The effects of biaxial tensile pre-strain on the forming limit of DP590 high-strength steel under high strain rate were investigated. The stress-strain curves of DP590 steel sheet under the biaxial tensile of differen...The effects of biaxial tensile pre-strain on the forming limit of DP590 high-strength steel under high strain rate were investigated. The stress-strain curves of DP590 steel sheet under the biaxial tensile of different load ratios were obtained. The forming limit diagrams（FLDs） of DP590 steel sheet under biaxial tensile pre-strain and electromagnetic hybrid forming were established. Results showed that the biaxial tensile pre-strain had significant effects on the formability of DP590 steel. The pre-strain in a certain range improved the forming limit of DP590 steel under high rate, and the forming limit increased with the pre-strain. The prestrain in the same direction of high rate increased the forming limit of the final deformation under complex strain paths conditions, but the pre-strain in the vertical direction decreased the minor strain under the high strain rate.展开更多
After constructing a stress and strain model, the valence bands of in-plane biaxial tensile strained Si is calculated by k·p method. In the paper we calculate the accurate anisotropy valance bands and the splitti...After constructing a stress and strain model, the valence bands of in-plane biaxial tensile strained Si is calculated by k·p method. In the paper we calculate the accurate anisotropy valance bands and the splitting energy between light and heavy hole bands. The results show that the valance bands are highly distorted, and the anisotropy is more obvious. To obtain the density of states （DOS） effective mass, which is a very important parameter for device modeling, a DOS effective mass model of biaxial tensile strained Si is constructed based on the valance band calculation. This model can be directly used in the device model of metal-oxide semiconductor field effect transistor （MOSFET）. It also a provides valuable reference for biaxial tensile strained silicon MOSFET design.展开更多
This paper mainly studies on the biaxial tensile strength and its calculative formula of a special made concrete. According to the Hill theory and the uniaxial tensile experiment results, the expression of the concret...This paper mainly studies on the biaxial tensile strength and its calculative formula of a special made concrete. According to the Hill theory and the uniaxial tensile experiment results, the expression of the concrete biaxial tensile strength is deduced, which is then combined with experiment data and checked. The result shows： the biaxial tensile strength of this kind of concrete is about 15%-30% lower than its uniaxial tensile strength, and the calculative value is basically consistent with the experiment value, with less than 11% difference. This kind of biaxial tension weakening effect is very important to the structure designs of concrete road. The author suggests further research.展开更多
The dynamic failure behavior of CoCrFeNi High-Entropy Alloy(HEA)under plane biaxial stress was investigated in detail.The dynamic biaxial tensile tests were conducted using an Electromagnetic Biaxial Split Hopkinson T...The dynamic failure behavior of CoCrFeNi High-Entropy Alloy(HEA)under plane biaxial stress was investigated in detail.The dynamic biaxial tensile tests were conducted using an Electromagnetic Biaxial Split Hopkinson Tensile Bar(EBSHTB)system.For comparison,the quasi-static uniaxial and biaxial tensile tests,as well as dynamic uniaxial tensile tests,were per-formed respectively.A cruciform specimen suitable for large plastic deformation was designed and employed in the experiments.The Finite Element Method(FEM)verified that the improved cruciform specimen could satisfy the basic requirements.The feasibility of the proposed specimen was further confirmed through loading tests.Finally,the quasi-static and dynamic yield loci of the HEA in the first quadrant of the principal stress space were plotted.The results indicate that the alloy exhibits obvious strain hardening effect and strain rate strengthening effect,the yield locus and plastic work contours can be accurately described by Hill'48 criterion.展开更多
The biaxial tensile behavior of isotropic Ti-6Al-4 V is characterized in this paper.A novel cruciform specimen was designed and optimized to achieve uniform stress and strain distribution within the gauge area.Biaxial...The biaxial tensile behavior of isotropic Ti-6Al-4 V is characterized in this paper.A novel cruciform specimen was designed and optimized to achieve uniform stress and strain distribution within the gauge area.Biaxial tensile tests were conducted at three different loading ratios by the biaxial testing machine.The Digital Image Correlation(DIC)technique was applied to determine strain distribution,and a high-speed camera was employed to record the fracture process.An Inverse Analysis(IA)approach with a combined experimental and numerical method was proposed to determine the true stresses at the gauge section of the specimen during biaxial tensile tests.The results indicate that the initial yield locus can be described by the Cazacu criterion accurately,whereas the Mises criterion can predict better the strengthening behavior of Ti-6Al-4 V in the first quadrant in the principal stress space.展开更多
