Search Results (4,319)

In situ physical coal fracturing is one of the key technologies for deep coal resource extraction, among which the liquid nitrogen cyclic freeze–thaw (LNCFT) technique demonstrates remarkable fracturing effects and promising application potential in physical coal breaking. To determine economically viable mining and coalbed methane (CBM) extraction cycles, this study builds on previous research and conducts a series of experiments to investigate the effects of different cold condition temperatures and freeze–thaw cycles on the mesoscopic surface structure and macroscopic mechanical properties of deep, water-rich coal-rock samples. A statistical damage constitutive model for saturated coal-rock under coupled freeze–thaw and loading, incorporating a damage threshold, was established to more accurately describe the damage patterns and mechanisms. The results indicate that lower cold condition temperatures lead to greater mesoscopic crack propagation, lower uniaxial compressive strength, and significantly reduced freeze–thaw failure cycles. Under −45 °C, saturated coal-rock samples experienced macroscopic failure after only 23 freeze–thaw cycles, which is 9 and 15 cycles fewer than those under −30 °C and −15 °C, respectively. Furthermore, measurements of wave velocities in three directions before and after testing revealed that freeze–thaw cycles caused particularly pronounced damage in the direction perpendicular to the bedding planes. Additionally, the established coupled statistical damage constitutive model provides a more accurate and intuitive analysis of the entire process from damage to failure under different cold conditions, showing that as the temperature decreases and freeze–thaw cycles increase, the coal-rock’s brittleness diminishes while plastic deformation and ductile failure characteristics are enhanced. In summary, for coal and CBM extraction using the LNCFT technique, it is recommended to extract gas once after approximately 35 cycles of liquid nitrogen injection. This study provides a theoretical basis for the application of liquid nitrogen cyclic freeze–thaw technology in deep coal fracturing. Full article

Samples of H13 tool steel were produced using the LENS^® laser additive manufacturing technique. Three variants of samples were produced such that during and 2 h after deposition, both the substrate and sample temperatures were maintained at 80, 180, and 350 °C. After the samples were produced, the effect of the substrate temperature on their metallurgical quality, microstructure, and mechanical properties was determined. No segregation of alloying elements was observed. The test results indicate that, depending on the temperature used, the structure of the H13 alloy is martensitic or martensitic-bainitic with a slight residual austenite content of up to 2.1%. Owing to structural changes, the obtained alloy is characterized by lower impact strength compared with conventionally produced alloys and high brittleness, particularly when using an annealing temperature of 350 °C. Isothermal annealing above the martensite start temperature results in extreme brittleness due to a partial structural transformation of martensite into bainite and probable carbide precipitation processes at the nanoscale. Full article

This study explores the machinability of Material Extrusion (MEX) printed parts made from carbon fiber-reinforced polylactic acid (PLA). MEX-printed parts typically exhibit high surface roughness, necessitating post-processing to enhance their quality. In this work, milling was used as a post-processing method to improve the surface finish. Response surface methodology (RSM) experimental design was employed to investigate the effects of cutting velocity, feed rate, and depth of cut on the surface quality of the machined surfaces. Results showed that the as-built MEX-printed sample exhibited a high average surface roughness (Sa) of ~7.982 µm, indicating the need for post-processing. Post-processing milling considerably enhances the Sa by reducing it to ~1.621 µm under the optimal condition. Statistical findings showed that all considered factors have significant influence on the Sa, with feed rate as the most influential one, contributing to 47.63% of the total variation. The Sa values varied from 1.834 µm to 4.146 µm due to changes in the considered factors. Increasing feed rate leads to the emergence of cavities and ridges along the deposited filaments associated with brittle removal mechanism, resulting in higher surface roughness. Full article

