Search Results (49)

Urban disaster screening requires transparent methods that can integrate heterogeneous open datasets without implying unsupported causal or probabilistic relationships. This study presents an open-data framework for screening flood-footprint population proxies and potential disruption to hospital accessibility in Bucharest, Romania. The analysis covers 104 archived hexagonal spatial units and combines a 100-year flood-depth scenario from the Joint Research Centre, WorldPop 2020 population estimates, hospital-routing outputs derived from OpenStreetMap, and a publicly available seismic screening surface from the European Facilities for Earthquake Hazard and Risk. Flood and seismic information are retained as distinct screening dimensions because the available data do not support modelling their causal interaction, temporal sequence, joint probability, earthquake-related infrastructure damage, or hospital capacity. For spatial units that remain connected to a hospital, a transparent two-domain service-priority index is calculated using flood-footprint population proxy and the potential change in hospital accessibility under the flood scenario. Units for which no hospital route is available are reported separately as binary service-disconnection alerts rather than being assigned an arbitrary numerical penalty. The robustness and interpretability of the framework are examined through network monotonicity, score boundedness, Pareto dominance, penalty-free rank invariance, and rank-acceptability analysis. The results are communicated using a Pareto frontier, rank trajectories across the full weight simplex, indicator-contribution decomposition, and an exact hypergeometric assessment of class overlap. The proposed framework provides a transparent first-order planning tool for identifying locations that may require more detailed investigation. It should be interpreted as a screening approach rather than as a probabilistic risk, cascading-hazard, infrastructure-damage, or service-loss model. Full article

This article examines the reuse of waste polyurethane foam (PUF) as a material in line with circular economy principles. The main objective was to evaluate how crushed polyurethane filler of different bulk densities—35 kg·m⁻³ (PUF35), 60 kg·m⁻³ (PUF60), and their blends at 1–5 wt%—affects the mechanical behaviour and structural integrity of hybrid composite systems and bonded laminated joints. An epoxy resin matrix was combined with 3D-printed polylactide (PLA) honeycomb structures, with rectangular and hexagonal core geometries. Static tensile tests showed that the blended filler (PUF35/60) preserves tensile strength and increases the modulus of elasticity for both core geometries, reaching maximum values at 4 wt% (3.8 GPa for rectangular, 3.6 GPa for hexagonal cores). In bonded lap joints, 1 wt% PUF35 resulted in the highest tensile adhesive bond strength (13.3 MPa). SEM confirmed a high-quality phase interface and continuous adhesive contact between the epoxy matrix and the 3D-printed PLA surface, with dominant cohesive failure and effective mechanical anchoring of foam particles, even near local printing defects. The results confirm mechanically recycled PUF as a promising filler for advanced sandwich structures and adhesive systems. Full article

Population aging has increased demand for walkable community healthcare for older adults. Using the six central districts of Nanjing as a case study, this study examines whether nominal 15 min access to community health service centers (CHSCs) translates into effective and equitable spatial access after accounting for pedestrian-network barriers, distance decay, and population competition. Based on the 2024 official CHSC roster (n = 60), a census-calibrated 100 m population grid, and an OpenStreetMap walking network, we computed walking times from 500 m hexagonal origins at 1.0 m/s. Binary coverage was compared with equal-supply Gaussian two-step floating catchment area accessibility, and population-weighted Lorenz–Gini measures were calculated overall and among covered older residents. Among 581,474 residents aged 65 years and older, only 28.1% could reach a CHSC within 15 min; 24.8% of covered residents fell below the first quartile of competition-adjusted accessibility. The weighted Gini coefficient was 0.861 overall and 0.506 among covered residents, and high-demand, low-effective areas contained 37.9% of the older population. Under the stated assumptions, the results indicate that nominal proximity overstates modeled equal-supply CHSC accessibility and that joint assessment of coverage, accessibility, conditional equity, and spatial typology can better screen areas for subsequent capacity audits, facility-siting assessment, or pedestrian-network improvement. Full article

