Nitin KOTKUNDE
,
Sashank SRINIVASAN
,
Geetha KRISHNA
,
Amit Kumar GUPTA
,
Swadesh Kumar SINGH
中国有色金属学报(英文版)
doi:10.1016/S1003-6326(16)64140-7
成形极限图是一种用来描述使板材不发生局部颈缩所需最大主应变的重要图形。它是一种预测板材变形过程中变形极限的方便、有效的工具。本研究中，在400°C和不同样品宽度的条件，通过Nakazima实验得到了Ti?6Al?4V合金的成形极限图。此外，为了使用成形极限图对材料参数进行理论预测，提出了不同的各向异性屈服准则(Barlat 1989, Barlat 1996, Hill 1993)和不同的硬化模型(Hollomon幂定律、Johnson?Cook(JC)模型、改进的Zerilli?Armstrong (m-ZA)和Arrhenius (m-Arr)模型)。结合所提出的屈服准则和本构模型，通过Marciniak和Kuczynski (M?K)理论确定了Ti?6Al?4V合金的成形极限图。结果表明：屈服模型对材料成形极限图的影响大于本构模型的影响。然而，材料的厚度缺陷系数(f0)与其硬化模型密切相关。Hill(1993)屈服准则最适合于成形极限图右边区域的预测，而Barlat(1989)屈服准最适合于成形极限图左边区域的预测。由于所得到的混合理论成形极限图兼具Barlat(1989)和Hill(1993)屈服模型和m-Arr硬化模型的优点，因此，它与实验得到的成形极限图吻合很好。
关键词:
Ti-6Al-4V合金
,
屈服准则
,
硬化模型
,
Marciniak-Kuczynsk理论
,
成形极限图
Industrial & Engineering Chemistry Research
The densities, viscosities, and conductivities were measured for the ternary solution NaCl + urea + H(2)O, the quintuple solution NaC1 Na(2)SO(4) KCl K(2)SO(4) + H(2)O, and their binary subsystems at 298.15 K. The results together with the densities, viscosities, and conductivities of multicomponent solutions reported in the literature were used to study the predictability of the Young's rule for density and conductivity, the rule of Patwardhan and Kumar for density, Flu's equation for the viscosity of mixed electrolyte solutions based on the Eyring's absolute rate theory and the rule of Patwardhan and Kumar, and the semiideal solution theory for thermodynamic and transport properties. The results show that all the tested equations can provide comparable and accurate predictions for the densities of multicomponent electrolyte solutions. The semiideal solution theory is applicable to the aqueous solutions of electrolytes and nonelectrolytes, and its predictions for the densities of the examined solutions are in nice agreement with the experimental results. The simple equation based on Eyring's absolute rate theory and the rule of Patwardhan and Kumar and the semiideal solution theory can provide nice predictions for the viscosity of the tested electrolyte solutions. The predictions for the viscosity of the ternary solution NaCl + urea + H(2)O by the semiideal solution theory are also in accordance with the measured viscosities. The semiideal solution theory can provide better predictions for the conductivities of the tested electrolyte solutions than the extended Young's rule, and their predictions are both in good agreement with the experimental results. The advantages of the semiideal solution theory are briefly discussed and reviewed.
关键词:
mixed-electrolyte-solutions;linear isopiestic relation;absolute rate;theory;aqueous-solutions;298.15 k;activity-coefficients;sodium-chloride;potassium-chloride;ternary subsystems;unified;approach
LU Lu
,
WANG Fu-zhong
,
WANG Zhao-xu
,
ZHU Guang-ya4
,
ZHANG Xing-xiang5
钢铁研究学报(英文版)
Based on test data from the hot forge experiments on Gleeble 1500, a Kumar type constitutive equation for 33Mn2V steel is established. Applying this constitutive equation in commercial FEM software of MSC/SuperForm 2005, the piercing process of 33Mn2V steel in Mannesmann mill is then simulated. The modeling results visualized the dynamic evolution of equivalent stress, especially inside the workpiece. It is shown that the non-uniform distribution of stress on the internal and external surface of the workpiece is a distinct characteristic of processing tube piercing. The numerical model was verified by comparing the values of calculated force parameters of the piercing process with those measured in laboratory conditions. And it shows that the Kumar-type constitutive relationship meets the practical needs.
关键词:
33Mn2V
,
constitutive equation
,
tube piercing process
,
thermo-mechanical coupling simulation
,
FEM analysis
张辉
,
郑桂丽
,
田毅
,
张志东
液晶与显示
doi:10.3788/YJYXS20163108.0740
基于 Pramoda Kumar 等人文章中关于向列相液晶反转壁中＋1缺陷处挠曲电效应的实验现象，我们利用 Landau-de Gennes 理论给出相应的理论分析。当对弱锚定的平行排列向列相液晶盒施加垂直基板的直流电压，在反转壁中的±1缺陷会发生旋转。对于其中的＋1缺陷，我们给出了外加电场作用下液晶分子的自由能表达式并通过模拟描述指向矢的方位角和极角的变化情况给出相应的缺陷处电场驱动的结构变化。模拟结果给出的挠曲电效应引起的方位角的变化角度与 Pramoda Kumar 等人的实验得到的在＋1缺陷处消光刷的变化情况是一致的。
关键词:
液晶
,
挠曲电效应
,
+1 缺陷
,
Landau-de Gennes 理论
熊煦
,
龚方红
,
蒋必彪
,
施海华
,
陶国良
,
刘春林
高分子材料科学与工程
利用差示扫描量热法结合Avrami方程研究了线性低密度聚乙烯(LLDPE)、LLDPE/SEBS及不同接枝率的LLDPE/SEBS-g-MAH的非等温结晶动力学.通过Gupta法、Jeziorny法和莫志深法分别对非等温结晶过程进行处理,结果显示,热塑性弹性体SEBS及其接枝物的加入阻碍了LLDPE分子链的规则排列,影响了链段在结晶扩散迁移规整排列的速度,使得结晶速率变慢,对LLDPE晶体生长起了抑制作用.但在所有结晶速率下,样品的Avrami指数n值均在1.1～1.5之间,说明LLDPE的结晶成核机理和生长方式没有改变.