The mineralogical, geochemical, and statistical characteristics of recent fluvial deposits from the Brahmaputra–Jamuna River, Bangladesh, were examined to determine their provenance, transport dynamics, and depositional environment. Sediments were analyzed using X-ray diffraction (XRD), wavelength dispersive X-ray fluorescence (WD-XRF), field emission scanning electron microscopy (FE-SEM), and electron probe microanalysis (EPMA). Grain size analysis revealed a predominance of medium-to-fine sand (mean grain size 1.77–3.43 ϕ), with moderately well-sorted textures (sorting: 0.33–0.77 ϕ), mesokurtic to leptokurtic distributions, and skewness values ranging from −0.21 to +0.30. Mineralogical results show a high quartz content with minor feldspar, mica, zircon, rutile, and iron-bearing minerals. Geochemical data indicates high SiO₂ (63.39%–70.94%) and Al₂O₃ (12.25%–14.20%) concentrations and calculated chemical index of alteration (CIA) values ranging from 60.90 to 66.82. The microstructural study revealed angular to sub-angular grains with conchoidal fractures and stepped microcracks, indicating brittle deformation under high-energy conditions, which is consistent with short transport distances, limited sedimentary recycling, and a derivation from mechanically weathered source rocks. Multivariate analyses (PCA and K-means clustering) of grain size parameters reveal two distinct sedimentary regimes, namely Cluster 1 as finer-grained (2.36 ϕ), poorly sorted sediments, and Cluster 2 as coarser (2.98 ϕ), well-sorted deposits. Discriminant function values (Y₂: 78.82–119.12; Y₃: −6.01 to −2.56; V₁: 1.457–2.442; V₂: 1.409–2.323) highlight shallow water, fluvial/deltaic aspects, and turbidite depositional environments. These findings advance the understanding of sedimentary dynamics within large, braided river basins and support future investigations into the sustainable management of fluvial depositional environments. Full article

We developed a model to predict the quality of fresh goji berries during storage by analyzing the correlations of their dielectric properties. The variations in these properties with storage temperature, time, and frequency were systematically characterized to inform the model. Leveraging these relationships, we developed a model to predict quality. The analysis integrated measurements of dielectric properties with assessments of texture and key physicochemical indicators. Results indicate that dielectric parameters exhibit significant frequency dependence. Complex impedance (Z), capacitance (Cp), and resistance (Rp) all decreased sharply with increasing frequency, with the most pronounced change observed in Cp. Conductance, G, and reactance, X, increased with frequency, reaching maximum increases of 360.86% and 87.79%, respectively. Under the specific test frequency of 163,280 Hz, a strong polynomial relationship was observed between the dielectric parameters and storage time, with all fitted models yielding ${\mathit{R}}_{adj}^2$ values above 0.94. The quality factor Q (a dimensionless number for the energy efficiency of a resonant circuit or medium) showed a near-perfect correlation with brittleness, while reactance, X, was correlated with springiness and cohesiveness, with correlation coefficients approaching 0.999 under the optimal test frequency. The constructed ANN model demonstrated high prediction accuracy for hardness, brittleness, elasticity, cohesiveness, chewiness, and soluble solids content (R² > 0.97, MSE < 5%) but performed poorly in predicting adhesiveness, stickiness, and rebound elasticity (R² < 0.9). The constructed LSSVM model showed good prediction performance for some indicators (hardness, springiness, cohesiveness, and SSC) (R² > 0.94), but its prediction accuracy was low for brittleness and chewiness (R² < 0.9). Overall, its performance and generalization ability were inferior to the ANN model. This study shows that ANN models based on dielectric properties establish a technical foundation for the non-destructive, automated monitoring of goji berry storage quality, thereby providing a critical tool for dynamic quality tracking and value assessment within integrated warehouse management systems. Full article

Lateral pipe-soil interaction is crucial for the on-bottom stability design of submarine pipelines, particularly on deep-water sloping silt seabeds. To address this, a mechanical-actuator facility has been specially designed and utilized to simulate the lateral instability process of a pipe on silt slopes (α) ranging from −15° to +15°. In this study, variations in the dimensionless submerged pipeline weight (G = 0.607–1.577) and initial embedment ratios (|e₀|/D = 0.01–0.50) are also considered. Experimental results reveal several key findings. First, brittle pipe-soil responses are observed: under embedment ratios larger than 0.05, the breakout soil resistance is dominated by suction due to negative pore pressure generation at the rear of the pipe, whereas under lower embedment ratios, it is primarily governed by interface friction and cohesion. Second, for a constant submerged pipeline weight (G = 1.092), the breakout drag force increases linearly with slope angle, whereas the breakout soil resistance decreases linearly—a difference attributed to the gravitational component W_ssinα. Specifically, compared to a horizontal flat seabed, the breakout lateral drag force increases by approximately 33% for upslope instability (α = +15°), but decreases by about 24% for downslope instability (α = −15°). Third, the dimensionless lateral-soil-resistance coefficient on silt increases nonlinearly and monotonically with the slope angle, a trend opposite to that reported for sandy seabeds. Finally, an improved model is proposed that explicitly incorporates silt slope angle, submerged pipeline weight, and embedment ratio. This study aims to offer valuable insights into the stability of pipelines on partially drained continental silt slopes and to support the adoption of slope-specific criteria in future engineering designs. Full article

