A coupled viscoplasticity damage constitutive model for concrete materials is developed within the framework of irreversible thermodynamics. Simultaneously the Hehnholtz free energy function and a non-associated flow ...A coupled viscoplasticity damage constitutive model for concrete materials is developed within the framework of irreversible thermodynamics. Simultaneously the Hehnholtz free energy function and a non-associated flow potential function are given, which include the internal variables of kinematic hardening, isotropic hardening and damage. Results from the numerical simulation show that the model presented can describe the deformatioa properties of the concrete without the formal hypotheses of yield criterion and failure criteria, such as the volume dilatancy under the compression, strain-rate sensitivity, stiffness degradation and stress-softening behavior beyond the peak stress which are brought by damages and fractures. Moreover, we could benefit from the application of the finite element method based oi1 this model under complex loading because of not having to choose different constitutive models based on the deformation level.展开更多
A numerical scheme is presented which enables the use of symmetric equation solvers in tangential stiffness programs for non-associated viscoplastic materials.
This paper presents the parametric variational principle for Perzyna model which is one of the main constitutive relations of viscoplasticity.The principle,by which the potential energy function is minimized under a c...This paper presents the parametric variational principle for Perzyna model which is one of the main constitutive relations of viscoplasticity.The principle,by which the potential energy function is minimized under a constrained condition transformed by the constitutive relations of viscoplasticity, is free from the bound of Drucker's postulate of plastic flow and consequently 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 unified viscoplasticity constitutive model for metal materials is developed within the framework of irreversible thermodynamics, and an expression for the Helmholtz free energy function involving the parameters refl...A unified viscoplasticity constitutive model for metal materials is developed within the framework of irreversible thermodynamics, and an expression for the Helmholtz free energy function involving the parameters reflecting kinematic hardening and isotropic hardening is given. At the same time a non-associated flow potential function including the corresponding state variables is also given, from which the flow equation and the evolution equations of the internal state variables are derived. Thus, a general theoretical framework constructing a unified viscoplasticity constitutive model is given. Compared with the typical unified viscoplasticity constitutive models, the presented model evidently satisfies the irreversible thermodynamics laws. Moreover, this method not only provides a new theoretical foundation for further development of the unified viscoplasticity constitutive model, but also gives a new theoretical framework for the stress-strain analysis of more materials.展开更多
The traditional unified viscoplasticity constitutive model can be only applied to metal materials.The study of the unified constitutive theory for metal materials has discovered the correlation between the classical p...The traditional unified viscoplasticity constitutive model can be only applied to metal materials.The study of the unified constitutive theory for metal materials has discovered the correlation between the classical plasticity theory and the unified viscoplasticity constitutive model,thus leading to the con-cepts of the classic plastic potential and yield surface in the unified constitutive model.Moreover,this research has given the continuous expression of the classical plastic multiplier and presented the corresponding constructive method,which extends its physical significance and lays down a good foundation for the application of the unified constitutive theory to the material analysis in more fields.This paper also introduces the unified constitutive model for metal materials and geo-materials.The numerical simulation indicates that the construction should be both reasonable and practical.展开更多
Silicon,a leading candidate for electrode material for lithium-ion batteries,has garnered significant attention.During the initial lithiation process,the alloying reaction between silicon and lithium transforms the pr...Silicon,a leading candidate for electrode material for lithium-ion batteries,has garnered significant attention.During the initial lithiation process,the alloying reaction between silicon and lithium transforms the pristine silicon microstructure from crystalline to amorphous,resulting in plastic deformation of the amorphous phase.This study proposes the free volume theory to develop a fully coupled Cahn-Hilliard phase-field model that integrates viscoplastic deformation,free volume evolution,and diffusion.This model investigates the chemophysical phenomenon of self-limiting behavior occurring during the initial lithiation of silicon anodes.Unlike most existing models,the proposed model considers free volume-dependent diffusion using a physically-based approach.The model’s temporal variation in the lithiated phase thickness aligns well with experimental results,confirming the model’s accuracy.Stress field calculations reveal the coexistence of compressive and tensile stresses within the lithiated phase,which may not cause the limiting effect under the frame of the stress-induced diffusion.Analyses indicate that high effective stress increases free volume,enhancing lithium diffusion and augmenting the diffusion coefficient.Reducing the diffusion coefficient in the lithiated phase due to free volume evolution is the primary cause of self-limiting lithiation.展开更多
