Search Results (631)

Self-drilling hollow bar micropiles (HBMPs), which integrate drilling, grouting, and reinforcement into a single process, have broad application prospects in mountainous transmission lines and offshore wind power projects. However, existing research has focused mainly on friction piles in soil layers, and there is a lack of systematic understanding of the load-transfer mechanism and bearing capacity calculation method for rock-socketed HBMPs. Based on field static load tests of rock-socketed HBMPs, this study systematically investigates the vertical bearing behavior and capacity calculation method of single rock-socketed HBMPs through a combination of test data analysis, finite element numerical simulation, and theoretical analysis. The field test results show that the load-settlement curves of rock-socketed HBMPs are of a slowly varying type, exhibiting mixed friction-end-bearing characteristics. After data screening, the average Q-s curve of Pile No. 1 and Pile No. 5 was taken as the benchmark, and the representative ultimate bearing capacity of a single pile determined by the 40 mm settlement criterion is 5860 kN. The test data of Pile No. 3 and Pile No. 4 were retained as independent validation data. A three-dimensional finite element model considering the cohesive contact behavior at the pile–rock/soil interface was established using ABAQUS. After calibration with the test results, the error between the simulated and measured bearing capacity is −3.4%, demonstrating good model reliability. Parametric analysis indicates that the bearing capacity increases linearly with the grouting volume increase rate $V_{\mathrm{inc}}$, with the expansion effect being the main enhancement mechanism; the improvement amplitude under hard rock conditions is significantly smaller than that in cohesive soils. The effect of uniaxial compressive strength $q_u$ of hard rock on bearing capacity is negligible because the capacity is controlled by the pile–rock interface shear strength. The bearing capacity increases approximately linearly with the rock-socketed depth $L_r$, and a minimum rock-socketed depth of 1.0 m is recommended. Analysis of the load-transfer mechanism shows that rock-socketed HBMPs rely mainly on shaft resistance (accounting for 90.6%), and the axial force decays significantly along the pile length. Elastic compression of the pile accounts for 78% of the pile head settlement, and the limited displacement at the pile tip leads to insufficient mobilization of end bearing. A modified bearing capacity formula considering the grouting expansion effect is established with shaft resistance as the core. A hierarchical validation strategy is adopted to test its predictive ability: for the finite element cases not participating in parameter calibration, the prediction error is within ±2%; for the field test piles, the prediction error is +7.9%; and for Pile No. 3 and Pile No. 4, the errors are +1.7% and −2.1%, respectively. These values are significantly better than those of existing methods (errors ranging from −72.1% to +54.5%). The research results can provide a theoretical basis for the design of single HBMP bearing capacity under rock-socketed conditions. Full article

Efficient heat dissipation represents a critical challenge for maintaining device performance and reliability in modern electronic devices. Polymer composites reinforced with graphite sheets have attracted attention as thermal interface materials because of their lightweight nature and excellent thermal transport properties. Herein, the effects of graphite sheet volume fraction, sheet thickness, folding angle, and sheet orientation on the through-thickness thermal conductivity of epoxy/graphite sheet composites were investigated using finite element (FE) modeling. A reduced folding angle and increased graphite sheet thickness enhanced the through-thickness thermal conductivity. However, for the same graphite volume fraction, reducing the folding angle enhanced thermal conductivity more effectively than increasing the graphite sheet thickness, indicating the dominant role of sheet orientation in the heat transport behavior. The influence of the folding angle became significant at higher graphite volume fractions due to the formation of more continuous conductive pathways. At a graphite sheet volume fraction of 0.5, the thermal conductivity decreased from 22.27 to 11.52 W m⁻¹ K⁻¹ upon increasing the folding from 15° to 90°. Finally, a semi-empirical model exhibiting good agreement with the FE results was developed, demonstrating that optimization of graphite sheet geometry is essential for improving the thermal performance of polymer-based thermal interface materials. Full article