The longitudinal displacement of the switch rail relative to the sleeper is a critical defect affecting the safety of railway switching operations, as the sleeper serves as the mounting base for the switch machine. Existing measurement methods that rely on the stock rail as a reference are susceptible to reference drift and cannot directly capture the displacement of the switch rail relative to its actuation base. This paper proposes a measurement method for the longitudinal displacement of the switch rail relative to the sleeper using the centers of multiple anchor bolts as reference benchmarks. Based on the fact that both the anchor bolts and the switch machine are fixed to the sleeper, the displacement of the switch rail relative to the bolt centers is equivalent to its displacement relative to the switch machine. Multiple anchor bolt centers on the sleeper are used to establish a stable reference frame. A self-developed mobile measurement device is employed to acquire three-dimensional structured light point clouds of the switch rail area. The coordinates of multiple anchor bolt centers are extracted through hexagon fitting. Abnormal coordinates are eliminated via joint adjustment of the multi-bolt centers, establishing a stable spatial reference frame that enables precise measurement of the longitudinal displacement of the switch rail relative to the sleeper. Field experiments on an operational No. 18 turnout successfully extracted the switch rail tip position and a longitudinal misalignment of −2 mm between the two switch rails. In simulation experiments, a creep displacement of 10 mm and multiple gross errors were artificially introduced; after three iterations, the final measured creep was 9.65 mm, with a deviation of only 0.35 mm, verifying the method’s accuracy and robustness under adverse conditions. Additional experiments on a No. 12 turnout with straight and curved switching states demonstrated that the standard deviation of the longitudinal spacing measurements between bolt centers was 1.17 mm under track switching conditions, confirming the method’s stability in the presence of switch machine movement. The proposed method achieves non-contact, automated measurement of the switch-rail-to-sleeper relative displacement, providing a practical technical pathway for turnout condition monitoring. Full article

Accurately predicting the mechanical response and failure of composite–metal hybrid bolted joints under thermo-mechanical coupled loads remains a critical challenge in aerospace engineering. This paper develops a temperature-dependent multi-scale progressive failure analysis model based on micromechanical failure theory. A hexagonal representative volume element (RVE) incorporating fibers, matrix and interphase is constructed, with a stress amplification factor enabling macro–meso stress–strain transformation. Dimensionless temperature corrections are applied to resin and interphase mechanical properties, and temperature-influenced mesoscopic failure criteria with corresponding stiffness degradation schemes are proposed. The nonlinear progressive damage simulation is implemented via the ABAQUS/UMAT subroutine. Static tensile tests on AC531/CCF800H composite-7075 aluminum alloy three-bolt double-shear joints are conducted at −70 °C, 20 °C and 120 °C. The results show excellent agreement between the simulations and experiments, with ultimate load errors < 5%. Low temperature increases load capacity by 3.91% via resin hardening and enhanced interfacial bonding, while high temperature reduces it by 9.07% due to resin softening. Failure modes shift from end-hole tensile fracture (−70 °C, 20 °C) to full-hole bearing failure (120 °C), governed by altered bolt load distribution and damage evolution paths. The proposed model provides reliable support for thermo-mechanical design and strength verification of aerospace composite structures. Full article

This study experimentally investigates the structural behavior of hexagonal- and square-shaped composite specimens subjected to vertical compression, vertical tension, and diagonal tension loading. The specimens were fabricated using four- and six-layer alkali-resistant (AR) glass textile reinforcements embedded in a modified cementitious mortar via pull, pour, and roll manufacturing techniques. The mechanical performance of polyvinyl alcohol (PVA) fiber-reinforced composite connectors and steel clamp-type elements was also evaluated at the joints of hexagonal specimens under vertical tension and lateral shear loading. The results show that increasing the number of textile layers significantly enhances structural performance. A 50% increase in textile layers improved load-carrying capacity by up to 56% in compression, 104% in tension, and 216% in diagonal tension. Corresponding increases of approximately 20–42% in ductility and up to 266% in energy dissipation capacity were observed. No failure occurred in the connecting elements, confirming their adequate stiffness, strength, and ductility. In addition, validated three-dimensional finite element models were developed to simulate the response of the hexagonal specimens. Overall, the proposed system demonstrates strong potential for applications such as infill walls, cladding, and sandwich panels due to its favorable strength, ductility, and energy absorption capacity. Full article