Soil responds to cavity expansion is inherently rate-dependent,especially in the case of fine-grained soils.To better understand such rate effects,self-boring pressuremeter tests were conducted on Kunming peaty soil w...Soil responds to cavity expansion is inherently rate-dependent,especially in the case of fine-grained soils.To better understand such rate effects,self-boring pressuremeter tests were conducted on Kunming peaty soil within a strain rate range of 0.1%/min to 5.0%/min.The results showed a clear dependence of cavity pressure and excess pore pressure(EPP)on strain ratesdboth increased with higher rates for a given radial displacement.In light of the experimental results,three cases of cylindrical cavity expansion were investigated using the finite element method and analytical method,partially drained expansion in Modified Cam-Clay(MCC)soil,and undrained and partially drained expansion in elastoviscoplastic(EVP)soil.The EVP behavior was and modeled using the MCC model and the overstress viscoplastic theory.The results indicated that over the strain rate range of 0.0001%/min and 50%/min,the rate response of cavity pressure for the case of partially drained expansion in MCC soil(permeability coefficient ranging from 5×10^(-6) m/s to 2.5×10^(-11) m/s)is not obvious,while the EPP response during undrained expansion in EVP soil shows rate-independent.Only the partially drained solution for cavity expansion in EVP soil captured the rate-sensitive responses of both cavity pressure and EPP,confirmed by the pressuremeter tests on the Kunming peaty soil,Saint-Herblain clay,and Burswood clay.This suggests that the rate effect results from a combination of drainage-related and time-dependent soil behavior.Parametric studies further demonstrated that both viscous behavior and the overconsolidation ratio significantly influence cylindrical cavity expansion response,and the drainage conditions during expansion can be assessed using a nondimensional velocity.展开更多
Salt caverns are widely used for energy storage.During gas storage,the internal gas pressure fluctuates cyclically in response to energy demand,making it essential to assess how these pressure variations affect rock d...Salt caverns are widely used for energy storage.During gas storage,the internal gas pressure fluctuates cyclically in response to energy demand,making it essential to assess how these pressure variations affect rock deformation.In this study,experiments were conducted under different cyclic gas pressure conditions to investigate this effect.The findings indicate that(1)the deformation process of salt rock can be segmented into three stages:the deceleration stage,the steady-state stage,and the acceleration stage.(2)When the axial pressure remains constant,both axial and radial deformations exhibit a stepwise increasing trend in response to cyclic gas pressure variations.Similarly,under axial graded loading,the deformations also demonstrate a progressive rise.By analyzing the deformation differences and model coefficient fluctuations within a single gas pressure cycle,it is found that radial deformation is higher sensitive to changes in cyclic gas pressure.(3)The axial deformation shows a stepwise increase,and the radial deformation showed a cyclic change with changing gas pressure.Therefore,the cyclic gas pressure influence factor α,axial loading influence factor β,and state variable σ^(*)are introduced to develop a viscoplastic ontological model that accounts for the impacts of cyclic gas pressure,confining pressure and axial stress.Validated by the deformation data,the new model can better fit both the axial deformation and the radial deformation of the three stages and has strong applicability and accuracy by changing only fewer parameters.The state variable rate shows the same stage as the deformation rate and residual strain of salt rock,which can better reflect the internal hardening of salt rock.展开更多
Squeezing phenomena can lead to severe loads in deep tunnels,especially in the presence of a low ratio of surrounding rock strength to overburden pressure.For this reason,it is highly imperative to analyze and identif...Squeezing phenomena can lead to severe loads in deep tunnels,especially in the presence of a low ratio of surrounding rock strength to overburden pressure.For this reason,it is highly imperative to analyze and identify a suitable methodology to estimate the squeezing potential and select a proper support system of rock mass.This study aims to reveal the causes of failure of Tishreen tunnel in the west of Syria and develop remediation measures accordingly so as to bring the tunnel back into service.The tunnel in question was subjected to successive failures such as buckling and spalling of side walls,floor heave,and extremely large convergence reaching the failure state of the tunnel lining.In this study,an effective way was demonstrated to evaluate the squeezing potential of the tunnel lining and appropriate modeling of the long-term response of a tunnel excavated in weak rock.Specifically,the causes of failure of Tishreen tunnel were first evaluated by empirical approaches.Then,a numerical model was developed using a timedependent constitutive model to investigate the time-dependent response of the tunnel lining.On this basis,this study proposed an effective reinforcement schemes including steel ribs,grout injection,ground anchors,and new lining of reinforced concrete.The results show that the Burger viscoplastic model simulates effectively the resulting deformation and creep behavior of squeezing ground.It is also observed that using a combined heavy support system can provide efficient control over squeezing deformation and maintain the serviceability of the tunnel under study.展开更多
