Search Results (914)

Gangue backfilling has become an important technique for promoting environmentally friendly and low-carbon coal mining. The long-term creep behavior of cemented backfill plays a critical role in maintaining stope stability and controlling surface subsidence during long-term service. Although considerable research has been conducted on cemented tailings backfill, systematic investigations on the triaxial creep evolution, long-term strength characteristics, confining pressure effects, and the applicability of the classical Burgers model for gangue–gypsum cemented backfill under engineering-relevant confining pressures remain limited. In this study, the experimental scheme was designed based on field monitoring data from practical backfill mining operations, which indicate that the in situ backfill generally remains stable without significant deformation or instability under normal working conditions. Multi-stage loading triaxial creep tests were conducted on gangue–gypsum cemented backfill under confining pressures of 1, 2, 3, and 4 MPa. The creep deformation characteristics were analyzed using Chen’s superposition method, while the long-term strength was computed via inflection point method of isochronous stress–strain curves. The parameters of the Burgers creep model were identified using the Levenberg–Marquardt optimization algorithm, and numerical verification was performed using FLAC3D. Our findings demonstrate that the creep deformation process of the backfill consists of three typical stages: instantaneous deformation, attenuated creep, and steady-state creep, and no accelerated creep was observed within the applied stress range. The absolute creep strain surges nonlinearly with increasing stress level (S_L), whereas higher confining pressure significantly suppresses the creep response of the material. Within the investigated stress range, the backfill exhibits mainly linear viscoelastic behavior, and its critical long-term strength is not less than 0.9 times the failure deviatoric stress (qf). Although confining pressure enhances the long-term strength, the strengthening effect weakens as the confining pressure increases. Model fitting outcomes imply that Burgers model precisely describes the creep behavior of gangue–gypsum cemented backfill under all test conditions, with correlation coefficients (R²) exceeding 0.97. The identified parameters show systematic variation with S_L, reflecting stiffness degradation and viscous evolution during loading. Numerical simulation results agree well with the experimental data, providing theoretical guidance for mixture proportion optimization, long-term stability evaluation, and stope support parameter design in gangue backfill mining engineering. Full article

Ultra-High-Performance Concrete (UHPC) is increasingly used in slender and prestressed structural members due to its superior strength and durability. However, inaccurate or incomplete prediction of creep deformation may lead to excessive long-term deflection, prestress loss, cracking, and potential serviceability or safety risks in buildings and infrastructure. Therefore, reliable prediction methods for UHPC creep are essential for both structural design and long-term performance assessment. In this study, a database containing 60 literature-derived UHPC creep records was compiled to investigate the creep coefficient at approximately 100 days. Pearson correlation analysis revealed strong interdependence among predictors and weak single-variable linear relationships, indicating that creep behavior is governed by nonlinear interactions. A feedforward backpropagation neural network (BPNN) trained using the Levenberg–Marquardt algorithm was developed to predict the creep coefficient. To maintain engineering interpretability, the fib Model Code 2020 (MC2020) formulation was adopted as a code-based benchmark and further calibrated using ridge regression. Results show that the calibrated MC2020 model improves prediction consistency, while the BPNN model provides the highest predictive accuracy. The proposed framework integrates machine-learning prediction with interpretable code-based calibration, contributing to the development of creep modeling approaches for UHPC and providing practical support for the safe design of UHPC structures. Full article

This study aims to investigate the influence of clay mineral content on the rheological properties and long-term deformation stability of clays, and to establish a unified model capable of quantitatively describing the nonlinear rheological behavior of clays with different mineral compositions. Direct shear rheological tests were conducted on specimens prepared with different mixing ratios of bentonite, kaolin, and quartz. Combined with micro-mechanism analysis, the controlling factors of clay rheological behavior were explored. The experimental results show that the creep stress threshold, elastic viscosity, and average plastic viscosity decrease significantly with increasing clay mineral content. The rheological deformation exhibits distinct nonlinear characteristics, and clay mineral content plays a controlling role in the rheological behavior. Based on experimental and mechanistic analysis, a unified rheological model was established, which reflects the material origin of rheology and captures nonlinear rheological characteristics. This model can predict the entire time-history mechanical behavior of clays with different mineral compositions across the three stages of instantaneous deformation, decay rheology, and steady-state rheology under different shear stress levels using a single set of parameters. Validation was performed through direct shear rheological tests under 50 working conditions for five types of clay specimens, demonstrating good consistency between the model calculations and experimental results. The unified rheological model reveals the material origin and physical essence of clay rheology, demonstrates high universality, and advances the understanding of the influence of mineral composition on rheology from the current phenomenological qualitative description to quantitative calculation for the first time, significantly enhancing its engineering application value. This provides a more reliable tool for predicting long-term deformation and assessing the stability of clay foundations. Full article