The Stewart–Gough Platform (SGP) is a spatial parallel manipulator offering high accuracy, rigidity, and adaptability, with applications spanning medical systems, marine engineering, agriculture, manufacturing, entertainment, aerospace, and architectural installations. This paper presents a comparative analytical and computational study of three SGP configurations: the regular SGP, with regular hexagonal base and top platforms; the Irregular-Parallel SGP, derived from the regular SGP by a novel graphical decomposition-and-modification procedure and characterized by similar symmetric hexagonal platforms with limbs preserved parallel; and the Irregular-Skewed SGP, in which the irregular hexagonal platforms of the Irregular-Parallel SGP are retained, but the limbs are connected in an inclined, alternating clockwise (or anticlockwise) topology. The Irregular–Skewed SGP is free from the constraint singularity that persists in the first two configurations and requires the shortest maximum actuator stroke. Static force analysis shows that the regular SGP and the Irregular–Parallel SGP both exhibit a rank-deficient rigidity matrix (rank = 3) across the geometric scaling range tested (radius ratios 1:2 to 1:10; inter-platform distances 100–1000 mm), whereas the Irregular-Skewed SGP achieves full rank (rank = 6) through inclined limb connectivity and is the only configuration capable of sustaining static equilibrium under the loading conditions examined. The forward kinematics of the Irregular-Parallel SGP is verified against a SolidWorks model: under a 9 mm uniform limb extension, the MATLAB and SolidWorks positions of node 7 agree to within 1.27 mm. The rotational workspace volume is equivalent across the three configurations, but the density of valid solution points within that workspace differs. The workspace within joint limits, alternating compression–tension force partition, and asymmetric stroke economy of the Irregular-Skewed SGP indicate applicability to kinetic facades and transformable interiors in architectural-robotics deployment. Full article

Additive manufacturing (AM) is a significant contributor to Industry 4.0. However, one considerable challenge is usually encountered by AM due to the bed size limitations of 3D printers, which prevent them from being adopted. An appropriate post-joining technique should be employed to address this issue properly. This study investigates the influence of key friction stir butt welding (FSBW) factors (FSBWFs), such as tool rotational speed (TRS), tool traverse speed (TTS), and pin profile (PP), on the weldability of 3D-printed PLA–Chromium (PC) composites (3PPCC). A filament containing 10% by weight of chromium reinforced in PLA was used to prepare samples. The material extrusion additive manufacturing process (MEX) was employed to prepare the 3D-printed PCC. A Taguchi-based design of experiments (DOE) (L9 orthogonal array) was employed to systematically assess weld hardness (WH), weld temperature (WT), weld strength (WS), and weld efficiency. As far as the 3D-printed samples were concerned, two distinct infill patterns (linear and tri-hexagonal) were also examined to evaluate their effect on joint performance; however, all other 3D printing factors were kept constant. Experimentally validated findings revealed that weld efficiency varied significantly with PP and infill pattern, with the square PP and tri-hexagonal infill pattern yielding the highest weld efficiency, i.e., 108%, with the corresponding highest WS of 30 MPa. The conical PP resulted in reduced WS. Hardness analysis demonstrated that tri-hexagonal infill patterns exhibited superior hardness retention, i.e., 46.1%, as compared to that of linear infill patterns, i.e., 34%. The highest WTs observed with conical PP were 132 °C and 118 °C for both linear and tri-hexagonal infill patterns, which were far below the melting point of PLA. The lowest WT was evaluated to be 65 °C with a tri-hexagonal infill, which is approximately equal to the glass transition temperature of PLA. Microscopic analysis using a coordinate measuring machine (CMM) indicated that optimal weld zones featured minimal void formation, directly contributing to improved weld performance. In addition, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were also performed on four deliberately selected samples to examine the microstructural features and elemental distribution in the weld zones, providing deeper insight into the correlation between morphology, chemical composition, and weld performance. Full article

