Search Results (6,972)

Addressing the core issue of rock mass failure and deformation induced by local water-induced uneven expansion in expansive soft rock tunnels, this study systematically analyzes the stress–displacement response of the rock mass under various working conditions. This analysis integrates physical model testing with FLAC3D 6.0 numerical simulation and covers four typical expansion zone configurations (vault, spandrel, haunch, invert) as well as multiple stages of stress loading. Leveraging the mathematical analogy between heat conduction and fluid seepage and combining it with a thermo-hydraulic coupling approach, the FLAC3D temperature field module precisely simulates the moisture-induced stress field. This overcomes the limitations of traditional tools for direct moisture field simulation and enables quantitative assessment of how localized expansion impacts tunnel lining failure. The study reveals that horizontal expansion zones significantly increase the risk of shear failure in tunnel structures. Expansion zones at the tunnel crown and base (invert) pose critical challenges to overall safety and exhibit a pronounced nonlinear relationship between stress loading and displacement. This research deepens the theoretical understanding of the interaction between localized non-uniform expansion and the surrounding rock mass and provides crucial technical guidance for optimizing tunnel support systems and improving disaster monitoring and prevention measures. Full article

The topic of the present study is the aerodynamic performance of a Natural Laminar Flow (NLF) wing for UAVs at low speed. The basis is a thoroughly tested NLF airfoil in the wind tunnel of NASA which is well-customized for light aircrafts. The aim of this work is the numerical verification that a typical wing design (tapered with moderate aspect ratio and wash-out), being constructed out of aerodynamically highly efficient NLF airfoils during cruise, can deliver high aerodynamic loading under minimal freestream turbulence as well as realistic atmospheric conditions of intermediate turbulence. Thus, high mission flexibility is achieved, e.g., short take off/landing capabilities on the deck of ship where moderate air turbulence is prevalent. Special attention is paid to the effect of the Wing Tip Vortex (WTV) under minimal inflow turbulence regimes. The flight conditions are take off or landing at moderate Reynolds number, i.e., one to two millions. The numerical simulation is based on an open source CFD code and parallel processing on a High Performance Computing (HPC) platform. The aim is the identification of both mean flow and turbulent structures around the wing and subsequently the formation of the wing tip vortex. Due to the purely three-dimensional character of the flow, the turbulence is resolved with advanced modeling, i.e., the Improved Delayed Detached Eddy Simulation (IDDES) which is well-customized to switch modes between Delayed Detached Eddy Simulation (DDES) and Wall-Modeled Large Eddy Simulation (WMLES), thus increasing the accuracy in the shear layer regions, the tip vortex and the wake, while at the same time keeping the computational cost at reasonable levels. IDDES also has the capability to resolve the transition of the boundary layer from laminar to turbulent, at least with engineering accuracy; thus, it serves as a high-fidelity turbulence model in this work. The study comprises an initial benchmarking of the code against wind tunnel measurements of the airfoil and verifies the adequacy of mesh density that is used for the simulation around the wing. Subsequently, the wing is positioned at near-stall conditions so that the aerodynamic loading, the kinematics of the flow and the turbulence regime in the wing vicinity, the wake and far downstream can be estimated. In terms of the kinematics of the WTV, a thorough examination is attempted which comprises its inception, i.e., the detachment of the boundary layer on the cut-off wing tip, the roll-up of the shear layer to form the wake and the motion of the wake downstream. Moreover, the effect of inflow turbulence of moderate intensity is investigated that verifies the bibliography with regard to the performance degradation of static airfoils in a turbulent atmospheric regime. Full article