This paper focused on the effect of pre-strain on forming limit curves(FLC)of 5754-O aluminum alloy sheet through utilizing biaxial tensile approach.Based on Swift model and Yld2000-2 d yield criterion,the dimensions ...This paper focused on the effect of pre-strain on forming limit curves(FLC)of 5754-O aluminum alloy sheet through utilizing biaxial tensile approach.Based on Swift model and Yld2000-2 d yield criterion,the dimensions of cruciform specimen was optimized through applying finite element method for increasing the strain at specimen center.After that,with the recommended specimen size,the cruciform specimen was tested under various stroke ratios to experimentally characterize the limit strains under different pre-strain levels.Subsequently,the biaxial tensile tests were simulated by Abaqus to obtain the limit strains and validate the material models.It can be observed in both experiments and simulations that the pre-strained uniaxial tension followed by plane tension or equi-biaxial tension can improve the formability of sheet metals.Besides,the strain path change affects the trend of first derivative of strain rate difference between neighboring points with respect to time.An early increase occurred and then fell back to the stable value,the steady evolution continued until to a new increase reaching the critical value.The M–K prediction approach was simulated to verify the influence of pre-strain on FLC.It can be found that the early increase peaks of the major strain incremental ratio rose with the amplitude of pre-strain.Finally,the phenomenon of pseudolocalization caused by the strain path change was explained through evolution of stress state inside the groove.展开更多
The biaxial tensile tests were carried out to investigate the deformation behavior and yield loci of dual-phase （DP） steel sheets under biaxial tensile conditions. The true stress-true strain curves of DP steel shee...The biaxial tensile tests were carried out to investigate the deformation behavior and yield loci of dual-phase （DP） steel sheets under biaxial tensile conditions. The true stress-true strain curves of DP steel sheets for different loading ratios were obtained, and the experimental yield loci were determined based on the equivalent plastic work principle. The experimental yield loci were compared to the theoretical yield loci based on Hi1148, Hi1190, Hi1193, Hosford, Barlat89, Yld2000-2d and Gotoh yield criteria. It is found that Yld2000-2d yield criterion can describe the general trends of experimental yield loci of DP steel sheets with comparably higher accuracy. Hosford criterion has the maximum error for DP590, whereas Hi1148 and Barlat89 have the maximum errors for DP780 and DP980.展开更多
Magnesium alloys are frequently subjected to biaxial stress during manufacturing process,however,the work hardening behavior under such circumstance are not well understood.In this study,the deformation mechanisms and...Magnesium alloys are frequently subjected to biaxial stress during manufacturing process,however,the work hardening behavior under such circumstance are not well understood.In this study,the deformation mechanisms and differential work hardening behavior of rolled AZ31 magnesium alloy sheets under biaxial loading are investigated.The change of plastic work contours with increasing plastic strain indicates the differential work hardening behavior of AZ31 magnesium alloy under biaxial stress state,resulting in higher macroscopic work hardening rates of biaxial loading than uniaxial loading,with the elastic-plastic transition part of work hardening extended and stage Ⅲ hardly emerged.Electron backscatter diffraction and Schmid factor analysis confirm the low activation of non-basalslip during biaxial loading tests.While the thickness strain is primarily accommodated by pyramidal<c+a>slip at the initial stage of biaxial deformation,{10–11}contraction twinning is activated at larger plastic strain.The low activation of non-basalslip also retards the dynamic recovery and cross-slip of basal and prismaticslips,leading to the differential work hardening behavior of AZ31 magnesium alloy under biaxial stress state.展开更多
