Search Results (279)

This study focuses on porous polyimide (PPI) lubricating materials for high-speed aerospace bearings. Based on their real microstructure, three-dimensional digital model reconstruction and mesoscale seepage characteristics were investigated. First, a sequence of two-dimensional slice images of PPI was obtained using micro-focus X-ray computed tomography (CT). Through image filtering, threshold segmentation, and three-dimensional reconstruction, a highly faithful digital model of the pore structure was constructed, and a quantified pore-network model was further extracted. Second, a multiple-relaxation-time lattice Boltzmann model based on the D3Q27 discrete scheme was established, and its accuracy and stability in complex boundaries and pressure-driven flows were verified using classic benchmark cases. Subsequently, the validated numerical model was applied to the reconstructed PPI pore structure to simulate and systematically analyze the single-phase seepage behavior of lubricating oil. The results show that the lubricant seepage exhibits a strong “preferential flow path” effect, with most of the flow transported through a small number of large-size throats. A clear quantitative relationship exists between the microscopic flow field structure—including velocity distribution, flow paths, and pressure gradient—and the pore-topology features, such as throat-size distribution, connectivity, and tortuosity. This verifies the mesoscale mechanism that “structure governs flow.” The complete technical chain established in this work—“real-structure reconstruction–numerical model validation–seepage mechanism analysis”—provides a reliable theoretical and numerical tool for gaining deeper insight into the lubricant transport behavior in porous polyimide and offers guidance for the microstructural design and optimization of this material. Full article

Through-plane electronic transport in porous membrane electrode assembly (MEA) electrodes is governed by the three-dimensional (3D) connectivity of the conducting phase. Here, we quantify the role of the spanning-cluster fraction $P_{\infty }$, defined as the fraction of conducting-phase voxels that belong to the $z$-spanning connected component in a finite reconstructed volume, on effective conductivity using scanning electron microscopy (SEM)-informed 3D reconstructions of four archetypal morphologies: a granular catalyst layer (CL), labeled CL1; a fibrous gas diffusion layer (GDL), labeled GDL1; an open-cell foam (OCF); and a micro-fibrous non-woven (MFM), labeled MFM1. Each morphology is reconstructed on a $150\times 150\times 150$ voxel grid, and $z$-spanning connectivity is identified with a 26-neighbor flood-fill algorithm. Steady-state conduction is solved by a finite-volume method (FVM) with an imposed potential difference between the z-faces and no-flux lateral boundaries. Although all samples exhibit through-thickness connectivity, the normalized conductivity ${\sigma }_{\mathrm{e}\mathrm{f}\mathrm{f}}/{\sigma }_{\mathrm{b}\mathrm{u}\mathrm{l}\mathrm{k}}$ varies widely, from $\approx 0.134$ (MFM1) to $\approx 0.706$ (OCF). The corresponding ${(P}_{\infty },{\sigma }_{eff}/{\sigma }_{bulk})$ pairs are $\left(0.996,\approx 0.306\right)$ for CL1, $\left(0.999,\approx 0.303\right)$ for GDL1, $\left(0.997,\approx 0.706\right)$ for OCF, and $\left(0.901,\approx 0.134\right)$ for MFM1. OCF exhibits the highest response due to vertically coherent channels, whereas MFM1 underperforms due to laminated constrictions; CL1 and GDL1 lie in an intermediate regime with nearly isotropic skeletons. Overall, the results show that while a $z$-spanning connected component is required for measurable conduction, the magnitude of ${\sigma }_{\mathrm{e}\mathrm{f}\mathrm{f}}$ is dictated by percolating-skeleton quality (bottlenecks, cross-sectional constrictions, and pathway alignment) rather than phase amount alone. The proposed descriptors therefore enable percolation-aware screening metrics for designing and comparing MEA-relevant GDL and CL microstructures. Full article

