Search Results (315)

The impact mechanism of long-term creep in gas-containing coal on coal and gas outbursts has not been fully elucidated and remains insufficiently understood for the purpose of disaster engineering control. This investigation conducted triaxial creep experiments on raw coal specimens under controlled confining pressures, axial stresses, and gas pressures. Through systematic analysis of coal’s physical responses across different loading conditions, we developed and validated a novel creep damage constitutive model for gas-saturated coal through laboratory data calibration. The key findings reveal three characteristic creep regimes: (1) a decelerating phase dominates under low stress conditions, (2) progressive transitions to combined decelerating–steady-state creep with increasing stress, and (3) triphasic decelerating–steady–accelerating behavior at critical stress levels. Comparative analysis shows that gas-free specimens exhibit lower cumulative strain than the 0.5 MPa gas-saturated counterparts, with gas presence accelerating creep progression and reducing the time to failure. Measured creep rates demonstrate stress-dependent behavior: primary creep progresses at 0.002–0.011%/min, decaying exponentially to secondary creep rates below 0.001%/min. Steady-state creep rates follow a power law relationship when subject to deviatoric stress (R² = 0.96). Through the integration of Burgers viscoelastic model with the effective stress principle for porous media, we propose an enhanced constitutive model, incorporating gas adsorption-induced dilatational stresses. This advancement provides a theoretical foundation for predicting time-dependent deformation in deep coal reservoirs and informs monitoring strategies concerning gas-bearing strata stability. This study contributes to the theoretical understanding and engineering monitoring of creep behavior in deep coal rocks. Full article

This study proposes a coupled constitutive model that captures the anisotropic failure characteristics and damage evolution of nickel-based single-crystal (SX) superalloys under various temperature conditions. The model accounts for both creep rate and material damage evolution, enabling accurate prediction of the typical three-stage creep curves, macroscopic fracture morphologies, and microstructural features under uniaxial tensile creep for specimens with different crystallographic orientations. Creep behavior of SX superalloys was simulated under multiple orientations and various temperature-stress conditions using the proposed model. The resulting creep curves aligned well with experimental observations, thereby validating the model’s feasibility and accuracy. Furthermore, a finite element model of cylindrical specimens was established, and simulations of the macroscopic fracture morphology were performed using a user-defined material subroutine. By integrating the rafting theory governed by interfacial energy density, the model successfully predicts the rafting morphology of the microstructure at the fracture surface for different crystallographic orientations. The proposed model maintains low programming complexity and computational cost while effectively predicting the creep life and deformation behavior of anisotropic materials. The model accurately captures the three-stage creep deformation behavior of SX specimens and provides reliable predictions of stress fields and microstructural changes at critical cross-sections. The model demonstrates high accuracy in life prediction, with all predicted results falling within a ±1.5× error band and an average error of 14.6%. Full article

This work aims to reveal the full-field strain evolution characteristics and failure mechanisms of anisotropic coal samples under creep loading. A series of compression tests combined with digital image correlation (DIC) monitoring were employed to characterize the strain evolution process of coal specimens with bedding angles of 0°, 30°, 60°, and 90°. Testing results show that the peak strength, peak strain, and the creep loading stage of coal are significantly influenced by the bedding angle. The peak strength initially decreases and then increases as the bedding angle increases. In addition, the creep failure of coal manifests as a process of instantaneous deformation, decelerating creep, steady-state creep, accelerating creep, and failure. Under graded creep loading conditions, coal specimens exhibit distinct creep characteristics at high stress levels. Moreover, the bedding angle significantly influences the strain field evolution of the coal samples. Finally, for coal specimens with bedding angles of 0° and 90°, the final macroscopic fracture pattern upon failure is characterized by longitudinal tensile splitting. In contrast, coal samples with bedding angles of 30° and 60° tend to exhibit failure along the bedding interfaces, forming tensile-shear fractures. The results of this study will provide theoretical guidance for the prevention, early warning, and safety management of coal mine disasters. Full article

