Tensile tests at different strain rates(0.0002, 0.002, 0.02, 1000 and 3000 s^(-1)) were carried out for 7N01 aluminum alloy. Low strain rate experiments(0.0002, 0.002 and 0.02 s^(-1)) were conducted using an electroni...Tensile tests at different strain rates(0.0002, 0.002, 0.02, 1000 and 3000 s^(-1)) were carried out for 7N01 aluminum alloy. Low strain rate experiments(0.0002, 0.002 and 0.02 s^(-1)) were conducted using an electronic mechanical universal testing machine, while high strain rate experiments(1000, 3000 s^(-1)) were carried out through a split Hopkinson tensile bar. The experimental results showed that 7N01 aluminum alloy is strain rate sensitive. By introducing a correction scheme of the strain rate hardening coefficient, a modified Johnson–Cook model was proposed to describe the flow behaviors of 7N01 aluminum alloy. The proposed model fitted the experimental data better than the original Johnson–Cook model in plastic flow under dynamic condition. Numerical simulations of the dynamic tensile tests were performed using ABAQUS with the modified Johnson–Cook model. Digital image correlation was used together with high-speed photography to study the mechanical characters of specimen at high strain rate. Good correlations between the experiments results, numerical predictions and DIC results are achieved. High accuracy of the modified Johnson-Cook model was validated.展开更多
为研究一种高强钢的静动态力学特性并构建Johnson-Cook本构模型,利用电子万能试验机进行了准静态压缩和拉伸试验,获取了材料在室温准静态条件下的应力-应变曲线、弹性模量和泊松比。通过分离式霍普金森压杆,在293~1073 K 5种温度和800~2...为研究一种高强钢的静动态力学特性并构建Johnson-Cook本构模型,利用电子万能试验机进行了准静态压缩和拉伸试验,获取了材料在室温准静态条件下的应力-应变曲线、弹性模量和泊松比。通过分离式霍普金森压杆,在293~1073 K 5种温度和800~2100 s^(-1)4种应变率下开展动态压缩试验,获得了材料在不同条件下的动态应力-应变曲线。最后,基于试验数据构建其Johnson-Cook本构模型,并对模型的准确性进行验证。结果表明:材料的屈服应力随着应变率的增加而增加,但增长幅度较小,应变率强化效应不显著;当应变率为1000 s^(-1)时,材料的屈服应力随温度升高而显著降低。通过本构模型计算得到的应力-应变曲线与试验结果吻合良好,表明模型能够较准确地预测材料的应力行为。展开更多
Gradient-dependent plasticity considering interactions and interplay among microstructures was included into JOHNSON-COOK model to calculate the temperature distribution in adiabatic shear band(ASB), the peak and aver...Gradient-dependent plasticity considering interactions and interplay among microstructures was included into JOHNSON-COOK model to calculate the temperature distribution in adiabatic shear band(ASB), the peak and average temperatures as well as their evolutions. The differential local plastic shear strain was derived to calculate the differential local plastic work and the temperature rise due to the microstructural effect. The total temperature in ASB is the sum of initial temperature, temperature rise at strain-hardening stage and non-uniform temperature due to the microstructural effect beyond the peak shear stress. The flow shear stress—average plastic shear strain curve, the temperature distribution, the peak and average temperatures in ASB are computed for Ti-6Al-4V. When the imposed shear strain is less than 2 and the shear strain rate is 1 000 s?1, the dynamic recovery and recrystalliza-tion processes occur. However, without the microstructural effect, the processes might have not occurred since heat diffusion decreases the temperature in ASB. The calculated maximum temperature approaches 1 500 K so that phase transformation might take place. The present predictions support the previously experimental results showing that the transformed and deformed ASBs are observed in Ti-6Al-4V. Higher shear strain rate enhances the possibility of dynamic recrystallization and phase transformation.展开更多
By using the widely used JOHNSON-COOK model and the gradient-dependent plasticity to consider microstructural effect beyond the occurrence of shear strain localization,the distributions of local plastic shear strain a...By using the widely used JOHNSON-COOK model and the gradient-dependent plasticity to consider microstructural effect beyond the occurrence of shear strain localization,the distributions of local plastic shear strain and deformation in adiabatic shear band(ASB)were analyzed.The peak local plastic shear strain is proportional to the average plastic shear strain,while it is inversely proportional to the critical