Molecular dynamics study of interfacial bonding strength of self-assembled monolayer-coated Au-epoxy and Au-Au systems

Interfacial adhesion between metals and organic polymers plays a crucial role in the mechanical properties and reliability performance of multiplayer thin film structures. To improve their interfacial bonding strength and so the reliability, the self-assembled monolayer (SAM) method is considered as an effective means. The present study is devoted to studying the effects of SAM coating on the interfacial bonding strength of the Au-epoxy and the Au-Au bonding structures through molecular dynamics (MD) simulation. Three different types of functionalized alkanethiol SAMs (SH(CH₂)_nX, X = CH₃, OH, NH₂) chemisorbed onto two different Au crystal planes, i.e., (1 0 0) and (1 1 1), are considered. The study starts from the characterization of the interfacial bonding strength of both the SAM-coated Au-epoxy and Au-Au systems, followed by the investigation of the dependence of the interfacial bonding strength on the chain lengths and tail groups of the n-alkanethiolates. A comparative study of the effects of the crystal orientation of Au substrate on the bonding strength is reported, and the elastic moduli of these SAMs through uniaxial tensile simulation are also examined. The calculated results are compared with the published experimental data, and also with each other to identify the optimal SAM candidate.Results show that the interfacial bonding strength of the SAM-coated Au-epoxy and Au-Au systems exhibits a strong dependency on the crystal orientation of Au substrate and also on the chain length of the monolayer where it tends to increase with an increasing SAM chain length. In specific, the interfacial bonding strength of the SH(CH₂)_nCH₃ SAM-coated Au-Au joint would reach a maximal value at the chain length n = 8 while that of the SAM/epoxy interface in the SH(CH₂)_nCH₃ SAM-coated Au-epoxy system attains a minimal value at n = 4 and becomes the maximum at n = 10, regardless of the crystal orientation of the Au substrates. Besides, the Au substrate with (1 1 1) crystal orientation would outperform the Au(1 0 0) substrate in the SAM/epoxy interfacial bonding strength of the SAM-coated Au-epoxy system while there is a totally opposite result for that of the SAM-coated Au-Au joint.     

Prestressed FRP and interface slip effect on interfacial stresses analysis: the new FRP sheets rigidity model

This paper presents an improved bi-material beam theory with adhesive interface and the new prestressed-fiber reinforced polymer (FRP) – model, which has been applied to the study the problem of interfacial stresses. This work explicitly considers the interfacial slip effect on the structural performance by including both the effect of adherend shear deformations and the fiber volume fraction of the prestressed laminates. This new method needs only one differential equation to determine both shear and normal interfacial stress, which is one aspect that has not been taken into account by the previous studies in the literature. A parametrical study is carried out to show the effects of some design variables, e.g., stiffness and thickness of adhesive layer and FRP plate.     

Analysis of stress intensity factor in orthotropic bi-material mixed interface crack

Adopting the complex function approach, the paper studies the stress intensity factor in orthotropic bi-material interface cracks under mixed loads. With consideration of the boundary conditions, a new stress function is introduced to transform the problem of bi-material interface crack into a boundary value problem of partial differential equations. Two sets of non-homogeneous linear equations with 16 unknowns are constructed. By solving the equations, the expressions for the real bi-material elastic constant εt and the real stress singularity exponents λt are obtained with the bi-material engineering parameters satisfying certain conditions. By the uniqueness theorem of limit,undetermined coefficients are determined, and thus the bi-material stress intensity factor in mixed cracks is obtained. The bi-material stress intensity factor characterizes features of mixed cracks. When orthotropic bi-materials are of the same material, the degenerate solution to the stress intensity factor in mixed bi-material interface cracks is in complete agreement with the present classic conclusion. The relationship between the bi-material stress intensity factor and the ratio of bi-material shear modulus and the relationship between the bi-material stress intensity factor and the ratio of bi-material Young's modulus are given in the numerical analysis.     

基于MEMS的光力学红外成像

非制冷红外成像仪以其优良的性价比和高可靠性而倍受关注。近期 ,非制冷的热机械型红外成像仪有望发展成为新的低价格高性能的红外成像设备。本文提出了一种新型光学读出的红外探测仪。此红外探测仪的核心器件焦平面阵列 (FPA)由无硅基底结构的微悬臂梁阵列构成。每个微悬臂梁独立地把入射的红外热辐射转化为被光学系统探测的热变形。它不需要读出电路、真空腔和制冷装置 ,其理论上的噪声等效温度差接近致冷型红外成像系统 ,而制作成本和难度将大幅降低。制作的无硅基底单层膜结构的FPA ,其单元尺寸为 2 0 0 μm× 1 0 0 μm ,阵列大小为 1 5 0× 1 0 0像素数。实验制作的系统探测到温度为 5 0 0K左右的热物体像 ,热像采样频率为 1 2幅 /秒。     