First-principles calculations and Monte Carlo simulations reveal that single-layer and double-layer VX_(2)(X=Cl,Br)can be tuned from antiferromagnetic(AFM)semiconductors to ferromagnetic(FM)state when biaxial tensile ...First-principles calculations and Monte Carlo simulations reveal that single-layer and double-layer VX_(2)(X=Cl,Br)can be tuned from antiferromagnetic(AFM)semiconductors to ferromagnetic(FM)state when biaxial tensile stress is applied.Their ground states are all T phase.The biaxial tensile stress at the phase transition point of the double-layer VX_(2) is larger than that of the single-layer VX_(2).The direct band gaps can be also manipulated by biaxial tensile stress as they increases with increasing tensile stress to a critical point and then decreases.The Neel temperature(´TN)of double-layer VX_(2) are higher than that of single-layer.As the stress increases,the TN of all materials tend to increase.The magnetic moment increases with the increase of biaxial tensile stress,and which become insensitive to stress after the phase transition points.Our research provides a method to control the electronic and magnetic properties of VX_(2) by stress,and the single-layer and double-layer VX_(2) may have potential applications in nano spintronic devices.展开更多
The photoluminescence （PL） and Raman spectra of undoped ZnO films deposited directly on Si substrate （sample A）,on Si substrate through a SiC buffer layer （sample B）,and on a ZnO crystal wafer （sample C） are i...The photoluminescence （PL） and Raman spectra of undoped ZnO films deposited directly on Si substrate （sample A）,on Si substrate through a SiC buffer layer （sample B）,and on a ZnO crystal wafer （sample C） are investigated. There are emission peaks centered at 3.18eV （ultraviolet,UV） and 2.38eV （green） in these sampies. Comparing the Raman spectra and the variation of the PL peak intensities with annealing atmosphere, we conclude that the luminescence of the samples is related to the tensile strain in the ZnO film due to the lattice mismatch between the film and the substrate. In particular, the tensile strain reduces the formation energy of OZn antisite oxygen defects,which generate the green emission center. After annealing in oxygen-rich atmosphere, many OZn defects are generated. Thus, the intensity of green emission in ZnO/Si hetero-structure materials increases due to tensile strain in ZnO films.展开更多
Sheet metal formed of lightweight materials such as aluminum sheeting has received great attention related to the reduction of vehicle emissions. This paper evaluates the anisotropic yield locus using Kuwabara＇s biax...Sheet metal formed of lightweight materials such as aluminum sheeting has received great attention related to the reduction of vehicle emissions. This paper evaluates the anisotropic yield locus using Kuwabara＇s biaxial tensile tester and stretches formability using Hecker＇s hemispheri- cal punch stretching test for aluminum 6016-T4 sheet material. The anisotropic yield locus of the A16016-T4 sheet measured is fitted well by the modified Drucker yield func- tion. Moreover the best fitting to the experimental stress- strain curve from the tensile test was obtained by taking an appropriate hardening model. Analytical study to predict the stretch formability by using Hora＇s Modified Maximum Force Criterion （MMFC） was performed. The predicted forming limit curves （FLC） based on various yield functions were compared with the experiments and discussed.展开更多
Aluminum alloys have drawn considerable attention in the area of automotive lightweight.High strength aluminum alloys are usually deformed at elevated temperatures due to their poor formability at room temperature.In ...Aluminum alloys have drawn considerable attention in the area of automotive lightweight.High strength aluminum alloys are usually deformed at elevated temperatures due to their poor formability at room temperature.In this work,the yield behavior of 7075 aluminum alloy in T6 temper(AA7075-T6)within the temperature ranging from 25°C to 230°C was investigated.Uniaxial and biaxial tensile tests with the aid of induction heating system were performed to determine the stress vs.strain curves and the yield loci of AA7075-T6 at elevated temperatures,respectively.Von Mises,Hill48 and Yld2000-2d yield criteria were applied to predicting yield loci which were compared with experimentally measured yield loci of the AA7075-T6.Results show that yield stress corresponding to the same equivalent plastic strain decreases with increasing temperature within the investigated temperature range and the shape of yield loci evolves nearly negligibly.The experimental yield locus expands with an increase of equivalent plastic strain at the same temperature and the work hardening rate of AA7075-T6 exhibits obvious stress-state-dependency.The nonquadratic Yld2000-2d yield criterion describes the yield surfaces of AA7075-T6 more accurately than the quadratic von Mises and Hill48 yield criteria,and an exponent of 14 in the Yld2000-2d yield function gives the optimal predictions for the AA7075-T6 at all investigated temperatures.展开更多
