The generalized Zhang-Zhu(GZZ)strength criterion was proposed as an extension to the Hoek-Brown criterion and the Mogi criterion.The introduction to mean normal stress results in a non-smooth and non-convex yield surf...The generalized Zhang-Zhu(GZZ)strength criterion was proposed as an extension to the Hoek-Brown criterion and the Mogi criterion.The introduction to mean normal stress results in a non-smooth and non-convex yield surface,which presents a challenge for updating plastic stress.Current research primarily focuses on modified smooth GZZ criteria or approximate solutions,which inevitably lead to increased computational costs or inaccuracies.In this paper,an accurate stress updating algorithm is proposed based on the original GZZ criterion.The algorithm operates entirely in the principal stress space,where numerical singularities at the intersection of yield surfaces are avoided by defining four different types of stress updating.This approach simplifies the GZZ criterion compared to its formulation in general stress space.The return mapping is employed to compute the updated stress and consistent stiffness matrix,facilitating calculations using both finite element implicit and explicit algorithms.Finally,the accuracy of the proposed method is validated using rock true triaxial test data and semianalytical solutions for stresses and displacement around a circular opening under the GZZ criterion.展开更多
Gradient-dependent plasticity is introduced into the phenomenological Johnson-Cook model to study the effects of strainhardening, strain rate sensitivity, thermal-softening, and microstructure. The microstructural eff...Gradient-dependent plasticity is introduced into the phenomenological Johnson-Cook model to study the effects of strainhardening, strain rate sensitivity, thermal-softening, and microstructure. The microstructural effect （interactions and interplay among microstructures） due to heterogeneity of texture plays an important role in the process of development or evolution of an adiabatic shear band with a certain thickness depending on the grain diameter. The distributed plastic shear strain and deformation in the shear band are derived and depend on the critical plastic shear strain corresponding to the peak flow shear stress, the coordinate or position, the internal length parameter, and the average plastic shear strain or the flow shear stress. The critical plastic shear strain, the distributed plastic shear strain, and deformation in the shear band are numerically predicted for a kind of steel deformed at a constant shear strain rate. Beyond the peak shear stress, the local plastic shear strain in the shear band is highly nonuniform and the local plastic shear deformation in the band is highly nonlinear. Shear localization is more apparent with the increase of the average plastic shear strain. The calculated distributions of the local plastic shear strain and deformation agree with the previous numerical and experimental results.展开更多
Soil undergoes both elastic and plastic deformations under different loading conditions. A relatively accurate constitutive model of soil behaviors should be capable of predicting the elastic and plastic deformations ...Soil undergoes both elastic and plastic deformations under different loading conditions. A relatively accurate constitutive model of soil behaviors should be capable of predicting the elastic and plastic deformations properly. Among a large number of elastoplastic constitutive models developed over the last several decades, constitutive models based on generalized plasticity have been successfully utilized in modeling the mechanical behavior of various soils. This paper attempts to present a review of the most recent developments of generalized plasticity models for geotechnical problems. After a brief review of generalized plasticity theories and constitutive models, limitations of the original Pastor-Zienkiewicz model in practical application are summarized. Afterwards, recent achievements in the generalized plasticity models for both saturated and unsaturated soils and their applicability are analyzed, and a general approach for modification of generalized plasticity models is highlighted.展开更多
Firstly, typical) gradient-dependent nonlocal inelastic models were briefly reviewed. Secondly, based on the principle of ‘gradient-dependent energy dissipation', a gradient-dependent constitutive model for plast...Firstly, typical) gradient-dependent nonlocal inelastic models were briefly reviewed. Secondly, based on the principle of ‘gradient-dependent energy dissipation', a gradient-dependent constitutive model for plasticity coupled with isotropic damage was presented in the framework of continuum thermodynamics. Numerical scheme for calculation of Laplacian term of damage field with the numerical results obtained by FEM calculation was proposed. Equations have been presented on the basis of Taylor series for both 2-dimensional and 3-dimensional cases, respectively. Numerical results have indicated the validity of the proposed gradient-dependent model and corresponding numerical scheme.展开更多
The present paper aims to establish a versatile strength theory suitable for elasto-plastic analysis of underground tunnel surrounding rock. In order to analyze the effects of intermediate principal stress and the roc...The present paper aims to establish a versatile strength theory suitable for elasto-plastic analysis of underground tunnel surrounding rock. In order to analyze the effects of intermediate principal stress and the rock properties on its deformation and failure of rock mass, the generalized nonlinear unified strength theory and elasto-plastic mechanics are used to deduce analytic solution of the radius and stress of tunnel plastic zone and the periphery displacement of tunnel under uniform ground stress field. The results show that: intermediate principal stress coefficient b has significant effect on the plastic range,the magnitude of stress and surrounding rock pressure. Then, the results are compared with the unified strength criterion solution and Mohr–Coulomb criterion solution, and concluded that the generalized nonlinear unified strength criterion is more applicable to elasto-plastic analysis of underground tunnel surrounding rock.展开更多
