Evaluation of hydromechanical shear behavior of unsaturated soils is still a challenging issue. The time and cost needed for conducting precise experimental investigation on shear behavior of unsaturated soils have en...Evaluation of hydromechanical shear behavior of unsaturated soils is still a challenging issue. The time and cost needed for conducting precise experimental investigation on shear behavior of unsaturated soils have encouraged several investigators to develop analytical, empirical, or semi-empirical models for predicting the shear behavior of unsaturated soils. However, most of the previously proposed models are for specimens subjected to the isotropic state of stress, without considering the effect of initial shear stress. In this study, a hydromechanical constitutive model is proposed for unsaturated collapsible soils during shearing, with consideration of the effect of the initial shear stress. The model implements an effective stress-based disturbed state concept (DSC) to predict the stress-strain behavior of the soil. Accordingly, material/state variables were defined for both the start of the shearing stage and the critical state of the soil. A series of laboratory tests was performed using a fully automated unsaturated triaxial device to verify the proposed model. The experimental program included 23 suction-controlled unsaturated triaxial shear tests on reconstituted specimens of Gorgan clayey loess wetted to different levels of suctions under both isotropic and anisotropic stress states. The results show excellent agreement between the prediction by the proposed model and the experimental results.展开更多
The strength of the sliding zone soil determines the stability of reservoir landslides.Fluctuations in water levels cause a change in the seepage field,which serves as both the external hydrogeological environment and...The strength of the sliding zone soil determines the stability of reservoir landslides.Fluctuations in water levels cause a change in the seepage field,which serves as both the external hydrogeological environment and the internal component of a landslide.Therefore,considering the strength changes of the sliding zone with seepage effects,they correspond with the actual hydrogeological circumstances.To investigate the shear behavior of sliding zone soil under various seepage pressures,24 samples were conducted by a self-developed apparatus to observe the shear strength and measure the permeability coefficients at different deformation stages.After seepage-shear tests,the composition of clay minerals and microscopic structure on the shear surface were analyzed through X-ray and scanning electron microscope(SEM)to understand the coupling effects of seepage on strength.The results revealed that the sliding zone soil exhibited strain-hardening without seepage pressure.However,the introduction of seepage caused a significant reduction in shear strength,resulting in strain-softening characterized by a three-stage process.Long-term seepage action softened clay particles and transported broken particles into effective seepage channels,causing continuous damage to the interior structure and reducing the permeability coefficient.Increased seepage pressure decreased the peak strength by disrupting occlusal and frictional forces between sliding zone soil particles,which carried away more clay particles,contributing to an overhead structure in the soil that raised the permeability coefficient and decreased residual strength.The internal friction angle was less sensitive to variations in seepage pressure than cohesion.展开更多
Based on the investigation of mechanical response and microstructure evolution of a commercial 7003 aluminum alloy under high-speed impact,a new simple and effective method was proposed to determine the critical strai...Based on the investigation of mechanical response and microstructure evolution of a commercial 7003 aluminum alloy under high-speed impact,a new simple and effective method was proposed to determine the critical strain required for the nucleation of adiabatic shear band(ASB).The deformation results of cylindrical and hat-shaped samples show that the critical strain required for ASB nucleation corresponds to the strain at the first local minimum after peak stress on the first derivative curve of true stress−true strain.The method of determining the critical strain for the nucleation of ASB through the first derivative of the flow stress curve is named the first derivative method.The proposed first derivative method is not only applicable to the 7003 aluminum alloy,but also to other metal materials,such as commercial purity titanium,WY-100 steel,and AM80 magnesium alloy.This proves that it has strong universality.展开更多
Non-seismically designed(NSD)beam-column joints are susceptible to joint shear failure under seismic loads.Although significant research is available on the seismic behavior of such joints of planar frames,the informa...Non-seismically designed(NSD)beam-column joints are susceptible to joint shear failure under seismic loads.Although significant research is available on the seismic behavior of such joints of planar frames,the information on the seismic behavior of joints of space frames(3D joints)is insufficient.The 3D joints are subjected to bi-directional excitation,which results in an interaction between the shear strength obtained for the joint in the two orthogonal directions separately.The bi-directional seismic behavior of corner reinforced concrete(RC)joints is the focus of this study.First,a detailed finite element(FE)model using the FE software Abaqus,is developed and validated using the test results from the literature.The validated modeling procedure is used to conduct a parametric study to investigate the influence of different parameters such as concrete strength,dimensions of main and transverse beams framing into the joint,presence or absence of a slab,axial load ratio and loading direction on the seismic behavior of joints.By subjecting the models to different combinations of loads on the beams along perpendicular directions,the interaction of the joint shear strength in two orthogonal directions is studied.The comparison of the interaction curves of the joints obtained from the numerical study with a quadratic(circular)interaction curve indicates that in a majority of cases,the quadratic interaction model can represent the strength interaction diagrams of RC beam to column connections with governing joint shear failure reasonably well.展开更多
A conceptual model of intermittent joints is introduced to the cyclic shear test in the laboratory to explore the effects of loading parameters on its shear behavior under cyclic shear loading.The results show that th...A conceptual model of intermittent joints is introduced to the cyclic shear test in the laboratory to explore the effects of loading parameters on its shear behavior under cyclic shear loading.The results show that the loading parameters(initial normal stress,normal stiffness,and shear velocity)determine propagation paths of the wing and secondary cracks in rock bridges during the initial shear cycle,creating different morphologies of macroscopic step-path rupture surfaces and asperities on them.The differences in stress state and rupture surface induce different cyclic shear responses.It shows that high initial normal stress accelerates asperity degradation,raises shear resistance,and promotes compression of intermittent joints.In addition,high normal stiffness provides higher normal stress and shear resistance during the initial cycles and inhibits the dilation and compression of intermittent joints.High shear velocity results in a higher shear resistance,greater dilation,and greater compression.Finally,shear strength is most sensitive to initial normal stress,followed by shear velocity and normal stiffness.Moreover,average dilation angle is most sensitive to initial normal stress,followed by normal stiffness and shear velocity.During the shear cycles,frictional coefficient is affected by asperity degradation,backfilling of rock debris,and frictional area,exhibiting a non-monotonic behavior.展开更多
Determination of Shear Bond strength(SBS)at interlayer of double-layer asphalt concrete is crucial in flexible pavement structures.The study used three Machine Learning(ML)models,including K-Nearest Neighbors(KNN),Ext...Determination of Shear Bond strength(SBS)at interlayer of double-layer asphalt concrete is crucial in flexible pavement structures.The study used three Machine Learning(ML)models,including K-Nearest Neighbors(KNN),Extra Trees(ET),and Light Gradient Boosting Machine(LGBM),to predict SBS based on easily determinable input parameters.Also,the Grid Search technique was employed for hyper-parameter tuning of the ML models,and cross-validation and learning curve analysis were used for training the models.The models were built on a database of 240 experimental results and three input variables:temperature,normal pressure,and tack coat rate.Model validation was performed using three statistical criteria:the coefficient of determination(R2),the Root Mean Square Error(RMSE),and the mean absolute error(MAE).Additionally,SHAP analysis was also used to validate the importance of the input variables in the prediction of the SBS.Results show that these models accurately predict SBS,with LGBM providing outstanding performance.SHAP(Shapley Additive explanation)analysis for LGBM indicates that temperature is the most influential factor on SBS.Consequently,the proposed ML models can quickly and accurately predict SBS between two layers of asphalt concrete,serving practical applications in flexible pavement structure design.展开更多