The viscoplastic friction and nanostructure formation mechanism of laser-clad Co-based coating were studied by rotary friction between laser-clad Co-Cr-Ni-Mo coating and WC-Co rod.The friction coefficient,friction int...The viscoplastic friction and nanostructure formation mechanism of laser-clad Co-based coating were studied by rotary friction between laser-clad Co-Cr-Ni-Mo coating and WC-Co rod.The friction coefficient,friction interface temperature and axial displacement—time curves during rotary friction process were measured.The results showed that all the curves firstly experienced rising stage and then steady stage.The rising stage corresponded to sliding friction while the steady stage corresponded to viscoplastic friction.After viscoplastic friction processing,three typical zones of viscoplastic deformation zone,thermo-mechanically affected zone,and original laser-clad zone can be observed successively from the friction surface to the interior.The viscoplastic deformation significantly crushed the network M23C7 phase in original laser-clad zone and made it dispersively distributed with equiaxial shape and in nano-scale.The viscoplastic zone,in width of 37-131 μm,is mainly characterized by refined M23C7 and α-Co phase with grain size bellow 50 nm,and even a small quantity of amorphous.Thus,the hardness of viscoplastic zone about HV997 was improved compared with the hardness of original laser-clad zone about HV600.展开更多
An additional isotropic internal variable is utilized to extend the Bodner-Partom unified viscoplastic constitutive model （original B-P） to improve the modeling of rate-dependent plasticity and cyclic hardening beha...An additional isotropic internal variable is utilized to extend the Bodner-Partom unified viscoplastic constitutive model （original B-P） to improve the modeling of rate-dependent plasticity and cyclic hardening behaviors of metals. The extended model （new B-P） contains two isotropic internal variables： one plays the role of representing the fast hardening in smaller inelastic strain range, while the other evolutes at slower speed accompanied by larger accumulated inelastic deformation, such as cyclic hardening. To examine the validity of the extended constitutive model, the rate-dependent plasticity of a Ni-base superalloy Udimet 720Li at 650℃ and 700℃ are characterized using both models. Not only numerical simulations are conducted for various loading conditions by implementing both models into ABAOUS using a user material subroutine, also a systematic comparison between two models is completed. Numerical results show that the extended material constants in the new model provide more flexible capability in modeling the inelastic behavior of the material with sound accuracy.展开更多
This work is focused on simulating the rheological effects in polyamide. An experimental study is carried out in order to assess such features of polyamide as: the hysteretic behavior, the strain rate dependence, and ...This work is focused on simulating the rheological effects in polyamide. An experimental study is carried out in order to assess such features of polyamide as: the hysteretic behavior, the strain rate dependence, and the stress relaxation. The material response in tension is investigated. Digital images correlation method(DIC) is employed in order to measure the material compressibility. A newly developed constitutive model, which was previously used to simulate the mechanical response of polyethylene subjected to moderate strains and compressive loadings, is applied to capture the large strain, inelastic behavior of polyamide in tension. The gathered experimental data are utilized to determine the values of constitutive constants of viscoelasticity and plasticity, which describe the rheological properties of polyamide. The determined material parameters are included in the text. Different strategies for evaluating the material parameters are discussed. The proposed constitutive equation is implemented into the finite element(FE) system, ABAQUS, by taking advantage of the user subroutine UMAT, which allows to define custom material laws. Some exemplary FE simulations that were used to investigate the performance of the developed subroutine are described.展开更多
Plastic limit load of viscoplastic thick-walled cylinder and spherical shell subjected to internal pressure is investigated analytically using a strain gradient plasticity theory. As a result, the current solutions ca...Plastic limit load of viscoplastic thick-walled cylinder and spherical shell subjected to internal pressure is investigated analytically using a strain gradient plasticity theory. As a result, the current solutions can capture the size effect at the micron scale. Numerical results show that the smaller the inner radius of the cylinder or spherical shell, the more significant the scale effects. Results also show that the size effect is more evident with increasing strain or strain-rate sensitivity index. The classical plastic-based solutions of the same problems are shown to be a special case of the present solution.展开更多
This paper presents preliminary results of three-dimensional thermomechanical finite-element models of a parameter study to compute the current temperature and stress distribution in the subduction zone of the central...This paper presents preliminary results of three-dimensional thermomechanical finite-element models of a parameter study to compute the current temperature and stress distribution in the subduction zone of the central Andes （16°S-26°S） up to a depth of 400 km, the bottom of the asthenosphere. For this purpose a simulation running over c. 50,000 years will be realized based on the geometry of a generic subduction zone and an elasto-viscoplastic Drucker-Prager rheology. The kinematic and thermal boundary conditions as well as the rheological parameters represent the current state of the study area. In future works the model will be refined using a systematic study of physical parameters in order to estimate the influence of the main parameters （e.g. viscosity, fault friction, velocity, shear heating） on the results of the reference model presented here. The reference model is kept as simple as possible to be able to estimate the influence of the parameters in future studies in the best possible way, whilst minimizing comnutational time.展开更多