The development of geotechnical plasticity is reviewed and some problems of applying the classical plastic mechanics (CPM) to geomaterials are analyzed, and then CPM’s three hypotheses not fitted the deformation mech...The development of geotechnical plasticity is reviewed and some problems of applying the classical plastic mechanics (CPM) to geomaterials are analyzed, and then CPM’s three hypotheses not fitted the deformation mechanism of geomaterials are pointed out. By giving up the three hypotheses, a generalized plastic potential theory can be obtained from solid mechanics directly, and then the traditional plastic mechanics can be changed to a more generalized plastic mechanics, namely generalized plastic mechanics (GPM). The GPM adopts the component theory as theoretical base, so it can reflect the influence of transition of stress path. The unreasonable phenomena such as excessive dilatancy caused by adopting the normality-flow law can be avoided, and the error caused by the arbitrary assumption of plastic potential surfaces cannot be produced. The yield surface theory, hardening laws and stress-strain relations of GPM are given, and a GPM including the rotation of principal stress axes is also established. It is pointed out that the yield condition is a state parameter as well as a test parameter, and it can only be given by test. After the practical application, it is shown that the GPM cannot only be applied to the modeling theory of geomaterials but also to other fields of geomechanics such as limit analysis.展开更多
Based on the expression proposed by WANG for the local plastic shear deformation distribution in the adiabatic shear band（ASB） using gradient-dependent plasticity,the effects of 10 parameters on the adiabatic shear ...Based on the expression proposed by WANG for the local plastic shear deformation distribution in the adiabatic shear band（ASB） using gradient-dependent plasticity,the effects of 10 parameters on the adiabatic shear sensitivity were studied.The experimental data for a flow line in the ASB obtained by LIAO and DUFFY were fitted by use of the curve-fitting least squares method and the proposed expression.The critical plastic shear strains corresponding to the onset of the ASB for Ti-6Al-4V were assessed at different assigned ASB widths.It is found that the proposed expression describes well the non-linear deformation characteristics of the flow line in the ASB.Some parameters in the JOHNSON-COOK model are back-calculated using different critical plastic shear strains.The adiabatic shear sensitivity decreases as initial static yield stress,work to heat conversion factor and strain-rate parameter decrease,which is opposite to the effects of density,heat capacity,ambient temperature and strain-hardening exponent.The present model can predict the ASB width evolution process.The predicted ASB width decreases with straining until a stable value is reached.The famous model proposed by DODD and BAI only can predict a final stable value.展开更多
To consider the effects of the interactions and interplay among microstructures, gradient-dependent models of second- and fourth-order are included in the widely used phenomenological Johnson-Cook model where the effe...To consider the effects of the interactions and interplay among microstructures, gradient-dependent models of second- and fourth-order are included in the widely used phenomenological Johnson-Cook model where the effects of strain-hardening, strain rate sensitivity, and thermal-softening are successfully described. The various parameters for 1006 steel, 4340 steel and S-7 tool steel are assigned. The distributions and evolutions of the local plastic shear strain and deformation in adiabatic shear band （ASB） are predicted. The calculated results of the second- and fourth- order gradient plasticity models are compared. S-7 tool steel possesses the steepest profile of local plastic shear strain in ASB, whereas 1006 steel has the least profile. The peak local plastic shear strain in ASB for S-7 tool steel is slightly higher than that for 4340 steel and is higher than that for 1006 steel. The extent of the nonlinear distribution of the local plastic shear deformation in ASB is more apparent for the S-7 tool steel, whereas it is the least apparent for 1006 steel. In fourth-order gradient plasticity model, the profile of the local plastic shear strain in the middle of ASB has a pronounced plateau whose width decreases with increasing average plastic shear strain, leading to a shrink of the portion of linear distribution of the profile of the local plastic shear deformation. When compared with the sec- ond-order gradient plasticity model, the fourth-order gradient plasticity model shows a lower peak local plastic shear strain in ASB and a higher magnitude of plastic shear deformation at the top or base of ASB, which is due to wider ASB. The present numerical results of the second- and fourth-order gradient plasticity models are consistent with the previous numerical and experimental results at least qualitatively.展开更多
In this paper, the generalized Prandtl-Reuss (P-R) constitutive equations of elastic-plastic material in the presence of finite deformations through a new approach are studied. It analyzes the generalized P-R equation...In this paper, the generalized Prandtl-Reuss (P-R) constitutive equations of elastic-plastic material in the presence of finite deformations through a new approach are studied. It analyzes the generalized P-R equation based on the material corotational rate and clarifies the puzzling problem of the simple shear stress oscillation mentioned in some literature. The paper proposes a modified relative rotational rate with which to constitute the objective rates of stress in the generalized P-R equation and concludes that the decomposition of total deformation rate into elastic and plastic parts is not necessary in developing the generalized P-R equations. Finally, the stresses of simple shear deformation are worked out.展开更多
