Journal of Applied Physics
Based on the developed multiple-scattering theory [C.-W. Nan and F. S. Jin, Phys. Rev. B 48, 8578 (1993)], an effective-medium theory (EMT) is proposed to treat coupled electromechanical behavior in composite media. The explicit relations for determining effective behavior of piezoelectric composites are derived. To illustrate the technique, numerical results of piezoelectric ceramic/epoxy composites for various particle shapes are presented over the whole range of concentrations. The EMT estimates are shown to be in good agreement with available experimental results. Porous piezoelectric ceramics are also discussed. The EMT predicts a similar critical behavior for heterogeneous piezoelectric materials to recent experiments.
关键词:
electromechanical properties;ceramics
张莉
,
马敬红
,
梁伯润
,
余亦华
高分子材料科学与工程
在氮气氛中采用热重分析的方法对热致液晶共聚酯60PHB/PEN的热降解动力学进行了研究.采用Friedman和Chang两种单一加热速率方法对活化能Ea、反应级数n和频率因子Z等降解反应动力学参数进行了分析.讨论了加热速率和计算方法对热稳定性及降解动力学参数的影响.
关键词:
热致液晶共聚酯
,
热降解
,
动力学
,
热稳定性
金属学报
Volu扣ne 27SeriesB1991AUTHOR INDEX CCAO Guanghan(曹光旱)············……6一B科6CAo weijie(曹卫恋)..················……5一B32oCAO Yilin(曹益林)··················……6一B443CHANG Xin(常听)···············……1一B48CHE Guang邻n(车广灿)·············一6一B科0CHEN Erbao(陈二保)···············……6一B410CHEN Jia....
关键词:
徐颖
,
温卫东
,
崔海坡
材料科学与工程学报
doi:10.3969/j.issn.1673-2812.2006.01.020
针对复合材料层板在冲击载荷下,各种损伤的产生和扩展是一个随载荷、时间和空间而演变的过程,发展了复合材料层合板低速冲击逐渐累积损伤预测方法.采用刚度退化技术和改进的Chang-Chang失效准则、显式有限元法来模拟复合材料层合板受到低速冲击下逐渐损伤过程.使用所发展的方法分析了[0m/90n/0m]铺层的复合材料层合板在低速冲击过程中的逐渐损伤扩展,结果表明本文的方法能较好地模拟复合材料层板在低速冲击下的损伤扩展及变形过程,计算结果与实验结果吻合较好;对不同冲击能量下层合板损伤扩展研究表明,冲击能量与分层损伤面积成线性关系.
关键词:
复合材料层合板
,
冲击
,
逐渐累积损伤
,
破坏机理
,
数值模拟
张鹏飞
,
金海波
复合材料学报
建立了有效的复合材料层合板结构冲击损伤分析方法,层合板面内损伤采用改进的Chang/Chang失效准则做判据,得到面内各类损伤形式.层间损伤采用与Mixed-Mode粘接元等效的TIEBREAK接触模拟.利用此分析方法,从复合材料薄壁结构设计需要出发,研究了在低能量冲击下,铺层的层间角度、铺层方向、铺层重叠对层合板结构冲击损伤阻抗的影响规律,并对它们的综合影响进行了总体分析,得到了能提高层合板结构损伤阻抗的铺层顺序设计指导.最后用该设计指导对某种铺层结构进行了重新设计和有限元模拟,验证了该设计指导的可行性和有效性.
