Search Results (349)

Previous studies have extensively applied the generalized consolidation theory, which incorporates a two-stress state variable framework, to predict the volumetric behavior of unsaturated expansive soils under varying mechanical stress and matric suction. A key requirement for this approach is a constitutive surface that links the soil void ratio to both net stress and matric suction. A large number of fitting parameters are typically needed to accurately fit a two-variable void ratio surface equation to laboratory test data. In this study, a single-stress state variable framework was adopted to describe the void ratio as a function of effective stress for unsaturated soils. The proposed approach was applied to fit void ratio–effective stress constitutive curves to laboratory test data for two different expansive clays. Additionally, a finite element model coupling variably saturated flow and stress–strain analysis was developed to simulate the volume change behavior of expansive clay subjected to moisture fluctuations. The model utilizes suction stress to compute the effective stress field and incorporates the dependency of soil modulus on volumetric water content based on the proposed void ratio–effective stress relationship. The developed numerical model was validated against a benchmark problem in which a layer of Regina expansive clay was subjected to a constant infiltration rate. The results demonstrate the effectiveness of the proposed model in simulating expansive soil deformations under varying moisture conditions over time. Full article

A numerical method is proposed for evaluating the axial stress–strain relationship of FRP-confined concrete. In this method, empirical formulae for the compressive strength and strain at peak stress of confined concrete are obtained by fitting experimental data collected from the literature. It is then assumed that when FRP-confined concrete and actively confined concrete are subjected to the same lateral strain and confining pressure at a specific loading stage, their axial stress–strain relationships are identical at that stage. Based on this assumption, a numerical method for the axial stress–strain relationship of FRP-confined concrete is developed by combining the stress–strain model of actively confined concrete with the axial–lateral strain correlation. Finally, the validity of this numerical method is verified with experimental data with various geometric and material parameters, demonstrating a reasonable agreement between predicted stress–strain curves and measured ones. A parametric analysis is conducted to reveal that the stress–strain curve is independent of the specimen length for strong FRP confinement with small failure strains, while the specimen length exhibits a significant effect on the softening branch for weak FRP confinement. Therefore, for weakly FRP-confined concrete, it is recommended to consider the specimen length effect in evaluating the axial stress–strain relationship. Full article

The polytetrafluoroethylene/aluminum (PTFE/Al) granular composite, a common formulation in impact-initiated energetic materials, undergoes mechanochemical coupling reactions under sufficiently strong dynamic loading. This investigation discusses the dynamic properties and the constitutive relationship of the PTFE/Al granular composite to provide a preliminary guide for the research on mechanical properties of a series of composite materials based on PTFE/Al as the matrix. Firstly, the 26.5Al-73.5PTFE (wt.%) composite specimens are prepared by preprocessing, mixing, molding, high-temperature sintering, and cooling. Then, the quasi-static compression and Hopkinson bar tests are performed to explore the mechanical properties of the PTFE/Al composite. Influences of the strain rate of loading on the yield stress, the ultimate strength, and the limited strain are also analyzed. Lastly, based on the experimental results, the material parameters in the Johnson–Cook constitutive model are obtained by the method of piecewise fitting to describe the stress–strain relation of the PTFE/Al composite. Combining the experimental details and the obtained material parameters, the numerical simulation of the dynamic compression of the PTFE/Al composite specimen is carried out by using the ANSYS/LS-DYNA platform. The results show that the computed stress–strain curves present a reasonable agreement with the experimental data. It should be declared that this research does not involve the energy release behavior of the 26.5Al-73.5PTFE (wt.%) reactive material because the material is not initiated within the strain rate range of the dynamic test in this paper. Full article

This contribution compares various theories dealing with the assessment of dislocation density in metals subjected to different straining levels. The paper examines both substructure development and the evolution of dislocation densities in 1xxx, 5xxx, and 6xxx Al alloys. Barlat’s dislocation model, Kocks–Mecking–Estrin (K-M-E) theory, and Kubin–Estrin (K-E) type modeling approaches were analyzed. The dislocation model parameters were determined from the microindentation profiles for the rolled Al alloys. It was shown that a strong correlation exists between the K-E and K-M-E models, confirming their reliability in describing the relationship between strain, stress, and dislocation density. These numerical approaches effectively capture the evolution of dislocation density with strain, making them suitable for the analysis of the accumulation of stored energy during deformation. The development of substructure during straining was inferred from the microindentation experiments, and the resulting dependencies tended to align with the characteristic curve observed in various metals. Full article

