Organic ferroelastics with metal free features and intrinsically light weight are highly desirable for future applications in flexible,smart and biocompatible devices.However,organoferroelastics with plastic phase tra...Organic ferroelastics with metal free features and intrinsically light weight are highly desirable for future applications in flexible,smart and biocompatible devices.However,organoferroelastics with plastic phase transition have rarely been reported yet.Herein,we discovered ferroelasticity in a pair of organic enantiomers,(1S and/or 1R)-2,10-camphorsultam(S-and R-CPS),which undergoes a high-T_(c)plastic phase transition.Both large entropies change of∼45 J mol^(-1)K^(-1)and evidently ductile deformation process confirm the plastic phase feature.Strip-like ferroelastic domain patterns and bidirectional domain movements have been observed via polarized light microscopy and nanoindentation technique,respectively.This work highlights the discovery of organic ferroelastic combining the features of enantiomers and plastic phase transition,which contributes insights into exploration of organic multifunctional materials.展开更多
Porous pre-sintered zirconia is subject to white machining during which its elasticity, plasticity and resistance to machining-induced damage determine its machinability and final quality. This study used nanoindentat...Porous pre-sintered zirconia is subject to white machining during which its elasticity, plasticity and resistance to machining-induced damage determine its machinability and final quality. This study used nanoindentation techniques and the Sakai＇s series elastic and plastic deformation model to extract the resistance to plastic deformation from the plane strain modulus and the contact hardness for presintered zirconia. The modulus and the resistance to plasticity were used to calculate the relative amount of elasticity and plasticity. The fracture energy and the normalized indentation absorbed energy were used to deconvolute the resistance to machining-induced cracking based on the Sakai-Nowak model. All properties were extracted at a 10 mN peak load and loading rates of 0.1-2 mN/s to determine the loading rate effects on these properties. We found that the resistance to plasticity and the resistance to machining-induced cracking were independent of the loading rate （ANOVA, p 〉 0.05）. The elastic and plastic displacements depended on the loading rate through power laws. This loading rate-dependent deformation behaviour was explained by the maximum shear stress generated underneath the indenter and the indentation energy. The plastic deformation components and the indentation absorbed energy at all loading rates were higher than the elastic deformation components and the elastic strain energy, respectively. Finally, we established the linkage among the pore structure, indentation behaviour and machinability of pre-sintered zirconia.展开更多
On the basis of the two geological factors rock structure and ground stress environment,a visco elastic plastic model is established to analyze the rock stability of dam foundation and dam abutment during excavation...On the basis of the two geological factors rock structure and ground stress environment,a visco elastic plastic model is established to analyze the rock stability of dam foundation and dam abutment during excavation by a kind of FE condensed method.Rock mechanics is applied in analysing the dynamic process of displacements,stresses,yielding destruction of construction base level,soft interface of dam foundation.Results of the FE analysis indicate that theories and methods in this paper are reasonable and reliable.展开更多
An analytical model is developed to assess the elastic-plastic dynamic response of fully backed sandwich plates under localized impulse load.The core is modeled as an elastic-perfectly plastic foundation.The top face ...An analytical model is developed to assess the elastic-plastic dynamic response of fully backed sandwich plates under localized impulse load.The core is modeled as an elastic-perfectly plastic foundation.The top face sheet is treated as an individual plate resting on the foundation.The elastic-plastic analysis for the top face sheet is based on a minimum principle in dynamic plasticity associated with the finite difference technique.The effects of spatial and temporal distributions of the impulsive loading on the dynamic response of sandwich plates are discussed.The model can be used to predict the impulse-induced local effect on fully backed sandwich plates.展开更多
An elastic and plastic mechanical model is proposed to characterize the normal contact of rough surfaces. The contact process is considered as three separated contact regimes, i.e., the fully elastic, mixed elastic一p...An elastic and plastic mechanical model is proposed to characterize the normal contact of rough surfaces. The contact process is considered as three separated contact regimes, i.e., the fully elastic, mixed elastic一plastic and fully plastic ones. The Hertzian elastic contact solutions and the classical fully plastic contact model of Abbott and Fires tone are used to model the contact behaviors of fully elastically deformed asperities and fully plastically deformed ones, respectively. For the mixed elastic-plastic regime, an improved Hermit interpolation method is applied to enforce the continuity and smoothness at the critical contact interference, and to decrease the interpolation waving effect by transforming the physical quantities of contact load into logarithmic coordinates. The contac t model of rough surfaces is formula ted by using the Greenwood and Williamson^ statistics analysis. Comparisons with the CEB, ZMC and KE models are then performed to examine the effects of plasticity index and mean separation. Agreeing well with the ZMC model, our results show that the total contact load of rough surfaces decreases with the increase in mean separation, and the difference between the prediction results of elastic models and the plastic ones also decreases, indicating that the contact behaviors mainly dominated by plastically deformed asperities have been changed to be controlled by elastically deformed ones. Larger plasticity index represents more plastically deformed asperities, inducing normal contact behaviors mainly dominated by plastic solutions.展开更多