夹杂对两相材料界面裂纹的影响

根据界面上应力和位移的连续条件,得到了单向拉伸状态下,含有椭圆夹杂的无限大双材料组合板的复势解。进一步通过求解Hilbert问题,得到了含有夹杂和半无限界面裂纹的无限大板的应力场,并由此给出了裂尖的应力强度因子K。计算了夹杂的形状、夹杂的位置、夹杂的材料选取以及上、下半平面材料与夹杂材料的不同组合对裂尖应力强度的影响。计算结果表明夹杂到裂尖的距离和夹杂材料的性质对K影响较大,对于不同材料组合,该影响有较大差异。夹杂距裂尖较近时,会对K产生明显屏蔽作用,随着夹杂远离裂尖,对K的影响也逐渐减小。另外,软夹杂对K有屏蔽作用,硬夹杂对K有反屏蔽作用,而夹杂形状对K几乎没有影响。     

力-热载荷下双金属复合管的屈曲失效研究

采用有限元方法研究了力-热载荷下双金属复合管的屈曲失效行为,通过三维有限元建模考虑了双金属复合管的准静态复合成型制造过程中产生的残余应力,分析了温度及内压两个主要参数对双金属复合管屈曲失效的影响。结果表明,高温导致材料发生软化,抑制了双金属复合管的屈曲;弯矩、内压及热载荷联合作用下,复合管内介质温度降低,复合管弯矩达到最大值对应的曲率减小,而弯曲承载能力增大,外基管的椭圆率也增大;内压变化对复合管的弯曲承载能力和外基管的椭圆率影响较小。     

压电效应下一维六方准晶双材料孔边裂纹的反平面问题研究

利用复变函数方法和保角变换技术研究了压电效应下一维六方准晶双材料中圆孔边单裂纹的反平面问题．考虑电不可渗透型边界条件,运用保角变换和Stroh公式得到了弹性体受远场剪切力和面内电载荷作用下裂纹尖端应力强度因子和能量释放率的解析解. 数值算例分析了几何参数、远场受力、电位移载荷对能量释放率的影响．结果表明：裂纹长度、耦合系数和远场剪切力的减小可以抑制裂纹的扩展．不考虑电场时,声子场应力对能量释放率的影响较小．本文的研究结果可作为研究一维六方压电准晶双材料孔边裂纹问题的理论基础,同时为压电准晶及其复合材料的设计、制备、优化和性能评估提供理论依据．     

半空间双相压电介质垂直边界附近圆孔对SH波的散射

利用“Green函数法”和“镜像法”对垂直边界附近含圆孔的半空间双相压电介质对SH波的散射问题进行分析,得到其稳态解。利用镜像法得到满足水平边界应力自由与电位移自由的波函数解析表达式。根据垂直边界连续性条件,利用“契合法”建立第一类Fredholm型积分方程组,得到圆孔周边的动应力集中系数与电场强度集中系数解析表达式。数值算例分析了入射波频率、入射角度、介质参数等对动应力集中系数与电场强度集中系数的影响,并与已有文献进行比较。计算表明,高频SH波垂直入射危害较大。     

双相介质半空间中圆孔对透射SH波的稳态分析

研究了平面SH波在半空间双相弹性介质中的传播。通过Green函数和积分方程方法,按照复变函数描述,对透射波被圆孔散射的情况进行稳态分析。将双相介质半空间沿界面剖分为1/4空间介质Ⅰ和含圆孔的1/4空间介质Ⅱ,分别构造了介质Ⅰ和介质Ⅱ中反平面点源荷载的Green函数,按双相介质中平面SH波的处理方法,给出介质Ⅰ和介质Ⅱ中的平面位移波,两种介质之间的相互作用力与对应Green函数的乘积沿界面的积分与平面位移波叠加得到介质Ⅰ和介质Ⅱ中的全部位移场。按照界面的位移连续条件,定解积分方程组,得到问题的稳态解,并给出圆孔位置和介质参数对散射的影响。     

双材料微梁阵列室温物体红外成像

针对近年出现的新概念光学读出双材料微梁阵列红外成像技术，提出了具有热变形放大效果的无硅基底回折腿间隔镀金的微梁单元结构,并建立了其热机械模型，在模型分析基础上，成功的设计制作了100×100像素的焦平面阵列(focal plane array,FPA).在构建的红外成像系统中，实现了对室温物体——人体的热成像，噪声等效温度差约为200mK.实验结果与热机械模型的分析一致. 关键词： 非制冷红外成像 光学读出 双材料微梁阵列