The Qinghai-Xizang Plateau of China faces challenges like thaw slumping,threatening slope stability and infrastructure.Understanding the mechanical properties of the roots of the dominant herbaceous plant species in t...The Qinghai-Xizang Plateau of China faces challenges like thaw slumping,threatening slope stability and infrastructure.Understanding the mechanical properties of the roots of the dominant herbaceous plant species in the alpine meadow layer of the permafrost regions on the Qinghai-Xizang Plateau is essential for evaluating their role in enhancing soil shear strength and mitigating slope deformation in these fragile environments.In this study,the roots of four dominant herbaceous plant species—Kobresia pygmaea,Kobresia humilis,Carex moorcroftii,and Leontopodium pusillum—that are widely distributed in the permafrost regions of the Qinghai-Xizang Plateau were explored to determine their mechanical properties and effects in enhancing soil shear strength.Through indoor single root tensile and root group tensile tests,we determined the root diameter,tensile force,tensile strength,tensile ratio,and strength frequency distributions.We also evaluated their contributions to inhibiting slope deformation and failure during the formation and development of thermal thaw slumps in the alpine meadow.The results showed that the distribution of the root diameter of the dominant plant species is mostly normal,while the tensile strength tends to be logarithmically normally distributed.The relationship between the root diameter and root tensile strength conforms to a power function.The theoretical tensile strength of the root group was calculated using the Wu-Waldron Model(WWM)and the Fiber Bundle Model(FBM)under the assumption that the cumulative single tensile strength of the root bundle is identical to the tensile strength of the root group in the WWM.The FBM considers three fracture modes:FBM-D(the tensile force on each single root is proportional to its diameter relative to the total sum of all the root diameters),FBM-S(the cross-sectional stress in the root bundle is uniform),and FBM-N(each tensile strength test of individual roots experiences an equal load).It was found that the model-calculated tensile strength of the root group was 162.60%higher than the test value.The model-derived tensile force of the root group from the FBM-D,FBM-S,and FBM-N was 73.10%,28.91%,and 13.47%higher than the test values,respectively.The additional cohesion of the soil provided by the roots was calculated to be 25.90-45.06 kPa using the modified WWM,67.05-38.15 kPa using the FBM-S,and 57.24-32.74 kPa using the FBM-N.These results not only provide a theoretical basis for further quantitative evaluation of the mechanical effects of the root systems of herbaceous plant species in reinforcing the surface soil but also have practical significance for the effective prevention and control of thermal thaw slumping disasters in the permafrost regions containing native alpine meadows on the Qinghai-Xizang Plateau using flexible plant protection measures.展开更多
Plant roots are widely known to provide mechanical reinforcement to soils against shearing and further increase slope stability.However,whether roots provide reinforcement to loess cyclic re-sistance and how various f...Plant roots are widely known to provide mechanical reinforcement to soils against shearing and further increase slope stability.However,whether roots provide reinforcement to loess cyclic re-sistance and how various factors affect roots reinforcement during seismic loading have rarely been studied.The objective is to conduct a series of cyclic direct simple shear tests and DEM numerical simulation to investigate the cyclic behaviour of rooted loess.The effects of initial static shear stress and loading frequency on the cyclic resistance of root-soil composites were first investigated.After that,cyclic direct simple shear simulations at constant volume were carried out based on the discrete element method(PFC^(3D))to investigate the effects of root geome-try,mechanical traits and root-soil bond strength on the cyclic strength of rooted loess.It was discovered that the roots could effectively improve the cyclic resistance of loess.The cyclic resistance of the root-soil composite decreases with the increase of the initial shear stress,then increases,and improves with the increase of the frequency.The simulation result show that increases in root elastic modulus and root-soil interfacial bond strength can all enhance the cyclic resistance of root-soil composites,and the maximum cyclic resistance of the root-soil composite was obtained when the initial inclination angle of the root system was 90°.展开更多
After the excavation of deep mining tunnels and underground caverns,the stability of surrounding rock controlled by structural planes is prone to structural damage and even engineering disasters due to three-dimension...After the excavation of deep mining tunnels and underground caverns,the stability of surrounding rock controlled by structural planes is prone to structural damage and even engineering disasters due to three-dimensional stress redistribution and multi-directional dynamic construction interference.However,the shear mechanical behavior,fracture evolution mechanism and precursor characteristics of rockmass under true triaxial stress and multi-directional coupling disturbance are not unclear.Therefore,this study carried out true triaxial shear tests on limestone intermittent structural planes under uni-,bi-and tri-directional coupling disturbances to analyze its mechanical behavior,fracture evolution mechanism and precursor characteristics.The results show that as the disturbance direction increase,the shear strength of limestone generally decreases,while the roughness of structural planes and the degree of anisotropy generally exhibit an increasing trend.The proportion of shear cracks on the structural plane increases with the increase of shear stress.The disturbance strain rate before failure shows a U-shaped trend.Near to disturbance failure,there were more high-energy and high-amplitude acoustic emission events near the structural plane,and b-value drops rapidly below 1,while lgN/b ratio increased to above 3.These findings provide experimental recognition and theoretical support for assessing the stability of rockmass under blasting excavation.展开更多
In geotechnical engineering,rock bolts are commonly used for reinforcement,while the surrounding rock mass bears varying degrees of shear loads.The shear rate affects the stability of bolted rock joints,especially in ...In geotechnical engineering,rock bolts are commonly used for reinforcement,while the surrounding rock mass bears varying degrees of shear loads.The shear rate affects the stability of bolted rock joints,especially in projects susceptible to dynamic shear loads.In laboratory experiments,fully-grouted bolts and energy-absorbing bolts were used as research objects,and artificial rock specimens with rough joints were fabricated to analyze the shear characteristics and damage mechanisms of bolted rock joints under cyclic shear conditions and different shear velocities.The results showed that as the shear rate increased,the shear strength of bolted rock joint specimens decreased.Degradation of asperities resulted in no obvious peak shear stress in the specimens.Energy-absorbing bolts exhibited greater deformation capacity,with significant necking phenomena and the ability to withstand larger shear displacements.In contrast,fully-grouted bolts,which have threaded surfaces that provide higher bonding performance,exhibited a reduced capacity for plastic deformation and were prone to breaking under smaller shear displacements.Although the shear stiffness of specimens reinforced by energy-absorbing bolts was slightly lower than that of fully-grouted bolt specimens,they demonstrated greater stability under various shear rates.The absorbed shear energy showed that energy-absorbing bolts had superior coordinated deformation capabilities,thus exhibiting greater absorbed shear energy than fully-grouted bolts.Overall,fully-grouted bolts are more suitable for projects requiring higher rock shear strength and overall stiffness.In contrast,energy-absorbing bolts are more suitable for coping with dynamic or fluctuating load conditions to maintain the relative stability of jointed rock masses.展开更多
