Borehole pressure relief helps prevent rock bursts.However,this may change the physical and mechan-ical properties of the surrounding rock,affect the variation of the plastic zone of the roadway,and lead to the failur...Borehole pressure relief helps prevent rock bursts.However,this may change the physical and mechan-ical properties of the surrounding rock,affect the variation of the plastic zone of the roadway,and lead to the failure of roadway support,thus threatening the safety of the roadway.In this paper,the variable angle shear test of drilled specimens under the action of static and dynamic loads is used to study the evolution of mechanical parameters of the specimens and their influence on the plastic zone of the sur-rounding rock.The shear strength decreases linearly with the increase of drilling diameter.With the increase of pre-static load level and dynamic load amplitude,the cohesion first increases and then decreases,and the internal friction angle decreases.Moreover,the shear failure surface changes from rough to smooth.The reasons include that the static load enhances the tooth cutting effect and the repeated friction of cracks caused by the dynamic load.Borehole pressure relief leads to an increase in the radius of the plastic zone of the surrounding rock following a quadratic function.The research results of this paper provide a theoretical basis for designing drilling unloading parameters and supporting parameters for rock burst roadways.展开更多
In order to study the distribution laws and types of plastic zone of surrounding rock in large-span roadway, we analyzed the distribution laws with different spans and lateral pressures using FLAC3D numerical calcu- l...In order to study the distribution laws and types of plastic zone of surrounding rock in large-span roadway, we analyzed the distribution laws with different spans and lateral pressures using FLAC3D numerical calcu- lation software. Based on the roadway support difficulty and distribution laws of the plastic zone of sur- rounding rock, we defined the large-span roadway and classified the types of large-span rectangular roadways. As a result, the distribution laws of the plastic zone on surrounding rock in a rectangular roadway with different spans and lateral pressures were obtained. The results show that the area of the plastic zone on surrounding rock increased with the increase of the spans and lateral pressures, and the plastic zone was symmetrical to the center line of roadway. At λ=0.5, 1.0, 1.5, and 2.0, the plastic zone presented ＂addle- shape＂ distribution, ＂ellipse＂ distribution, ＂thin and high＂ distribution and ＂inverse trapezium＂ distribu- tion, respectively. In addition, we classified the roadways into four types according to the different lateral pressures and spans, including small-span, moderate-span, large-span and extreme-large-span roadways.展开更多
Dilation angle is a significant parameter needed for numerical simulation of tunnels.Even though dilation parameter is physically variable and dependent on confinement and experienced shear plastic strain based on the...Dilation angle is a significant parameter needed for numerical simulation of tunnels.Even though dilation parameter is physically variable and dependent on confinement and experienced shear plastic strain based on the existing dilation models,numerical simulations of tunnels and underground openings with constant dilation parameter usually lead to satisfactory results in practical use.This study aims to find out why constant dilation angle is enough under practical conditions to simulate numerically tunnels and underground excavations in spite of the fact that dilation angle is variable in laboratory and experimental scale.With this aim,this work studies how mobilized dilation angle varies in a plastic zone surrounding a tunnel.For the circular tunnel under uniform in situ stress field,the stepwise finite difference approximation analytical solution considering strain softening rock mass behavior with mobilized dilation angle was used to study how mobilized dilation angle varies in plastic zone around tunnel under very different conditions.In practical conditions determined in this study,dilative behavior of all over the plastic zone around the tunnel can be approximated to constant dilation angle in the middle region of the plastic zone.Moreover,the plastic zone displacements for mobilized and constant dilation angle models are compared with each other.Further investigation under more general non-uniform in situ stress conditions and non-circular tunnels is performed by using the commercial finite difference software to numerically simulate the Mine-by experimental tunnel of AECL(Atomic Energy of Canada Limited)and the arched tunnel.Although the Mine-by and arched tunnels were numerically simulated based on the mobilized dilation angle model,the variability associated with dilation angle around the simulated Mine-by and arched tunnels is insignificant,and dilation angle is approximately constant in the plastic zone.展开更多