An X-ray fluorescence online analyzer was applied to the analysis of samples of known composition and concentration containing rare earth elements (REEs) and heavy metals (HMs), which were specially prepared by the authors (working samples). Reference samples were used for Th and U. The statistical parameters (detection limit, accuracy, and sensitivity) of the measurements of the spectra were calculated and a thorough assessment of the results was carried out. For large-volume samples, detection limits of 20–100 ppm for REEs and 10–140 ppm for HMs were achieved within 600 s. For thin-layer samples and similar geometries, detection limits for light and medium REEs improved to 3–20 ppm. The methodological possibilities for quantitative analysis of the REEs and HMs were examined and a rather simple approach with an easy implementation was developed. The method was tested in automatic measurements using concentrations in the range of 1000–4000 ppm, as a simulation of real-life measurements, and to determine the stability of the analyzer and the consistency of the results obtained. The results show that the online XRF analyzer can be applied for reliable detection and quantification of REEs and HMs at the ppm level. With these results, we are closer to obtaining results under conditions representative of those on real-world mining conveyor belts. Full article

This paper focuses on the characterization of the micro-leakage channel geometry in the flange-gasket rough contact interface of hazardous chemicals transport vehicles. This work represents the first step in a multi-physics simulation framework for optical-fiber-based micro-leakage monitoring. Directly establishing a full-scale contact model from micron-scale rough peaks and valleys to the decimeter-scale flange structure would lead to extremely high computational costs; a nonlinear contact model based on quasi-representative volume element (quasi-RVE) and quasi-periodic boundary condition (quasi-PBC) is proposed in this paper. Quasi-RVE refers to a local region selected from the overall rough surface. Unlike a traditional RVE that requires strict geometric periodicity, the quasi-RVE is only approximately consistent with the overall surface with respect to key morphological parameters and volume parameters. Quasi-PBC only imposes in-plane displacement compatibility constraint on the relative side boundary without imposing periodic constraints in the peak-valley height direction. In this paper, the average interface gap and its distribution are selected as the geometric descriptors of the micro-leakage channel, and the reliability of the contact model is verified by comparing with the existing experimental and numerical results. On this basis, the influences of surface roughness, gasket material and loading conditions on the geometric characteristics of the micro-leakage channel are further analyzed. The results show that the lower stiffness gasket is easier to fit with the rough flange surface under the same load conditions, so as to obtain a larger contact area and a smaller average gap. The quasi-RVE contact model established in this paper can effectively reduce the computational scale of contact analysis of the rough sealing interface, and provide reliable channel geometric information for subsequent micro-leakage fluid simulation and optical fiber signal response simulation. Full article

This work explores the organization of a supply system within a military transportation network. The nodes of the studied network, comprising suppliers and recipients of supplies (representing delivery and collection points), were geographically identified, as well as the volume of cargo transported in each connection. The idea was to improve the efficiency of supply within the network, understood as minimizing total transportation costs. Calculations were performed using three methods: North–West Corner Method (N-WCM), least cost in the matrix method (LCMM), and Vogel’s Approximation Method (VAM). As a result of the calculations, basic feasible solutions (BFS) were obtained for each method, satisfying the constraint conditions. Each BFS was degenerate, because each contained m + n − 1 basic (non-zero) elements. In accordance with the calculation methodology, optimization was performed for each BFS using the potential method. For N-WCM and LCMM, up to five iterations were required, while for VAM, only one iteration was sufficient, confirming the best performance for this method. In addition to the total transport costs, additional criteria such as total distance, fuel consumption and CO₂ emissions were considered. Full article