关键词:
非等温结晶动力学
,
差示扫描量热分析
,
接枝
,
马来酸酐
,
线性低密度聚乙烯
任强
,
孙春燕
,
刘伟
高分子材料科学与工程
对茂金属聚乙烯(mPE-1)和传统的Ziegler-Natta聚乙烯(PE7042)的非等温结晶行为进行了研究.用DSC测试了两种聚乙烯的非等温结晶过程,采用Jeziorny法、莫志深法和Gupta法等对所得数据进行了分析.结果发现,mPE-1的结晶速率比PE7042低.在实验范围内,两种物料的非等温结晶动力学符合莫志深方程,并给出了动力学参数F(T)和a值.
关键词:
茂金属催化剂
,
聚乙烯
,
非等温结晶
,
结晶动力学
Journal of Physics-Condensed Matter
Nb(2)AsC showed superior mechanical properties to those of other layered ternary carbides (Kumar et al 2005 Appl. Phys. Lett. 86 111904). In the present density functional calculation, the underlying mechanism is interpreted by astonishing bonding features of Nb(2)AsC. The Nb d-As (p(x) + p(y)) and Nb d-As p(z) bonding states locate in the same energy range as those of Nb d-C p bonding, which indicates that the Nb-As bond has similar bonding strength as the Nb-C bond does; and thereafter, Nb(2)AsC has improved mechanical properties compared to the others. The present reported bonding features are interestingly different from those experienced by T(2)AlC (T=Ti, V, Cr, and Nb), wherein the weak T-Al coupling was separated from T-C bonding states in the higher energy level by a pseudogap. This work proposes an effective method to strengthen the relative weaker T-A (A is the A-group element) bonding in layered ternary carbides.
关键词:
ti3sic2;solids;gpa
袁清华
,
张文明
,
黄重国
,
任学平
稀有金属
doi:10.3969/j.issn.0258-7076.2009.04.005
采用普通工业TC4板料,在MTS高温拉伸试验系统上进行了不同变形条件的恒速拉伸试验,研究材料的高温变形行为.分析了5类通用高温本构关系对该材料真实应力应变曲线的拟合情况.最终,采用经典的Kumar模型建立了TC4的高温本构关系.利用MARC分析TC4机身盒形零件的气压成形过程,依据正交试验原理确定FEA仿真方案,并对成形模具进行了设计.以壁厚标准差为评价指标,采用极差分析法确定各因素对指标的影响程度和最佳工艺参数,并通过气压成形试验获得满足质量要求的零件.
关键词:
TC4(Ti-6Al-4V)
,
本构关系
,
气压成形
,
有限元分析
Weiyan LÜ
,
Lin LI
,
Li WANG
,
Yanlin HE
,
Shuigen HUANG
材料科学技术（英文）
Phase diagram information of the Fe-C, Fe-Al and Al-C systems are reviewed and the Fe-Al-C system is assessed. A FeAlC database is created by combining a set of thermodynamic parameters established by Kumar and SSOL database in Thermo-Calc software package. Ternary phase diagrams are calculated with FeAlC and the newly developed Thermo-Calc databases SSOL2 and SSOL4. The FeAlC database is the best one to describe the Fe-Al-C system. A1 and A3 values on the vertical section containing 1.5 wt pct Al are calculated with the FeAlC database in this work. To validate the thermodynamic calculation, critical temperatures Ac1 and Ac3 are determined by using dilatometer analysis. There exist some errors between the calculated values and the experimental results. So further optimization of the Fe-Al-C system regarding bcc and fcc phases is necessary. The experimental data in this work could be of some value in further optimization.
关键词:
Fe-Al-C
,
null
,
null
刘雨龙
,
王辅忠
中国冶金
使用MSC.Superform 2005有限元仿真软件,结合无锡西姆莱斯钢管有限公司提供的曼内斯曼穿管机结构,建立基于33Mn2V钢的三维有限元仿真模型.仿真设计采用静力隐式算法,结合Kumar本构模型对实心坯二辊斜轧穿孔过程进行热力耦合有限元模拟分析.模拟结果显示了穿管过程中出现的开裂等质量缺陷,而且缺陷位置处的塑性应变与试验计算值吻合.模拟结果表明:椭圆形孔腔以及管坯下压量是导致管口与导板摩擦过大并产生开裂的主要原因.为实际生产产品质量提高以及同行业进行相关仿真设计提供一定的参考.
关键词:
二辊斜轧
,
开裂
,
热力耦合
,
有限元仿真
