中国力学学会学术大会2005.doc

中国力学学会学术大会2005 ( CCTAM2005 ) 应变梯度偶应力理论的三场杂交元方法研究* 李雷1 吴长春2 谢水生1 1有色金属研究总院,有色金属材料制备加工国家重点实验室,北京,100088 2上海交通大学建工学院,上海,200240 摘要: 为解释金属材料在微米和亚微米量级时所体现出的尺度效应现象,Fleck和Hutchinson提出了应变梯度偶应力塑性理论,该理论建立在Toupin-Mindlin线弹性应变梯度理论框架内,在经典塑性理论基础上考虑了应变梯度的影响.其中包括只考虑旋转梯度影响的偶应力理论(CS)和同时计及旋转和拉伸梯度的理论(SG).这两种理论的特点是在本构模型引入材料特征长度参数,刻画微结构尺度效应.Gao与Huang等提出了一个基于细观机制的MSG应变梯度理论.Acharya和Bassani在经典塑性理论的框架内,把应变梯度作为提高材料切线模量的内变量,避免了高阶应力和高阶边界条件的出现.Chen和Wang基于一般的偶应力理论,建立了将偶应力理论和内变量方法相结合的新的应变梯度硬化理论. 本文将重点研究Fleck-Hutchinson偶应力应变梯度理论的数值实施方法.由于该理论引入了旋转梯度,需要单元C1连续,这对传统位移元来说非常苛刻.Herrmann采用Lagrange乘子法引入旋转约束,设计了几种仅要求C0连续的混合单元.但这类混合元变量众多,且主对角线上有零元素,给存储和求解带来一系列困难.Xia通过改造板元构造了满足C1连续的单元,他们指出,在应变梯度起作用时,该单元性能有所恶化.Shu等为了降低单元连续性要求,从一般的偶应力理论出发,采用罚函数法放松了旋转自由度约束,取得了较好的效果.随后,Shu等发展了一组混合元用于应变梯度材料计算,避免了构造C1类单元的困难,却暴露出混合元法的一系列弊病,如单元会出现零能模式,系统离散方程组非正定等.总的来说,目前可用的单元不多. 在一般的偶应力理论下,微结构的转角是独立变量,与周围宏观介质的转动没有必然联系,当二者之间的相对转动为零时,蜕化为简化的偶应力理论.因此,从一般的偶应力理论出发,可避免单元C1连续性要求的困难.另一方面,为简化理论分析,Fleck-Hutchinson应变梯度塑性理论采用了材料不可压缩假定,这就对单元提出了更高的要求,普通位移型单元在材料不可压缩时有体积自锁现象.Pian等已证明,对于近不可压缩问题,杂交元仍可获得满意的解答.鉴此,本文基于一般的偶应力理论,导出了杂交元的应力优化条件,据此构造了C0类连续的三类变量杂交元,数值结果表明,该单元对可压缩和不可压缩状态的梯度材料均可给出合理的数值结果,再现材料的尺度效应. 关键词: 有限元方法,杂交元,偶应力理论,尺度效应,能量相容条件 纳米压痕实验的准连续介质模拟 曾凡林 孙毅 (哈尔滨工业大学航天科学与力学系,哈尔滨 150001) 摘要:用准连续介质方法(quasicontinuum method,QC方法) 模拟了大规模原子的镍薄膜的在纳米压痕实验下的行为.QC方法是一种采用连续介质(有限元)和分子动力学相结合的方法,在所研究对象绝大部分不受关注的区域采用有限元的方法处理,而在需要重点观察的区域采用分子动力学的方法来处理.既能证了问题研究的精度,又保证了处理问题的规模.本文中压头为矩形压头,宽度为28.2 ,长度与镍薄膜宽度一致,完全刚性.镍薄膜的长宽高分别为3000 ,1500 ,1500 ,附* 国家自然科学基金资助项目(资助号:10172078, 50374014) 中国学术会议在线 1中国力学学会学术大会2005 ( CCTAM2005 ) 着在刚性基底上.压头位置处于镍薄膜中间,如图1所示.通过模拟,研究了镍薄膜在纳米压痕实验下以下几个方面的行为.1,载荷位移响应.在载荷位移曲线上除了反应晶体弹性性质的直线外还有数次的载荷突然下降过程.2,位错成核现象.与载荷位移曲线上的载荷突然下降相对应的在受压的晶体上发现了位错成核现象,说明载荷的下降是因为位错成核引起的.3,位错的发射机制.用弹性能,表面能和位错对反应能分析了位错的发射机制,理论值与计算值吻合较好.4,几何必需位错密度.用一个简单的模型计算了几何必须位错密度.此外还考虑了边界条件对模拟结果的影响.通过此工作,很好地模拟和了解了FCC晶体在发生塑性变形的初始阶段的一系列行为和作用机制.QC方法是一种在微纳米力学数值模拟中非常有前途的方法. 关键词:准连续介质方法,分子动力学,纳米压痕实验,位错 图1,镍的纳米压痕实验模拟的准连续介质模型 利用交错模型预测蒙脱土/尼龙纳米复合材料刚度 戴瑛1,嵇醒1,Y.-W. Mai2 (1.固体力学教育部重点实验室,航空航天与力学学院,同济大学,上海200092;2.先进材料技术中心,悉尼大学,澳大利亚) 22d2a2lMMT platelets 摘要: 蒙脱土增强尼龙6是一种纳米复合材料1, 2.其突出的特点是在很低的百分含量下就可以对基体某些性能(模量,强度等)有较好的改进,如重量百分量5-6的蒙脱土对尼龙6模量的提高量需要3倍的玻璃纤维才能达到3.蒙脱土增强尼龙6在合成和性能测试等方面已有了大量的研究和结果,但对蒙脱土增强尼龙6的机理研究却远不充分4. Nylon-6 (a) MTT对纳米复合材料刚度的提高已有了一些定性和定量的研究5.以往的用于纤维复合材料的理论和方法被借用于预测纳米尺度的复合材料,如混合率6,Halpin-Tsai方程3和Mori-Tanaka方法3等,另有学者根据蒙脱土薄片周围的微结构假设建立了混杂的三相平行模型(combined parallel-series three-phase model)7和分级模型(hierarchical model)8等. b J ger9在预测矿物化胶原蛋白纤维时采用了交错排列模型,由于在模型中引入了剪切变形,使得到的模量预测结果远高于平行模型.在胶原蛋白纤维中矿物化胶原蛋白薄片为纳米尺度并有很高的比表面积,而蒙脱土片也有类似的结构,其厚度约为1nm,表面积约为750m2/g 4.