During the excavation of the underground cavern at the Baihetan hydropower station, significant time-dependent deformation of the surrounding rock was observed, posing a serious challenge to the long-term stability control of the caverns. In this study, numerical models of the layered excavation for typical monitoring sections in the main and auxiliary powerhouses on both banks of the Baihetan hydropower station were established using a viscoplastic damage model. The time-dependent deformation responses of the surrounding rock during the entire underground cavern excavation process were successfully simulated, and the deformation and failure mechanisms of the surrounding rock during layered excavation were analyzed in combination with field monitoring data. The results demonstrate that the maximum stress trajectories at the right-bank powerhouse under higher stress conditions exceeded those at the left-bank powerhouse by 6 MPa after the powerhouse excavation. A larger stress difference caused stress trajectories to move closer to the rock strength surface, therefore making creep failure more likely to occur in the right bank. Targeted reinforcement in high-disturbance zones of the right-bank powerhouse reduced the damage progression rate at borehole openings from 0.295 per month to 0.0015 per month, effectively suppressing abrupt deformations caused by cumulative damage. These findings provide a basis for optimizing the excavation design of deep underground caverns. Full article

Rock slopes exhibiting anti-inclined interbedded strata have widespread distribution and complex deformation mechanisms. In this study, we used a physical model test with basal friction to replicate the evolution process of the slope deformation. Digital Image Correlation (DIC) and Particle Image Velocimetry (PIV) methods were used to capture the variation in slope velocity and displacement fields. The results show that the slope deformation is conducted by bending of soft rock layers and accumulated overturning of hard blocks along numerous cross joints. As the faces of the rock columns come back into contact, the motion of the slope can progressively stabilize. Destruction of the toe blocks triggers the formation of the landslides within the toppling zone. The toppling fracture zones form by tracing tensile fractures within soft rocks and cross joints within hard rocks, ultimately transforming into a failure surface which is located above the hinge surface of the toppling motion. The evolution of the slope deformation mainly undergoes four stages: the initial shearing, the free rotation, the creep, and the progressive failure stages. Full article

The precise prediction of soil settlement under applied loads is of paramount importance in the field of geotechnical engineering. Conventional analytical approaches often lack the capacity to accurately represent the rate-dependent deformations exhibited by soft soils. Creep affects the integrity of geotechnical structures and can lead to loss of serviceability or even system failure. Over time, they deform, the soil structure can be weakened, and consequently, the risk of collapse increases. Despite extensive research, regarding the creep characteristics of soft soils, the prediction of creep deformation remains a substantial challenge. This study explores soil consolidation settlement by employing three different material models: the Soft Soil Creep (SSC) model implemented in PLAXIS 2D, alongside two user-defined elasto-viscoplastic models, specifically Creep-SCLAY1S and the non-associated creep model for Structured Anisotropic Clay (n-SAC). Through the simulation of laboratory experiments and the Lilla Mellösa test embankment situated in Sweden, the investigation evaluates the strengths and weaknesses of these models. The results demonstrate that the predictions produced by the SSC, n-SAC, and Creep-SCLAY1S models are in close correspondence with the field observations, in contrast to the more simplistic elastoplastic model. The n-SAC and Creep-SCLAY1S models adeptly represent the stress–strain response in CRS test simulations; however, they tend to over-predict horizontal deformations in field assessments. Further investigation is advisable to enhance the ease of use and relevance of these sophisticated models. Full article

