Prediction of fatigue life in aircraft double lap bolted joints using several multiaxial fatigue criteria

In this research, the effects of torque tightening on the fatigue strength of 2024-T3 aluminium alloy double lap bolted joints have been studied via experimental and multiaxial fatigue analysis. To do so, three sets of the specimens were prepared and each subjected to different levels of torque i.e. 1, 2.5 and 5 N m and then fatigue tests were carried out at various cyclic longitudinal load levels. A non-linear finite element ANSYS code was used to obtain stress and strain distribution in the joint plates due to torque tightening of bolt and longitudinal applied loads. Fatigue lives of the specimens were estimated with six different multiaxial fatigue criteria by means of local stress and strain distribution obtained from finite element analysis. Multiaxial fatigue analysis and experimental results revealed that the fatigue life of double lap bolted joints were improved by increasing the clamping force due to compressive stresses which appeared around the hole.     

Effect of a preload force on anchor system frequency

The interrelationship between preload forces and natural frequencies of anchors was obtained from the structure of an anchor and its mechanical characteristics. We established a numerical model for the dynamic analysis of a bolt support system taking into consideration the working surroundings of the anchor. The natural frequency distribution of the system under various preload forces of the anchor was analyzed with ANSYS. Our results show that each order of the system frequency varied with an increase in preload forces. A single order frequency decreased with an increase in the preload force. A preload force affected low-order frequencies more than high-order frequencies. We obtained a functional relationship by fitting preload forces and fundamental frequencies, which was in agreement with our theoretical considerations. This study provides theoretical support for the detection of preload forces.     

Fabrication and analysis of cylindrical resin AFM microcantilevers

In this paper a new method of fabricating cylindrical resin microcantilevers using the Direct Digital Manufacturing (DDM) technique of Micro-stereolithography (MSL) is described. The method is rapid and commercially viable, allowing the fabrication of atomic force microscope (AFM) cantilevers which exhibit much larger spring constants than those currently commercial available. This allows for experimentation in a force regime orders of magnitude higher than currently possible using the AFM. This makes these cantilevers ideally suited for AFM-based depth sensing indentation. Due to their geometry, the assumptions used in the standard Euler-Bernoulli beam theory usually used to analyse AFM cantilevers may no longer be valid. Therefore approximate analytical solutions based on Timoshenko beam theory have been derived for the stiffness and resonant frequency of these cantilevers. Prototypes of the cantilevers have been fabricated and tested. Results show good agreement between experiment and theory.     

桁架设计一般方法和误区探讨

重点分析了桁架的设计过程中容易被工程师忽略的支座设计，通过三种建模方式的比较，阐述了不同支座约束对桁架结构内力计算的影响，算例说明了实际工程的支座变形以及柱顶位移会对桁架结构造成杆件承载力小于实际内力的情况，还给出了滑动支座的节点详图，以指导工程实践。     

基于SolidWorks软件下进行螺杆压缩机转子受力计算

利用螺杆压缩机的型线端面数据点及型线的接触线数据点,通过给定螺杆压缩机转子参数,在Solid Works里绘制出对应的三维模拟。利用Solid Works里面自带的Simulation模块,对螺杆压缩机进行有限元分析,计算出转子静态下的气体轴向力和径向力,对螺杆压缩机的设计及轴承选型提供很好的理论依据。本文以一种双螺杆制冷压缩机转子为例,利用本方法计算出螺杆压缩机阴阳转子吸排气端的气体径向及排气端气体轴向力。     

基于DSMO的无位置BLDCM控制策略研究

永磁无刷直流电机(BLDCM)是多变量、强耦合的非线性系统,为改善连续域的控制方法不能较好预测系统的稳定性,提出基于离散滑模观测器(DSMO)的无位置BLDCM控制方法,并引入Sigmoid函数作为滑模观测器的控制函数,以削弱抖振;同时构建离散反电动势观测器直接提取反电动势信号,并利用李雅普诺夫理论证明其稳定性,进一步引入坐标旋转数字计算(CORDIC)算法,以提高电机转子位置的估算精度。实验结果表明,该控制策略能准确估计电机转子位置,同时削弱观测器的抖振问题,提高系统精度和可靠性。     

D型复合材料管连接性能研究

格构式复合材料塔采用了通过钢制螺栓机械连接的D型复合材料管,其中复合材料管制孔和螺栓预紧力对杆件承载力影响还没有相关研究,其承载特性不太清楚。为准确掌握D型复合材料管的连接性能,通过D型复合材料管的塔节间模型节点试验,得到复合材料杆件连接孔端部以劈裂和剪切破坏为主;通过有限元模型分析了螺栓预紧力对D型复合材料管连接性能的影响,结果表明D型复合材料塔用抗剪螺栓的预紧扭矩宜控制为220 N?m。     

动叶可调引风机变频改造的经济性论证

随着当前全国节能减排工作的全面展开,火力发电厂节能改造项目都相互跟风,并没有结合本厂的实际情况进行全面论证。文章针对国内330MW火力发电机组的双级动叶可调引风机进行变频改造的经济性进行论证,在满足设计规范要求下,分析引风机变频改造后的节能情况。在机组负荷率变化的情况下,对应引风机变频改造后的节能情况进行论述,以寻求引风机变频改造对应的最佳锅炉运行负荷率,力求引风机变频改造后能获得较高的经济性,为同类型机组提供改造的参考意义。     

双凹槽叶顶轴流风机噪声预估及叶片静力结构分析

叶顶结构型式对轴流风机性能、噪声及叶片静力特性等均有一定影响。以OB-84型带后置导叶的轴流式通风机为对象,采用Fluent数值模拟软件及Ansys有限元分析模块,通过比较开槽前后风机轴功率的变化探讨双凹槽叶顶结构的节能效果,分析了原叶顶及双凹槽叶顶下风机噪声及叶片的静力结构特性。研究表明:双凹槽叶顶下风机轴功率有所下降,设计工况下轴功率较原叶顶时下降了3.96%,可在一定程度下降低风机的能耗;双凹槽叶顶下风机噪声有较大幅度提高,设计工况下噪声较原叶顶时增长约14.88%,给风机正常运行带来不利影响;不同叶顶下叶片的静强度校核结果均满足要求,即采用双凹槽叶顶结构不会引起叶片的变形及断裂失效。     

磁性液体传感器一阶悬浮力的理论计算和仿真分析

一阶悬浮力是磁性液体传感器的设计关键。利用任意多物理场直接耦合分析软件COMSOL multiphysics仿真分析了磁性液体一阶悬浮力,一阶悬浮力在最大偏心距纵坐标为-2.5mm,横坐标在-20~25mm的范围内呈周期分布,其平均值为38.43N。同时对没考虑磁场和流场耦合情况下的一阶悬浮力进行了理论计算,仿真和理论计算均表明一阶悬浮力与偏心距离间存在非线性关系,一阶悬浮力的理论计算结果大于仿真分析结果,偏心距越大,理论计算与仿真分析的结果相差越大。磁性液体传感器的设计应该考虑磁场和流场的耦合作用。