Based on the experimental results of super-elastic NiTi alloy, a three-dimensional super-elastic constitutive model including both of stress-induced martensite transformation and plasticity is constructed in a framewo...Based on the experimental results of super-elastic NiTi alloy, a three-dimensional super-elastic constitutive model including both of stress-induced martensite transformation and plasticity is constructed in a framework of general inelasticity. In the proposed model, transformation hardening, reverse transformation of stress-induced martensite, elastic mismatch between the austenite and martensite phases, and temperature-dependence of transformation stress and elastic modulus of each phase are considered. The plastic yielding of martensite occurred under high stress is addressed by a bilinear isotropic hardening rule. Drucker-Prager-typed transformation surfaces are employed to describe the asymmetric behavior of NiTi alloy in tension and compression. The prediction capability of the proposed model is verified by comparing the simulated results with the correspondent experimental ones. Based on backward Euler＇s integration, a new expression of consistent tangent modulus is derived. The proposed model is then implemented into a finite element package ABAQUS by user-subroutine UMAT. Finally, the validity of such implementation was verified by some numerical samples.展开更多
A new viscoelastic-plastic （VEP） constitutive model for sea ice dynamics was developed based on continuum mechanics. This model consists of four components： Kelvin-Vogit viscoelastic model, Mohr-Coulomb yielding cr...A new viscoelastic-plastic （VEP） constitutive model for sea ice dynamics was developed based on continuum mechanics. This model consists of four components： Kelvin-Vogit viscoelastic model, Mohr-Coulomb yielding criterion, associated normality flow rule for plastic rehololgy, and hydrostatic pressure. The numerical simulations for ice motion in an idealized rectangular basin were made using smoothed particle hydrodynamics （SPH） method, and compared with the analytical solution as well as those based on the modified viscous plastic（VP） model and static ice jam theory. These simulations show that the new VEP model can simulate ice dynamics accurately. The new constitutive model was further applied to simulate ice dynamics of the Bohai Sea and compared with the traditional VP, and modified VP models. The results of the VEP model are compared better with the satellite remote images, and the simulated ice conditions in the JZ20-2 oil platform area were more reasonable.展开更多
The effect of soft elasticity, i.e., a relatively small value of the ratio of Young＇s modulus to yield strength and plastic compressibility on the indentation of isotropically hardening elastic-viscoplastic solids is...The effect of soft elasticity, i.e., a relatively small value of the ratio of Young＇s modulus to yield strength and plastic compressibility on the indentation of isotropically hardening elastic-viscoplastic solids is investigated. Calcu- lations are carried out for indentation of a perfectly sticking rigid sharp indenter into a cylinder modeling indentation of a half space. The material is characterized by a finite strain elastic-viscoplastic constitutive relation that allows for plas- tic as well as elastic compressibility. Both soft elasticity and plastic compressibility significantly reduce the ratio of nomi- nal indentation hardness to yield strength. A linear relation is found between the nominal indentation hardness and the log- arithm of the ratio of Young＇s modulus to yield strength, but with a different coefficient than reported in previous studies. The nominal indentation hardness decreases rapidly for small deviations from plastic incompressibility and then decreases rather slowly for values of the plastic Poisson＇s ratio less than 0.25. For both soft elasticity and plastic compressibility, the main reason for the lower values of indentation hardness is related to the reduction in the hydrostatic stress level in the material below the indenter.展开更多
A Harten-Lax-van Leer-contact （HLLC） approximate Riemann solver is built with elastic waves （HLLCE） for one-dimensional elastic-plastic flows with a hypo- elastic constitutive model and the von Mises＇ yielding cr...A Harten-Lax-van Leer-contact （HLLC） approximate Riemann solver is built with elastic waves （HLLCE） for one-dimensional elastic-plastic flows with a hypo- elastic constitutive model and the von Mises＇ yielding criterion. Based on the HLLCE, a third-order cell-centered Lagrangian scheme is built for one-dimensional elastic-plastic problems. A number of numerical experiments are carried out. The numerical results show that the proposed third-order scheme achieves the desired order of accuracy. The third-order scheme is used to the numerical solution of the problems with elastic shock waves and elastic rarefaction waves. The numerical results are compared with a reference solution and the results obtained by other authors. The comparison shows that the pre- sented high-order scheme is convergent, stable, and essentially non-oscillatory. Moreover, the HLLCE is more efficient than the two-rarefaction Riemann solver with elastic waves （TRRSE）展开更多
