Search Results (147)

This study examines the effects of kraft lignin, milled hemp stalks, and dicumyl peroxide (DCP) crosslinking on polybutylene succinate (PBS) composites, focusing on rheological, mechanical, and thermal properties as well as accelerated weathering and fungal performance. Two composite series were produced via twin-screw extrusion, (a) simple blends (B-series) and (b) DCP-crosslinked formulations (R-series), with emphasis on hybrid lignin–hemp composites (B-PLH and R-PLH). Rheological analysis showed that hemp fiber increased viscosity, while lignin reduced it, and DCP further enhanced shear-thinning behavior. Mechanical testing confirmed that R-PLH exhibited a 16% increase in flexural strength (42.6 MPa) and a 2.4-fold increase in flexural modulus (1785 MPa) over neat PBS, but tensile strength declined by 19%. Thermal analysis revealed a 14–26% reduction in mass loss rate and increased char formation (up to 16.3% in R-PLH), indicating improved thermal stability. Water absorption showed that hemp fibers increased hydrophilicity, further increased by DCP. Accelerated weathering led to significant color change and surface degradation, particularly in R-PLH. Despite lignocellulosic content, all composites exhibited ≤2% fungal degradation, indicating limited mass loss due to fungal exposure under conditions used in this study. Overall, B-PLH and R-PLH offer a balance of stiffness and thermal stability, though trade-offs in tensile strength and weathering resistance should be considered for sustainable applications. Full article

This study presents a validated numerical investigation into the seismic liquefaction potential of fine-grained reclaimed sediments commonly encountered in coastal, containment, and reclamation projects. Fine-grained reclaimed sediments pose a particular challenge for seismic liquefaction assessment due to their low permeability, high fines content, and complex cyclic response under earthquake loading. A fully coupled, nonlinear finite element model was developed using the Pressure-Dependent Multi-Yield (PDMY) constitutive framework, calibrated against laboratory Cyclic Direct Simple Shear (CDSS) tests and verified using in situ Cone Penetration Tests with pore pressure measurement (CPTu). The model effectively captured the dynamic response of saturated sediments, including excess pore pressure generation, cyclic mobility, and post-liquefaction behavior, under three earthquake ground motions: Livermore, Chi-Chi, and Loma Prieta. Results showed that near-surface layers (0–2.3 m) experienced full liquefaction within two to three cycles, with excess pore pressure ratios (R_u) approaching 1.0 and peak pressures closely matching laboratory data with less than 10% deviation. The numerical approach revealed that traditional CPT-based cyclic resistance methods underestimated liquefaction susceptibility in intermediate layers due to limitations in accounting for pore pressure redistribution, evolving permeability, and seismic amplification effects. In contrast, the finite element model captured progressive strength degradation, revealing strength gain in deeper layers due to consolidation, while upper zones remained vulnerable due to low confinement and resonance effects. A critical threshold of R_u ≈ 0.8 was identified as the onset of rapid shear strength loss. The findings confirm the advantage of advanced numerical modeling over empirical methods in capturing the complex cyclic behavior of reclaimed sediments and support the adoption of performance-based seismic design for such geotechnically sensitive environments. Full article

This study investigates hygrothermal durability of bio-epoxy composites reinforced with carbon, E-glass, basalt, and flax fibres. Fibre yarns and bio-composites were exposed for 3000 h at 60 °C and 98% relative humidity. The tensile strength reduction in the fibres and the interfacial shear strength (IFSS) reduction in the composites were assessed after ageing. Chemical deterioration was evaluated using energy-dispersive X-ray spectroscopy (EDS); morphological changes in fibres and composites fracture surfaces were examined using a scanning electron microscope (SEM). Results indicated that the durability was significantly influenced by fibre types. Tensile strength reduction was higher in carbon, glass and basalt compared to flax yarns because of chemical degradation of the sizing layer in synthetic fibres, while only physical damage was observed in flax. The IFSS reduction was highest in flax composites (10%), and lowest in carbon (4%). EDS indicated the hydrolysis and erosion of fibre sizing, with reduced silica content in glass and basalt fibres. SEM revealed matrix-dominated failure in carbon/bio-epoxy, interfacial debonding in glass and basalt composites, fibre slip and pull-out in flax/bio-epoxy. Overall, the results highlighted damage propagation pathways and demonstrated that bio-epoxy composites exhibited reasonable performance under hygrothermal ageing, supporting their potential as a sustainable alternative in durability-critical applications. Full article