The accumulation of fatigue damage is primarily caused by cyclic plastic deformation. In low-cycle fatigue, cyclic plastic deformation is the dominant deformation mode. In high-cycle fatigue, although most deformation is elastic, plastic deformation may still occur in localized regions of stress concentration and plays a critical role in the initiation of fatigue cracks. Considering that cyclic plastic deformation can be characterized by hysteresis loops, this study modifies the flow stress equation and the cyclic plastic deformation relationship based on stress–strain hysteresis loops at half-life cycles under different strain amplitudes. An improved model for life prediction that incorporates the effects of strain amplitude is proposed. The results of experiments on 310S stainless steel and 1045 carbon steel demonstrate that the model achieved prediction errors within a factor of two and provided reliable predictions for both high-cycle and low-cycle fatigue life across the entire ε-N curve. Full article

Silty clay is extensively distributed in northern China. Numerous seismic events have demonstrated that underground structures embedded in silty clay strata are prone to severe damage during earthquakes. This study employs dynamic cyclic triaxial tests on undisturbed and remolded specimens (50–300 kPa confining pressures) to pioneer the quantification of pressure-amplified structural superiority. The experimental results reveal that: (1) Undisturbed soils exhibit 20–30% higher maximum shear stress (τ_dmax) and shear modulus (G_dmax) than remolded counterparts at 300 kPa, far exceeding the <5% deviation at 50 kPa due to enhanced particle-cementation synergy under pressure. (2) The normalized shear modulus ratio (G_d/G_dmax) exhibits low sensitivity to confining pressure, with G_d/G_dmax–γ_d relationship curves predominantly confined within a narrow band range. A triphasic evolutionary characteristic is manifested in the progressive reduction of G_d/G_dmax with increasing shear strain (γ_d), and quasi-linear attenuation is observed within the shear strain range of 1 × 10⁻⁴ ≤ γ_d ≤ 1 × 10⁻². (3) Remolded and undisturbed specimens demonstrate close correspondence in damping ratio (λ_d) across consolidation pressures. Under identical γ_d conditions, undisturbed specimens consistently exhibit lower λ_d values than remolded counterparts, attributable to enhanced energy dissipation resulting from structural homogenization in remolded soils, with λ_dmax magnitudes ranging between 0.2 and 0.3. The research provides mechanistic insights for seismic design of underground structures in silty clay terrains, particularly regarding disturbance sensitivity under deep burial conditions. Full article

Coral sand is characterized by unique particle morphology and pore structure, which result in pronounced dilatancy and a high internal friction angle during shear. The dilatancy angle is a critical parameter for finite element analyses of sand foundation bearing capacity; the inappropriate selection of this parameter can lead to significant computational errors. In this research, a series of consolidated drained triaxial tests were conducted on coral sand samples from the South China Sea to investigate the dilatancy behavior and its effect on shear strength parameters. A dilatancy equation for coral sand was proposed, incorporating the dilatancy index, relative density, and mean effective stress. The results indicate the following: (1) Within the confining pressure range of 25–400 kPa, the stress–strain curves exhibit varying degrees of strain softening. When the effective confining pressure reaches 400 kPa, the dilatant behavior is nearly suppressed, resulting in a transition from dilatancy to contraction; (2) The peak internal friction angle decreases significantly with increasing effective confining pressure. However, the sensitivity to confining pressure varies for samples with different relative densities (Dr = 30–90%), with denser samples showing a more rapid reduction in peak friction angle; (3) At a confining pressure of 25 kPa, the maximum dilatancy angle of coral sand samples reaches 44.2°, significantly exceeding the typical range observed in terrestrial quartz sands. This difference may be attributed to the irregular and angular characteristics of the coral sand particles; (4) Based on Bolton’s dilatancy theory, a dilatancy equation applicable to coral sand was developed, demonstrating a strong linear relationship among the dilatancy index (I_R), relative density (Dr), and peak mean effective stress (p′_f). These findings provide valuable guidance for the selection of strength parameters for engineering applications involving coral sand. Full article

The shear strength of a steel shear wall (SSW) is typically governed by the yield strength of the steel. However, changes in mechanical properties beyond yielding—particularly those related to steel hardening and the effects of gravity loads—are not yet fully understood. These factors are critical for accurately assessing the shear capacity of SSWs during seismic events. In the current study, a method to calculate the shear force–displacement curve of a steel shear wall while considering the compression effect is presented, which incorporates both steel hardening and gravity effects. The analysis derives strains in tensile strips undergoing shear deformation using a strip model. Corresponding stresses are then determined using the stress–strain relationships obtained from tensile tests of the steel. Furthermore, the vertical stress induced by gravity loads is modeled using a three-segment distribution proposed before. For each tensile strip, the tension field stress is calculated by accounting for reductions due to vertical stress and the influence of steel hardening through the von Mises yield criterion. This approach enables the development of a shear force–displacement curve, which is subsequently validated against results from an experimentally verified finite element model. The findings demonstrate that the pushover curves predicted by this method closely align with those obtained from finite element analysis. Notably, the results indicate that the shear strength provided by the CAN/CSA-S16-01 equation may be overestimated by approximately 4%, 9%, and 18% when the vertical compression stresses are 50, 100, and 150 MPa for a wall with a slenderness of 150, respectively. Full article