Localized rock failures,like cracks or shear bands,demand specific attention in modeling for solids and structures.This is due to the uncertainty of conventional continuum-based mechanical models when localized inelas...Localized rock failures,like cracks or shear bands,demand specific attention in modeling for solids and structures.This is due to the uncertainty of conventional continuum-based mechanical models when localized inelastic deformation has emerged.In such scenarios,as macroscopic inelastic reactions are primarily influenced by deformation and microstructural alterations within the localized area,internal variables that signify these microstructural changes should be established within this zone.Thus,localized deformation characteristics of rocks are studied here by the preset angle shear experiment.A method based on shear displacement and shear stress differences is proposed to identify the compaction,yielding,and residual points for enhancing the model's effectiveness and minimizing subjective influences.Next,a mechanical model for the localized shear band is depicted as an elasto-plastic model outlining the stress-displacement relation across both sides of the shear band.Incorporating damage theory and an elasto-plastic model,a proposed damage model is introduced to replicate shear stressdisplacement responses and localized damage evolution in intact rocks experiencing shear failure.Subsequently,a novel nonlinear mathematical model based on modified logistic growth theory is proposed for depicting the shear band's damage evolution pattern.Thereafter,an innovative damage model is proposed to effectively encompass diverse rock material behaviors,including elasticity,plasticity,and softening behaviors.Ultimately,the effects of the preset angles,temperature,normal stresses and the residual shear strength are carefully discussed.This discovery enhances rock research in the proposed damage model,particularly regarding shear failure mode.展开更多
Mg alloy often undergoes shear deformation during industrial processing.While its anisotropy and tension-compression asymmetry have been thoroughly studied under uniaxial loading,the understanding for shear loading is...Mg alloy often undergoes shear deformation during industrial processing.While its anisotropy and tension-compression asymmetry have been thoroughly studied under uniaxial loading,the understanding for shear loading is still lacking.This study employed a rolled AZ31B plate with typical basal texture to investigate the shear behaviors.Positive and negative simple shear experiments were performed at different angles in the transverse plane,whereby the visco-plastic self-consistent model was calibrated to reveal the deformation mechanisms and predict the mechanical responses at various orientations.Positive-negative shear asymmetry is present because extension twinning preferentially operates in one shear direction but is suppressed in the opposite direction.Simple shear induces multiple twin variants,thus impedes twin growth and slows the consumption of matrix,as compared to in-plane compression.For slip dominated simple shear,the interaction between loading-induced rigid body rotation and slip-induced crystal rotation produces distinct hardening behaviors,namely orthogonally asymmetric mechanical responses at complementary loading angles,which is largely absent in uniaxial loading.Finally,simulation results verify that positive-negative shear asymmetry appears only when the deviatoric normal stress on the sheet plane is non-zero.Positive-negative shear asymmetry persists except for the conditions of shear plane parallel to sheet plane,or shear direction parallel or perpendicular to rolling direction.展开更多
This study investigated the mechanical responses and debonding mechanisms of a bolt-resin-rock composite anchoring sys-tem subjected to cyclic shear loading.A systematic analysis was conducted on the effects of the in...This study investigated the mechanical responses and debonding mechanisms of a bolt-resin-rock composite anchoring sys-tem subjected to cyclic shear loading.A systematic analysis was conducted on the effects of the initial normal load(Fsd),cyclic shear dis-placement amplitude(ud),frequency(f),and rock type on the shear load,normal displacement,shear wear characteristics,and strain field evolution.The experimental results showed that as Fsd increased from 7.5 to 120 kN,both the peak and residual shear loads exhibited in-creasing trends,with increments ranging from 1.98%to 35.25%and from 32.09%to 86.74%,respectively.The maximum shear load of each cycle declined over the cyclic shear cycles,with the rate of decrease slowing and stabilizing,indicating that shear wear primarily oc-curred at the initial cyclic shear stage.During cyclic shearing,the normal displacement decreased spirally with the shear displacement,im-plying continuous shear contraction.The spiral curves display sparse upwards and dense downward trends,with later cycles dominated by dynamic sliding along the pre-existing shear rupture surface,which is particularly evident in coal.The bearing capacity of the anchoring system varies with the rock type and is governed by the coal strength in coal,resin-rock bonding in sandstone#1 and sandstone#2,com-bined resin strength and resin-rock bonding in sandstone#3(sandstone#1,sandstone#2 and sandstone#3,increasing strength order),and resin strength and bolt-resin bonding in limestone.Cyclic shear loading induces anisotropic interfacial degradation,characterized by es-calating strain concentrations and predominant resin-rock interface debonding,with the damage severity modulated by the rock type.展开更多
Premature adiabatic shear localization caused by strain softening is a roadblock for the application of body-centered cubic(BCC)structured high-entropy alloy(HEAs)in the impact field.A micron-scale orthorhombic-phase(...Premature adiabatic shear localization caused by strain softening is a roadblock for the application of body-centered cubic(BCC)structured high-entropy alloy(HEAs)in the impact field.A micron-scale orthorhombic-phase(O-phase)strengthened TiZrVNbAl alloy was developed to delay adiabatic shear failure and enhance dynamic ductility.The O-phase can not only reduce the slip length,but also promote the pinning and tangling of the dislocations near the phase boundaries.The introduction of the O-phase transformed the strain hardening rate from negative to positive,resulting in a significantly improved dynamic shear resistance.Meanwhile,slip transfer across the O-phase via dislocation cutting mechanisms and a reduction of slip band spacing guaranteed dynamic deformation uniformity.Benefiting from the introduction of the O-phase,the alloy exhibits an excellent stored energy density(∼446 J/cm^(3),surpass the reported BCC-HEAs and typical titanium alloys),a large dynamic fracture strain(∼42%)and a considerable dynamic specific yield strength(∼241 MPa cm^(3)g^(-1)).The present study presents an effective approach for developing BCC-HEAs with excellent dynamic shear resistance and plasticity.展开更多
The growing demand for geothermal energy exploration and deep engineering projects necessitates a deeper understanding of rock behavior under extreme thermal conditions.This study investigates the effect of thermal tr...The growing demand for geothermal energy exploration and deep engineering projects necessitates a deeper understanding of rock behavior under extreme thermal conditions.This study investigates the effect of thermal treatment on the shear behavior of sedimentary sandstone and igneous granite,which are abundant in the Earth's crust.Direct shear tests were conducted on rock joints at room temperature(RT),250℃,and 500℃.The results show that the joints in sandstone and granite exhibit improved compressive and shear strength up to a temperature threshold of 200℃–350℃,followed by significant weakening beyond this range.This study investigated key parameters,including normal and shear stiffness,maximum joint closure,peak and residual shear strengths,internal friction angle,dilation angle,and cohesion.The compressive behavior of both rock types followed a modifiedBandis's equation.The peak shear strength followed Patton's bilinear and Jaeger's nonlinear failure criteria more accurately than the Mohr–Coulomb criterion.The results of this study provide valuable insights into the temperature-dependent behavior of sandstone and granite joints under compressive and shear loads,and their interoperation was strongly dependent on the mineralogical and structural components of the two rock types.These results have advanced our understanding of the temperature-dependent behavior of rock fractures,improving the safety of underground structures under thermal effects.展开更多
Understanding the anchorage performance of en-echelon joints under cyclic shear loading is crucial for optimizing support strategies in jointed rock masses.This study examines the anchorage effects on enechelon joints...Understanding the anchorage performance of en-echelon joints under cyclic shear loading is crucial for optimizing support strategies in jointed rock masses.This study examines the anchorage effects on enechelon joints with various orientations using laboratory cyclic shear tests.By comparing unbolted and bolted en-echelon joints,we analyze shear zone damage,shear properties,dilatancy,energy absorption,and acoustic emission characteristics to evaluate anchoring effects across shear cycles and joint orientations.Results reveal that bolted en-echelon joints experience more severe shear zone damage after cycles,with bolt deformation correlating to shear zone width.Bolted en-echelon joints exhibit faster shear strength deterioration and higher cumulative strength loss compared to unbolted ones,with losses ranging from 20.04%to 72.76%.The compressibility of en-echelon joints reduces the anchoring effect during shear cycles,leading to lower shear strength of bolted en-echelon joints in later stages of shear cycles compared to unbolted ones.Bolts reinforce en-echelon joints more effectively at non-positive angles,with the best performance observed at 0°and-60°.Anchorage accelerates the transition from rolling friction to sliding friction in the shear zone,enhancing energy absorption,which is crucial for rock projects under dynamic shear loading.Additionally,rock bolts expedite the transition of the cumulative AE hits and cumulative AE energy curves from rapid to steady growth,indicating that strong bolt-rock interactions accelerate crack initiation,propagation,and energy release.展开更多
