The loading history and crystal orientation effects on the size-dependency of single crystal diamond properties

Much research has been conducted to study the size-dependency of material properties, as can be found from the open literature. Recent results on combined size, rate and thermal effects further demonstrate the dominant influence of specimen size on material strength, as compared with the loading rate and thermal effects. However, little has been done to understand the loading history and crystal orientation effects on the size-dependency of material properties. To evaluate the safety and integrity of MEMS devices under general loading conditions, a series of molecular dynamics simulations are performed to investigate the size-dependency of single crystal diamond properties with various crystal orientations under shear/tension and tension/shear loading conditions. It appears from the preliminary findings that the loading history and crystal orientation do have certain influence on the size-dependency of material properties. Specifically, the failure pattern is insensitive to the loading history, which provides useful information for formulating a multi-scale material model under general loading conditions.     

Structural design of high-performance capacitive accelerometers using parametric optimization with uncertainties

Electrostatic or capacitive accelerometers are among the highest volume microelectromechanical systems (MEMS) products nowadays. The design of such devices is a complex task, since they depend on many performance requirements, which are often conflicting. Therefore, optimization techniques are often used in the design stage of these MEMS devices. Because of problems with reliability, the technology of MEMS is not yet well established. Thus, in this work, size optimization is combined with the reliability-based design optimization (RBDO) method to improve the performance of accelerometers. To account for uncertainties in the dimensions and material properties of these devices, the first order reliability method is applied to calculate the probabilities involved in the RBDO formulation. Practical examples of bulk-type capacitive accelerometer designs are presented and discussed to evaluate the potential of the implemented RBDO solver.     

Flutter instability of laminated composite shear deformable flat panels exposed to a supersonic coplanar gas flow of arbitrary direction

Flutter instability of symmetrically laminated anisotropic composite flat panels exposed to a coplanar supersonic flow of arbitrary direction is analysed Due to the complexity of the problem, the solution is obtained via the Rayleigh-Ritz procedure generalized to the case of non-conservative systems. Towards the same goal, the concept of the stability parabola coupled with Sylvester's determinant technique are used to determine the flutter boundary. The structural plate model incorporates the effects of transverse shear as well as the material anisotropy and heterogeneity while the aerodynamic loads are expressed in terms of the supersonic quasi-steady 2-dimensional approximation. The numerical results underline the strong influence played by transverse shear, as well as the inadequacy of the classical Kirchhoff model when applied to a panel which does not fulfil the requirements of a thin plate and/or when its material exhibits a weak rigidity in transverse shear     

High-aspect-ratio bulk micromachining of titanium

Recent process developments have permitted the highly anisotropic bulk micromachining of titanium microelectromechanical systems (MEMS). By using the metal anisotropic reactive ion etching with oxidation (MARIO) process, arbitrarily high-aspect-ratio structures with straight sidewalls and micrometre-scale features have been bulk micromachined into titanium substrates of various thicknesses, ranging from 0.5-mm sheet down to 10-microm free-standing titanium foils. Bulk micromachined structures are generally free of residual stresses and are preferred when large, rigid, flat and/or high-force actuators are desired. However, so far there has been a limited ability to select materials on the basis of specific application in bulk micromachining, primarily because of the predominance of MEMS processes dedicated to single-crystal silicon, such as silicon deep reactive ion etching. The MARIO process permits the creation of bulk titanium MEMS, which offers potential for the use of a set of material properties beyond those provided by traditional semiconductor-based MEMS. Consequently, the MARIO process enables the fabrication of novel devices that capitalize on these assets to yield enhanced functionalities that would not be possible with traditional micromechanical material systems.     

Static behavior of composite beams using various refined shear deformation theories

Static behavior of composite beams with arbitrary lay-ups using various refined shear deformation theories is presented. The developed theories, which do not require shear correction factor, account for parabolical variation of shear strains and consequently shear stresses through the depth of the beam. In addition, they have strong similarity with Euler–Bernoulli beam theory in some aspects such as governing equations, boundary conditions, and stress resultant expressions. A two-noded C¹ finite element with six degree-of-freedom per node which accounts for shear deformation effects and all coupling coming from the material anisotropy is developed to solve the problem. Numerical results are performed for symmetric and anti-symmetric cross-ply composite beams under the uniformly distributed load and concentrated load. The effects of fiber angle and lay-ups on the shear deformation parameter and extension-bending-shear-torsion response are investigated.     