Different from general underground engineering, the micro-damage prior to failure of the surrounding rock has a significant influence on the geological disposal of high-level radioactive waste. However, the quantitative research on pre-failure dilatancy damage characteristics and stress path influence of hard brittle rocks under high stress levels is insufficient currently, and especially, the stress path under simultaneous unloading of axial and confining pressures is rarely discussed. Therefore, three representative mechanical experimental studies were conducted on the Beishan granite in the pre-selected area for high-level radioactive waste (HLW) geological disposal in China, including increasing axial pressure with constant confining pressure (path I), increasing axial pressure with unloading confining pressure (path II), and simultaneous unloading of axial and confining pressures (path III). Using the deviatoric stress ratio as a reference, the evolution laws and characteristics of stress–strain relationships, deformation modulus, generalized Poisson’s ratio, dilatancy index, and dilation angle during the path bifurcation stage were quantitatively analyzed and compared. The results indicate that macro-deformation and the plastic dilatancy process exhibit strong path dependency. The critical value and growth gradient of the dilatancy parameter for path I are both the smallest, and the suppressive effect of the initial confining pressure is the most significant. The dilation gradient of path II is the largest, but the degree of dilatancy before the critical point is the smallest due to its susceptibility to fracture. The critical values of the dilatancy parameters for path III are the highest and are minimally affected by the initial confining pressure, indicating the most significant dilatancy properties. Establish the relationship between the deformation parameters and the crack-induced volumetric strain and define the damage variable accordingly. The critical damage state and the damage accumulation process under various stress paths were examined in detail. The results show that the damage evolution is obviously differentiated with the bifurcation of the stress paths, and three different types of damage curve clusters are formed, indicating that the damage accumulation path is highly dependent on the stress path. The research findings quantitatively reveal the differences in deformation response and damage characteristics of Beishan granite under varying stress paths, providing a foundation for studying the nonlinear mechanical behavior and damage failure mechanisms of hard brittle rock under complex loading conditions. Full article

The long-term immersion of coal rock may affect its mechanical properties and failure modes, potentially impacting the stability of coal pillars. This work aims to investigate the influence of the immersion duration on the mechanical properties and fracture evolution processes of coal, employing acoustic emission detection and the digital image correlation (DIC) method. The work focuses on the weakening law of the coal pillar dam in contact with water and obtains a model of the strength deterioration after different periods of water immersion. The stress–strain curves of coal specimens with varying immersion durations are obtained. The results show that the peak absorption rate of coal samples immersed in water transpires within 24 h, with fundamental saturation being achieved at between 25 and 30 days at saturation moisture content of 1.97%. The specimen’s compressive stress after being immersed in water for 7 days is 3.34 MPa, with strain of 0.18%. The cracking stress is 15.60 MPa, with strain of 0.54%. The peak stress is recorded at 27.65 MPa, with strain of 0.92%. The complete rupture stress measures 23.37 MPa, with the maximum strain at 0.95%. During the yielding stage, the specimen has the highest strain increment of 0.38%. Short-term immersion brings about an increase in the coal sample’s plasticity, exhibiting a relatively minor softening impact of water, resulting in comparatively intact fragmentation and modest breakage. A negative exponential function relationship is observed between the compressive strength of coal and the immersion duration. The mechanical reduction relationship is utilized to analyze the failure patterns of coal pillars in underground reservoirs. With prolonged water immersion, the damage area expands to include the coal pillars and the surrounding rock of the excavation area. Full article