The Cambrian Period represents a critical yet debated interval in the global transition from “Aragonite Seas” to “Calcite Seas”. This study reconstructs the physicochemical evolution of paleoseawater through microstructural analysis and trace element geochemistry of Cambrian oolitic rocks in the northern Sichuan Basin, South China. Our results demonstrate that micrite envelopes on ooid margins and early submarine cements (Stage 1) effectively least-altered signals, resisting diagenetic alteration. Consequently, the maximum values of trace element in these fabrics serve as reliable proxies for paleoseawater reconstruction. Ooids from the upper Canglangpu Formation to the Longwangmiao Formation (Lower Cambrian, Series 2) are characterized by concentric laminations with tangential ultrastructures, high Sr contents (up to 1536 ppm), and high seawater molar Mg/Ca ratios (hereafter mMg/Ca, up to 5.02). These features contrast sharply with the radial fabrics, low Sr contents (<400 ppm), and low seawater mMg/Ca ratios (<0.4) observed in the Xixiangchi Formation (Upper Cambrian, Furongian). Integrating regional data with global correlations, this study confirms that Aragonite Sea conditions persisted on the northern margin of the Yangtze Block until at least the late Early Cambrian (Stage 4). The Middle Cambrian (Miaolingian) represents a pivotal transitional interval, leading to a complete shift to a stable Calcite Sea by the Late Cambrian (Furongian). These findings provide crucial regional constraints for refining the Phanerozoic model of seawater chemical evolution. Full article

The application of advanced imaging techniques, particularly computed tomography (CT), photogrammetric scanning, and three-dimensional reconstructions of body surfaces and skeletal remains, is becoming a crucial component of Forensic Anthropology. These tools enable a non-invasive and highly standardized analysis of both intact cadavers and human remains recovered from terrestrial or aquatic environments, providing reliable support in identification processes, traumatological reconstruction, and the assessment of taphonomic processes. In the context of estimating the Post-Mortem Interval (PMI) and the Post-Mortem Submersion Interval (PMSI), digital imaging allows for the objective and reproducible documentation of morphological changes associated with decomposition, saponification, skeletonization, and taphonomic patterns specific to the recovery environment. Specifically, CT enables the precise assessment of gas accumulation, transformations in residual soft tissues, and structural bone modifications, while photogrammetry and 3D reconstructions facilitate the longitudinal monitoring of transformative processes in both terrestrial and underwater contexts. These observations enhance the reliability of PMI/PMSI estimates through integrated models that combine morphometric, taphonomic, and environmental data. Beyond PMI/PMSI estimation, imaging techniques play a central role in anthropological bioprofiling, facilitating the estimation of age, sex, and stature, the analysis of dental characteristics, and the evaluation of antemortem or perimortem trauma, including damage caused by terrestrial or fauna. Three-dimensional documentation also provides a permanent, shareable archive suitable for comparative analyses, ensuring transparency and reproducibility in investigations. Although not a complete substitute for traditional autopsy or anthropological examination, imaging serves as an essential complement, particularly in cases where the integrity of remains must be preserved or where environmental conditions hinder the direct handling of osteological material. Future directions include the development of AI-based predictive models for PMI/PMSI estimation using automated analysis of post-mortem changes, greater standardization of imaging protocols for aquatic remains, and the use of digital sensors and multimodal techniques to characterize microstructural alterations not detectable by the naked eye. The integration of high-resolution imaging and advanced analytical algorithms promises to further enhance the reconstructive accuracy and interpretative capacity of Forensic Anthropology. Full article

The long-term interfacial reliability of Cu/Al brazed joints is critical for power equipment but is often compromised by severe intermetallic compound (IMC) degradation during thermal aging. This study investigates the evolution mechanism and mechanical stability of Cu/Al joints brazed with 0.5 wt.% Ga-modified Zn-15Al filler metal, aged at 200 °C for up to 1000 h. Microstructural evolution, diffusion kinetics, and mechanical properties were systematically characterized using SEM, EDS, nanoindentation, and shear testing. Results indicate that the unmodified control interface degrades via Zn-diffusion-driven “in situ Cu depletion” of the Cu₉Al₄ layer, leading to severe embrittlement. In contrast, the addition of Ga induces a “sacrificial reconstruction” mechanism, where the outer CuAl₂ layer transforms into a dense lamellar ternary structure via cellular decomposition. This reconstructed layer acts as an effective diffusion barrier and “Zn sink,” trapping infiltrating atoms and preserving the structural integrity of the underlying Cu₉Al₄ phase. Consequently, the Ga-modified joints demonstrate superior shear strength retention and an optimized H/E ratio throughout the aging process, shifting the failure mode from brittle cleavage to a toughened lamellar peeling mechanism. This work elucidates how Ga-modulated phase reconstruction fundamentally enhances interfacial stability, offering a theoretical basis for high-reliability interconnects. Full article

