In order to evaluate the performance of deep geological disposal of radioactive waste,an underground research laboratory(URL)was constructed by Andra in the Callovo-Oxfordian(COx)claystone formation at the Meuse/Haute...In order to evaluate the performance of deep geological disposal of radioactive waste,an underground research laboratory(URL)was constructed by Andra in the Callovo-Oxfordian(COx)claystone formation at the Meuse/Haute-Marne(MHM).The construction of URL induced the excavation damage of host formations,and the ventilation in the galleries desaturated the host formation close to the gallery wall.Moreover,it is expected that the mechanical behaviour of COx claystone is time-dependent.This study presents a constitutive model developed to describe the viscoplastic behaviour of unsaturated and damaged COx claystone.In this model,the unsaturation effect is considered by adopting the Bishop effective stress and the van Genuchten(VG)water retention model.In terms of the viscoplastic behaviour,the nonstationary flow surface(NSFS)theory for unsaturated soils is used with consideration of the coupled effects of strain rate and suction on the yield stress.A progressive hardening law is adopted.Meanwhile,a non-associated flow rule is used,which is similar to that in Barcelona basic model(BBM).In addition,to describe the damage effect induced by suction change and viscoplastic loading,a damage function is defined based on the crack volume proportion.This damage function contains two variables:unsaturated effective stress and viscoplastic volumetric strain,with the related parameters determined based on the mercury intrusion porosimetry(MIP)tests.For the model validation,different tests on COx claystone under different loading paths are simulated.Comparisons between experimental and simulated results indicated that the present model is able to well describe the viscoplastic behaviour of damaged COx claystone,including swelling/shrinkage,triaxial extension and compression,and triaxial creep.展开更多
Excavation and control of tunneling responses in swelling soft-rock tunnels of Sichuan-Tibet railway under seepage conditions were studied.For this,a fractional viscoplastic(FVP)model for swelling soft rocks was estab...Excavation and control of tunneling responses in swelling soft-rock tunnels of Sichuan-Tibet railway under seepage conditions were studied.For this,a fractional viscoplastic(FVP)model for swelling soft rocks was established by introducing Abel dashpot and unsteady viscosity coefficient,considering additional swelling deformation and damage of rock caused by humidity effect.In view of the FVP model,the viscoplastic deformation solutions for rock mass surrounding tunnel under seepage conditions were derived and long-term mechanical responses of swelling rocks upon tunnel excavation were analyzed.Next,a stress release coefficient considering seepage and creep was proposed,based on which control responses considering stress release and failure mechanism of stress release measures were analyzed.The results showed that:(i)The one-dimensional(1D)FVP model has a good application for swelling rock and the three-dimensional(3D)FVP model could well describe the whole creep process of rock mass despite a much higher creep attenuation rate in the first stage of creep;and(ii)An appropriate stress release and deformation of surrounding rocks could effectively reduce the supporting resistance.However,upon a large stress release,the radius of plastic region could increase significantly,and the strength of the surrounding rock mass decreases greatly.The proposed solution could provide a theoretical framework for capturing the excavation and support responses for tunneling in swelling rock mass in consideration of time effect.展开更多
By combining the Bodner-Partom constitutive model and equivalent stress function,finite element methods and program on analyzing non-elastic deformation and stressfor thermal viscoplastic material are studied in this ...By combining the Bodner-Partom constitutive model and equivalent stress function,finite element methods and program on analyzing non-elastic deformation and stressfor thermal viscoplastic material are studied in this paper, and it's the first timethat this material model is used in a kind of engineering software-MARC. Thermalviscoplastic behavior of high temperature alloy GH536 specimen with gap is analyzedby this program. The research results show it is feasible to analyze thermal viscoplasticbehavior of specimen or structure by applying B-P model.展开更多
The optimization problems belong to the family of the most important engineering problems. The objective of this paper is to proposed a very efficient numerical algo- rithm which is involved in an optimal design proce...The optimization problems belong to the family of the most important engineering problems. The objective of this paper is to proposed a very efficient numerical algo- rithm which is involved in an optimal design procedure in the field of viscoplasticity phenomena. Because of the complexity of design procedure, particularly in the field of viscoplas- ticity, the finite element method is used. This method provides a good structural discretization and very efficient mathematical describing of time-rate effects. Accord- ing to the design specifications, which will dictate a limiting design strain, using the proposed algorithm, the design life of the considered structure will be covered. For the justification of the proposed method an example is presented. On the basis of specifications data and environment conditions, an operating pressure of a pressure vessel is obtained.展开更多
