Search Results (881)

With its excellent physical and mechanical properties, granite is often the first choice for the foundation material for dams in water conservancy engineering. However, alteration can profoundly change the mineral composition, structure, and mechanical behavior of deep granite, posing critical challenges to project safety. The Quwu Mountain area in Baiyin, Gansu Province, a proposed pumped storage reservoir, exposes extensive Silurian granite. Engineering investigation shows that different levels of clay and hydrothermal alteration have taken place in the granite rock mass, and the level of alteration exhibits a distinct vertical zonation as revealed by borehole core logging. In this study, we quantitatively characterize the porosity, compressive strength, wave velocity, and shear parameters of altered granite of different degrees through mineralogical analysis, laboratory tests, and in situ testing. In order to guide the construction in this area, we establish a classification system that distinguishes weak, moderate, and strong alteration degree, based on macroscopic features, RQD, and clay mineral content. Results of this paper show that alteration is dominated by potassium feldspathization and kaolinitization, leading to increased porosity (4–10%) and structural loosening. Strongly altered granite exhibits severe mechanical degradation, moderately altered granite retains medium strength, and weakly altered granite approaches the properties of fresh rock. This research can provide technical support for engineering safety design and risk prevention in the Quwushan reservoir area, but its applicability to other regions requires further validation. Full article

Water level fluctuations in reservoir areas subject bank slopes to intense wet–dry cycles (WDCs), compromising rock mass stability. This study investigates the macro–meso damage evolution of yellow sandstone from the Wudongde Reservoir. Specimens subjected to 0–20 WDCs were analyzed using nuclear magnetic resonance (NMR) alongside Brazilian splitting, uniaxial, and triaxial compression tests. Results indicate that porosity increases linearly with WDC, rising from 6.12% to 17.61% after 20 cycles, driven by the transformation of micropores into macropores. Macroscopic mechanical parameters, particularly tensile strength and cohesion, exhibit significant exponential and sharp decay, respectively, while the internal friction angle remains relatively stable. Notably, increasing confining pressure effectively mitigates WDC-induced deterioration by inhibiting microcrack propagation. The damage mechanism is primarily attributed to the dissolution of clay binder and uneven mineral swelling/shrinkage, whereas the rigid mineral skeleton remains largely intact. These findings provide a theoretical basis for quantifying rock damage and predicting slope stability in complex hydrological environments. Full article

Initial excavation-induced damage may alter water-driven weakening and failure in bedded shale, yet direct experimental evidence from comparable loading–hydration routes remains limited. In this study, uniaxial compression tests with acoustic emission (AE) monitoring were conducted on bedded shale from the Longmaxi Formation in the Sichuan Basin, China, under two routes, i.e., direct saturation (DS) and pre-damage followed by saturation (PDRS), across seven bedding orientations from 0° to 90°. Pre-damage was introduced by loading–unloading to 0.6 of the orientation-dependent peak strength, producing measurable defects and reducing P-wave velocity by an average of 1.23% while preserving the overall anisotropic pattern of wave propagation. Compared with DS, PDRS caused clear mechanical deterioration, with mean reductions of 37.63% in peak strength and 31.14% in elastic modulus. Both routes retained pronounced bedding-angle dependence, although the locations of minimum strength and stiffness differed between them. AE activity in the PDRS group generally initiated earlier and accumulated more persistently before peak stress. RA–AF analysis showed that tensile-like cracking dominated across all bedding orientations in PDRS, whereas the DS group exhibited stronger orientation-dependent variation in cracking mode. The b-value range was also narrower in PDRS than in DS, indicating reduced dispersion of event-size statistics among orientations. Macroscopically, failure evolved from more distributed multi-crack and mixed-mode patterns in DS to more localized dominant-fracture failure with reduced branching in PDRS. Overall, the results suggest that pre-damage before saturation changes the subsequent weakening and fracture development of bedded shale during reloading. Full article

