Gravity is the most important load source in mining and geotechnical engineering,which causes both the stress level and stress gradient inside geomaterials.Different from the stress level,the influence of gravity-indu...Gravity is the most important load source in mining and geotechnical engineering,which causes both the stress level and stress gradient inside geomaterials.Different from the stress level,the influence of gravity-induced stress gradient on the behaviour of the material is still unknown.An in-deep study on it will help to promote the understanding of material behaviour,especially for those cases related to unconventional gravity such as terrestrial ng physical modelling and extraterrestrial resource exploitation(g is the terrestrial gravitational acceleration).In this study,a high-order homogenization for granular materials is proposed at first,in which the stress gradient is drawn into the constitutive representation by adopting a representative volume element(RVE).The consolidation and shear strength behaviour of RVE are then investigated by performing numerical biaxial tests.The results show that all the compressibility,shear strength,shear stiffness,volumetric deformation,and critical state behaviour show a stress gradient dependence.A coupling between stress gradient,stress level,and material properties is also observed.These observations suggest that,besides the stress level,extra attention needs to be paid to material responses related to stress gradient during engineering practices.展开更多
In order to optimize the conditions for residual stress measurement using a two-dimensional X-ray diffraction (2D-XRD) in terms of both efficiency and accuracy. The measurements have been conducted on three stainless ...In order to optimize the conditions for residual stress measurement using a two-dimensional X-ray diffraction (2D-XRD) in terms of both efficiency and accuracy. The measurements have been conducted on three stainless steel specimens in this study. The three specimens were processed by annealing, a cavitating jet in air and a disc grinder, with each method introducing different residual stresses at the surface. The specimens were oscillated in the ω-direction, representing a right-hand rotation of the specimen about the incident X-ray beam. The range of the oscillation, Δω, was varied and optimum Δω was determined. Moreover, combinations of the tilt angle between the specimen surface normal and the diffraction vector, ψ, with the rotation angle about its surface normal, f, have been studied with a view to find the most optimum condition. The results show that the use of ω oscillations is an effective method for improving analysis accuracy, especially for large grain metals. The standard error rapidly decreased with increasing range of the ω oscillation, especially for the annealed specimen which generated strong diffraction spots due to its large grain size.展开更多
In practical engineering,the total vertical stress in the soil layer is not constant due to stress diffusion,and varies with time and depth.Therefore,the purpose of this paper is to investigate the effect of stress di...In practical engineering,the total vertical stress in the soil layer is not constant due to stress diffusion,and varies with time and depth.Therefore,the purpose of this paper is to investigate the effect of stress diffusion on the two-dimensional(2D)plane strain consolidation properties of unsaturated soils when the stress varies with time and depth.A series of semi-analytical solutions in terms of excess pore air and water pressures and settlement for 2D plane strain consolidation of unsaturated soils can be derived with the joint use of Laplace transform and Fourier sine series expansion.Then,the inverse Laplace transform of the semi-analytical solution is given in the time domain using a self-programmed code based on Crump’s method.The reliability of the obtained solutions is proved by the degeneration.Finally,the 2D plots of excess pore pressures and the curves of settlement varying with time,considering different physical parameters of unsaturated soil stratum and depth-dependent stress,are depicted and analyzed to study the 2D plane strain consolidation properties of unsaturated soils subjected to the depthdependent stress.展开更多
Two-dimensional stress wares in n general incompressible elastic solid are investigated. First, baxic equations for simple wares and shock waves are presented for a general strain energy junction. Then the characteris...Two-dimensional stress wares in n general incompressible elastic solid are investigated. First, baxic equations for simple wares and shock waves are presented for a general strain energy junction. Then the characteristic ware speeds and the associated characteristic vectors are deduced. It is shown that there usually exist two simple waves and two shock wares. Finally, two examples are given for the case of plane strain deformation and antiplane strain deformation, respectively. It is proved that, in the case of plane strain deformation, the oblique reflection problem of a plane shock is not solvable in general.展开更多
Gradient structures(GS)play a crucial role in achieving a balance between strength and plasticity in metals and alloys.However,there is still a lack of understanding of the mechanisms that maintain a plasticity gradie...Gradient structures(GS)play a crucial role in achieving a balance between strength and plasticity in metals and alloys.However,there is still a lack of understanding of the mechanisms that maintain a plasticity gradient to prevent the premature failure of fine grains in GS materials.In this work,by incorporating experimental data and the Hall-Petch relationship,we develop a size-dependent crystal plasticity model to investigate the deformation mechanisms for enhancing the strength and plasticity in polycrystalline high entropy alloys.The simulations of the GS model align well with the experimental results,exhibiting strong strain and stress gradients to improve the mechanical properties.Under the conditions of significant de-formation incompatibility,the strain gradient predominantly drives the enhancement of plasticity mechanisms.As the de-formation incompatibility decreases,the stress gradient begins to play a significant role in comparison with the strain gradient.This shift is attributed to the regular variations in dislocation density within different domains.As the grain size gradients and loads decrease,the dislocation density becomes more uniform across the domains,hindering the formation of strong domain boundaries.While this may impede the activation of strain gradients,it facilitates the activation of stress gradients as a supplementary measure.By designing multilayered GS structures to alter the distribution of dislocation density,we can control the activation levels of stress and strain gradients,thereby influencing the plasticity mechanisms and mechanical properties of the material.展开更多