Soft rock squeezing deformation mainly consists of pre-peak damage-dilatancy and post-peak fracture-bulking at the excavation unloading instant,and creep-dilatancy caused by time-dependent damage and fracturing.Based ...Soft rock squeezing deformation mainly consists of pre-peak damage-dilatancy and post-peak fracture-bulking at the excavation unloading instant,and creep-dilatancy caused by time-dependent damage and fracturing.Based on the classic elastoplastic and Perzyna over-stress viscoplastic theories,as well as triaxial unloading confining pressure test and triaxial unloading creep test results,an elastoplastic and viscoplastic damage constitutive model is established for the short-and long-term dilatancy and fracturing behavior of soft rock squeezing deformation.Firstly,the criteria for each deformation and failure stage are expressed as a linear function of confining pressure.Secondly,the total damage evolution equation considering time-dependent damage is proposed,including the initial damage produced at the excavation instant,in which the damage variable increases exponentially with the lateral strain,and creep damage.Thirdly,a transient five-stages elasto-plastic constitutive equation for the short-term deformation after excavation that comprised of elasticity,pre-peak damage-dilatancy,post-peak brittle-drop,linear strain-softening,and residual perfectly-plastic regimes is developed based on incremental elasto-plastic theory and the nonassociated flow rule.Fourthly,regarding the timedependent properties of soft rock,based on the Perzyna viscoplastic over-stress theory,a viscoplastic damage model is set up to capture creep damage and dilatancy behavior.Viscoplastic strain is produced when the stress exceeds the initial static yield surface fs;the distance between the static yield surface fs and the dynamic yield surface fd determines the viscoplastic strain rate.Finally,the established constitutive model is numerically implemented and field applied to the-848 m belt conveyer haulage roadway of Huainan Panyidong Coal Mine.Laboratory test results and in-situ monitoring results validate the rationality of the established constitutive model.The presented model takes both the transient and time-dependent damage and fracturing into consideration.展开更多
Compared with the traditional rigid plastic/rigid viscoplastic(RP/RVP) FEM(based on iteration solution),RP/RVP FEM based on linear programming (LP) has some remarkable advantages,such as it’s free of convergence prob...Compared with the traditional rigid plastic/rigid viscoplastic(RP/RVP) FEM(based on iteration solution),RP/RVP FEM based on linear programming (LP) has some remarkable advantages,such as it’s free of convergence problem and its convenience in contact,rigid zone,and friction force treatment.The numerical model of RP/RVP FEM based on LP for axisymmetrical metal forming simulation is studied,and some related key factors and its treatment methods in formulation of constraint condition are proposed.Some solution examples are provided to validate its accuracy and efficiency.展开更多
This paper presents the optimal control variational principle for Perzyna modelwhich is one of the main constitutive relation of viscoplasticity in dynamics. And itcould also be transformed to solve the parametric qua...This paper presents the optimal control variational principle for Perzyna modelwhich is one of the main constitutive relation of viscoplasticity in dynamics. And itcould also be transformed to solve the parametric quadratic programming problem.The FEM form of this problem and its implementation have also been discussed in thepaper.展开更多
A viscoplastic constitutive model incorporating the cyclic deformation be-havior with mean strain is presented. In the model,a memory parameter q of strainamplitude is proposed,the evolution equations of back stresses...A viscoplastic constitutive model incorporating the cyclic deformation be-havior with mean strain is presented. In the model,a memory parameter q of strainamplitude is proposed,the evolution equations of back stresses are formulated,an ap-propriate defini展开更多
The dynamic torsional buckling and post-buckling of elasto-plastic circular cylindrical shell isstudied.By the usage of the Bodner-Partom constitutive relation,the present visco-plastic problem is treat-ed as an ortho...The dynamic torsional buckling and post-buckling of elasto-plastic circular cylindrical shell isstudied.By the usage of the Bodner-Partom constitutive relation,the present visco-plastic problem is treat-ed as an orthotropic elastic problem.Based on the nonlinear large deflection shell therory,the governingdynamic buckling equation is solved by the Runge-Kutta method,and the critical buckling stress is deter-mined by the B-R criterion.The present paper is mainly focused on the imperfection sensitivity,the strainrate sensitivity,and the dynamic post-buckling characters for the shell loaded dynamically with a constantshear strain rate.Numerical results show that the critical shear stress and imperfection sensitivity will in-crease with the increase of strain rate.It is found that the elastic buckling stress is more sensitive toimperfection than the visco-plastic buckling.The present research also reveals some dynamic post-bucklingcharacters for the cylindrical shell,and it is shown that the shell will展开更多