Conventional consolidation tests on reconstituted specimens of numerous natural soft clays show a decreasing of creep index Cae with increasing soil density. Based on all selected and conducted experimental results, a...Conventional consolidation tests on reconstituted specimens of numerous natural soft clays show a decreasing of creep index Cae with increasing soil density. Based on all selected and conducted experimental results, a modified creep index Cae＊ defined in double logarithmic plane lge-lgt, was plotted for various clays, from which Cae＊ can be assumed as a constant for different soil densities. Then, the modified creep index was applied to a newly developed elastic viscoplastic model. In this way, the modified creep index Ca＊ can naturally take into account the nonlinear Cae revealing the influence of soil density in the soil assemblies without additional parameters. Finally, the enhanced model was incorporated into the finite element code ABAQUS and used to simulate a consolidation test and a test embankment. The improvement of simulations by the modified creep index was highlighted by comparing simulations using the conventional creep index Cae.展开更多
Recently,stress-based dilatancy criteria have become essential tools to design underground facilities in salt formations such as gas storage caverns.However,these criteria can depend critically on the volumetric strai...Recently,stress-based dilatancy criteria have become essential tools to design underground facilities in salt formations such as gas storage caverns.However,these criteria can depend critically on the volumetric strain measurements used to deduce the dilatancy onset.Results from conventional triaxial compression tests can show different volumetric behavior depending on the loading conditions,as well as on the measurement techniques.In order to obtain a quantitative understanding of this problem,an experimental program was carried out and the testing procedure was investigated numerically under homogeneous and heterogeneous stress states.The experimental results showed that the deviatoric stress corresponding to the dilatancy onset was significantly dependent on the measurement techniques.With a heterogeneous stress state,the simulation results revealed that the strain measurements at different scales (referred to as local,hybrid or global) can provide different volumetric results with moderate to significant deviations from the idealized behavior,and hence different onsets of dilatancy.They also proved that,under low confinement,tensile stresses can take place within the compressed specimen,leading to a great deviation of the dilatancy onset from the idealized behavior.From both experimental and numerical investigations,the difference in sensitivity to the measurement techniques between the deviatoric and the volumetric behaviors is explained by the relatively small values of the volumetric strain.The non-ideal laboratory conditions have more impact on this strain than on the deviatoric one.These findings can have implications for the interpretation of the dilatancy behavior of rock salt,and hence on the geomechanical design aspects in salt formations.展开更多
This paper introduced a novel microstructure-based constitutive model designed to comprehensively characterize the intricate mechanical behavior of anisotropic clay rocks under the influence of water saturation.The pr...This paper introduced a novel microstructure-based constitutive model designed to comprehensively characterize the intricate mechanical behavior of anisotropic clay rocks under the influence of water saturation.The proposed model encompasses elastoplastic deformation,time-dependent behavior,and induced damage.A two-step homogenization process incorporates mineral compositions and porosity to determine the macroscopic elastic tensor and plastic yield criterion.The model also considers interfacial debonding between the matrix and inclusions to capture rock damage.The application of the proposed model is demonstrated through an analysis of Callovo-Oxfordian clayey rocks,specifically in the context of radioactive waste disposal in France.Model parameters are determined,followed by numerical simulations of various laboratory tests including lateral decompression tests with constant mean stress,triaxial compression tests under different water saturation conditions,and creep tests.The numerical results are compared with corresponding experimental data to assess the efficacy of the proposed model.展开更多
An energy-dissipation based viscoplastic consistency model is presented to describe the performance of concrete under dynamic loading. The development of plasticity is started with the thermodynamic hypotheses in orde...An energy-dissipation based viscoplastic consistency model is presented to describe the performance of concrete under dynamic loading. The development of plasticity is started with the thermodynamic hypotheses in order that the model may have a sound theoretical background. Independent hardening and softening and the rate dependence of concrete are described separately for tension and compression. A modified implicit backward Euler integration scheme is adopted for the numerical computation. Static and dynamic behavior of the material is illustrated with certain numerical examples at material point level and structural level, and compared with existing experimental data. Results validate the effectiveness of the model.展开更多