Hydraulic fracture growth is significantly influenced by the minimum horizontal principal stress gradient and the fracturing fluid pressure gradient.However,these gradients are often neglected in scaled physical model...Hydraulic fracture growth is significantly influenced by the minimum horizontal principal stress gradient and the fracturing fluid pressure gradient.However,these gradients are often neglected in scaled physical modeling experiments due to difficulties in reproducing them.This study uses centrifugal hypergravity to simulate both gradients and investigate their effects on fracture propagation.Artificial mortar specimens(ϕ200 mm×400 mm)are fractured under 1g(normal gravity),50g,and 100g.Results show that compared to 1g,fractures under 50g and 100g exhibit increasingly uneven propagation,with higher g-values leading to greater asymmetry.To interpret this,a theoretical analysis based on fracture mechanics is conducted.When the fluid pressure gradient exceeds the stress gradient,a positive net gradient is generated,increasing net pressure at the lower fracture tip.This raises the stress intensity factor at the lower tip,promoting downward growth.As g increases,the disparity becomes more significant,resulting in greater fracture deviation.In conclusion,this study,for the first time,has verified and explained that the net gradient can change the propagation of hydraulic fractures,providing important guidance for wellbore placement under stress gradients.展开更多
Stress in plants refers to adverse changes in their functioning.The occurrence and intensity of a stress can be assessed by alterations in plant traits,termed stress indicators.The ultimate goal of this study was to t...Stress in plants refers to adverse changes in their functioning.The occurrence and intensity of a stress can be assessed by alterations in plant traits,termed stress indicators.The ultimate goal of this study was to test whether six morpho-physiological plant traits,frequently used as stress indicators,respond consistently across species to various environmental stressors,with the aim of detecting universal stress indicators in forest tree species.We examined changes in vertical increment,leaf/needle size,shoot length,needle longevity,photosynthetic efficiency and fluctuating asymmetry in three common European tree species,mountain birch(Betula pubescens var.pumila),Norway spruce(Picea abies)and Scots pine(Pinus sylvestris)along three environmental gradients(elevation,pollution and seashore)from forests to stressful open environments.Data were collected in 2003,2004 and 2005 from 297 trees growing naturally across 36 sites in north-western Russia.Fluctuating asymmetry was the only trait that did not vary among sites with differing levels of environmental stress.Leaf/needle size and shoot length occasionally changed along stress gradients,but the magnitude and direction of these changes differed by gradient type and species,resulting in no significant overall stress effect for either trait.In contrast,photosynthetic efficiency,vertical increment and needle longevity consistently decreased from low-stress to high-stress sites.The overall effect was significant for each of these three traits despite the magnitudes of these decreases differed depending on the gradient type and location,species,study year and individual tree.Replication at spatial,temporal and taxonomic levels ensured the robustness and reliability of our results that photosynthetic efficiency,vertical growth and needle longevity reliably captured a general stress syndrome and may serve as stress indicators in forest species.展开更多
The stress gradient of surrounding rock and reasonable prestress of support are the keys to ensuring the stability of roadways.The elastic-plastic analytical solution for surrounding rock was derived based on unified ...The stress gradient of surrounding rock and reasonable prestress of support are the keys to ensuring the stability of roadways.The elastic-plastic analytical solution for surrounding rock was derived based on unified strength theory.A model for solving the stress gradient of the surrounding rock with the intermediate principal stress parameter b was established.The correctness and applicability of the solution for the stress gradient in the roadway surrounding rock was verified via multiple methods.Furthermore,the laws of stress,displacement,and the plastic zone of the surrounding rock with different b values and prestresses were revealed.As b increases,the stress gradient in the plastic zone increases,and the displacement and plastic zone radius decrease.As the prestress increases,the peak stress shifts toward the sidewalls,and the stress and stress gradient increments decrease.In addition,the displacement increment and plastic zone increment were proposed to characterize the support effect.The balance point of the plastic zone area appears before that of the displacement zone.The relationship between the stress gradient compensation coefficient and the prestress is obtained.This study provides a research method and idea for determining the reasonable prestress of support in roadways.展开更多
Objective:To explore the feasibility of two-dimensional shear wave elastography in evaluating calf skeletal muscle stiffness in diabetic nephropathy patients with medial tibial stress syndrome.Methods:A total of 48 di...Objective:To explore the feasibility of two-dimensional shear wave elastography in evaluating calf skeletal muscle stiffness in diabetic nephropathy patients with medial tibial stress syndrome.Methods:A total of 48 diabetic nephropathy patients with medial tibial stress syndrome from January 2020 to December 2022 were included as the study group,and 48 patients with diabetic nephropathy during the same period were included as the control group.Both groups were detected by two-dimensional shear wave elastography with ultrasonic equipment,and Young‘s modulus of the tibialis anterior muscle,tibialis posterior muscle,and gastrocnemius muscle were observed and analyzed in the two groups.Results:The Young‘s modulus values of tibialis anterior muscle,tibialis posterior muscle,and gastrocnemius muscle in the study group were significantly lower than those in the control group(P<0.05).Conclusion:Two-dimensional shear wave elastography is feasible for the evaluation of calf skeletal muscle stiffness in diabetic nephropathy patients with medial tibial stress syndrome,and has high accuracy and repeatability.This technique can be used to diagnose,treat and monitor muscle lesions in patients with diabetic nephropathy,and can also be used to assess muscle fatigue and exercise capacity,which has broad application prospects.展开更多