Existing freeze–thaw cycle tests are based on freeze–thaw cycles under fully constrained conditions, but under natural conditions, the vertical deformation of soil during freeze–thaw cycles is much greater than the lateral deformation. Therefore, to better simulate the freeze–thaw process of shallow soil under natural conditions, a method of preparing specimens is proposed. Specimens with five freeze–thaw cycle gradients, four water content gradients and three dry density gradients were prepared. This method realises the top-unconstrained role of the specimens during freeze–thaw cycles and provides space for vertical deformation. At the same time, it enables the observation of height and surface degradation. Triaxial tests of shallow Ili loess were carried out after indoor freeze–thaw cycles under fixed confining pressure (100 kPa). The results show that surface degradation and vertical deformation of Ili loess without top restraint increase gradually with the number of freeze–thaw cycles; strength decreases gradually and damage morphology changes from shear to bulging. Threshold conditions for the transition from softening to hardening in the strength curve of Ili shallow loess are proposed, as well as damage parameters related to freeze–thaw cycles, water content, and dry density. A coupled damage constitutive model applicable to shallow Ili loess has been established that takes these three factors into account. Full article

The rapid expansion of carbon-fiber-reinforced polymer (CFRP) applications in aerospace, automotive, and energy sectors has intensified concerns over end-of-life waste and the absence of efficient recycling solutions. Plasma-assisted solvolysis has emerged as a promising hybrid approach, combining oxidative chemical treatment with plasma activation to accelerate matrix degradation. In this study, CFRP cylinders (6.4 cm height, 5.5 cm internal, and 6.0 cm external diameter) were processed in a closed-loop plasma solvolysis system under varied operational parameters, including plasma power, plasma gas composition, and nitric acid concentration. The mechanical performance of the recovered carbon fibers was assessed through single-fiber tensile and microbond tests, evaluating both tensile and interfacial properties. In most cases, the recycled fibers retained—or even exceeded—the tensile strength of their virgin counterparts, reaching up to 1.49 times that of the virgin fibers. Young’s modulus, though more variable, ranged from 0.48 to 1.67 times the reference value depending on treatment conditions. Elongation at break generally increased, particularly in the 24K (24,000-filaments) fiber sets, suggesting improved surface ductility. Weibull statistical analysis indicated higher consistency in 3K (3000-filaments) fiber batches compared to 24K, whereas interfacial shear strength was moderately retained across conditions. Overall, balanced plasma and acid conditions enabled efficient fiber recovery with high strength and interfacial performance, validating plasma-assisted solvolysis as a viable route for recovering high-performance fibers suitable for structural reuse, in alignment with circular economy principles. Full article

Composite materials are widely utilized for their excellent properties; however, the mismatch in phase response during processing often induces surface and subsurface damage. While reducing the cutting depth is a common strategy to improve quality, it shifts the material removal mechanism from shear to ploughing–extrusion, which can, in fact, degrade the final surface integrity. Energy field assistance is a promising approach to suppress this issue, yet its underlying mechanism remains insufficiently understood. This study investigates high-silicon aluminum alloy by combining turning experiments with molecular dynamics simulations to elucidate the origin and evolution of damage under different energy fields, establishing a correlation between microscopic processes and observable defects. In conventional turning, damage propagation is driven by particle accumulation and dislocation interlocking. Ultrasonic vibration softens the material and confines plastic deformation to the near-surface region, although excessively high transient peaks can lead to process instability. Laser remelting turning disperses stress within the remelted layer, significantly inhibiting defect expansion, but its effectiveness is highly sensitive to variations in cutting depth. The hybrid approach, laser remelting ultrasonic vibration turning, leverages the dispersion buffering effect of the remelted layer and the localized plastic deformation from ultrasonication to reduce peak loads, control deformation depth, and suppress defects, while simultaneously mitigating the depth sensitivity of damage and maintaining removal efficiency. This work clarifies the mechanism by which a composite energy field controls damage in the micro-cutting of high-silicon aluminum alloy, providing practical guidance for the high-quality machining of composite materials. Full article