Effects of transverse loads on longitudinal stress strain behaviors and longitudinal constant tensile loads on transverse stress strain behaviors of single ply of nylon cord rubber composite are studied respectively u...Effects of transverse loads on longitudinal stress strain behaviors and longitudinal constant tensile loads on transverse stress strain behaviors of single ply of nylon cord rubber composite are studied respectively under biaxial tensile condition with cruciform specimen. Effects of transverse constant tensile load on longitudinal tensile mechanical properties are indistinctive compared with corresponding uniaxial longitudinal tensile mechanical properties. It can be relative to larger difference between longitudinal and transverse mechanical properties. Its dominating failure mode is typical fiber dominated mode; However, Experiment results indicate that transverse mechanical properties of nylon cord rubber composite with longitudinal constant tensile loads are distinct from its uniaxial transverse tensile mechanical properties. It can be attribute to action of longitudinal tension that makes material rigidify in the direction perpendicular to fiber, Mode of failure is representative of matrix dominated failure. For the measurement of large deformation up to 50 percent, a special CCD imaging method is employed in the experimental investigation that makes measurement of large deformations more precise.展开更多
Commercially pure(CP)titanium is thermally processed and subjected to biaxial stress.However,the evolution of the microstructural deformation mechanisms under such circumstances is not adequately understood.In this st...Commercially pure(CP)titanium is thermally processed and subjected to biaxial stress.However,the evolution of the microstructural deformation mechanisms under such circumstances is not adequately understood.In this study,the mechanical responses and microstructural deformation mechanisms of TA2 CP titanium sheets under equi-biaxial loading at room temperature(RT),300℃,and 400℃were studied.The activated slip and twinning systems were investigated by transmission electron microscopy(TEM)after polished cruciform specimens were biaxially tensile-tested at RT and elevated temperatures.The results show that{11¯22}contraction twinning and{10¯12}extension twinning are the main deforma-tion mechanisms of RT biaxial deformation,while dislocation glide is predominant in biaxial deformation at 300℃and 400℃.This difference yields varied work-hardening behaviors at RT and elevated tem-peratures.In biaxial deformation at 400℃,the main slip trace type is multiple slip.The interaction of different slip systems in multiple slip created shear deformation concentration areas and further induced cross-slip.However,in biaxial deformation at 300℃,the amounts of simplex and multiple slip were significantly reduced compared to those at 400℃because the lower temperature increased the critical resolved shear stress and insufficient activated slip systems were available for grain deformation.There-fore,several stress-concentration areas were generated with the activation of cross-slip.展开更多
基金Funded by the National Natural Science Foundation of China(Nos.51205298 and 51475345)the China Postdoctoral Science Foundation(No.2014M552096)the Open Fund Project of State Key Laboratory of Materials Processing and Die&Mould Technology,Huazhong University of Science and Technology(No.P2015-01)
文摘The effects of biaxial tensile pre-strain on the forming limit of DP590 high-strength steel under high strain rate were investigated. The stress-strain curves of DP590 steel sheet under the biaxial tensile of different load ratios were obtained. The forming limit diagrams（FLDs） of DP590 steel sheet under biaxial tensile pre-strain and electromagnetic hybrid forming were established. Results showed that the biaxial tensile pre-strain had significant effects on the formability of DP590 steel. The pre-strain in a certain range improved the forming limit of DP590 steel under high rate, and the forming limit increased with the pre-strain. The prestrain in the same direction of high rate increased the forming limit of the final deformation under complex strain paths conditions, but the pre-strain in the vertical direction decreased the minor strain under the high strain rate.
基金supported by the National Natural Science Foundation of China (Grant Nos. 60976068 and 60936005)the Cultivation Fund of the Key Scientific and Technical Innovation Project,Ministry of Education of China (Grant No. 78083)
文摘After constructing a stress and strain model, the valence bands of in-plane biaxial tensile strained Si is calculated by k·p method. In the paper we calculate the accurate anisotropy valance bands and the splitting energy between light and heavy hole bands. The results show that the valance bands are highly distorted, and the anisotropy is more obvious. To obtain the density of states （DOS） effective mass, which is a very important parameter for device modeling, a DOS effective mass model of biaxial tensile strained Si is constructed based on the valance band calculation. This model can be directly used in the device model of metal-oxide semiconductor field effect transistor （MOSFET）. It also a provides valuable reference for biaxial tensile strained silicon MOSFET design.
