Comparison of Superplastic Formabiliity Predictions Using 2-D Plane Strain and 3-D Modeling

Computational simulations of superplastic forming by 2-D plane strain including simple analytical and finite element and 3-D finite element modeling were compared with each other. The piece being formed was a rectangular pan with a female die. The effect of die entrance radii upon pressurization rate and thickness distribution was examined. Experimental work was conducted on superplastic aluminum-lithium 8090 material for comparison with predictions from simulations.     

Analysis of a mode III crack problem in a functionally graded coating-substrate system with finite thickness

This paper presents an analysis of the static problem of model III crack of a functionally graded coating-substrate system with an internal crack perpendicular to the interface under antiplane shear loading when the coating layer and substrate have finite thickness. After the Fourier transform method is employed, the expressions of the displacement components can be obtained. Integral transforms are employed to reduce the problem to a singular integral equation that can be solved numerically. The influences of the nonhomogeneity constant, relative crack length and thickness ratio are quantitatively studied.     

三维四步方形编织结构的几何建模

研究三维复合材料的编织结构是分析这种材料力学性能的前提。从三维编织工艺和实际的编织过程出发,针对方形编织结构提出了一种单元几何模型。该模型以携纱器循环一周返回到起始位置所形成的纱线编织结构作为单元,保证了纤维束的连续性和材料整体结构的完整性。对每根纱线,选取它在编织体各个区域内合适的控制点,过这些控制点拟合成三次样条曲线,以此模拟纱线的空间结构中心线。最后得到纱线和编织体的结构。     

Modeling the 3-D Rotational and Translational Motion of a Halbach Rotor Above a Split-Sheet Guideway

When a Halbach rotor is simultaneously rotated and translationally moved above a split-sheet aluminum guideway a traveling time-varying magnetic field is created in the air gap. This field induces eddy currents in the guideway that can simultaneously create suspension and propulsion forces. If the rotor is offset from the center then a re-centering guidance force can also be created. As the forces are created in a highly inductive way the use of magnets circumvents any low power factor issues and enables a relatively high lift-to-weight ratio to be attained in comparison to using windings. The conductive and nonconductive regions are modeled by using a steady-state convective A- $phi$ formulation. The Halbach rotor is modeled using a 3-D analytic based model and is coupled to the conductive guideway region using boundary conditions. The steady-state rotation of the Halbach rotor is modeled by incorporating complex terms in the analytic model. The accuracy of the steady-state model is confirmed by comparing it with a 3-D transient finite-element Magsoft Flux model (with no translation) and with experimental results (with both rotation and translation). The effect of the rotor width on performance is also investigated.      

Creep of sintered porous micron-silver: nanoindentation experiment and theoretical analysis

Journal of Materials Science - Nano/micron-silver paste has been applied in high-temperature packaging of chips as a potential lead-free solder. At specific sintering temperature, the particle size...     

离心泵建模和装配过程演示

根据离心泵结构图,利用UGNX软件对一个离心泵进行三维造型,分别建立了叶轮、前后泵盖、泵壳、支架、泵轴、密封组件等零件的实体模型,并对零件进行了装配．对离心泵装配过程进行了动画演示,并配以语音讲解,将离心泵的装配过程直观的体现出来．     

Initial experiment for embossing a 3-D microstructure on the inside wall of a wound tube by an electromagnetic compression process

The purpose of this study is to discuss the feasibility of an economical electromagnetic forming (EMF) process to fast manufacture microstructure on the inside well of a wound thin tube. To form the three-dimensional (3-D) microstructure on the inside wall, a copper film is wound onto the forming mandrel and then inserted into the forming coil that provides external compressive force on the tube surface using the EMF process. This study proposes an inexpensive method that uses a reverse electro-discharge machining process with a homocentric path to manufacture the forming mandrel. The thickness effects of the single tube on the formed microstructure are investigated by an economical EMF device with low voltage and high capacitance. In addition, a composite tube is proposed to prevent electromagnetic field loss, reduce the gap, and provide good contact force. By using a composite tube in an EMF process, the forming depth and the profile completeness of the microstructure are improved.     

3-D Modeling of Pyroelectric Sensor Arrays Part II: Modulation Transfer Function

The modulation transfer function (MTF) for a pyroelectric infrared sensor array is determined from a finite-element simulation. Consideration of the full thermoelectromechanical coupling and use of a 3-D sensor model result in a good agreement between calculated and measured data.      

光电干扰系统基于UML的C3I系统软件建模

将C^3I系统实时获取信息、传输信息、处理信息进行态势分析与估计,然后自动决策应用于光电干扰系统软件设计,能大幅度提高光电干扰系统的效能,从而提高战区C^3I系统的攻击与防卫效能。首先描述光电干扰系统的功能需求,利用C^4ISR与UML体系结构的高层处理过程提出UML建模的框架;接着应用UML遵循RUP的核心思想和基本原则对光电干扰系统软件进行了建模,逐步进行了需求收集、系统分析与系统设计,在每个过程均用一系列UML图来形象化地表示;最后提出了在建模过程中应注意的问题。利用已成为事实上标准并且符合人们思维习惯的UML进行系统建模,开发周期相对短,产品较丰富并且保证了系统开发和维护人员对系统的理解,系统分析、系统设计以及系统维护的一致性,更重要的是模型建立后可直接编程实现。     