在完全剥离的蒙脱土/尼龙6纳米复合材料的模量预测中,对蒙脱土薄片我们采用了J ger的二维理想交错排列模式(图1a).图1b是代表性体积单元和针对蒙脱土/尼龙6纳米复合材料进行的特征变形区划分.其中A(蒙脱土片),B和D(尼龙6)区是拉伸变形区,C区(尼龙6)承受拉伸和剪切两种变形.在本文模型中,我们考虑了蒙脱土片的变形,在变形区域的划分上也对J ger模型进行了改进. FA FD FBD B A (b) C A 假设A和B区的变形是线性的,C和D区是均匀的,则各区的力和变形之间的关系为: B A区: M=KA (FA + FAB) D B区: N=KB (FAB + FB) C区: N=KC ( FA -FAB)FAFB FD 中国学术会议在线 中国力学学会学术大会2005 ( CCTAM2005 ) (1) M=KCD FCD 图1 (a)交错模型和(b)代表性 体积单元及变形区划分 D区: N= KD FD =KD (FCD+ FAB -FB ) 其中,FA, FB, FC, FD, FAB和 FCD是四个区中的作用力; M和 N是蒙脱土和尼龙(B区)的伸长变形;KA, KB, KC, KD 和KCD是各区的拉伸和剪切柔性系数,分别为 357911130123V %Youngs Modulus (GPa)Test results of Ref.3FEMStaggered model of JagerPresent staggered model图2蒙脱土/尼龙6纳米复合材料预测结果 与实验结果的比较 hbElKhbEaKhlGbKhdEaKhdElKNylonCDNylonDNylonCNylonBMMTA=2, 2,2,2,2代表性体积单元所受的合力和总伸长量分别为F总=FA + FB + FD 和 总= M+ N,则,纳米复合材料的弹性模量为 中国力学学会学术大会2005 ( CCTAM2005 ) 半导体稳态vQHD模型的数值模拟 胡新 (北京大学力学与工程科学系,北京,100871) 摘要:随着现代半导体器件的特征尺寸越来越小,我们必须考虑量子效应的作用.由Wigner Fokker-Planck方程,我们可以推导出vQHD(Viscous Quantum Hydrodynamic)模型1.vQHD模型能够给出可靠的数值结果,其结果显示出共穿隧道二极管(RTD, Resonant Tunnelling Diode)一些典型的非线性现象,比如负阻效应(negative differential resistivity)和迟滞(hysteresis)现象2.但是,vQHD模型的数值模拟是相当耗时的,因而我们考虑采用稳态vQHD模型: 1qqdivJDnq= (1) 22020116qqBBDqkTJJqqndivnnVnqnmkTmmn+ h0qqJDJ= + (2) ()(divVqnC = ) (3) 用中心差分离散以上方程组并采用Newton-Raphson方法求解离散的非线性方程组.我们给出了偏压V的结果.当偏压增加 很小时,我们认为变量的变化都很小,所以可以将V0=VU=的结果作为初值来计算VU时的稳态vQHD模型.但是,当偏压增加到使电流变化很大时,由于Newton-Raphson方法对初值的敏感性,Newton-Raphson方法是不能正确求解非线性方程组的.这时我们必须采用vQHD模型来计算.最终我们就可以得到RTD的I-V曲线. V =+参考文献 1 A. Arnold, J.A. Carrilo, and E. Dhamo. On the periodic Wigner-Poisson-Fokker-Planck system. J. Math. Anal. Appl. 275 (2002), 263-276 2 A. Juengel, and S. Tang. Numerical approximation of the viscous quantum hydrodynamic model for semiconductors, (submitted). 两平行亲水板间液泡形貌的转变 刘建林 冯西桥 余寿文 清华大学工程力学系,北京100084 本文研究了两块平行板之间的液泡在板间距离发生变化时的形状改变(如图1所示).针对图示两种几何构形,结合Young方程和Laplace方程,可以分别写出其自由能表达式.对于常压差情况下,可以得到其发生临界转变的方程.对于常体积情况,首先得到了可能出现的四种构形的体积相图.然后进一步得到了构形发生改变时的构形力. 中国学术会议在线 4中国力学学会学术大会2005 ( CCTAM2005 ) 图1 液泡的两种几何形貌 原子在台阶表面上的吸附和扩散行为研究 张吉桥2 余寿文 冯西桥 (清华大学工程力学系,北京 100084) 摘要:台阶是固体表面常见的缺陷之一,如晶面在非平衡条件消除以后,表面会发生小面化,把原来光滑平坦的表面形成一个有许多台阶的表面.原子在台阶表面上的吸附和扩散行为不同于平坦表面上的行为,并且容易形成纳米结构,因此这方面的研究引起人们的广泛兴趣.台阶与吸附原子之间通过它们的弹性场相互作用,相互作用能对表面自由能密度有贡献,因而影响吸附原子在表面上的吸附和扩散行为.本文研究原子在台阶表面上的吸附和扩散行为,把台阶和吸附原子模拟为力偶极子,通过求解台阶和吸附原子各自产生的弹性场,从而得到台阶与吸附原子之间的相互作用能.以钨原子为例进行了数值计算,结果表明,吸附原子在台阶下部形成最稳定的吸附态,台阶对下台面上扩散的吸附原子形成捕获势,对上台面上扩散的吸附原子形成反射势.这些结果和实验结果符合得很好,同时还较好地反映出表面相互作用的实质. 纳米尺度下表/界面应力对材料力学行为的影响 王建祥 段慧玲 黄筑平 (北京大学,北京大学力学与工程科学系先进复合材料中心,北京100871) 2 张吉桥,男,1980年10月生,广东省从化市人,汉族.清华大学工程力学系博士研究生,研究方向为表面效应分析. 