文摘This paper mainly studies on the biaxial tensile strength and its calculative formula of a special made concrete. According to the Hill theory and the uniaxial tensile experiment results, the expression of the concrete biaxial tensile strength is deduced, which is then combined with experiment data and checked. The result shows： the biaxial tensile strength of this kind of concrete is about 15%-30% lower than its uniaxial tensile strength, and the calculative value is basically consistent with the experiment value, with less than 11% difference. This kind of biaxial tension weakening effect is very important to the structure designs of concrete road. The author suggests further research.
基金supported by the National Natural Science Foundation of China (Nos.11922211,11832015,11527803)the 111 Project,China (No.BP0719007)the Science Challenge Project,China (No.TZ2018001).
文摘The dynamic failure behavior of CoCrFeNi High-Entropy Alloy(HEA)under plane biaxial stress was investigated in detail.The dynamic biaxial tensile tests were conducted using an Electromagnetic Biaxial Split Hopkinson Tensile Bar(EBSHTB)system.For comparison,the quasi-static uniaxial and biaxial tensile tests,as well as dynamic uniaxial tensile tests,were per-formed respectively.A cruciform specimen suitable for large plastic deformation was designed and employed in the experiments.The Finite Element Method(FEM)verified that the improved cruciform specimen could satisfy the basic requirements.The feasibility of the proposed specimen was further confirmed through loading tests.Finally,the quasi-static and dynamic yield loci of the HEA in the first quadrant of the principal stress space were plotted.The results indicate that the alloy exhibits obvious strain hardening effect and strain rate strengthening effect,the yield locus and plastic work contours can be accurately described by Hill'48 criterion.
基金the financial support from National Natural Science Foundation of China(Nos.11922211,11832015,11527803)the 111 Project,China(No.BP0719007)Science Challenge Project,China(No.TZ2018001).
文摘The biaxial tensile behavior of isotropic Ti-6Al-4 V is characterized in this paper.A novel cruciform specimen was designed and optimized to achieve uniform stress and strain distribution within the gauge area.Biaxial tensile tests were conducted at three different loading ratios by the biaxial testing machine.The Digital Image Correlation(DIC)technique was applied to determine strain distribution,and a high-speed camera was employed to record the fracture process.An Inverse Analysis(IA)approach with a combined experimental and numerical method was proposed to determine the true stresses at the gauge section of the specimen during biaxial tensile tests.The results indicate that the initial yield locus can be described by the Cazacu criterion accurately,whereas the Mises criterion can predict better the strengthening behavior of Ti-6Al-4 V in the first quadrant in the principal stress space.
基金supported by the National Natural Science Foundation of China(Grant No.51875027)the China Postdoctoral Science Foundation(No.2018M630058)assistances of the program for the financial support。
文摘This paper focused on the effect of pre-strain on forming limit curves(FLC)of 5754-O aluminum alloy sheet through utilizing biaxial tensile approach.Based on Swift model and Yld2000-2 d yield criterion,the dimensions of cruciform specimen was optimized through applying finite element method for increasing the strain at specimen center.After that,with the recommended specimen size,the cruciform specimen was tested under various stroke ratios to experimentally characterize the limit strains under different pre-strain levels.Subsequently,the biaxial tensile tests were simulated by Abaqus to obtain the limit strains and validate the material models.It can be observed in both experiments and simulations that the pre-strained uniaxial tension followed by plane tension or equi-biaxial tension can improve the formability of sheet metals.Besides,the strain path change affects the trend of first derivative of strain rate difference between neighboring points with respect to time.An early increase occurred and then fell back to the stable value,the steady evolution continued until to a new increase reaching the critical value.The M–K prediction approach was simulated to verify the influence of pre-strain on FLC.It can be found that the early increase peaks of the major strain incremental ratio rose with the amplitude of pre-strain.Finally,the phenomenon of pseudolocalization caused by the strain path change was explained through evolution of stress state inside the groove.
基金This research was funded by National Natural Science Foundation of China （51275026） and State Key Laboratory of Development and Application Technology of Automotive Steels （Bao Steel Y 12ECEQ07Y）.
