The flow curves of 300M steel exhibit a transition from stress peak presence to stress peak absence as the strain rate increases. It is difficult to establish dynamic recrystallization(DRX) kinetics models suitable fo...The flow curves of 300M steel exhibit a transition from stress peak presence to stress peak absence as the strain rate increases. It is difficult to establish dynamic recrystallization(DRX) kinetics models suitable for strain rates where there are no stress peaks in the flow curves using the existing Avrami equation, and the optimal processing parameters for forging can be scarcely acquired.In this study, the high-temperature flow and DRX behavior of 300M steel are investigated by performing isothermal compression tests at temperatures between 1173–1423K with strain rates between 0.001–50 s-1. Distinct stress peaks can be found in the flow curves at low strain rates, and the average grain size decreases with the increase in the strain rate at the same temperature. The DRX mechanism is a discontinuous DRX, and the grain boundary migration plays an important role in the DRX process. In contrast, no stress peak is observed in the flow curves at high strain rates, and the average grain size no longer decreases with the strain rate increase at the same temperature. The DRX mechanism in this case is a continuous DRX. The demarcated strain rate is calculated based on the characteristics of the obtained flow curves and grain sizes. The recrystallization volume fraction model and prediction grain size model at high strain rates are established. In combination with the existing DRX kinetics models at low strain rates, the processing parameters can be optimized to produce components with excellent mechanical properties.展开更多
A method determining molecular weight distribution index D (MWD) from viscosity versus shear stress flow curves for polypropylene has been presented.Based on the experimental data,the correlation between the viscosity...A method determining molecular weight distribution index D (MWD) from viscosity versus shear stress flow curves for polypropylene has been presented.Based on the experimental data,the correlation between the viscosity η of molten polypropylene and its MWD can be expressed as η/η-0=｛1+a(τD)+m｝+{-1},where η-0 is the zero shear viscosity, τ is the shear stress, a and m are empirical parameters.Furthermore,a simpler method to estimate the MWD from only two experimental data,i.e.the melt index (MI) and the zero shear viscosity has also been presented,the calculated results are in good agreement with the data from GPC measurements.展开更多
The flow curvesshear-rate rangeby using theof bagasse Kraft black liquor over aof 10-1 s- 1-103s- 1 were investigatedRheometric RFSII rheometerExperimental results show that Bagasse black liquorsare non-Newtonian flui...The flow curvesshear-rate rangeby using theof bagasse Kraft black liquor over aof 10-1 s- 1-103s- 1 were investigatedRheometric RFSII rheometerExperimental results show that Bagasse black liquorsare non-Newtonian fluids instead of Newtonian fluidsat higher solids contents, and the viscosities of blackliquor would decrease about 2-3 orders of magnitudewith an increase in the shear rates. The apparentviscosity and flow behavior of bagasse black liquorare also affected by its solids content, and the highersolids content the more shear-thinning bagasse blackliquor fluid is. In addition, the power-law equationwas utilized to fit these flow curves at differentconditions. Finally, the significances ofshear-thinning properties of bagasse black liquor inthe chemical recovery system, such as frictioncalculation of pipe and design optimization of thewhole recovery system, were presented.展开更多
通过V ISS IM模拟方法,对常发性拥挤的扩散规律进行研究,得出拥挤扩散时的波动性、延滞性、传递性等特点,对相邻检测站间的排队车辆数和排队长度拥挤指标进行量化。采用变换后的累计流量曲线(N曲线)对拥挤持续时间进行预测,并与真实值...通过V ISS IM模拟方法,对常发性拥挤的扩散规律进行研究,得出拥挤扩散时的波动性、延滞性、传递性等特点,对相邻检测站间的排队车辆数和排队长度拥挤指标进行量化。采用变换后的累计流量曲线(N曲线)对拥挤持续时间进行预测,并与真实值进行比较分析,验证了该预测方法的有效性。展开更多
基金supported by the National Natural Science Foundation for Distinguished Young Scholars of China(Grant No.51725504)the State Key Program of National Natural Science Foundation of China(Grant No.51435007)
文摘The flow curves of 300M steel exhibit a transition from stress peak presence to stress peak absence as the strain rate increases. It is difficult to establish dynamic recrystallization(DRX) kinetics models suitable for strain rates where there are no stress peaks in the flow curves using the existing Avrami equation, and the optimal processing parameters for forging can be scarcely acquired.In this study, the high-temperature flow and DRX behavior of 300M steel are investigated by performing isothermal compression tests at temperatures between 1173–1423K with strain rates between 0.001–50 s-1. Distinct stress peaks can be found in the flow curves at low strain rates, and the average grain size decreases with the increase in the strain rate at the same temperature. The DRX mechanism is a discontinuous DRX, and the grain boundary migration plays an important role in the DRX process. In contrast, no stress peak is observed in the flow curves at high strain rates, and the average grain size no longer decreases with the strain rate increase at the same temperature. The DRX mechanism in this case is a continuous DRX. The demarcated strain rate is calculated based on the characteristics of the obtained flow curves and grain sizes. The recrystallization volume fraction model and prediction grain size model at high strain rates are established. In combination with the existing DRX kinetics models at low strain rates, the processing parameters can be optimized to produce components with excellent mechanical properties.
文摘A method determining molecular weight distribution index D (MWD) from viscosity versus shear stress flow curves for polypropylene has been presented.Based on the experimental data,the correlation between the viscosity η of molten polypropylene and its MWD can be expressed as η/η-0=｛1+a(τD)+m｝+{-1},where η-0 is the zero shear viscosity, τ is the shear stress, a and m are empirical parameters.Furthermore,a simpler method to estimate the MWD from only two experimental data,i.e.the melt index (MI) and the zero shear viscosity has also been presented,the calculated results are in good agreement with the data from GPC measurements.
文摘The flow curvesshear-rate rangeby using theof bagasse Kraft black liquor over aof 10-1 s- 1-103s- 1 were investigatedRheometric RFSII rheometerExperimental results show that Bagasse black liquorsare non-Newtonian fluids instead of Newtonian fluidsat higher solids contents, and the viscosities of blackliquor would decrease about 2-3 orders of magnitudewith an increase in the shear rates. The apparentviscosity and flow behavior of bagasse black liquorare also affected by its solids content, and the highersolids content the more shear-thinning bagasse blackliquor fluid is. In addition, the power-law equationwas utilized to fit these flow curves at differentconditions. Finally, the significances ofshear-thinning properties of bagasse black liquor inthe chemical recovery system, such as frictioncalculation of pipe and design optimization of thewhole recovery system, were presented.