中国学术会议在线 5中国力学学会学术大会2005 ( CCTAM2005 ) 本文总结了考虑表/界面应力影响的非均质材料力学行为研究中的几个问题.首先介绍任意均匀本征应变作用下纳米尺度球形夹杂的Eshelby张量和任意均匀远场应力作用下的应力集中张量的性质;其次介绍具有纳米尺度球形夹杂的非均质材料宏观等效模量的理论预测;然后介绍纳米介孔材料等效模量的分析结果,特别指出,当介孔的表面弹性模量达到一定值时,介孔材料的某些弹性模量可以超过无孔母材的弹性模量,并指出了可能的表面改性途径;最后介绍了具有表/界面应力影响的情况下Eshelby张量,应力集中张量和等效弹性模量等遵循的简单标度律. 微孔洞长大尺度效应的位错动力学模拟 黄敏生 李振环3 (华中科技大学力学系,430074) 摘要:本文对二维(2D)无限大体中孤立微孔洞长大的微尺度效应进行了详细的离散位错动力学模拟分析.为了模拟微尺度下基体的离散位错机制,基体塑性通过线弹性场中大量离散刃型位错的动力学响应进行刻画,位错运动的晶格阻力,萌生,湮灭以及阻碍等位错短程作用通过一系列的本构法则进行描述.边值问题通过叠加位错场和边界像场进行求解,其中,含孔洞基体中刃型位错的位移及应力应变场根据Eshelby(1983)提出的应力函数方法求得;用于满足边界条件的像场通过有限元计算得到.针对含微孔洞的F.C.C.和B.C.C.单晶材料,重点探讨了应力状态,等效应变,位错源/障碍密度以及晶格排布形式等对微孔洞长大的尺度效应的影响. 关键词:微孔洞,尺度效应,滑移系,离散位错,应力函数法 多晶金属材料力学行为的云纹干涉法研究 郭智强 谢惠民 刘宝琛 戴福隆 (清华大学工程力学系 北京 100084) 摘要:细观塑性变形和细观本构理论的研究是当今固体力学研究的重要课题之一,细观尺度内包括位错,滑移,晶粒,界面等重要力学行为.多晶金属材料是常用的结构材料,了解这些材料在细观尺度力学行为对改进材料设计改善材料力学性能具有重要意义.在多晶粒金属材料试件中,由于晶粒大小与试件尺度相比不可忽略,因此使得试件在力学性能上表现出各向异性,在拉伸过程中,其应力应变场会出现不均匀分布现象.研究晶粒和界面的力学行为是力学工作者和设计工作者关注的问题. 本文用云纹干涉法研究多晶粒铝试样在拉伸过程中的细观变形场,观察记录了在特定载荷下的晶界滑错,晶粒的刚体转动,以及三晶交界处的变形场和应变场,观察在人工诱发裂纹情况下裂纹的扩展.为理论建模和数值计算提供实验依据. 关键词:晶粒 滑错 云纹干涉法 3联系作者,E-mail:zhli68 中国学术会议在线 6中国力学学会学术大会2005 ( CCTAM2005 ) 开孔泡沫材料弹塑性行为的三维数值模拟和宏观模型研究 甘益翔,陈常青*,沈亚鹏 (西安交通大学工程力学系,西安,710049) 摘要:本文利用三维Voronoi构型来模拟多孔介质的微细观组织与结构,并结合有限元方法对开孔泡沫材料的弹塑性宏观力学响应进行了数值分析,在此基础上提出了一个宏观的弹塑性本构模型.数值分析结果表明,在较低的相对密度范围内,采用Voronoi模型分析所得的泡沫材料弹性常数与理想Kelvin模型的分析结果接近;但随着相对密度的升高,理想Kelvin模型预测的杨氏模量和体积模量偏高.通过对弹性开孔泡沫材料在多轴压缩响应的数值研究发现,微结构的屈曲是泡沫材料在压缩过程中起主要作用的变形机理,弹性多孔材料的多轴失效服从最大压缩主应力准则.该结果与已有的实验结果相吻合.文中还利用Voronoi细观模型系统研究了弹塑性三维开孔泡沫材料的多轴压缩响应,得到了开孔泡沫材料在不同的比例加载状态下的力学行为.利用所得的数值结果和Chen和Lu(Int. J. Solids & Struct., 2000, Vol. 37, 7769)针对一般弹塑性材料提出的理论模型框架,建立了能够描述泡沫材料多轴行为的唯象模型.模型验证结果表明,所提出的唯象模型对于多孔材料在在比例加载情况下的响应具有很好的描述能力.文中还对现有的其它唯象模型进行了比较,发现本文基于Chen-Lu的唯象模型更为合理. 大变形镁合金晶粒表面滑移机理SEM原位观测试验研究 王习术14,靳丽2 1, 清华大学航天航空学院工程力学,100084,北京 2, 上海交通大学材料科学与工程学院,200030,上海 摘要:目前镁合金基于其汽车工业轻量化,环境保护等的要求,已经得到迅速发展,最为热门的是用镁合金制造发动机外壳及其他复杂结构产品,这就要求镁合金具有很好的变形能力.通过反复挤压的工艺方法已经制造出延伸率达40%左右的细晶镁合金材料,晶粒尺寸在1 m左右.但是,随着晶粒尺寸的减少,材塑性变形能力增加而材料的屈服强度逐渐偏离Hall-Petch关系().本研究通过几种大变形镁合金试样,在SEM原位拉伸试验过程中,对数个晶粒尺寸大小的观测范围,对塑性变形形式与特征进行了实时跟踪.如下图所示.这些结果表明:(1)较大晶粒表面更容易形成滑移,(2)总体滑移线与外加载荷方向呈40左右,(3)滑移条带按照一定角度呈蠕动扩展方式进行,(4)滑移的物理机制是晶粒位错连续偏转和移动造成,(5) 连续塑性滑移造成晶粒表面出现微裂纹,微裂纹主要出现在晶粒内而不是晶粒界面,裂纹的扩展导致断裂. 