The research gap addressed in this study is the lack of a transparent and quantitative evaluation of the governing parameters influencing deflection behavior in reinforced concrete (RC) beams reinforced with glass fiber-reinforced polymer (GFRP) bars. The objective of this study is to identify and quantify the relative importance of the key parameters controlling deflection in GFRP-reinforced RC beams, which exhibit fundamentally different behavior compared to steel-reinforced beams due to the linear-elastic response of GFRP bars until rupture. To achieve this objective, the method integrates explainable artificial intelligence (XAI) techniques, including SHapley Additive exPlanations (SHAP), Pearson correlation heatmap, scatter plot analysis, and sensitivity analysis—with experimental structural data obtained from beams with three different concrete strength classes. The main contribution of this study is the quantitative ranking and interpretation of the governing parameters affecting deflection behavior through a transparent and data-driven framework. Key parameters—including elastic modulus (Ec), compressive strength (fck), creep coefficient (φ), failure moment (Mexp), effective moment of inertia (Ieff), and applied load (P)—were evaluated. The results consistently indicate that stiffness- and capacity-related parameters dominate the deflection response. Sensitivity analysis reveals that the failure moment (Mexp) is the most influential parameter, contributing approximately 23% of the total relative influence on deflection, followed by compressive strength (fck) and cracking-related parameters. Pearson correlation heatmap and scatter plot analyses further confirm strong relationships between deflection and Ec, fck, φ, and Ieff. The proposed framework improves the interpretability of deflection prediction in GFRP-reinforced RC beams and provides a transparent basis for serviceability-based structural design and performance-oriented assessment. Full article

To give more insight into the microstructural evolution and deformation mechanisms governing the long-term service performance of additively manufactured TiAl-based composites at elevated temperatures, this study investigated the high-temperature compressive creep behavior of a laser powder bed-fused LaB₆ reinforced high-Nb TiAl-based composite after hot isostatically pressing (HIP), with emphasis on the creep response and dynamic recrystallization (DRX) mechanisms under different applied stress levels. The results showed that, as the applied stress increased from 200 MPa to 450 MPa, the steady-state creep rate rose from 2.88 × 10⁻⁸ s⁻¹ to 3.85 × 10⁻⁷ s⁻¹. Stress exponent analysis indicated that creep deformation was predominantly controlled by dislocation climb, and no tertiary creep stage was observed within the investigated stress range. At 200 MPa and 300 MPa, a certain fraction of recrystallized grains formed during prolonged creep exposure. When the stress increased to 400 MPa, the recrystallization process was restricted due to the limited creep duration. In contrast, at 450 MPa, the accelerated accumulation of strain energy significantly promoted recrystallization. Both continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) were identified, jointly governing the microstructural evolution. Superior creep resistance can be attributed to multiple synergistic strengthening mechanisms, including the refined α₂/γ lamellar structure induced by HIP treatment, the strong pinning effect of dispersed La₂O₃ nanoparticles on dislocation motion, and the suppression of diffusion-controlled dislocation climb by Nb addition. These combined effects enhance the high-temperature creep performance of the TiAl composite and provide important insights for the application of LPBF-fabricated TiAl-based composites under elevated-temperature service conditions. Full article

Dredged Fill Soil, as a primary foundation material in reclamation projects, exhibits complex physical and mechanical properties, characterized by a high plasticity index, high water content, low density, high compressibility, large void ratio, and low bearing capacity. Its creep behavior is highly sensitive to temperature changes. This study systematically investigates the temperature-dependent creep behavior of reclaimed soil from Humen Port through laboratory experiments, theoretical modeling, and experimental validation. Triaxial creep tests conducted at different temperatures (5 °C, 15 °C, 25 °C, 35 °C) show that increasing temperature significantly exacerbates creep deformation: under undrained conditions, creep strain at 35 °C is nearly 300% higher than at 5 °C, while drainage reduces the strain by approximately 29.3%. Based on these results, a Burgers-type creep constitutive model considering temperature effects is developed, incorporating the impact of temperature on viscosity and elastic modulus. The model’s predictions show good agreement with the experimental results (15 °C: R² = 0.9788; 35 °C: R² = 0.9890), confirming the model’s validity. The research findings provide theoretical and practical references for the long-term stability evaluation and engineering design of reclaimed foundations in complex marine environments. Full article