plastic shear strain corresponding to the peak flow shear stress.The relative plastic shear deformation between the top and base of ASB depends on the thickness of ASB and the average plastic shear strain.A parametric study was carried out to study the influence of constitutive parameters on shear strain localization.Higher values of static shear strength and work to heat conversion factor lead to lower critical plastic shear strain so that the shear localization is more apparent at the same average plastic shear strain.Higher values of strain-hardening exponent,strain rate sensitive coefficient,melting point,thermal capacity and mass density result in higher critical plastic shear strain,leading to less apparent shear localization at the same average plastic shear strain.The strain rate sensitive coefficient has a minor influence on the critical plastic shear strain,the distributions of local plastic shear strain and deformation in ASB.The effect of strain-hardening modulus on the critical plastic shear strain is not monotonous.When the maximum critical plastic shear strain is reached,the least apparent shear localization occurs.展开更多
The dynamic compression experiments with Split-Hopkinson Pressure Bar(SHPB)were performed on AZ31 magnesium alloy rolled sheet specimens in the normal direction(AZ31-ND)with{0002}texture at the temperature of 293-523 ...The dynamic compression experiments with Split-Hopkinson Pressure Bar(SHPB)were performed on AZ31 magnesium alloy rolled sheet specimens in the normal direction(AZ31-ND)with{0002}texture at the temperature of 293-523 K and the strain rate of 0.001-2200 s^−1.The temperature term in Johnson-Cook(JC)constitutive model had been reasonably modified.This advantage made constitutive model promising for decribing the dynamic deformation behavior of AZ31-ND with{0002}texture more accurately.The obtained true stress-true plastic strain curves agreed well with the measured results in a wide range of strain rates and temperatures.The thermal softeninging,strain and strain rate hardening effect on the AZ31-ND with{0002}texture were discussed.The adiabatic shear band(ASB)of AZ31-ND with{0002}texture hat shaped specimen was successfully predicted by combining modified JC constitutive model and numerical simulation,which was also validated by Electron Back-Scattered Diffraction(EBSD)map under the same boundary condition.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
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
基金Projects(51275532,U1334208)supported by the National Natural Science Foundation of ChinaProject(2015BAG13B01)supported by National Science and Technology Support Program,China+2 种基金Project(2016YFB1200602-33)supported by the National Key R&D Program of ChinaProject(NCET-12-0549)supported by the New Century Excellent Talents in University,ChinaProject(CSUZC201527)supported by the Open-Fund for the Valuable and Precision Instruments of Central South University,China
文摘Tensile tests at different strain rates(0.0002, 0.002, 0.02, 1000 and 3000 s^(-1)) were carried out for 7N01 aluminum alloy. Low strain rate experiments(0.0002, 0.002 and 0.02 s^(-1)) were conducted using an electronic mechanical universal testing machine, while high strain rate experiments(1000, 3000 s^(-1)) were carried out through a split Hopkinson tensile bar. The experimental results showed that 7N01 aluminum alloy is strain rate sensitive. By introducing a correction scheme of the strain rate hardening coefficient, a modified Johnson–Cook model was proposed to describe the flow behaviors of 7N01 aluminum alloy. The proposed model fitted the experimental data better than the original Johnson–Cook model in plastic flow under dynamic condition. Numerical simulations of the dynamic tensile tests were performed using ABAQUS with the modified Johnson–Cook model. Digital image correlation was used together with high-speed photography to study the mechanical characters of specimen at high strain rate. Good correlations between the experiments results, numerical predictions and DIC results are achieved. High accuracy of the modified Johnson-Cook model was validated.