1/20yykd =+* Email: CChen 4 通讯作者 Email: xshwang 中国学术会议在线 7中国力学学会学术大会2005 ( CCTAM2005 ) 图1 变形初期 图2 =135MPa时晶粒局部滑移形貌 图3 =163MPa时晶粒局部滑移形貌 图4 =183MPa时晶粒局部滑移形貌 Modeling of Mechanics of interface of biological nanostructural composites Baohua Ji (Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China) Abstract: Organic-inorganic hybrid biological composites have refined microstructures from the nanoscale up to the macroscale. We have previously studied the fracture strength of nanometer sized mineral platelet, and found that the mineral platelet can hold the theoretical strength of mineral at the nanoscale even with the presence of flaws. However, we are not clear about the interface strength between protein and mineral and how the length scale influences their interface strength. In this work, I try to study the mechanics of interface of the biological materials by both continuum modeling and the atomistic modeling. A simple fracture model is firstly developed based on a tension-shear chain model (TSC). The model reveals that the interface strength is reversely scale with the square root of the characteristic size of the mineral platelet, exhibiting the same scaling law as that of fracture strength of mineral. In addition, large aspect ratio of mineral platelet can further enhance the interface strength. Afterwards, an atomistic model is developed to study the micro-mechanism of the interfacial slipping strength between protein and mineral at the atomistic scale. The MD simulation shows that the macroscopic smooth sliding between protein layer and mineral platelet is achieved by stick-slip of single protein molecular chains alternatively among the molecules. Therefore the interface strength is determined by the ability of the chain molecules anchoring at the substrate at a specific instant during the slipping which influenced by the temperature and the velocity of slipping. The MD simulation also shows that the chain structure of protein is an important mechanism to enhance the 中国学术会议在线 8中国力学学会学术大会2005 ( CCTAM2005 ) interfacial slipping strength and interface toughness of bio-nanocomposites. Acknowledgements This work is supported by the National Natural Science Foundation of China through Grant No. 10442002 and National Basic Research Program of China through Grant No. 2004CB619304 . Mechanical Tensile Behavior and Microstructure Evolution for Poly(vinylidene fluoride-trifluorethylene) copolymer thin films F. Fang, M. Z. Zhang, J. F. Huang ( Department of Engineering Mechanics, FML, Tsinghua University, Beijing, China 100084 ) Abstract: Ferroelectric materials form one important class of the functional materials. In recent years there has been increasing recognition of the importance of polymeric ferroelectric materials. Compared with ferroelectric ceramics or single crystals, polymeric ferroelectric materials show those advantages of lower density, easier processing, more