Sintering is a key processing route to consolidate nuclear fuel powders into dense compacts, yet the atomic-level mechanisms governing the sintering of actinide compounds remain poorly understood. Herein, the sintering kinetics and structural evolution of uranium mononitride (UN) nanoparticles are investigated using molecular dynamics (MD) simulations. A three-stage sintering mechanism is revealed based on the symmetrical dual nanoparticle models: initial surface diffusion and neck formation, followed by interface amorphization driven by shear stress, and finally, lattice reconstruction and recrystallization, which peak during the cooling process. By studying the effect of sintering temperature, we find that near-complete densification with good structural integrity is achieved at 1900 K, whereas further increasing the temperature (to 2000 K) led to microstructural instability and near-overburning. In addition, holding time exhibits a clear saturation effect, with variations in holding time showing no significant impact on sintering morphology or density. Therefore, sintering temperature is the dominant factor determining sintering quality. The atomic level insights provided by this work reveal the nonlinear temperature dependence and time saturation effect of UN nanoparticle sintering, and provide a theoretical basis for the prediction, design, and optimization of nuclear fuel sintering process. Full article

Oxidation can lead to intrinsic degradation and loss in the load-bearing capacity of ceramic matrix composites (CMCs) in high-temperature service, thereby compromising structural integrity and operational safety. To elucidate the mechanism of its oxidation effects, this study predicted the oxygen diffusion coefficient within 2.5D woven C/SiC fibre bundles based on gas diffusion and oxidation kinetics theory, and subsequently constructed a meso-scale constitutive model incorporating oxidation damage and fibre defect distribution. Furthermore, a micro-scale framework for yarns was established by integrating interfacial slip behaviour, and an RVE model for 2.5D woven C/SiC was constructed based on X-ray computed tomography reconstruction of the actual microstructure. Building upon this foundation, an oxidation constitutive model applicable to loading–unloading cycles was proposed and validated through high-temperature oxidation tests at 700 °C, 900 °C, and 1100 °C. Results demonstrate that this model effectively characterizes the strength degradation and stiffness reduction caused by oxidation, enabling prediction of CMCs’ mechanical properties under oxidizing conditions and providing a physics-based foundation for the reliable design and life assessment of C/SiC components operating in oxidizing environments. Full article

Aeolian sand in arid mining regions is highly susceptible to wind erosion, posing serious threats to ecological stability and surface engineering safety. To enhance its resistance, this study applied the microbially induced carbonate precipitation (MICP) technique and conducted wind tunnel experiments combined with SEM and XRD analyses to examine the effects of cementing solution type and concentration, bacteria-to-cementation-solution ratio (B/C ratio), and spraying volume on the wind erosion behavior of MICP-treated aeolian sand. Results show that the cementing solution type and concentration jointly control erosion resistance. The MgO-based system exhibited the best performance at a B/C ratio of 1:2, reducing erosion loss by 47.2% compared with the CaCl₂ system, while a 1.0 mol/L concentration further decreased loss by 97.4% relative to 0.5 mol/L. Increasing the spraying volume from 0.6 to 1.2 L/m² reduced erosion loss by 70–99%, and a moderate B/C ratio (1:2) ensured balanced microbial activity and uniform CaCO₃ deposition. Microstructural observations confirmed that MICP strengthened the sand through CaCO₃ crystal attachment, pore filling, and interparticle bridging, forming a dense surface crust with enhanced integrity. From a symmetry perspective, the microbially induced mineralization process promotes a more symmetric and spatially uniform distribution of carbonate precipitates at particle contacts and within pore networks. This symmetry-enhanced microstructural organization plays a key role in improving the macroscopic stability and wind erosion resistance of aeolian sand. Overall, MICP improved wind erosion resistance through a coupled biological induction–chemical precipitation–structural reconstruction mechanism, providing a sustainable approach for eco-friendly sand stabilization and wind erosion control in arid mining regions. Full article