Driven by the evolution of electric drive systems in electric vehicles, aerospace, and industrial machine tools, high-speed operation has become a key direction in motor development. While progress in emerging manufacturing technologies and novel materials has partially alleviated the inherent contradiction between electromagnetic performance and mechanical strength in high-speed rotors, traditional approaches—including geometric optimization of flux bridges and center posts, macroscopic material replacement, and structural reinforcements—tend to make the multi-physics trade-offs increasingly complex. The application of dual-phase soft magnetic laminate presents a promising alternative. By achieving localized regulation of rotor characteristics, this approach effectively decouples electromagnetic performance from mechanical constraints. Although the technical merits have been verified, the existing literature lacks a systematic overview of the fabrication technologies and application status of dual-phase soft magnetic material laminate. Hence, this paper aims to provide a comprehensive review of recent fabrication approaches and development trends, thereby serving as a fundamental reference for researchers aiming to integrate this material into innovative rotor topologies. Full article

Carbonate reservoirs in the Shunbei area develop pronounced fracture networks after acidized hydraulic fracturing and thus have the potential to be repurposed as underground gas storage (UGS) after hydrocarbon depletion. Characterizing their mechanical behavior is essential for safe UGS operation; however, deep to ultra-deep natural cores are difficult to obtain, and conventional macroscopic tests often cannot provide parameters that meet engineering requirements. To address this issue, nanoindentation combined with QEMSCAN (Quantitative Evaluation of Minerals by Scanning Electron Microscopy) was employed to quantify microscale mineral distributions and the mechanical properties of the major constituents. The investigated rock is calcite-dominated (89.62%), with minor quartz (9.89%) and trace feldspar-group minerals (1.89%). Minerals are randomly embedded, and soft–hard phase boundaries are widely distributed. A finite–discrete element method (FDEM) model was then constructed and calibrated in ABAQUS. The discrepancies in uniaxial compressive strength and elastic modulus relative to laboratory results were 6.51% and 9.91%, respectively, indicating good agreement in both mechanical response and failure mode. Parametric analyses using three additional models with different mineral proportions show that damage preferentially initiates at mineral phase boundaries and stress concentration zones induced by end constraints. Microcracks then propagate and coalesce into a dominant compressive–shear band, and final failure is mainly governed by slip along the shear band with localized tensile cracking. With increasing quartz and feldspar contents, enhanced heterogeneity and a higher density of phase boundaries lead to a higher density of crack nucleation sites and increased crack branching, and the failure pattern transitions from a single shear-band–controlled mode to a more network-like fracture system. Moreover, macroscopic strength is not determined solely by the intrinsic strength of individual minerals; heterogeneity and phase-boundary characteristics strongly govern microcrack behavior, such that higher hard-phase contents may result in a lower peak strength. Full article

Granular materials exhibit complex mechanical behaviors during unloading, yet the underlying micro- and meso-scale mechanisms remain unclear. This study employs a discrete element method to simulate a series of triaxial tests on sand and pebble specimens with varying initial densities under different unloading stress paths. While dense specimens demonstrate strain softening and dilatancy, loose samples exhibit shear contraction. To quantify the underlying fabric evolution, persistent homology (PH) theory is adopted to analyze the particle contact force networks. The results reveal that the average strength of this network correlates strongly with the macroscopic stress–strain response. For dense samples, network strength rapidly increases to a peak coinciding with the deviatoric stress maximum, then gradually decreases with further shear. Crucially, this evolution is path-dependent: the average contact force network strength increases approximately 20% more during unloading in the minor principal stress direction compared to unloading in the major principal stress direction. This quantitative analysis of force chain degradation provides a mechanistic explanation for the observed strain softening, highlighting the dominant role of the unloading stress path. In contrast, loose specimens, which initially lack an obvious force chain network, show negligible microstructural evolution during unloading. Full article