flexible and easier to compliant with different forms of surfaces. Their lower mechanical and acoustic impedance also makes them good candidates as sensors and transducers in ultrasonic cardiac image, blood pressure and pulse measurements, touch sensors in robotics, etc. Among them, copolymers of vinylidene fluoride and trifluoroethylene (P(VDF-TrFE) are materials of great interest because of their outstanding dielectric and ferroelectric behavior. The copolymer thin films used in this investigation were prepared by solution-casting method. They were later treated with two different processing procedures. One is putting the solution-cast thin films directly into the vacuum oven and annealed at 135 for 2 hours. The thin films thus obtained are termed as directly annealed thin films. The other is first uniaxially stretching the solution cast thin films at room temperature to five times of the original length, and then annealing at 135oC for 2 hours. The thin films obtained are termed as stretched thin films. Thin films obtained by the above two processing methods have thicknesses ranging from 15-30 m. Thin films were cut into pieces 60mm long and 5 mm in width. The sample axes for the stretched thin films were oriented in the extended direction, while there was no such requirement for the annealed thin film samples because they are isotropic. Due to the viscoelasticity of the polymeric materials, the stress-strain behavior is dependent on the strain rate. The tensile tests were carried out at a constant crosshead speed of 0.2mm/min, and 5-7 samples were used to obtain the stress-strain behavior for both directly annealed and stretched thin films. In order to reveal the morphology and microstructure change during the uniaxial tensile measurements, samples before and after the tensile tests were examined in a Hitachi S-4500 filed emission scanning electron microscope. X-ray experiments were conducted in a reflection mode by using a MX18A-HF X x-ray diffractometer with CuK radiation (wavelength 0.154nm), operated at 40kV and 30mA. It was found that for the directly annealed thin films, there is little phase transformation from to phase. The distinct morphology change for the annealed sample is the dilation of the lamellae size and an increase in porosity. The samples show a typical polymeric brittle fracture feature. For the stretched copolymer thin films, an almost linearly strengthening stage occurs in the stress-strain curve after yielding, and the maximum strain at fracture and the tensile strength is much larger