Granite is widely used in buildings, stone carvings, and sculptures, where long-term durability is strongly influenced by the micromechanical behavior of its constituent minerals and mineral interfaces. However, conventional rock mechanics tests cannot resolve the mechanical heterogeneity at the mineral scale, particularly at mineral interfaces. To address this limitation, a systematic nanoindentation study was conducted to quantitatively characterize the elastic modulus, hardness, creep behavior, residual deformation, and fracture toughness of both individual minerals and mineral interfaces in granite, and to clarify their mechanical contrasts and interrelationships. The results show that the constituent minerals quartz, feldspar, and biotite exhibit elastic modulus of 121.9 GPa, 115.6 GPa, and 66.3 GPa, respectively. Quartz and feldspar show relatively better mechanical properties, whereas biotite exhibits the weakest mechanical behavior. Hardness shows the same trend. In contrast, creep displacement and residual indentation depth follow the opposite order, i.e., quartz < feldspar < biotite. In addition, the elastic modulus and hardness of mineral interfaces are lower than those of the adjacent minerals, whereas their creep displacement and residual indentation depth are higher. The dispersion of these micromechanical parameters for mineral interfaces is generally greater than that of the adjacent minerals. The fracture toughness values of both minerals and mineral interfaces were also obtained: mineral fracture toughness ranges from 3.1 to 6.2 MPa·m^0.5, while mineral interfaces range from 0.7 to 4.3 MPa·m^0.5. Further analysis of the micromechanical parameters indicates that elastic modulus, hardness, and fracture toughness exhibit clear positive correlations among minerals, mineral interfaces, and the mineral aggregate. Comparatively, the correlations are strongest for minerals and weakest for mineral interfaces. Full article

Mineral resources serve as a critical foundation for China’s energy system, with the Ordos Basin’s Tarangole mining area being a key mineral production base in the central and western regions. To support the restoration, development, and productivity enhancement of the mining area, this research systematically investigates the geological and mechanical properties of the sandstone in the region. Herein the innovation lies in its comprehensive analysis of the influence mechanisms of multiple factors—such as geological groups, particle size, evaluation indicators, sampling depth, temperature, and creep rate—on the mechanical behavior of sandstone. The study, through engineering geological surveys and mechanical testing of frozen sandstone (including uniaxial and triaxial creep tests), led to the following key findings: (1) the sandstone in the area is prone to softening and disintegration, classified as soft to moderately soft rock (UCS range: 5.14–10.26 MPa in natural state), with a basic quality grade of IV–V. (2) The thermal conductivity and specific heat capacity of the rock vary significantly with temperature. The recommended freezing temperature is −5 °C, based on engineering experience and economic considerations. (3) Freezing can effectively enhance the strength of sandstone (e.g., the strength of medium- and coarse-grained sandstone increases by 5 MPa at −20 °C compared to −10 °C), although it still falls within the category of extremely soft rock. (4) The water-ice phase transition induced by low temperatures significantly enhances the overall strength, stiffness, and deformation resistance of saturated sandstone. Accordingly, freezing measures can effectively enhance rock mass strength under low-temperature conditions. It is recommended that mining operations be prioritized during winter or colder seasons to ensure construction safety and efficiency. Full article

The long-term behavior of reinforced concrete (RC) structures under sustained loading is strongly affected by creep and cracking, particularly under service conditions where tension stiffening and curvature changes are significant. This study investigates the flexural response of cracked RC beams through combined numerical and experimental analyses. A new 1D finite element model is proposed, integrating nonlinear material behavior, damage mechanics, and time-dependent effects, including creep in both compression and tension. The model relies on a layered fiber section approach and uses a Newton–Raphson iterative procedure to solve equilibrium, allowing accurate prediction of strain, curvature, and internal force evolution over time. The model shows excellent agreement with experimental observations and ABAQUS simulations, accurately capturing deflection trends and crack development. Its performance is further validated using a database of 55 RC beams, including specimens with recycled aggregates and fiber reinforcement. Across this dataset, 84.5% of predicted deflections fall within ±1 mm of measured values, with an R² of 0.960, demonstrating strong reliability. A Sobol-based sensitivity analysis identifies load ratio as the most influential parameter on long-term deflection, followed by concrete strength and humidity. Overall, the model offers an efficient and robust tool for long-term deflection prediction, bridging simplified design rules and complex 3D simulations. Full article