In order to study the rules of distribution in a plastic zone of rocks, surrounding a roadway, affected by tectonic stress, we first analyzed the mechanics of a roadway affected by tectonic stress and derived a theore...In order to study the rules of distribution in a plastic zone of rocks, surrounding a roadway, affected by tectonic stress, we first analyzed the mechanics of a roadway affected by tectonic stress and derived a theoretical formula for the plastic zone of rocks surrounding a roadway. We also analyzed the distribution characteristics of the plastic zone under different levels of tectonic stress, vertical pressure, cohesion and friction angle of the surrounding rock. Secondly, we used numerical simulation to analyze the range and shape features of the plastic zone of rocks surrounding the roadway, given different tectonic stress levels. Finally we used a rock drilling detector to carry out field measurements on the broken state of rock surrounding the roadway at the –700 substation and channels in the Xinzhuang mine of the Shenhuo mining area. Given the measured ground stress, we analyzed the relationship between tectonic stress and the distribution of this plastic zone. Our results show that the range of the plastic zone at the top and bottom of the roadway increases with an increase in tectonic stress and this increase is especially obvious at the roadway corner.展开更多
This paper discusses the calculation of plastic zone properties around circular tunnels to rock-masses that satisfy the Hoek–Brown failure criterion in non-hydrostatic condition,and reviews the calculation of plastic...This paper discusses the calculation of plastic zone properties around circular tunnels to rock-masses that satisfy the Hoek–Brown failure criterion in non-hydrostatic condition,and reviews the calculation of plastic zone and displacement,and the basis of the convergence–confinement method in hydrostatic condition.A two-dimensional numerical simulation model was developed to gain understanding of the plastic zone shape.Plastic zone radius in any angles around the tunnel is analyzed and measured,using different values of overburden(four states)and stress ratio(nine states).Plastic zone radius equations were obtained from fitting curve to data which are dependent on the values of stress ratio,angle and plastic zone radius in hydrostatic condition.Finally validation of this equation indicate that results predict the real plastic zone radius appropriately.展开更多
The fracture investigations of the planar lattices made of ductile cell walls are currently limited to bending-dominated hexagonal honeycomb. In this paper, the plastic zones of stretching-dominated lattices, includin...The fracture investigations of the planar lattices made of ductile cell walls are currently limited to bending-dominated hexagonal honeycomb. In this paper, the plastic zones of stretching-dominated lattices, including Kagome and triangular lattices, are estimated by analyzing their effective yield loci. The normalized in-plane yield loci of these two lattices are almost identical convex curves enclosed by 4 straight lines, which is almost independent of the relative density but is highly sensitive to the principal stress directions. Therefore, the plastic zones around the crack tip of Kagome and triangular are estimated to be quite different to those of the continuum solid and also hexagonal lattice. The plastic zones predictions by convex yield surfaces of both lattices are validated by FE calculations, although the shear lag region caused by non-local bending effect in the Kagome lattice enlarges the plastic zone in cases of small ratio of rp/l.展开更多
Reproducing kernel particle Method （RKPM） is a meshless technology which has proven very useful for solving problems of elastic plastic fracture mechanics. The mode I plastic zone shape at the crack-tip in a work-ha...Reproducing kernel particle Method （RKPM） is a meshless technology which has proven very useful for solving problems of elastic plastic fracture mechanics. The mode I plastic zone shape at the crack-tip in a work-hard ening material is obtained using RKPM. Ramberg-Osgood stress-strain relation is assumed and the crack-tip stress intensity factor （SIF） before and after formation of the plastic zone are examined. To impose the essential boundary conditions, penalty method is used. To construct the shape functions in the vicinity of the crack and crack-tip, both the diffraction and visibility criteria are employed. A comparison between two conventional treatments, visibility and diffraction, to crack discontinuity is conducted. The effects of different dilation parameters on SIF under plane-stress and plane-strain conditions are ~tudied. Results including plastic zone shape are compared with finite element method （FEM） to show the accuracy of RKPM. The main objective is to study the effects of different dilation parameters on SIF under plane stress and plane strain conditions and to obtain the mode I plastic zone shape at the crack-tip in a work hardening material using RKPM.展开更多
A plastic deformation zone near a screw dislocation is treated as an equivalent transformation inclusion by means of the Eshelby inclusion theory. A closed form solution for determining the interaction between a screw...A plastic deformation zone near a screw dislocation is treated as an equivalent transformation inclusion by means of the Eshelby inclusion theory. A closed form solution for determining the interaction between a screw dislocation and a plastically deformed zone of an arbitrary shape is obtained by using the solution between a dislocation and an equivalent transformation inclusion.展开更多
