Search Results (4,244)

Coal gangue manufactured sand (CGS), a sustainable substitute for natural sand, offers both resource and environmental benefits; however, the micro-mechanisms underlying performance deterioration at different replacement levels remain unclear. In this study, cube specimens with 25%, 50%, 75%, and 100% CGS were tested in uniaxial compression, and the results were integrated with PFC2D discrete-element simulations and SEM observations to establish an energy–force-chain–crack coupling framework. Experiments and simulations showed close agreement in peak stress, peak strain, and overall curve shape (errors generally <5%). With increasing replacement, the interfacial transition zone (ITZ) evolves from a dense three-phase ITZ (NS–CGS–CA; natural sand–CGS–coarse aggregate) to a degraded two-phase ITZ (CGS–CA), accompanied by more pores and microcracks; the proportion of Adhesive cracks decreases while Cohesive (intra-particle) cracks increase. Concurrently, continuous force-chain networks deteriorate into localized short-chain clusters; the peak and fraction of strain-energy decrease, whereas frictional/damping dissipation rises—together driving a macroscopic transition from ductile to brittle behavior. At 28 d, SEM images and DEM evolution of cracks/force chains/energy exhibit strong consistency, further confirming that low replacement (25% and 50%) favors stable load-transfer paths and suppresses early cracking, whereas high replacement (75% and 100%)—through ITZ degradation and force-chain instability—induces more concentrated cracking and higher energy dissipation, thereby diminishing mechanical performance. Full article

The study focuses on the T-shaped tunnel scenario with protective doors, performs explosion tests using aluminized explosives, and investigates the propagation patterns and loading characteristics of explosion shock waves in the straight tunnel, at the T-shaped junction, and within the semi-enclosed space in front of the protective door. It was observed that, in comparison to TNT explosives, the overpressure curve of aluminized explosives in the near-explosion zone exhibited a two- batch characteristic. The second batch presented the maximum overpressure peak. In contrast, in the far zone, the curve displayed a stable triangular waveform. In the main tunnel of the T-shaped opening with protective doors, it was found that the back blast surface located in front of the entrance to the main tunnel experienced the maximum momentum, which could be as high as 12 times greater than that of the reflection area on the blast-facing surface at the entrance of the main tunnel and the shock-wave pressure wave pattern can be divided into four batch. The regularities of each measurement point in multiple tests show consistency, highlighting the influence laws of the geometric structure on the wave pattern and load distribution. In addition, this paper integrates LS-DYNA numerical simulation with aerodynamics theory to reveal that shock waves generate expansion waves and oblique shock waves as they pass through the T-shaped opening. After two reflections off the main tunnel wall and the door, a stable propagation waveform is established. In addition, through dimensional analysis and in combination with the experimental results, the momentum at key positions was analyzed and predicted. This study offers a reference for the design of relevant engineering protection measures. Full article

Sixteen beam–column joints with different column types and connection configurations were designed and tested to identify suitable joints for low-rise prefabricated square steel tube (SST) columns and H-beams. The columns included hollow square steel tube (HSST) and concrete-filled square steel tube (CFSST) types, while the joints consisted of welded, end plate, flange-connected, and angle connector plate configurations. Cyclic loading tests were conducted to examine failure modes, hysteresis and skeleton curves, stiffness degradation, and cumulative energy dissipation. The results showed that joints with angle connector plates outperformed welded, end-plate, and flange-connected joints. The height of the triangular stiffener was found to be a critical factor, with a 144 mm stiffener increasing the ultimate bending moment by 78.65% for CFSST and 79.3% for HSST columns, along with notable improvements in stiffness and energy dissipation. Based on Eurocode 3, angle connector plate joints with high stiffeners were classified as semi-rigid and full-strength. A combined assessment of mechanical behavior and economic efficiency indicated that this joint type provides the highest cost-effectiveness and significant application potential. Full article

The mechanical properties of dental implants are critical for their durability. The purpose of this study was to determine the maximum force required to induce full pull-out of a titanium implant from the bone and to characterize the mechanical behavior during this process. First, pull-out tests were performed on monolithic implants embedded in bovine ribs and foam blocks that mimic the mechanical parameters of human bone, allowing a quantitative evaluation of implant–bone interface strength and a comparison of geometric variants. Second, the extraction process was recreated in a three dimensional finite element model incorporating nonlinear interface contact and parameterization, enabling the reproduction of load–displacement curves; the results obtained showed good agreement with the experiment. Third, the fracture surfaces were observed macroscopically and by scanning electron microscopy/energy dispersive spectroscopy. The results demonstrated significant distinctions in the forces required to extract implants with varying thread geometries, clearly indicating the impact of implant design on their mechanical stability. The presented FEM-based methodology provides a reliable tool to study mechanical interactions at the implant–bone interface. The findings obtained can improve our understanding of implant behavior in biological systems and provide a basis for further optimization of their design. Full article

