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
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
Field evidence has shown that large-scale and unstable discontinuous planes in the rock mass surrounding tunnels in rich water region are probably generated after excavation. The tunnel surrounding rock was divided in...Field evidence has shown that large-scale and unstable discontinuous planes in the rock mass surrounding tunnels in rich water region are probably generated after excavation. The tunnel surrounding rock was divided into three zones, including elastic zone, plastic damage zone and shear fracture zone for assessing the stability of the tunnel surrounding rock. By local hydrogeology, the stresses of surrounding rock of Jinshazhou circular tunnel was analyzed and the stress solutions on the elastic and plastic damage zones were obtained by applying the theories of fluid-solid coupling and elasto-plastic damage mechanics. The shear fracture zone generated by joints was studied and its range was determined by using Molar-Coulomb strength criterion. Finally, the correctness of the theoretical results was validated by comparing the scopes of shear fracture zones calculated in this paper with those from literature.展开更多
This study uses the digital image correlation technique to measure the crack tip displacement field at various crack lengths in U71MnG rail steel,and the interpolated continuous displacement field was obtained by fitt...This study uses the digital image correlation technique to measure the crack tip displacement field at various crack lengths in U71MnG rail steel,and the interpolated continuous displacement field was obtained by fitting with a back propagation(BP)neural network.The slip and stacking of dislocations affect crack initiation and growth,leading to changes in the crack tip field and the fatigue characteristics of crack growth.The Christopher-James-Patterson(CJP)model describes the elastic stress field around a growing fatigue crack that experiences plasticity-induced shielding.In the present work,this model is modified by including the effect of the dislocation field on the plastic zone of the crack tip and hence on the elastic field by introducing a plastic flow factorρ,which represents the amount of blunting of the crack tip.The Levenberg-Marquardt(L-M)nonlinear least squares method was used to solve for the stress intensity factors.To verify the accuracy of this modified CJP model,the theoretical and experimental plastic zone errors before and after modification were compared,and the variation trends of the stress intensity factors and the plastic flow factorρwere analysed.The results show that the CJP model,with the introduction ofρ,exhibits a good blunting trend.In the low plasticity state,the modified model can accurately describe the experimental plastic zone,and the modified stress intensity factors are more accurate,which proves the effectiveness of dislocation correction.This plastic flow correction provides a more accurate crack tip field model and improves the CJP crack growth relationship.展开更多
A number of rockburst accidents occurring in soft coal seams have shown that the rockburst mechanism involved in soft coal seams is significantly different from that involved in hard coal seams. Therefore, the method ...A number of rockburst accidents occurring in soft coal seams have shown that the rockburst mechanism involved in soft coal seams is significantly different from that involved in hard coal seams. Therefore, the method used to evaluate rockburst in hard coal seams is not applicable to soft coal seams. This paper established an energy integral model for the rockburst-inducing area and a friction work calculation model for the plastic area. If the remaining energy after the coal seam is broken in the rockburstinducing area is greater than the friction work required for the coal to burst out, then a rockburst accident will occur. Mechanisms of ‘‘quaking without bursting" and ‘‘quaking and bursting" are clarified for soft coal seams and corresponding control measures are proposed as the optimization of roadway layouts and use of ‘‘three strong systems"(strong de-stressing, strong supporting, and strong monitoring).展开更多
Numerical modelling is a common routine for slope stability analysis in the complex terrain,and the accuracy of topographic survey has a great impact on the results.In this study,a combination of unmanned aerial vehic...Numerical modelling is a common routine for slope stability analysis in the complex terrain,and the accuracy of topographic survey has a great impact on the results.In this study,a combination of unmanned aerial vehicle(UAV)photogrammetry and 3D laser scanning technique was first proposed to establish a high-precision digital elevation model(DEM),which could be accurate to 0.2 m,fulfilling the engineering requirements.Then,a series of 3D/2D finite element models(FEM)were constituted on the basis of DEM to investigate the slope stability in the complex terrain.The results indicate that the deformation of complex terrain slope is chiefly triggered by compression-shear failure and the failure zones are mostly distributed on the middle-upper part and the scarp.Furthermore,the complex terrain slope is divided into concave,convex,concave-convex and convex-concave slope according to the topographical curvature,and the factor of safety(FOS)is as follows:the maximum value 1.8504 for the concave-convex slope,the minimum value 1.1129 for the convexconcave slope,and the median for either concave or convex slope.The inflection points and curvature of the slope jointly determine the shape of nonlinear slope,dominating the morphological effect on the slope stability,so the rational use of section morphological effect will be conducive to the overall stability of the slope.For four representative slopes,the plastic deformation first emerges into the middle,then progressively develops to the upper,and finally forms the connected failure zones.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