The average stretching direction,local rotation angular,and stretching ratio parameters of molecular trains were used to express the rheology deformation.Based on this micro geometrical deformation,the macro deformati...The average stretching direction,local rotation angular,and stretching ratio parameters of molecular trains were used to express the rheology deformation.Based on this micro geometrical deformation,the macro deformation of medium was expressed.Then,using intrinsic elasticity concept,the stress-strain relation was obtained.In this theoretic formulation,the response functions of extension ratio and rotation angular were used to express the rheology feature of medium.For medium composed by incompressible molecular trains,the local rotation angular divides rheology deformation into three kinds:viscoelastic deformation or elasticity enhancement,viscoplastic deformation or elasticity degenerate and constant elasticity range.These results explain the experimental features of rheology deformation well.展开更多
基金the National Natural Science Foundation of China(No.90410012)
文摘A coupled viscoplasticity damage constitutive model for concrete materials is developed within the framework of irreversible thermodynamics. Simultaneously the Hehnholtz free energy function and a non-associated flow potential function are given, which include the internal variables of kinematic hardening, isotropic hardening and damage. Results from the numerical simulation show that the model presented can describe the deformatioa properties of the concrete without the formal hypotheses of yield criterion and failure criteria, such as the volume dilatancy under the compression, strain-rate sensitivity, stiffness degradation and stress-softening behavior beyond the peak stress which are brought by damages and fractures. Moreover, we could benefit from the application of the finite element method based oi1 this model under complex loading because of not having to choose different constitutive models based on the deformation level.
文摘A numerical scheme is presented which enables the use of symmetric equation solvers in tangential stiffness programs for non-associated viscoplastic materials.
文摘This paper presents the parametric variational principle for Perzyna model which is one of the main constitutive relations of viscoplasticity.The principle,by which the potential energy function is minimized under a constrained condition transformed by the constitutive relations of viscoplasticity, is free from the bound of Drucker's postulate of plastic flow and consequently suitable for solving the nonassociated plastic flow problems. Furthermore, the paper has proven the presented principle and discussed the creep problem.
基金Supported by the National Natural Science Foundation of China (Grant NO. 90410012)
文摘A unified viscoplasticity constitutive model for metal materials is developed within the framework of irreversible thermodynamics, and an expression for the Helmholtz free energy function involving the parameters reflecting kinematic hardening and isotropic hardening is given. At the same time a non-associated flow potential function including the corresponding state variables is also given, from which the flow equation and the evolution equations of the internal state variables are derived. Thus, a general theoretical framework constructing a unified viscoplasticity constitutive model is given. Compared with the typical unified viscoplasticity constitutive models, the presented model evidently satisfies the irreversible thermodynamics laws. Moreover, this method not only provides a new theoretical foundation for further development of the unified viscoplasticity constitutive model, but also gives a new theoretical framework for the stress-strain analysis of more materials.
基金Supported by the National Natural Science Foundation of China (Grant No. 90410012)
文摘The traditional unified viscoplasticity constitutive model can be only applied to metal materials.The study of the unified constitutive theory for metal materials has discovered the correlation between the classical plasticity theory and the unified viscoplasticity constitutive model,thus leading to the con-cepts of the classic plastic potential and yield surface in the unified constitutive model.Moreover,this research has given the continuous expression of the classical plastic multiplier and presented the corresponding constructive method,which extends its physical significance and lays down a good foundation for the application of the unified constitutive theory to the material analysis in more fields.This paper also introduces the unified constitutive model for metal materials and geo-materials.The numerical simulation indicates that the construction should be both reasonable and practical.
基金the National Natural Science Foundation of China under grant No.12372173the Natural Science Foundation of Shanghai under grant No.23ZR1468600.
文摘Silicon,a leading candidate for electrode material for lithium-ion batteries,has garnered significant attention.During the initial lithiation process,the alloying reaction between silicon and lithium transforms the pristine silicon microstructure from crystalline to amorphous,resulting in plastic deformation of the amorphous phase.This study proposes the free volume theory to develop a fully coupled Cahn-Hilliard phase-field model that integrates viscoplastic deformation,free volume evolution,and diffusion.This model investigates the chemophysical phenomenon of self-limiting behavior occurring during the initial lithiation of silicon anodes.Unlike most existing models,the proposed model considers free volume-dependent diffusion using a physically-based approach.The model’s temporal variation in the lithiated phase thickness aligns well with experimental results,confirming the model’s accuracy.Stress field calculations reveal the coexistence of compressive and tensile stresses within the lithiated phase,which may not cause the limiting effect under the frame of the stress-induced diffusion.Analyses indicate that high effective stress increases free volume,enhancing lithium diffusion and augmenting the diffusion coefficient.Reducing the diffusion coefficient in the lithiated phase due to free volume evolution is the primary cause of self-limiting lithiation.