The performance of resin anchoring agents in deep coal mine roadways is significantly compromised by water-bearing and chemically aggressive conditions, posing a major threat to support system reliability. This study aims to systematically quantify this performance deterioration and develop a more resilient material solution for these challenging environments. A comprehensive experimental program was conducted, including uniaxial compression, pull-out, and interface shear tests, accompanied by the systematic improvement of the resin formulation and microstructural analysis via Scanning Electron Microscopy (SEM). The results showed that increasing borehole water content to 30% reduced the compressive strength of conventional resin by over 40%, while acidic environments (pH = 5) caused a 70% drop in its interfacial shear strength. In contrast, an improved formulation incorporating hydroxypropyl acrylate and a super absorbent polymer (SAP) exhibited a 20% higher initial strength, maintained over 85% of its strength under water saturation, and retained functional residual strength in acidic conditions. SEM analysis confirmed that the improved resin’s denser microstructure suppressed interfacial microcrack formation. The findings demonstrate that the improved formulation provides a robust material basis for enhancing the long-term durability and safety of anchorage support systems in extreme underground engineering environments. Full article

The construction sector’s environmental footprint is driving the adoption of sustainable modular timber systems. The WikiHouse Skylark is a promising open-source model whose structural reliability depends on the performance of its critical plywood TIE joints. This study presents an experimental investigation of full-scale TIE joints fabricated from 18 mm Pinus radiata plywood in three variants: Standard (STD), Weather-Resistant (HR), and Fire-Resistant (FR). Monotonic tensile and shear tests were conducted to evaluate load–displacement behavior and failure modes. While the mean ultimate strengths varied between panel types, with HR highest in tension (7.7 kN) and FR highest in shear (8.2 kN), the most critical finding was the effect of the treatments on failure mode. The FR treatment induced a brittle fracture with significantly reduced ductility, in contrast to the more ductile tearing observed in STD and HR panels. This highlights a clear strength–ductility trade-off introduced by the fire-retardant treatment, a key consideration for structural design in modular timber construction. This dataset provides an essential empirical foundation for the numerical modeling and design guidelines of WikiHouse TIE joints, advancing the development of resilient and sustainable prefabricated housing. Full article

Bamboo fiber is a prime green fiber due to its renewability, biodegradability, and high specific strength. Bamboo-fiber-reinforced epoxy (BFRE) composites have seen extensive use and shown great promise for natural biofiber-reinforced friction materials. Inspired by the decussated fiber alignment of bovine enamel, this study investigated how fiber orientation influences the tribological properties of BFRE composites. Specifically, the proportion of fibers oriented vertically to the surface was varied at seven levels: 0%, 25%, 33%, 50%, 67%, 75%, and 100%. The tribological performance was assessed through wear reciprocating testing and microscopic morphological characterization techniques. Results indicate that the bio-inspired fiber decussation can reduce the wear loss of the BFRE composites. Among all bio-inspired BFRE composites, BFRE composites with 67% vertical fibers achieve the best wear resistance. The vertical fibers in the BFRE composites can withstand pressure to provide a “compression–rebound” effect, while the parallel fibers can resist shear stress. The decussated structure inhibits crack initiation and propagation during wear and promotes transfer film formation, reducing wear loss. The findings expand understanding of the correlation between the bovine-tooth-like decussated structure and its tribological mechanisms, thereby offering essential guidance for the biomimetic design of high-performance BFRE composites for friction material application. Full article

In rock slopes with a three-section landslide, the locking section is the key control factor. This study conducted double-sided freeze–thaw tests on a scale model of a rock slope with a three-section landslide in a cold region. We monitored the changes in frost heave force, strain, and fracture during the water–ice phase change and investigated the effect of the trailing edge tensile crack length on the frost heave fracture of the locking section. A crack frost heave model was proposed based on rock and fracture mechanics to explore the mechanism of slope crack freeze–thaw weathering. According to the results, the slope shoulder froze first, with the freezing front progressing from the slope shoulder to the interior of the rock mass. The fracture failure in the three-section rock slopes was mostly caused by the frost heave of the trailing-edge tensile cracks. The largest frost heave force and locking section deformation occurred when the temperature of the top of the trailing edge tensile crack decreased from −3.5 °C to −6 °C (whereas that of the bottom of the crack dropped from 0 °C to −2.6 °C). Additionally, the results demonstrate that the frost heave force is positively correlated with the length of the trailing edge tension crack, and shear marks are virtually absent on the tensile fracture surface. Full article