Laser powder bed fusion (LPBF) of AA7075 is severely constrained by a narrow process window and susceptibility to defect formation (hot cracking and porosity), which often dominates performance. In this study, 5 wt.% AlCoCrFeNi_2.1 high-entropy alloy (HEA) particles, volumetric energy density (VED = 74–222 J·mm⁻³), and subsequent T6 heat treatment were systematically investigated to reveal their combined effects on defect structure, crystallographic texture/substructure, and tensile behaviour. Quantitative EBSD shows a measurable grain refinement in the as-built state (average grain size 13.44 → 11.80 µm, ~12%) accompanied by a pronounced weakening of the <001> fibre texture (maximum MRD 4.94 → 2.38), indicating disrupted epitaxial growth and a more dispersed orientation distribution. After T6, the reinforced alloy retains a higher low-angle boundary fraction (31.62% vs. 24.17% in unreinforced AA7075) and a higher kernel average misorientation (0.80° vs. 0.60°), consistent with particle-stabilised substructure retention and retarded recovery. Across all VEDs, AA7075-HEA exhibits higher microhardness (compared with AA7075, the addition of HEA increases the hardness by roughly 20–50 HV) and tensile strength, with the intermediate VED (140.74 J·mm⁻³, T6 states) yielding the best performance. While macroscopic cracking is not fully eliminated, the results clarify that HEA-enabled texture/substructure modifications can contribute to enhanced defect tolerance and are more effectively translated into tensile performance when the as-built defect severity is controlled. These findings provide quantitative insights into defect–microstructure–property coupling in LPBF AA7075-HEA composites from as-built to T6 states. Full article

The precursor infiltration and pyrolysis (PIP) route is widely adopted to fabricate carbon fiber-reinforced silicon carbide (C_f/SiC) composites; however, the atomic-scale restructuring of the pyrolytic carbon/silicon carbide (PyC/SiC) interface during ceramization—and its impact on mechanical integrity—remains elusive. Here, reactive molecular dynamics (ReaxFF MD) simulations elucidate the coupled thermochemical–mechanical evolution of polycarbosilane (PCS) precursors on PyC substrates with orientation angles (OAs) of 0°, 25°, 55°, and 85°. Dynamic pyrolysis triggers a pivotal transition from sp² to sp³ hybridization at the interface. High-OA substrates (55° and 85°) present a dense population of reactive edge sites, fostering extensive cross-interfacial covalent bonding. Subsequent shear loading reveals that these pyrolysis-induced chemical bridges govern failure modes, shifting from interlayer sliding dominated by weak non-bonded interactions (0°) to ductile fracture featuring uniform plasticity and crack deflection. The OA = 55° interface attains a theoretical peak shear strength of 15 GPa and exhibits the most favorable combination of high strength and ductile failure under tensile loading, owing to an optimal balance between reactive site availability and interlayer steric openness. In contrast, the OA = 85° interface, despite comparable peak stress, fails via brittle crack penetration into the SiC matrix. By correlating atomistic structure with macroscopic performance, this study provides a bottom-up framework for engineering C_f/SiC composites via interfacial texturing and optimized pyrolysis protocols. Full article

Human activities significantly influence the risk levels of natural disasters, with the construction industry contributing heavily to waste production and resource depletion as the global population grows and housing demand rises. This research seeks to mitigate some of these impacts. To reduce the demand for natural aggregates, compressed earth blocks (CEBs) were formulated using recycled waste materials—specifically crushed concrete and glass sand—stabilized with cement. The resulting blocks exhibited physical, mechanical, and thermal properties that position them as viable candidates for construction purposes. Investigating the microstructure of these masonry units and its correlation with their macroscopic properties provides the technical foundation necessary for the building industry to adopt them in sustainable architecture for hot and humid climates. Methodologies including thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and SEM image analysis (SEM-IA) demonstrated strong correlations across the 12 formulations (four matrices at three cement concentrations each). For instance, matrices with 15% cement by weight—which achieved compressive strengths between 6.2 and 7.3 MPa—showed greater mass loss associated with intralayer water and hydration products, a reduction in both porosity and the interfacial transition zone (ITZ), and higher concentrations of silica and calcium. Full article

In this study, CT scanning technology was combined with ImageJ 1.54r and Avizo 3D 2022 professional image analysis software to quantify porosity. The aim was to reveal the intrinsic correlation between the pore structure characteristics and the macroscopic properties of vegetated concrete. A combination of 3D reconstruction, fractal analysis and multi-parameter regression modelling techniques was utilised to quantify the association between pore parameters and material properties. The mechanistic role of pore structure in regulating the strength–permeability trade-off relationship was elucidated. The results show that: (1) aggregate particle size and porosity are significantly negatively correlated with the compressive strength of vegetated concrete and strongly positively correlated with the water permeability coefficient, while the effects of both of them on the pH value of the material are negligible; (2) the porosity obtained by the image analysis method meets the design requirements of the target porosity, and the deviation between the computed 3D porosity from CT scanning and the 2D sliced porosity is less than 1%. The image analysis porosity is slightly lower than the measured value, a deviation within a reasonable range. (3) There is a robust positive correlation between the fractal dimension of the vegetated concrete structural surface and porosity. With increasing aggregate size, porosity gradually increases, pore network connectivity is significantly enhanced, and the fractal dimension increases correspondingly. (4) Function fitting analysis confirms that the correlation between the connected porosity and the compressive strength and permeability coefficient is more significant than that of the cross-sectional porosity. Specifically, compressive strength is significantly negatively correlated with equivalent pore size and fractal dimension, and the water permeability coefficient is strongly positively correlated with these two parameters. This study can provide important theoretical support and engineering reference for the optimization of the mix proportion and performance control of vegetated concrete. Full article