基金The financial support of the National Natural Science Foundation of China(Grant Nos.41972293,42272337)the Science Fund for Distinguished Young Scholars of Hubei Province(Grant No.2023AFA078)are gratefully acknowledged.
文摘Soil responds to cavity expansion is inherently rate-dependent,especially in the case of fine-grained soils.To better understand such rate effects,self-boring pressuremeter tests were conducted on Kunming peaty soil within a strain rate range of 0.1%/min to 5.0%/min.The results showed a clear dependence of cavity pressure and excess pore pressure(EPP)on strain ratesdboth increased with higher rates for a given radial displacement.In light of the experimental results,three cases of cylindrical cavity expansion were investigated using the finite element method and analytical method,partially drained expansion in Modified Cam-Clay(MCC)soil,and undrained and partially drained expansion in elastoviscoplastic(EVP)soil.The EVP behavior was and modeled using the MCC model and the overstress viscoplastic theory.The results indicated that over the strain rate range of 0.0001%/min and 50%/min,the rate response of cavity pressure for the case of partially drained expansion in MCC soil(permeability coefficient ranging from 5×10^(-6) m/s to 2.5×10^(-11) m/s)is not obvious,while the EPP response during undrained expansion in EVP soil shows rate-independent.Only the partially drained solution for cavity expansion in EVP soil captured the rate-sensitive responses of both cavity pressure and EPP,confirmed by the pressuremeter tests on the Kunming peaty soil,Saint-Herblain clay,and Burswood clay.This suggests that the rate effect results from a combination of drainage-related and time-dependent soil behavior.Parametric studies further demonstrated that both viscous behavior and the overconsolidation ratio significantly influence cylindrical cavity expansion response,and the drainage conditions during expansion can be assessed using a nondimensional velocity.
基金supported by the National Natural Science Foundation of China (No.52274073)National Key R&D Program of China (No.2024YFB4007100)+2 种基金Chongqing Natural Science Foundation Innovation and Development Joint Fund (Municipal Education Commission)(No.CSTB2024NSCQ-LZX0056)Open Research Fund of State Key Laboratory of Geomechanics and Geotechnical Engineering Safety (No.SKLGGES-024006)financial support from the Rut and Sten Brand Foundation
文摘Salt caverns are widely used for energy storage.During gas storage,the internal gas pressure fluctuates cyclically in response to energy demand,making it essential to assess how these pressure variations affect rock deformation.In this study,experiments were conducted under different cyclic gas pressure conditions to investigate this effect.The findings indicate that(1)the deformation process of salt rock can be segmented into three stages:the deceleration stage,the steady-state stage,and the acceleration stage.(2)When the axial pressure remains constant,both axial and radial deformations exhibit a stepwise increasing trend in response to cyclic gas pressure variations.Similarly,under axial graded loading,the deformations also demonstrate a progressive rise.By analyzing the deformation differences and model coefficient fluctuations within a single gas pressure cycle,it is found that radial deformation is higher sensitive to changes in cyclic gas pressure.(3)The axial deformation shows a stepwise increase,and the radial deformation showed a cyclic change with changing gas pressure.Therefore,the cyclic gas pressure influence factor α,axial loading influence factor β,and state variable σ^(*)are introduced to develop a viscoplastic ontological model that accounts for the impacts of cyclic gas pressure,confining pressure and axial stress.Validated by the deformation data,the new model can better fit both the axial deformation and the radial deformation of the three stages and has strong applicability and accuracy by changing only fewer parameters.The state variable rate shows the same stage as the deformation rate and residual strain of salt rock,which can better reflect the internal hardening of salt rock.
文摘Squeezing phenomena can lead to severe loads in deep tunnels,especially in the presence of a low ratio of surrounding rock strength to overburden pressure.For this reason,it is highly imperative to analyze and identify a suitable methodology to estimate the squeezing potential and select a proper support system of rock mass.This study aims to reveal the causes of failure of Tishreen tunnel in the west of Syria and develop remediation measures accordingly so as to bring the tunnel back into service.The tunnel in question was subjected to successive failures such as buckling and spalling of side walls,floor heave,and extremely large convergence reaching the failure state of the tunnel lining.In this study,an effective way was demonstrated to evaluate the squeezing potential of the tunnel lining and appropriate modeling of the long-term response of a tunnel excavated in weak rock.Specifically,the causes of failure of Tishreen tunnel were first evaluated by empirical approaches.Then,a numerical model was developed using a timedependent constitutive model to investigate the time-dependent response of the tunnel lining.On this basis,this study proposed an effective reinforcement schemes including steel ribs,grout injection,ground anchors,and new lining of reinforced concrete.The results show that the Burger viscoplastic model simulates effectively the resulting deformation and creep behavior of squeezing ground.It is also observed that using a combined heavy support system can provide efficient control over squeezing deformation and maintain the serviceability of the tunnel under study.