The generalized plasticity constitutive equations that simulate, in a unified manner, the stress-strain response and the creep behavior of rockfill materials are derived using the concept of elastoplasticity. A single...The generalized plasticity constitutive equations that simulate, in a unified manner, the stress-strain response and the creep behavior of rockfill materials are derived using the concept of elastoplasticity. A single yield surface is assumed to capture the onset of plastic strains with, however, two separate potential functions for the stress-induced plastic strains and the creep strains,respectively. The involved tensors and scalars are then specified directly, following the generalized plasticity method, to substantiate the constitutive equations. The model thus obtained is verified using triaxial compression experiments, true triaxial experiments and triaxial creep experiments. The effectiveness of the model is also demonstrated by a successful application in studying the behavior of a high concrete face rockfill dam(CFRD). It is found that for a high CFRD with a long construction period, neglecting the creep of rockfill materials during construction results in an underestimation of the deformation of the dam.The deformation and stress of the concrete slabs may also be considerably underestimated.展开更多
Solar evaporation is recognized as a prospective technique to produce freshwater from non-drinkable water using inexhaustible solar energy.However,it remains a challenge to fabricate low-cost solar evaporators with ob...Solar evaporation is recognized as a prospective technique to produce freshwater from non-drinkable water using inexhaustible solar energy.However,it remains a challenge to fabricate low-cost solar evaporators with obviously reduced water evaporation enthalpy to achieve high evaporation rates.Herein,N,O dual-doped carbon foam(NCF)is fabricated from the lowtemperature carbonization of poly(ethylene terephthalate)(PET)waste by melamine/molten salts at 340℃.During carbonization,melamine reacts with carboxylic acids of PET degradation products to yield a crosslinking network,and then molten salts catalyze the decarboxylation and dehydration to construct a stable framework.Owing to rich N,O-containing groups,3D interconnected pores,super-hydrophilicity,and ultra-low thermal conductivity(0.0599 W m^(−1) K^(−1)),NCF not only achieves high light absorbance(ca.99%)and solar-to-thermal conversion,but also promotes the formation of water cluster to reduce water evaporation enthalpy by ca.37%.Consequently,NCF exhibits a high evaporation rate(2.4 kg m^(−2) h^(−1)),surpassing the-state-of-the-art solar evaporators,and presents good antiacid/basic abilities,long-term salt-resistance,and self-cleaning ability.Importantly,a large-scale NCF-based outdoor solar desalination device is developed to produce freshwater.The daily freshwater production amount per unit area(6.3 kg)meets the two adults’daily water consumption.The trash-to-treasure strategy will give impetus to the development of low-cost,advanced solar evaporators from waste plastics for addressing the global freshwater shortage.展开更多
The generalized self-consistent finite-element iterative averaging method was adopted to analyze the elasto-plastic tensile properties of SiC whiskers reinforced aluminum matrix composites. The effects of varying fibe...The generalized self-consistent finite-element iterative averaging method was adopted to analyze the elasto-plastic tensile properties of SiC whiskers reinforced aluminum matrix composites. The effects of varying fiber's aspect ratio and volume fraction on the macroscopic elasto-plastic deformation of the composites were studied. By the analysis of microscopic stress fields, the relation between the propagation of the elasto-plastic region in the matrix and the macroscopic elasto-plastic deformation of composites was discussed. It was found that the propagation of the plastic region in the matrix between the fiber's ends would affect prominently the elasto-plastic tensile behaviour of the composites. It was shown that the characterization of the stress-strain response in terms of the 0.2% offset yield strength is incomplete.展开更多
The effect of kinematic hardening behavior on the shakedown behaviors of structure has been investigated by performing shakedown analysis for some specific problems. The results obtained only show that the shakedown l...The effect of kinematic hardening behavior on the shakedown behaviors of structure has been investigated by performing shakedown analysis for some specific problems. The results obtained only show that the shakedown limit loads of structures with kinematic hardening model are larger than or equal to those with perfectly plastic model of the same initial yield stress. To further investigate the rules governing the different shakedown behaviors of kinematic hardening structures, the extended shakedown theorem for limited kinematic hardening is applied, the shakedown condition is then proposed, and a general analytical solution for the structural shakedown limit load is thus derived. The analytical shakedown limit loads for fully reversed cyclic loading and non-fully reversed cyclic loading are then given based on the general solution. The resulting analytical solution is applied to some specific problems： a hollow specimen subjected to tension and torsion, a flanged pipe subjected to pressure and axial force and a square plate with small central hole subjected to biaxial tension. The results obtained are compared with those in literatures, they are consistent with each other. Based on the resulting general analytical solution, rules governing the general effects of kinematic hardening behavior on the shakedown behavior of structure are clearly.展开更多