than those of the directly annealed thin films. Structure analysis indicates that there is apparent 中国学术会议在线 9中国力学学会学术大会2005 ( CCTAM2005 ) phase transformation from to phase. It was suggested that the elastic elongation of this newly formed phase contributes to the linearly strengthening stage after yielding in its stress-strain curve. SEM morphology shows that the porosity does not change very much while apparent shear bands occurs during the tension, which is consistent with the long yielding process exhibiting in its stress-strain curve. Cryogenic mechanical properties of polymer nanocomposites Shao-Yun Fu5 ( Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100080, China ) Abstract:With the rapid development of spacecraft and superconductive cable technologies, polymers are being used in these cryogenic applications. The requirements for polymers in these special applications are quite high and enhanced cryogenic mechanical properties are needed. One effective way to improve cryogenic mechanical properties of polymers is to incorporate nanofillers like SiO2 and MMT into polymers. In this work, epoxy and polyimide nanocomposites containing SiO2 and MMT nanofillers were prepared via in-situ sol-gel process and in-situ polymerization process etc. The cryogenic mechanical properties including tensile strength, modulus, failure strain and impact energy at 77 K of the nanocomposites were studied in detail. The mechanical properties at room temperature were also given for the purpose of comparison with the cryogenic mechanical properties. The fracture surfaces of the nanocomposites were examined with scanning electron microscopy (SEM) to look insight into the strengthening and toughening mechanisms. Keywords: Epoxy resin; Tensile properties; Thermal expansion; Low temperature 用纳米压痕仪表征压电薄膜和电沉积镍镀层的薄膜力学性能 周益春61,2,郑学军1,2,黄勇力2,章莎2 1先进材料及其流变特性教育部重点实验室,湖南省,湘潭大学,411105 2湘潭大学材料与光电物理学院,湖南省,湘潭大学,411105 摘要:本文用纳米压痕仪表征了两种典型薄膜即脆性薄膜/脆性基底的压电薄膜和韧性薄膜/韧性基底即电沉积镍镀层薄膜的5 Tel./Fax: +86-10-62659040. Email address: syfu 6 联系电话e-mail:zhouyc 中国学术会议在线 10中国力学学会学术大会2005 ( CCTAM2005 ) 力学性能.首先用激光沉积法和化学有机物沉积法在单晶硅基底上制备出了PZT压电薄膜,用电沉积的方法在钢基底上制备出了镍镀层薄膜;然后,提出了用纳米压痕方法表征压电薄膜界面断裂韧性和残余应力的理论模型以及用纳米压痕方法表征镍镀层薄膜本构关系和残余应力的理论模型;通过实验,用纳米压痕方法表征了压电薄膜的界面断裂韧性和残余应力以及镍镀层薄膜的本构关系和残余应力. 微纳米尺度器件的力学行为研究 方岱宁 (清华大学工程力学系,北京100084) 摘要:在微米尺度,本文研究了微米尺度梁谐振器的力热耦合问题.采用Fourier变换与Laplace变换相结合的方法求解梁的横向振动,并对不同边界条件与初始条件进行分析.结果表明,由于力热耦合,梁的振动频率会略有增加,振幅发生衰减,而且,这些特性与梁的尺寸有关.相比之下,不考虑耦合时,梁的振动频率只与厚长比有关,为等幅振动.在纳米尺度,为了反映非线性原子势函数对纳米材料宏观力学行为的作用,把原子势的信息引入宏观力学的分析方法,提出了一个分子力学方法.