文摘The biaxial tensile tests were carried out to investigate the deformation behavior and yield loci of dual-phase （DP） steel sheets under biaxial tensile conditions. The true stress-true strain curves of DP steel sheets for different loading ratios were obtained, and the experimental yield loci were determined based on the equivalent plastic work principle. The experimental yield loci were compared to the theoretical yield loci based on Hi1148, Hi1190, Hi1193, Hosford, Barlat89, Yld2000-2d and Gotoh yield criteria. It is found that Yld2000-2d yield criterion can describe the general trends of experimental yield loci of DP steel sheets with comparably higher accuracy. Hosford criterion has the maximum error for DP590, whereas Hi1148 and Barlat89 have the maximum errors for DP780 and DP980.
基金the financial support from the National Key R&D Program of China(2018YFC0808800)the National Natural Science Foundation of China(Nos.51875398 and 51471116)the Sichuan Science and Technology Program(2019ZDZX0001).
文摘Magnesium alloys are frequently subjected to biaxial stress during manufacturing process,however,the work hardening behavior under such circumstance are not well understood.In this study,the deformation mechanisms and differential work hardening behavior of rolled AZ31 magnesium alloy sheets under biaxial loading are investigated.The change of plastic work contours with increasing plastic strain indicates the differential work hardening behavior of AZ31 magnesium alloy under biaxial stress state,resulting in higher macroscopic work hardening rates of biaxial loading than uniaxial loading,with the elastic-plastic transition part of work hardening extended and stage Ⅲ hardly emerged.Electron backscatter diffraction and Schmid factor analysis confirm the low activation of non-basalslip during biaxial loading tests.While the thickness strain is primarily accommodated by pyramidal<c+a>slip at the initial stage of biaxial deformation,{10–11}contraction twinning is activated at larger plastic strain.The low activation of non-basalslip also retards the dynamic recovery and cross-slip of basal and prismaticslips,leading to the differential work hardening behavior of AZ31 magnesium alloy under biaxial stress state.
基金supported by the National Natural Science Foundation of China(Grant Nos.11904312 and 11904313)the Project of Hebei Educational Department,China(Grant Nos.ZD2018015 and QN2018012)the Natural Science Foundation of Hebei Province,China(Grant No.A2019203507).
文摘First-principles calculations and Monte Carlo simulations reveal that single-layer and double-layer VX_(2)(X=Cl,Br)can be tuned from antiferromagnetic(AFM)semiconductors to ferromagnetic(FM)state when biaxial tensile stress is applied.Their ground states are all T phase.The biaxial tensile stress at the phase transition point of the double-layer VX_(2) is larger than that of the single-layer VX_(2).The direct band gaps can be also manipulated by biaxial tensile stress as they increases with increasing tensile stress to a critical point and then decreases.The Neel temperature(´TN)of double-layer VX_(2) are higher than that of single-layer.As the stress increases,the TN of all materials tend to increase.The magnetic moment increases with the increase of biaxial tensile stress,and which become insensitive to stress after the phase transition points.Our research provides a method to control the electronic and magnetic properties of VX_(2) by stress,and the single-layer and double-layer VX_(2) may have potential applications in nano spintronic devices.
文摘The photoluminescence （PL） and Raman spectra of undoped ZnO films deposited directly on Si substrate （sample A）,on Si substrate through a SiC buffer layer （sample B）,and on a ZnO crystal wafer （sample C） are investigated. There are emission peaks centered at 3.18eV （ultraviolet,UV） and 2.38eV （green） in these sampies. Comparing the Raman spectra and the variation of the PL peak intensities with annealing atmosphere, we conclude that the luminescence of the samples is related to the tensile strain in the ZnO film due to the lattice mismatch between the film and the substrate. In particular, the tensile strain reduces the formation energy of OZn antisite oxygen defects,which generate the green emission center. After annealing in oxygen-rich atmosphere, many OZn defects are generated. Thus, the intensity of green emission in ZnO/Si hetero-structure materials increases due to tensile strain in ZnO films.
基金Supported by National Research Foundation of Korea(NFR)grant funded by the Korea Government(MEST)(No.2014R1A2A2A01005903)Priority Research Center Program(No.2010-0020089)
文摘Sheet metal formed of lightweight materials such as aluminum sheeting has received great attention related to the reduction of vehicle emissions. This paper evaluates the anisotropic yield locus using Kuwabara＇s biaxial tensile tester and stretches formability using Hecker＇s hemispheri- cal punch stretching test for aluminum 6016-T4 sheet material. The anisotropic yield locus of the A16016-T4 sheet measured is fitted well by the modified Drucker yield func- tion. Moreover the best fitting to the experimental stress- strain curve from the tensile test was obtained by taking an appropriate hardening model. Analytical study to predict the stretch formability by using Hora＇s Modified Maximum Force Criterion （MMFC） was performed. The predicted forming limit curves （FLC） based on various yield functions were compared with the experiments and discussed.