Sand production is often characterized as a two-stage process,in which material failure occurs near the cavity,leading to the formation of a plastic zone,from which particles are detached and transported out because o...Sand production is often characterized as a two-stage process,in which material failure occurs near the cavity,leading to the formation of a plastic zone,from which particles are detached and transported out because of continuous hydrodynamic erosion under the effects of the produced fluid flow.The plastic zone porosity is affected by coupled processes,while the plastic zone permeability has a significant impact on the performance of sand production prediction,especially in weak sandstone reservoirs.Large-scale sand production experiments were conducted using a customized high-pressure consolidation apparatus.The results show that specific stress-fluid pressure conditions may create a plastic zone around a hole,which has lower permeability than the intact zone.The plastic zone comprises two subzones:a high-permeability shear band zone and a low-permeability compaction zone.During sand production,sand migrates from the compaction zone through the shear band zone to the perforation hole.Thus,sand production is associated with the increased permeability and porosity in the compaction zone.Existing sand prediction models were modified according to the new findings,resulting in a modified model with improved performance.The modified model was validated using the sanding data from a weak sandstone reservoir in Kazakhstan.展开更多
In view of fine cracks occurred on the surface of BNbRE continuous casting slabs for heavy rail in the practical production, the effect of two factors, i.e. deformation temperature, deformation velocity, on thermo pla...In view of fine cracks occurred on the surface of BNbRE continuous casting slabs for heavy rail in the practical production, the effect of two factors, i.e. deformation temperature, deformation velocity, on thermo plasticity of BNbRE steel at the third brittle zone was quantitatively investigated on GLEEBLE-1500D thermal-mechanical simulator after measuring the RA-T curve of BNbRE steel. The results provide experimental data for optimizing the technology of continuous casting secondary cooling zone and avoiding the occurrence of fine surface cracks.展开更多
Recent observations by electron microscopy have shown that a dislocation-free zone (DFZ) exists between the crack tip and the pile-up of dislocations in the plastic zone. Shang, S. J., Ohr, S. M. and Majumdar, B. S., ...Recent observations by electron microscopy have shown that a dislocation-free zone (DFZ) exists between the crack tip and the pile-up of dislocations in the plastic zone. Shang, S. J., Ohr, S. M. and Majumdar, B. S., Burns, S. J. have discussed the problem of the plastic zone at a crack tip in isotropic elastic medium. We know that the hard second phase, which neither causes very large stress concentration nor leads to micrographic split, can improve the bearing capacity of the materials. Therefore, it is necessary to discuss the problem of the plastic zone at a crack tip while the hard second phase exists.展开更多
The analysis of plastic loosening zone of tunnels with cold condition,high in situ stress,and weak stratum is the key scientific problem of tunnel construction in cold areas.Based on the unified strength theory and co...The analysis of plastic loosening zone of tunnels with cold condition,high in situ stress,and weak stratum is the key scientific problem of tunnel construction in cold areas.Based on the unified strength theory and considering the coupling effect of high in situ stress and low-temperature field,the analytical model of the plastic loosening zone of tunnel surrounding rocks was proposed,and the influence laws of physical parameters(initial ground stress,freezing temperature,excavation radius,and intermediate principal stress)was explored.The results illustrate that:(1)with the coupling of low temperature and stress fields,the in-situ stress has a more significant effect on the radius of the plastic loosening zone of the tunnel surrounding rocks,showing a nonlinear correlation.When the in situ stress is small,the influence of the temperature field on the radius of the plastic loosening zone is more obvious.(2)The radius of the plastic loosening zone of the tunnel surrounding rocks increases synchronously with the excavation radius and gradually decreases with the increase of the intermediate principal stress.(3)The greater the temperature difference in the low-temperature field,the tunnel stability has a more significant response to the intermediate principal stress and is positively correlated with the coefficient of the intermediate principal stress.(4)In the actual project,the proposed model can well describe the mechanical behavior and deformation characteristics of tunnel surrounding rocks in low-temperature environment,showing applicability.The research results are expected to provide a theoretical basis for the study of tunnel stability in cold areas.展开更多
The triangular zone cracks in 2101 duplex stainless steel produced by the vertical continuous caster have troubled company A for a long time. To simulate the temperature and thermal stress distributions in the solidif...The triangular zone cracks in 2101 duplex stainless steel produced by the vertical continuous caster have troubled company A for a long time. To simulate the temperature and thermal stress distributions in the solidification process of 2101 duplex stainless steel produced by the vertical continuous caster, a two-dimensional viscoelastic-plastic thermomechanically coupled finite element model was established by the secondary development of the commercial nonlinear finite element analysis software MSC Marc. The results show that the thermal stress on the surface reaches a maximum at the exit of the mould, and the highest thermal stresses at the centre of the wide face and the narrow face are 75 and 115 MPa, respectively. Meanwhile, the internal temperature of slab is still higher than the solidus temperature, resulting in no thermal stress. The slab shows different high-temperature strengths and suffers from different stresses at different positions; thus, the risk of cracking also varies. At a location of 6-8 m from the meniscus, the temperature of the triangular zone is 1270-1360℃ and the corresponding permissible high-temperature strength is about 10-30 MPa, while the thermal stress at this time is 60 MPa, which is higher than the high-temperature strength. As a result, triangular zone cracks form easily.展开更多