The development of cement composites that simultaneously achieve high compressive strength and low density remains a fundamental scientific challenge, particularly because optimizing weight reduction often compromises mechanical performance under sustained high-pressure conditions. In modern construction—especially high-rise buildings, large-span structures, and underground projects—there is an urgent applied need for lightweight materials that can reduce structural self-weight, enhance seismic resilience, simplify foundation design, and improve construction efficiency without sacrificing load-bearing capacity or long-term durability. To address this dual problem, this study investigates high-pressure-resistant lightweight cement composites incorporating hollow glass microspheres (HGMSs) of three different particle sizes as functional fillers, modified with isobutyl triethoxy silane (IBTES) to strengthen interfacial bonding. Ten formulations with varying HGMS types and dosages (5%, 10%, and 15% by volume) were systematically evaluated through creep tests, uniaxial compression experiments, X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The scientific results demonstrate marked qualitative and quantitative improvements: the optimal formulation (25 μm HGMS at 5% dosage) exhibited a 22.01% reduction in creep deformation and a 67.85% increase in compressive strength compared to plain cement, while bulk density was reduced by 8.8–19.0%. Enhanced hydration was confirmed by a 23.6% reduction in residual Ca(OH)₂ content and a 31.2% increase in chemically bound water, indicating more complete formation of calcium silicate hydrate (C–S–H) gel. Energy evolution analysis revealed a prolonged elastic energy accumulation stage (increasing from 56% to 95% of total compression duration), signifying a transition toward quasi-ductile failure behavior. From an applied perspective, these quantitative enhancements translate directly into practical construction benefits: the 8.8–19.0% density reduction enables lighter structural components, easing transportation and installation; the 67.85% higher compressive strength ensures reliable performance in high-pressure environments; and the 22.01% lower creep deformation guarantees long-term dimensional stability. Collectively, these findings confirm that the HGMS-IBTES-modified composite offers a scalable, high-performance solution for advanced construction applications where both weight reduction and superior pressure resistance are critical. Full article

Intervertebral disc (IVD) viscoelasticity is governed primarily by fluid transport driven by coupled osmotic and mechanical pressure gradients. Disc degeneration disrupts this balance through glycosaminoglycan loss and reduced cartilage endplate permeability. However, how degeneration interacts with compressive loading to regulate fluid-driven viscoelastic behavior at the whole-disc level remains unclear. To address this gap, a probabilistic biphasic swelling finite element framework was employed to simulate fluid-driven viscoelastic behavior of the IVD. Fifty discs were generated by varying anterior–posterior length, lateral width, nucleus pulposus volume ratio, wedge angle, and disc height. These discs were subjected to swelling, creep, and relaxation protocols under multiple compressive magnitudes for both healthy and degenerated conditions. Time-dependent responses were quantified using rheological models comprising two viscoelastic elements and one elastic element. Predicted intradiscal pressure, disc height, and viscoelastic responses fell within reported experimental ranges. Degeneration primarily governed fluid-dependent behavior. It reduced osmotic pressure, limited fluid mobility, and delayed axial equilibration. These changes decreased swelling displacement, increased creep deformation, and prolonged characteristic time constants, while minimally affecting instantaneous elastic response. In contrast, loading magnitude modulated the extent of viscoelastic deformation and progressively reduced degeneration-related differences in long-term creep displacement and long-term relaxation time constant. Collectively, degeneration governs fluid-dependent viscoelastic mechanisms, whereas loading magnitude modulates their expression. This study systematically examines how degeneration and load magnitude interact to regulate fluid-driven viscoelastic behavior of the IVD. By combining probabilistic geometry with biphasic swelling mechanics, it addresses a critical gap in understanding load–degeneration interactions in disc hydration-dependent mechanics. Full article