Microsensors and actuators for macrofluidic control

Microsensors and actuators suitable for macrofluidic control have been designed, fabricated, tested, and optimized over the span of the last decade. MEMS-based shear stress sensor arrays using polysilicon hot filaments have been fabricated on both rigid (silicon) and flexible (parylene) substrate for application on all types of fluid dynamic and aerodynamic surfaces. In addition, MEMS bubble flap-type pneumatic actuators have been tested and used in turbulent boundary layer drag reduction in conjunction with the rigid MEMS shear stress sensor arrays acting as high-speed shear stress imagers. The flexible MEMS bubble actuator arrays have also been used with the flexible shear stress sensor arrays for generating maneuvering forces in the wind tunnel for a delta wing model and on UAV-type radio-controlled aircraft.     

Unusual Behavior of a MEMS Resonator in Superfluid 4He

Novel mechanical resonators based on micro-electro-mechanical systems (MEMS) technology were developed for the study of superfluid ⁴He. The MEMS device is composed of two parallel plates, the movable plate suspended by four serpentine springs above the substrate, forming a shear mechanical oscillator. A specific device with a 1.25 μm gap was tested in the superfluid phase of ⁴He. At temperatures below 400 mK the device exhibits nonlinear and hysteretic behavior when the excitation exceeds a threshold. The anomalies are reminiscent of quantum turbulence and vorticity effects observed in other mechanical oscillators such as tuning forks or vibrating grids.     

SiC nanowire-based SU-8 with enhanced mechanical properties for MEMS structural layer design

In addition to being used for pattern transfer, the negative photoresist SU-8 is widely used as a structural material in microelectromechanical systems(MEMS). Due to its good photopatternability, SU-8 has lower manufacturing costs than many other materials, but its mechanical properties are relatively weak to some extent, which limits its performance. The mechanical properties of epoxy-like SU-8 can be enhanced by adding micro-or nano-fillers such as carbon nanotube, clay, and SiC nanowire, which have superior elastic modulus. In this study, SiC nanowires were used to improve the mechanical properties of SU-8 while the SU-8 retains its photopatternability.The SiC nanowires were uniformly dispersed in SU-8 by stirring and ultrasonication. SU-8 materials with different SiC nanowire contents were fabricated into dog bone samples by lithography. The elastic modulus, storage modulus, and damping factor of the samples were measured by the Dynamic mechanical analysis(DMA)Q800. The experiment result shows that the rigidity and toughness increased, and the damping reduced. The2 wt% SiC nanowires-reinforced SU-8 had a 73.88% increase in elastic modulus and a 103.4% increase in elongation at break. Furthermore, a spring component made by SiC-doped SU-8 could withstand greater acceleration.The SiC nanowires-reinforced SU-8 has the potential to meet higher requirements in the design and manufacture of MEMS and greatly reduce the manufacturing costs of MEMS devices.     

微构件所受超声辐射力理论研究

为了将超声波俘获技术应用到微机电系统中,以达到对微构件进行无损、非接触遥操纵的目的,开展了微构件在超声波场中所受辐射力的理论研究．计算机仿真结果表明：微构件的材料与尺寸、介质的密度、超声波的声学参数等都对微构件所受辐射力产生影响,同时,利用超声驻波场技术实现对微构件的操纵是可行的．     

基于n阶GBT初始轴向载荷影响下FGM梁的振动特性

研究了初始轴向载荷影响下弹性地基功能梯度材料(FGM)梁的振动特性。基于一种拓展的n阶广义剪切变形梁理论(n-GBT),以轴向位移、剪切变形挠度与弯曲变形挠度为基本未知函数,应用Hamilton原理,建立了该系统自由振动问题力学模型的控制方程。引入边界控制参数,采用一种改进型广义微分求积(MGDQ)法获得了FGM梁的静动态响应。通过算例验证并给出了GBT阶次n的理想取值,丰富梁理论的同时,可供验证或改进其它各种剪切变形梁理论;提供的数值分析方法切实可行,拓展了GDQ法的使用范围。最后,着重讨论并分析了初始轴向载荷、边界条件、梯度指标、地基刚度、跨厚比等参数对FGM梁振动特性的影响。     

A Size-Dependent Functionally Graded Higher Order Plate Analysis Based on Modified Couple Stress Theory and Moving Kriging Meshfree Method

A size-dependent computational approach for bending, free vibration and buckling analyses of isotropic and sandwich functionally graded (FG) microplates is in this study presented. We consider both shear deformation and small scale effects through the generalized higher order shear deformation theory and modified couple stress theory (MCST). The present model only retains a single material length scale parameter for capturing properly size effects. A rule of mixture is used to model material properties varying through the thickness of plates. The principle of virtual work is used to derive the discrete system equations which are approximated by moving Kriging interpolation (MKI) meshfree method. Numerical examples consider the inclusions of geometrical parameters, volume fraction, boundary conditions and material length scale parameter. Reliability and effectiveness of the present method are confirmed through numerical results.     