The present work is concerned with a penny-shaped Dugdale crack embedded in an infinite space of one-dimensional （1D） hexagonal quasicrystals and subjected to two identical axisymmetric temperature loadings on the u...The present work is concerned with a penny-shaped Dugdale crack embedded in an infinite space of one-dimensional （1D） hexagonal quasicrystals and subjected to two identical axisymmetric temperature loadings on the upper and lower crack surfaces. Applying Dugdale hypothesis to thermo-elastic results, the extent of the plastic zone at the crack tip is determined. The normal stress outside the plastic zone and crack surface displacement are derived in terms of special functions. For a uniform loading case, the corresponding results are presented by simpli- fying the preceding results. Numerical calculations are carried out to show the influence of some parameters.展开更多
The elastic-plastic stress distribution and the elastic-plastic boundary con- figuration near a crack surface region are significant but hard to obtain by means of the conventional analysis. A crack line analysis meth...The elastic-plastic stress distribution and the elastic-plastic boundary con- figuration near a crack surface region are significant but hard to obtain by means of the conventional analysis. A crack line analysis method is developed in this paper by consid- ering the crack surface as an extension of the crack line. The stresses in the plastic zone, the length, and the unit normal vector of the elastic-plastic boundary near a crack surface region are obtained for an antiplane crack in an elastic-perfectly plastic solid. The usual small scale yielding assumptions are not needed in the analysis.展开更多
Crack line analysis is an effective way to solve elastic-plastic crack problems. Application of the method does not need the traditional small-scale yielding conditions and can obtain sufficiently accurate solutions n...Crack line analysis is an effective way to solve elastic-plastic crack problems. Application of the method does not need the traditional small-scale yielding conditions and can obtain sufficiently accurate solutions near the crack line. To address mode- Ⅲ crack problems under the perfect elastic-plastic condition, matching procedures of the crack line analysis method axe summarized and refined to give general forms and formulation steps of plastic field, elastic-plastic boundary, and elastic-plastic matching equations near the crack line. The research unifies mode-III crack problems under different conditions into a problem of determining four integral constants with four matching equations. An example is given to verify correctness, conciseness, and generality of the procedure.展开更多
The near crack line analysis method has been used in the present paper,The classical small scale yielding conditions have been completely abandoned in the analyses and one inappropriate matching condition used to be u...The near crack line analysis method has been used in the present paper,The classical small scale yielding conditions have been completely abandoned in the analyses and one inappropriate matching condition used to be used at the elasticplastic boundary has been corrected.The reasonable solution of the plastic stresses near the crack line region has been established.By matching the plastic stresses with the exact elastic stresses at the elastic-plastic boundary,the plastic stresses the length of the plastic zone and the unit normal vector of the elastic-plastic boundary near the crock line region have been obtained for a mode I crack under uniaxial tension,as well as a mode I crack under biaxial tension,which shows that for both conditions the plastic stress componentsσy, and σsy.he length of the plastic zone and the unit normal vector of the elastic-plastic boundary are quite the same while the plastic stress σs is different.展开更多
The results in Ref. [1] are not suitable for the cases of β≥2. For this reason, byusing the methods in Ref [1] and Ref [2], we derive the general expressions ofamsotropic plastic fields at a rapidly propagating plan...The results in Ref. [1] are not suitable for the cases of β≥2. For this reason, byusing the methods in Ref [1] and Ref [2], we derive the general expressions ofamsotropic plastic fields at a rapidly propagating plane-stress crack-tip for both thecases of β=2 and β>2 .展开更多
The constitutive equation was deduced. The results were obtained from theelastic and elastoplastical analysis of the cylinder sample applied with different ratios ofload on both the inner and outer sides and different...The constitutive equation was deduced. The results were obtained from theelastic and elastoplastical analysis of the cylinder sample applied with different ratios ofload on both the inner and outer sides and different moduli ratio. The factors affecting thedevelopment of the plastic field of the cylinder with finite radius were shown. The resultsshow that the different moduli ratio is the most important factor in the development of theplastic zone. The slight fluctuation of the ratio will bring multiplied increment of the displacement, which may result in the final destruction of the engineering material.展开更多
基金supported by the National Natural Science Foundation of China(Nos.52374100,52525401,and 52304150)Outstanding Young Talent Project of Shanxi Province(No.SJYC2024301)Research Project Supported by Shanxi Scholarship Council of China(No.2023-041).
