基于欧拉 伯努利梁和铁木辛柯梁理论的功能梯度材料模量测定

为测定功能梯度材料的弹性模量和剪切模量,引入梁理论并将梁沿长度方向离散,建立单元平衡方程后可得到弹性模量和剪切模量分布;假设弹性模量为沿长度方向的线性函数或指数函数,用有限元软件仿真计算功能梯度材料梁单元节点处的挠度和转角,然后用插值法构造变形特征函数,并计算得出弹性模量和剪切模量,且计算值与理论值的误差较小.计算结果还表明,采用铁木辛柯梁理论不仅可以得到弹性模量,还可以计算剪切模量,且弹性模量计算结果比用欧拉-伯努利梁计算结果更接近真实值,但铁木辛柯梁理论中需测定转角,对测定过程的要求会更加严格。     

步步为营——如何调试操作系统加载阶段的故障

上一期我们介绍了系统固件(BIOS)寻找不同类型的引导设备的方法,描述了固件向引导设备移交执行权的过程。对于从硬盘引导,首先接受控制权的是位于硬盘的0面0道0扇区中的主引导记录(Main Boot Record),简称MBR。MBR一共有512个字节,起始处为长度不超过     

半自动弯针机的设计与实现——用于悬臂式环氧树脂探针卡的制造

首先介绍了在半导体芯片制造中,环氧树脂探针卡的作用及其制作工艺.基于探针的弯曲需严格符合一定的设计规格,阐述了半自动弯针机的设计,详细说明基于MicroLynx控制器对步进电机的控制,实现对探针的针尖长度及弯曲角度的精确控制.该项技术已应用于探针卡的实际生产中.     

基于同源性分析的嵌入式设备固件漏洞检测

嵌入式设备的制造过程研产分离,导致不同的固件可能包含相同的第三方库,进而相同设备的不同版本甚至是不同设备的固件中都存在大量相同的已公开漏洞。针对该问题,基于第三方库同源性分析提出一种嵌入式设备固件漏洞检测方法,为固件漏洞修复提供参考,减少不必要的重复分析。通过对固件分类,并采用二进制差量分析、字符串常量匹配、模糊哈希3种方法分析第三方库同源性,从而检测同类固件中存在的漏洞。实验结果表明,该方法能够有效检测D-Link系列路由器固件中的缓冲区溢出和越界漏洞,以及Linksys系列路由器固件中的远程命令注入漏洞。     

多个电控板固件的在线升级方案设计与应用

为具有多个电控板的家电设备设计了一种固件在线升级方案，通过一定时间间隔轮询的方式逐个对可以升级的电控进行升级，针对空调内部不同作用的电控板，采用单分区或带有备份区域的双分区OTA升级方案，同时设计了在升级过程中防变砖的处理措施以提升整体的可靠性。该方案不仅能确保固件正确高效地升级成功，还可以确保在升级过程中出现异常情况时能自动恢复原固件，从而不影响设备的运行。方案控制逻辑简单易实现，具有较高的可靠性及良好的用户体验。     

智能IoT固件安全研究样本库的设计与实现

随着物联网设备的爆发式增长,人们对物联网设备的安全性也愈发重视,大量研究人员对物联网设备的安全性进行研究。为了给物联网固件安全研究提供分析和实验样本,本文广泛搜集、整理了主流物联网厂商的设备固件,设计了固件信息分析与提取方法对收集的固件进行处理,最后使用Django开源Web应用框架实现了可视化的固件样本管理系统,为相关物联网固件安全研究提供有力支撑。     

自动电磁除杂技术在烟草除杂工艺中的应用

在造纸法薄片生产的原料加工、输送过程中,由于原料中含有大量的铁质杂物,会造成设备关键加工部位异常磨损和损坏,严重影响加工过程的在制品质量.为实现对原料生产工艺环节中铁质杂物的自动去除和收集,设计了一套自动电磁除杂机系统,并从磁选机体、电磁吸盘、加磁模块、传动机构、料位高度探测、PLC等工控设备以及控制软件方面,对该系统进行详细阐述.试验结果表明,该系统能够系统、高效地去除造纸法再造烟叶原料中含有的大量铁质杂物.     

嵌入式系统引导介质简便切换的启动方法设计

本文基于微处理器S5PV210提出了一种在eMMC和TF卡存储器之间简便切换的方法,通过改变设备的供电电压值触发电压比较器输出状态翻转,从而控制电子开关切换供电回路来切换引导介质.为了保证比较器输出不会因供电电压的微小干扰而引起抖动,将比较器设计成滞回比较器.该方法适用于多种嵌入式设备,为设备系统固件烧写和升级提供便利.     