文摘为研究一种高强钢的静动态力学特性并构建Johnson-Cook本构模型,利用电子万能试验机进行了准静态压缩和拉伸试验,获取了材料在室温准静态条件下的应力-应变曲线、弹性模量和泊松比。通过分离式霍普金森压杆,在293~1073 K 5种温度和800~2100 s^(-1)4种应变率下开展动态压缩试验,获得了材料在不同条件下的动态应力-应变曲线。最后,基于试验数据构建其Johnson-Cook本构模型,并对模型的准确性进行验证。结果表明:材料的屈服应力随着应变率的增加而增加,但增长幅度较小,应变率强化效应不显著;当应变率为1000 s^(-1)时,材料的屈服应力随温度升高而显著降低。通过本构模型计算得到的应力-应变曲线与试验结果吻合良好,表明模型能够较准确地预测材料的应力行为。
基金Project(2004F052) supported by the Educational Department of Liaoning Province, China
文摘Gradient-dependent plasticity considering interactions and interplay among microstructures was included into JOHNSON-COOK model to calculate the temperature distribution in adiabatic shear band(ASB), the peak and average temperatures as well as their evolutions. The differential local plastic shear strain was derived to calculate the differential local plastic work and the temperature rise due to the microstructural effect. The total temperature in ASB is the sum of initial temperature, temperature rise at strain-hardening stage and non-uniform temperature due to the microstructural effect beyond the peak shear stress. The flow shear stress—average plastic shear strain curve, the temperature distribution, the peak and average temperatures in ASB are computed for Ti-6Al-4V. When the imposed shear strain is less than 2 and the shear strain rate is 1 000 s?1, the dynamic recovery and recrystalliza-tion processes occur. However, without the microstructural effect, the processes might have not occurred since heat diffusion decreases the temperature in ASB. The calculated maximum temperature approaches 1 500 K so that phase transformation might take place. The present predictions support the previously experimental results showing that the transformed and deformed ASBs are observed in Ti-6Al-4V. Higher shear strain rate enhances the possibility of dynamic recrystallization and phase transformation.
基金Project(2004F052) supported by the Education Department of Liaoning Province,China
文摘By using the widely used JOHNSON-COOK model and the gradient-dependent plasticity to consider microstructural effect beyond the occurrence of shear strain localization,the distributions of local plastic shear strain and deformation in adiabatic shear band(ASB)were analyzed.The peak local plastic shear strain is proportional to the average plastic shear strain,while it is inversely proportional to the critical plastic shear strain corresponding to the peak flow shear stress.The relative plastic shear deformation between the top and base of ASB depends on the thickness of ASB and the average plastic shear strain.A parametric study was carried out to study the influence of constitutive parameters on shear strain localization.Higher values of static shear strength and work to heat conversion factor lead to lower critical plastic shear strain so that the shear localization is more apparent at the same average plastic shear strain.Higher values of strain-hardening exponent,strain rate sensitive coefficient,melting point,thermal capacity and mass density result in higher critical plastic shear strain,leading to less apparent shear localization at the same average plastic shear strain.The strain rate sensitive coefficient has a minor influence on the critical plastic shear strain,the distributions of local plastic shear strain and deformation in ASB.The effect of strain-hardening modulus on the critical plastic shear strain is not monotonous.When the maximum critical plastic shear strain is reached,the least apparent shear localization occurs.
基金This work was supported by Surface of the State Natural Science Fund Projects(No.51571145)City of Ningbo“science and technology innovation 2025”major special project(new energy vehicle lightweight magnesium alloy material precision forming technology).
文摘The dynamic compression experiments with Split-Hopkinson Pressure Bar(SHPB)were performed on AZ31 magnesium alloy rolled sheet specimens in the normal direction(AZ31-ND)with{0002}texture at the temperature of 293-523 K and the strain rate of 0.001-2200 s^−1.The temperature term in Johnson-Cook(JC)constitutive model had been reasonably modified.This advantage made constitutive model promising for decribing the dynamic deformation behavior of AZ31-ND with{0002}texture more accurately.The obtained true stress-true plastic strain curves agreed well with the measured results in a wide range of strain rates and temperatures.The thermal softeninging,strain and strain rate hardening effect on the AZ31-ND with{0002}texture were discussed.The adiabatic shear band(ASB)of AZ31-ND with{0002}texture hat shaped specimen was successfully predicted by combining modified JC constitutive model and numerical simulation,which was also validated by Electron Back-Scattered Diffraction(EBSD)map under the same boundary condition.
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.