文摘Borehole pressure relief helps prevent rock bursts.However,this may change the physical and mechan-ical properties of the surrounding rock,affect the variation of the plastic zone of the roadway,and lead to the failure of roadway support,thus threatening the safety of the roadway.In this paper,the variable angle shear test of drilled specimens under the action of static and dynamic loads is used to study the evolution of mechanical parameters of the specimens and their influence on the plastic zone of the sur-rounding rock.The shear strength decreases linearly with the increase of drilling diameter.With the increase of pre-static load level and dynamic load amplitude,the cohesion first increases and then decreases,and the internal friction angle decreases.Moreover,the shear failure surface changes from rough to smooth.The reasons include that the static load enhances the tooth cutting effect and the repeated friction of cracks caused by the dynamic load.Borehole pressure relief leads to an increase in the radius of the plastic zone of the surrounding rock following a quadratic function.The research results of this paper provide a theoretical basis for designing drilling unloading parameters and supporting parameters for rock burst roadways.
基金Financial supports are from the National Natural Science Foun-dation of China (No. 50874104)the Scientific Research Indus-trialization Project of Jiangsu Universities (No. JH07-023)
文摘In order to study the distribution laws and types of plastic zone of surrounding rock in large-span roadway, we analyzed the distribution laws with different spans and lateral pressures using FLAC3D numerical calcu- lation software. Based on the roadway support difficulty and distribution laws of the plastic zone of sur- rounding rock, we defined the large-span roadway and classified the types of large-span rectangular roadways. As a result, the distribution laws of the plastic zone on surrounding rock in a rectangular roadway with different spans and lateral pressures were obtained. The results show that the area of the plastic zone on surrounding rock increased with the increase of the spans and lateral pressures, and the plastic zone was symmetrical to the center line of roadway. At λ=0.5, 1.0, 1.5, and 2.0, the plastic zone presented ＂addle- shape＂ distribution, ＂ellipse＂ distribution, ＂thin and high＂ distribution and ＂inverse trapezium＂ distribu- tion, respectively. In addition, we classified the roadways into four types according to the different lateral pressures and spans, including small-span, moderate-span, large-span and extreme-large-span roadways.
文摘Dilation angle is a significant parameter needed for numerical simulation of tunnels.Even though dilation parameter is physically variable and dependent on confinement and experienced shear plastic strain based on the existing dilation models,numerical simulations of tunnels and underground openings with constant dilation parameter usually lead to satisfactory results in practical use.This study aims to find out why constant dilation angle is enough under practical conditions to simulate numerically tunnels and underground excavations in spite of the fact that dilation angle is variable in laboratory and experimental scale.With this aim,this work studies how mobilized dilation angle varies in a plastic zone surrounding a tunnel.For the circular tunnel under uniform in situ stress field,the stepwise finite difference approximation analytical solution considering strain softening rock mass behavior with mobilized dilation angle was used to study how mobilized dilation angle varies in plastic zone around tunnel under very different conditions.In practical conditions determined in this study,dilative behavior of all over the plastic zone around the tunnel can be approximated to constant dilation angle in the middle region of the plastic zone.Moreover,the plastic zone displacements for mobilized and constant dilation angle models are compared with each other.Further investigation under more general non-uniform in situ stress conditions and non-circular tunnels is performed by using the commercial finite difference software to numerically simulate the Mine-by experimental tunnel of AECL(Atomic Energy of Canada Limited)and the arched tunnel.Although the Mine-by and arched tunnels were numerically simulated based on the mobilized dilation angle model,the variability associated with dilation angle around the simulated Mine-by and arched tunnels is insignificant,and dilation angle is approximately constant in the plastic zone.