Background: Functional lumbar segmental instability (FLSI) is a clinically significant subtype of nonspecific low back pain, characterized by impaired motor control during mid-range spinal motion. Despite its prevalence, diagnostic approaches remain fragmented, and no single clinical test reliably captures its complexity. This scoping review aims to synthesize current evidence on the reliability, validity, subclassification, and predictive value of manual tests used in the evaluation of FLSI, and to identify conceptual and methodological gaps in the literature. Methods: A structured search was conducted across five databases (PubMed, Scopus, Web of Science, CINAHL, Embase) between May and August 2025. Twenty-four empirical studies and eleven foundational conceptual sources were included. Data were charted into five thematic domains: conceptual frameworks, diagnostic accuracy, reliability, subclassification models, and predictive value. Methodological appraisal was performed using QUADAS and QAREL tools. Results: The Passive Lumbar Extension Test (PLET) demonstrated the most consistent reliability and clinical utility. The Prone Instability Test (PIT) and Posterior Shear Test (PST) showed variable performance depending on protocol standardization. Subclassification models distinguishing functional, structural, and combined instability achieved high inter-rater agreement. Screening tools for sub-threshold lumbar instability (STLI) showed preliminary feasibility. Predictive validity of manual tests for rehabilitation outcomes was inconsistent, suggesting the need for multivariate models. Conclusions: Manual tests can support the clinical evaluation of FLSI when interpreted within structured diagnostic frameworks. Subclassification models and composite test batteries enhance diagnostic precision, but standardization and longitudinal validation remain necessary. Future research should prioritize protocol harmonization, integration of sensor-based technologies, and stratified outcome studies to guide individualized rehabilitation planning. Full article

The manufacturing industry, in general, and the plastic industry, in particular, have been developing new materials and process methods that need a correct study and optimization. Nowadays, the main approach to optimize these processes is using numerical methods and, in the case of particulate materials, the Discrete Elements Method to estimate the particles interactions. But those mathematical models use some parameters that depend on the material and must be calibrated, thus requiring an important computational and experimental cost. In this study, we integrate different speed-up procedures and present a general calibration method of Low-Density Polyethylene particles, to obtain the calibrated solid density and Poisson’s ratio of the material, the restitution, static and rolling friction factors in the particle-to-particle and particle-to-wall interactions, and the contact model variables (damping factor, stiffness factor, and energy density). For this calibration, four different tests were carried out, both experimentally and with simulations, obtaining the bulk density, the repose and shear angles, and the dropped powder. All these response variables were compared between simulations and experimental tests, and using genetic algorithms, the input parameters (design variables) were calibrated after 85 iterations, obtaining a Mean Absolute Percentage Error of the response variables lower than 2% compared to the experimental results. Full article

Based on the high strength and superior deformation control capabilities of rock strata, a novel cantilever anti-floating ledge has been proposed to resist the floating of underground structures in rock strata. To explore the actual anti-floating effect and working performance of the structure, laboratory shear tests were designed based on the actual project. The shear characteristics and failure evolution process were then discussed using the Particle Flow Code (PFC) numerical simulation. The main conclusions are as follows. The shear stress–shear displacement curve of the cantilever anti-floating ledge can be described as six stages according to the different states of stress and deformation. With the increase in groundwater buoyancy, the damage to the cantilever anti-floating ledge occurs successively from the ledge, the concrete–rock interface, the connection between the ledge and the side wall, and the connection between the ledge and the bottom plate. Local damage and delamination of the interface do not affect the structural strength, but structural cracks should be prevented from continuing to form and connect. It is necessary to pay attention to the stress and deformation state of the crack-prone area mentioned above, improve the reinforcement ratio in the crack-prone area, and strengthen the bond between the concrete and the rock. Full article