Excessive vibration during human knee joint movement poses challenges to biomechanical performance and comfort, which this study aims to mitigate through the design of a bio-inspired honeycomb-based vibration-damping structure, for the purpose of optimizing dynamic vibration absorption efficiency. Three honeycomb geometries—regular triangle, square, and regular hexagon—were evaluated via dynamic mechanical simulation, identifying the regular hexagon as the most effective base configuration. Using the control variable method within reasonable parameter ranges, finite element analysis was employed to systematically examine the influence of wall thickness, side length, and gradient of the regular hexagonal honeycomb on its damping performance. The findings demonstrate that vibration damping is maximized under a configuration with a wall thickness of 1.8 mm, a side length of 6 mm, and a gradient of 110%. Full article

This study investigated the mechanical properties of a boltless hexagonal segment lining structure in TBM tunnels through a 1:10 scale similarity model test. The analysis considered the effects of burial depth and lateral pressure coefficient. A gypsum-diatomite composite simulated C50 concrete segments, and a custom loading system applied equivalent soil-water loads. The tests examined variations in bending moment, axial force and displacement. The results demonstrate that: (1) The tongue-and-groove joints behave like hinges, effectively reducing joint bending moments. (2) The unique staggered interlocking structure induces significantly higher axial forces at the joints than traditional rectangular segments, increasing susceptibility to stress concentration. (3) Increased burial depth has the most significant impact on the tunnel crown, where the bending moment, axial force, and displacement change most notably. (4) The lateral pressure coefficient (λ) alters the joint load transfer mechanism by modifying the structure’s triaxial stress state. An optimal λ of 0.6 maximizes axial force transfer efficiency, while excessively high values impair horizontal load-bearing capacity. (5) Structural failure was ductile, with a final ovality slightly exceeding 10‰. The findings of this study can provide a reference for the design and application of similar boltless hexagonal segment tunnels. Full article

Metals with a hexagonal close-packed (HCP) structure such as magnesium, titanium and zirconium constitute key structural materials in the aerospace, automotive, biomedical and nuclear energy industries. Their welding and regeneration by conventional methods is hindered due to the limited number of slip systems, high reactivity and susceptibility to the formation of defects. Laser technologies offer precise energy control, minimization of the heat-affected zone and the possibility of producing joints and coatings of high quality. This article constitutes a comprehensive review of the state of knowledge concerning laser welding, cladding and regeneration of HCP metals. The physical mechanisms of laser beam interactions are discussed including the dynamics of the keyhole channel, Marangoni flows and the formation of gas defects. The characteristics of the microstructure of joints are presented including the formation of α′ martensite in titanium, phase segregation in magnesium and hydride formation in zirconium. Particular attention is devoted to residual stresses, techniques of cladding protective coatings for nuclear energy with Accident Tolerant Fuel (ATF) and advanced numerical modeling using artificial intelligence. The perspectives for the development of technology are indicated including the concept of the digital twin and intelligent real-time process control systems. Full article

This work quantifies downtime caused by cyberattacks for eight critical urban services in Milan by coupling sectoral Continuous-Time Markov Chains (CTMCs) with an approximately equal-area H3 hexagonal grid of the city. The pipeline ingests OpenStreetMap infrastructure, simulates coupled failure/repair dynamics across sectors (power, telecom, hospitals, ambulance stations, banks, ATMs, surveillance, and government offices), and reports availability, outage burden (area under the infected/down curve, or AUC), and multi-sector distress probabilities. Cross-sector dependencies (e.g., power→telecom) are modeled via a joint CTMC on sector up/down states; uncertainty is quantified with nested bootstraps (inner bands for stochastic variability, and outer bands for parameter uncertainty). Economic impacts use sector-specific cost priors with sensitivity analysis (PRCC). Spatial drivers are probed via hotspot mapping (Getis–Ord $G_i^{*}$, local Moran’s I) and spatial regression on interpretable covariates. In a baseline short decaying attack, healthcare remains the most available tier, while power and banks bear a higher burden; coupling increases P(≥$k\mathrm{sectors}\mathrm{down})$ and per-sector AUC relative to an independent counterfactual, with paired-bootstrap significance at $\alpha =0.05$ for ATMs, banks, hospitals, and ambulance stations. Government offices are borderline, and telecom shows the same direction of effect but is not significant at $\alpha =0.05$. Under a persistent/adaptive attacker, citywide downtime and P(≥2) rise substantially. Costs are dominated by telecom/bank/power under literature-informed penalties, and uncertainty in those unit costs explains most of the variance in total loss. Spatial analysis reveals statistically significant hotspots where exposure and dependency pressure are high, while a diversified local service mix appears protective. All code and plots are fully reproducible with open data. Full article