The temperature rise caused by plastic deformation during the quick upsetting of tin-lead alloy and mild steel was investigated via experiments and numerical simulations aiming at a better understanding of the heat ge...The temperature rise caused by plastic deformation during the quick upsetting of tin-lead alloy and mild steel was investigated via experiments and numerical simulations aiming at a better understanding of the heat generation mechanism in friction welding. The results show that the compression amount and deformation temperature influence significantly the temperature rise during the upsetting of tin-lead alloy. The temperature rise increases with increasing the compression but decreases with increasing the deformation temperature. The simulation results are in good agreement with the experimental inspection for Sn63A alloy. The simulation results of mild steel present a similar tendency with tin-lead alloy. Moreover, the temperature rise of mild steel at elevated temperatures is comparable to that of tin-lead alloy at low temperatures.展开更多
The shakedown behavior of structures subjected to a combined loading of constant and cyclic loads has been well researched.For some specified problems,shakedown limit loads have been obtained.However,the general effec...The shakedown behavior of structures subjected to a combined loading of constant and cyclic loads has been well researched.For some specified problems,shakedown limit loads have been obtained.However,the general effect of combined loading on the structural shakedown has not yet been presented.The general analytic solution of the elastic shakedown limit load is thus derived for a structure subjected to combined loading.Polizzotto's extended static shakedown theorem for combined loading is applied.The stress field in equilibrium with the external constant load required in Polizzotto's extended theorem is constructed by subtracting the reference elastic stress field of the peak cyclic load from the elastic-plastic stress field of the combined constant load and peak cyclic load.The shakedown condition of the stress field is then derived according to the extended theorem.Through the analytical analysis of the shakedown condition,the structural shakedown behavior under combined loading is investigated.A general solution of the shakedown limit load is then derived,and the effects of the combined loading on the shakedown behavior are proposed.The obtained general analytical result is applied to a hollow tension specimen under constant tension and alternating torsion and a plate with a central hole under constant and cyclic tension.The results are consistent with the solutions reported in the literature.展开更多
Under the hypothesis that all the perfectly plastic stress components at a orach tip are the functions of θ only, making use of yield conditions and equilibrium equations. we derive the generally analytical expressio...Under the hypothesis that all the perfectly plastic stress components at a orach tip are the functions of θ only, making use of yield conditions and equilibrium equations. we derive the generally analytical expressions of the perfectly plastic stress field at a crack tip. Applying these generally analytical expressions to the concrete cracks, the analytical expressions of perfectly plastic stress fields at the tips of Mode Ⅰ Mode Ⅱ, Mode Ⅲ and Mixed Mode Ⅰ-Ⅱ cracks are obtained.展开更多
Under the condition that all the perfectly plastic stress components at a crack tip are the functions of ? only, making use of equilibrium equations and Von-Mises yield condition containing Poisson ratio, in this pape...Under the condition that all the perfectly plastic stress components at a crack tip are the functions of ? only, making use of equilibrium equations and Von-Mises yield condition containing Poisson ratio, in this paper, we derive the generally analytical expressions of perfectly plastic stress field at a stationary plane-strain crack tip. Applying these generally analytical expressions to the concrete cracks, the analytical expressions of perfectly plastic stress fields at the stationary tips of Mode I, Mode II and Mixed-Mode I-II plane-strain cracks are obtained. These analytical expressions contain Poisson ratio.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
About 1.3 billion tons of waste is being generated in the world annually. This waste is a cause of various diseases. Open dumping of waste also destroys valuable agricultural land. Various researchers have beneficiall...About 1.3 billion tons of waste is being generated in the world annually. This waste is a cause of various diseases. Open dumping of waste also destroys valuable agricultural land. Various researchers have beneficially used plastic waste in cement concrete and asphalt concrete in the past. This study aims at the use of aggregates, made from different types of plastic waste, as partial replacement of coarse aggregates in asphalt mixes. For this purpose waste is collected from different hospitals of the city. Sorted plastic from the waste consists of 64% low density polyethene, 32% high density polyethene and 4% of polypropylene. Plastic waste is shredded, heated and after cooling, pulverizes manually and mechanically. Specific gravity of plastic aggregates is 0.96. Water absorption and soundness values are 4.68% and 7.68% respectively. Impact, crushing and Loss Angeles values of plastic aggregates are 0.7%, 0.5%, and 1.1% respectively. Replacement of natural aggregates by plastic aggregates in asphalt mixes is done up to 25% with 5% incremental increase. Density of asphalt mixes decreases to 2060 kg/m<sup>3</sup>. Consequently flow increases to 5.73 mm. Maximum stability is at 20% replacement i.e. 34.57 KN. Cost analysis of the study indicates that 205% increase in stability are observed with 219% increase in cost.展开更多
基金the financial support provided by the National Key R&D Program of China(Grant No.2022YFB2302102)the National Natural Science Foundation of China(Grant Nos.42472340 and 42072308).