Industrial areas, which represent a specific type of urbanised area with an extremely high concentration of material reserves, can be considered key anthropogenic raw material reservoirs in the context of urban mining. Industrial areas, characterised by a high material density and a specific composition of structural systems, show extraordinary potential for providing secondary raw materials with high material and energy value. This increases the need for their systematic evaluation. The aim of the present study was to define the role of the selected industrial area as a strategic node for secondary raw material extraction, to identify the structure and quality of “urban deposits” in the selected location of the Ostrava–Karviná region (CZ), and to provide an analytical framework for its integration into circular planning processes. The methodological approach is based on a combination of pre-demolition audit, material flow mapping, spatial analysis, and structural element characterisation. It is becoming apparent that industrial areas have a high material density and contain significant amounts of recyclable metals, reinforced concrete elements, etc. These stocks are often concentrated in structural systems with predictable geometries, such as serial assembly prefabricated and steel frames, allowing for more accurate estimates of recoverable volumes. The results show that the incorporation of industrial areas into the process of urban mining can significantly reduce the consumption of primary raw materials, mitigate the environmental impacts associated with the extraction of raw materials, and, at the same time, promote the regeneration of industrial areas (or brownfields) through the planned decomposition of structures. The inclusion of urban mining in urban development strategies and the regeneration of industrial sites leads to the prediction that urban mining is one of the key elements for achieving a material-efficient and low-carbon urban environment. Full article

Polylactic acid (PLA) scaffolds with triply periodic minimal surface (TPMS) structures have become ideal scaffolds in the field of bone defect repair due to their good designability, connectivity, biocompatibility, and degradability. However, it is currently difficult to obtain the scaffold degradation rate and osteogenic efficacy from in vivo experiments, making it challenging to provide recommendations for scaffold design. In this study, an algorithm to construct a TPMS scaffold–interfacial layer–tissue three-phase composite model was developed using polylactic acid hydrolysis and bone remodeling as the governing equations to simulate scaffold degradation and tissue osteogenesis behavior under an external mechanical stimulus. This method is based on a numerical calculation framework that can more closely simulate the in vivo environment, characterizing the changes in the overall macroscopic mechanical properties of tissue under the influence of scaffold degradation and tissue osteogenesis. The results confirmed the accelerating effect of mechanical stimulation on scaffold degradation and its promoting effect on new bone formation. Under 10% compressive loading, the Schwarz P representative volume element (RVE) lost 33% of its apparent modulus within initial days, while the lidinoid RVE, despite showing a much higher initial modulus, dropped to only 20% of its initial value over the same period. In addition, the mechanical performance of the fused TPMS RVE was not simply linear, even though the surface equations are combined linearly. These results provide a new method for pre-designing scaffold structures based on numerical simulation results using the finite element simulation. Full article

Reinforced concrete (RC) slabs with internal voids are increasingly used to improve material efficiency; however, their residual structural performance after fire exposure remains insufficiently understood. This study presents a numerical investigation of RC slabs with different void geometries using a three-dimensional nonlinear Finite Element (FE) model. A sequential thermal–structural approach was adopted, in which fire exposure was simulated through transient thermal analysis, and the resulting spatial distribution of maximum temperatures was used to assign residual material properties to each FE based on its local peak temperature, followed by structural analysis under ambient conditions. A parametric study was conducted on seven slab configurations, including two solid slabs and five voided slabs with spherical, elliptical, ellipsoidal, capsule, and biaxial capsule geometries. To ensure a consistent evaluation, two reference solid slabs were considered: a 230 mm thick slab to enable comparison under identical geometric conditions, and a 160 mm thick slab representing equivalent concrete volume to assess material efficiency. Fire exposure was applied according to the ISO 834 standard fire curve for durations of 30, 60, and 90 min. The results indicate that voided slabs exhibit higher deflections than the solid slab of identical thickness due to reduced stiffness, while achieving comparable performance relative to the solid slab with equivalent concrete volume. These findings highlight the trade-off between structural stiffness and material efficiency under increasing fire exposure time. Full article