The scaled suction caisson repre sents an innovative design featuring a bio-inspired sidewall modeled after snake skin,commonly utilized in offshore mooring platforms.In comparison with traditional suction caissons,th...The scaled suction caisson repre sents an innovative design featuring a bio-inspired sidewall modeled after snake skin,commonly utilized in offshore mooring platforms.In comparison with traditional suction caissons,this bio-inspired design demonstrates reduced penetration resistance and enhanced pull-out capacity due to the anisotropic shear behaviors of its sidewall.To investigate the shear behavior of the bio-inspired sidewall under pull-out load,direct shear tests were conducted between the bio-inspired surface and sand.The research demonstrates that the interface shear strength of the bio-inspired surface significantly surpasses that of the smooth surface due to interlocking effects.Additionally,the interface shear strength correlates with the aspect ratio of the bio-inspired surface,shear angle,and particle diameter distribution,with values increasing as the uniformity coefficient Cudecreases,while initially increasing and subsequently decreasing with increases in both aspect ratio and shear angle.The ratio between the interface friction angleδand internal friction angle δ_(s) defines the interface effect factor k.For the bio-inspired surface,the interface effect factor k varies with shear angleβ,ranging from 0.9 to 1.12.The peak value occurs at a shear angleβof 60°,substantially exceeding that of the smooth surface.A method for calculating the relative roughness R_(N) is employed to evaluate the interface roughness of the bio-inspired surface,taking into account scale dimension and particle diameter distribution effects.展开更多
Introduction: Bracket debonding is a frequent issue that clinicians encounter, leading to increased chair time, lost revenue, and material usage. In addition to patient compliance with their diet recommendations, the ...Introduction: Bracket debonding is a frequent issue that clinicians encounter, leading to increased chair time, lost revenue, and material usage. In addition to patient compliance with their diet recommendations, the preparation and conditioning of teeth for bonding significantly influence bond strength and consequently impact orthodontic treatment success and efficiency. Because of OBA-MCP’s (orthodontic bonding adhesive with modified calcium phosphate) decreased shear bond strength (SBS), the purpose of this study was to evaluate the effects of conditioning with 5.25% sodium hypochlorite (NaOCl) before etching in the bonding protocol. Materials and Methods: 90 extracted teeth were divided into 3 groups to be bonded with orthodontic brackets with different bonding protocols: 1) Transbond XT with regular bonding protocol (etch + prime + adhesive);2) OBA-MCP with regular bonding protocol;and 3) OBA-MCP with NaOCl prior to acid etching in the regular bonding protocol. SBS (in Newtons) were measured using an MTS universal testing machine with a custom jig to apply a vertical force onto the bracket and ARI (adhesive remnant index) scores were recorded for each sample after de-bond to rate the amount of adhesive remaining. Results: The addition of NaOCl to the bonding protocol statistically significantly increased the SBS of OBA-MCP to comparable levels to Transbond XT. The ARI scores showed that when NaOCl was added, more adhesive remained. Conclusion: The addition of NaOCl to the bonding protocol can increase the SBS of adhesives with historically weaker bond strengths. However, the increased amount of adhesive remaining and the increased time spent during bonding must be considered. Further testing can be done in vivo to demonstrate the practicality of this new procedure.展开更多
To reveal the effects of environmental and loading conditions, as well as asphalt properties on the nonlinear rheological behavior of asphalt, the large amplitude oscillation shear(LAOS) test was introduced, and the F...To reveal the effects of environmental and loading conditions, as well as asphalt properties on the nonlinear rheological behavior of asphalt, the large amplitude oscillation shear(LAOS) test was introduced, and the Fourier transform rheology, Lissajous curve method, and the LAOS fatigue test have been applied to investigate the nonlinear rheological behavior of asphalt binders. The research results indicate that a decrease in temperature, an increase in shear frequency and strain level, the introduction of polymer modifiers, and the aging effect of asphalt can significantly increase the nonlinearity of asphalt, manifested by the higher relative magnitude of the third harmonic and zero-strain nonlinear coefficient. For the two polymer modifiers selected in this study, the 4%polyurethane modifier exhibits a higher nonlinear lifting effect than the 4% styrene-butadiene-styrene(SBS). The impact of long-term aging on nonlinear viscoelasticity is observably greater than that of short-term aging. The zero-strain nonlinear coefficient estimated based on the average value method can accurately characterize the nonlinear viscoelasticity of asphalt, which can serve as an effective supplement to the relative magnitude of the third harmonic. All asphalts exhibit shear thinning behavior under the test temperature of 24℃, and the decrease in test temperature, the increase in shear rate and strain level, the introduction of modifiers, and the aging effect of asphalt all exacerbate the shear thinning behavior of asphalt. In addition, the fatigue failure process of asphalt materials is accompanied by an increasing degree of nonlinearity.展开更多
Landslides frequently occurred in Jurassic red strata in the Three Gorges Reservoir(TGR)region in China.The Jurassic strata consist of low mechanical strength and poor permeability of weak silty mudstone layer,which m...Landslides frequently occurred in Jurassic red strata in the Three Gorges Reservoir(TGR)region in China.The Jurassic strata consist of low mechanical strength and poor permeability of weak silty mudstone layer,which may cause slope instability during rainfall.In order to understand the strength behavior of Jurassic silty mudstone shear zone,the so-called Shizibao landslide located in Guojiaba Town,Zigui County,Three Gorges Reservoir(TGR)in China is selected as a case study.The shear strength of the silty mudstone shear zone is strongly influenced by both the water content and the normal stress.Therefore,a series of drained ring shear tests were carried out by varying the water contents(7%,12%,17%,and 20%,respectively)and normal stresses(200,300,400,and 500 kPa,respectively).The result revealed that the residual friction coefficient and residual friction angle were power function relationships with water content and normal stress.The peak cohesion of the silty mudstone slip zone increased with water content to a certain limit,above which the cohesion decreased.In contrast,the residual cohesion showed the opposite trend,indicating the cohesion recovery above a certain limit of water content.However,both the peak and residual friction angle of the silty mudstone slip zone were observed to decrease steadily with increased water content.Furthermore,the macroscopic morphological features of the shear surface showed that the sliding failure was developed under high normal stress at low water content,while discontinuous sliding surface and soil extrusion were occurred when the water content increased to a saturated degree.The localized liquefaction developed by excess pore water pressure reduced the frictional force within the shear zone.Finally,the combined effects of the slope excavation and precipitation ultimately lead to the failure of the silty mudstone slope;however,continuous rainfall is the main factor triggering sliding.展开更多
文摘Evaluation of hydromechanical shear behavior of unsaturated soils is still a challenging issue. The time and cost needed for conducting precise experimental investigation on shear behavior of unsaturated soils have encouraged several investigators to develop analytical, empirical, or semi-empirical models for predicting the shear behavior of unsaturated soils. However, most of the previously proposed models are for specimens subjected to the isotropic state of stress, without considering the effect of initial shear stress. In this study, a hydromechanical constitutive model is proposed for unsaturated collapsible soils during shearing, with consideration of the effect of the initial shear stress. The model implements an effective stress-based disturbed state concept (DSC) to predict the stress-strain behavior of the soil. Accordingly, material/state variables were defined for both the start of the shearing stage and the critical state of the soil. A series of laboratory tests was performed using a fully automated unsaturated triaxial device to verify the proposed model. The experimental program included 23 suction-controlled unsaturated triaxial shear tests on reconstituted specimens of Gorgan clayey loess wetted to different levels of suctions under both isotropic and anisotropic stress states. The results show excellent agreement between the prediction by the proposed model and the experimental results.