Testing and the estimation methods for predicting the life of crack initiation and crack growth for P92 steel using a circular sharp notched round bar specimen (CNS) under strain-controlled creep and fatigue conditions have been reported previously. A unique estimation method for the cycle-sequential characteristics of tensile and compressive peak stresses is proposed; specifically, the nominal stress range ${∆\sigma }_{net}={{(\sigma }_{max}-{\sigma }_{min})}_{net}$ and the measurement of crack length using the direct current electric potential drop (DCPD) method were adopted. This method was effective in specifying the failure life and crack initiation life by verifying the crack growth length. However, to show the universality of these results, it is important to compare the experimental results obtained under strain-controlled creep and fatigue conditions with those obtained under stress-controlled creep and fatigue conditions and with those for smooth specimens estimated based on the linear and nonlinear damage summation rule. Furthermore, it may also be important to compare these results with those of smooth specimens estimated based on the Manson–Coffin law when the failure life is fatigue-dominant. Considering these aspects, detailed experiments and analyses were systematically conducted for P92 steel in this study, and the above comparisons were conducted. The results aid in achieving a unified understanding of the law of fracture life, including those under stress- and strain-controlled creep and fatigue conditions. Full article

This study presents a stability assessment of rock slopes, considering the joint systems of the rock walls of Wojciech Bednarski Park. Special emphasis was placed on analysing the orientation and infill characteristics of the identified joint sets. Based on archival data and newly conducted geological surveys, stability calculations were performed for eight representative cross-sections corresponding to designated sectors. Numerical analyses were conducted using a finite element method (FEM) programme, based on the actual structure of the rock mass, specifically its discontinuities. This ensured a reliable reflection of the real conditions governing the slope instability mechanisms. Factors of safety were estimated with the Shear Strength Reduction Technique. The results indicate that slope failure is highly unlikely in Sectors 1 and 2 (FS > 1.50), unlikely but not fully meeting the safety criteria in Sector 3 (FS < 1.50), and highly probable in Sectors 4 and 6 (FS << 1.00), where unstable rock blocks and deeper structural slides are anticipated. In Sector 5, failure is considered probable (FS < 1.30) due to rockfalls, unstable blocks, and creeping weathered cover. For Sectors 7 and 8, assuming debris cover above the rock walls, failure is unlikely (FS > 1.50). In contrast, under the assumption of weathered material, it becomes probable in Sector 7 (FS < 1.30), and remains unlikely in Sector 8 (FS > 1.50). Due to the necessity of adopting several modelling assumptions, the results should be interpreted primarily in qualitative terms. The outcomes of this research provide a critical basis for assessing the stability of rock slopes within Wojciech Bednarski Park and support decision-making processes related to its planned revitalisation. Full article

The escalating disasters caused by the movement of shallow buried strata in China’s western mining areas are increasingly threatening operational safety. A critical issue in ensuring secure mining practices in these areas is the creep failure of weakly cemented soft rock under low-stress conditions. The unique particle contact mechanisms in weakly cemented mudstone, combined with the persistence of the cemented materials and the particulate matter they form, lead to mechanical responses that differ significantly from those of typical soft rocks during loading. Building on an existing multivariate linear regression equation for new similar materials, this study developed qualified weakly cemented medium similar materials, offering appropriate materials for long-term creep tests of weakly cemented formations. This was accomplished by employing orthogonal proportioning tests. The principal findings of our investigation are as follows: The new, similar material exhibits low strength and prominent creep characteristics, accurately simulating weakly cemented materials in western mining areas. The concentration of rosin–alcohol solution has a measurable impact on key parameters, such as σ_c, E, and γ in the weakly cemented similar material specimens. Furthermore, the creep characteristics of the specimens diminish progressively with an increase in the proportion of iron powder (I) and barite powder (B). The material was applied to a similar indoor model test simulating the weakly cemented material surrounding the auxiliary haulage roadway in Panel 20314 of the Gaojialiang Coal Mine, with speckle analysis employed for detailed examination. The experimental findings suggest that both the conventional mechanical properties and long-term creep characteristics of the material align with the required specifications, offering robust support for achieving optimal outcomes in the similar model test. Full article