The rapid advancement of high-performance computing has spurred growing demand for miniaturized, high-density, high-power, and highly reliable electronic packaging. Through-silicon via (TSV), as a pivotal technology enabling high-density integrated packaging, achieves vertical interconnection that reduces signal latency and power consumption while substantially improving system integration. However, inherent challenges persist due to coefficient of thermal expansion mismatches among heterogeneous materials in TSV and parasitic effects introduced by high-density TSV arrays, leading to critical concerns regarding thermomechanical reliability and signal integrity. This study focuses on TSV structures, investigating their thermomechanical reliability and electrical performance. First, the macro–micro model of 2.5D package structure was established to address cross-scale challenges based on Representative Volume Element (RVE) homogenization and sub-model technique. Then, an equivalent circuit model integrating transmission line network theory was developed and validated through full-wave electromagnetic simulations using S-parameter analysis to analyze signal transmission characteristics. Finally, by introducing an improved multi-objective grasshopper algorithm, the structural parameters of TSV are co-optimized using a genetic algorithm back propagation network (GA-BP) and an improved multi-objective grasshopper algorithm (IMOGOA) to enhance both thermomechanical reliability and electrical characteristics simultaneously. The proposed approach offers a practical and effective solution for improving the reliability and performance of high-density integrated packaging, providing valuable insights for future packaging design and optimization. Full article

Magnesium (Mg) alloys are promising for automotive lightweighting and the low-altitude economy, yet their reliability is challenged by stress corrosion cracking (SCC). To realize a quantitative and physics-based evaluation of SCC resistance, this study develops a mesoscale simulation framework coupling dislocation density-based crystal plasticity with an anodic dissolution phase-field model. A 2D representative volume element is constructed for randomly textured polycrystalline Mg to investigate the synergistic acceleration of corrosion by dislocation slip and hydrostatic stress. Results show that heterogeneous dislocation multiplication induced by pre-deformation is the decisive factor in corrosion path selection. In soft-oriented grains, high dislocation densities elevate the interface kinetic coefficient to levels substantially higher than those in hard-oriented regions. Notably, within such soft grains, the contribution of dislocation density to the interface kinetic coefficient can be up to 7.7 times that of hydrostatic stress, establishing dislocation-induced lattice disorder as the primary accelerator for transgranular corrosion. Hard-oriented grains effectively impede corrosion propagation due to restricted dislocation proliferation. This study elucidates how grain orientation-dependent dislocation evolution regulates corrosion morphology, revealing that the random texture delays overall structural failure based on a “weakest-link” mechanism. Full article

This study numerically investigates the aerodynamic and thermal interactions between a full-scale metro train and the surrounding airflow within a confined tunnel environment using steady-state Reynolds-averaged Navier–Stokes (RANS) simulations. The six-car train, with a total length of 108 m and a cross-sectional area of 5.97 m², operates in a tunnel with a 9.83 square meter cross-section, resulting in a high blockage ratio of approximately 60 percent. The Shear Stress Transport (SST) k–ω turbulence model and a high-resolution finite-volume mesh comprising over 8.5 million elements were employed to capture detailed near-wall phenomena. Six representative motion scenarios were analyzed, including early acceleration, peak cruising, and deceleration phases, with realistic thermal boundary conditions applied by assigning the tunnel air temperature as 29.2 °C and the train surface temperature as 35.0 °C. Velocity, pressure, temperature, and turbulence kinetic energy distributions were extracted from both longitudinal and cross-sectional planes. In addition to visual contour assessments, pointwise and spatially averaged field data were examined to quantify the development of airflow structures, pressure distribution, and thermal behavior. The results reveal speed-dependent aerodynamic resistance, pronounced recirculation and stagnation zones around the train nose and tail, and variations in convective heat transfer rates that evolve with train velocity. These findings provide insights into tunnel ventilation design and thermal management for underground metro operations, representing a novel integration of full-scale computational fluid dynamics (CFD) with thermal characterization under realistic conditions. Full article