基金supported by the Major Program of the National Natural Science Foundation of China (Grant No.42090055)the National Major Scientific Instruments and Equipment Development Projects of China (Grant No.41827808)the National Nature Science Foundation of China (Grant No.42207216).
文摘The strength of the sliding zone soil determines the stability of reservoir landslides.Fluctuations in water levels cause a change in the seepage field,which serves as both the external hydrogeological environment and the internal component of a landslide.Therefore,considering the strength changes of the sliding zone with seepage effects,they correspond with the actual hydrogeological circumstances.To investigate the shear behavior of sliding zone soil under various seepage pressures,24 samples were conducted by a self-developed apparatus to observe the shear strength and measure the permeability coefficients at different deformation stages.After seepage-shear tests,the composition of clay minerals and microscopic structure on the shear surface were analyzed through X-ray and scanning electron microscope(SEM)to understand the coupling effects of seepage on strength.The results revealed that the sliding zone soil exhibited strain-hardening without seepage pressure.However,the introduction of seepage caused a significant reduction in shear strength,resulting in strain-softening characterized by a three-stage process.Long-term seepage action softened clay particles and transported broken particles into effective seepage channels,causing continuous damage to the interior structure and reducing the permeability coefficient.Increased seepage pressure decreased the peak strength by disrupting occlusal and frictional forces between sliding zone soil particles,which carried away more clay particles,contributing to an overhead structure in the soil that raised the permeability coefficient and decreased residual strength.The internal friction angle was less sensitive to variations in seepage pressure than cohesion.
基金National Natural Science Foundation of China (No. U20A20275)Natural Science Foundation of Hunan Province,China (No. 2021JJ40096)。
文摘Based on the investigation of mechanical response and microstructure evolution of a commercial 7003 aluminum alloy under high-speed impact,a new simple and effective method was proposed to determine the critical strain required for the nucleation of adiabatic shear band(ASB).The deformation results of cylindrical and hat-shaped samples show that the critical strain required for ASB nucleation corresponds to the strain at the first local minimum after peak stress on the first derivative curve of true stress−true strain.The method of determining the critical strain for the nucleation of ASB through the first derivative of the flow stress curve is named the first derivative method.The proposed first derivative method is not only applicable to the 7003 aluminum alloy,but also to other metal materials,such as commercial purity titanium,WY-100 steel,and AM80 magnesium alloy.This proves that it has strong universality.
文摘Non-seismically designed(NSD)beam-column joints are susceptible to joint shear failure under seismic loads.Although significant research is available on the seismic behavior of such joints of planar frames,the information on the seismic behavior of joints of space frames(3D joints)is insufficient.The 3D joints are subjected to bi-directional excitation,which results in an interaction between the shear strength obtained for the joint in the two orthogonal directions separately.The bi-directional seismic behavior of corner reinforced concrete(RC)joints is the focus of this study.First,a detailed finite element(FE)model using the FE software Abaqus,is developed and validated using the test results from the literature.The validated modeling procedure is used to conduct a parametric study to investigate the influence of different parameters such as concrete strength,dimensions of main and transverse beams framing into the joint,presence or absence of a slab,axial load ratio and loading direction on the seismic behavior of joints.By subjecting the models to different combinations of loads on the beams along perpendicular directions,the interaction of the joint shear strength in two orthogonal directions is studied.The comparison of the interaction curves of the joints obtained from the numerical study with a quadratic(circular)interaction curve indicates that in a majority of cases,the quadratic interaction model can represent the strength interaction diagrams of RC beam to column connections with governing joint shear failure reasonably well.
基金financially supported by the National Natural Science Foundation of China(Grant No.42172292)Taishan Scholars Project Special Funding,and Shandong Energy Group(Grant No.SNKJ 2022A01-R26).
文摘A conceptual model of intermittent joints is introduced to the cyclic shear test in the laboratory to explore the effects of loading parameters on its shear behavior under cyclic shear loading.The results show that the loading parameters(initial normal stress,normal stiffness,and shear velocity)determine propagation paths of the wing and secondary cracks in rock bridges during the initial shear cycle,creating different morphologies of macroscopic step-path rupture surfaces and asperities on them.The differences in stress state and rupture surface induce different cyclic shear responses.It shows that high initial normal stress accelerates asperity degradation,raises shear resistance,and promotes compression of intermittent joints.In addition,high normal stiffness provides higher normal stress and shear resistance during the initial cycles and inhibits the dilation and compression of intermittent joints.High shear velocity results in a higher shear resistance,greater dilation,and greater compression.Finally,shear strength is most sensitive to initial normal stress,followed by shear velocity and normal stiffness.Moreover,average dilation angle is most sensitive to initial normal stress,followed by normal stiffness and shear velocity.During the shear cycles,frictional coefficient is affected by asperity degradation,backfilling of rock debris,and frictional area,exhibiting a non-monotonic behavior.
基金the University of Transport Technology under grant number DTTD2022-12.
文摘Determination of Shear Bond strength(SBS)at interlayer of double-layer asphalt concrete is crucial in flexible pavement structures.The study used three Machine Learning(ML)models,including K-Nearest Neighbors(KNN),Extra Trees(ET),and Light Gradient Boosting Machine(LGBM),to predict SBS based on easily determinable input parameters.Also,the Grid Search technique was employed for hyper-parameter tuning of the ML models,and cross-validation and learning curve analysis were used for training the models.The models were built on a database of 240 experimental results and three input variables:temperature,normal pressure,and tack coat rate.Model validation was performed using three statistical criteria:the coefficient of determination(R2),the Root Mean Square Error(RMSE),and the mean absolute error(MAE).Additionally,SHAP analysis was also used to validate the importance of the input variables in the prediction of the SBS.Results show that these models accurately predict SBS,with LGBM providing outstanding performance.SHAP(Shapley Additive explanation)analysis for LGBM indicates that temperature is the most influential factor on SBS.Consequently,the proposed ML models can quickly and accurately predict SBS between two layers of asphalt concrete,serving practical applications in flexible pavement structure design.