Expanded polystyrene (EPS) foam concrete is attractive for lightweight building applications, yet its practical use is often limited by weak EPS–cement interfacial bonding, which promotes interfacial debonding and crack propagation and thereby compromises mechanical performance. Although nano-SiO₂ (NS) has been reported to improve EPS–cement compatibility, the interfacial strengthening mechanism is still not fully clarified across scales, especially the molecular-level interactions that govern the formation of a robust interfacial transition zone (ITZ). Herein, EPS particles were modified with NS and a multi-scale framework (macro tests, micro-characterization, and molecular dynamics (MD) simulations) was employed to establish a mechanistic linkage between interfacial chemistry/structure and macroscopic performance. The results show that an optimal NS dosage of 9% (by cement mass) increases the 28-day compressive strength and flexural strength of EPS concrete by up to 18.3% and 11.2%, respectively, compared with the unmodified system. SEM, XRD, and FTIR collectively indicate a denser interfacial microstructure, increased hydration-product accumulation near the EPS surface, refined interfacial porosity, and the occurrence of condensation-related reactions involving NS. MD simulations further reveal that NS facilitates the formation of molecular bridges between EPS and C–S–H through hydrogen bonding and ionic interactions, which enhances interfacial adhesion and contributes to improved ITZ thermal stability. This study provides a cross-scale mechanistic understanding for designing high-performance EPS foam concrete via targeted interfacial engineering. MD simulations further suggest that NS enhances interfacial bonding by increasing the occurrence of hydrogen-bond networks and ionic associations at the EPS/C–S–H interface, as evidenced by the intensified interaction-related distributions and peaks in the simulation outputs. Full article

Eutectic alloys stand out for their ability to combine high strength and good ductility; a behaviour rooted in their characteristic two-phase microstructure—lamellar or globular—formed at a constant solidification temperature that minimizes segregation and suppresses brittle phases. Their low interfacial energy limits microcrack propagation, while interfacial sliding and dislocation blocking at phase boundaries enhance both strength and toughness. In this work, we investigate how controlled microstructural modifications influence the behaviour of the eutectic high-entropy alloy AlCoCrFeNi2.1, composed of B2 (Ni–Al-rich) and L12 (Co–Fe–Ni-rich) phases. Because these phases exhibit distinct mechanical responses, microconstituent morphology becomes a design parameter. Powder metallurgy is the only processing route capable of providing the level of microstructural control required in this study. It preserves the rapidly solidified eutectic architecture of gas-atomised powders while allowing its intentional transformation during consolidation. Two strategies were implemented: (i) tuning the thermal–electrical input in Spark Plasma Sintering (SPS) and Electrical Resistance Sintering (ERS), and (ii) engineering the particle size distribution, including a bimodal design that enhances surface-energy-driven morphological transitions. SPS enables a gradual lamellar-to-globular evolution, whereas ERS induces ultrafast transformations governed by current intensity. The bimodal PSD significantly accelerates globularisation at lower energy input. EBSD-KAM (Electron Backscatter Diffraction—Kernel Average Misorientation) mapping identifies the lamellar B2 phase as metastable and highly strained, while globular B2 domains show reduced dislocation density. Nanoindentation confirms that intrinsic phase properties remain unchanged, whereas microhardness scales with morphology and lamellar spacing. These results demonstrate that the macroscopic mechanical response is governed by microstructure, establishing powder metallurgy as a uniquely powerful pathway for microstructure-driven design in eutectic HEAs. Full article