Milk products are a diverse group of foods and important sources of essential nutrients, including high-quality proteins, fatty acids, vitamins, and minerals. Among their key quality attributes, texture is particularly critical, as it strongly influences consumer perception and overall product quality. Numerous devices and techniques have been developed to evaluate the texture of milk products, most of which rely on mechanical tests such as puncture, compression, shearing, creep, and relaxation. Instrumental evaluations are essential for correlating physical measurements with sensory perceptions, yet several challenges limit their reliability. Inconsistencies in testing protocols—such as reporting force versus penetration depth versus force versus time; variations in testing temperature, sample shape and dimensions; probe geometry; compression depth; and container size for semisolid samples contribute to discrepancies across studies. Additionally, many studies omit these critical methodological details, reducing reproducibility and comparability. This review systematically examines the current methods used to assess dairy product texture, identifies gaps and challenges in standardization, and provides guidance to support future research aimed at obtaining accurate, reproducible, and meaningful texture measurements. Full article

Natural rock materials, containing micro-cracks and pore defects, significantly alter their mechanical behavior. This study investigated fracture interactions of red sandstone containing double close-round holes (diameter: 10 mm; bridge angle: 30°, 45°, 60°, 90°) using acoustic emission (AE) monitoring and the discrete element simulations method (DEM), which was a novel methodology for revealing dynamic failure mechanisms. The uniaxial compression tests showed that hole geometry critically controlled failure modes: specimens with 0° bridge exhibited elastic–brittle failure with intense AE energy releases and large fractures, while 45° arrangements displayed elastic–plastic behaviors with stable AE signal responses until collapse. The quantitative AE analysis revealed that the fracture-type coefficient k had a distinct temporal clustering characteristic, demonstrating the spatiotemporal synchronization of tensile and shear crack initiation and propagation. Furthermore, numerical simulations identified a critical stress redistribution phenomenon, that axial compressive force chains concentrated along the loading axis, forming continuous longitudinal compression zones, while radial tensile dispersion dominated hole peripheries. Crucially, specimens with 45° and 90° bridges induced prominently symmetric tensile fractures (85° to horizontal direction) and shear-dominated failure near junctions. These findings can advance damage prediction in discontinuous geological media and offer direct insights for optimizing excavation sequences and support design in cavern engineering. Full article

Reservoir landslides undergo saturated–unsaturated transitions under hydrological variations. Matric suction significantly influences slip-zone soil strength. Existing studies lack analysis of suction–rate–strength coupling, while Amontons’ model fails for cohesive soils. This study investigated Huangtupo landslide slip-zone soil in the upper reaches of the Yangtze River using pressure plate and saturated salt solution methods to determine the soil–water characteristic curve. Suction-controlled ring shear tests were conducted under three matric suction levels ($\Psi$ = 0, 200, and 700 kPa) across net normal stresses (${\sigma }_{net}$ = 100–800 kPa) and shear rates ($\dot{\gamma }$ = 0.05–200 mm/min). Key findings revealed the following: (1) significant suction–rate coupling effects were shown, with 700 kPa suction yielding 30% higher residual strength than saturated conditions, validating matric suction’s role in enhancing effective stress and particle contact strength; (2) residual cohesion showed strong logarithmic correlation with shear rate, with the fastest growth below 10 mm/min, while the residual friction angle varied minimally (0.68°), contributing little to overall strength; (3) a bivariate model relating residual cohesion to $\dot{\gamma }$ and $\Psi$ was established, overcoming traditional single-factor limitations. The study demonstrates that dual-parameter Coulomb modeling effectively captures multi-field coupling mechanisms in unsaturated slip-zone soils, providing theoretical foundations for landslide deformation prediction and engineering design under dynamic hydrological conditions. Full article