To investigate the seepage and deformation failure characteristics of deep unloaded rock mass under cyclic loading and unloading disturbance, a series of triaxial cyclic loading and unloading tests were conducted on granite. These tests were performed under varying seepage pressures and unloading conditions to analyze the mechanical properties, seepage behavior, and fracture failure characteristics of the material. The findings indicate the following: (1) An increase in seepage pressure and unloading magnitude results in pronounced radial expansion characteristics in the rock specimens following cyclic loading and unloading. Additionally, the axial, radial, and volumetric residual strains exhibit a nonlinear acceleration in growth as the number of cyclic loading and unloading applications increases. (2) The elastic modulus of rocks exhibits two distinct phases: an initial rapid decline followed by a steady-state decrease. Concurrently, Poisson’s ratio demonstrates an initial decrease, which is subsequently followed by a consistent increase. Furthermore, when considering the effects of unloading, the inflection point of the Poisson’s ratio curve will occur earlier. (3) The interplay between seepage pressure and unloading conditions markedly exacerbates the damage and degradation of the rock. Specifically, under conditions of 70% unloading and a seepage pressure of 4 MPa, the peak stress of the rock specimen is reduced by 21.90%, and the peak intensity permeability increases by 446.70%. (4) Under conditions of high confining pressure and elevated seepage pressure, V-shaped conjugate shear fracture surfaces are likely to develop during the cyclic loading failure of granite, accompanied by a limited number of secondary shear cracks. Concurrently, tensile failure surfaces that are parallel to the maximum principal stress are also observed under the influence of unloading. Full article

This study evaluated the effect of delay time and storage conditions after airborne-particle abrasion on the shear bond strength between base metal alloys (BMA) and self-adhesive resin cement. It also assessed whether vacuum sealing or re-airborne-particle abrasion could counteract the time-related degradation of bond strength. Sixty BMA specimens were airborne-particle-abraded and divided into six groups (n = 10): immediate bonding; 1-day, 7-day, and 14-day delays; 14-day vacuum-sealed; and 14-day delay with re-airborne-particle abrasion. Resin cement was applied to standardized bond areas, and composite rods were bonded. All specimens were stored in water at 37 °C for 24 h before shear bond strength testing. Failure modes were examined under a stereomicroscope. One-way ANOVA revealed significant differences among groups (p < 0.05). Immediate bonding yielded the highest strength (26.50 ± 2.74 MPa). Bond strength declined with delays, namely, 1-day (21.19 ± 4.94 MPa), 7-day (15.20 ± 4.52 MPa), and 14-day (16.01 ± 4.69 MPa), with no significant difference between the 7- and 14-day groups. Vacuum sealing for 14 days preserved bond strength (25.92 ± 3.94 MPa) comparable to immediate bonding. Re-airborne-particle abrasion restored bond strength (20.66 ± 3.70 MPa). Prolonged delays resulted in 100% adhesive failures, whereas immediate bonding and intervention groups showed 80% adhesive and 20% mixed failures. Delayed bonding after airborne-particle abrasion significantly reduces bond strength due to oxide layer formation on the BMA surface. However, surface sealing might prevent surface oxidation and maintain bonding potential, while re-airborne-particle abrasion can restore bond strength when delays are unavoidable. Clinically, bonding should be performed immediately after airborne-particle abrasion, or appropriate surface management protocols should be implemented to maintain optimal adhesion. Full article