基金supported by the Qinghai Science and Technology Department Project(2025-QY-225)the National Natural Science Foundation of China(42267024)the Second Comprehensive Scientific Investigation and Research Project of the Qinghai-Xizang Plateau(2019QZKK0905).
文摘The Qinghai-Xizang Plateau of China faces challenges like thaw slumping,threatening slope stability and infrastructure.Understanding the mechanical properties of the roots of the dominant herbaceous plant species in the alpine meadow layer of the permafrost regions on the Qinghai-Xizang Plateau is essential for evaluating their role in enhancing soil shear strength and mitigating slope deformation in these fragile environments.In this study,the roots of four dominant herbaceous plant species—Kobresia pygmaea,Kobresia humilis,Carex moorcroftii,and Leontopodium pusillum—that are widely distributed in the permafrost regions of the Qinghai-Xizang Plateau were explored to determine their mechanical properties and effects in enhancing soil shear strength.Through indoor single root tensile and root group tensile tests,we determined the root diameter,tensile force,tensile strength,tensile ratio,and strength frequency distributions.We also evaluated their contributions to inhibiting slope deformation and failure during the formation and development of thermal thaw slumps in the alpine meadow.The results showed that the distribution of the root diameter of the dominant plant species is mostly normal,while the tensile strength tends to be logarithmically normally distributed.The relationship between the root diameter and root tensile strength conforms to a power function.The theoretical tensile strength of the root group was calculated using the Wu-Waldron Model(WWM)and the Fiber Bundle Model(FBM)under the assumption that the cumulative single tensile strength of the root bundle is identical to the tensile strength of the root group in the WWM.The FBM considers three fracture modes:FBM-D(the tensile force on each single root is proportional to its diameter relative to the total sum of all the root diameters),FBM-S(the cross-sectional stress in the root bundle is uniform),and FBM-N(each tensile strength test of individual roots experiences an equal load).It was found that the model-calculated tensile strength of the root group was 162.60%higher than the test value.The model-derived tensile force of the root group from the FBM-D,FBM-S,and FBM-N was 73.10%,28.91%,and 13.47%higher than the test values,respectively.The additional cohesion of the soil provided by the roots was calculated to be 25.90-45.06 kPa using the modified WWM,67.05-38.15 kPa using the FBM-S,and 57.24-32.74 kPa using the FBM-N.These results not only provide a theoretical basis for further quantitative evaluation of the mechanical effects of the root systems of herbaceous plant species in reinforcing the surface soil but also have practical significance for the effective prevention and control of thermal thaw slumping disasters in the permafrost regions containing native alpine meadows on the Qinghai-Xizang Plateau using flexible plant protection measures.
文摘Plant roots are widely known to provide mechanical reinforcement to soils against shearing and further increase slope stability.However,whether roots provide reinforcement to loess cyclic re-sistance and how various factors affect roots reinforcement during seismic loading have rarely been studied.The objective is to conduct a series of cyclic direct simple shear tests and DEM numerical simulation to investigate the cyclic behaviour of rooted loess.The effects of initial static shear stress and loading frequency on the cyclic resistance of root-soil composites were first investigated.After that,cyclic direct simple shear simulations at constant volume were carried out based on the discrete element method(PFC^(3D))to investigate the effects of root geome-try,mechanical traits and root-soil bond strength on the cyclic strength of rooted loess.It was discovered that the roots could effectively improve the cyclic resistance of loess.The cyclic resistance of the root-soil composite decreases with the increase of the initial shear stress,then increases,and improves with the increase of the frequency.The simulation result show that increases in root elastic modulus and root-soil interfacial bond strength can all enhance the cyclic resistance of root-soil composites,and the maximum cyclic resistance of the root-soil composite was obtained when the initial inclination angle of the root system was 90°.
基金support received from the National Natural Science Foundation of China(Nos.52274145,52469019,and 52109119)the Guangxi Natural Science Foundation(No.2025GXNSFAA069165)the Chinese Postdoctoral Science Fund Project(No.2022M723408).
文摘After the excavation of deep mining tunnels and underground caverns,the stability of surrounding rock controlled by structural planes is prone to structural damage and even engineering disasters due to three-dimensional stress redistribution and multi-directional dynamic construction interference.However,the shear mechanical behavior,fracture evolution mechanism and precursor characteristics of rockmass under true triaxial stress and multi-directional coupling disturbance are not unclear.Therefore,this study carried out true triaxial shear tests on limestone intermittent structural planes under uni-,bi-and tri-directional coupling disturbances to analyze its mechanical behavior,fracture evolution mechanism and precursor characteristics.The results show that as the disturbance direction increase,the shear strength of limestone generally decreases,while the roughness of structural planes and the degree of anisotropy generally exhibit an increasing trend.The proportion of shear cracks on the structural plane increases with the increase of shear stress.The disturbance strain rate before failure shows a U-shaped trend.Near to disturbance failure,there were more high-energy and high-amplitude acoustic emission events near the structural plane,and b-value drops rapidly below 1,while lgN/b ratio increased to above 3.These findings provide experimental recognition and theoretical support for assessing the stability of rockmass under blasting excavation.
基金partially funded by the National Natural Science Foundation of China(Grant Nos.52179098 and 41907251)the State Scholarship Fund of China(Grant No.202306650001).
文摘In geotechnical engineering,rock bolts are commonly used for reinforcement,while the surrounding rock mass bears varying degrees of shear loads.The shear rate affects the stability of bolted rock joints,especially in projects susceptible to dynamic shear loads.In laboratory experiments,fully-grouted bolts and energy-absorbing bolts were used as research objects,and artificial rock specimens with rough joints were fabricated to analyze the shear characteristics and damage mechanisms of bolted rock joints under cyclic shear conditions and different shear velocities.The results showed that as the shear rate increased,the shear strength of bolted rock joint specimens decreased.Degradation of asperities resulted in no obvious peak shear stress in the specimens.Energy-absorbing bolts exhibited greater deformation capacity,with significant necking phenomena and the ability to withstand larger shear displacements.In contrast,fully-grouted bolts,which have threaded surfaces that provide higher bonding performance,exhibited a reduced capacity for plastic deformation and were prone to breaking under smaller shear displacements.Although the shear stiffness of specimens reinforced by energy-absorbing bolts was slightly lower than that of fully-grouted bolt specimens,they demonstrated greater stability under various shear rates.The absorbed shear energy showed that energy-absorbing bolts had superior coordinated deformation capabilities,thus exhibiting greater absorbed shear energy than fully-grouted bolts.Overall,fully-grouted bolts are more suitable for projects requiring higher rock shear strength and overall stiffness.In contrast,energy-absorbing bolts are more suitable for coping with dynamic or fluctuating load conditions to maintain the relative stability of jointed rock masses.
基金supported by the China Scholarship Council Program(Grant No.202008320274)it is also supported by Technical University of Munich.