As a new structure of solid matter quasicrystal brings profound new ideas to the traditional condensed matter physics, its elastic equations are more complicated than that of traditional crystal. A contact problem of ...As a new structure of solid matter quasicrystal brings profound new ideas to the traditional condensed matter physics, its elastic equations are more complicated than that of traditional crystal. A contact problem of decagonal two? dimensional quasicrystal material under the action of a rigid flat die is solved satisfactorily by introducing displacement function and using Fourier analysis and dual integral equations theory, and the analytical expressions of stress and displacement fields of the contact problem are achieved. The results show that if the contact displacement is a constant in the contact zone, the vertical contact stress has order -1/2 singularity on the edge of contact zone, which provides the important mechanics parameter for contact deformation of the quasicrystal.展开更多
Once an opening is created in deep underground,the stresses surrounding the opening will be redistributed,inducing a gradient stress field.To understand how the ground rock in such a gradient stress field responses to...Once an opening is created in deep underground,the stresses surrounding the opening will be redistributed,inducing a gradient stress field.To understand how the ground rock in such a gradient stress field responses to dynamic stress loading,the gradient stress distribution at a circular opening was first analyzed and the propagation of 1D stress wave in rock mass under gradient stress field was theoretically derived.By using an implicit to explicit solution method in LS-DYNA code,the dynamic mechanical behaviors of rock in gradient stress field were numerically investigated.The results indicate that the damage is mainly produced at or near the free face,partly due to the straight action of compressive stress wave and the tensile stress wave generated at the free face.The range of the induced damage zone is narrowed under the conditions of higher gradient stress rate and lower dynamic stress amplitude.However,under lower gradient stress field and higher dynamic stress,the damage becomes severer and wider with discontinuous failure regions.展开更多
Based on the stress distribution characteristics of rock burst multiple sites, the criterion of horizontal stress inducing layer dislocation rock burst was established. Accordingly, the influencing factors were analyz...Based on the stress distribution characteristics of rock burst multiple sites, the criterion of horizontal stress inducing layer dislocation rock burst was established. Accordingly, the influencing factors were analyzed. The analysis results indicate that the stress condition, edge of etastic zone depth, supporting strength, and the friction angle and cohesion among coal stratum, roof and floor are sensitive factors. By introducing double-couple model, the layer dislocation rock burst was explained and the energy radiation characteristics were analyzed. The SOS micro-seismic monitoring system was applied to observe the rock burst hazards about a mining face. The results show that P- and S-wave energy radiations produced by rock burst have directional characteristics. The energy radiation characteristics of the 22 rock bursts occurring on 79Z6 long-wall face are basically the same as theoretical results, that is, the ratio of S-wave energy of sensor 4 to 6 is about 1.5 and that of P-wave is smaller than 0.5. The consistency of the monitored characteristics of the energy radiation theoretically increases with the total energy increasing.展开更多
A3D finite element model(FEM)with realistic field measurements of temperature distributions is proposed to investigate the thermal stress variation in the steel–concrete composite bridge deck system.First,a brief lit...A3D finite element model(FEM)with realistic field measurements of temperature distributions is proposed to investigate the thermal stress variation in the steel–concrete composite bridge deck system.First,a brief literaturereview indicates that traditional thermal stress calculation in suspension bridges is based on the2D plane structure with simplified temperature profiles on bridges.Thus,a3D FEM is proposed for accurate stress analysis.The focus is on the incorporation of full field arbitrary temperature profile for the stress analysis.Following this,the effect of realistic temperature distribution on the structure is investigated in detail and an example using field measurements of Aizhai Bridge is integrated with the proposed3D FEM model.Parametric studies are used to illustrate the effect of different parameters on the thermal stress distribution in the bridge structure.Next,the discussion and comparison of the proposed methodology and simplified calculation method in the standard is given.The calculation difference and their potential impact on the structure are shown in detail.Finally,some conclusions and recommendations for future bridge analysis and design are given based on the proposed study.展开更多
A new oxidation kinetics model is established for high-temperature oxidation. We assume that the interface reaction is fast enough and the oxidation rate is controlled by diffusion process at high temperature. By intr...A new oxidation kinetics model is established for high-temperature oxidation. We assume that the interface reaction is fast enough and the oxidation rate is controlled by diffusion process at high temperature. By introducing the growth stress gradient we modify the classical oxidation parabolic law. The modified factor of the oxidation rate constant is a function of growth strain, environment oxygen concentration, and temperature. The modeling results show that the stress gradient effect on the oxidation rate cannot be ignored. Growth strain will dominate whether the stress gradient effect promotes or slows down the oxidation process. The stress gradient effect becomes weaker at higher temperature. This effect is amplified at higher concentrations of environmental oxygen. Applied mechanical loads do not affect the oxidation rate. This model is available for high temperature oxidation of metals and alloys.展开更多
This paper studied the thermal stresses of ceramicl metal gradient thermal barrier coating which combines the conceptions of ceramic thermal barrier coating （TBC） and functionally gradient material （FGM）. Thermal ...This paper studied the thermal stresses of ceramicl metal gradient thermal barrier coating which combines the conceptions of ceramic thermal barrier coating （TBC） and functionally gradient material （FGM）. Thermal stresses and residual thermal stresses were calculated by an ANSYS finite element analysis software. Negative thermal expansion coefficient method was proposed and element birth and death method was applied to analyze the residual thermal stresses which have non-uniform initial temperature field. The numerical results show a good agreement with the analytical results and the experimental results.展开更多