The elastic-plastic stress distribution and the elastic-plastic boundary con- figuration near a crack surface region are significant but hard to obtain by means of the conventional analysis. A crack line analysis meth...The elastic-plastic stress distribution and the elastic-plastic boundary con- figuration near a crack surface region are significant but hard to obtain by means of the conventional analysis. A crack line analysis method is developed in this paper by consid- ering the crack surface as an extension of the crack line. The stresses in the plastic zone, the length, and the unit normal vector of the elastic-plastic boundary near a crack surface region are obtained for an antiplane crack in an elastic-perfectly plastic solid. The usual small scale yielding assumptions are not needed in the analysis.展开更多
In this paper, the magnetic-elastic-plastic deformation behavior is studied for a ferromagnetic plate with simple supports. The perturbation formula of magnetic force is first derived based on the perturbation techniq...In this paper, the magnetic-elastic-plastic deformation behavior is studied for a ferromagnetic plate with simple supports. The perturbation formula of magnetic force is first derived based on the perturbation technique, and is then applied to the analysis of deformation characteristics with emphasis laid on the analyses of modes, symmetry of deformation and influences of incident angle of applied magnetic field on the plate deformation. The theoretical analyses offer explanations why the configuration offer- romagnetic rectangular plate with simple supports under an oblique magnetic field is in-wavy type along the x-direction, and why the largest deformation of the ferromagnetic plate occurs at the incident angle of 45°for the magnetic field. A numerical code based on the finite element method is developed to simulate quantitatively behaviors of the nonlinearly coupled multi-field problem. Some characteristic curves are plotted to illustrate the magneto--elastic-plastic deflections, and to reveal how the deflections can be influenced by the incident angle of applied magnetic field. The deformation characteristics obtained from the numerical simulations are found in good agreement with the theoretical analyses.展开更多
The near crack line analysis method has been used in the present paper,The classical small scale yielding conditions have been completely abandoned in the analyses and one inappropriate matching condition used to be u...The near crack line analysis method has been used in the present paper,The classical small scale yielding conditions have been completely abandoned in the analyses and one inappropriate matching condition used to be used at the elasticplastic boundary has been corrected.The reasonable solution of the plastic stresses near the crack line region has been established.By matching the plastic stresses with the exact elastic stresses at the elastic-plastic boundary,the plastic stresses the length of the plastic zone and the unit normal vector of the elastic-plastic boundary near the crock line region have been obtained for a mode I crack under uniaxial tension,as well as a mode I crack under biaxial tension,which shows that for both conditions the plastic stress componentsσy, and σsy.he length of the plastic zone and the unit normal vector of the elastic-plastic boundary are quite the same while the plastic stress σs is different.展开更多
Crack line analysis is an effective way to solve elastic-plastic crack problems. Application of the method does not need the traditional small-scale yielding conditions and can obtain sufficiently accurate solutions n...Crack line analysis is an effective way to solve elastic-plastic crack problems. Application of the method does not need the traditional small-scale yielding conditions and can obtain sufficiently accurate solutions near the crack line. To address mode- Ⅲ crack problems under the perfect elastic-plastic condition, matching procedures of the crack line analysis method axe summarized and refined to give general forms and formulation steps of plastic field, elastic-plastic boundary, and elastic-plastic matching equations near the crack line. The research unifies mode-III crack problems under different conditions into a problem of determining four integral constants with four matching equations. An example is given to verify correctness, conciseness, and generality of the procedure.展开更多
Detecting stress concentration, especially critical stress state leading to structure damage or failure, is one of the most important tasks of equipment diagnosis. Metal magnetic memory technique needs further researc...Detecting stress concentration, especially critical stress state leading to structure damage or failure, is one of the most important tasks of equipment diagnosis. Metal magnetic memory technique needs further research to evaluate stress concentration quantitatively due to ambiguous physical mechanism, though it has potential to detect early defects in ferromagnetic materials. Mild Q235 steel defective specimens in demagnetization state were loaded in tension up to visible necking, with magnetic memory signals measurement made at increasing stress levels. Magnetic signals varied greatly under first several loadings and subsequently tended to stability in the elastic region, which showed that the magnetization always approaches the anhysteretic magnetization curve and was explained by the theory of magnetomechanical effect. In the plastic stage, an abnormal wave occurred in the stress concentration zone and its height value was sensitive to plastic deformation levels and dependent on the distance between the probe and defect, in accordance with the simulation results based on the magnetic dipole model. Different magnetic signal characteristics in the elastic-plastic region indicate that the magnetic memory technique can identify macroyielding and early damage, which is of profound significance for ensuring safe operation of equipment in service.展开更多