- The Bodner-Partom constitutive equation is used to study the viscoplastic torsional bucklingof perfect cylindrical shell. By treating the viscoplastic shell as an orthotropic shell at each moment and neglecting the ...- The Bodner-Partom constitutive equation is used to study the viscoplastic torsional bucklingof perfect cylindrical shell. By treating the viscoplastic shell as an orthotropic shell at each moment and neglecting the inertia term, the critical torque is determined from a set of homogeneous linear equations. The strain rate sensitivity is mainly discussed in the present paper.展开更多
This paper presents the parametric variational principle for Perzyna model which isone of the main constitutive relations of viscoplasticity.The principle,by which the potentialenergy function is minimized under a con...This paper presents the parametric variational principle for Perzyna model which isone of the main constitutive relations of viscoplasticity.The principle,by which the potentialenergy function is minimized under a constrained condition transformed by the constitutiverelations of viscoplasticity,is free from the bound of Drucker’s postulate of plastic flow andconsequently suitable for solving the nonassociated plastic flow problems.Furthermore,the paper has proven the presented principle and discussed the creep problem.展开更多
A numerical scheme is presented which enables the use of symmetric equationsolvers in tangential stiffness programs for non-associated viscoplastic materials.
Perzyna model in viscoplasticity has been studied by the parametric variationalprinciple,which could be transformed into solving the parametric quadratic programmingproblem.The FEM form of this problem and its impleme...Perzyna model in viscoplasticity has been studied by the parametric variationalprinciple,which could be transformed into solving the parametric quadratic programmingproblem.The FEM form of this problem and its implementation have also been discussed inthe paper.展开更多
With many major projects under construction,more and more attention is paid to rheological mechanical properties of rock mass,and extensive researches are carried out for rheological constitutive modeling of rock mass...With many major projects under construction,more and more attention is paid to rheological mechanical properties of rock mass,and extensive researches are carried out for rheological constitutive modeling of rock mass.Based on viscoplastic theory,a new rheological constitutive model is proposed.The rationality and validity of proposed model are verified through the creep test data.The results show that the rheological constitutive model based on viscoplastic theory is able to simulate the typical creep curves of rock mass and the identified parameters are reasonable.Therefore,the rheological constitutive model could be used to describe the rheological mechanical behaviour of rock mass.展开更多
A viscoplastic constitutive model is introduced,which takes into accountnonproportional cyclic additional hardening and the effects of nonproportional cyclicloading history and inelastic strain amplitude history.In th...A viscoplastic constitutive model is introduced,which takes into accountnonproportional cyclic additional hardening and the effects of nonproportional cyclicloading history and inelastic strain amplitude history.In the model,a variable q ofmemory on the inelastic strain amplitude during loading is introduced,a newnonproportionality is defined,a cyclic saturated isotropic deformation resistanceparameter Q,is given,and the evolution equations of the isotropic deformationresistance with the memory on the previous loading history are proposed.The presentmodel is applied to the description of the complex cyclic deformation behavior of1Cr18Ni9Ti stainless steel,and the predictions are in good agreement with theexperimental results.This shows that the model describes the deformation behavior ofnonproportional cyclic loadings and their histories very well.展开更多
This paper studies the dynamic behavior of large deformation of sphericalshells impacted by a flat-nosed missile.By using isometric transformations,thedeformation modes are given.On the basis of Perzyna-Symonds viscop...This paper studies the dynamic behavior of large deformation of sphericalshells impacted by a flat-nosed missile.By using isometric transformations,thedeformation modes are given.On the basis of Perzyna-Symonds viscoplasticconstitutive equations,the motion equations of the shells are obtained by rigid-viscoplastic variational principle.A comparison made between the numerical resultsand experimental ones indicates that the two groups of results are in conformity witheach other.展开更多