基金Financial support for this work, provided by the research fund of the State Key Laboratory of Coal Resources and Mine Safety of the China University of Mining & Technology (No.08kf11) is gratefully ac-knowledged
文摘In order to study the rules of distribution in a plastic zone of rocks, surrounding a roadway, affected by tectonic stress, we first analyzed the mechanics of a roadway affected by tectonic stress and derived a theoretical formula for the plastic zone of rocks surrounding a roadway. We also analyzed the distribution characteristics of the plastic zone under different levels of tectonic stress, vertical pressure, cohesion and friction angle of the surrounding rock. Secondly, we used numerical simulation to analyze the range and shape features of the plastic zone of rocks surrounding the roadway, given different tectonic stress levels. Finally we used a rock drilling detector to carry out field measurements on the broken state of rock surrounding the roadway at the –700 substation and channels in the Xinzhuang mine of the Shenhuo mining area. Given the measured ground stress, we analyzed the relationship between tectonic stress and the distribution of this plastic zone. Our results show that the range of the plastic zone at the top and bottom of the roadway increases with an increase in tectonic stress and this increase is especially obvious at the roadway corner.
文摘This paper discusses the calculation of plastic zone properties around circular tunnels to rock-masses that satisfy the Hoek–Brown failure criterion in non-hydrostatic condition,and reviews the calculation of plastic zone and displacement,and the basis of the convergence–confinement method in hydrostatic condition.A two-dimensional numerical simulation model was developed to gain understanding of the plastic zone shape.Plastic zone radius in any angles around the tunnel is analyzed and measured,using different values of overburden(four states)and stress ratio(nine states).Plastic zone radius equations were obtained from fitting curve to data which are dependent on the values of stress ratio,angle and plastic zone radius in hydrostatic condition.Finally validation of this equation indicate that results predict the real plastic zone radius appropriately.
基金supported by the National Natural Science Foundation of China (No.10502027)the National Fundamental Research Program of China (No.G2006CB601202)
文摘The fracture investigations of the planar lattices made of ductile cell walls are currently limited to bending-dominated hexagonal honeycomb. In this paper, the plastic zones of stretching-dominated lattices, including Kagome and triangular lattices, are estimated by analyzing their effective yield loci. The normalized in-plane yield loci of these two lattices are almost identical convex curves enclosed by 4 straight lines, which is almost independent of the relative density but is highly sensitive to the principal stress directions. Therefore, the plastic zones around the crack tip of Kagome and triangular are estimated to be quite different to those of the continuum solid and also hexagonal lattice. The plastic zones predictions by convex yield surfaces of both lattices are validated by FE calculations, although the shear lag region caused by non-local bending effect in the Kagome lattice enlarges the plastic zone in cases of small ratio of rp/l.
文摘Reproducing kernel particle Method （RKPM） is a meshless technology which has proven very useful for solving problems of elastic plastic fracture mechanics. The mode I plastic zone shape at the crack-tip in a work-hard ening material is obtained using RKPM. Ramberg-Osgood stress-strain relation is assumed and the crack-tip stress intensity factor （SIF） before and after formation of the plastic zone are examined. To impose the essential boundary conditions, penalty method is used. To construct the shape functions in the vicinity of the crack and crack-tip, both the diffraction and visibility criteria are employed. A comparison between two conventional treatments, visibility and diffraction, to crack discontinuity is conducted. The effects of different dilation parameters on SIF under plane-stress and plane-strain conditions are ~tudied. Results including plastic zone shape are compared with finite element method （FEM） to show the accuracy of RKPM. The main objective is to study the effects of different dilation parameters on SIF under plane stress and plane strain conditions and to obtain the mode I plastic zone shape at the crack-tip in a work hardening material using RKPM.
基金Project supported by the National Basic Research Program of China (No.2004CB619303)the National Science Foundation of China (No.10572088).