基金Project(51101126) supported by the National Natural Science Foundation of ChinaProjects(20110491684,2012T50817) supported by the China Postdoctoral Science FoundationProject(20110942K) supported by the Open Fund of State Key Laboratory of Powder Metallurgy,China
文摘The viscoplastic friction and nanostructure formation mechanism of laser-clad Co-based coating were studied by rotary friction between laser-clad Co-Cr-Ni-Mo coating and WC-Co rod.The friction coefficient,friction interface temperature and axial displacement—time curves during rotary friction process were measured.The results showed that all the curves firstly experienced rising stage and then steady stage.The rising stage corresponded to sliding friction while the steady stage corresponded to viscoplastic friction.After viscoplastic friction processing,three typical zones of viscoplastic deformation zone,thermo-mechanically affected zone,and original laser-clad zone can be observed successively from the friction surface to the interior.The viscoplastic deformation significantly crushed the network M23C7 phase in original laser-clad zone and made it dispersively distributed with equiaxial shape and in nano-scale.The viscoplastic zone,in width of 37-131 μm,is mainly characterized by refined M23C7 and α-Co phase with grain size bellow 50 nm,and even a small quantity of amorphous.Thus,the hardness of viscoplastic zone about HV997 was improved compared with the hardness of original laser-clad zone about HV600.
文摘An additional isotropic internal variable is utilized to extend the Bodner-Partom unified viscoplastic constitutive model （original B-P） to improve the modeling of rate-dependent plasticity and cyclic hardening behaviors of metals. The extended model （new B-P） contains two isotropic internal variables： one plays the role of representing the fast hardening in smaller inelastic strain range, while the other evolutes at slower speed accompanied by larger accumulated inelastic deformation, such as cyclic hardening. To examine the validity of the extended constitutive model, the rate-dependent plasticity of a Ni-base superalloy Udimet 720Li at 650℃ and 700℃ are characterized using both models. Not only numerical simulations are conducted for various loading conditions by implementing both models into ABAOUS using a user material subroutine, also a systematic comparison between two models is completed. Numerical results show that the extended material constants in the new model provide more flexible capability in modeling the inelastic behavior of the material with sound accuracy.
文摘This work is focused on simulating the rheological effects in polyamide. An experimental study is carried out in order to assess such features of polyamide as: the hysteretic behavior, the strain rate dependence, and the stress relaxation. The material response in tension is investigated. Digital images correlation method(DIC) is employed in order to measure the material compressibility. A newly developed constitutive model, which was previously used to simulate the mechanical response of polyethylene subjected to moderate strains and compressive loadings, is applied to capture the large strain, inelastic behavior of polyamide in tension. The gathered experimental data are utilized to determine the values of constitutive constants of viscoelasticity and plasticity, which describe the rheological properties of polyamide. The determined material parameters are included in the text. Different strategies for evaluating the material parameters are discussed. The proposed constitutive equation is implemented into the finite element(FE) system, ABAQUS, by taking advantage of the user subroutine UMAT, which allows to define custom material laws. Some exemplary FE simulations that were used to investigate the performance of the developed subroutine are described.
基金supported by the Ph. D. Programs Foundation of Ministry of Education of China(No. 20050403002)
文摘Plastic limit load of viscoplastic thick-walled cylinder and spherical shell subjected to internal pressure is investigated analytically using a strain gradient plasticity theory. As a result, the current solutions can capture the size effect at the micron scale. Numerical results show that the smaller the inner radius of the cylinder or spherical shell, the more significant the scale effects. Results also show that the size effect is more evident with increasing strain or strain-rate sensitivity index. The classical plastic-based solutions of the same problems are shown to be a special case of the present solution.
文摘This paper presents preliminary results of three-dimensional thermomechanical finite-element models of a parameter study to compute the current temperature and stress distribution in the subduction zone of the central Andes （16°S-26°S） up to a depth of 400 km, the bottom of the asthenosphere. For this purpose a simulation running over c. 50,000 years will be realized based on the geometry of a generic subduction zone and an elasto-viscoplastic Drucker-Prager rheology. The kinematic and thermal boundary conditions as well as the rheological parameters represent the current state of the study area. In future works the model will be refined using a systematic study of physical parameters in order to estimate the influence of the main parameters （e.g. viscosity, fault friction, velocity, shear heating） on the results of the reference model presented here. The reference model is kept as simple as possible to be able to estimate the influence of the parameters in future studies in the best possible way, whilst minimizing comnutational time.
