In order to research the flow behavior of 20CrMnTi and obtain its constitutive equation, the isothermal compression tests of 20CrMnTi were carried out using the Gleeble-3500 thermo-simulation machine, up to a 60% heig...In order to research the flow behavior of 20CrMnTi and obtain its constitutive equation, the isothermal compression tests of 20CrMnTi were carried out using the Gleeble-3500 thermo-simulation machine, up to a 60% height reduction of the sample at strain rate range from 0.01 s 1 to 10 s 1 and deformation temperature range from 1123 K to 1273 K. According to the experimental results, the constitutive equation of 20CrMnTi was established based on Arrhenius model. In addition, the compensation of strain was taken into account and a new method of modifying the constitutive equation was proposed by introducing a coefficient K related to the deformation temperature and stain rate, which effectively improved the prediction accuracy of the developed constitutive equation. The results show that the flow stress decreases with increasing deformation temperature and decreasing strain rate, and the proposed constitutive equation well predicts the flow stress of 20CrMnTi during the high temperature deformation.展开更多
A recently proposed model coupling with the solid-fluid of the saturated sand was utilized to study the deformation band. Based on the critical state plasticity model by Borja and Andrade, the hydraulic conductivity t...A recently proposed model coupling with the solid-fluid of the saturated sand was utilized to study the deformation band. Based on the critical state plasticity model by Borja and Andrade, the hydraulic conductivity tensor was naturally treated as a function of the spatial discretization matrix about the displacement and the stress field, allowing a more realistic representation of the physical phenomenon. The fully Lagrangian form of the Darcy law was resolved by Piola algorithm, and then the flow law was gained, leading to the implementation of a modified model of the saturated sand. Then the criterion for the onset of localization was derived and utilized to detect instability. The constitutive model was implemented in a finite element program coded by FORTRAN, which was used to predict the formation and development of shear bands in plane strain compression of saturated sand. At last, the formation mechanism of the shear band was discussed. It is shown that the model works well, and the simulation sample bifurcates at 1.18% axial strain, which is in a good qualitative agreement with the experiment. The pore pressure greatly affects the onset and development of the deformation band, and it obviously increases around the localization-prone regions with the direction toward the outer side of the normal of the shear band, while the pore stress flows nearly horizontally and is distributed equally far away the shear band region.展开更多
The hot deformation behavior of Al?6.2Zn?0.70Mg?0.30Mn?0.17Zr alloy was investigated by isothermal compressiontest on a Gleeble?3500machine in the deformation temperature range between623and773K and the strain rate ra...The hot deformation behavior of Al?6.2Zn?0.70Mg?0.30Mn?0.17Zr alloy was investigated by isothermal compressiontest on a Gleeble?3500machine in the deformation temperature range between623and773K and the strain rate range between0.01and20s?1.The results show that the flow stress decreases with decreasing strain rate and increasing deformation temperature.Basedon the experimental results,Arrhenius constitutive equations and artificial neural network(ANN)model were established toinvestigate the flow behavior of the alloy.The calculated results show that the influence of strain on material constants can berepresented by a6th-order polynomial function.The ANN model with16neurons in hidden layer possesses perfect performanceprediction of the flow stress.The predictabilities of the two established models are different.The errors of results calculated by ANNmodel were more centralized and the mean absolute error corresponding to Arrhenius constitutive equations and ANN model are3.49%and1.03%,respectively.In predicting the flow stress of experimental aluminum alloy,the ANN model has a betterpredictability and greater efficiency than Arrhenius constitutive equations.展开更多
A new phenomenological and empirically-based constitutive model was proposed to modify the term in the original Johnson−Cook constitutive model.The new model can be used to describe and predict the flow stress of AA10...A new phenomenological and empirically-based constitutive model was proposed to modify the term in the original Johnson−Cook constitutive model.The new model can be used to describe and predict the flow stress of AA1070 aluminum with different initial grain sizes in the hot working process.This developed model considers thermal softening,strain-rate hardening,strain hardening,initial grain size,and interactions with each other and can correctly model the behavior of AA1070 at elevated temperature with different strains,strain rates,and initial grain sizes.The hot flow behavior of AA1070 was investigated through compression tests over wide ranges of temperature from 623 to 773 K,strain rate from 0.005 to 0.5 s−1 and initial grain size from 50 to 450μm.Results show that the initial grain size has a significant effect on the flow behavior of AA1070.Then,correlation coefficient(R),average absolute relative error(AARE),and relative error were examined for comparative predictability of the model.Results show that flow stresses for different initial grain sizes calculated by the new proposed model perfectly correlate with experimental ones,with a mean relative error of 1.19%,which confirms that the new modified Johnson−Cook relation can give a precise estimation of the hot flow stress of AA1070 aluminum by considering the initial grain size.展开更多