A simple and effective method for analyzing the stress distribution in a Functionally Gradient Material(FGM) layer on the su;face of a structural component is proposed in this paper. Generally, the FGM layer is very t...A simple and effective method for analyzing the stress distribution in a Functionally Gradient Material(FGM) layer on the su;face of a structural component is proposed in this paper. Generally, the FGM layer is very thin compared with the characteristic length of the structural component, and the nonhomogeneity exists only in the thin layer. Based on these features, by choosing a small parameter I which characterizes the stiffness of the layer relative to the component, and expanding the stresses and displacements on the two sides of the interface according to the parameter lambda, then asymptotically using the continuity conditions of the stresses and displacements on the interface, a decoupling computing process of the coupling control equations of the layer and the structural component is realized. Finally, two examples are given to illustrate the application of the method proposed.展开更多
Based on the thermal stress distribution for functionally gradient material (FGM) plates, a Genetic Algorithm (GA) method for the thermal stresses optimum design of FGM plate with computer technologies is given. The m...Based on the thermal stress distribution for functionally gradient material (FGM) plates, a Genetic Algorithm (GA) method for the thermal stresses optimum design of FGM plate with computer technologies is given. The minimum thermal stresses combination distribution for FGM is obtained.展开更多
In this contribution,the microscopic fracture mechanism and extension criterion for mixed type crack in ductile material under plane mixed mode loading are investigated in details.A universal extension criterion for t...In this contribution,the microscopic fracture mechanism and extension criterion for mixed type crack in ductile material under plane mixed mode loading are investigated in details.A universal extension criterion for the mixed type crack,i.e.the crack propagates along the direction of the maximum gradient of equivalent stress,is suggested.This new criterion is used to predict the propagation direction of mixed type crack,showing a good agreement with other theories for different types of mode mixity.Moreover,the numerical verification is also carried out for the case of an edge crack with different mixed mode loadings.Finally,a potential application to three-dimensional fracture in the ductile material induced by holes is also discussed.展开更多
The interface crack problems in the two-dimensional(2D)decagonal quasicrystal(QC)coating are theoretically and numerically investigated with a displacement discontinuity method.The 2D general solution is obtained base...The interface crack problems in the two-dimensional(2D)decagonal quasicrystal(QC)coating are theoretically and numerically investigated with a displacement discontinuity method.The 2D general solution is obtained based on the potential theory.An analogy method is proposed based on the relationship between the general solutions for 2D decagonal and one-dimensional(1D)hexagonal QCs.According to the analogy method,the fundamental solutions of concentrated point phonon displacement discontinuities are obtained on the interface.By using the superposition principle,the hypersingular boundary integral-differential equations in terms of displacement discontinuities are determined for a line interface crack.Further,Green’s functions are found for uniform displacement discontinuities on a line element.The oscillatory singularity near a crack tip is eliminated by adopting the Gaussian distribution to approximate the delta function.The stress intensity factors(SIFs)with ordinary singularity and the energy release rate(ERR)are derived.Finally,a boundary element method is put forward to investigate the effects of different factors on the fracture.展开更多
Concentration gradient and fluid shear stress(FSS)for cell microenvironment were investigated through microfluidic technology.The Darcy–Weisbach equation combined with computational fluid dynamics modeling was exploi...Concentration gradient and fluid shear stress(FSS)for cell microenvironment were investigated through microfluidic technology.The Darcy–Weisbach equation combined with computational fluid dynamics modeling was exploited to design the microfluidic chip,and the FSS distribution on the cell model with varying micro-channels(triangular,conical,and elliptical).The diffusion with the incompressible laminar flow model by solving the time-dependent diffusion–convection equation was applied to simulate the gradient profiles of concentration in the micro-channels.For the study of single cell in-depth,the FSS was investigated by the usage of polystyrene particles and the concentration diffusion distribution was studied by the usage of different colors of dyes.A successful agreement between model simulations and experimental data was obtained.Finally,based on the established method,the communication between individual cells was envisaged and modeled.The developed method provides valuable insights and allows to continuously improve the design of microfluidic devices for the study of single cell,the occurrence and development of tumors,and therapeutic applications.展开更多
基金supported by the National Natural Science Foundation of China(Nos.41902273,41772338)the China Postdoctoral Science Foundation(No.2019M661986)+2 种基金the Natural Science Foundation of Jiangsu Province(No.BK20190637)the Jiangsu Planned Projects for Postdoctoral Research Funds(No.2019K194)financial support by the State Key Laboratory for Geomechanics and Deep Underground Engineering,China University of Mining and Technology(Nos.Z19007,Z19009)。
文摘Gravity is the most important load source in mining and geotechnical engineering,which causes both the stress level and stress gradient inside geomaterials.Different from the stress level,the influence of gravity-induced stress gradient on the behaviour of the material is still unknown.An in-deep study on it will help to promote the understanding of material behaviour,especially for those cases related to unconventional gravity such as terrestrial ng physical modelling and extraterrestrial resource exploitation(g is the terrestrial gravitational acceleration).In this study,a high-order homogenization for granular materials is proposed at first,in which the stress gradient is drawn into the constitutive representation by adopting a representative volume element(RVE).The consolidation and shear strength behaviour of RVE are then investigated by performing numerical biaxial tests.The results show that all the compressibility,shear strength,shear stiffness,volumetric deformation,and critical state behaviour show a stress gradient dependence.A coupling between stress gradient,stress level,and material properties is also observed.These observations suggest that,besides the stress level,extra attention needs to be paid to material responses related to stress gradient during engineering practices.