关键词:
冲击损伤
,
分层损伤
,
TIEBREAK接触
,
铺层顺序
,
损伤阻抗
Acta Materialia
In a first report [Jin ZH.. Gumbsch P, Ma E, Albe K, Lu K, Hahn H, et al. Scripta Mater 2006;54:1163], interactions between screw dislocation and coherent twin boundary (CTB) were studied via molecular dynamics simulations for three face-centered cubic (fcc) metals, Cu, Ni and Al. To complement those preliminary results, purely stress-driven interactions between 60 degrees non-screw lattice dislocation and CTB are considered in this paper. Depending on the material and the applied strain, slip has been observed to interact with the boundary in different ways. If a 60 degrees dislocation is forced by an external stress into a CTB, it dissociates into different partial dislocations gliding into the twin as well as along the twin boundary. A sessile dislocation lock may be generated at the CTB if the transited slip is incomplete. The details of the interaction are controlled by the material-dependent energy barriers for the formation of Shockley partial dislocations from the site where the lattice dislocation impinges upon the boundary. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
关键词:
dislocation;slip;twinning;twin grain boundary;molecular dynamics;molecular-dynamics simulation;grain-boundaries;nanocrystalline;materials;cross-slip;rate sensitivity;deformation;copper;strength;aluminum;fcc
LIU Yongning
,
ZHU Jinhua
,
ZHOU Huijiu Xi'an Jiaotong University
,
Xi'an
,
China A.Kildegaard
,
J.A.Kristensen Department of Mechanical Engineering
,
Aalborg University
,
Denmark Dept.of Materials Science and Engineering Xi'an Jiaotong University
,
Xi'an 710049
,
China
金属学报(英文版)
The dynamic fracture toughness of a mild steel has been studied at different loading rates and temperatures.The material exhibits a transition from tough to brittle fracture with the chang- ing loading rate alone.Analysis of the fracture process by the theory of thermal activation suggests that the fracture activation energy approximates to the bond energy of the{100}of a unit cell.The toughness can be resolved into two parts,J-(fd)=J_a+J_l,where J_a is the athermal part,being independent on temperature and loading rate,while J_l=(K/K_o)~(1/n)exp(Q_f/nkT),which controls the fracture process is temperature and load- ing rate dependent.The transition of fracture mechanism caused by both temperature and loading rate is associated with the thermal movement of atoms.
关键词:
mild steel
,
null
,
null
,
null
曹春海
,
杨名
,
张世远
,
杨森祖
,
崔旭高
,
尤立星
,
吉争鸣
,
康琳
,
许伟伟
低温物理学报
doi:10.3969/j.issn.1000-3258.2003.03.002
采用Nd0.7Sr0.3MnO3/SrTiO3/YBa2Cu3O7-δ的异质结构,研究了自旋极化准粒子的注入效应.在56μm宽的YBCO膜条上成功地制备了与超导膜条同样宽度但不同长度的六个注入结区,长度L分别为80μm, 40μm, 20μm, 10μm, 5μm和2μm.80nm厚的YBCO薄膜在16K温度下Jc为2×105A/cm2.Iin=0.5mA的自旋电流注入下,随L从80μm逐渐顺次减小时,注入效率η=ΔJc/ΔJin逐渐增大.而当L≤20μm后,η不再增加,达到几乎相同的值(～6).初步分析认为这与自旋极化准粒子在超导膜内的有效自旋扩散长度有关.异质结构中YBCO薄膜的超导电性以及注入窗口的尺寸对获得大的自旋注入效率十分重要.
关键词:
注入效率
,
自旋准粒子
,
巨磁阻
,
异质材料
王艳龙
,
蔡敬标
,
陆晓峰
,
朱晓磊
复合材料学报
doi:10.13801/j.cnki.fhclxb.20160328.005
针对含孔复合材料点阵夹层结构在面内压缩载荷作用下的失效模式及其影响因素问题，通过实验对含孔复合材料点阵夹层结构失效模式进行了研究；基于3D Hashin准则和Chang-Chang刚度退化准则建立了含孔复合材料点阵夹层结构有限元渐进损伤失效分析模型，并将计算结果与实验结果进行了对比；基于有限元分析方法探讨了开孔形状、开孔率以及开孔位置对其极限承载力的影响。结果表明：当点阵夹层结构面板厚度较大时，含孔复合材料点阵夹层结构的主要失效模式为面板圧溃；通过对比有限元计算结果和实验结果，极限承载力的最大误差约为12%，失效位置与实验结果一致；当点阵夹层结构的对称面与载荷方向平行且孔的中心在对称面上时，面内压缩强度与开孔位置无关，主要受到开孔形状和开孔率的影响；当点阵夹层结构对称面与载荷方向垂直且孔的中心在对称面上时，边距大于一个胞元，面内压缩强度基本不变，边距小于一个胞元，面内压缩强度下降。
关键词:
点阵夹层结构
,
开孔率
,
开孔位置
,
开孔形状
,
压缩强度