机房无人化管理的上机卡设计

针对当前高校中机房管理的现状,提出了一种新的管理方法,利用USB接口实现公共机房的无人化管理.为了实现无人化管理,首先设计一块基于USB接口的智能上机卡,然后设计出该设备在PC机上的驱动程序.在此基础上,设计出在PC机上管理和使用该设备的监控程序以及管理程序.文章着重讨论了上机卡的硬件设计和上机卡内部的固件程序设计.     

基于Pro/ENGINEER的弯曲件展开长度计算

一、引言弯曲件的展开长度计算,是设计弯曲件冲压模具的一项重要内容。在利用Pro/ENGINEER的钣金功能进行钣金设计时,Pro/ENGINEER可以自动计算展开长度,但其计算方式比较单一,不能适应普遍的情况。本文探讨利用Pro/ENGINEER的钣金功能,通过设置自定义折弯表的方式,进行弯曲件展开长度计算的通用方法。     

柔性太阳翼叠层电池弯曲适应性仿真与设计

航天器在轨进、出地影时，基于复合结构柔性基板的柔性太阳翼叠层电池在高、低温交变作用下会产生热弯曲变形。针对这一问题，采用有限元建模仿真，分析由太阳电池、盖片胶和抗辐照玻璃盖片组成的叠层电池的弯曲适应性，计算不同结构尺寸、不同叠层材料参数的叠层电池在跨中弯曲载荷下的最大应力。借助响应面技术研究设计变量与复合结构性能之间的关系，采用目标驱动优化分析，获得理想的结构尺寸参数。结果表明：叠层电池的宏观力学性能取决于微观不同叠层材料的组合方式；等效弹性模量不是定值，而是与叠层材料的参数有关；弯曲工况的失效模式取决于电池单体的最大拉应力，而不是宏观表征的整体弯曲强度。     

Dynamic stiffness formulation and free vibration analysis of a spinning composite beam

The dynamic stiffness matrix of a spinning composite beam is developed and then used to investigate its free vibration characteristics. Of particular interest in this study is the inclusion of the bending–torsion coupling effect that arises from the ply orientation and stacking sequence in laminated fibrous composites. The theory is particularly intended for thin-walled composite beams and does not include the effects of shear deformation and rotatory inertia. Hamilton’s principle is used to derive the governing differential equations, which are solved for harmonic oscillation. Exact expressions for the bending displacement, bending rotation, twist, bending moment, shear force and torque at any cross-section of the beam, are also obtained in explicit analytical form. The dynamic stiffness matrix, which relates the amplitudes of loads to those of responses at the end of the spinning beam in free vibration is then derived by imposing the boundary conditions. This enables natural frequency calculation of a spinning composite beam at various spinning speeds to be made by applying the Wittrick–Williams algorithm to the resulting dynamic stiffness matrix. The spinning speed at which the fundamental natural frequency tends to zero is the critical speed, which is established for a composite shaft that has been taken from the literature as an example. The results are discussed and some are compared with published ones. The paper concludes with some remarks.     

Midpoint difference method for analysing beam structures

The midpoint difference method is organized for analyzing beam structures by approximating the solution of the differential equation of the elastic deflection curve. The method requires the generation and solution of a system of simultaneous, algebraic equations which yield the deflection, slope, bending moment and shear at specified points along the span of the beam. The method is rather simple and well suited for programming on the digital computer.

All of the basic equations necessary for developing an analysis of a beam structure are established and the application of the method is given in the paper. Some general comments are made about the development of a computer program and about the solution of the system of simultaneous equations peculiar to this method of analysis.     

Bending and stress responses of the hybrid axisymmetric system via state-space method and 3D-elasticity theory

This research presents bending responses of hybrid laminated nanocomposite reinforced axisymmetric circular/annular plates (HLNRACP/ HLNRAAP) within the framework of non-polynomial under mechanical loading and various type of initially stresses via the three-dimensional elasticity theory. The current structure is on the Pasternak type of elastic foundation and torsional interaction. The state-space approach and differential quadrature method (SS-DQM) are studied to present the bending characteristics of the current structure by considering various boundary conditions. To predict the material properties of the bulk, the role of mixture and Halpin–Tsai equations are studied. For modeling the circular plate, a singular point is studied. Finally, a parametric study investigates the impacts of various types of distribution of laminated layers, stacking sequence on the stress/strain information of the HLNRACP/ HLNRAAP. Results reveal that the system's static stability and bending behavior improve due to increasing the value of Winkler and Pasternak factors, and the stress distribution becomes more uniform.