The structural integrity of nuclear graphite is paramount for the lifespan of High-Temperature Gas-Cooled Reactors. The nuclear graphite components operate under extreme conditions involving high temperature, pressure, and intense neutron irradiation, leading to complex service behavior that is difficult to characterize only by experimental methods. This study employs the finite element method (FEM) to assess component stress and failure risk. The ManUMAT simulation method was first validated against irradiation data for Gilsocarbon graphite from an Advanced Gas-Cooled Reactor and was subsequently applied to stress–strain analysis of the nuclear graphite bricks in the HTR-PM side reflector layer. The 3D micropore structure of nuclear graphite was obtained via X-μCT and reconstructed in Avizo to establish an FEM model based on the actual pore geometry. Simulations of nuclear graphite over a 30 full-power-year service period predicted a significant contraction on the core-side and minimal thermal expansion on the out-side driven by the neutron doses. This research establishes a finite element framework that extends the ManUMAT approach by integrating a realistic pore structure model, thereby providing a foundation for quantifying the microstructural effects on macroscopic performance. Full article

Hydrogen energy is vital for a clean, low-carbon society, and proton exchange membrane fuel cells (PEMFCs) represent a core technology for the conversion of hydrogen chemical energy into electrical energy. When PEMFC single cells are stacked under assembly force for high power output, their porous electrodes (gas diffusion layers, GDLs; catalyst layers, CLs) undergo compressive deformation, altering internal transport processes and affecting cell performance. However, existing microscale studies on PEMFC porous electrodes insufficiently consider compression (especially in CLs) and have limitations in obtaining compressed microstructures. This study proposes a combined framework from a microstructure perspective. It integrates the finite element method (FEM) with computational fluid dynamics (CFD). It reconstructs microstructures of GDL, CL, and GDL-bipolar plate (BP) interface. FEM simulates elastic compressive deformation, and CFD calculates transport properties (solid zone: heat/charge conduction via Laplace equation; fluid zone: gas diffusion/liquid permeation via Fick’s/Darcy’s law). Validation shows simulated stress–strain curves and transport coefficients match experimental data. Under 2.5 MPa, GDL’s gas diffusivity drops 16.5%, permeability 58.8%, while conductivity rises 2.9-fold; CL compaction increases gas resistance but facilitates electron/proton conduction. This framework effectively investigates compression-induced transport property changes in PEMFC porous electrodes. Full article

This article presents an assessment of the mechanical properties of biochars in the context of their potential application as bone graft substitutes. The samples were obtained from selected hardwood species and subjected to pyrolysis at temperatures of 400 °C, 600 °C, 800 °C and 1000 °C. To assess the mechanical properties, a classical three-point bending test was employed alongside Digital Image Correlation (DIC), which enabled analysis of displacement and strain distribution. The results indicate that biochars derived from hornbeam pyrolysed (carbonised) at 800 °C achieve Young’s modulus values of up to 5.69 ± 0.76 GPa and those, carbonised at 1000 °C, reached flexural (bend) strength values of up to 0.01897 ± 0.00211 GPa. These parameters fall within the range of cancellous bone properties and the lower range of cortical bone properties of the mandible, suggesting their potential suitability for reconstructing load-bearing bone structures with limited mechanical demand, including the mandible. The results highlight the effect of pyrolysis temperature on the microstructure and mechanical properties of the material and indicate the need for further studies on biocompatibility and surface functionalisation. Plant-derived biochars, owing to their natural porosity and properties comparable to bone tissue, may represent a promising alternative to currently used biomaterials in bone tissue engineering. Full article

Numerical modeling of asphalt concrete and other asphalt mixes used in road engineering is an actively developed research field. In this study, a framework combining the following aspects is presented: (1) reliable reconstruction of the real samples; (2) using realistic material models of the microstructure constituents; and (3) providing high numerical efficiency. Asphalt concrete microstructure was reconstructed using image processing. The Burgers material model was applied to the subdomains identified as the mastic, and the linear elastic model was used for the aggregate particles. In order to increase the numerical efficiency, the developed homogenization method was used to accelerate the finite element analysis. The main novelty of this study is the integration of the Burgers material model with the numerical homogenization in the small strains range. A homogenization error measured in the maximum norm was smaller than 7% in the presented numerical examples (6.8% for the elasticity and 6.9% for the viscoelasticity problem, respectively). Simultaneously, the observed reduction in the number of degrees of freedom was larger than 510 times. The obtained results confirmed the applicability of the developed methodology to the analysis of the viscoelastic materials in the range of the small strains. Full article