In patients with respiratory failure, mechanical ventilation aims to balance respiratory muscle loading and gas exchange. The interplay between the ventilator and the respiratory muscles is an increasingly recognized factor in tailoring ventilatory support. Surface electromyography (sEMG) offers a non-invasive modality to monitor the respiratory muscles. The sEMG signal, however, requires elaborate processing, which is limitedly standardized and documented. This paper presents the Respiratory Surface Electromyography (ReSurfEMG) package, an open-source Python package for respiratory sEMG analysis developed to address these challenges. ReSurfEMG integrates denoising, feature extraction, and quality assessment in one dedicated library. The effects of over- and under-filtering were compared to ReSurfEMG default settings regarding waveform duration, time-to-peak, amplitude, electrical time product (ETP), pseudo-slope, pseudo-signal-to-noise ratio (SNR), area under the baseline (AUB), and bell-curve error. Under-filtering increased amplitudes (+21%) and ETPs (+10%). Over-filtering smoothed sEMG waveforms, reducing amplitude (−58%), ETP (−39%), and pseudo-slope (−49%), while waveform duration and time-to-peak increased. Default ReSurfEMG settings provided the highest SNRs with similar or lower AUBs and bell-curve errors. The ReSurfEMG library integrates advanced methods dedicated to respiratory sEMG analysis. Systematic assessment using ReSurfEMG showed that signal processing settings affect sEMG features. ReSurfEMG enables reproducible signal processing, facilitating the standardization of respiratory sEMG analysis. Full article

Student dropout remains a persistent challenge in higher education, with substantial personal, institutional, and societal costs. We developed a modular dropout prediction pipeline that couples data preprocessing with multi-model benchmarking and a governance-ready explainability layer. Using 17,883 undergraduate records from a Moroccan higher education institution, we evaluated nine algorithms (logistic regression (LR), decision tree (DT), random forest (RF), k-nearest neighbors (k-NN), support vector machine (SVM), gradient boosting, Extreme Gradient Boosting (XGBoost), Naïve Bayes (NB), and multilayer perceptron (MLP)). On our test set, XGBoost attained an area under the receiver operating characteristic curve (AUC–ROC) of 0.993, F1-score of 0.911, and recall of 0.944. Subgroup reporting supported governance and fairness: across credit–load bins, recall remained high and stable (e.g., <9 credits: precision 0.85, recall 0.932; 9–12: 0.886/0.969; >12: 0.915/0.936), with full TP/FP/FN/TN provided. A Shapley additive explanations (SHAP)-based layer identified risk and protective factors (e.g., administrative deadlines, cumulative GPA, and passed-course counts), surfaced ambiguous and anomalous cases for human review, and offered case-level diagnostics. To assess generalization, we replicated our findings on a public dataset (UCI–Portugal; tables only): XGBoost remained the top-ranked (F1-score 0.792, AUC–ROC 0.922). Overall, boosted ensembles combined with SHAP delivered high accuracy, transparent attribution, and governance-ready outputs, enabling responsible early-warning implementation for student retention. Full article

Hourly PM_2.5 concentrations were measured from February to May 2025 by a network of low-cost sensors located in urban Kraków and its surrounding municipalities. Temporal variability associated with the transition from the heating period to the spring months, together with spatial contrasts, were assessed with principal component analysis (PCA), urban–rural difference curves, and a detailed examination of the most severe smog episode (12–13 February). Particle trajectories generated with the HYSPLIT dispersion model, run in a coarse-grained, 36-task parallel configuration, were combined with kernel density mapping to trace emission pathways. The results show that peak concentrations coincide with the heating season; rural sites recorded higher amplitudes and led the urban signal by up to several hours, implicating external sources. Time-series patterns, PCA loadings, and HYSPLIT density fields provided mutually consistent evidence of pollutant advection toward the city. Parallelizing HYSPLIT on nine central processing unit (CPU) cores reduced the runtime from more than 600 s to about 100 s (speed-up ≈ 6.5), demonstrating that routine episode-scale analyses are feasible even on modest hardware. The findings underline the need to extend monitoring and mitigation beyond Kraków’s administrative boundary and confirm that coarse-grained parallel HYSPLIT modeling, combined with low-cost sensor data and relatively basic statistics, offers a practical framework for rapid source attribution. Full article