颜色编码三维测量系统的结构参数设计及仿真

提出了基于结构光颜色编码技术的三维测量系统,利用条纹的颜色对光平面的投影角进行编码,以实现三维物体形状测量和重建。该系统主要由数字式光处理器、彩色摄像机和计算机组成,具有结构新颖,简单可靠等特点,且无需扫描,仅需采集一幅景物的编码图案就能得到产生一幅全帧深度图像所需的全部信息,非常适合于高速、实时在线测量。根据系统的主要设计指标及对可测空间的分析,对系统的结构参数进行了优化设计,以保证系统具有最大的可测空间及最佳的遮挡特性。对典型的平面类三维面形——斜面进行了仿真实验,得到系统在 Z 轴(深度方向)、X 轴、Y 轴方向的测量误差分别为 0.31%,0.22%,0.23%,达到了系统的预期要求。     

3-D Modeling of Pyroelectric Sensor Arrays Part I: Multiphysics Finite-Element Simulation

When modeling pyroelectric sensors, not all relevant and coupled physical phenomena could be considered contemporaneously up to now. We describe a method to examine problems with coupled thermal, electrical, and mechanical fields using finite-element software. Modeling the complex interaction between the physical fields is realized by implementing a two-step approach that takes advantage of the internal computational routines of finite-element programs. The method will be exemplified on a standard pyroelectric sensor array, whose efficient 3-D modeling and simulation is demonstrated using a public accessible commercial finite element software.      

基于激光测距的移动机器人3-D环境感知系统设计

采用2-D扫描的激光测距传感器与精密转动云台设计并实现了非结构化环境下的移动机器人感知系统,通过传感器平台俯仰与水平的转动实现了3-D环境感知。针对噪声干扰提出了一种动态自适应滤波器,通过时间与空间上相邻测量值的分析实现了实时动态的滤波。在3-D环境的地形重建过程中,结合中值滤波器与高斯滤波器实现了高度图的平滑与插补。通过地形平坦性分析判断移动机器人的可行区域与障碍区域,从而为移动机器人导航过程中的环境建模与路径规划提供了支持。     

在LabVIEW平台上构建一种二维运动控制系统

介绍了如何在LabVIEW平台上开发一种实验教学用二维运动控制系统，描述了系统的整体结构和软件的设计方法，重点讨论了如何利用LabVIEW的并行机制处理多任务并行问题，如何解决运动实时性问题。     

Anti-plane problem of periodic interface cracks in a functionally graded coating-substrate structure

In this paper, the interface cracking between a functionally graded material (FGM) and an elastic substrate is analyzed under antiplane shear loads. Two crack configurations are considered, namely a FGM bonded to an elastic substrate containing a single crack and a periodic array of interface cracks, respectively. Standard integral-transform techniques are employed to reduce the single crack problem to the solution of an integral equation with a Cauchy-type singular kernel. However, for the periodic cracks problem, application of finite Fourier transform techniques reduces the solution of the mixed-boundary value problem for a typical strip to triple series equations, then to a singular integral equation with a Hilbert-type singular kernel. The resulting singular integral equation is solved numerically. The results for the cases of single crack and periodic cracks are presented and compared. Effects of crack spacing, material properties and FGM nonhomogeneity on stress intensity factors are investigated in detail.     

高速旋转物体的频闪结构光三维面形测量系统

提出了一个用于测量高速旋转物体三维面形的频闪结构光照明系统。系统自动跟踪检测旋转物体的转动信息,再用该信息同步控制光源发光和摄像系统工作,记录下旋转物体在闪光时刻的瞬间“静止”图像。使用该系统产生持续时间为424s的同步频闪结构光,对转速为每分钟1080转的家用电风扇旋转叶片三维面形进行测量,证明该系统能够准确地获得旋转叶片的瞬间静止图像,便于重建旋转叶片每个瞬间时刻的三维面形。同时,该系统还具备人工设定光源发光频率的功能,可以拓宽应用到无重复特征信号的高速运动物体三维面形测量。     

Modeling the nanoindentation of elastoplastic materials with nonlinear adaptive springs (NASs)

In this paper, the /spl beta/-material concept helps to elaborate and explore a new model for the indentation cycle of elastoplastic materials. The proposed approach takes into account the nonlinear behavior of homogeneous and isotropic materials. It uses the idea of a nonlinear adaptive spring (NAS) with changing properties according to the depth of penetration to accurately reproduce the material behavior in loading and unloading stages. The properties of the adopted NAS are included in its own stiffness function /spl kappa/ appearing in the form of an infinite sum of which the convergence and some properties are discussed in detail. This new model, which allows the indentation cycle to be reproduced whatever the penetration depth, permits at the same time a direct calculation of the involved energy terms. It also provides the possibility to perform separate analysis of the plastic energy, which allows distinguishing between different types of the material behavior and a better understanding of its nature. A validation is accomplished by applying the method to three different materials.     

基于三维弹性理论的碳纤维板中Lamb波建模

基于主动Lamb波的结构健康监测是目前复合材料结构损伤监测技术研究的热点之一,了解Lamb波的传播特性对进行可靠的损伤监测非常重要.本文结合经典三维弹性理论与Lamb波的运动位移方程,对碳纤维复合材料板中传播的Lamb波传播特性进行了建模研究,在此基础上推导了碳纤维板的相速度频散曲线,并讨论了Lamb波传播方向与坐标轴之间的夹角及碳纤维铺层方向对频散曲线的影响,建模结果证明了这种建模方法的正确性.     

三维形貌测量中自动调焦系统的设计

在相移干涉显微镜中增加了自动调焦系统,使其快速获取高清晰干涉图像,提高了三维形貌的测量速度和测量精度。调焦系统采用图像自动调焦方法,分别以图像标准差函数和图像最大熵函数作为粗调函数和精调函数。实验表明本系统自动调焦范围扩大到150m,自动调焦精度为0.3m,调焦时间为4-8s。