In the digital image correlation research of fatigue crack growth rate,the accuracy of the crack tip position determines the accuracy of the calculation of the stress intensity factor,thereby affecting the life predic...In the digital image correlation research of fatigue crack growth rate,the accuracy of the crack tip position determines the accuracy of the calculation of the stress intensity factor,thereby affecting the life prediction.This paper proposes a Gauss-Newton iteration method for solving the crack tip position.The conventional linear fitting method provides an iterative initial solution for this method,and the preconditioned conjugate gradient method is used to solve the ill-conditioned matrix.A noise-added artificial displacement field is used to verify the feasibility of the method,which shows that all parameters can be solved with satisfactory results.The actual stress intensity factor solution case shows that the stress intensity factor value obtained by the method in this paper is very close to the finite element result,and the relative error between the two is only−0.621%;The Williams coefficient obtained by this method can also better define the contour of the plastic zone at the crack tip,and the maximum relative error with the test plastic zone area is−11.29%.The relative error between the contour of the plastic zone defined by the conventional method and the area of the experimental plastic zone reached a maximum of 26.05%.The crack tip coordinates,stress intensity factors,and plastic zone contour changes in the loading and unloading phases are explored.The results show that the crack tip change during the loading process is faster than the change during the unloading process;the stress intensity factor during the unloading process under the same load condition is larger than that during the loading process;under the same load,the theoretical plastic zone during the unloading process is higher than that during the loading process.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
Effect of Explosion on underground structures where drilled on the stony materials can be affected by explosive strength and rock mass properties of tunnel. In this paper, it has been studied on effect of explosion of...Effect of Explosion on underground structures where drilled on the stony materials can be affected by explosive strength and rock mass properties of tunnel. In this paper, it has been studied on effect of explosion of 10 tons TNT on the round tunnel (diameter: 10 m) in 25 m depth in the mass rocks (RMR > 90) to estimate stability of tunnel to construct underground structure. Regarding to the studied stones, geo-mechanical indices of rock mass have been found to use as strength criteria in UDEC. In the next step, tunnel in real dimensions and founded indices is modeled with UDEC and analyzed stably. Explosion wave indices are found by UFC Instruction and other experimental relations to administer force from explosion wave on the model. Finally, on the base of FISH, indices of explosion wave are administrated in UDEC and tunnel is analyzed dynamically. According to modeling in depth of 25 m, amount of displacement of drilled tunnel in mass rocks (RMR < 90) is very lower than standard criterion and the tunnel is very stable. Development of plastic zone, vertical and horizontal displacement of rock mass around the tunnel, speed variations and stress from explosion wave are modeled and recorded as the graphs and figures.展开更多
Fracture parameters of welded joints with different strength matching and crack depth in weld metal are investigated by using the methods of elastoplastic finite element analysis and three point bend specimen test. Th...Fracture parameters of welded joints with different strength matching and crack depth in weld metal are investigated by using the methods of elastoplastic finite element analysis and three point bend specimen test. The results show that for shallow crack, the plastic zone turns large in loading process, and the fracture toughness turns high. The extent of the plastic zone of overmatched joint is larger than that of undermatched joint because it will extends to parent metal from the weld metal in loading process for the same CTOD value. The plastic zone of undermatched joint is restricted within the weld, and the size of that is small. Overmatched joint shows the fracture behaviour of shallow crack may more easily than the undermatched joint, while the two sorts of joint specimens have the same crack depth. Therefore, the fracture-resistant capability of overmatched weld is better than that of undermatched weld. when the toughness of weld metals is similar for both overmatched and undermatched joints.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