文摘In order to optimize the conditions for residual stress measurement using a two-dimensional X-ray diffraction (2D-XRD) in terms of both efficiency and accuracy. The measurements have been conducted on three stainless steel specimens in this study. The three specimens were processed by annealing, a cavitating jet in air and a disc grinder, with each method introducing different residual stresses at the surface. The specimens were oscillated in the ω-direction, representing a right-hand rotation of the specimen about the incident X-ray beam. The range of the oscillation, Δω, was varied and optimum Δω was determined. Moreover, combinations of the tilt angle between the specimen surface normal and the diffraction vector, ψ, with the rotation angle about its surface normal, f, have been studied with a view to find the most optimum condition. The results show that the use of ω oscillations is an effective method for improving analysis accuracy, especially for large grain metals. The standard error rapidly decreased with increasing range of the ω oscillation, especially for the annealed specimen which generated strong diffraction spots due to its large grain size.
基金supported by the National Natural Science Foundation of China(Grant Nos.12172211 and 41630633)the National Key Research and Development Project of China(Grant No.2019YFC1509800).
文摘In practical engineering,the total vertical stress in the soil layer is not constant due to stress diffusion,and varies with time and depth.Therefore,the purpose of this paper is to investigate the effect of stress diffusion on the two-dimensional(2D)plane strain consolidation properties of unsaturated soils when the stress varies with time and depth.A series of semi-analytical solutions in terms of excess pore air and water pressures and settlement for 2D plane strain consolidation of unsaturated soils can be derived with the joint use of Laplace transform and Fourier sine series expansion.Then,the inverse Laplace transform of the semi-analytical solution is given in the time domain using a self-programmed code based on Crump’s method.The reliability of the obtained solutions is proved by the degeneration.Finally,the 2D plots of excess pore pressures and the curves of settlement varying with time,considering different physical parameters of unsaturated soil stratum and depth-dependent stress,are depicted and analyzed to study the 2D plane strain consolidation properties of unsaturated soils subjected to the depthdependent stress.
文摘Two-dimensional stress wares in n general incompressible elastic solid are investigated. First, baxic equations for simple wares and shock waves are presented for a general strain energy junction. Then the characteristic ware speeds and the associated characteristic vectors are deduced. It is shown that there usually exist two simple waves and two shock wares. Finally, two examples are given for the case of plane strain deformation and antiplane strain deformation, respectively. It is proved that, in the case of plane strain deformation, the oblique reflection problem of a plane shock is not solvable in general.
基金supported by the National Natural Science Foundation of China(Grant Nos.12372069,12172123,and 12072109)the Natural Science Foundation of Hunan Province(Grant No.2022JJ20001)the Hunan Provincial Innovation Foundation for Postgraduate(Grant No.CX20220378).
文摘Gradient structures(GS)play a crucial role in achieving a balance between strength and plasticity in metals and alloys.However,there is still a lack of understanding of the mechanisms that maintain a plasticity gradient to prevent the premature failure of fine grains in GS materials.In this work,by incorporating experimental data and the Hall-Petch relationship,we develop a size-dependent crystal plasticity model to investigate the deformation mechanisms for enhancing the strength and plasticity in polycrystalline high entropy alloys.The simulations of the GS model align well with the experimental results,exhibiting strong strain and stress gradients to improve the mechanical properties.Under the conditions of significant de-formation incompatibility,the strain gradient predominantly drives the enhancement of plasticity mechanisms.As the de-formation incompatibility decreases,the stress gradient begins to play a significant role in comparison with the strain gradient.This shift is attributed to the regular variations in dislocation density within different domains.As the grain size gradients and loads decrease,the dislocation density becomes more uniform across the domains,hindering the formation of strong domain boundaries.While this may impede the activation of strain gradients,it facilitates the activation of stress gradients as a supplementary measure.By designing multilayered GS structures to alter the distribution of dislocation density,we can control the activation levels of stress and strain gradients,thereby influencing the plasticity mechanisms and mechanical properties of the material.