基金Supported by National Natural Science Foundation of China(Grant No.51805375).
文摘Aluminum alloys have drawn considerable attention in the area of automotive lightweight.High strength aluminum alloys are usually deformed at elevated temperatures due to their poor formability at room temperature.In this work,the yield behavior of 7075 aluminum alloy in T6 temper(AA7075-T6)within the temperature ranging from 25°C to 230°C was investigated.Uniaxial and biaxial tensile tests with the aid of induction heating system were performed to determine the stress vs.strain curves and the yield loci of AA7075-T6 at elevated temperatures,respectively.Von Mises,Hill48 and Yld2000-2d yield criteria were applied to predicting yield loci which were compared with experimentally measured yield loci of the AA7075-T6.Results show that yield stress corresponding to the same equivalent plastic strain decreases with increasing temperature within the investigated temperature range and the shape of yield loci evolves nearly negligibly.The experimental yield locus expands with an increase of equivalent plastic strain at the same temperature and the work hardening rate of AA7075-T6 exhibits obvious stress-state-dependency.The nonquadratic Yld2000-2d yield criterion describes the yield surfaces of AA7075-T6 more accurately than the quadratic von Mises and Hill48 yield criteria,and an exponent of 14 in the Yld2000-2d yield function gives the optimal predictions for the AA7075-T6 at all investigated temperatures.
文摘Effects of transverse loads on longitudinal stress strain behaviors and longitudinal constant tensile loads on transverse stress strain behaviors of single ply of nylon cord rubber composite are studied respectively under biaxial tensile condition with cruciform specimen. Effects of transverse constant tensile load on longitudinal tensile mechanical properties are indistinctive compared with corresponding uniaxial longitudinal tensile mechanical properties. It can be relative to larger difference between longitudinal and transverse mechanical properties. Its dominating failure mode is typical fiber dominated mode; However, Experiment results indicate that transverse mechanical properties of nylon cord rubber composite with longitudinal constant tensile loads are distinct from its uniaxial transverse tensile mechanical properties. It can be attribute to action of longitudinal tension that makes material rigidify in the direction perpendicular to fiber, Mode of failure is representative of matrix dominated failure. For the measurement of large deformation up to 50 percent, a special CCD imaging method is employed in the experimental investigation that makes measurement of large deformations more precise.
基金support from the National Key R&D Program of China(No.2020YFA0405901),National Natural Science Foundation of China(No.51875398),the Sichuan Science and Technology Program(No.2019ZDZX0001)the Science and Technology on Reactor System Design Technology Laboratory,Nuclear Power Institute of China.In addition,we would like to thank Zhejiang Institute of Tianjin University,Ningbo.
文摘Commercially pure(CP)titanium is thermally processed and subjected to biaxial stress.However,the evolution of the microstructural deformation mechanisms under such circumstances is not adequately understood.In this study,the mechanical responses and microstructural deformation mechanisms of TA2 CP titanium sheets under equi-biaxial loading at room temperature(RT),300℃,and 400℃were studied.The activated slip and twinning systems were investigated by transmission electron microscopy(TEM)after polished cruciform specimens were biaxially tensile-tested at RT and elevated temperatures.The results show that{11¯22}contraction twinning and{10¯12}extension twinning are the main deforma-tion mechanisms of RT biaxial deformation,while dislocation glide is predominant in biaxial deformation at 300℃and 400℃.This difference yields varied work-hardening behaviors at RT and elevated tem-peratures.In biaxial deformation at 400℃,the main slip trace type is multiple slip.The interaction of different slip systems in multiple slip created shear deformation concentration areas and further induced cross-slip.However,in biaxial deformation at 300℃,the amounts of simplex and multiple slip were significantly reduced compared to those at 400℃because the lower temperature increased the critical resolved shear stress and insufficient activated slip systems were available for grain deformation.There-fore,several stress-concentration areas were generated with the activation of cross-slip.