文摘The generalized Zhang-Zhu(GZZ)strength criterion was proposed as an extension to the Hoek-Brown criterion and the Mogi criterion.The introduction to mean normal stress results in a non-smooth and non-convex yield surface,which presents a challenge for updating plastic stress.Current research primarily focuses on modified smooth GZZ criteria or approximate solutions,which inevitably lead to increased computational costs or inaccuracies.In this paper,an accurate stress updating algorithm is proposed based on the original GZZ criterion.The algorithm operates entirely in the principal stress space,where numerical singularities at the intersection of yield surfaces are avoided by defining four different types of stress updating.This approach simplifies the GZZ criterion compared to its formulation in general stress space.The return mapping is employed to compute the updated stress and consistent stiffness matrix,facilitating calculations using both finite element implicit and explicit algorithms.Finally,the accuracy of the proposed method is validated using rock true triaxial test data and semianalytical solutions for stresses and displacement around a circular opening under the GZZ criterion.
基金This work was financially supported by the Educational Department of Liaoning Province (No.2004F052) and the National Natural Science Foundation of China (No. 50309004).
文摘Gradient-dependent plasticity is introduced into the phenomenological Johnson-Cook model to study the effects of strainhardening, strain rate sensitivity, thermal-softening, and microstructure. The microstructural effect （interactions and interplay among microstructures） due to heterogeneity of texture plays an important role in the process of development or evolution of an adiabatic shear band with a certain thickness depending on the grain diameter. The distributed plastic shear strain and deformation in the shear band are derived and depend on the critical plastic shear strain corresponding to the peak flow shear stress, the coordinate or position, the internal length parameter, and the average plastic shear strain or the flow shear stress. The critical plastic shear strain, the distributed plastic shear strain, and deformation in the shear band are numerically predicted for a kind of steel deformed at a constant shear strain rate. Beyond the peak shear stress, the local plastic shear strain in the shear band is highly nonuniform and the local plastic shear deformation in the band is highly nonlinear. Shear localization is more apparent with the increase of the average plastic shear strain. The calculated distributions of the local plastic shear strain and deformation agree with the previous numerical and experimental results.
基金supported by the Central Public Welfare Fund of China (Grant No.Y710005)the China Scholarship Council (CSC)
文摘Soil undergoes both elastic and plastic deformations under different loading conditions. A relatively accurate constitutive model of soil behaviors should be capable of predicting the elastic and plastic deformations properly. Among a large number of elastoplastic constitutive models developed over the last several decades, constitutive models based on generalized plasticity have been successfully utilized in modeling the mechanical behavior of various soils. This paper attempts to present a review of the most recent developments of generalized plasticity models for geotechnical problems. After a brief review of generalized plasticity theories and constitutive models, limitations of the original Pastor-Zienkiewicz model in practical application are summarized. Afterwards, recent achievements in the generalized plasticity models for both saturated and unsaturated soils and their applicability are analyzed, and a general approach for modification of generalized plasticity models is highlighted.
文摘Firstly, typical) gradient-dependent nonlocal inelastic models were briefly reviewed. Secondly, based on the principle of ‘gradient-dependent energy dissipation', a gradient-dependent constitutive model for plasticity coupled with isotropic damage was presented in the framework of continuum thermodynamics. Numerical scheme for calculation of Laplacian term of damage field with the numerical results obtained by FEM calculation was proposed. Equations have been presented on the basis of Taylor series for both 2-dimensional and 3-dimensional cases, respectively. Numerical results have indicated the validity of the proposed gradient-dependent model and corresponding numerical scheme.
文摘The present paper aims to establish a versatile strength theory suitable for elasto-plastic analysis of underground tunnel surrounding rock. In order to analyze the effects of intermediate principal stress and the rock properties on its deformation and failure of rock mass, the generalized nonlinear unified strength theory and elasto-plastic mechanics are used to deduce analytic solution of the radius and stress of tunnel plastic zone and the periphery displacement of tunnel under uniform ground stress field. The results show that: intermediate principal stress coefficient b has significant effect on the plastic range,the magnitude of stress and surrounding rock pressure. Then, the results are compared with the unified strength criterion solution and Mohr–Coulomb criterion solution, and concluded that the generalized nonlinear unified strength criterion is more applicable to elasto-plastic analysis of underground tunnel surrounding rock.