Based on Brillouin optical time-domain reflectometry (BOTDR) technology, this study integrates laboratory tensile tests and similarity simulation experiments to systematically investigate the relationship between overlying strata collapse and fiber strain during coal seam mining. An analytical expression was established to describe the correlation between overlying strata displacement and fiber strain. The horizontal fiber monitoring results indicate that fiber strain accurately captures the evolution of overlying strata collapse and exhibits strong agreement with actual displacement height. When the working face advanced to 115 m and 155 m, the rock strata primarily underwent stress adjustment with minimal failure. At 195 m, the collapse zone expanded significantly, resulting in a notable increase in fiber strain. By 240 m, severe roof failure occurred, forming a complete caving zone in the goaf. The fiber strain curve exhibited a characteristic “double convex peak” pattern, with peak positions closely corresponding to rock fracture locations, further validating the feasibility of fiber monitoring in coal seam mining. Vertical fiber monitoring clearly delineated the evolution of the “three-zone” structure (caving zone, fracture zone, and bending subsidence zone) in the overlying strata. The fiber strain underwent a staged transformation from compressive strain to tensile strain, followed by stable compaction. The “stepped” characteristics of the strain curve effectively represented the heights of the three zones, highlighting the progressive and synchronized nature of rock failure. These findings demonstrate that fiber strain effectively characterizes the collapse height and evolution of overlying strata, enabling precise identification of rock fracture locations. This research provides scientific insights and technical support for roof stability assessment and mine safety management in coal seam mining. Full article

This paper presents a study on the uniaxial compressive behavior of fully grouted concrete bond beam block masonry prisms. A total of 45 (i.e., 9 hollow and 36 fully grouted) specimens were tested, and the failure modes and initial crack were reported. The effects of block strength, grout strength, and loading scheme on the compressive strength of the fully grouted prism were discussed. The results show that the compressive strength of bond beam block prisms increased with an increase in grouting, while they were less affected by the block strength; the peak strength of the grouted block masonry was, on average, 35.1% higher than the hollow masonry prism. In addition, although the specimens’ strength was lower under cyclic compression than under monotonic compression loading, the difference in their specified compressive strength was statistically insignificant. The stress–strain curve of block masonry under uniaxial compression was also obtained. Through nonlinear fitting, the compressive stress–strain relationship of grouted masonry, considering masonry strength parameters, was established, which demonstrated alignment with prior experimental studies. This study not only provides a strength calculation method for grouted masonry structures using high-strength blocks in the code for the design of masonry structures in China but also offers a dedicated stress–strain curve for precise finite element analysis and the design of masonry structures. 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

This study investigates damage characteristics of red sandstone under dynamic loads to clarify the effects of construction disturbances and blasting on the stability of surrounding rock during mountain tunnel construction in water-rich strata. Dynamic impact experiments at various loads were conducted using the Split Hopkinson Pressure Bar (SHPB) instrument, complemented by simulations of the fracturing process in saturated sandstone using finite element software. This analysis systematically examines the post-fracture granularity mass fraction, stress-strain curves, peak stress-average strain rate relationship, and fracture patterns. The dynamic response mechanism of red sandstone during the process of tunnel blasting construction was thoroughly investigated. Experimental results reveal that the peak stress and failure strain exhibit strain rate dependency, increasing from 45.65 MPa to 115.34 MPa and 0.95% to 5.23%, respectively, as strain rate elevates from 35.53 s⁻¹ to 118.71 s⁻¹. The failure process of red sandstone is divided into four stages: crack closure, nearly elastic phase, rapid crack development, and rapid unloading. Dynamic peak stress and average strain rate in sandstone demonstrate an approximately linear relationship, with the correlation coefficient being 0.962. Under different impact loads, fractures in specimens typically expand from the edges to the center and evolve from internal squeezing fractures to external development. Peak stress, degree of specimen breakage, and energy dissipation during fracturing are significantly influenced by the strain rate. The numerical simulations confirmed experimental findings while elucidating the failure mechanism in surrounding rocks under varying strain rates. This work pioneers a multiscale analysis framework bridging numerical simulation with a blasting construction site, addressing the critical gap in time-dependent deformation during tunnel excavation. Full article

In this study, the effect of plastic residual strain on the corrosion behavior of ZK60 magnesium alloy was systematically revealed using a research method combining experimental characterization and numerical simulation. Based on the multiphysical field coupling theory, a numerical model containing deformation field, corrosion phase field, and material transfer field was constructed, and the dynamic simulation of plastic residual strain-induced corrosion damage was successfully realized. Tafel polarization curves obtained from electrochemical tests were fitted to the key parameters of the secondary current distribution. The kinetic parameter L controlling the corrosion rate in the phase-field model was innovatively determined by the inverse calibration method, and a quantitative relationship between the kinetics of electrochemical corrosion and the phase-field theory was established. The corrosion depth distribution of the pre-strained specimens is quantitatively characterized and the results are in agreement with the finite element simulation results. The coupled strain-corrosion analysis method proposed in this study provides a theoretical basis for the design and life prediction of corrosion resistance of components under complex stress states. Full article