Due to the large emissions of greenhouse gases from the burning of fossil fuels and people’s demand for green materials and energy, the development of environmentally friendly triboelectric nanogenerators (TENGs) is becoming increasingly significant. Silk fibroin (SF) is considered an ideal biopolymer candidate for fabricating green TENGs due to its biodegradability and renewability. However, its intrinsic brittleness and relatively weak triboelectric performance severely limit its practical applications. In this study, SF was physically blended with poly(ethylenimine) (PEI), a polymer rich in amino groups, to fabricate SF/PEI composite films. The resulting films were employed as tribopositive layers and paired with a poly(tetrafluoroethylene) (PTFE) tribonegative layer to assemble high-performance TENGs. Experimental results revealed that the incorporation of PEI markedly enhanced the flexibility and electron-donating capability of composite films. By optimizing the material composition, the SF/PEI-based TENG achieved an open-circuit voltage as high as 275 V and a short-circuit current of 850 nA, with a maximum output power density of 13.68 μW/cm². Application tests demonstrated that the device could serve as an efficient self-powered energy source, capable of lighting up 66 LEDs effortlessly through simple hand tapping and driving small electronic components such as timers. In addition, the device can function as a highly sensitive self-powered sensor, capable of generating rapid and distinguishable electrical responses to various human motions. This work not only provides an effective strategy to overcome the intrinsic limitations of SF-based materials but also opens up new avenues for the development of high-performance and environmentally friendly technologies for energy harvesting and sensing. Full article

To reveal the mesoscopic fracture mechanism of fissured concrete, this study employed the discrete element method (DEM) and adopted the parallel bond model (PBM) within the two-dimensional particle flow code (PFC2D) to construct a mesoscopic model of concrete semi-circular bending (SCB) specimens with prefabricated fissures. Three sets of schemes were designed by varying prefabricated fissure angles (0–45°), aggregate contents (30–45%), and porosities (3–6%), and numerical simulations of three-point bending loads were conducted to explore the effects of each parameter on the crack propagation law and load-bearing performance of the specimens. Validation was performed by comparing the simulated load–displacement curves with the typical quasi-brittle mechanical characteristics of concrete (exhibiting “linear elastic rise–pre-peak stress fluctuation–nonlinear decline”) and verifying that the DEM could accurately capture the entire process from microcrack initiation at the aggregate–mortar interface, crack deflection/bifurcation induced by pores, to macroscopic fracture penetration—consistent with the known mesoscopic damage evolution law of concrete. The results indicate that the crack propagation mode evolves from straight extension to tortuous branching as parameters change. Moreover, the peak strength first increases and then decreases with the increase in each parameter: when the fissure angle is 15°, the aggregate content is 35%, and the porosity is 4%, the specimens achieve an optimal balance between crack propagation resistance and energy dissipation, resulting in the best load-bearing performance. Specifically, the prefabricated fissure angle dominates the stress type (tension–shear transition); aggregates regulate crack resistance through a “blocking–diverting” effect; and pores, acting as defects, influence stress concentration. This study verifies the reliability of DEM in simulating concrete fracture behavior, enriches the mesoscopic fracture theory of concrete, and provides reliable references for the optimization of concrete material proportioning (e.g., aggregate–porosity ratio adjustment) and anti-cracking design of infrastructure (e.g., pavement, tunnel linings) in engineering practices. Full article