In order to establish the constitutive relationship of high-ductility cementitious composites(HDCCs)under uniaxial tensile load and to guide the structural design of HDCCs,based on the analysis of the existing uniaxia...In order to establish the constitutive relationship of high-ductility cementitious composites(HDCCs)under uniaxial tensile load and to guide the structural design of HDCCs,based on the analysis of the existing uniaxial tensile constitutive relationship and ideal elastoplastic linear strain-hardening model,a bilinear tensile constitutive equation of HDCCs was proposed.The points of nominal initial cracking and nominal maximum stress were adopted as control points of the line segment,and the constitutive relationship of HDCCs was established.Five series of uniaxial tensile stress-strain curves of HDCCs were combined to perform an experimental application of the constitutive equation,along with an analysis of the key parameters.The experimental results confirm the ability of the constitutive equation to overcome the problem of insufficient or excessive redundancy of existing models in terms of calculation bearing capacity.Specifically,the measured maximum stress value is larger than the nominal value,and the ratio between the two values ranges from 1.08 to 1.22.Additionally,the tensile strain at the softening point obtained by fitting a straight line with the valley points of the strain-hardening stage curve is greater than or equal to the tensile strain at the measured maximum stress point and the ratio of the fitted values to the measured values ranges from 1.00 to 1.19.展开更多
A netbook, Internet-enabled and with extra portability, has been fast-growing in the domain of information technology (IT) in recent years. Compared with standardized laptops or desktop computers, a netbook's key f...A netbook, Internet-enabled and with extra portability, has been fast-growing in the domain of information technology (IT) in recent years. Compared with standardized laptops or desktop computers, a netbook's key features include a shrunken-down and lightweight laptop that is "easy to learn, easy to work, and easy to play". This research is to empirically test the influence of user perceptions of this new form of IT (usability, compatibility and relative advantage) associated with playfulness and attitude toward purchase intention. In addition, personal innovativeness of an individual plays an important role in the antecedents of such perceptions. A test of this model, two-stage approach, confirmatory factor analysis (CFA) and structural equation model (SEM) are employed to validate the casual model from among 227 usable respondents who have been using a laptop for more than two years. Results showed support for eleven of twelve research hypotheses, and one new path linking personal innovativeness with attitude toward using is found to be non-siznificant.展开更多
In order to investigate the effect of microvoids on the mechanical behavior of casting magnesium alloy,a spherical void-cell model of the material was presented.The velocity and strain fields of the model were obtaine...In order to investigate the effect of microvoids on the mechanical behavior of casting magnesium alloy,a spherical void-cell model of the material was presented.The velocity and strain fields of the model were obtained from the assumption that the material matrix is homogeneous and incompressible.The hardening and softening functions,which respectively reflect the deformation-hardening and void-softening behaviors of the material,were presented and introduced to an endochronic constitutive equation for describing the mechanical behavior of the material including microvoids.The corresponding numerical algorithm and finite element procedure were developed and applied to the analyses of the elastoplastic response and the porosity of casting magnesium alloy ZL102.The computed results show satisfactory agreement with experimental data.展开更多
In contrast to the previous studies of knowledge capital from the perspective of enterprises, this study discusses the employee knowledge capital formation mechanism in the supply chain using social network method fro...In contrast to the previous studies of knowledge capital from the perspective of enterprises, this study discusses the employee knowledge capital formation mechanism in the supply chain using social network method from the perspective of social capital s~'ucture, taking individual employees as the study objects. 150 effective questionnaires of three groups were returned by multistage cluster sampling, and then they were analyzed through regression and the structural equation model. The results are as follows: (1) the acquisition of social capital and knowledge capital is affected by the network structure position of the employees in the supply chain; (2) the knowledge capital is affected by how much social capital the employees obtained in the supply chain; (3) social capital is an intermediary variable to affect the knowledge capital in the network structure. Finally, related suggestions for the supply chain management and the subsequent studies are proposed. 1展开更多
Based on the crystal plasticity theory and interatomic potential, in this paper a new thermo-elasto-plasticity constitutive model is proposed to study the behavior of metal crystals at finite temperature. By applying ...Based on the crystal plasticity theory and interatomic potential, in this paper a new thermo-elasto-plasticity constitutive model is proposed to study the behavior of metal crystals at finite temperature. By applying the present constitutive model, the stress-strain curves under uniaxial tension at different temperatures are calculated for the typical crystal A1, and the calculated results are compared with the experimental results. From the comparisons, it can be seen that the present theory has the capability to describe the thermo-elasto-plastic behavior of metal crystals at finite temperature through a concise and explicit calculation process.展开更多