Size-dependent longitudinal and transverse wave propagation in embedded nanotubes with consideration of surface effects

In this article, the size-dependent free vibration of nanotubes with surface effects is investigated. An efficient shell-core-shell model is introduced to simulate the structure which includes the effect of additional surface elasticity and surface residual stresses. Love??s continuum model for longitudinal wave propagation is employed, which accounts for the effects of lateral contractions on the axial vibration of the structure. On the other hand, the Timoshenko beam model is modified to include the surface effects as well as shear deformations for transverse vibration of nanotubes under axial load. Temperature effects on material properties are also investigated to show the general trend of size dependencies. The generalized differential equation for each case is derived under general external loadings using Hamilton??s principle. The axial vibration is analyzed for different material types and boundary conditions. The linear stiffness modulus is assumed for the elastic bed in both directions with due dependence on the size of the nanotubes.     

Effects of material microstructure on blunt projectile penetration of a nickel-based super alloy

Engine fan-blade containment systems, required in many aviation applications, are frequently manufactured from high-temperature superalloys, such as Inconel-718. As in many other applications, there is an incessant desire to maximize mechanical properties of the containment component while minimizing its weight. However, a thorough understanding of the impact behavior of the various heat treatments of these alloys in engine fan-blade containment applications does not currently exist. Due to this incomplete state of knowledge, a combined experimental–analytical investigation was conducted at CWRU in collaboration with researchers at NASA GRC. As a part of this investigation, thin plates of Inconel-718, in both annealed and precipitation hardened conditions were subjected to semi-quantitative high speed penetration tests. Dynamic compression and top hat shear localization tests using a split Hopkinson pressure bar were also conducted as part of a more fundamental assessment of this material. The measured dynamic material response in compression was used to develop a material model which adequately described the dynamic behavior of IN-718 in both the annealed and precipitation hardened states. Moreover, a transient large deformation thermo-elastic-viscoplastic finite element code is used to understand the local thermo-mechanical fields during impact in both the annealed and precipitation hardened microstructures. The results from these studies show that the annealed material demonstrated superior penetration resistance when compared with the hardened material. The annealed IN-718 absorbed more energy through multiple deformation modes and did not show any susceptibility to shear localization, which was in contrast to the precipitation hardened material. These results, therefore, suggest a precipitation hardened condition may not be optimal for impact energy absorption applications, such as, in engine fan-blade containment.     

基于微机电系统的纳米力学测量装置的研制

阐述了一种基于微机电系统的纳米力学测量方法和系统。开发了一种多功能的纳牛力致动器,可同时满足微拉伸测试系统、原子力显微镜等系统的需要,该致动器基于微机电系统,以静电侧向梳齿为基本结构,采用变间隙设计结构,实现小芯片尺寸、低压驱动、高分辨率(nN量级)和大输出力（大于1 mN）,并介绍了该测试系统的原理、结构、微机电系统的安装以及一些相关实验结果。     

复合材料梁的几何精确非线性建模及非经典效应

基于Hodges的广义Timoshenko梁理论对具有任意剖面形状、任意材料分布及大变形的复合材料梁进行几何精确非线性建模,采用旋转张量分解法计算梁内任意一点的应变,采用变分渐近法确定梁剖面的任意翘曲,采用平衡方程由二次渐近精确的应变能导出广义Timoshenko应变能,采用广义Hamilton原理建立梁的几何精确非线性运动方程。将所建模型用于复合材料梁的静动力分析,通过与实验数据的对比,验证了建模方法的准确性,并进一步研究了剖面翘曲及横向剪切变形非经典效应对复合材料梁的影响。研究表明,剖面翘曲对复合材料梁的静变形和固有频率有显著影响,横向剪切变形对复合材料梁的静变形和固有频率的影响与梁的长度/剖面高度比有关。     