基金supports of Basic Science Center Program for Multiphase Evolution in Hyper-gravity of the National Natural Science Foundation of China(No.51988101)National Natural Science Foundation of China(Nos.52109138 and 52122403)Young Elite Scientists Sponsorship Program by CAST(No.2023QNRC001).
文摘Hydraulic fracture growth is significantly influenced by the minimum horizontal principal stress gradient and the fracturing fluid pressure gradient.However,these gradients are often neglected in scaled physical modeling experiments due to difficulties in reproducing them.This study uses centrifugal hypergravity to simulate both gradients and investigate their effects on fracture propagation.Artificial mortar specimens(ϕ200 mm×400 mm)are fractured under 1g(normal gravity),50g,and 100g.Results show that compared to 1g,fractures under 50g and 100g exhibit increasingly uneven propagation,with higher g-values leading to greater asymmetry.To interpret this,a theoretical analysis based on fracture mechanics is conducted.When the fluid pressure gradient exceeds the stress gradient,a positive net gradient is generated,increasing net pressure at the lower fracture tip.This raises the stress intensity factor at the lower tip,promoting downward growth.As g increases,the disparity becomes more significant,resulting in greater fracture deviation.In conclusion,this study,for the first time,has verified and explained that the net gradient can change the propagation of hydraulic fractures,providing important guidance for wellbore placement under stress gradients.
基金supported by the Research Council(formerly Academy)of Finland(projects 122133,214824,362731,and researcher posts of M.V.Kozlov)EC through the BALANCE project carried out under contract EVK2-2002-00169,and the University of Turku。
文摘Stress in plants refers to adverse changes in their functioning.The occurrence and intensity of a stress can be assessed by alterations in plant traits,termed stress indicators.The ultimate goal of this study was to test whether six morpho-physiological plant traits,frequently used as stress indicators,respond consistently across species to various environmental stressors,with the aim of detecting universal stress indicators in forest tree species.We examined changes in vertical increment,leaf/needle size,shoot length,needle longevity,photosynthetic efficiency and fluctuating asymmetry in three common European tree species,mountain birch(Betula pubescens var.pumila),Norway spruce(Picea abies)and Scots pine(Pinus sylvestris)along three environmental gradients(elevation,pollution and seashore)from forests to stressful open environments.Data were collected in 2003,2004 and 2005 from 297 trees growing naturally across 36 sites in north-western Russia.Fluctuating asymmetry was the only trait that did not vary among sites with differing levels of environmental stress.Leaf/needle size and shoot length occasionally changed along stress gradients,but the magnitude and direction of these changes differed by gradient type and species,resulting in no significant overall stress effect for either trait.In contrast,photosynthetic efficiency,vertical increment and needle longevity consistently decreased from low-stress to high-stress sites.The overall effect was significant for each of these three traits despite the magnitudes of these decreases differed depending on the gradient type and location,species,study year and individual tree.Replication at spatial,temporal and taxonomic levels ensured the robustness and reliability of our results that photosynthetic efficiency,vertical growth and needle longevity reliably captured a general stress syndrome and may serve as stress indicators in forest species.
基金Project(52274130)supported by the National Natural Science Foundation of ChinaProject(ZR2024ZD22)supported by the Major Basic Research Project of the Shandong Provincial Natural Science Foundation,China+2 种基金Project(2023375)supported by the Guizhou University Research and Innovation Team,ChinaProject(Leading Fund(2023)09)supported by the Natural Science Research Fund of Guizhou University,ChinaProject(JYBSYS2021101)supported by the Open Fund of Key Laboratory of Safe and Effective Coal Mining,Ministry of Education,China。
文摘The stress gradient of surrounding rock and reasonable prestress of support are the keys to ensuring the stability of roadways.The elastic-plastic analytical solution for surrounding rock was derived based on unified strength theory.A model for solving the stress gradient of the surrounding rock with the intermediate principal stress parameter b was established.The correctness and applicability of the solution for the stress gradient in the roadway surrounding rock was verified via multiple methods.Furthermore,the laws of stress,displacement,and the plastic zone of the surrounding rock with different b values and prestresses were revealed.As b increases,the stress gradient in the plastic zone increases,and the displacement and plastic zone radius decrease.As the prestress increases,the peak stress shifts toward the sidewalls,and the stress and stress gradient increments decrease.In addition,the displacement increment and plastic zone increment were proposed to characterize the support effect.The balance point of the plastic zone area appears before that of the displacement zone.The relationship between the stress gradient compensation coefficient and the prestress is obtained.This study provides a research method and idea for determining the reasonable prestress of support in roadways.