In this study, we investigated non-captive four-striped mice (Rhabdomys pumilio) for evidence that adult neurogenesis occurs in the adult brain of animal models in natural environment. Ki-67 (a marker for cell prol...In this study, we investigated non-captive four-striped mice (Rhabdomys pumilio) for evidence that adult neurogenesis occurs in the adult brain of animal models in natural environment. Ki-67 (a marker for cell proliferation) and doublecortin (a marker for immature neurons) immunos-taining conifrmed that adult neurogenesis occurs in the active sites of subventricular zone of the lateral ventricle with the migratory stream to the olfactory bulb, and the subgranular zone of the dentate gyrus of the hippocampus. No Ki-67 proliferating cells were observed in the striatum substantia nigra, amygdala, cerebral cortex or dorsal vagal complex. Doublecortin-immunore-active cells were observed in the striatum, third ventricle, cerebral cortex, amygdala, olfactory bulb and along the rostral migratory stream but absent in the substantia nigra and dorsal vagal complex. The potential neurogenic sites in the four-striped mouse species could invariably lead to increased neural plasticity.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
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
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
The major reason of the failure of jointed rock-mass is the formation of the plastic zone near the crack tip ofⅠ-Ⅱmixed crack which leads to the growth,propagation of the branched crack under load condition.In the p...The major reason of the failure of jointed rock-mass is the formation of the plastic zone near the crack tip ofⅠ-Ⅱmixed crack which leads to the growth,propagation of the branched crack under load condition.In the paper,the failure judgment of mini-plastic zone's displacement is derived by the Mises yielding rule.The anchor cable is simulated by the different link elements and inflicting pre-strains according to the difference of mechanism of the consolidated segment and free segment.The stress and strain fields near crack tip of twain collinear cracks of different angles and consolidated conditions are simulated by iso-parametric element with eight nodes.The iso-parametric element with eight nodes is degenerated to singular element at crick tip to simulate crack.It is shown that the mini plastic zone's displacement near the crack tip begins to increase,then decreases with the increase of the angle of the crack.The better consolidated condition is,the smaller the angle of crack tip is when the mini plastic zone's displacement near the crack tip arrives at the biggest value.The mini plastic zone's displacement near the crack Tip 2 is bigger than that near the crack Tip 3.The crack is easier to failure with the increase of load.展开更多
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.
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The Program for New Century Excellent Talents in University ( No. NCET-06-0649)the Natural Science Foundation of Hubei Province (No.2005ABA303)
文摘Field evidence has shown that large-scale and unstable discontinuous planes in the rock mass surrounding tunnels in rich water region are probably generated after excavation. The tunnel surrounding rock was divided into three zones, including elastic zone, plastic damage zone and shear fracture zone for assessing the stability of the tunnel surrounding rock. By local hydrogeology, the stresses of surrounding rock of Jinshazhou circular tunnel was analyzed and the stress solutions on the elastic and plastic damage zones were obtained by applying the theories of fluid-solid coupling and elasto-plastic damage mechanics. The shear fracture zone generated by joints was studied and its range was determined by using Molar-Coulomb strength criterion. Finally, the correctness of the theoretical results was validated by comparing the scopes of shear fracture zones calculated in this paper with those from literature.
基金Supported by Sichuan Science and Technology Program of China (Grant No.2022YFH0075)Opening Project of State Key Laboratory of Performance Monitoring and Protecting of Rail Transit Infrastructure of China (Grant No.HJGZ2021113)Independent Research Project of State Key Laboratory of Traction Power of China (Grant No.2022TPL_T13)。
文摘This study uses the digital image correlation technique to measure the crack tip displacement field at various crack lengths in U71MnG rail steel,and the interpolated continuous displacement field was obtained by fitting with a back propagation(BP)neural network.The slip and stacking of dislocations affect crack initiation and growth,leading to changes in the crack tip field and the fatigue characteristics of crack growth.The Christopher-James-Patterson(CJP)model describes the elastic stress field around a growing fatigue crack that experiences plasticity-induced shielding.In the present work,this model is modified by including the effect of the dislocation field on the plastic zone of the crack tip and hence on the elastic field by introducing a plastic flow factorρ,which represents the amount of blunting of the crack tip.The Levenberg-Marquardt(L-M)nonlinear least squares method was used to solve for the stress intensity factors.To verify the accuracy of this modified CJP model,the theoretical and experimental plastic zone errors before and after modification were compared,and the variation trends of the stress intensity factors and the plastic flow factorρwere analysed.The results show that the CJP model,with the introduction ofρ,exhibits a good blunting trend.In the low plasticity state,the modified model can accurately describe the experimental plastic zone,and the modified stress intensity factors are more accurate,which proves the effectiveness of dislocation correction.This plastic flow correction provides a more accurate crack tip field model and improves the CJP crack growth relationship.