This paper presents an elasto-viscoplastic consistent tangent oper-ator (CTO) based boundary element formulation, and application for calculation ofpath-domain independent J integrals (extension of the classical J int...This paper presents an elasto-viscoplastic consistent tangent oper-ator (CTO) based boundary element formulation, and application for calculation ofpath-domain independent J integrals (extension of the classical J integrals) in non-linear crack analysis. When viscoplastic deformation happens, the effective stressesaround the crack tip in the nonlinear region is allowed to exceed the loading sur-face, and the pure plastic theory is not suitable for this situation. The concept ofconsistency employed in the solution of increment viscoplastic problem, plays a cru-cial role in preserving the quadratic rate asymptotic convergence of iterative schemesbased on Newton’s method. Therefore, this paper investigates the viscoplastic crackproblem, and presents an implicit viscoplastic algorithm using the CTO concept in aboundary element framework for path-domain independent J integrals. Applicationsare presented with two numerical examples for viscoplastic crack problems and Jintegrals.展开更多
For a compression-shear mixed mode interface crack, it is difficult to solve the stress and strain fields considering the material viscosity, the crack-tip singularity,the frictional effect, and the mixed loading leve...For a compression-shear mixed mode interface crack, it is difficult to solve the stress and strain fields considering the material viscosity, the crack-tip singularity,the frictional effect, and the mixed loading level. In this paper, a mechanical model of the dynamic propagation interface crack for the compression-shear mixed mode is proposed using an elastic-viscoplastic constitutive model. The governing equations of propagation crack interface at the crack-tip are given. The numerical analysis is performed for the interface crack of the compression-shear mixed mode by introducing a displacement function and some boundary conditions. The distributed regularities of stress field of the interface crack-tip are discussed with several special parameters. The final results show that the viscosity effect and the frictional contact effect on the crack surface and the mixed-load parameter are important factors in studying the mixed mode interface cracktip fields. These fields are controlled by the viscosity coefficient, the Mach number, and the singularity exponent.展开更多
The plane strain compression of a rectangular block is numerically investigated for thestudy of dynamic shear band development in thermo-elasto-viscoplastic materials from an internal in-homogeneity.As expected,it pla...The plane strain compression of a rectangular block is numerically investigated for thestudy of dynamic shear band development in thermo-elasto-viscoplastic materials from an internal in-homogeneity.As expected,it plays an important role in triggering the onset of shear localization aswell as thermal softening.And the competition between the strain,strain-rate hardening and thermalsoftening exists throughout the process.It is found that shear band develops at a 4 5-degree angle to thecompression axis.In the light of given patterns of deformation and temperature,shear band evolutionaccelerated by thermal softening is retarded by the inertial effects.Interestingly,a similar temperatureband is also formed along the trajectory of the localized deformation band.The calculations also showthe energy evolution during the coupled thermo-mechanical process of shear band propagation.Final-ly,the mesh effect is discussed in terms of the numerical results from two different meshes.展开更多
文摘In order to evaluate the performance of deep geological disposal of radioactive waste,an underground research laboratory(URL)was constructed by Andra in the Callovo-Oxfordian(COx)claystone formation at the Meuse/Haute-Marne(MHM).The construction of URL induced the excavation damage of host formations,and the ventilation in the galleries desaturated the host formation close to the gallery wall.Moreover,it is expected that the mechanical behaviour of COx claystone is time-dependent.This study presents a constitutive model developed to describe the viscoplastic behaviour of unsaturated and damaged COx claystone.In this model,the unsaturation effect is considered by adopting the Bishop effective stress and the van Genuchten(VG)water retention model.In terms of the viscoplastic behaviour,the nonstationary flow surface(NSFS)theory for unsaturated soils is used with consideration of the coupled effects of strain rate and suction on the yield stress.A progressive hardening law is adopted.Meanwhile,a non-associated flow rule is used,which is similar to that in Barcelona basic model(BBM).In addition,to describe the damage effect induced by suction change and viscoplastic loading,a damage function is defined based on the crack volume proportion.This damage function contains two variables:unsaturated effective stress and viscoplastic volumetric strain,with the related parameters determined based on the mercury intrusion porosimetry(MIP)tests.For the model validation,different tests on COx claystone under different loading paths are simulated.Comparisons between experimental and simulated results indicated that the present model is able to well describe the viscoplastic behaviour of damaged COx claystone,including swelling/shrinkage,triaxial extension and compression,and triaxial creep.