微机电系统的发展及其应用

微机电系统是在微电子技术基础上产生和发展起来的多学科交叉的前沿科学研究领域，是面向21世纪的高新科技．介绍了微机电系统产生的背景影响、组成特征和基础研究内容，综述了微机电系统技术基础所涉及的材料、微机械设计和模、微细加工技术以及微封装与测试等领域，并对微机电系统的应用、典型的微器件、国内外的发展现状及前景进行全面分析．在此基础上，论述了MEMS技术目前存在的问题和未来发展的趋势．     

Simulation of elasto-plastic behaviour of an artificial 3D-structure under dynamic loading

From the meso-mechanical point of view, the internal structure of a material considerably influences its plastic deformation pattern at the meso-scale level. 2D calculations have shown that the consideration of an internal structure in an explicit form allows us to describe some experimentally observed phenomena, such as plastic strain localisation, material fragmentation, shear and rotation of grain conglomerates, etc. Real structural effects are three-dimensional by nature and in many cases can not be simulated in the framework of a 2D model. It is, therefore, a challenge to perform 3D-modelling for meso-volume behaviour under loading, taking into account material internal structure, and to investigate the phenomena caused by structural effects. In this paper, a special routine to generate a 3D heterogeneous structure is proposed. To calculate a 3D polycrystalline test-piece under plane shock wave as an example, we solve a dynamic problem and obtain numerical solutions using the finite-difference method. The results of 3D simulations are analysed and compared with those for a 2D set.     

环氧基紫外负性光刻胶的特性、应用工艺与展望

环氧基紫外负性光刻胶(SU-8)是一种近几年发展起来的新型的光刻胶材料。它是一种双酚A酚醛缩水甘油醚环氧树脂溶解于GBL(r-Butyrolactone)而形成的高分子有机聚合物胶体．SU-8胶作为一种光刻材料，由于其独特的光学性能，力学性能和化学性能等，在MEMS(Micro—electro—mechanic—system)研究领域正受到了越来越多的关注，目前已被广泛的应用于MEMS器件的制备中。本文介绍了它的结构性能以及发展前景并报道了我们在其加工工艺上的研究进展。     

Anisotropic bending-torsion coupling for warping in a non-linear beam

 MEMS devices made from single crystal silicon often contain rod-like structures that are operated in bending and/or torsion. The design of these devices usually relies upon simple mechanical theories that ignore the coupling between these two modes of operation. In this paper, we develop a theory that is capable of accounting for the material coupling in the bending and twisting of single crystal beams which arises from anisotropic elastic properties and apply it in selected examples to the case of silicon. The generalized Saint–Venant torsion theory, which is valid for isotropic materials, is extended to arbitrary anisotropic linear elastic materials. The anisotropic material behavior couples the bending and torsion behavior. Thus, for the geometrically linear case, we find two warping functions associated with the bending moments and one warping function which is associated with the torsion moment. These warping patterns or functions are then taken as inputs to a geometrically non-linear formulation. Due to the presence of the additional warping functions, we find the existence of non-standard bi-moment and bi-shears which play an important role under certain conditions of extreme deformations. The final complexity of the non-linear formulation dictates the usage of a numerical solution procedure for practical computations. Here we employ a finite element scheme to solve the governing equations. Example computations elucidate the importance of the coupling effects by examining beams cut from (1 0 0) type silicon wafers. RID="⋆" ⋆ Dedicated to the memory of Prof. Mike Crisfield, for his cheerfulness and co-operation as a colleague and friend over many years. S.Klinkel gratefully acknowledges the financial support of the Deutsche Forschungsgemeinschaft (DFG) for a research fellowship at the University of California at Berkeley.     

微悬臂梁法向弹性系数的标定方法与分析

微机械加工制造的微悬臂梁/探针在科学研究和工业生产中有着重要的应用,作为原子力显微镜中的关键核心组件,微悬臂/探针结构在许多领域如表面特性研究和微加工等领域扮演着重要的角色.目前,尤其在生物、化学、和危险物品的检测上已经成为一个重要的平台.除了尺度测量外,当人们对表面力和原子间的相互作用力需要更准确和绝对的数值时,需要对微悬臂的弹性系数进行准确的标定,弹性系数的测量精度影响测量力学量的最终结果.本文对目前发展起来的几种标定方法,如参考悬臂梁的标定方法、悬臂梁的共振法和悬臂梁的热噪声振动法,从原理上和试验上进行总结和分析,对相应测试方法和影响测试精度的相关因素进行评述.