This study investigates the influence of moisture on the mechanical behavior of fine soil mixtures from the São Luís region, applied as subballast layers in railway track structures. Two samples were analyzed: a non-lateritic sandy soil (NA’, AM03) and a lateritic clayey soil (LG’, AM09). The research included physical and chemical characterization tests, as well as repeated load triaxial tests to determine the resilient modulus and shakedown limits, complemented by numerical simulations using the SysTrain 2.0 software. The samples showed average resilient modulus values of 577 MPa and 638 MPa, respectively. Tests were conducted under optimum moisture content and under moisture 1% above the optimum, induced by capillary rise in compacted samples. The results indicated that under 1% above optimum moisture, the shakedown limits were reduced by up to 50% for AM03 and 25% for AM09, demonstrating greater stability for the lateritic soil. In addition, it was observed that as stress ratios increased, the shakedown limits for both moisture conditions tended to converge. Numerical simulations confirmed the adverse influence of increased moisture on the occurrence of shakedown in both samples. For AM03, the simulations revealed progressive failure under elevated moisture, indicating a more severe stress redistribution within the subballast layer. In contrast, AM09 remained within the shakedown regime under both conditions, although it exhibited higher values of $S_1/S_{1\max }$ under moisture above optimum, suggesting a greater tendency toward plastic creep. These findings highlight the critical importance of moisture control for the sustainable performance of railway substructures. This study contributes to understanding environmental vulnerability in transportation infrastructure and supports the development of more resilient and sustainable railway systems. Full article

With the further implementation and development of the Western Development Strategy, studying the mechanical behavior and deformation characteristics of deep-buried tunnels in layered hard rock under high ground stress conditions holds considerable engineering significance. To study the mechanical properties and long-term deformation and failure characteristics of different bedding stratified rocks, this research employed an MTS815 electro-hydraulic servo rock testing system and a French TOP rheometer. Triaxial compression tests, rheological property tests, and long-term cyclic and unloading tests were conducted on shale samples under varying confining pressures and bedding angles. The results indicate that (1) under triaxial compression, shale demonstrates pronounced anisotropic behavior. When the confining pressure is constant, the peak strength of the rock sample exhibits a “U”-shaped variation with the bedding angle (its minimum value at 60°). For a fixed bedding angle, the peak strength of the rock sample progressively increases as the confining pressure rises. (2) The mode of shale failure varies with the angle: at 0°, shale exhibits conjugate shear failure; at 30°, shear slip failure along the bedding is controlled by the bedding weak plane; at 60° and 90°, failure occurs through the bedding. (3) During the creep process of layered shale, brittle failure characteristics are evident, with microcracks within the sample gradually failing at stress concentration points. The decelerated and stable creep stages are prominent; while the accelerated creep stage is less noticeable, the creep rate increases with increasing stress level. (4) Under low confining pressure, the peak strength during cyclic loading and unloading creep processes is lower than that of conventional triaxial tests when the bedding plane dip angles are 0° and 30°, which is the opposite at 60° and 90°. (5) In the cyclic loading and unloading process, Poisson’s ratio gradually increases, whereas the elastic modulus, shear modulus, and bulk modulus gradually decrease. Full article

Inconel 600 alloy has gained consideration as a favourable material for heat and power applications, particularly in turbine blades, due to its superior mechanical behaviour encompassing strength, toughness, oxidation resistance, and ductility. Tungsten Inert Gas (TIG) welding is one of the preferred techniques for joining these alloys. Therefore, the investigation of the mechanical behaviour after the welding process is crucial for selecting the appropriate technique for joining Inconel 600 sheets. This research focuses on investigating the microstructure and mechanical behaviour of TIG-welded Inconel 600 through a series of tests, such as tensile, fatigue, creep, and hardness evaluations. In addition, microstructural analysis is combined with these mechanical evaluations to simulate the operating conditions experienced by turbine blades. Key parameters such as yield strength, tensile strength, and elongation have been evaluated through these analyses. The Ramberg–Osgood relationship has been investigated using the engineering and true stress–strain curves obtained from the welded specimens. The results of the fatigue test illustrate the relationship between strain amplitude and the number of cycles to failure for single and double-edge notched specimens. The test was performed at two different loads including 400 MPa and 250 MPa at a constant temperature of 650 °C, and the corresponding strain-time curves were recorded. The results showed rapid creep failure at 650 °C, suggesting that TIG welding may need to be optimized for high temperature applications. Full article