As oil and gas exploration advances, the development of deep, low-permeability, high-temperature, and high-salinity reservoirs poses increasing challenges. To address this, a novel amphoteric surfactant (TASS) was synthesized via free radical polymerization, and a high-performance water-based fracturing fluid system was developed. The system exhibited excellent thermal and salt resistance, with viscosity decreasing by less than 3.3% after 72 h at 150 °C and 20 wt% NaCl. It demonstrated clear shear-thinning behavior and strong elasticity. Interfacial activity tests showed that increasing NaCl concentrations reduced interfacial tension from 28.5 to 24.3 mN/m, while the contact angle on sandstone surfaces decreased significantly, indicating enhanced wettability and oil flow. Field applications further confirmed its effectiveness, with oil and gas production increasing by 81% and 133%, respectively, and a payback period of around 10 days. These results highlight the TASS fracturing fluid as a promising solution for stimulation in complex reservoirs. Unlike conventional betaine-type VES, the silane-grafted amphoteric design of TASS ensures viscosity retention at 220 °C and 25 wt% salinity. Full article

The synergistic preparation of geopolymer from lithium slag, fly ash, and slag for underground construction can facilitate the extensive recycling of lithium slag. The effects of different activator moduli and water–binder ratios on the mechanical properties and damage mechanisms of the lithium-slag-based geopolymer were investigated by uniaxial compression tests and acoustic emission (AE) monitoring. The results show that, based on a comprehensive evaluation of peak stress, crack closure stress, plastic deformation stress, and elastic modulus, the optimal activator modulus is determined to be 1.0, and the optimal water-to-binder ratio is 0.42. At low modulus values (0.8 and 1.0) and low water–binder ratio (0.42), the AE events exhibit a steady pattern, indicating slow crack initiation and propagation within the geopolymer; with the increasing activator modulus and water-to-binder ratios, the frequency of AE events increases significantly, indicating more-frequent crack propagation and stress mutation within the geopolymer. Similarly, when the modulus is 0.8 or 1.0 and the water–binder ratio is 0.42, the sample presents a macroscopic tensile failure mode; as the modulus and water–binder ratio increase, the sample presents a tensile–shear composite failure mode. The energy evolution laws of geopolymer specimens with different activator moduli and water-to-binder ratios were analyzed, and a damage constitutive model was established. The results indicate that, with optimized mix proportions, the material can be used as a supporting material for underground spaces. Full article

Background: Adhesion to enamel is influenced by surface preparation, which affects the micromechanical retention of resin-based materials. Sodium hypochlorite (NaOCl) deproteinization has been proposed as a pretreatment to improve acid etching efficacy, but the optimal application time remains unclear. Methods: This in vitro study evaluated the effect of 5% NaOCl pretreatment at three exposure times (15, 30, and 60 s) on shear bond strength (SBS), the adhesive remnant index (ARI), and enamel etching patterns. Extracted human premolars (n = 140) were divided into four groups: the control (acid etching only) and three experimental groups. SBS was tested per ISO 11405, while ARI scores were assessed under stereomicroscopy, and surface morphology was examined by scanning electron microscopy (SEM). Results: The 30-s NaOCl group exhibited the highest SBS (20.9 MPa) compared with the control (15.9 MPa, p < 0.05) and 15-s (14.9 MPa, p < 0.05) groups. SEM analysis showed predominantly Type I–II etching patterns for the 30-s group, irregular Type III for 15 s, and overetched Type IV with loss of prism definition for 60 s, compromising the adhesive interface. ARI scores indicated 86.7% of samples in the 30-s group retained all adhesive on enamel (score 3). Conclusions: A 30-s 5% NaOCl pretreatment before acid etching improved enamel micromorphology and bonding performance compared to shorter or longer exposures. The intermediate duration provided effective deproteinization without structural damage, whereas prolonged exposure degraded the enamel microstructure. This protocol may offer a simple, cost-effective method to enhance clinical adhesive procedures, though prolonged exposure (60 s) should be avoided due to structural degradation of the enamel microstructure. Full article