Carbon nanotubes (MWCNTs) were synthesized in situ on para-aramid fabrics (gCPO) via a low-temperature (450 °C) chemical vapor deposition (CVD) process to enhance interfacial pull-out, frictional, and fracture toughness characteristics. FESEM analysis confirmed CNT coverage on fiber surfaces, while FTIR, Raman, and XRD results indicated limited structural modification without significant polymer degradation. The CNT-functionalized fabrics exhibited a 66.19% increase in maximum pull-out force, 55.32% improvement in interlacement rupture strength, and a three-fold rise in intra-yarn shear resistance compared with control fabrics (KPO). The static and kinetic friction coefficients increased by 26.67% and 16.67%, respectively, due to CNT-induced surface roughness, enhancing inter-fiber load transfer and reducing slippage. Single-yarn pull-out tests revealed notable gains in energy dissipation and fracture toughness (up to 1769 J/m²), whereas multi-yarn pull-out performance decreased due to excessive friction surpassing filament strength. The study demonstrates that low-temperature MWCNT growth enables effective interfacial reinforcement of soft para-aramid fabrics, establishing a novel framework for meso-scale mechanical screening of flexible nano-ballistic composites. 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

The long-term stability of grout-reinforced fractured rock masses in acidic groundwater environments after tunnel fires is critical for the safe operation of underground engineering. In this study, grouting reinforcement tests were performed on fractured diorite specimens using a high-strength fast-anchoring agent (HSFAA), and their mechanical degradation and microstructural evolution mechanisms were investigated under coupled high-temperature (25–1000 °C) and acidic corrosion (pH = 2) conditions. Multi-scale characterization techniques, including uniaxial compression strength (UCS) tests, X-ray computed tomography (CT), scanning electron microscopy (SEM), three-dimensional (3D) topographic scanning, and X-ray diffraction (XRD), were employed systematically. The results indicated that the synergistic thermo-acid interaction accelerated mineral dissolution and induced structural reorganization, resulting in surface whitening of specimens and decomposition of HSFAA hydration products. Increasing the prefabricated fracture angles (0–60°) amplified stress concentration at the grout–rock interface, resulting in a reduction of up to 69.46% in the peak strength of the specimens subjected to acid corrosion at 1000 °C. Acidic corrosion suppressed brittle disintegration observed in the uncorroded specimens at lower temperature (25–600 °C) by promoting energy dissipation through non-uniform notch formation, thereby shifting the failure modes from shear-dominated to tensile-shear hybrid modes. Quantitative CT analysis revealed a 34.64% reduction in crack volume (V_ca) for 1000 °C acid-corroded specimens compared to the control specimens at 25 °C. This reduction was attributed to high-temperature-induced ductility, which transformed macroscale crack propagation into microscale coalescence. These findings provide critical insights for assessing the durability of grouting reinforcement in post-fire tunnel rehabilitation and predicting the long-term stability of underground structures in chemically aggressive environments. Full article

The reactivation of the Longdongpo ancient colluvial landslide in Sinan County, Guizhou Province represents a typical multi-factor coupled failure. Based on detailed geological investigations and FLAC^3D fluid–solid coupling numerical simulations, this study reveals its complex reactivation mechanisms. The analysis demonstrates that long-term groundwater action has significantly weakened the slip zone at the soil–bedrock interface, causing strength degradation and inducing prolonged quasi-stable creep deformation of the slope. The artificial cut slopes formed in the middle-to-lower sections disrupted the original stress field and induced localized plastic deformation. Crucially, the numerical simulation identified a 5 m rainfall infiltration depth as the threshold triggering abrupt instability; when exceeding this critical value (simulated as 10 m and 16 m infiltration depths), pore water pressure surged (>2.7 MPa) and displacement dramatically increased (>2.2 m), reducing shear strength along the potential failure surface to critical levels. This process culminated in the full connection of the shear surface and the landslide’s catastrophic reactivation. This work quantitatively elucidates the chain-reaction mechanism of “long-term groundwater weakening → engineering disturbance initiation → critical-depth rainfall infiltration triggering”, providing vital quantitative evidence for regional ancient landslide risk prevention. Full article