基金Authors are thankful to Dr.Chen Xu of Ningbo University for his instructive discussions.The authors are also grateful for the support provided by the National Natural Science Foundation of China(Grant Nos.41972274 and 42207176)Ningbo Natural Science Foundation(Grant No.2022J116)for this research work.
文摘Excavation and control of tunneling responses in swelling soft-rock tunnels of Sichuan-Tibet railway under seepage conditions were studied.For this,a fractional viscoplastic(FVP)model for swelling soft rocks was established by introducing Abel dashpot and unsteady viscosity coefficient,considering additional swelling deformation and damage of rock caused by humidity effect.In view of the FVP model,the viscoplastic deformation solutions for rock mass surrounding tunnel under seepage conditions were derived and long-term mechanical responses of swelling rocks upon tunnel excavation were analyzed.Next,a stress release coefficient considering seepage and creep was proposed,based on which control responses considering stress release and failure mechanism of stress release measures were analyzed.The results showed that:(i)The one-dimensional(1D)FVP model has a good application for swelling rock and the three-dimensional(3D)FVP model could well describe the whole creep process of rock mass despite a much higher creep attenuation rate in the first stage of creep;and(ii)An appropriate stress release and deformation of surrounding rocks could effectively reduce the supporting resistance.However,upon a large stress release,the radius of plastic region could increase significantly,and the strength of the surrounding rock mass decreases greatly.The proposed solution could provide a theoretical framework for capturing the excavation and support responses for tunneling in swelling rock mass in consideration of time effect.
基金This project was supported by NPU Youth Science Technology Innovation Foundation (020102).
文摘By combining the Bodner-Partom constitutive model and equivalent stress function,finite element methods and program on analyzing non-elastic deformation and stressfor thermal viscoplastic material are studied in this paper, and it's the first timethat this material model is used in a kind of engineering software-MARC. Thermalviscoplastic behavior of high temperature alloy GH536 specimen with gap is analyzedby this program. The research results show it is feasible to analyze thermal viscoplasticbehavior of specimen or structure by applying B-P model.
文摘The optimization problems belong to the family of the most important engineering problems. The objective of this paper is to proposed a very efficient numerical algo- rithm which is involved in an optimal design procedure in the field of viscoplasticity phenomena. Because of the complexity of design procedure, particularly in the field of viscoplas- ticity, the finite element method is used. This method provides a good structural discretization and very efficient mathematical describing of time-rate effects. Accord- ing to the design specifications, which will dictate a limiting design strain, using the proposed algorithm, the design life of the considered structure will be covered. For the justification of the proposed method an example is presented. On the basis of specifications data and environment conditions, an operating pressure of a pressure vessel is obtained.
基金financially supported by the National Natural Science Foundation of China(Grant No.52074258,Grant No.41941018,Grant No.51974289,and Grant No.51874232)the Natural Science Basic Research Program of Shaanxi Province(Shaanxi Coal and Chemical Industry Group Co.,Ltd.Joint Fund Project,Grant No.2021JLM-06)the open project of State Key Laboratory of Shield Machine and Boring Technology(Grant No.E01Z440101)。
文摘Soft rock squeezing deformation mainly consists of pre-peak damage-dilatancy and post-peak fracture-bulking at the excavation unloading instant,and creep-dilatancy caused by time-dependent damage and fracturing.Based on the classic elastoplastic and Perzyna over-stress viscoplastic theories,as well as triaxial unloading confining pressure test and triaxial unloading creep test results,an elastoplastic and viscoplastic damage constitutive model is established for the short-and long-term dilatancy and fracturing behavior of soft rock squeezing deformation.Firstly,the criteria for each deformation and failure stage are expressed as a linear function of confining pressure.Secondly,the total damage evolution equation considering time-dependent damage is proposed,including the initial damage produced at the excavation instant,in which the damage variable increases exponentially with the lateral strain,and creep damage.Thirdly,a transient five-stages elasto-plastic constitutive equation for the short-term deformation after excavation that comprised of elasticity,pre-peak damage-dilatancy,post-peak brittle-drop,linear strain-softening,and residual perfectly-plastic regimes is developed based on incremental elasto-plastic theory and the nonassociated flow rule.Fourthly,regarding the timedependent properties of soft rock,based on the Perzyna viscoplastic over-stress theory,a viscoplastic damage model is set up to capture creep damage and dilatancy behavior.Viscoplastic strain is produced when the stress exceeds the initial static yield surface fs;the distance between the static yield surface fs and the dynamic yield surface fd determines the viscoplastic strain rate.Finally,the established constitutive model is numerically implemented and field applied to the-848 m belt conveyer haulage roadway of Huainan Panyidong Coal Mine.Laboratory test results and in-situ monitoring results validate the rationality of the established constitutive model.The presented model takes both the transient and time-dependent damage and fracturing into consideration.