文摘A plastic deformation zone near a screw dislocation is treated as an equivalent transformation inclusion by means of the Eshelby inclusion theory. A closed form solution for determining the interaction between a screw dislocation and a plastically deformed zone of an arbitrary shape is obtained by using the solution between a dislocation and an equivalent transformation inclusion.
基金sponsored by the Nazarbayev University(Grant No.OPCRP2022006).
文摘Sand production is often characterized as a two-stage process,in which material failure occurs near the cavity,leading to the formation of a plastic zone,from which particles are detached and transported out because of continuous hydrodynamic erosion under the effects of the produced fluid flow.The plastic zone porosity is affected by coupled processes,while the plastic zone permeability has a significant impact on the performance of sand production prediction,especially in weak sandstone reservoirs.Large-scale sand production experiments were conducted using a customized high-pressure consolidation apparatus.The results show that specific stress-fluid pressure conditions may create a plastic zone around a hole,which has lower permeability than the intact zone.The plastic zone comprises two subzones:a high-permeability shear band zone and a low-permeability compaction zone.During sand production,sand migrates from the compaction zone through the shear band zone to the perforation hole.Thus,sand production is associated with the increased permeability and porosity in the compaction zone.Existing sand prediction models were modified according to the new findings,resulting in a modified model with improved performance.The modified model was validated using the sanding data from a weak sandstone reservoir in Kazakhstan.
基金Project supported bythe Inner Mongolian Autonomous Region Educational Department (NJ050667)
文摘In view of fine cracks occurred on the surface of BNbRE continuous casting slabs for heavy rail in the practical production, the effect of two factors, i.e. deformation temperature, deformation velocity, on thermo plasticity of BNbRE steel at the third brittle zone was quantitatively investigated on GLEEBLE-1500D thermal-mechanical simulator after measuring the RA-T curve of BNbRE steel. The results provide experimental data for optimizing the technology of continuous casting secondary cooling zone and avoiding the occurrence of fine surface cracks.
文摘Recent observations by electron microscopy have shown that a dislocation-free zone (DFZ) exists between the crack tip and the pile-up of dislocations in the plastic zone. Shang, S. J., Ohr, S. M. and Majumdar, B. S., Burns, S. J. have discussed the problem of the plastic zone at a crack tip in isotropic elastic medium. We know that the hard second phase, which neither causes very large stress concentration nor leads to micrographic split, can improve the bearing capacity of the materials. Therefore, it is necessary to discuss the problem of the plastic zone at a crack tip while the hard second phase exists.
基金Postdoctoral Fellowship Program of CPSF,Grant/Award Number:GZC20240167Chengdu University of Technology Postgraduate Innovative Cultivation Program,Grant/Award Number:CDUT2022BJCX007Huzhou Key Laboratory Fund,Grant/Award Number:HGB23E002。
文摘The analysis of plastic loosening zone of tunnels with cold condition,high in situ stress,and weak stratum is the key scientific problem of tunnel construction in cold areas.Based on the unified strength theory and considering the coupling effect of high in situ stress and low-temperature field,the analytical model of the plastic loosening zone of tunnel surrounding rocks was proposed,and the influence laws of physical parameters(initial ground stress,freezing temperature,excavation radius,and intermediate principal stress)was explored.The results illustrate that:(1)with the coupling of low temperature and stress fields,the in-situ stress has a more significant effect on the radius of the plastic loosening zone of the tunnel surrounding rocks,showing a nonlinear correlation.When the in situ stress is small,the influence of the temperature field on the radius of the plastic loosening zone is more obvious.(2)The radius of the plastic loosening zone of the tunnel surrounding rocks increases synchronously with the excavation radius and gradually decreases with the increase of the intermediate principal stress.(3)The greater the temperature difference in the low-temperature field,the tunnel stability has a more significant response to the intermediate principal stress and is positively correlated with the coefficient of the intermediate principal stress.(4)In the actual project,the proposed model can well describe the mechanical behavior and deformation characteristics of tunnel surrounding rocks in low-temperature environment,showing applicability.The research results are expected to provide a theoretical basis for the study of tunnel stability in cold areas.