文摘Localized rock failures,like cracks or shear bands,demand specific attention in modeling for solids and structures.This is due to the uncertainty of conventional continuum-based mechanical models when localized inelastic deformation has emerged.In such scenarios,as macroscopic inelastic reactions are primarily influenced by deformation and microstructural alterations within the localized area,internal variables that signify these microstructural changes should be established within this zone.Thus,localized deformation characteristics of rocks are studied here by the preset angle shear experiment.A method based on shear displacement and shear stress differences is proposed to identify the compaction,yielding,and residual points for enhancing the model's effectiveness and minimizing subjective influences.Next,a mechanical model for the localized shear band is depicted as an elasto-plastic model outlining the stress-displacement relation across both sides of the shear band.Incorporating damage theory and an elasto-plastic model,a proposed damage model is introduced to replicate shear stressdisplacement responses and localized damage evolution in intact rocks experiencing shear failure.Subsequently,a novel nonlinear mathematical model based on modified logistic growth theory is proposed for depicting the shear band's damage evolution pattern.Thereafter,an innovative damage model is proposed to effectively encompass diverse rock material behaviors,including elasticity,plasticity,and softening behaviors.Ultimately,the effects of the preset angles,temperature,normal stresses and the residual shear strength are carefully discussed.This discovery enhances rock research in the proposed damage model,particularly regarding shear failure mode.
基金supports of the National Key Research and Development Program of China(Grant No.2023YFB3710900)the National Natural Science Foundation of China(Grant Nos.52071211 and 52071208)。
文摘Mg alloy often undergoes shear deformation during industrial processing.While its anisotropy and tension-compression asymmetry have been thoroughly studied under uniaxial loading,the understanding for shear loading is still lacking.This study employed a rolled AZ31B plate with typical basal texture to investigate the shear behaviors.Positive and negative simple shear experiments were performed at different angles in the transverse plane,whereby the visco-plastic self-consistent model was calibrated to reveal the deformation mechanisms and predict the mechanical responses at various orientations.Positive-negative shear asymmetry is present because extension twinning preferentially operates in one shear direction but is suppressed in the opposite direction.Simple shear induces multiple twin variants,thus impedes twin growth and slows the consumption of matrix,as compared to in-plane compression.For slip dominated simple shear,the interaction between loading-induced rigid body rotation and slip-induced crystal rotation produces distinct hardening behaviors,namely orthogonally asymmetric mechanical responses at complementary loading angles,which is largely absent in uniaxial loading.Finally,simulation results verify that positive-negative shear asymmetry appears only when the deviatoric normal stress on the sheet plane is non-zero.Positive-negative shear asymmetry persists except for the conditions of shear plane parallel to sheet plane,or shear direction parallel or perpendicular to rolling direction.
基金The financial support from the National Natural Science Foundation of China(Nos.52174092,42472338,and 51904290)the Natural Science Foundation of Jiangsu Province,China(No.BK20220157)+1 种基金the Fundamental Research Funds for the Central Universities,China(No.2022YCPY0202)the Open Fund of Key Laboratory of Safety and High-efficiency Coal Mining,Ministry of Education(Anhui University of Science and Technology)(No.JYBSYS202311)。
文摘This study investigated the mechanical responses and debonding mechanisms of a bolt-resin-rock composite anchoring sys-tem subjected to cyclic shear loading.A systematic analysis was conducted on the effects of the initial normal load(Fsd),cyclic shear dis-placement amplitude(ud),frequency(f),and rock type on the shear load,normal displacement,shear wear characteristics,and strain field evolution.The experimental results showed that as Fsd increased from 7.5 to 120 kN,both the peak and residual shear loads exhibited in-creasing trends,with increments ranging from 1.98%to 35.25%and from 32.09%to 86.74%,respectively.The maximum shear load of each cycle declined over the cyclic shear cycles,with the rate of decrease slowing and stabilizing,indicating that shear wear primarily oc-curred at the initial cyclic shear stage.During cyclic shearing,the normal displacement decreased spirally with the shear displacement,im-plying continuous shear contraction.The spiral curves display sparse upwards and dense downward trends,with later cycles dominated by dynamic sliding along the pre-existing shear rupture surface,which is particularly evident in coal.The bearing capacity of the anchoring system varies with the rock type and is governed by the coal strength in coal,resin-rock bonding in sandstone#1 and sandstone#2,com-bined resin strength and resin-rock bonding in sandstone#3(sandstone#1,sandstone#2 and sandstone#3,increasing strength order),and resin strength and bolt-resin bonding in limestone.Cyclic shear loading induces anisotropic interfacial degradation,characterized by es-calating strain concentrations and predominant resin-rock interface debonding,with the damage severity modulated by the rock type.
基金supported by the YEQISUN Joint Funds of the National Natural Science Foundation of China(Grant No.U2241234)the National Natural Science Foundation of China(Grant No.52301127).
文摘Premature adiabatic shear localization caused by strain softening is a roadblock for the application of body-centered cubic(BCC)structured high-entropy alloy(HEAs)in the impact field.A micron-scale orthorhombic-phase(O-phase)strengthened TiZrVNbAl alloy was developed to delay adiabatic shear failure and enhance dynamic ductility.The O-phase can not only reduce the slip length,but also promote the pinning and tangling of the dislocations near the phase boundaries.The introduction of the O-phase transformed the strain hardening rate from negative to positive,resulting in a significantly improved dynamic shear resistance.Meanwhile,slip transfer across the O-phase via dislocation cutting mechanisms and a reduction of slip band spacing guaranteed dynamic deformation uniformity.Benefiting from the introduction of the O-phase,the alloy exhibits an excellent stored energy density(∼446 J/cm^(3),surpass the reported BCC-HEAs and typical titanium alloys),a large dynamic fracture strain(∼42%)and a considerable dynamic specific yield strength(∼241 MPa cm^(3)g^(-1)).The present study presents an effective approach for developing BCC-HEAs with excellent dynamic shear resistance and plasticity.
基金the ORSP at Abu Dhabi University,UAE,for funding this project(Grant No.19300751).
文摘The growing demand for geothermal energy exploration and deep engineering projects necessitates a deeper understanding of rock behavior under extreme thermal conditions.This study investigates the effect of thermal treatment on the shear behavior of sedimentary sandstone and igneous granite,which are abundant in the Earth's crust.Direct shear tests were conducted on rock joints at room temperature(RT),250℃,and 500℃.The results show that the joints in sandstone and granite exhibit improved compressive and shear strength up to a temperature threshold of 200℃–350℃,followed by significant weakening beyond this range.This study investigated key parameters,including normal and shear stiffness,maximum joint closure,peak and residual shear strengths,internal friction angle,dilation angle,and cohesion.The compressive behavior of both rock types followed a modifiedBandis's equation.The peak shear strength followed Patton's bilinear and Jaeger's nonlinear failure criteria more accurately than the Mohr–Coulomb criterion.The results of this study provide valuable insights into the temperature-dependent behavior of sandstone and granite joints under compressive and shear loads,and their interoperation was strongly dependent on the mineralogical and structural components of the two rock types.These results have advanced our understanding of the temperature-dependent behavior of rock fractures,improving the safety of underground structures under thermal effects.
