To obtain the influence of fluid pressure and temperature on warm hydroforming of 5A06-O aluminum alloy sheet, the unified mechanics equilibrium equations, which take through- thickness normal stress and friction into...To obtain the influence of fluid pressure and temperature on warm hydroforming of 5A06-O aluminum alloy sheet, the unified mechanics equilibrium equations, which take through- thickness normal stress and friction into account, were established in spherical coordinate system. The distribution of through-thickness normal stress in the thickness direction was determined. The relation between through-thickness normal stress and fluid pressure was also analyzed in different regions of cylindrical cup. Based on the method of subtracting one increasing function from another, the constitutive equation of 5A06-O applied to warm hydroforming was established and in a good agreement with uniaxial tensile data. Based on whether the thickness variation was taken into account, two mechanic models were established to do the comparative study. The results for the studied case show that the calculated stress values are pretty close according to the two models and consistent with results of finite element analysis; the thickness distribution in flange computed by the second model conforms to the experimental data. Finally, the influences of fluid pressure on the flange thickness and radial stress were analyzed.展开更多
For better controllability in actuations,it is desirable to create Functionally Graded Shape Memory Alloys（FG-SMAs）in the actuation direction.It can be achieved by applying different heat treatment processes to crea...For better controllability in actuations,it is desirable to create Functionally Graded Shape Memory Alloys（FG-SMAs）in the actuation direction.It can be achieved by applying different heat treatment processes to create the gradient along the radius of a SMA cylinder.Analytical solutions are derived to predict the macroscopic behaviors of such a functionally graded SMA cylinder.The Tresca yield criterion and linear hardening are used to describe the different phase transformations with different gradient parameters.The numerical results for an example of the model exhibit different pseudo-elastic behaviors from the non-gradient case,as well as a variational hysteresis loop for the transformation,providing a mechanism for easy actuation control.When the gradient disappears,the model can degenerate to the non-gradient case.展开更多
The high-temperature deformation behavior of a beta Ti-3.0 Al-3.5 Cr-2.0 Fe-0.1 B alloy was investigated by a Gleeble-1500 D thermal simulator. The height reduction was 50%, corresponding to a true strain of 0.693. Th...The high-temperature deformation behavior of a beta Ti-3.0 Al-3.5 Cr-2.0 Fe-0.1 B alloy was investigated by a Gleeble-1500 D thermal simulator. The height reduction was 50%, corresponding to a true strain of 0.693. The strain rate ranging from 0.01 to 10.00 s^-1 and the deformation temperature ranging from 800 to 950 ℃ were considered.The flow stress and the apparent activation energy for deformation, along with the constitutive equation, were used to analyze the behavior of the Ti-3.0 Al-3.5 Cr-2.0 Fe-0.1 B alloy. The processing map was established. The effect of strain rate on the microstructure at 850 ℃ was evaluated.The flow stress-strain curves indicated that the peak flow stresses increased along with an increase in the strain rate and decreased as the deformation temperature increased.Based on the true stress-true strain curves, the constitutive equation was established and followed as the ε= 6.58×10-（10）[sinh（0.0113σ）]-（3.44）exp（-245481.3/RT）. The processing map exhibited the ＂unsafe＂ region at the strain rate of10 s^-1 and the temperature of 850 ℃,and the rest region was ＂safe＂. The deformation microstructure demonstrated that both dynamic recovery（DRV） and dynamic recrystallization（DRX） existed during deformation. At the lower strain rate of 0.01 s^-1, the main deformation mechanism was the DRV, and the DRX was the dominant deformation mechanism at the higher strain rate of 1.00 s^-1.展开更多
In order to optimize the deformation processing, the hot deformation behavior of Co-Cr-Mo-Cu （here- after named as Co-Cu） alloy was studied in this paper at a deformation temperature range of 950-1150 ℃ and a strai...In order to optimize the deformation processing, the hot deformation behavior of Co-Cr-Mo-Cu （here- after named as Co-Cu） alloy was studied in this paper at a deformation temperature range of 950-1150 ℃ and a strain rate range of 0.008-5 s^-1. Based on the true stress-true strain curves, a constitutive equation in hyperbolic sin function was established and a hot processing map was drawn. It was found that the flow stress of the Co-Cu alloy increased with the increase of the strain rate and decreased with the increase of the deforming temperature. The hot processing map indicated that there were two unstable regions and one well-processing region. The microstructure, the hardness distribution and the electro- chemical properties of the hot deformed sample were investigated in order to reveal the influence of the hot deformation. Microstructure observation indicated that the grain size increased with the increase of the deformation temperature but decreased with the increase of the strain rate. High temperature and low strain rate promoted the crystallization process but increased the grain size, which results in a reduction in the hardness. The hot deformation at high temperature （1100-1150 ℃） would reduce the corrosion resistance slightly. The final optimized deformation process was： a deformation temperature from 1050to 1100 ℃, and a strain rate from 0.008 to 0.2 s^-1, where a completely recrystallized and homogeneously distributed microstructure would be obtained.展开更多