文摘Objective:To explore the feasibility of two-dimensional shear wave elastography in evaluating calf skeletal muscle stiffness in diabetic nephropathy patients with medial tibial stress syndrome.Methods:A total of 48 diabetic nephropathy patients with medial tibial stress syndrome from January 2020 to December 2022 were included as the study group,and 48 patients with diabetic nephropathy during the same period were included as the control group.Both groups were detected by two-dimensional shear wave elastography with ultrasonic equipment,and Young‘s modulus of the tibialis anterior muscle,tibialis posterior muscle,and gastrocnemius muscle were observed and analyzed in the two groups.Results:The Young‘s modulus values of tibialis anterior muscle,tibialis posterior muscle,and gastrocnemius muscle in the study group were significantly lower than those in the control group(P<0.05).Conclusion:Two-dimensional shear wave elastography is feasible for the evaluation of calf skeletal muscle stiffness in diabetic nephropathy patients with medial tibial stress syndrome,and has high accuracy and repeatability.This technique can be used to diagnose,treat and monitor muscle lesions in patients with diabetic nephropathy,and can also be used to assess muscle fatigue and exercise capacity,which has broad application prospects.
文摘As a new structure of solid matter quasicrystal brings profound new ideas to the traditional condensed matter physics, its elastic equations are more complicated than that of traditional crystal. A contact problem of decagonal two? dimensional quasicrystal material under the action of a rigid flat die is solved satisfactorily by introducing displacement function and using Fourier analysis and dual integral equations theory, and the analytical expressions of stress and displacement fields of the contact problem are achieved. The results show that if the contact displacement is a constant in the contact zone, the vertical contact stress has order -1/2 singularity on the edge of contact zone, which provides the important mechanics parameter for contact deformation of the quasicrystal.
基金Projects(51904101,51774131,51604109)supported by the National Natural Science Foundation of ChinaProject(2017M622524)supported by the Postdoctoral Science Foundation of China。
文摘Once an opening is created in deep underground,the stresses surrounding the opening will be redistributed,inducing a gradient stress field.To understand how the ground rock in such a gradient stress field responses to dynamic stress loading,the gradient stress distribution at a circular opening was first analyzed and the propagation of 1D stress wave in rock mass under gradient stress field was theoretically derived.By using an implicit to explicit solution method in LS-DYNA code,the dynamic mechanical behaviors of rock in gradient stress field were numerically investigated.The results indicate that the damage is mainly produced at or near the free face,partly due to the straight action of compressive stress wave and the tensile stress wave generated at the free face.The range of the induced damage zone is narrowed under the conditions of higher gradient stress rate and lower dynamic stress amplitude.However,under lower gradient stress field and higher dynamic stress,the damage becomes severer and wider with discontinuous failure regions.
基金Project(2012LWB63) supported by the Fundamental Research Funds for the Central Universities, ChinaProject(SZBF2011-6-B35) supported by the Priority Acadamic Program Development of Jiangsu Higher Education Institutions (PAPD),China
文摘Based on the stress distribution characteristics of rock burst multiple sites, the criterion of horizontal stress inducing layer dislocation rock burst was established. Accordingly, the influencing factors were analyzed. The analysis results indicate that the stress condition, edge of etastic zone depth, supporting strength, and the friction angle and cohesion among coal stratum, roof and floor are sensitive factors. By introducing double-couple model, the layer dislocation rock burst was explained and the energy radiation characteristics were analyzed. The SOS micro-seismic monitoring system was applied to observe the rock burst hazards about a mining face. The results show that P- and S-wave energy radiations produced by rock burst have directional characteristics. The energy radiation characteristics of the 22 rock bursts occurring on 79Z6 long-wall face are basically the same as theoretical results, that is, the ratio of S-wave energy of sensor 4 to 6 is about 1.5 and that of P-wave is smaller than 0.5. The consistency of the monitored characteristics of the energy radiation theoretically increases with the total energy increasing.
基金Project(2015CB057701)supported by the National Basic Research Program of ChinaProject(51308071)supported by the National Natural Science Foundation of China+3 种基金Project(13JJ4057)supported by Natural Science Foundation of Hunan Province,ChinaProject(201408430155)supported by the Foundation of China Scholarship CouncilProject(2015319825120)supported by the Traffic Department of Applied Basic Research,ChinaProject(12K076)supported by the Open Foundation of Innovation Platform in Hunan Provincial Universities,China
文摘A3D finite element model(FEM)with realistic field measurements of temperature distributions is proposed to investigate the thermal stress variation in the steel–concrete composite bridge deck system.First,a brief literaturereview indicates that traditional thermal stress calculation in suspension bridges is based on the2D plane structure with simplified temperature profiles on bridges.Thus,a3D FEM is proposed for accurate stress analysis.The focus is on the incorporation of full field arbitrary temperature profile for the stress analysis.Following this,the effect of realistic temperature distribution on the structure is investigated in detail and an example using field measurements of Aizhai Bridge is integrated with the proposed3D FEM model.Parametric studies are used to illustrate the effect of different parameters on the thermal stress distribution in the bridge structure.Next,the discussion and comparison of the proposed methodology and simplified calculation method in the standard is given.The calculation difference and their potential impact on the structure are shown in detail.Finally,some conclusions and recommendations for future bridge analysis and design are given based on the proposed study.