文摘Compared with the traditional rigid plastic/rigid viscoplastic(RP/RVP) FEM(based on iteration solution),RP/RVP FEM based on linear programming (LP) has some remarkable advantages,such as it’s free of convergence problem and its convenience in contact,rigid zone,and friction force treatment.The numerical model of RP/RVP FEM based on LP for axisymmetrical metal forming simulation is studied,and some related key factors and its treatment methods in formulation of constraint condition are proposed.Some solution examples are provided to validate its accuracy and efficiency.
文摘This paper presents the optimal control variational principle for Perzyna modelwhich is one of the main constitutive relation of viscoplasticity in dynamics. And itcould also be transformed to solve the parametric quadratic programming problem.The FEM form of this problem and its implementation have also been discussed in thepaper.
文摘A viscoplastic constitutive model incorporating the cyclic deformation be-havior with mean strain is presented. In the model,a memory parameter q of strainamplitude is proposed,the evolution equations of back stresses are formulated,an ap-propriate defini
基金The present work was financially supported by the National Science Foundation of China(No.19472042)
文摘The dynamic torsional buckling and post-buckling of elasto-plastic circular cylindrical shell isstudied.By the usage of the Bodner-Partom constitutive relation,the present visco-plastic problem is treat-ed as an orthotropic elastic problem.Based on the nonlinear large deflection shell therory,the governingdynamic buckling equation is solved by the Runge-Kutta method,and the critical buckling stress is deter-mined by the B-R criterion.The present paper is mainly focused on the imperfection sensitivity,the strainrate sensitivity,and the dynamic post-buckling characters for the shell loaded dynamically with a constantshear strain rate.Numerical results show that the critical shear stress and imperfection sensitivity will in-crease with the increase of strain rate.It is found that the elastic buckling stress is more sensitive toimperfection than the visco-plastic buckling.The present research also reveals some dynamic post-bucklingcharacters for the cylindrical shell,and it is shown that the shell will
文摘- The Bodner-Partom constitutive equation is used to study the viscoplastic torsional bucklingof perfect cylindrical shell. By treating the viscoplastic shell as an orthotropic shell at each moment and neglecting the inertia term, the critical torque is determined from a set of homogeneous linear equations. The strain rate sensitivity is mainly discussed in the present paper.
文摘This paper presents the parametric variational principle for Perzyna model which isone of the main constitutive relations of viscoplasticity.The principle,by which the potentialenergy function is minimized under a constrained condition transformed by the constitutiverelations of viscoplasticity,is free from the bound of Drucker’s postulate of plastic flow andconsequently suitable for solving the nonassociated plastic flow problems.Furthermore,the paper has proven the presented principle and discussed the creep problem.
文摘A numerical scheme is presented which enables the use of symmetric equationsolvers in tangential stiffness programs for non-associated viscoplastic materials.
基金The Project Supported by the National Natural Science Foundation of China
文摘Perzyna model in viscoplasticity has been studied by the parametric variationalprinciple,which could be transformed into solving the parametric quadratic programmingproblem.The FEM form of this problem and its implementation have also been discussed inthe paper.