通过建立石墨片与单壁碳管的本构关系,得到了单壁碳管的单向拉伸应力-应变曲线,并预测了单壁碳管的拉伸模量与破坏应变.所得结果与分子动力学模拟进行对比,基本一致. 关键词: 力热耦合;微米梁谐振器;积分变换;分子力学方法;纳米碳管;单向拉伸 Mechanism of the Micropattern Formation of the Protein at Lipid Bilayer Junctions Shi-Qing Huang, Xi-Qiao Feng, Shou-Wen Yu (Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China) Abstract: Complex micropatterns of spatial rearrangement of receptors at intercellular junctions are an important aspect of intercellular communication,through which cells interact with each other and their environment. Disproportionately few studies, however, have attempted to examine the structure and dynamics of proteins in intermembrane junctions, and the mechanism of the micropatterns formation is controversial. Raghuveer and The corresponding author(通讯作者), E-mail: fangdn 中国学术会议在线 11中国力学学会学术大会2005 ( CCTAM2005 ) Groves et al. introduced a simple artificial intermembrane junction system to explore mechanics behind the pattern and structure formation by membrane-bound proteins. Their studies demonstrate that membrane mechanical forces alone, i.e. in the absence of specific biochemical interactions, can drive m-scale organization of membrane proteins. Theoretical efforts to analyze the process of pattern formation are worthwhile both from the perspective of creating model systems that might eventually illuminate the mechanisms behind biological protein reorganization and from the more general perspective of creating new classes of self-assembled, biologically inspired, or biologically templated materials. Our aims in this article are: presenting a quantitative investigation of the principles governing molecular reorganization events during initial stages of cellular recognition; understanding how the binding kinetics, lateral mobility of the membrane proteins, membrane bending effects, etc. influence molecular organization and recognition; and elucidating how some parameters determine the formation of spatio-temporal patterns at cell signaling junctions. Fracture Mechanics Analysis of Smart-Cut Technology Xi-Qiao Feng7, Mei Xu Department of Engineering Mechanics, Tsinghua University, Beijing 100084, Abstract: Smart-Cut is a recently established, advanced technology for fabricating high-quality silicon-on-insulator (SOI) systems and has found various successful applications. It meets almost all the high requirements for processing and manufacturing SOI wafers, which provide the basis of ultra-large-scale integration device structures of modern microeletronic industry. A fundamental study is presented on the basic mechanisms in the Smart-Cut