文摘The development of geotechnical plasticity is reviewed and some problems of applying the classical plastic mechanics (CPM) to geomaterials are analyzed, and then CPM’s three hypotheses not fitted the deformation mechanism of geomaterials are pointed out. By giving up the three hypotheses, a generalized plastic potential theory can be obtained from solid mechanics directly, and then the traditional plastic mechanics can be changed to a more generalized plastic mechanics, namely generalized plastic mechanics (GPM). The GPM adopts the component theory as theoretical base, so it can reflect the influence of transition of stress path. The unreasonable phenomena such as excessive dilatancy caused by adopting the normality-flow law can be avoided, and the error caused by the arbitrary assumption of plastic potential surfaces cannot be produced. The yield surface theory, hardening laws and stress-strain relations of GPM are given, and a GPM including the rotation of principal stress axes is also established. It is pointed out that the yield condition is a state parameter as well as a test parameter, and it can only be given by test. After the practical application, it is shown that the GPM cannot only be applied to the modeling theory of geomaterials but also to other fields of geomechanics such as limit analysis.
基金Project(20081102)supported by the Doctor Startup Foundation of Liaoning Province,China
文摘Based on the expression proposed by WANG for the local plastic shear deformation distribution in the adiabatic shear band（ASB） using gradient-dependent plasticity,the effects of 10 parameters on the adiabatic shear sensitivity were studied.The experimental data for a flow line in the ASB obtained by LIAO and DUFFY were fitted by use of the curve-fitting least squares method and the proposed expression.The critical plastic shear strains corresponding to the onset of the ASB for Ti-6Al-4V were assessed at different assigned ASB widths.It is found that the proposed expression describes well the non-linear deformation characteristics of the flow line in the ASB.Some parameters in the JOHNSON-COOK model are back-calculated using different critical plastic shear strains.The adiabatic shear sensitivity decreases as initial static yield stress,work to heat conversion factor and strain-rate parameter decrease,which is opposite to the effects of density,heat capacity,ambient temperature and strain-hardening exponent.The present model can predict the ASB width evolution process.The predicted ASB width decreases with straining until a stable value is reached.The famous model proposed by DODD and BAI only can predict a final stable value.
基金Item Sponsored by Educational Department of Liaoning Province of China (2004F052)
文摘To consider the effects of the interactions and interplay among microstructures, gradient-dependent models of second- and fourth-order are included in the widely used phenomenological Johnson-Cook model where the effects of strain-hardening, strain rate sensitivity, and thermal-softening are successfully described. The various parameters for 1006 steel, 4340 steel and S-7 tool steel are assigned. The distributions and evolutions of the local plastic shear strain and deformation in adiabatic shear band （ASB） are predicted. The calculated results of the second- and fourth- order gradient plasticity models are compared. S-7 tool steel possesses the steepest profile of local plastic shear strain in ASB, whereas 1006 steel has the least profile. The peak local plastic shear strain in ASB for S-7 tool steel is slightly higher than that for 4340 steel and is higher than that for 1006 steel. The extent of the nonlinear distribution of the local plastic shear deformation in ASB is more apparent for the S-7 tool steel, whereas it is the least apparent for 1006 steel. In fourth-order gradient plasticity model, the profile of the local plastic shear strain in the middle of ASB has a pronounced plateau whose width decreases with increasing average plastic shear strain, leading to a shrink of the portion of linear distribution of the profile of the local plastic shear deformation. When compared with the sec- ond-order gradient plasticity model, the fourth-order gradient plasticity model shows a lower peak local plastic shear strain in ASB and a higher magnitude of plastic shear deformation at the top or base of ASB, which is due to wider ASB. The present numerical results of the second- and fourth-order gradient plasticity models are consistent with the previous numerical and experimental results at least qualitatively.
文摘In this paper, the generalized Prandtl-Reuss (P-R) constitutive equations of elastic-plastic material in the presence of finite deformations through a new approach are studied. It analyzes the generalized P-R equation based on the material corotational rate and clarifies the puzzling problem of the simple shear stress oscillation mentioned in some literature. The paper proposes a modified relative rotational rate with which to constitute the objective rates of stress in the generalized P-R equation and concludes that the decomposition of total deformation rate into elastic and plastic parts is not necessary in developing the generalized P-R equations. Finally, the stresses of simple shear deformation are worked out.