The mechanical performance of cast iron is strongly governed by the morphology of its graphite phase, yet establishing a quantitative link between microstructure and macroscopic properties remains a challenge. In this study, a three-dimensional finite element method (FEM)-based micromechanical framework is proposed to analyze and predict the mechanical behavior of cast iron with representative graphite morphologies, spheroidal and flake graphite. Realistic representative volume elements (RVEs) are reconstructed based on experimental microstructural characterization and literature-based X-ray computed tomography data, ensuring geometric fidelity and statistical representativeness. Cohesive zone modeling (CZM) is implemented at the graphite/matrix interface and within the graphite phase to simulate interfacial debonding and brittle fracture, respectively. Full-field simulations of plastic strain and stress evolution under uniaxial tensile loading reveal that spheroidal graphite promotes uniform deformation, delayed damage initiation, and enhanced ductility through effective stress distribution and progressive plastic flow. In contrast, flake graphite induces severe stress concentration at sharp tips, leading to early microcrack nucleation and rapid crack propagation along the flake planes, resulting in brittle-like failure. The simulated stress–strain responses and failure modes are consistent with experimental observations, validating the predictive capability of the model. This work establishes a microstructure–property relationship in multiphase alloys through a physics-informed computational approach, demonstrating the potential of FEM-based modeling as a powerful tool for performance prediction and microstructure-guided design of cast iron and other heterogeneous materials. Full article

In this study, the joining of Cu/Al tubes was achieved using the magnetic pulse-assisted semi-solid brazing (MPASSB) technique. A coupled finite element method–smoothed particle hydrodynamics (FEM-SPH) model was established to analyze the influence mechanism of solid–liquid interface interaction on pore formation during the brazing forming process. The results indicate that the MPASSB technique can produce Cu/Al tube joints with excellent metallurgical bonding and performance at 390 °C, and no brittle Cu/Al intermetallic compounds (IMCs) are formed in the joints. Additionally, a stronger solid–liquid interface interaction and a higher surface roughness of the tubes lead to easier peeling of the copper matrix from the interface, thereby promoting pore formation. Mechanical property tests show that the shear strength of the joints prepared by this method can reach 63.3 MPa, and the fracture occurs in the brazing seam area adjacent to the copper–side interface. The MPASSB technique is expected to provide a feasible technical approach for the high-quality joining of dissimilar Cu/Al materials. Full article

This study assesses the flexural performance of concrete beams repaired with externally bonded carbon-fiber-reinforced polymer (CFRP) patches under controlled damage conditions. Prismatic beams (7 × 7 × 28 cm) underwent three-point bending tests in four configurations: uncracked, uncracked-reinforced, cracked-unrepaired, and cracked-repaired. Pre-existing damage was caused by mid-span notches at a = 7, 21, and 35 mm. CFRP patches were placed on the tension face, and the ultimate load and failure mode were recorded. Repairing CFRP beams increased maximum load by up to 240% compared to unrepaired counterparts, and the failure characteristic changed from brittle shear to ductile flexural. Strengthening uncracked beams also yielded significant benefits. These findings show that patch-type CFRP reinforcement effectively recovers and enhances flexural performance across a wide range of crack severity, and they provide quantitative guidelines for determining repair levels depending on original crack depth. Full article

To investigate the deterioration pattern of the rheological properties of high-viscosity high-elasticity asphalt (HVEA) under UV and salt freeze–thaw (SFT) cycle environments, two snowmelt salts were used for coupled aging tests, along with temperature sweep, bending beam rheological (BBR), and Fourier-transform infrared spectroscopy (FT-IR) tests. The results showed that both snowmelt salts could enhance the high-temperature rutting resistance of HVEA, in which the enhancement effect of NaCl was more significant. With the increase in salt concentration, the BBR stiffness of HVEA decreased and then increased, while the m-value showed the opposite trend, indicating that the addition of snowmelt salt impaired its low-temperature creep performance. Additionally, UV-SFT aging would exacerbate the degradation of low-temperature crack resistance. The temperature sensitivity of HVEA gradually decreased with the drop of viscosity temperature sensitivity (VTS) value; salt corrosion further significantly reduced its temperature sensitivity. UV-SFT aging would significantly weaken fatigue performance of HVEA, especially after 15 cycles. FT-IR test showed that UV-SFT resulted in the enhancement of S=O and C=C characteristic peaks, suggesting that the HVEA underwent oxidization and chemical aging, which increased the low-temperature brittleness. Full article