The aim of the manuscript is to analyze the influence of the magnetic orientation of steel microfibers (length 13 mm, diameter 0.2 mm) on the mechanical properties and fracture propagation of cementitious composites. The series varied in terms of the volumetric content of the fibers, 0%, 1% and 2% (V_f), and the orientation variant, random (S) or magnetic (S-M, B = 80 mT). Three-point bending tests were performed with force-deflection curve (F-δ) registration. The flexural tensile strength (f_ct,fl), the flexural elastic modulus (E_f), the work of fracture up to a specified residual load level (W_f) and deflection level (W_f*), as well as the compressive strength (f_c) were determined. The improvement of the mechanical properties was noted for magnetically oriented fibers in reference to random arrangement (f_ct,fl: 90–133%; f_c: 12–34%; W_f*: 98–146%). The efficiency factor (η_X) was introduced to determine the change in property per fiber content unit, which enabled comparison regardless of the fiber dosage. As the higher η_X values were determined for 1% content (e.g., f_ct,fl equal to 133%/p.p for V_f = 1% and 45%/p.p for V_f = 2%), further increase in dosage was expected to cause reduced improvement. Different fracture mechanisms were noted for S and S-M composites by means of the Digital Image Correlation method. Full article

IoT (Internet of Things)-enabled solar irradiance sensors are evolving toward energy harvesting, interoperability, and open-source availability, yet current solutions remain either costly, closed, or limited in robustness. Based on a thorough literature review and identification of future trends, we propose an open-source smart wireless sensor that employs a small photovoltaic module simultaneously as sensing element and energy harvester. The device integrates an ESP32 microcontroller, precision ADC (Analog-to-Digital converter), and programmable load to sweep the PV (photovoltaic) I–V (Current–Voltage) curve and compute irradiance from electrical power and solar-cell temperature via a calibrated third-order polynomial. Supporting Modbus RTU (Remote Terminal Unit)/TCP (Transmission Control Protocol), MQTT (Message Queuing Telemetry Transport), and ZigBee, the sensor operates from batteries or supercapacitors through sleep–wake cycles. Validation against industrial irradiance meters across 0–1200 W/m² showed average errors below 5%, with deviations correlated to irradiance volatility and sampling cadence. All hardware, firmware, and data-processing tools are released as open source to enable reproducibility and distributed PV monitoring applications. Full article

In this study, we explored the evolution of mechanical properties in hydroxyl-terminated polybutadiene (HTPB) propellants under fatigue loading by performing fatigue tests with varying maximum stresses and cycle numbers, followed by uniaxial tensile tests on post-fatigue specimens. Residual elongation was used as a key parameter to characterize mechanical behavior, while scanning electron microscopy (SEM) provided insights into the mesostructural morphological changes that occur under different loading conditions, revealing the mechanisms responsible for variations in mechanical properties. The results show that, as the number of loading cycles increases, residual elongation decreases, with three distinct phases of decline—slow change, gradual decline, and rapid deterioration—depending on the stress levels. SEM analysis identified damage mechanisms such as “dewetting” and particle fragmentation at the mesostructural level, which compromise the material’s structural integrity, leading to reduced residual elongation. A novel aspect of this study is the application of Williams–Landel–Ferry (WLF) theory to construct a master curve describing residual elongation decay. This approach enabled the development of a generalized model to predict the material’s degradation under fatigue loading, with experimental validation of the fitted evolution model, offering a new and effective method for assessing the long-term performance of HTPB propellants. Full article

Understanding the combined effects of water and dynamic disturbance on rock behavior is essential for deep underground engineering, where groundwater and blasting often coexist. Existing studies have mainly emphasized static weakening by water or the strength characteristics under impact, while the energy evolution process remains insufficiently addressed. To fill this gap, uniaxial impact compression tests were conducted on dry and water-saturated skarn specimens using a separated Split Hopkinson Pressure Bar system. The relationship between peak stress and impact pressure was analyzed, and the total input energy, releasable elastic strain energy, and dissipated energy were quantified to examine their evolution with strain. The results indicate that water saturation significantly reduces dynamic strength and modifies the damage process. During the compaction and elastic stages, dissipated energy is low but slightly higher in water-saturated specimens due to microcrack initiation. In the plastic stage, dry specimens exhibit faster energy dissipation, while water-saturated specimens show reduced capacity for crack propagation dissipation. Damage–strain curves follow an S-shaped pattern, with water-saturated specimens presenting higher damage growth rates in the plastic stage. These findings clarify the energy-based damage mechanisms of skarn under impact loading and provide theoretical support for evaluating stability in water-rich underground environments. Full article