Variations in the groundwater chemical environment are a critical factor affecting the mechanical property degradation and structural alteration of coal measure strata. Addressing the engineering challenges commonly encountered in coal mining areas of Northwest China, where groundwater with varying pH leads to difficulties in controlling surrounding rock in underground spaces, this study established a comprehensive experimental methodology integrating mechanical loading, nuclear magnetic resonance (NMR) quantitative pore analysis, and scanning electron microscopy (SEM) microstructural characterization. The study revealed the mechanical degradation mechanisms and microstructural evolution characteristics of coal measure coarse sandstone under groundwater environments with different pH values (6–10). With prolonged immersion time, the peak strength and elastic modulus of the coarse sandstone exhibited exponential decay across all pH environments. NMR analysis revealed that the porosity evolved through a path of “increase–decrease–re-increase,” while the macroscopic mechanical failure mode shifted from brittle to brittle-ductile and finally to ductile characteristics. Micropores continuously transformed into medium and large pores, and the macroscopic failure mode exhibited a transition from brittle to brittle-ductile. The findings indicate that groundwater with varying acidity/alkalinity systematically alters the integrity and load-bearing capacity of coal measure coarse sandstone through the complex mechanism of “mineral dissolution (acidic H⁺ corrosion, alkaline OH⁻ hydrolysis)—structural damage—pore/fracture evolution—mechanical degradation.” This mechanism not only reveals the essence of progressive rock damage in weak acid to moderately strong alkaline environments but also provides important insights for the integrity, sealing capacity, and permeability modification of various underground engineering applications, such as CO₂ geological storage, unconventional natural gas development, and underground space utilization. Full article

Accurate determination of the physico-mechanical parameters of rock and soil masses is fundamental to the quantitative stability analysis and engineering mitigation of open-pit mine slopes. However, existing studies often rely on generalized parameters and lack systematic empirical data based on full-hole in situ core sampling to quantitatively verify the link between microscopic mineralogy and macroscopic instability. To address this gap, this study investigates the mineral composition, microstructure, and hydro-mechanical behavior of geotechnical materials, using the XG Open-pit Coal Mine in Inner Mongolia as a case study. Field drilling and sampling with a cumulative depth of 1500.7 m were conducted, combined with systematic laboratory tests. The results reveal significant lithological heterogeneity within the mining area. Specifically, hard rocks (e.g., fine sandstone) constitute the stable framework of the slope, whereas mudstones rich in hydrophilic clay minerals, along with low-strength coal seams, form potential weak sliding interfaces. Quantitative X-ray Diffraction (XRD) analysis reveals that the weak mudstone layers contain up to 32.4% hydrophilic expansive minerals (montmorillonite and illite/smectite). Scanning Electron Microscopy (SEM) and slake durability tests demonstrate that the mudstone is characterized by well-developed micropores (1–2 μm) and loose cementation. Theoretical analysis indicates that upon saturation, the strength of these weak layers is reduced by over 40%, causing the factor of safety (FoS) to drop from a stable 1.48 to a critical 0.89. Based on these findings, the slope instability mechanism driven by “Stiffness Mismatch and Hydro-Weakening” is elucidated. Consequently, targeted reinforcement and drainage measures are proposed to provide a scientific basis for safe mining operations. Full article

In this study, Inconel 600 alloy with reductions of 20%, 50%, and 80% was obtained through cold rolling, and the effects of plastic deformation on its mechanical properties and corrosion behavior in a hydrofluoric acid (HF) solution were systematically investigated. The results show that cold rolling induces pronounced work hardening, with both hardness and strength increasing continuously with increasing reduction, while the ductility decreases accordingly. The alloy with 80% reduction exhibits the highest strength, with an ultimate tensile strength of 1270 MPa and a yield strength of 1210 MPa. In contrast, the macroscopic corrosion resistance of the alloy in HF solution remains essentially unchanged with increasing deformation, although a slight intensification of pitting corrosion is observed. The combined effects of deformation-induced pitting and passivation enhancement resulted in retention of corrosion resistance. These findings demonstrate that appropriate control of cold rolling enables effective mechanical strengthening of Inconel 600 without significantly sacrificing its corrosion performance in aggressive fluorine containing environments. Full article