To address the problem of corrosion, glass fiber-reinforced polymer (GFRP) bars have been introduced as a viable alternative to conventional steel reinforcement in concrete structures. While extensive research has been conducted on the flexural behavior of RC beams reinforced with steel and GFRP bars over both normal-term and long-term periods, studies focusing on fresh concrete beams are almost non-existent. Consequently, this research investigates the impact of steel and GFRP longitudinal reinforcement, as well as the influence of varying concrete compressive strengths, on the flexural behavior of RC beams. The study employs 3-point bending experiments and machine learning (ML) predictive analyses. Specifically, the short-term (fresh) concrete reinforcement compatibility and the effects of steel and GFRP bar reinforcements on beam flexural behavior were examined across three concrete compressive strength categories: low (C25), moderate (C35), and high (C50). A notable contribution of this research is the application of different ML regression models, utilizing Python’s library, for deflection prediction of RC beams. The failure mechanisms of the beams under static loading conditions were analyzed, revealing that composite bar RC beams failed through flexural cracking and demonstrated ductile behavior, whereas steel bar RC beams exhibited brittle failure characterized by shear cracks and sudden failure modes. The ML regression models successfully predicted the deflection values of RC beams under ultimate loads, achieving an average accuracy of 91.3%, which was deemed highly satisfactory. Among the 18 beams tested, the highest ultimate load was obtained for the SC50-1 beam at 87.46 kN. In contrast, while the steel-reinforced beams exhibited higher load-bearing capacities, it was observed that the GFRP-reinforced beams showed greater deflection and ductility, particularly in beams with low and medium concrete strengths. Based on these findings, it is recommended that the Gradient Boosting Regressor, an AI regression model, be utilized to guide researchers in evaluating the load-carrying and bending capacity of structural beam elements. Full article

This study examines the flexural behavior of reinforced concrete (RC) beams that utilize steel, glass fiber-reinforced polymer (GFRP), and hybrid steel–GFRP longitudinal bars. It considers variations in stirrup material (steel or GFRP) and stirrup spacing (100 mm or 200 mm). Nine beam specimens were subjected to three-point bending tests until failure. Their performance was assessed based on ultimate load, deflection, stiffness, ductility, energy absorption, and failure mode. The experimental program aimed to isolate the effects of transverse reinforcement detailing and to elucidate the role of stirrup characteristics in governing the transition between flexure and shear-controlled behavior. The findings indicated that both the type of reinforcement and the configuration of stirrups significantly influenced structural performance. Steel-reinforced beams demonstrated stable and ductile flexural behavior, whereas GFRP-reinforced beams supported loads up to 18% higher but experienced abrupt failure in brittle shear with restricted ductility. Hybrid beams effectively integrated the benefits of both materials: The HS100 specimen, which featured closely spaced steel stirrups, achieved the highest ultimate load (162.5 kN), maximum deflection (19.7 mm), and greatest energy absorption (2450 kN·mm). In contrast, beams utilizing GFRP stirrups exhibited early diagonal cracking and abrupt failure, even with closely spaced stirrups. The study indicates that hybrid steel–GFRP reinforcement can enhance the strength, ductility, and toughness of reinforced concrete beams, contingent upon the application of sufficient steel confinement. The findings provide practical recommendations for enhancing hybrid RC design by positioning steel in tension and utilizing steel stirrups for confinement, while effectively employing GFRP in compression zones or in corrosive environments. Full article

This study investigates the combined effects of compression along the grain by 20% after steaming (pleating), and thermal treatment on the mechanical and physical properties of beech (Fagus sylvatica L.) and sessile oak (Quercus petraea (Matt.) Liebl.). Pleating significantly increased plasticity and maximum deflection, reaching 339% of untreated values in beech and 337% in oak. However, it reduced bending strength and modulus of elasticity to about 50%. Keeping the specimen compressed for 5 h (fixation) during the thermo-hydro-mechanical modification process of pleating further decreased the modulus of elasticity to 26%–29% of untreated levels. Thermal treatment at 160 °C increased bending strength of fixated specimens to 120.5% in beech and 125.3% in oak, partially restoring strength, while at 200 °C, it decreased drastically to 26.7% and 21.5%, respectively. Density was reduced by thermal treatment, with oven-dry values decreasing by 6.2% (beech) and 12.7% (oak) at 160 °C, and by 18.2% and 25.1% at 200 °C. The results indicate that high-temperature treatment (200 °C) leads to wood with brittle properties. Full article