For a homogeneous,continuous,and isotropic material whose constitutive relationships meets with the Ramberg-Osgood law(R-O law),the energy in the elastoplastic indentation with a ball indenter was theoretically analyz...For a homogeneous,continuous,and isotropic material whose constitutive relationships meets with the Ramberg-Osgood law(R-O law),the energy in the elastoplastic indentation with a ball indenter was theoretically analyzed,and the proportional superposition of energy in pure elasticity and pure plasticity during indentation was considered based on the equivalence of energy density.Subsequently,a Proportional Superposition-based Elasto Plastic Model(PS-EPM)was developed to describe the relationships between the displacement and the load during the ball indentation.Furthermore,a new test method of Ball Indentation based on Elastoplastic Proportional Superposition(BI-EPS)was developed to obtain the constitutive relationships of R-O law materials.The load–displacement curves predicted using the PS-EPM model were found to agree closely with the Finite Element Analysis(FEA)results.Moreover,the stress vs.strain curves predicted using the BI-EPS method were in better agreement with those obtained by FEA.Additionally,ball indentation was performed on eleven types of metal materials including five types of aluminum alloys and six types of steel.The test results showed that the stress vs.strain relationships and the tensile strength values predicted using the proposed BI-EPS method agreed well with the results obtained using conventional uniaxial tensile tests.展开更多
Using the finite element code ANSYS/LS-DYNA, a dynamic finite element modelwith an elastic-linear-kinematic-hardening plastic material is established to analyzeelastic-plastic stresses in the railhead in the impact pr...Using the finite element code ANSYS/LS-DYNA, a dynamic finite element modelwith an elastic-linear-kinematic-hardening plastic material is established to analyzeelastic-plastic stresses in the railhead in the impact process of wheel and rail occurring at thegap of rail joint. The model is based on the discrete elastic support condition of the rails, whichis suitable for the actual situation of wheel/track rolling contact. In the analysis the influencesof axle load, yield stress and tangent modulus of rail material on the stresses and strains areinvestigated in detail. The distribution of stresses and strains in the jointed railhead are given.It is found that the axle load, yield stress and tangent modulus of rail material greatly affect thestresses and strains in the railhead during impacting. The study provides a reliable method anduseful datum for the further research on fatigue and wear of railhead and improving the rail jointmode.展开更多
Some possible alternative solutions of near-tip fields are studied for plane-strain Mode-I qua- si-static steady crack growth in incompressible(v=1/2)elastic perfectly-plastic media.A group of four-sector so- lutions ...Some possible alternative solutions of near-tip fields are studied for plane-strain Mode-I qua- si-static steady crack growth in incompressible(v=1/2)elastic perfectly-plastic media.A group of four-sector so- lutions and a three-sector solution in which the elastic-unloading region vanishes are given.Stress functions,plas- tic flow factors and plastic strains in each region are also given.展开更多
An analysis of buckling/snapping and bending behaviors of magneto-elastic-plastic interaction and coupling for cantilever rectangular soft ferromagnetic plates is presented. Based on the expression of magnetic force f...An analysis of buckling/snapping and bending behaviors of magneto-elastic-plastic interaction and coupling for cantilever rectangular soft ferromagnetic plates is presented. Based on the expression of magnetic force from the variational principle of ferromagnetic plates, the buckling and bending theory of thin plates, the Mises yield criterion and the increment theory for plastic deformation, we establish a numerical code to quantitatively simulate the behaviors of the nonlinearly multi-fields coupling problems by the finite element method. Along with the phenomena of buckling/snapping and bending, or the characteristic curve of deflection versus magnitude of applied magnetic fields being numerically displayed, the critical loads of buckling/snapping, and the influences of plastic deformation and the width of plate on these critical loads, the plastic regions expanding with the magnitude of applied magnetic field, as well as the evolvement of deflection configuration of the plate are numerically obtained in a case study.展开更多
The reverse analysis provides a convenient method to determine four elastic-plastic parameters through an indentation curve such as Young s modulus E, hardness H, yield strength σy and strain hardening exponent n. In...The reverse analysis provides a convenient method to determine four elastic-plastic parameters through an indentation curve such as Young s modulus E, hardness H, yield strength σy and strain hardening exponent n. In this paper, mathematical analysis on a reverse algorithm from Dao model （Dao et al., Acta Mater., 2001, 49, 3899） was carried out, which thought that only when 20 ≤E＊/σ0.033≤ 26 and 0.3n≤ 0.5, the reverse algorithm would yield two solutions of n by dimensionless function Π2. It is shown that, however, there are also two solutions of n when 20≤E＊/σ0.033≤ 26 and 0≤n0.1. A unique n can be obtained by dimensionless function Π3 instead of Π2 in these two ranges. E and H can be uniquely determined by a full indentation curve, and σy can be determined if n is unique. Furthermore, sensitivity analysis on obtaining n from dimensionless function Π3 or Π2 has been made.展开更多
基金supported by the National Natural Science Foundation of China(No.22271131)the Department of Science and Technology in Jiangxi Province(No.20225BCJ23029).