基金Financial supports for this work by the National Program on Key Basic Research Project (No.210CB226800)the National Natural Science Foundation of China (Nos.51274022 and 51174016)
文摘A number of rockburst accidents occurring in soft coal seams have shown that the rockburst mechanism involved in soft coal seams is significantly different from that involved in hard coal seams. Therefore, the method used to evaluate rockburst in hard coal seams is not applicable to soft coal seams. This paper established an energy integral model for the rockburst-inducing area and a friction work calculation model for the plastic area. If the remaining energy after the coal seam is broken in the rockburstinducing area is greater than the friction work required for the coal to burst out, then a rockburst accident will occur. Mechanisms of ‘‘quaking without bursting" and ‘‘quaking and bursting" are clarified for soft coal seams and corresponding control measures are proposed as the optimization of roadway layouts and use of ‘‘three strong systems"(strong de-stressing, strong supporting, and strong monitoring).
基金supported by the National Key Research and Development Program of China(Grant No.2018YFC0808706)the Projects of Shaanxi Province Education Department Science and Technology Research Plan(Grant No.20JK0501,21JK0502)。
文摘Numerical modelling is a common routine for slope stability analysis in the complex terrain,and the accuracy of topographic survey has a great impact on the results.In this study,a combination of unmanned aerial vehicle(UAV)photogrammetry and 3D laser scanning technique was first proposed to establish a high-precision digital elevation model(DEM),which could be accurate to 0.2 m,fulfilling the engineering requirements.Then,a series of 3D/2D finite element models(FEM)were constituted on the basis of DEM to investigate the slope stability in the complex terrain.The results indicate that the deformation of complex terrain slope is chiefly triggered by compression-shear failure and the failure zones are mostly distributed on the middle-upper part and the scarp.Furthermore,the complex terrain slope is divided into concave,convex,concave-convex and convex-concave slope according to the topographical curvature,and the factor of safety(FOS)is as follows:the maximum value 1.8504 for the concave-convex slope,the minimum value 1.1129 for the convexconcave slope,and the median for either concave or convex slope.The inflection points and curvature of the slope jointly determine the shape of nonlinear slope,dominating the morphological effect on the slope stability,so the rational use of section morphological effect will be conducive to the overall stability of the slope.For four representative slopes,the plastic deformation first emerges into the middle,then progressively develops to the upper,and finally forms the connected failure zones.
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 National Natural Science Foundation of China(Grant No.51675446)Independent Research Project of State Key Laboratory of Traction Power(Grant No.2019TPL-T13).
文摘In the digital image correlation research of fatigue crack growth rate,the accuracy of the crack tip position determines the accuracy of the calculation of the stress intensity factor,thereby affecting the life prediction.This paper proposes a Gauss-Newton iteration method for solving the crack tip position.The conventional linear fitting method provides an iterative initial solution for this method,and the preconditioned conjugate gradient method is used to solve the ill-conditioned matrix.A noise-added artificial displacement field is used to verify the feasibility of the method,which shows that all parameters can be solved with satisfactory results.The actual stress intensity factor solution case shows that the stress intensity factor value obtained by the method in this paper is very close to the finite element result,and the relative error between the two is only−0.621%;The Williams coefficient obtained by this method can also better define the contour of the plastic zone at the crack tip,and the maximum relative error with the test plastic zone area is−11.29%.The relative error between the contour of the plastic zone defined by the conventional method and the area of the experimental plastic zone reached a maximum of 26.05%.The crack tip coordinates,stress intensity factors,and plastic zone contour changes in the loading and unloading phases are explored.The results show that the crack tip change during the loading process is faster than the change during the unloading process;the stress intensity factor during the unloading process under the same load condition is larger than that during the loading process;under the same load,the theoretical plastic zone during the unloading process is higher than that during the loading process.