基金Sponsored by the Natural Science Foundation of Fujian Province(Grant No.2008J0171)
文摘With many major projects under construction,more and more attention is paid to rheological mechanical properties of rock mass,and extensive researches are carried out for rheological constitutive modeling of rock mass.Based on viscoplastic theory,a new rheological constitutive model is proposed.The rationality and validity of proposed model are verified through the creep test data.The results show that the rheological constitutive model based on viscoplastic theory is able to simulate the typical creep curves of rock mass and the identified parameters are reasonable.Therefore,the rheological constitutive model could be used to describe the rheological mechanical behaviour of rock mass.
基金The project supported by National Natural Science Foundation of China
文摘A viscoplastic constitutive model is introduced,which takes into accountnonproportional cyclic additional hardening and the effects of nonproportional cyclicloading history and inelastic strain amplitude history.In the model,a variable q ofmemory on the inelastic strain amplitude during loading is introduced,a newnonproportionality is defined,a cyclic saturated isotropic deformation resistanceparameter Q,is given,and the evolution equations of the isotropic deformationresistance with the memory on the previous loading history are proposed.The presentmodel is applied to the description of the complex cyclic deformation behavior of1Cr18Ni9Ti stainless steel,and the predictions are in good agreement with theexperimental results.This shows that the model describes the deformation behavior ofnonproportional cyclic loadings and their histories very well.
基金This subject was SHpported by the Natural Science Foundation of Shanxi
文摘This paper studies the dynamic behavior of large deformation of sphericalshells impacted by a flat-nosed missile.By using isometric transformations,thedeformation modes are given.On the basis of Perzyna-Symonds viscoplasticconstitutive equations,the motion equations of the shells are obtained by rigid-viscoplastic variational principle.A comparison made between the numerical resultsand experimental ones indicates that the two groups of results are in conformity witheach other.
基金The project supported by National Natural Science Foundation of China(9713008)Zhejiang Natural Science Foundation Special Funds No. RC.9601
文摘This paper presents an elasto-viscoplastic consistent tangent oper-ator (CTO) based boundary element formulation, and application for calculation ofpath-domain independent J integrals (extension of the classical J integrals) in non-linear crack analysis. When viscoplastic deformation happens, the effective stressesaround the crack tip in the nonlinear region is allowed to exceed the loading sur-face, and the pure plastic theory is not suitable for this situation. The concept ofconsistency employed in the solution of increment viscoplastic problem, plays a cru-cial role in preserving the quadratic rate asymptotic convergence of iterative schemesbased on Newton’s method. Therefore, this paper investigates the viscoplastic crackproblem, and presents an implicit viscoplastic algorithm using the CTO concept in aboundary element framework for path-domain independent J integrals. Applicationsare presented with two numerical examples for viscoplastic crack problems and Jintegrals.
基金Project supported by the National Natural Science Foundation of China(No.11302054)the Fundamental Research Funds for the Central Universities(No.HEUCF130216)
文摘For a compression-shear mixed mode interface crack, it is difficult to solve the stress and strain fields considering the material viscosity, the crack-tip singularity,the frictional effect, and the mixed loading level. In this paper, a mechanical model of the dynamic propagation interface crack for the compression-shear mixed mode is proposed using an elastic-viscoplastic constitutive model. The governing equations of propagation crack interface at the crack-tip are given. The numerical analysis is performed for the interface crack of the compression-shear mixed mode by introducing a displacement function and some boundary conditions. The distributed regularities of stress field of the interface crack-tip are discussed with several special parameters. The final results show that the viscosity effect and the frictional contact effect on the crack surface and the mixed-load parameter are important factors in studying the mixed mode interface cracktip fields. These fields are controlled by the viscosity coefficient, the Mach number, and the singularity exponent.
基金the National Natural Sciences Foundation of China
文摘The plane strain compression of a rectangular block is numerically investigated for thestudy of dynamic shear band development in thermo-elasto-viscoplastic materials from an internal in-homogeneity.As expected,it plays an important role in triggering the onset of shear localization aswell as thermal softening.And the competition between the strain,strain-rate hardening and thermalsoftening exists throughout the process.It is found that shear band develops at a 4 5-degree angle to thecompression axis.In the light of given patterns of deformation and temperature,shear band evolutionaccelerated by thermal softening is retarded by the inertial effects.Interestingly,a similar temperatureband is also formed along the trajectory of the localized deformation band.The calculations also showthe energy evolution during the coupled thermo-mechanical process of shear band propagation.Final-ly,the mesh effect is discussed in terms of the numerical results from two different meshes.