Q345 steel is usually used on structures working under high temperature where creep deformation could endanger their structural integrity. In order to support the application of steel structures made of Q345 under high temperature, a fracture analysis on defective Q345 steel in the process of small-scale creep crack propagation has been performed. Three-dimensional finite element models with a semi-elliptical surface crack have been established, and the crack propagation process of Q345 steel has been simulated at 400 °C. The constraint effect near the crack tip in the process of creep crack propagation has been analyzed using the J-A₂ two-parameter method in which the influence of the crack aspect ratio, loading level, and biaxial loading ratio was studied. The previously developed constraint-based R6 procedure was adopted to assess the structural integrity of the cracked structure under small-scale creep conditions. The results showed that small-scale creep crack propagation behavior exhibits great influence on both crack tip fields and a constraint effect near the crack tip. The increase in the biaxial loading ratio, loading level, and aspect ratio of the crack could lead to an increase in the J integral, an enhancement of the constraint effect, and a decrease in the safe area in the failure assessment diagram for the cracked structure in the process of small-scale creep crack propagation. Full article

Exhaust manifolds accumulate creep and fatigue damage under cyclic thermal loading, leading to localized failure. Understanding a material’s mechanical behavior is crucial for accurate life assessment. This study systematically investigated the low-cycle fatigue (LCF) and creep–fatigue interaction behaviors of medium-silicon molybdenum ductile iron. It was found that QTRSi4Mo exhibited cyclic hardening at room temperature and 400 °C, whereas it exhibited cyclic softening at 600 °C and 700 °C for low-cycle stress–strain responses. During creep–fatigue tests with hold time, variations in the strain amplitude did not alter the hysteresis loop shape or the hardening/softening characteristics of the material. They only induced a slight upward shift in the yield center. Additionally, stress relaxation primarily occurred in the initial phase of the hold period, so the hold duration had little effect on the final stress value. The investigation of creep–fatigue life models highlighted that accurately characterizing the damage induced by stress relaxation during the hold stage is critical for creep damage evaluation. The calculated creep damage results differed greatly from the experimental results of the time fraction model (TF). A combined approach using the strain energy density dissipation model (T-SEDE) and the Ostergren method demonstrated excellent predictive capability for creep–fatigue life. Full article

Energy storage systems are gaining increasing attention as a solution to the inherent intermittency of renewable energy sources such as solar and wind power. Among large-scale energy storage technologies, compressed air energy storage (CAES) stands out for its natural sealing properties and cost-efficiency. Having abundant salt resources, the thick and regionally extensive salt deposits in Unit B of Southern Ontario, Canada, demonstrate significant potential for CAES development. In this study, optimization for essential CAES salt cavern parameters are conducted using geological data from Unit B salt deposit. Cylinder-shaped and ellipsoid-shaped caverns with varying diameters are first simulated to determine the optimal geometry. To optimize the best operating pressure range, stationary simulations are first conducted, followed by tightness evaluation and long-term stability simulation that assess plastic and creep deformation. The results indicate that a cylinder-shaped cavern with a diameter 1.5 times its height provides the best balance between storage capacity and structural stability. While ellipsoid shape reduces stress concentration significantly, it also leads to increased deformation in the shale interlayers, making them more susceptible to failure. Additionally, the findings suggest that the optimal operating pressure lies between 0.4 and 0.7 times the vertical stress, maintaining large capacity and minor gas leakage, and developing the least creep deformation. Full article