基金Project supported by the National Basic Research Program (973) of China (No 90505015)the National Natural Science Foundation of China (Nos 90816006 and 10732050)
文摘A new oxidation kinetics model is established for high-temperature oxidation. We assume that the interface reaction is fast enough and the oxidation rate is controlled by diffusion process at high temperature. By introducing the growth stress gradient we modify the classical oxidation parabolic law. The modified factor of the oxidation rate constant is a function of growth strain, environment oxygen concentration, and temperature. The modeling results show that the stress gradient effect on the oxidation rate cannot be ignored. Growth strain will dominate whether the stress gradient effect promotes or slows down the oxidation process. The stress gradient effect becomes weaker at higher temperature. This effect is amplified at higher concentrations of environmental oxygen. Applied mechanical loads do not affect the oxidation rate. This model is available for high temperature oxidation of metals and alloys.
文摘This paper studied the thermal stresses of ceramicl metal gradient thermal barrier coating which combines the conceptions of ceramic thermal barrier coating （TBC） and functionally gradient material （FGM）. Thermal stresses and residual thermal stresses were calculated by an ANSYS finite element analysis software. Negative thermal expansion coefficient method was proposed and element birth and death method was applied to analyze the residual thermal stresses which have non-uniform initial temperature field. The numerical results show a good agreement with the analytical results and the experimental results.
文摘A simple and effective method for analyzing the stress distribution in a Functionally Gradient Material(FGM) layer on the su;face of a structural component is proposed in this paper. Generally, the FGM layer is very thin compared with the characteristic length of the structural component, and the nonhomogeneity exists only in the thin layer. Based on these features, by choosing a small parameter I which characterizes the stiffness of the layer relative to the component, and expanding the stresses and displacements on the two sides of the interface according to the parameter lambda, then asymptotically using the continuity conditions of the stresses and displacements on the interface, a decoupling computing process of the coupling control equations of the layer and the structural component is realized. Finally, two examples are given to illustrate the application of the method proposed.
文摘Based on the thermal stress distribution for functionally gradient material (FGM) plates, a Genetic Algorithm (GA) method for the thermal stresses optimum design of FGM plate with computer technologies is given. The minimum thermal stresses combination distribution for FGM is obtained.
基金supported by the Natural Science Foundation of Shannxi (No. 2005A19)the Open Foundation of Engineering Key Laboratory of Disaster Prevention and Structural Safety,Guangxi Univ.(No. 2008TMKF004)the National Natural Science Foundation (Nos. 10932007 and 11172228)
文摘In this contribution,the microscopic fracture mechanism and extension criterion for mixed type crack in ductile material under plane mixed mode loading are investigated in details.A universal extension criterion for the mixed type crack,i.e.the crack propagates along the direction of the maximum gradient of equivalent stress,is suggested.This new criterion is used to predict the propagation direction of mixed type crack,showing a good agreement with other theories for different types of mode mixity.Moreover,the numerical verification is also carried out for the case of an edge crack with different mixed mode loadings.Finally,a potential application to three-dimensional fracture in the ductile material induced by holes is also discussed.
基金the National Natural Science Foundation of China (Nos. 11572289,1171407,11702252,and 11902293)the China Postdoctoral Science Foundation (No. 2019M652563)。
文摘The interface crack problems in the two-dimensional(2D)decagonal quasicrystal(QC)coating are theoretically and numerically investigated with a displacement discontinuity method.The 2D general solution is obtained based on the potential theory.An analogy method is proposed based on the relationship between the general solutions for 2D decagonal and one-dimensional(1D)hexagonal QCs.According to the analogy method,the fundamental solutions of concentrated point phonon displacement discontinuities are obtained on the interface.By using the superposition principle,the hypersingular boundary integral-differential equations in terms of displacement discontinuities are determined for a line interface crack.Further,Green’s functions are found for uniform displacement discontinuities on a line element.The oscillatory singularity near a crack tip is eliminated by adopting the Gaussian distribution to approximate the delta function.The stress intensity factors(SIFs)with ordinary singularity and the energy release rate(ERR)are derived.Finally,a boundary element method is put forward to investigate the effects of different factors on the fracture.
基金National Natural Science Foundation of China(No.21804045)Fujian Provincial Department of Science and Technology(No.2019I0014)Promotion Program for Young and Middle-aged Teachers in Science and Technology Research of Huaqiao University(No.ZQN-PY612)。
文摘Concentration gradient and fluid shear stress(FSS)for cell microenvironment were investigated through microfluidic technology.The Darcy–Weisbach equation combined with computational fluid dynamics modeling was exploited to design the microfluidic chip,and the FSS distribution on the cell model with varying micro-channels(triangular,conical,and elliptical).The diffusion with the incompressible laminar flow model by solving the time-dependent diffusion–convection equation was applied to simulate the gradient profiles of concentration in the micro-channels.For the study of single cell in-depth,the FSS was investigated by the usage of polystyrene particles and the concentration diffusion distribution was studied by the usage of different colors of dyes.A successful agreement between model simulations and experimental data was obtained.Finally,based on the established method,the communication between individual cells was envisaged and modeled.The developed method provides valuable insights and allows to continuously improve the design of microfluidic devices for the study of single cell,the occurrence and development of tumors,and therapeutic applications.