Two constitutive models,the modified Johnson-Cook model and the logarithm linear relation model based on empirical approach and data analysis,were presented to illustrate compressive deformation of magnesium alloys AZ...Two constitutive models,the modified Johnson-Cook model and the logarithm linear relation model based on empirical approach and data analysis,were presented to illustrate compressive deformation of magnesium alloys AZ80 under multiple loading directions and strain rates.The results of stress-strain curve analysis and sensitivity index analysis suggested that the stress held large fluctuations in loading direction of 90°.Model testing signified that the logarithm linear relation model was more proper than the modified Johnson-Cook model in view of relative mean square error and correlation coefficients.Moreover,numerical simulation building on established models also indicated that the logarithm linear model is more precise than the modified Johnson-Cook model.展开更多
The hot compressive deformation behavior of hot isostatically pressed Ti-47.5Al-2Cr-2Nb-0.2W-0.2B alloy using gas atomization powders was systematically investigated and the processing map was obtained in the temperat...The hot compressive deformation behavior of hot isostatically pressed Ti-47.5Al-2Cr-2Nb-0.2W-0.2B alloy using gas atomization powders was systematically investigated and the processing map was obtained in the temperature range of 1323-1473 Kand strain rate range of 0.001-0.5s^（-1）.The calculated activation energy in the above variational ranges of temperature and strain rate possesses a low activation energy value of approximately 365.6kJ/mol based on the constitutive relationship models developed with the Arrhenius-type constitutive model respectively considering the strain rate and deformation temperature.The hot working flow behavior during the deformation process was analyzed combined with the microstructural evolution.Meanwhile,the processing maps during the deformation process were established based on the dynamic material model and Prasad instability criterion under different deformation conditions.Finally,the optimal hot processing window of this alloy corresponding to the wide temperature range of 1353-1453 Kand the low strain rate of 0.001-0.1s^（-1） was obtained.展开更多
基金co-supported by the International Cooperation of RFBR-NSFC (No. 51111120088)the financial support from the National Natural Science Foundation of China (No. 50975014)
文摘To obtain the influence of fluid pressure and temperature on warm hydroforming of 5A06-O aluminum alloy sheet, the unified mechanics equilibrium equations, which take through- thickness normal stress and friction into account, were established in spherical coordinate system. The distribution of through-thickness normal stress in the thickness direction was determined. The relation between through-thickness normal stress and fluid pressure was also analyzed in different regions of cylindrical cup. Based on the method of subtracting one increasing function from another, the constitutive equation of 5A06-O applied to warm hydroforming was established and in a good agreement with uniaxial tensile data. Based on whether the thickness variation was taken into account, two mechanic models were established to do the comparative study. The results for the studied case show that the calculated stress values are pretty close according to the two models and consistent with results of finite element analysis; the thickness distribution in flange computed by the second model conforms to the experimental data. Finally, the influences of fluid pressure on the flange thickness and radial stress were analyzed.
基金the financial support of National Natural Science Foundation of China (no.11502284, 51505483, 11772041)the Fundamental Research Funds for the Central Universities (3122016C006) of China
文摘For better controllability in actuations,it is desirable to create Functionally Graded Shape Memory Alloys（FG-SMAs）in the actuation direction.It can be achieved by applying different heat treatment processes to create the gradient along the radius of a SMA cylinder.Analytical solutions are derived to predict the macroscopic behaviors of such a functionally graded SMA cylinder.The Tresca yield criterion and linear hardening are used to describe the different phase transformations with different gradient parameters.The numerical results for an example of the model exhibit different pseudo-elastic behaviors from the non-gradient case,as well as a variational hysteresis loop for the transformation,providing a mechanism for easy actuation control.When the gradient disappears,the model can degenerate to the non-gradient case.