Wind turbine blades feature complex geometries and operate under harsh conditions, including high curvature gradients, nonlinear deformations, elevated humidity, and particulate contamination. This study presents the design and kinematic analysis of a novel climbing robot based on a 10R folding metamorphic mechanism. The robot employs a hybrid wheel-leg drive and adaptively reconfigures between rectangular and hexagonal topologies to ensure precise adhesion and efficient locomotion along blade leading edges and windward surfaces. A high-order kinematic model, derived from a modified Grubler–Kutzbach criterion augmented by rotor theory, captures the mechanism’s intricate motion characteristics. We analyze the degrees of freedom (DOF) and motion branch transitions for three representative singular configurations, elucidating their evolution and constraint conditions. A scaled-down prototype, integrating servo actuators, vacuum adhesion, and multi-modal sensing on an MDOF control platform, was fabricated and tested. Experimental results demonstrate a configuration switching time of 6.3 s, a single joint response time of 0.4 s, and a maximum crawling speed of 125 mm/s, thereby validating stable adhesion and surface tracking performance. This work provides both theoretical insights and practical validation for the intelligent maintenance of wind turbine blades. Full article

Rockfall poses a significant hazard in steep terrain, where complex ground interactions cause falling boulders to deviate from straight-line paths. While lateral dispersion is commonly used to describe the distribution of deposited boulders from rockfall events, it does not provide any insight into the complexity of boulder trajectories while in motion. This study introduces tortuosity, a metric typically applied in porous media hydraulic analysis, as a novel approach for quantifying the deviation of rockfall paths from linearity. Using high-resolution UAV-based LiDAR data and RocFall3 (Version 1.017) simulation software, this research investigates the effects of terrain model resolution, boulder shape, and boulder mass on tortuosity values for 20,000 simulated rockfalls on a columnar jointed basalt slope in Boise, ID, USA. Results show that increasing terrain resolution leads to higher tortuosity values due to the increased presence of terrain asperities. Spherical boulders exhibited higher tortuosity than hexagonal ones, and tortuosity decreased with increasing mass for spheres, likely due to their momentum overcoming minor terrain features. Hexagonal boulders, constrained by their angular shape, showed less variability in tortuosity across resolutions and sizes. These findings emphasize the limitations of low-resolution publicly available LiDAR data and highlight the critical influence of accurate boulder representation in simulation models. Full article

Transient liquid-phase bonding (TLPB) enables the low-temperature fabrication of encapsulated solder joints with high-temperature resistance and electromigration resilience; yet, Ni-Sn TLPB joints suffer from brittle fracture due to intermetallic compounds (IMCs). This study investigates the Co, Cu, and Pt alloying effects on Ni₃Sn via formation energy, molecular dynamics, and first-principles calculations. Occupancy models of Ni_6−xM_xSn₂ (M = Co, Cu, and Pt) were established, with the lattice parameters, B/G ratios, fracture toughness (K_IC), and stress–strain behaviors analyzed. The results reveal that Co enhances fracture toughness and reduces Ni₃Sn anisotropy, mitigating microcrack risks, while Cu/Pt introduce antibonding interactions (Cu–Sn and Pt–Sn), weakening the bonding strength. The classical B/G brittleness criterion proves inapplicable in Ni–M–Sn systems due to mixed bonding (metallic/covalent) and the hexagonal structure’s limited slip systems. The Ni_6−xCo_xSn₂ formation improves toughness with a low Co content, supported by an electronic structure analysis (density of states and Bader charges). The thermodynamic stability and reduced molar shrinkage (Ni + Sn → Ni₃Sn) confirm Co’s efficacy in optimizing Ni–Sn solder joints. Full article