文摘The triangular zone cracks in 2101 duplex stainless steel produced by the vertical continuous caster have troubled company A for a long time. To simulate the temperature and thermal stress distributions in the solidification process of 2101 duplex stainless steel produced by the vertical continuous caster, a two-dimensional viscoelastic-plastic thermomechanically coupled finite element model was established by the secondary development of the commercial nonlinear finite element analysis software MSC Marc. The results show that the thermal stress on the surface reaches a maximum at the exit of the mould, and the highest thermal stresses at the centre of the wide face and the narrow face are 75 and 115 MPa, respectively. Meanwhile, the internal temperature of slab is still higher than the solidus temperature, resulting in no thermal stress. The slab shows different high-temperature strengths and suffers from different stresses at different positions; thus, the risk of cracking also varies. At a location of 6-8 m from the meniscus, the temperature of the triangular zone is 1270-1360℃ and the corresponding permissible high-temperature strength is about 10-30 MPa, while the thermal stress at this time is 60 MPa, which is higher than the high-temperature strength. As a result, triangular zone cracks form easily.
基金supported by the National Natural Science Foundation of China(No.11102171)Program for New Century Excellent Talents in University of Ministry of Education of China(NCET-13-0973)+1 种基金The support from Sichuan Provincial Youth Science and Technology Innovation Team(2013-TD-0004)Scientific Research Foundation for Returned Scholars(Ministry of Education of China)are acknowledged as well
文摘The present work is concerned with a penny-shaped Dugdale crack embedded in an infinite space of one-dimensional （1D） hexagonal quasicrystals and subjected to two identical axisymmetric temperature loadings on the upper and lower crack surfaces. Applying Dugdale hypothesis to thermo-elastic results, the extent of the plastic zone at the crack tip is determined. The normal stress outside the plastic zone and crack surface displacement are derived in terms of special functions. For a uniform loading case, the corresponding results are presented by simpli- fying the preceding results. Numerical calculations are carried out to show the influence of some parameters.
基金supported by the National Natural Science Foundation of China (No.10672196)
文摘The elastic-plastic stress distribution and the elastic-plastic boundary con- figuration near a crack surface region are significant but hard to obtain by means of the conventional analysis. A crack line analysis method is developed in this paper by consid- ering the crack surface as an extension of the crack line. The stresses in the plastic zone, the length, and the unit normal vector of the elastic-plastic boundary near a crack surface region are obtained for an antiplane crack in an elastic-perfectly plastic solid. The usual small scale yielding assumptions are not needed in the analysis.
基金supported by the National Natural Science Foundation of China (No.10672196)
文摘Crack line analysis is an effective way to solve elastic-plastic crack problems. Application of the method does not need the traditional small-scale yielding conditions and can obtain sufficiently accurate solutions near the crack line. To address mode- Ⅲ crack problems under the perfect elastic-plastic condition, matching procedures of the crack line analysis method axe summarized and refined to give general forms and formulation steps of plastic field, elastic-plastic boundary, and elastic-plastic matching equations near the crack line. The research unifies mode-III crack problems under different conditions into a problem of determining four integral constants with four matching equations. An example is given to verify correctness, conciseness, and generality of the procedure.
文摘The near crack line analysis method has been used in the present paper,The classical small scale yielding conditions have been completely abandoned in the analyses and one inappropriate matching condition used to be used at the elasticplastic boundary has been corrected.The reasonable solution of the plastic stresses near the crack line region has been established.By matching the plastic stresses with the exact elastic stresses at the elastic-plastic boundary,the plastic stresses the length of the plastic zone and the unit normal vector of the elastic-plastic boundary near the crock line region have been obtained for a mode I crack under uniaxial tension,as well as a mode I crack under biaxial tension,which shows that for both conditions the plastic stress componentsσy, and σsy.he length of the plastic zone and the unit normal vector of the elastic-plastic boundary are quite the same while the plastic stress σs is different.
文摘The results in Ref. [1] are not suitable for the cases of β≥2. For this reason, byusing the methods in Ref [1] and Ref [2], we derive the general expressions ofamsotropic plastic fields at a rapidly propagating plane-stress crack-tip for both thecases of β=2 and β>2 .
文摘The constitutive equation was deduced. The results were obtained from theelastic and elastoplastical analysis of the cylinder sample applied with different ratios ofload on both the inner and outer sides and different moduli ratio. The factors affecting thedevelopment of the plastic field of the cylinder with finite radius were shown. The resultsshow that the different moduli ratio is the most important factor in the development of theplastic zone. The slight fluctuation of the ratio will bring multiplied increment of the displacement, which may result in the final destruction of the engineering material.