In order to accurately characterize the temperature dependence of the high-temperature performance of asphalt pavement surface layer materials, this paper studies the effects of temperature, load, and number of actions on the high-temperature anti-rutting performance of asphalt pavement surface layer materials (AC-13 and AC-16 mixtures), based on indoor rutting tests, and constructs a high-temperature performance temperature-dependent model and rutting prediction model for surface layer materials. The results show that as the temperature increases, the dynamic stability of the mixture decreases in an S-shaped curve, and the rut depth increases exponentially. The temperature-dependent model transition temperatures for the dynamic stability of 70#, 50#, 30#, SBS, and HMB asphalt mixtures are 39 °C, 44 °C, 46 °C, 56 °C, and 56 °C, respectively. The dynamic stability of modified asphalt mixtures is significantly higher than that of base asphalt mixtures. The depth of wheel ruts is affected by temperature, load, and the number of actions. The variation ranges of the load index k_P, the temperature index k_T, and the number of actions index k_N are 0.727–1.222, 1.926–2.177, and 0.133–0.295, respectively. The correlation coefficients of the wheel rut prediction model are all above 0.95, and the depth of wheel ruts can be predicted by the model. Full article

Acrylic is increasingly being used in structural engineering applications due to its characteristics of light weight, capability of bulk polymerization, and absence of self-destruction risk, compared to tempered glass. However, structural acrylic exhibits creep behavior when subjected to prolonged loading. In order to study the creep performance of structural acrylic base material and coupons connected using the bulk polymerization technique, short-term tensile tests and long-term creep tests were conducted, and the effect of annealing temperature controlled in the bulk polymerization process was considered. The results show that annealing temperature significantly affects the quality of bulk polymerization. The Burgers model accurately describes the viscoelastic behavior of acrylic, and the Prony series converted from the parameters in the Burgers model can be directly implemented in Abaqus and accurately simulates the creep behavior of acrylic. The equation proposed in this study, on the basis of the Findley model, is precise enough to predict the creep curves of acrylic base material and connecting coupons. The Time–Stress Superposition Principle is valid when the time is greater than the threshold value. Full article

While methods like cyclic triaxial testing and p-y model updating theory exist in geotechnical and offshore wind engineering, they have not been systematically applied to solve the specific deformation problems of offshore PV piles. This study investigates a specific offshore photovoltaic (PV) project in Qinhuangdao City, Hebei Province. Initially, field tests of horizontal static load on steel pipe pile foundations were conducted. A finite element model (FEM) of single piles was subsequently developed and validated. Further analysis examined the failure modes, initial stiffness, and ultimate resistance of offshore PV single piles in sandy soil foundations under varying pile diameters and embedment depths. The hyperbolic p-y curve model was modified by incorporating pile diameter size effects and embedment depth considerations. Key findings reveal the following: (1) The predominant failure mechanism of fixed offshore PV monopiles manifests as wedge-shaped failure in shallow soil layers. (2) Conventional API specifications and standard hyperbolic models demonstrate significant deviations in predicting p-y (horizontal soil resistance-pile displacement) curves, whereas the modified hyperbolic model shows good agreement with field measurements and numerical simulations. This research provides critical data support and methodological references for calculating the horizontal bearing capacity of offshore PV steel pipe pile foundations. Full article

Underreamed anchor bolts, as an emerging anchoring element in geotechnical engineering, operate via a fundamentally distinct load transfer mechanism compared with conventional friction type anchors. The accurate and reliable prediction of their ultimate bearing capacity constitutes a pivotal technological impediment to their broader engineering adoption. Firstly, this paper systematically elucidates the constituent mechanisms of underreamed anchor resistance and their progressive load transfer trajectory. Subsequently, in situ full-scale pull-out experiments are leveraged to decompose the load–displacement response throughout its entire evolution. The multi-stage development law and the underlying mechanisms governing the evolution of anchorage characteristics are thereby elucidated. Based on the experimental dataset, a three-dimensional elasto-plastic numerical model is rigorously established. The model delineates, at high resolution, the failure mechanism of surrounding soil mass and the spatiotemporal evolution of its three-dimensional displacement field. A definitive critical displacement criterion for the attainment of the ultimate bearing capacity of underreamed anchors is established. Consequently, analytical models for the ultimate side frictional stress and end-bearing capacity at the limit state are advanced, effectively circumventing the parametric uncertainties inherent in extant empirical formulations. Ultimately, characteristic parameters of the elasto-plastic branch of the load–displacement curve are extracted. An ultimate bearing capacity prognostic framework, founded on an optimized hyperbolic model, is established. Its superior calibration fidelity to the evolving load–displacement response and its demonstrable engineering applicability are rigorously substantiated. Full article