文摘Organic ferroelastics with metal free features and intrinsically light weight are highly desirable for future applications in flexible,smart and biocompatible devices.However,organoferroelastics with plastic phase transition have rarely been reported yet.Herein,we discovered ferroelasticity in a pair of organic enantiomers,(1S and/or 1R)-2,10-camphorsultam(S-and R-CPS),which undergoes a high-T_(c)plastic phase transition.Both large entropies change of∼45 J mol^(-1)K^(-1)and evidently ductile deformation process confirm the plastic phase feature.Strip-like ferroelastic domain patterns and bidirectional domain movements have been observed via polarized light microscopy and nanoindentation technique,respectively.This work highlights the discovery of organic ferroelastic combining the features of enantiomers and plastic phase transition,which contributes insights into exploration of organic multifunctional materials.
基金supported by the JCU Collaboration Grants Scheme awarded to L.Yin
文摘Porous pre-sintered zirconia is subject to white machining during which its elasticity, plasticity and resistance to machining-induced damage determine its machinability and final quality. This study used nanoindentation techniques and the Sakai＇s series elastic and plastic deformation model to extract the resistance to plastic deformation from the plane strain modulus and the contact hardness for presintered zirconia. The modulus and the resistance to plasticity were used to calculate the relative amount of elasticity and plasticity. The fracture energy and the normalized indentation absorbed energy were used to deconvolute the resistance to machining-induced cracking based on the Sakai-Nowak model. All properties were extracted at a 10 mN peak load and loading rates of 0.1-2 mN/s to determine the loading rate effects on these properties. We found that the resistance to plasticity and the resistance to machining-induced cracking were independent of the loading rate （ANOVA, p 〉 0.05）. The elastic and plastic displacements depended on the loading rate through power laws. This loading rate-dependent deformation behaviour was explained by the maximum shear stress generated underneath the indenter and the indentation energy. The plastic deformation components and the indentation absorbed energy at all loading rates were higher than the elastic deformation components and the elastic strain energy, respectively. Finally, we established the linkage among the pore structure, indentation behaviour and machinability of pre-sintered zirconia.
文摘On the basis of the two geological factors rock structure and ground stress environment,a visco elastic plastic model is established to analyze the rock stability of dam foundation and dam abutment during excavation by a kind of FE condensed method.Rock mechanics is applied in analysing the dynamic process of displacements,stresses,yielding destruction of construction base level,soft interface of dam foundation.Results of the FE analysis indicate that theories and methods in this paper are reasonable and reliable.
基金supported by the National Natural Science Foundation of China (No.10602005)
文摘An analytical model is developed to assess the elastic-plastic dynamic response of fully backed sandwich plates under localized impulse load.The core is modeled as an elastic-perfectly plastic foundation.The top face sheet is treated as an individual plate resting on the foundation.The elastic-plastic analysis for the top face sheet is based on a minimum principle in dynamic plasticity associated with the finite difference technique.The effects of spatial and temporal distributions of the impulsive loading on the dynamic response of sandwich plates are discussed.The model can be used to predict the impulse-induced local effect on fully backed sandwich plates.
文摘An elastic and plastic mechanical model is proposed to characterize the normal contact of rough surfaces. The contact process is considered as three separated contact regimes, i.e., the fully elastic, mixed elastic一plastic and fully plastic ones. The Hertzian elastic contact solutions and the classical fully plastic contact model of Abbott and Fires tone are used to model the contact behaviors of fully elastically deformed asperities and fully plastically deformed ones, respectively. For the mixed elastic-plastic regime, an improved Hermit interpolation method is applied to enforce the continuity and smoothness at the critical contact interference, and to decrease the interpolation waving effect by transforming the physical quantities of contact load into logarithmic coordinates. The contac t model of rough surfaces is formula ted by using the Greenwood and Williamson^ statistics analysis. Comparisons with the CEB, ZMC and KE models are then performed to examine the effects of plasticity index and mean separation. Agreeing well with the ZMC model, our results show that the total contact load of rough surfaces decreases with the increase in mean separation, and the difference between the prediction results of elastic models and the plastic ones also decreases, indicating that the contact behaviors mainly dominated by plastically deformed asperities have been changed to be controlled by elastically deformed ones. Larger plasticity index represents more plastically deformed asperities, inducing normal contact behaviors mainly dominated by plastic solutions.