基金Project(2014JC024)supported by the Interdisciplinary Training Project of Shandong University,China
文摘In order to research the flow behavior of 20CrMnTi and obtain its constitutive equation, the isothermal compression tests of 20CrMnTi were carried out using the Gleeble-3500 thermo-simulation machine, up to a 60% height reduction of the sample at strain rate range from 0.01 s 1 to 10 s 1 and deformation temperature range from 1123 K to 1273 K. According to the experimental results, the constitutive equation of 20CrMnTi was established based on Arrhenius model. In addition, the compensation of strain was taken into account and a new method of modifying the constitutive equation was proposed by introducing a coefficient K related to the deformation temperature and stain rate, which effectively improved the prediction accuracy of the developed constitutive equation. The results show that the flow stress decreases with increasing deformation temperature and decreasing strain rate, and the proposed constitutive equation well predicts the flow stress of 20CrMnTi during the high temperature deformation.
基金Project(2006G007-C) supported by the Foundation of the Science and Technology Section of Ministry of Railway of ChinaProject(77206) supported by the Excellent PhD Thesis Innovation Foundation of Central South University,China
文摘A recently proposed model coupling with the solid-fluid of the saturated sand was utilized to study the deformation band. Based on the critical state plasticity model by Borja and Andrade, the hydraulic conductivity tensor was naturally treated as a function of the spatial discretization matrix about the displacement and the stress field, allowing a more realistic representation of the physical phenomenon. The fully Lagrangian form of the Darcy law was resolved by Piola algorithm, and then the flow law was gained, leading to the implementation of a modified model of the saturated sand. Then the criterion for the onset of localization was derived and utilized to detect instability. The constitutive model was implemented in a finite element program coded by FORTRAN, which was used to predict the formation and development of shear bands in plane strain compression of saturated sand. At last, the formation mechanism of the shear band was discussed. It is shown that the model works well, and the simulation sample bifurcates at 1.18% axial strain, which is in a good qualitative agreement with the experiment. The pore pressure greatly affects the onset and development of the deformation band, and it obviously increases around the localization-prone regions with the direction toward the outer side of the normal of the shear band, while the pore stress flows nearly horizontally and is distributed equally far away the shear band region.
基金Project(2016GK1004) supported by the Science and Technology Major Project of Hunan Province,China
文摘The hot deformation behavior of Al?6.2Zn?0.70Mg?0.30Mn?0.17Zr alloy was investigated by isothermal compressiontest on a Gleeble?3500machine in the deformation temperature range between623and773K and the strain rate range between0.01and20s?1.The results show that the flow stress decreases with decreasing strain rate and increasing deformation temperature.Basedon the experimental results,Arrhenius constitutive equations and artificial neural network(ANN)model were established toinvestigate the flow behavior of the alloy.The calculated results show that the influence of strain on material constants can berepresented by a6th-order polynomial function.The ANN model with16neurons in hidden layer possesses perfect performanceprediction of the flow stress.The predictabilities of the two established models are different.The errors of results calculated by ANNmodel were more centralized and the mean absolute error corresponding to Arrhenius constitutive equations and ANN model are3.49%and1.03%,respectively.In predicting the flow stress of experimental aluminum alloy,the ANN model has a betterpredictability and greater efficiency than Arrhenius constitutive equations.
文摘A new phenomenological and empirically-based constitutive model was proposed to modify the term in the original Johnson−Cook constitutive model.The new model can be used to describe and predict the flow stress of AA1070 aluminum with different initial grain sizes in the hot working process.This developed model considers thermal softening,strain-rate hardening,strain hardening,initial grain size,and interactions with each other and can correctly model the behavior of AA1070 at elevated temperature with different strains,strain rates,and initial grain sizes.The hot flow behavior of AA1070 was investigated through compression tests over wide ranges of temperature from 623 to 773 K,strain rate from 0.005 to 0.5 s−1 and initial grain size from 50 to 450μm.Results show that the initial grain size has a significant effect on the flow behavior of AA1070.Then,correlation coefficient(R),average absolute relative error(AARE),and relative error were examined for comparative predictability of the model.Results show that flow stresses for different initial grain sizes calculated by the new proposed model perfectly correlate with experimental ones,with a mean relative error of 1.19%,which confirms that the new modified Johnson−Cook relation can give a precise estimation of the hot flow stress of AA1070 aluminum by considering the initial grain size.