This study presents an integrated digital and archaeometric investigation of the Roman fortress of Sacidava, located in Dobrogea, Romania. Combining 3D digital reconstruction and advanced material analysis, the research explores both the original architecture and the preserved state of the site. Using Autodesk Fusion 360, a complete 3D model was developed, digitally restoring the fortress as it likely appeared in the 4th century AD and enabling the generation of precise plans, sections, and photogrammetric elevations. Mortar samples from the eight towers of the Sacidava fortress were examined through scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), atomic force microscopy (AFM), and confocal laser scanning microscopy (CLSM), revealing phyllosilicate-rich matrices, carbonated lime residues, and heterogeneous microstructures. The most severe degradation was found in the towers facing the Danube (E2, F, G), which was strongly influenced by humidity and salt crystallization, while the southern towers (A–C) retained more stable textures. Hydroxyapatite (HAp) treatments visibly improved the surface condition by reducing roughness and sealing active pores. For the first time, chromatic parameters were correlated with environmental factors, such as pH, moisture, and salt content. ImageJ-based pseudo-computed tomography (pseudo-CT), principal component analysis (PCA), and dendrogram analyses confirmed a clear pattern of deterioration near the ancient port area, where increased acidity and moisture coincided with darker surface coloration and deeper microstructural alteration. Full article

The mechanical performance of cast iron is strongly governed by the morphology of its graphite phase, yet establishing a quantitative link between microstructure and macroscopic properties remains a challenge. In this study, a three-dimensional finite element method (FEM)-based micromechanical framework is proposed to analyze and predict the mechanical behavior of cast iron with representative graphite morphologies, spheroidal and flake graphite. Realistic representative volume elements (RVEs) are reconstructed based on experimental microstructural characterization and literature-based X-ray computed tomography data, ensuring geometric fidelity and statistical representativeness. Cohesive zone modeling (CZM) is implemented at the graphite/matrix interface and within the graphite phase to simulate interfacial debonding and brittle fracture, respectively. Full-field simulations of plastic strain and stress evolution under uniaxial tensile loading reveal that spheroidal graphite promotes uniform deformation, delayed damage initiation, and enhanced ductility through effective stress distribution and progressive plastic flow. In contrast, flake graphite induces severe stress concentration at sharp tips, leading to early microcrack nucleation and rapid crack propagation along the flake planes, resulting in brittle-like failure. The simulated stress–strain responses and failure modes are consistent with experimental observations, validating the predictive capability of the model. This work establishes a microstructure–property relationship in multiphase alloys through a physics-informed computational approach, demonstrating the potential of FEM-based modeling as a powerful tool for performance prediction and microstructure-guided design of cast iron and other heterogeneous materials. Full article

The multi-factor coupling mechanism of droplet impact dynamics remains unclear due to insufficient analysis of leaf structure–droplet interaction and inadequate integration of simulations and experiments, limiting precision pesticide application. To address this, we developed a droplet impact model using the Volume of Fluid (VOF) method combined with high-speed camera experiments and systematically analyzed the effects of impact velocity, angle, and droplet size on slip behavior via response surface methodology. Methodologically, we innovatively integrated 3D reverse modeling technology to reconstruct soybean leaf microstructures, overcoming the limitations of traditional planar models that ignore topological features. This approach, coupled with the VOF method, enabled precise tracking of droplet spreading, retraction, and slip processes. Scientifically, our study advances beyond previous single-factor analyses by revealing the synergistic mechanisms of impact parameters through response surface methodology, identifying impact angle as the most critical factor (42.3% contribution), followed by velocity (28.7%) and droplet size (19.5%). Model validation demonstrated high consistency between simulation predictions and experimental observations, confirming its reliability. Practically, the optimized parameter combination (90° impact angle, 1.5 m/s velocity, and 300 μm droplet size) reduced slip displacement by over 50% compared to non-optimized conditions, providing a quantitative tool for spray parameter control. This work enhances the understanding of droplet–leaf interaction mechanisms and offers technical guidance for improving pesticide deposition efficiency in agricultural production. Full article