基金supported by the New Century Excellent Talents in University (No.NCET05-0796)National Natural Science Foundation of China (No.50625515)the Innovation Foundation of Southwest Jiaotong University (2008)
文摘Based on the experimental results of super-elastic NiTi alloy, a three-dimensional super-elastic constitutive model including both of stress-induced martensite transformation and plasticity is constructed in a framework of general inelasticity. In the proposed model, transformation hardening, reverse transformation of stress-induced martensite, elastic mismatch between the austenite and martensite phases, and temperature-dependence of transformation stress and elastic modulus of each phase are considered. The plastic yielding of martensite occurred under high stress is addressed by a bilinear isotropic hardening rule. Drucker-Prager-typed transformation surfaces are employed to describe the asymmetric behavior of NiTi alloy in tension and compression. The prediction capability of the proposed model is verified by comparing the simulated results with the correspondent experimental ones. Based on backward Euler＇s integration, a new expression of consistent tangent modulus is derived. The proposed model is then implemented into a finite element package ABAQUS by user-subroutine UMAT. Finally, the validity of such implementation was verified by some numerical samples.
基金The authors would like to acknowledge the supports by the National Natural Science Foundation of China under contract No.40206004partly by the East-Asia and Pacific Program of US National Science Foundation under contract No.INT-9912246.
文摘A new viscoelastic-plastic （VEP） constitutive model for sea ice dynamics was developed based on continuum mechanics. This model consists of four components： Kelvin-Vogit viscoelastic model, Mohr-Coulomb yielding criterion, associated normality flow rule for plastic rehololgy, and hydrostatic pressure. The numerical simulations for ice motion in an idealized rectangular basin were made using smoothed particle hydrodynamics （SPH） method, and compared with the analytical solution as well as those based on the modified viscous plastic（VP） model and static ice jam theory. These simulations show that the new VEP model can simulate ice dynamics accurately. The new constitutive model was further applied to simulate ice dynamics of the Bohai Sea and compared with the traditional VP, and modified VP models. The results of the VEP model are compared better with the satellite remote images, and the simulated ice conditions in the JZ20-2 oil platform area were more reasonable.
文摘The effect of soft elasticity, i.e., a relatively small value of the ratio of Young＇s modulus to yield strength and plastic compressibility on the indentation of isotropically hardening elastic-viscoplastic solids is investigated. Calcu- lations are carried out for indentation of a perfectly sticking rigid sharp indenter into a cylinder modeling indentation of a half space. The material is characterized by a finite strain elastic-viscoplastic constitutive relation that allows for plas- tic as well as elastic compressibility. Both soft elasticity and plastic compressibility significantly reduce the ratio of nomi- nal indentation hardness to yield strength. A linear relation is found between the nominal indentation hardness and the log- arithm of the ratio of Young＇s modulus to yield strength, but with a different coefficient than reported in previous studies. The nominal indentation hardness decreases rapidly for small deviations from plastic incompressibility and then decreases rather slowly for values of the plastic Poisson＇s ratio less than 0.25. For both soft elasticity and plastic compressibility, the main reason for the lower values of indentation hardness is related to the reduction in the hydrostatic stress level in the material below the indenter.
基金Project supported by the National Natural Science Foundation of China(Nos.11172050 and11672047)the Science and Technology Foundation of China Academy of Engineering Physics(No.2013A0202011)
文摘A Harten-Lax-van Leer-contact （HLLC） approximate Riemann solver is built with elastic waves （HLLCE） for one-dimensional elastic-plastic flows with a hypo- elastic constitutive model and the von Mises＇ yielding criterion. Based on the HLLCE, a third-order cell-centered Lagrangian scheme is built for one-dimensional elastic-plastic problems. A number of numerical experiments are carried out. The numerical results show that the proposed third-order scheme achieves the desired order of accuracy. The third-order scheme is used to the numerical solution of the problems with elastic shock waves and elastic rarefaction waves. The numerical results are compared with a reference solution and the results obtained by other authors. The comparison shows that the pre- sented high-order scheme is convergent, stable, and essentially non-oscillatory. Moreover, the HLLCE is more efficient than the two-rarefaction Riemann solver with elastic waves （TRRSE）
基金supported by the National Natural Science Foundation of China (No.10672196)
文摘The elastic-plastic stress distribution and the elastic-plastic boundary con- figuration near a crack surface region are significant but hard to obtain by means of the conventional analysis. A crack line analysis method is developed in this paper by consid- ering the crack surface as an extension of the crack line. The stresses in the plastic zone, the length, and the unit normal vector of the elastic-plastic boundary near a crack surface region are obtained for an antiplane crack in an elastic-perfectly plastic solid. The usual small scale yielding assumptions are not needed in the analysis.