     

Artificial Bee Colony (ABC) for multi-objective design optimization of composite structures

In this paper, we present a generic method/model for multi-objective design optimization of laminated composite components, based on Vector Evaluated Artificial Bee Colony (VEABC) algorithm. VEABC is a parallel vector evaluated type, swarm intelligence multi-objective variant of the Artificial Bee Colony algorithm (ABC). In the current work a modified version of VEABC algorithm for discrete variables has been developed and implemented successfully for the multi-objective design optimization of composites. The problem is formulated with multiple objectives of minimizing weight and the total cost of the composite component to achieve a specified strength. The primary optimization variables are the number of layers, its stacking sequence (the orientation of the layers) and thickness of each layer. The classical lamination theory is utilized to determine the stresses in the component and the design is evaluated based on three failure criteria: failure mechanism based failure criteria, maximum stress failure criteria and the tsai-wu failure criteria. The optimization method is validated for a number of different loading configurations—uniaxial, biaxial and bending loads. The design optimization has been carried for both variable stacking sequences, as well fixed standard stacking schemes and a comparative study of the different design configurations evolved has been presented. Finally the performance is evaluated in comparison with other nature inspired techniques which includes Particle Swarm Optimization (PSO), Artificial Immune System (AIS) and Genetic Algorithm (GA). The performance of ABC is at par with that of PSO, AIS and GA for all the loading configurations.     

基于超细长弹性杆模型的斜拉索静力构形分析

以超细长弹性杆模型研究了斜拉索自重和可拉伸情形下的静态位形.建立了斜拉索一般意义下的超细长弹性杆平衡方程,分三种情况讨论了其平衡位形对应的挠性线、索力及索长.(1)忽略抗弯刚度时,其退化为仅考虑弹性拉伸时斜拉索的平衡方程,此时求得其挠性线方程与已有结论一致;(2)忽略弹性拉伸时,其退化为仅考虑抗弯刚度时斜拉索的平衡方程,求得其挠性线方程比忽略抗弯刚度时的结论多一项一阶修正项;(3)同时考虑弹性拉伸和抗弯刚度情形时,求得其近似挠性线方程.以苏通大桥和某实验室斜拉索为例,分别计算了以上三种不同情形下的斜拉索的静力参数,并分析了在不同索长和索力情况下抗弯刚度和弹性拉伸对斜拉索几何构形的影响.     

Mechanical property evaluation and failure analysis of cantileveredLIGA nickel microposts

An experimental apparatus has been built to measure the elastic modulus and bending strength (modulus of rupture) of LIGA nickel posts. The apparatus uses the static cantilever beam bending approach to measure mechanical properties in a direction parallel to the growth direction. Experimental results are presented for two sets of largely identical posts constructed using an overplating method. One set was electroplated using a Watts bath, and the other set was electroplated using a sulfamate bath. For the Watts bath, the measured modulus of elasticity was slightly lower than that of bulk nickel (182 GPa), while, for the sulfamate bath, it was approximately half (93 GPa). The strength properties of the two sets of posts also differ dramatically. Microhardness measurements, Focused Ion Beam (FIB) images of grain structure, and scanning electron microscopy (SEM) micrographs of failure regions are used to further characterize and explain the differences in the results. This integrated testing approach yields a consistent set of data regarding material properties, grain size/structure and failure mechanisms. Potential sources of experimental error are also identified and improvements in experiment design are suggested to reduce these errors     

The interaction of plane frames with elastic foundation having normal and shear moduli of subgrade reactions

The interaction of plane frames with an elastic foundation, of the Winkler type, having normal and shear moduli of subgrade reactions was studied.

An exact stiffness matrix for a beam element on an elastic foundation having only a normal modulus of subgrade reaction was modified to include the shear modulus of subgrade reaction of the foundation as well as the axial force in the beam. A computer program was written and used in two case studies. In the first case study the convergence of the modified element was tested: in the second it was employed to study the effect of the foundation normal and shear moduli of subgrade reactions on the bending moments in a selected plane frame. The results indicated that bending moments might be considerably affected according to the type of frame and loading.     

Free vibrations of rectangular unsymmetrically laminated composite plates with internal line supports

Free vibrations of rectangular unsymmetrically laminated composite plates with internal line supports in one or two directions are studied. The static beam functions, which are the complete solutions of a unit width strip taken from the plate in the direction parallel to the edges of the plate and under a series of transverse static sinusoidal loads, are used as the trial functions of the transverse bending deflection of the plate. Besides, the vibrating bar functions are used as the trial functions of the in-plane stretching deformation of the plate. The Rayleigh–Ritz method is applied to arrive at the governing eigenfrequency equation in which the coupling effect of bending and stretching is contained. Different transverse boundary conditions combining with various in-plane constraints are considered in the analysis. The effects of fiber orientation angles and locations of internal line supports on eigenfrequencies of cross-ply and antisymmetric angle-ply laminated composite plates of two layers are investigated in detail. Convergence and comparison study show the correctness and effectiveness of the proposed method. Sets of valuable results are presented for the first time, which can serve as benchmarks for future reference.