Reliable determination of the in-plane biaxial mechanical behavior of particle-reinforced composite adhesives under multiaxial stress conditions requires cruciform specimen geometries that achieve high stress uniformity in the measurement zone. In this study, the elastic response obtained from uniaxial tensile tests was verified through representative volume element (RVE)-based micromechanical analyses by systematically examining mesh sensitivity and RVE edge size convergence across multiple random microparticle distributions under periodic boundary conditions. The probability density characterization of the effective elastic constants indicated that the remaining scatter is mainly governed by microstructural randomness and decreases as the RVE edge size increases, supporting a nearly direction-independent effective stiffness associated with the random microparticle distribution. The RVE-predicted mean tensile modulus remained in close agreement with experiments, with relative deviations of approximately −2% to +2% across the investigated reinforcement levels. The validated material parameters were based on a dynamic XGBoost (eXtreme Gradient Boosting) surrogate model driven by the geometric design variables, fillet radius and center thickness, combined with an adapted version of the LIPOTR (Lipschitz Optimization with Trust Region) algorithm. The initial and optimized geometries were then compared using both experimentally determined elastic properties and selected RVE-predicted engineering constants for the 2, 6, and 10 wt% materials. The significant reductions in the equivalent S_eqv, normal S₁₁ and S₂₂, and shear S₁₂ stress variations within the gauge zone of the optimized candidate geometry resulted in improved stress homogeneity. Full article

We study 2D RVEs based on microstructures inspired by limpet teeth with the objective of efficiently identifying auxetic designs and building surrogates for effective elastic response. The starting point is an unbalanced database; thus, we run a weighted random forest classifier and a neural network classifier to balance it. The resulting feature importances provide an interpretable ranking of 18 geometric and material variables and guide importance-biased Monte Carlo sampling. Random forest and FCNN classifiers are used to prioritize candidates. Dataset rebalancing is achieved by adding newly FEM-confirmed auxetic samples and applying clustering-guided downsampling to the non-auxetic majority. On this final set, a multi-output FCNN regressor predicts nine targets: inclusion volume fractions and minima/means/maxima of Young’s modulus and Poisson’s ratio. Overall, the framework supports rapid, interpretable screening and property prediction for auxetic composite designs while reducing the need for repeated FEM evaluations. Full article

Building on a previous work presented by the authors, this study extends a fast stress retrieval method to long-fiber angle-ply laminates subjected to constant bending and torque moments. The fiber/matrix interface stress state is efficiently estimated using global deformation data obtained from a finite element analysis performed on a coarse model, potentially employing a homogenized material. Radial basis functions (RBFs) are utilized to bridge the macroscale and microscale, enabling the extraction of appropriate boundary conditions at the representative volume element (RVE) level. A collocation-based Kansa method, also leveraging RBF, is then applied to a carefully selected set of points to determine the local stress distribution. The accuracy of the proposed approach is assessed by comparing its results with high-fidelity FEM sub-modeling. Full article

The gravitational field represents the fundamental stress field in geotechnical engineering. Its influence on soil mechanical behavior is manifested not only through variations in stress magnitude but also through stress gradient effects. However, existing soil mechanics frameworks and classical continuum-based numerical methods cannot characterize the intrinsic mechanical response of granular media under stress gradient conditions. Based on a previously established higher-order continuum theory incorporating stress gradient effects, this study develops a multiscale coupled Finite Element Method–Discrete Element Method (FEM–DEM) numerical framework. The method is implemented using Esys-escript in conjunction with the open-source discrete element platform Yade. By embedding representative volume elements (RVEs) at the finite element level and introducing gravity-induced stress gradients within the RVE using the discrete element method, stress gradient transfer and multiscale coupling are achieved. The proposed method is validated through numerical simulations of triaxial compression and trapdoor tests. The results demonstrate that the method can capture the microscale mechanisms associated with stress gradient effects and effectively resolve the constitutive solution difficulty encountered in the previously proposed generalized continuum framework incorporating stress gradients. The developed framework provides a new numerical tool for investigating the mechanical behavior of granular media under stress gradient conditions, with potential applications in geotechnical problems governed by gravitational fields, including deep underground engineering and extraterrestrial environments with non-conventional gravity. Full article