基金the National Natural Science Foundation of China (10672070, 10302009)the National Basic Research Program of China (2007CB607560)+1 种基金the Program for New Century Talented (NCET-06-0896) the Natural Science Fund of Gansu Province
文摘In this paper, the magnetic-elastic-plastic deformation behavior is studied for a ferromagnetic plate with simple supports. The perturbation formula of magnetic force is first derived based on the perturbation technique, and is then applied to the analysis of deformation characteristics with emphasis laid on the analyses of modes, symmetry of deformation and influences of incident angle of applied magnetic field on the plate deformation. The theoretical analyses offer explanations why the configuration offer- romagnetic rectangular plate with simple supports under an oblique magnetic field is in-wavy type along the x-direction, and why the largest deformation of the ferromagnetic plate occurs at the incident angle of 45°for the magnetic field. A numerical code based on the finite element method is developed to simulate quantitatively behaviors of the nonlinearly coupled multi-field problem. Some characteristic curves are plotted to illustrate the magneto--elastic-plastic deflections, and to reveal how the deflections can be influenced by the incident angle of applied magnetic field. The deformation characteristics obtained from the numerical simulations are found in good agreement with the theoretical analyses.
文摘The near crack line analysis method has been used in the present paper,The classical small scale yielding conditions have been completely abandoned in the analyses and one inappropriate matching condition used to be used at the elasticplastic boundary has been corrected.The reasonable solution of the plastic stresses near the crack line region has been established.By matching the plastic stresses with the exact elastic stresses at the elastic-plastic boundary,the plastic stresses the length of the plastic zone and the unit normal vector of the elastic-plastic boundary near the crock line region have been obtained for a mode I crack under uniaxial tension,as well as a mode I crack under biaxial tension,which shows that for both conditions the plastic stress componentsσy, and σsy.he length of the plastic zone and the unit normal vector of the elastic-plastic boundary are quite the same while the plastic stress σs is different.
基金supported by the National Natural Science Foundation of China (No.10672196)
文摘Crack line analysis is an effective way to solve elastic-plastic crack problems. Application of the method does not need the traditional small-scale yielding conditions and can obtain sufficiently accurate solutions near the crack line. To address mode- Ⅲ crack problems under the perfect elastic-plastic condition, matching procedures of the crack line analysis method axe summarized and refined to give general forms and formulation steps of plastic field, elastic-plastic boundary, and elastic-plastic matching equations near the crack line. The research unifies mode-III crack problems under different conditions into a problem of determining four integral constants with four matching equations. An example is given to verify correctness, conciseness, and generality of the procedure.
基金supported by National Natural Science Foundation of China(Grant No. 10772061)Heilongjiang Provincial Natural Science Foundation of China(Grant No. A200907)Specialized Research Fundfor the Doctoral Program of Higher Education of China(Grant No.20092322120001)
文摘Detecting stress concentration, especially critical stress state leading to structure damage or failure, is one of the most important tasks of equipment diagnosis. Metal magnetic memory technique needs further research to evaluate stress concentration quantitatively due to ambiguous physical mechanism, though it has potential to detect early defects in ferromagnetic materials. Mild Q235 steel defective specimens in demagnetization state were loaded in tension up to visible necking, with magnetic memory signals measurement made at increasing stress levels. Magnetic signals varied greatly under first several loadings and subsequently tended to stability in the elastic region, which showed that the magnetization always approaches the anhysteretic magnetization curve and was explained by the theory of magnetomechanical effect. In the plastic stage, an abnormal wave occurred in the stress concentration zone and its height value was sensitive to plastic deformation levels and dependent on the distance between the probe and defect, in accordance with the simulation results based on the magnetic dipole model. Different magnetic signal characteristics in the elastic-plastic region indicate that the magnetic memory technique can identify macroyielding and early damage, which is of profound significance for ensuring safe operation of equipment in service.
