浅谈机械制图中图样尺寸标注的教法

众所周知,机械图样是工程界的技术语言.要使学生掌握这门"语言",应抓住两个关键问题:一是图形表达;二是尺寸标注.这里主要讨论机械制图的尺寸注法.在制图教学中,尽管将尺寸标注既作为重点,又作为难点,但是教学效果往往还是不尽如人意,甚至在学生学完本课程后,标注尺寸时仍然是错漏百出.要提高图样尺寸标注这部分内容的教学效果,可将尺寸标注要达到的正确、完整、清晰、合理的四项基本要求分散到三个阶段进行教学.同时,尚需不断研究、改进其教学方法.     

纳米尺度下的金属玻璃显现超级力学性能

美国研究人员开发出一种新方法,只需简单地减小尺寸,即可使一些脆性材料的韧性变得更为强劲。此项科研成果刊登在2月7日《自然·材料学》杂志的网络版上。     

电缆桥架结构设计的快捷方法

针对厂家在电缆桥架结构设计上应如何符合规范所面临的困难,对电缆桥架的设计方法进行了讨论,并建立一种快捷方法。设计人员可以参照该方法进行强度、刚度和稳定性设计;同时该方法对于比较快捷地确定桥架结构的尺寸和形状有指导意义。     

Auto CAD中公差标注形式及其设置技巧

通过对AutoCAD绘图中公差标注的各种常见形式的变化及其标注方法分析,用实例说明了"公差"选项卡下各个输入(选择)项的设置和处理技巧,对恰当地使用标注设置,规范、美观地完成各种公差尺寸标注具有指导意义.     

装配尺寸链在托辊装配中的应用

托辊在加工和装配过程中很难保证轴承内圈与中心轴配合,轴承外圈与轴承座配合,两端压盖与辊筒端面紧密帖合。通过对托辊原结构进行分析与改进,可简化加工难度和装配难度,并对改进后的结构进行尺寸链计算,合理分配各零件的极限偏差,既降低了生产成本,又满足了使用要求。     

大尺寸玻化地砖铺装质量控制初探

文章就大尺寸玻化地砖铺贴后出现空鼓、起拱现象的原因进行了分析,并指出应从设计、地砖质量、施工方法方面采取相应的措施加以控制。     

螺纹切削加工指令在数控车床上的应用

本文是通过螺纹的尺寸分析、刀具的装刀与对刀和普通螺纹的编程指令几个方面阐述了螺纹加工指令在数控车床上的应用.     

Formation mechanism and size prediction of bubble in opposite-flowing T-shaped microchannel

Bubble formation in an opposite-flowing T-shaped microchannel with 40 μm in depth and 120 μm in width was real-time visualized and investigated experimentally by means of a high speed camera. N2 bubbles were generated in glycerol-water mixtures with different concentrations of surfactant sodium dodecyl sulfate (SDS). And the images were captured by the high speed camera linked to a computer. Results indicated that the bubble formation process can be distinguished into three consecutive stages, i.e., expansion, collapse and pinching off. The bubble size decreases with the increase of liquid flow rate and viscosity of liquid phase as well as the decrease of gas flow rate. The surface tension of the liquid phase has no measurable influence on the bubble size. Moreover, a new approach to predicting the size of bubbles formed in the T-shaped microchannel is proposed. And the predicted values agree well with the experimental data.     

Vibration shape testing of space sheet structure

The space sheet for a solar array structure is large in dimension, and flexible to induce complex distortion. It is difficult to measure the distortion. A large-scale flexible test prototype system is built for sheet structure vibration monitoring based on the vibration information of the solar array in space. The system provides an intelligent test method for flexible space structure with embedded sensors and non-visualization reinstruction. Multiple fiber Bragg grating （FBG） sensors are packaged and embedded into the structure with spatial division multiplexing （SDM） and wavelength division multiplexing （WDM）. The sensor interrogator distinguishes wavelength shifts that can be turned into curvature of the curve. The structure shape is reconstructed based on the curvature information and the arc-length, and then displayed. The experiment shows that the system has a high FBG sensitivity. The reconstruction algorithm is fast with high precision. The system has great potential for use in health monitoring of the space sheet structure.     

截面尺寸对玻璃纤维包裹加固砖柱效果的影响

为研究截面尺寸对玻璃纤维加固砖柱轴压性能的影响,进行了39个(13组)不同截面尺寸的砖砌体柱经玻璃纤维增强材料全长包裹加固后的轴心受压试验,分析了试件截面尺寸、砂浆强度以及黏贴层数等因素对加固后试件极限强度的影响.试验结果表明:这种加固方式能不同程度提高砖柱的极限承载力,极限强度随加固层数线性变化.参照FRP加固混凝土柱的基本原理,建立了FRP加固砖柱的有效约束区与非有效约束区.