基金The National Key Research and Development Program of China(No.2018YFC0406701)the National Natural Science Foundation of China(No.51778133,51739008)
文摘In order to establish the constitutive relationship of high-ductility cementitious composites(HDCCs)under uniaxial tensile load and to guide the structural design of HDCCs,based on the analysis of the existing uniaxial tensile constitutive relationship and ideal elastoplastic linear strain-hardening model,a bilinear tensile constitutive equation of HDCCs was proposed.The points of nominal initial cracking and nominal maximum stress were adopted as control points of the line segment,and the constitutive relationship of HDCCs was established.Five series of uniaxial tensile stress-strain curves of HDCCs were combined to perform an experimental application of the constitutive equation,along with an analysis of the key parameters.The experimental results confirm the ability of the constitutive equation to overcome the problem of insufficient or excessive redundancy of existing models in terms of calculation bearing capacity.Specifically,the measured maximum stress value is larger than the nominal value,and the ratio between the two values ranges from 1.08 to 1.22.Additionally,the tensile strain at the softening point obtained by fitting a straight line with the valley points of the strain-hardening stage curve is greater than or equal to the tensile strain at the measured maximum stress point and the ratio of the fitted values to the measured values ranges from 1.00 to 1.19.
文摘A netbook, Internet-enabled and with extra portability, has been fast-growing in the domain of information technology (IT) in recent years. Compared with standardized laptops or desktop computers, a netbook's key features include a shrunken-down and lightweight laptop that is "easy to learn, easy to work, and easy to play". This research is to empirically test the influence of user perceptions of this new form of IT (usability, compatibility and relative advantage) associated with playfulness and attitude toward purchase intention. In addition, personal innovativeness of an individual plays an important role in the antecedents of such perceptions. A test of this model, two-stage approach, confirmatory factor analysis (CFA) and structural equation model (SEM) are employed to validate the casual model from among 227 usable respondents who have been using a laptop for more than two years. Results showed support for eleven of twelve research hypotheses, and one new path linking personal innovativeness with attitude toward using is found to be non-siznificant.
基金Project(10872221)supported by the National Natural Science Foundation of China
文摘In order to investigate the effect of microvoids on the mechanical behavior of casting magnesium alloy,a spherical void-cell model of the material was presented.The velocity and strain fields of the model were obtained from the assumption that the material matrix is homogeneous and incompressible.The hardening and softening functions,which respectively reflect the deformation-hardening and void-softening behaviors of the material,were presented and introduced to an endochronic constitutive equation for describing the mechanical behavior of the material including microvoids.The corresponding numerical algorithm and finite element procedure were developed and applied to the analyses of the elastoplastic response and the porosity of casting magnesium alloy ZL102.The computed results show satisfactory agreement with experimental data.
文摘In contrast to the previous studies of knowledge capital from the perspective of enterprises, this study discusses the employee knowledge capital formation mechanism in the supply chain using social network method from the perspective of social capital s~'ucture, taking individual employees as the study objects. 150 effective questionnaires of three groups were returned by multistage cluster sampling, and then they were analyzed through regression and the structural equation model. The results are as follows: (1) the acquisition of social capital and knowledge capital is affected by the network structure position of the employees in the supply chain; (2) the knowledge capital is affected by how much social capital the employees obtained in the supply chain; (3) social capital is an intermediary variable to affect the knowledge capital in the network structure. Finally, related suggestions for the supply chain management and the subsequent studies are proposed. 1
基金supported by the National Natural Science Foundation of China(Grant Nos.11021262,11172303 and 11132011)National Basic Research Program of China(Grant No.2012CB937500)
文摘Based on the crystal plasticity theory and interatomic potential, in this paper a new thermo-elasto-plasticity constitutive model is proposed to study the behavior of metal crystals at finite temperature. By applying the present constitutive model, the stress-strain curves under uniaxial tension at different temperatures are calculated for the typical crystal A1, and the calculated results are compared with the experimental results. From the comparisons, it can be seen that the present theory has the capability to describe the thermo-elasto-plastic behavior of metal crystals at finite temperature through a concise and explicit calculation process.