基金Project supported by the National Natural Science Foundation of China （Nos. 41240024, 41372285, 41272317, 51278449, and 51238009）, the Research Fund for the Doctoral Program of Higher Education of China （No. 20110073120012）, and the European Project CREEP （PIAPP-GA-2011-286397）
文摘Conventional consolidation tests on reconstituted specimens of numerous natural soft clays show a decreasing of creep index Cae with increasing soil density. Based on all selected and conducted experimental results, a modified creep index Cae＊ defined in double logarithmic plane lge-lgt, was plotted for various clays, from which Cae＊ can be assumed as a constant for different soil densities. Then, the modified creep index was applied to a newly developed elastic viscoplastic model. In this way, the modified creep index Ca＊ can naturally take into account the nonlinear Cae revealing the influence of soil density in the soil assemblies without additional parameters. Finally, the enhanced model was incorporated into the finite element code ABAQUS and used to simulate a consolidation test and a test embankment. The improvement of simulations by the modified creep index was highlighted by comparing simulations using the conventional creep index Cae.
文摘Recently,stress-based dilatancy criteria have become essential tools to design underground facilities in salt formations such as gas storage caverns.However,these criteria can depend critically on the volumetric strain measurements used to deduce the dilatancy onset.Results from conventional triaxial compression tests can show different volumetric behavior depending on the loading conditions,as well as on the measurement techniques.In order to obtain a quantitative understanding of this problem,an experimental program was carried out and the testing procedure was investigated numerically under homogeneous and heterogeneous stress states.The experimental results showed that the deviatoric stress corresponding to the dilatancy onset was significantly dependent on the measurement techniques.With a heterogeneous stress state,the simulation results revealed that the strain measurements at different scales (referred to as local,hybrid or global) can provide different volumetric results with moderate to significant deviations from the idealized behavior,and hence different onsets of dilatancy.They also proved that,under low confinement,tensile stresses can take place within the compressed specimen,leading to a great deviation of the dilatancy onset from the idealized behavior.From both experimental and numerical investigations,the difference in sensitivity to the measurement techniques between the deviatoric and the volumetric behaviors is explained by the relatively small values of the volumetric strain.The non-ideal laboratory conditions have more impact on this strain than on the deviatoric one.These findings can have implications for the interpretation of the dilatancy behavior of rock salt,and hence on the geomechanical design aspects in salt formations.
文摘This paper introduced a novel microstructure-based constitutive model designed to comprehensively characterize the intricate mechanical behavior of anisotropic clay rocks under the influence of water saturation.The proposed model encompasses elastoplastic deformation,time-dependent behavior,and induced damage.A two-step homogenization process incorporates mineral compositions and porosity to determine the macroscopic elastic tensor and plastic yield criterion.The model also considers interfacial debonding between the matrix and inclusions to capture rock damage.The application of the proposed model is demonstrated through an analysis of Callovo-Oxfordian clayey rocks,specifically in the context of radioactive waste disposal in France.Model parameters are determined,followed by numerical simulations of various laboratory tests including lateral decompression tests with constant mean stress,triaxial compression tests under different water saturation conditions,and creep tests.The numerical results are compared with corresponding experimental data to assess the efficacy of the proposed model.
基金supported by the National Natural Science Foundation of China (No.90510018)
文摘An energy-dissipation based viscoplastic consistency model is presented to describe the performance of concrete under dynamic loading. The development of plasticity is started with the thermodynamic hypotheses in order that the model may have a sound theoretical background. Independent hardening and softening and the rate dependence of concrete are described separately for tension and compression. A modified implicit backward Euler integration scheme is adopted for the numerical computation. Static and dynamic behavior of the material is illustrated with certain numerical examples at material point level and structural level, and compared with existing experimental data. Results validate the effectiveness of the model.
文摘The average stretching direction,local rotation angular,and stretching ratio parameters of molecular trains were used to express the rheology deformation.Based on this micro geometrical deformation,the macro deformation of medium was expressed.Then,using intrinsic elasticity concept,the stress-strain relation was obtained.In this theoretic formulation,the response functions of extension ratio and rotation angular were used to express the rheology feature of medium.For medium composed by incompressible molecular trains,the local rotation angular divides rheology deformation into three kinds:viscoelastic deformation or elasticity enhancement,viscoplastic deformation or elasticity degenerate and constant elasticity range.These results explain the experimental features of rheology deformation well.