基金co-supported by the National Natural Science Foundation of China(Nos.11872320 and 12072294)。
文摘For a homogeneous,continuous,and isotropic material whose constitutive relationships meets with the Ramberg-Osgood law(R-O law),the energy in the elastoplastic indentation with a ball indenter was theoretically analyzed,and the proportional superposition of energy in pure elasticity and pure plasticity during indentation was considered based on the equivalence of energy density.Subsequently,a Proportional Superposition-based Elasto Plastic Model(PS-EPM)was developed to describe the relationships between the displacement and the load during the ball indentation.Furthermore,a new test method of Ball Indentation based on Elastoplastic Proportional Superposition(BI-EPS)was developed to obtain the constitutive relationships of R-O law materials.The load–displacement curves predicted using the PS-EPM model were found to agree closely with the Finite Element Analysis(FEA)results.Moreover,the stress vs.strain curves predicted using the BI-EPS method were in better agreement with those obtained by FEA.Additionally,ball indentation was performed on eleven types of metal materials including five types of aluminum alloys and six types of steel.The test results showed that the stress vs.strain relationships and the tensile strength values predicted using the proposed BI-EPS method agreed well with the results obtained using conventional uniaxial tensile tests.
基金National Natural Science Foundation of China(No.599355100)Foundation for Excellent PhD Thesis of University of Ministry of Education of China (No.200048)
文摘Using the finite element code ANSYS/LS-DYNA, a dynamic finite element modelwith an elastic-linear-kinematic-hardening plastic material is established to analyzeelastic-plastic stresses in the railhead in the impact process of wheel and rail occurring at thegap of rail joint. The model is based on the discrete elastic support condition of the rails, whichis suitable for the actual situation of wheel/track rolling contact. In the analysis the influencesof axle load, yield stress and tangent modulus of rail material on the stresses and strains areinvestigated in detail. The distribution of stresses and strains in the jointed railhead are given.It is found that the axle load, yield stress and tangent modulus of rail material greatly affect thestresses and strains in the railhead during impacting. The study provides a reliable method anduseful datum for the further research on fatigue and wear of railhead and improving the rail jointmode.
基金Project supported by the State Education Commission under a funding program for Excellent University Young Faculties and National Natural Science Foundation of China.
文摘Some possible alternative solutions of near-tip fields are studied for plane-strain Mode-I qua- si-static steady crack growth in incompressible(v=1/2)elastic perfectly-plastic media.A group of four-sector so- lutions and a three-sector solution in which the elastic-unloading region vanishes are given.Stress functions,plas- tic flow factors and plastic strains in each region are also given.
基金Project supported by the National Natural Sciences Fund of China(Nos.10302009 and 10672070)the Natural Sciences Fund of Gansu Province(3ZS051-A25-012)the Excellent Doctors' Fund of Lanzhou University
文摘An analysis of buckling/snapping and bending behaviors of magneto-elastic-plastic interaction and coupling for cantilever rectangular soft ferromagnetic plates is presented. Based on the expression of magnetic force from the variational principle of ferromagnetic plates, the buckling and bending theory of thin plates, the Mises yield criterion and the increment theory for plastic deformation, we establish a numerical code to quantitatively simulate the behaviors of the nonlinearly multi-fields coupling problems by the finite element method. Along with the phenomena of buckling/snapping and bending, or the characteristic curve of deflection versus magnitude of applied magnetic fields being numerically displayed, the critical loads of buckling/snapping, and the influences of plastic deformation and the width of plate on these critical loads, the plastic regions expanding with the magnitude of applied magnetic field, as well as the evolvement of deflection configuration of the plate are numerically obtained in a case study.
基金supported by the National Natural Science Foundation of China (Nos. 11002121, 11002122,and 10828205)the Natural Science Foundation of Hu-nan Province for Innovation Group (No. 09JJ7004)+2 种基金the Key Special Program for Science and Technology of Hu-nan Province (No. 2009FJ1002)and the Natural Science Foundation of Xiangtan University (No. 09XZX04)One of the authors (C. Lu) is also grateful to the support from the Australian Research Council (No. DP0985450)
文摘The reverse analysis provides a convenient method to determine four elastic-plastic parameters through an indentation curve such as Young s modulus E, hardness H, yield strength σy and strain hardening exponent n. In this paper, mathematical analysis on a reverse algorithm from Dao model （Dao et al., Acta Mater., 2001, 49, 3899） was carried out, which thought that only when 20 ≤E＊/σ0.033≤ 26 and 0.3n≤ 0.5, the reverse algorithm would yield two solutions of n by dimensionless function Π2. It is shown that, however, there are also two solutions of n when 20≤E＊/σ0.033≤ 26 and 0≤n0.1. A unique n can be obtained by dimensionless function Π3 instead of Π2 in these two ranges. E and H can be uniquely determined by a full indentation curve, and σy can be determined if n is unique. Furthermore, sensitivity analysis on obtaining n from dimensionless function Π3 or Π2 has been made.