基金financially supported by the National Natural Science Foundation of China (No.42172292)Taishan Scholars Project Special Funding,and Shandong Energy Group (No.SNKJ2022A01-R26)funded by the China Scholarship Council (CSC No.202006220274)。
文摘Understanding the anchorage performance of en-echelon joints under cyclic shear loading is crucial for optimizing support strategies in jointed rock masses.This study examines the anchorage effects on enechelon joints with various orientations using laboratory cyclic shear tests.By comparing unbolted and bolted en-echelon joints,we analyze shear zone damage,shear properties,dilatancy,energy absorption,and acoustic emission characteristics to evaluate anchoring effects across shear cycles and joint orientations.Results reveal that bolted en-echelon joints experience more severe shear zone damage after cycles,with bolt deformation correlating to shear zone width.Bolted en-echelon joints exhibit faster shear strength deterioration and higher cumulative strength loss compared to unbolted ones,with losses ranging from 20.04%to 72.76%.The compressibility of en-echelon joints reduces the anchoring effect during shear cycles,leading to lower shear strength of bolted en-echelon joints in later stages of shear cycles compared to unbolted ones.Bolts reinforce en-echelon joints more effectively at non-positive angles,with the best performance observed at 0°and-60°.Anchorage accelerates the transition from rolling friction to sliding friction in the shear zone,enhancing energy absorption,which is crucial for rock projects under dynamic shear loading.Additionally,rock bolts expedite the transition of the cumulative AE hits and cumulative AE energy curves from rapid to steady growth,indicating that strong bolt-rock interactions accelerate crack initiation,propagation,and energy release.
基金supported by the National Natural Science Foundation of China(Grant Nos.52371301 and 52471289)。
文摘The scaled suction caisson repre sents an innovative design featuring a bio-inspired sidewall modeled after snake skin,commonly utilized in offshore mooring platforms.In comparison with traditional suction caissons,this bio-inspired design demonstrates reduced penetration resistance and enhanced pull-out capacity due to the anisotropic shear behaviors of its sidewall.To investigate the shear behavior of the bio-inspired sidewall under pull-out load,direct shear tests were conducted between the bio-inspired surface and sand.The research demonstrates that the interface shear strength of the bio-inspired surface significantly surpasses that of the smooth surface due to interlocking effects.Additionally,the interface shear strength correlates with the aspect ratio of the bio-inspired surface,shear angle,and particle diameter distribution,with values increasing as the uniformity coefficient Cudecreases,while initially increasing and subsequently decreasing with increases in both aspect ratio and shear angle.The ratio between the interface friction angleδand internal friction angle δ_(s) defines the interface effect factor k.For the bio-inspired surface,the interface effect factor k varies with shear angleβ,ranging from 0.9 to 1.12.The peak value occurs at a shear angleβof 60°,substantially exceeding that of the smooth surface.A method for calculating the relative roughness R_(N) is employed to evaluate the interface roughness of the bio-inspired surface,taking into account scale dimension and particle diameter distribution effects.
文摘Introduction: Bracket debonding is a frequent issue that clinicians encounter, leading to increased chair time, lost revenue, and material usage. In addition to patient compliance with their diet recommendations, the preparation and conditioning of teeth for bonding significantly influence bond strength and consequently impact orthodontic treatment success and efficiency. Because of OBA-MCP’s (orthodontic bonding adhesive with modified calcium phosphate) decreased shear bond strength (SBS), the purpose of this study was to evaluate the effects of conditioning with 5.25% sodium hypochlorite (NaOCl) before etching in the bonding protocol. Materials and Methods: 90 extracted teeth were divided into 3 groups to be bonded with orthodontic brackets with different bonding protocols: 1) Transbond XT with regular bonding protocol (etch + prime + adhesive);2) OBA-MCP with regular bonding protocol;and 3) OBA-MCP with NaOCl prior to acid etching in the regular bonding protocol. SBS (in Newtons) were measured using an MTS universal testing machine with a custom jig to apply a vertical force onto the bracket and ARI (adhesive remnant index) scores were recorded for each sample after de-bond to rate the amount of adhesive remaining. Results: The addition of NaOCl to the bonding protocol statistically significantly increased the SBS of OBA-MCP to comparable levels to Transbond XT. The ARI scores showed that when NaOCl was added, more adhesive remained. Conclusion: The addition of NaOCl to the bonding protocol can increase the SBS of adhesives with historically weaker bond strengths. However, the increased amount of adhesive remaining and the increased time spent during bonding must be considered. Further testing can be done in vivo to demonstrate the practicality of this new procedure.
基金supported by the National Key Research and Development Program of China(2023YFB2603500).
文摘To reveal the effects of environmental and loading conditions, as well as asphalt properties on the nonlinear rheological behavior of asphalt, the large amplitude oscillation shear(LAOS) test was introduced, and the Fourier transform rheology, Lissajous curve method, and the LAOS fatigue test have been applied to investigate the nonlinear rheological behavior of asphalt binders. The research results indicate that a decrease in temperature, an increase in shear frequency and strain level, the introduction of polymer modifiers, and the aging effect of asphalt can significantly increase the nonlinearity of asphalt, manifested by the higher relative magnitude of the third harmonic and zero-strain nonlinear coefficient. For the two polymer modifiers selected in this study, the 4%polyurethane modifier exhibits a higher nonlinear lifting effect than the 4% styrene-butadiene-styrene(SBS). The impact of long-term aging on nonlinear viscoelasticity is observably greater than that of short-term aging. The zero-strain nonlinear coefficient estimated based on the average value method can accurately characterize the nonlinear viscoelasticity of asphalt, which can serve as an effective supplement to the relative magnitude of the third harmonic. All asphalts exhibit shear thinning behavior under the test temperature of 24℃, and the decrease in test temperature, the increase in shear rate and strain level, the introduction of modifiers, and the aging effect of asphalt all exacerbate the shear thinning behavior of asphalt. In addition, the fatigue failure process of asphalt materials is accompanied by an increasing degree of nonlinearity.
基金funded by the National Science Foundation of China(CN)(Nos.42090054,41922055,41931295)the Key Research and Development Program of Hubei Province of China(No.2020BCB079)。
文摘Landslides frequently occurred in Jurassic red strata in the Three Gorges Reservoir(TGR)region in China.The Jurassic strata consist of low mechanical strength and poor permeability of weak silty mudstone layer,which may cause slope instability during rainfall.In order to understand the strength behavior of Jurassic silty mudstone shear zone,the so-called Shizibao landslide located in Guojiaba Town,Zigui County,Three Gorges Reservoir(TGR)in China is selected as a case study.The shear strength of the silty mudstone shear zone is strongly influenced by both the water content and the normal stress.Therefore,a series of drained ring shear tests were carried out by varying the water contents(7%,12%,17%,and 20%,respectively)and normal stresses(200,300,400,and 500 kPa,respectively).The result revealed that the residual friction coefficient and residual friction angle were power function relationships with water content and normal stress.The peak cohesion of the silty mudstone slip zone increased with water content to a certain limit,above which the cohesion decreased.In contrast,the residual cohesion showed the opposite trend,indicating the cohesion recovery above a certain limit of water content.However,both the peak and residual friction angle of the silty mudstone slip zone were observed to decrease steadily with increased water content.Furthermore,the macroscopic morphological features of the shear surface showed that the sliding failure was developed under high normal stress at low water content,while discontinuous sliding surface and soil extrusion were occurred when the water content increased to a saturated degree.The localized liquefaction developed by excess pore water pressure reduced the frictional force within the shear zone.Finally,the combined effects of the slope excavation and precipitation ultimately lead to the failure of the silty mudstone slope;however,continuous rainfall is the main factor triggering sliding.