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Effect of Explosion on underground structures where drilled on the stony materials can be affected by explosive strength and rock mass properties of tunnel. In this paper, it has been studied on effect of explosion of 10 tons TNT on the round tunnel (diameter: 10 m) in 25 m depth in the mass rocks (RMR > 90) to estimate stability of tunnel to construct underground structure. Regarding to the studied stones, geo-mechanical indices of rock mass have been found to use as strength criteria in UDEC. In the next step, tunnel in real dimensions and founded indices is modeled with UDEC and analyzed stably. Explosion wave indices are found by UFC Instruction and other experimental relations to administer force from explosion wave on the model. Finally, on the base of FISH, indices of explosion wave are administrated in UDEC and tunnel is analyzed dynamically. According to modeling in depth of 25 m, amount of displacement of drilled tunnel in mass rocks (RMR < 90) is very lower than standard criterion and the tunnel is very stable. Development of plastic zone, vertical and horizontal displacement of rock mass around the tunnel, speed variations and stress from explosion wave are modeled and recorded as the graphs and figures.
文摘Fracture parameters of welded joints with different strength matching and crack depth in weld metal are investigated by using the methods of elastoplastic finite element analysis and three point bend specimen test. The results show that for shallow crack, the plastic zone turns large in loading process, and the fracture toughness turns high. The extent of the plastic zone of overmatched joint is larger than that of undermatched joint because it will extends to parent metal from the weld metal in loading process for the same CTOD value. The plastic zone of undermatched joint is restricted within the weld, and the size of that is small. Overmatched joint shows the fracture behaviour of shallow crack may more easily than the undermatched joint, while the two sorts of joint specimens have the same crack depth. Therefore, the fracture-resistant capability of overmatched weld is better than that of undermatched weld. when the toughness of weld metals is similar for both overmatched and undermatched joints.
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 .
基金supported by Individual Faculty Research GrantSwiss-South Africa Joint Research Progamme(SSAJRP)
文摘In this study, we investigated non-captive four-striped mice (Rhabdomys pumilio) for evidence that adult neurogenesis occurs in the adult brain of animal models in natural environment. Ki-67 (a marker for cell proliferation) and doublecortin (a marker for immature neurons) immunos-taining conifrmed that adult neurogenesis occurs in the active sites of subventricular zone of the lateral ventricle with the migratory stream to the olfactory bulb, and the subgranular zone of the dentate gyrus of the hippocampus. No Ki-67 proliferating cells were observed in the striatum substantia nigra, amygdala, cerebral cortex or dorsal vagal complex. Doublecortin-immunore-active cells were observed in the striatum, third ventricle, cerebral cortex, amygdala, olfactory bulb and along the rostral migratory stream but absent in the substantia nigra and dorsal vagal complex. The potential neurogenic sites in the four-striped mouse species could invariably lead to increased neural plasticity.
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.
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the National Natural Science Foundation of China(Nos.51009015 and 51274051)
文摘The major reason of the failure of jointed rock-mass is the formation of the plastic zone near the crack tip ofⅠ-Ⅱmixed crack which leads to the growth,propagation of the branched crack under load condition.In the paper,the failure judgment of mini-plastic zone's displacement is derived by the Mises yielding rule.The anchor cable is simulated by the different link elements and inflicting pre-strains according to the difference of mechanism of the consolidated segment and free segment.The stress and strain fields near crack tip of twain collinear cracks of different angles and consolidated conditions are simulated by iso-parametric element with eight nodes.The iso-parametric element with eight nodes is degenerated to singular element at crick tip to simulate crack.It is shown that the mini plastic zone's displacement near the crack tip begins to increase,then decreases with the increase of the angle of the crack.The better consolidated condition is,the smaller the angle of crack tip is when the mini plastic zone's displacement near the crack tip arrives at the biggest value.The mini plastic zone's displacement near the crack Tip 2 is bigger than that near the crack Tip 3.The crack is easier to failure with the increase of load.