基金supported by the National Key Research and Development Program of China(Grant No.2017YFC0404806)the National Natural Science Foundation of China(Grant Nos.51779152,51539006)
文摘The generalized plasticity constitutive equations that simulate, in a unified manner, the stress-strain response and the creep behavior of rockfill materials are derived using the concept of elastoplasticity. A single yield surface is assumed to capture the onset of plastic strains with, however, two separate potential functions for the stress-induced plastic strains and the creep strains,respectively. The involved tensors and scalars are then specified directly, following the generalized plasticity method, to substantiate the constitutive equations. The model thus obtained is verified using triaxial compression experiments, true triaxial experiments and triaxial creep experiments. The effectiveness of the model is also demonstrated by a successful application in studying the behavior of a high concrete face rockfill dam(CFRD). It is found that for a high CFRD with a long construction period, neglecting the creep of rockfill materials during construction results in an underestimation of the deformation of the dam.The deformation and stress of the concrete slabs may also be considerably underestimated.
基金supported by National Natural Science Foundation of China(No.51903099 and 51991353)100 Talents Program of Hubei Provincial Government,Huazhong University of Science and Technology(No.3004013134 and 2021XXJS036)+1 种基金the Innovation and Talent Recruitment Base of New Energy Chemistry and Device(No.B21003)the Open Research Fund of State Key Laboratory of Polymer Physics and Chemistry,Changchun Institute of Applied Chemistry,Chinese Academy of Sciences.
文摘Solar evaporation is recognized as a prospective technique to produce freshwater from non-drinkable water using inexhaustible solar energy.However,it remains a challenge to fabricate low-cost solar evaporators with obviously reduced water evaporation enthalpy to achieve high evaporation rates.Herein,N,O dual-doped carbon foam(NCF)is fabricated from the lowtemperature carbonization of poly(ethylene terephthalate)(PET)waste by melamine/molten salts at 340℃.During carbonization,melamine reacts with carboxylic acids of PET degradation products to yield a crosslinking network,and then molten salts catalyze the decarboxylation and dehydration to construct a stable framework.Owing to rich N,O-containing groups,3D interconnected pores,super-hydrophilicity,and ultra-low thermal conductivity(0.0599 W m^(−1) K^(−1)),NCF not only achieves high light absorbance(ca.99%)and solar-to-thermal conversion,but also promotes the formation of water cluster to reduce water evaporation enthalpy by ca.37%.Consequently,NCF exhibits a high evaporation rate(2.4 kg m^(−2) h^(−1)),surpassing the-state-of-the-art solar evaporators,and presents good antiacid/basic abilities,long-term salt-resistance,and self-cleaning ability.Importantly,a large-scale NCF-based outdoor solar desalination device is developed to produce freshwater.The daily freshwater production amount per unit area(6.3 kg)meets the two adults’daily water consumption.The trash-to-treasure strategy will give impetus to the development of low-cost,advanced solar evaporators from waste plastics for addressing the global freshwater shortage.
基金Supported by the Key Project of the Natural Science Foundation of China
文摘The generalized self-consistent finite-element iterative averaging method was adopted to analyze the elasto-plastic tensile properties of SiC whiskers reinforced aluminum matrix composites. The effects of varying fiber's aspect ratio and volume fraction on the macroscopic elasto-plastic deformation of the composites were studied. By the analysis of microscopic stress fields, the relation between the propagation of the elasto-plastic region in the matrix and the macroscopic elasto-plastic deformation of composites was discussed. It was found that the propagation of the plastic region in the matrix between the fiber's ends would affect prominently the elasto-plastic tensile behaviour of the composites. It was shown that the characterization of the stress-strain response in terms of the 0.2% offset yield strength is incomplete.
基金Supported by National Science and Technology Major Project of China(Grant No.2013ZX04003031)National Natural Science Foundation of China(Grant No.51575474)+1 种基金Hebei Provincial College Innovation Team Leader Training Program of China(Grant No.LJRC012)Hebei Provincial Natural Science Foundation of China(Grant No.E2015203223)
文摘The effect of kinematic hardening behavior on the shakedown behaviors of structure has been investigated by performing shakedown analysis for some specific problems. The results obtained only show that the shakedown limit loads of structures with kinematic hardening model are larger than or equal to those with perfectly plastic model of the same initial yield stress. To further investigate the rules governing the different shakedown behaviors of kinematic hardening structures, the extended shakedown theorem for limited kinematic hardening is applied, the shakedown condition is then proposed, and a general analytical solution for the structural shakedown limit load is thus derived. The analytical shakedown limit loads for fully reversed cyclic loading and non-fully reversed cyclic loading are then given based on the general solution. The resulting analytical solution is applied to some specific problems： a hollow specimen subjected to tension and torsion, a flanged pipe subjected to pressure and axial force and a square plate with small central hole subjected to biaxial tension. The results obtained are compared with those in literatures, they are consistent with each other. Based on the resulting general analytical solution, rules governing the general effects of kinematic hardening behavior on the shakedown behavior of structure are clearly.