基金financially supported by the.National Natural Science Foundation of China (No.51401027)the China Postdoctoral Science Foundation Funded Project (No.2016M591040)
文摘The high-temperature deformation behavior of a beta Ti-3.0 Al-3.5 Cr-2.0 Fe-0.1 B alloy was investigated by a Gleeble-1500 D thermal simulator. The height reduction was 50%, corresponding to a true strain of 0.693. The strain rate ranging from 0.01 to 10.00 s^-1 and the deformation temperature ranging from 800 to 950 ℃ were considered.The flow stress and the apparent activation energy for deformation, along with the constitutive equation, were used to analyze the behavior of the Ti-3.0 Al-3.5 Cr-2.0 Fe-0.1 B alloy. The processing map was established. The effect of strain rate on the microstructure at 850 ℃ was evaluated.The flow stress-strain curves indicated that the peak flow stresses increased along with an increase in the strain rate and decreased as the deformation temperature increased.Based on the true stress-true strain curves, the constitutive equation was established and followed as the ε= 6.58×10-（10）[sinh（0.0113σ）]-（3.44）exp（-245481.3/RT）. The processing map exhibited the ＂unsafe＂ region at the strain rate of10 s^-1 and the temperature of 850 ℃,and the rest region was ＂safe＂. The deformation microstructure demonstrated that both dynamic recovery（DRV） and dynamic recrystallization（DRX） existed during deformation. At the lower strain rate of 0.01 s^-1, the main deformation mechanism was the DRV, and the DRX was the dominant deformation mechanism at the higher strain rate of 1.00 s^-1.
基金financially supported by the National Natural Science Foundation of China (Nos. 81071262, 31271024 and 31470930)the Funding from Northeastern University ("985 program", Nos. N141008001 and LZ2014018), China
文摘In order to optimize the deformation processing, the hot deformation behavior of Co-Cr-Mo-Cu （here- after named as Co-Cu） alloy was studied in this paper at a deformation temperature range of 950-1150 ℃ and a strain rate range of 0.008-5 s^-1. Based on the true stress-true strain curves, a constitutive equation in hyperbolic sin function was established and a hot processing map was drawn. It was found that the flow stress of the Co-Cu alloy increased with the increase of the strain rate and decreased with the increase of the deforming temperature. The hot processing map indicated that there were two unstable regions and one well-processing region. The microstructure, the hardness distribution and the electro- chemical properties of the hot deformed sample were investigated in order to reveal the influence of the hot deformation. Microstructure observation indicated that the grain size increased with the increase of the deformation temperature but decreased with the increase of the strain rate. High temperature and low strain rate promoted the crystallization process but increased the grain size, which results in a reduction in the hardness. The hot deformation at high temperature （1100-1150 ℃） would reduce the corrosion resistance slightly. The final optimized deformation process was： a deformation temperature from 1050to 1100 ℃, and a strain rate from 0.008 to 0.2 s^-1, where a completely recrystallized and homogeneously distributed microstructure would be obtained.
基金Item Sponsored by National Natural Science Foundation of China(11271339)Plan for Scientific Innovation Talent of Henan Province of China
文摘Two constitutive models,the modified Johnson-Cook model and the logarithm linear relation model based on empirical approach and data analysis,were presented to illustrate compressive deformation of magnesium alloys AZ80 under multiple loading directions and strain rates.The results of stress-strain curve analysis and sensitivity index analysis suggested that the stress held large fluctuations in loading direction of 90°.Model testing signified that the logarithm linear relation model was more proper than the modified Johnson-Cook model in view of relative mean square error and correlation coefficients.Moreover,numerical simulation building on established models also indicated that the logarithm linear model is more precise than the modified Johnson-Cook model.
基金the financial supports from the National Natural Science Foundation of China(Grant Nos.51301157 and 51434007)the National High Technology Research and Development Program of China 863 Program(Grant No.2013AA031103)
文摘The hot compressive deformation behavior of hot isostatically pressed Ti-47.5Al-2Cr-2Nb-0.2W-0.2B alloy using gas atomization powders was systematically investigated and the processing map was obtained in the temperature range of 1323-1473 Kand strain rate range of 0.001-0.5s^（-1）.The calculated activation energy in the above variational ranges of temperature and strain rate possesses a low activation energy value of approximately 365.6kJ/mol based on the constitutive relationship models developed with the Arrhenius-type constitutive model respectively considering the strain rate and deformation temperature.The hot working flow behavior during the deformation process was analyzed combined with the microstructural evolution.Meanwhile,the processing maps during the deformation process were established based on the dynamic material model and Prasad instability criterion under different deformation conditions.Finally,the optimal hot processing window of this alloy corresponding to the wide temperature range of 1353-1453 Kand the low strain rate of 0.001-0.1s^（-1） was obtained.