The water-level fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR) experiences seasonal submergence and exposure, resulting in soil structure degradation and intensified erosion. This study investigated how flooding duration affects root development and the erosion resistance of root–soil complexes in the WLFZ of the TGR. Two representative herbaceous species were chosen for this study: Xanthium sibiricum, an annual with a taproot system, and Cynodon dactylon, a perennial with a fibrous root system. Root traits, soil erodibility K-value, shear strength, and soil texture were measured from plant and soil samples collected at different flooding durations (145–175 m elevations). Our results showed that prolonged flooding significantly suppressed root growth, particularly in the 145–155 m zone, where root length density and root tips were markedly reduced (p < 0.05). Soil erodibility increased with flooding duration, with erodibility K-values ranging from 0.050 ± 0.002 to 0.062 ± 0.001 t·hm²·h/(MJ·mm·hm²), while shear strength declined correspondingly. Textural shifts from silty loam to silt were observed at zones experiencing extended flooding, contributing to aggregate instability and decreased internal friction angles. Notably, Cynodon dactylon demonstrated superior soil reinforcement capacity compared to Xanthium sibiricum, with its root volume and surface area significantly correlated with reduced K-values (p < 0.01) and enhanced shear strength (p < 0.001), enabling it to better prevent bank erosion under flooding conditions. These findings underscore the importance of root morphological traits in maintaining soil stability under hydrological stress and highlight the potential of perennial fibrous-rooted species for vegetation-based erosion control in fine-textured riparian zones. This study provides a theoretical basis and practical reference for ecological restoration in the WLFZ of the TGR and similar environments. Full article

This study presents a high-performance external strengthening strategy for reinforced concrete (RC) beam–column joints, integrating near-surface mounted (NSM) Carbon Fiber Reinforced Polymer (C-FRP) ropes with externally bonded C-FRP sheets. The X-shaped ropes, anchored diagonally on both principal joint faces and complemented by vertical ropes at column corners, provide enhanced core confinement and shear reinforcement. C-FRP sheets applied to the beam’s plastic hinge region further increase flexural strength and delay localized failure. Three full-scale, shear-deficient RC joints were subjected to cyclic lateral loading. The unstrengthened specimen (JB0V) exhibited rapid stiffness deterioration, premature joint shear cracking, and unstable hysteretic behavior. In contrast, the specimen strengthened solely with X-shaped C-FRP ropes (JB0VF2X2c) displayed a markedly slower rate of stiffness degradation, delayed crack development, and improved energy dissipation stability. The fully retrofitted specimen (JB0VF2X2c + C-FRP) demonstrated the most pronounced gains, with peak load capacity increased by 65%, equivalent viscous damping enhanced by 55%, and joint shear deformations reduced by more than 40%. Even at 4% drift, it retained over 90% of its peak strength, while localizing damage away from the joint core—a performance unattainable by the unstrengthened configuration. These results clearly establish that the combined C-FRP rope–sheet system transforms the seismic response of deficient RC joints, offering a lightweight, non-invasive, and rapidly deployable retrofit solution. By simultaneously boosting shear resistance, ductility, and energy dissipation while controlling damage localization, the technique provides a robust pathway to extend service life and significantly enhance post-earthquake functionality in critical structural connections. Full article

Icing represents a significant hazard to the flight safety of unmanned aerial vehicles (UAVs), particularly affecting critical aerodynamic surfaces such as air intakes, wings, and empennages. While conventional adhesive electrothermal de-icing systems are straightforward to operate, they present safety concerns, including a 15–25% increase in system weight, elevated anti-/de-icing power consumption, and the risk of interlayer interface delamination. To address the objectives of reducing weight and power consumption, this study introduces an innovative electrothermal–structural–durability co-design strategy. This approach successfully led to the development of a glass fiber-reinforced polymer (GFRP) component that integrates anti-icing functionality with structural load-bearing capacity, achieved through an embedded hot-pressing process. A stress-damage cohesive zone model was utilized to accurately quantify the threshold of mechanical performance degradation under electrothermal cycling conditions, elucidating the evolution of interfacial stress and the mechanism underlying interlayer failure. Experimental data indicate that this novel component significantly enhances heating performance compared to traditional designs. Specifically, the heating rate increased by approximately 202%, electrothermal efficiency improved by about 13.8% at −30 °C, and interlayer shear strength was enhanced by approximately 30.5%. This research offers essential technical support for the structural optimization, strength assessment, and service life prediction of UAV anti-icing and de-icing systems in the aerospace field. Full article