and the relationship between porosity and elastic modulus was established. Secondly, the thermal diffusion coefficient was predicted. The relationship between porosity and thermal diffusion coefficient was determined. The accuracy of the multiscale method was verified by comparative analysis with the tensile experiment and the thermal diffusion experiment, respectively. Finally, based on the results of the model analysis, the correlation equations between thermal diffusion coefficient, porosity and elastic modulus were established. Thereby, new ideas are provided for the assessment of porosity and elastic properties of the composites. Full article

The steel industry is responsible for 7–9% of global CO₂ emissions. Shifting from primary iron ore to recycled scrap in electric arc furnace (EAF) steelmaking offers significant decarbonization potential, reducing carbon intensity by 60–70%. However, increased scrap use in EAF operations leads to higher nitrogen absorption, which can degrade mechanical properties. Nitrogen dissolves into molten steel, where it forms Cottrell atmospheres at dislocations in the following processing steps, intensifying strain aging and reducing ductility. This study establishes a precipitation criterion based on the TiN solubility product to prevent harmful liquid TiN formation, enabling effective nitrogen fixation via fine TiN precipitates (5–20 nm). Multiscale characterization techniques, such as TEM and EBSD, show that Ti reduces the number of mobile N atoms by 60–70%, evidenced by a 50–65% decrease in Snoek/SKK peak intensities. Excessive titanium can refine ferrite grain size and prevents harmful TiN inclusions. Titanium microalloying presents a cost-effective, sustainable strategy to reduce strain aging in scrap-rich EAF steels, enabling more sustainable steel production without sacrificing material properties. Full article