文摘The temperature rise caused by plastic deformation during the quick upsetting of tin-lead alloy and mild steel was investigated via experiments and numerical simulations aiming at a better understanding of the heat generation mechanism in friction welding. The results show that the compression amount and deformation temperature influence significantly the temperature rise during the upsetting of tin-lead alloy. The temperature rise increases with increasing the compression but decreases with increasing the deformation temperature. The simulation results are in good agreement with the experimental inspection for Sn63A alloy. The simulation results of mild steel present a similar tendency with tin-lead alloy. Moreover, the temperature rise of mild steel at elevated temperatures is comparable to that of tin-lead alloy at low temperatures.
基金Sponsored by the National Natural Science Foundation of China(Grant No.51575474)the College Innovation Team Leader Training Program of Province(Grant No.LJRC012)the Natural Science Foundation of Hebei Province,China(Grant No.E2015203220)
文摘The shakedown behavior of structures subjected to a combined loading of constant and cyclic loads has been well researched.For some specified problems,shakedown limit loads have been obtained.However,the general effect of combined loading on the structural shakedown has not yet been presented.The general analytic solution of the elastic shakedown limit load is thus derived for a structure subjected to combined loading.Polizzotto's extended static shakedown theorem for combined loading is applied.The stress field in equilibrium with the external constant load required in Polizzotto's extended theorem is constructed by subtracting the reference elastic stress field of the peak cyclic load from the elastic-plastic stress field of the combined constant load and peak cyclic load.The shakedown condition of the stress field is then derived according to the extended theorem.Through the analytical analysis of the shakedown condition,the structural shakedown behavior under combined loading is investigated.A general solution of the shakedown limit load is then derived,and the effects of the combined loading on the shakedown behavior are proposed.The obtained general analytical result is applied to a hollow tension specimen under constant tension and alternating torsion and a plate with a central hole under constant and cyclic tension.The results are consistent with the solutions reported in the literature.
文摘Under the hypothesis that all the perfectly plastic stress components at a orach tip are the functions of θ only, making use of yield conditions and equilibrium equations. we derive the generally analytical expressions of the perfectly plastic stress field at a crack tip. Applying these generally analytical expressions to the concrete cracks, the analytical expressions of perfectly plastic stress fields at the tips of Mode Ⅰ Mode Ⅱ, Mode Ⅲ and Mixed Mode Ⅰ-Ⅱ cracks are obtained.
文摘Under the condition that all the perfectly plastic stress components at a crack tip are the functions of ? only, making use of equilibrium equations and Von-Mises yield condition containing Poisson ratio, in this paper, we derive the generally analytical expressions of perfectly plastic stress field at a stationary plane-strain crack tip. Applying these generally analytical expressions to the concrete cracks, the analytical expressions of perfectly plastic stress fields at the stationary tips of Mode I, Mode II and Mixed-Mode I-II plane-strain cracks are obtained. These analytical expressions contain Poisson ratio.
文摘The results in Ref. [1] are not suitable for the cases of β≥2. For this reason, byusing the methods in Ref [1] and Ref [2], we derive the general expressions ofamsotropic plastic fields at a rapidly propagating plane-stress crack-tip for both thecases of β=2 and β>2 .
文摘About 1.3 billion tons of waste is being generated in the world annually. This waste is a cause of various diseases. Open dumping of waste also destroys valuable agricultural land. Various researchers have beneficially used plastic waste in cement concrete and asphalt concrete in the past. This study aims at the use of aggregates, made from different types of plastic waste, as partial replacement of coarse aggregates in asphalt mixes. For this purpose waste is collected from different hospitals of the city. Sorted plastic from the waste consists of 64% low density polyethene, 32% high density polyethene and 4% of polypropylene. Plastic waste is shredded, heated and after cooling, pulverizes manually and mechanically. Specific gravity of plastic aggregates is 0.96. Water absorption and soundness values are 4.68% and 7.68% respectively. Impact, crushing and Loss Angeles values of plastic aggregates are 0.7%, 0.5%, and 1.1% respectively. Replacement of natural aggregates by plastic aggregates in asphalt mixes is done up to 25% with 5% incremental increase. Density of asphalt mixes decreases to 2060 kg/m<sup>3</sup>. Consequently flow increases to 5.73 mm. Maximum stability is at 20% replacement i.e. 34.57 KN. Cost analysis of the study indicates that 205% increase in stability are observed with 219% increase in cost.
