李尧
,
彭书华
,
杨俊杰
稀有金属
doi:10.13373/j.cnki.cjrm.2014.06.006
在不同脉冲电流条件下对纯钽试样进行拉伸实验,结果表明脉冲电流降低了加工硬化程度,可改善金属的塑性变形能力,并且随着脉冲电流密度的增加,其抗拉强度降低,延伸率提高,当电流密度J=7.64×102 A·cm-2时,延伸率达到50.7％,提高幅度为10％,同时抗拉强度从380 MPa降低至300 MPa,降幅为21％.针对实测的流动应力应变曲线,结合Hollomon模型和Voce模型,考虑脉冲电流对加工硬化的影响,提出H-V综合模型,建立塑性变形本构方程,反映脉冲电流对应力应变的影响.在一定脉冲电流条件下,确定了每种模型的9个最佳参数,利用已确定的模型对拉伸应力应变曲线进行模拟,并与实测的曲线对比验证.模拟结果显示,在变形初期阶段,3种模型之间模拟结果差别都很小,并且模拟值与实际值差异很小,预测准确度较高.随着应变的增大,差异越来越明显,H-V综合模型、Voce模型、Hollomon模型对大应变的模拟精度依次增加,3种模型的趋势线拟合决定系数R2分别为0.99900,0.96409和0.88368,均方差分别为2.42,26.32,39.26.H-V模型模拟效果最佳,能更准确地描述纯钽在电致塑性效应过程中的应力流动行为.
关键词:
电致塑性效应
,
脉冲电流
,
本构方程
,
加工硬化
,
应力
,
应变
刘卫卫
,
张律
,
岳春光
,
苏佳楠
,
白朴存
,
陈瑶
稀有金属材料与工程
结合仪器化微米划入和仪器化微米压入对(BNNT-BNNP)/(ZrB2-SiC)超高温陶瓷复合材料的形变强化效果及机理进行研究,并利用光学金相显微镜(OM)、冷场发射扫描电镜(SEM)和高分辨透射电镜(HR-TEM)分别对压痕和划痕、样品断口形貌及显微组织结构进行分析.结果表明,(BNNT-BNNP)/(ZrB2-SiC)超高温陶瓷复合材料具有显著的形变强化效应,且随着(BNNT-BNNP)含量的增多,复合材料的形变强化效果愈加明显.复合材料在放电等离子烧结制备的冷却阶段,因其组成相热膨胀系数的显著差异,导致ZrB2相内形成大量位错,且以固定位错为主.这些固定位错将阻碍可动位错的运动,使复合材料塑性变形的阻力增大,导致复合材料呈现明显的形变强化效应.
关键词:
超高温陶瓷
,
形变强化
,
位错
,
仪器化划入
,
仪器化压入
Y.N. Kwon and Y.-W. Chang(Center for Advanced Aerospace Materials (CAAM)
,
Pohang University of Science and Technology
,
Pohang 790-784. Korea Manuscript received 26 August 1996)
金属学报(英文版)
Superplastic forming of a thin sheet into complex shape is an important manufacturing process especially in aerospace industry. The main objective of modeling the superplastic forming process is to predict the forming pressure-time cycle to maintain the optimum strain rate and the resulting thickness distribution. There have been many attempts to model superplastic forming process using the various techniques including finite element method. However, most of these attempts so far have disregarded the strain hardening effect which occurs in several superplastic materials. In this study,we have used ABAQUS finite element code to predict the suitable processing variables during an axisymmetric cup forming of Supral 100 and 7075Al alloys to examine the strain hardening effects on forming. The performance of numerical results was then compared with the experimental results.
关键词:
:superplastic forming
,
null
,
null
,
null
,
null
TANG Changguo
,
ZHU Jinhua
,
ZHANG Yuhua
,
ZHOU HuijiuResearch Institute for Strength of Metals. Xi'an Jiaotong University. Xi'an. China
金属学报(英文版)
Variable strain rate tension tests for 4 metallic materials show that as the strain rate in creases the strain hardening exponent n decreases. The trend follows a two stage linear relation between n and Ig (?). When (?) < (?)cp, i.e. under quasi-static loading, n can be considered as a constant, but when (?)>(?)cp, n decreases rapidly till an ideal plastic state. n = 0. The characterizations and mechanisms of softening induced by high (?) are discussed.
关键词:
strain rate
,
null
,
null
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null