High-entropy alloy (HEA) multilayers represent a promising class of advanced coating materials due to their superior mechanical properties, corrosion resistance, and irradiation tolerance. However, the specific role of interface coherency on the creep behavior of HEA multilayers remains unclear. In this work, FCC/BCC Al-Cr-Fe-Ni HEA multilayers with different coherency were prepared by precisely controlling the modulated period (λ) via RF magnetron sputtering. Their room-temperature creep properties were systematically investigated through nanoindentation under different loading rates. The results reveal a strong dependence of creep resistance and deformation mechanisms on the interface coherency. HEA multilayers with semicoherent interfaces (λ = 16 nm) exhibit the highest creep resistance, where creep is primarily mediated by atomic diffusion or interface slip. In contrast, samples dominated by coherent interfaces or grain boundaries (λ = 8, 32, and 80 nm) demonstrate dislocation slip-dominated creep. This work elucidates how interfacial coherency dictates the transition between diffusion-mediated and dislocation-mediated creep mechanisms in HEA multilayers, providing critical insights for the design of next-generation creep-resistant nanostructured coatings. Full article

This study investigates the mechanical behavior of jointed rock mass tunnels through numerical simulations using UDEC software. Focusing on the time-dependent variation in joint shear stiffness, a theoretical model is proposed to characterize the evolution of shear stiffness over time. Based on this model, numerical simulations are conducted to analyze tunnel stability and associated deformation patterns. A variable shear stiffness model is first established in UDEC, which effectively captures the evolution of shear creep displacement along rock joints. Incorporating this model, an adaptive support scheme involving locally extended rock bolts is introduced to improve long-term tunnel stability. The proposed approach is further validated through a comparative analysis with field monitoring data obtained from a tunnel in Yunnan Province. The results indicate that creep effects significantly influence tunnel behavior, leading to rapid increases in crown settlement and expansion of the surrounding rock disturbance zone during the early stages following excavation. Optimizing the bolt layout is shown to effectively reduce the extent of the disturbed zone and enhance the tunnel’s load-bearing capacity. Finally, a novel reinforcement optimization method for jointed rock mass tunnels is proposed, along with a key threshold value for assessing tunnel stability, thereby providing theoretical support for practical engineering applications. Full article

This study presents a reliable methodology for analyzing reinforced ultra-high-performance fiber-reinforced concrete (UHPFRC) elements by linking material behavior to structural performance. A non-linear finite element model (NLFEM) is proposed to simulate the tensile response of reinforced UHPFRC elements, with particular emphasis on shrinkage effects. The model operates in two phases: the first simulates shrinkage during specimen storage and the second simulates the mechanical tensile test, using the internal stresses from the first phase as initial conditions. The model was validated through an experimental program involving reinforced UHPFRC ties. The NLFEM accurately reproduced the load–displacement response using average UHPFRC tensile parameters obtained from a simplified Four-Point bending test Inverse Analysis method (4P-IA). It reliably predicted the shrinkage strain range and its impact on stiffness loss during microcrack initiation and stabilization, where tension-stiffening behavior is critical. Additionally, the simulation from the model captured the transition from microcracking to macrocrack formation and the role of fiber bridging in maintaining stiffness. The predicted shrinkage strain aligns with values reported in the literature and represents a conservative upper bound, neglecting the potential effects of creep and relaxation. Overall, the NLFEM effectively simulates the full tension-stiffening behavior of reinforced UHPFRC, including three-dimensional effects, and provides a reliable tool for structural analysis and design. Full article

The precise control of piezoelectric actuators is limited by inherent hysteresis, creep, and nonlinear behavior, which necessitate high-resolution displacement sensing for effective closed-loop operation. Although optical interferometers can achieve nanometer and sub-nanometer resolution, their practical implementation is often constrained by complex optical alignment, sensitivity to environmental disturbances, and limited robustness in high-speed measurements. Optical triangulation sensors offer a more robust and straightforward alternative; however, their resolution is typically insufficient for nanometer-scale displacement measurements. In this study, a novel optical triangulation sensor based on a two-stage geometric optical amplification scheme is proposed for measuring the expansion of piezoelectric stacks. The method relies purely on geometric optical amplification and does not require interferometric techniques or complex signal processing. Using off-the-shelf optical components and an industrial imaging sensor, the proposed system achieves a displacement resolution of 109.6 nm, a repeatability of 74.62 nm, and an accuracy of 98.81% with a maximum error of 207.14 nm under hysteresis measurements. The achieved resolution is primarily limited by the spatial resolution of the camera sensor, indicating that further improvements are possible through optimization of the optical configuration or the use of higher-resolution imaging devices. Owing to its simplicity and robustness, the proposed sensor is well suited for real-time closed-loop control of piezoelectric actuators. Full article