综合控制焊接变形和防止热裂纹的新方法——双向预置应力法

提出一种既可控制薄板焊接变形又可防止焊接热裂纹产生的随焊同步进行的双向预置应力法,阐明该方法的基本原理并对该法防止高强铝合金LY12薄板焊接热裂纹和控制其焊后变形的有效性进行研究。在自行研制的预置应力设备上进行试验验证。双向预置应力下焊接试验结果表明,采用这一新方法可以有效地控制高强铝合金LY12的焊接变形及焊接热裂纹的产生。     

压力容器焊接热裂纹形成原因及其防止措施

介绍了焊接热裂纹形成机理，通过实例分析产生焊接缺陷的主要原因，并提出相应的防止措施。     

热变形对机床的影响与控制

机床热变形是机械制造业中常见的一种不正常的现象,由于热变形的产生,使得机床实际工作时的精度降低,影响零件的加工精度。在机床设计中减少热源的发热量、改变热源的位置、转移热源所产生的热量、设法让热变形向不影响精度的方向发展、采用自动热补偿装置以及选用合适的润滑冷却装置等,是防止和控制机床热变形的有效措施。     

高锰钢铸件与低合金钢焊接热裂纹的预防

从高锰钢和低合金钢的材料性能及焊接性着手,结合生产实际,通过采取切实可行的工艺措施,防止焊接热裂纹的产生.     

磨削裂纹产生的原因及其防止方法

过对淬火工件回火温度、磨削热、磨削用量等的分析,找出高硬度及高碳含量工件磨削裂纹产生原因,并提出防止方法。     

25CrNiMoV耳轴电渣焊裂纹分析及处理

分析了25CrNiMoV耳轴焊缝裂纹的产生原因，并对焊接工艺进行了大胆而有益的尝试，即采用提高预热温度、焊接部分阶段调整焊接参数、焊后紧急后热等方法防止裂纹产生。试验后，外观检验、超声波探伤均满足设计要求，从而证明采用此方法防止裂纹是可行的。     

杯形阀阀盖焊接工艺

分析了杯形阀阀盖十字形和T字形(I形坡口)焊接接头产生热裂纹的原因,制订了工艺改进方案,通过相关的试验验证,确定了防止热应力产生的有效措施。     

铸铁件常见缺陷产生的原因与防止

主要介绍了铸铁件中常见的几种缺陷,如气孔、渣孔、缩松、硫松、热裂、冷裂产生的原因及防止方法.     

手工电弧焊中若干问题

8.什么叫冷裂纹?一般是什么原因产生的?如何防止冷裂纹? 在较低的温度下(一般为<200～300℃)下产生的裂纹称冷裂纹。产生冷裂纹是由于焊缝或热影响区产生淬硬组织,有扩散氢气的存在及高的焊接收缩应力。防止办法:产品焊接时予热,焊条烘干,焊后去氢热处理,选用合理的焊接顺序,减少焊接应力等。 9.什么叫延迟裂纹?一般采用什么措施避免产生延迟裂纹? 延迟裂纹是冷裂纹的一种形式,是焊接完成后过一段时期才出现的裂纹。     

与热变形作斗争

本文介绍了消除热变形误差的两种方式:预防和补偿。还叙述了防止误差产生和补偿误差的方法,对机床和环境的要求及所得到的效果。     

无心外圆磨床取料系统改造

KC-500A无心外圆磨床是用来磨削铁路货车轴承的专用设备。对该设备进行了改造，使之可加工其它类型的产品，并扩大了加工范围，达到了加工产品的工艺要求。     

链传动中松边垂度和张力变化的分析方法

分析了链传动在实际运转过程中，紧边链条与链轮上不同圆相切的情况，从这一角度出发，当中心距和链节数以链条松、紧边与2链轮分度圆相切为条件确定后，链条紧边与链轮不同的圆相切将导致松边垂度和张力变化。     

Torsion of thin-walled beams of open cross-section with influence of shear

An approximate analytical approach to the torsion of thin-walled beams of open cross-section with influence of shear is presented. It is assumed that the normal stresses in the cross-section contour direction are small compared to the normal stresses in the beam longitudinal direction that can be ignored in the stress–strain relations. The stresses and displacements are obtained in the closed analytical form. It is assumed that transverse load can be reduced to moments of torsion only, with respect to the cross-section shear centre. The beam will be subjected to torsion, with respect to the shear centre, i.e. the principal cross-section sectorial coordinate, in the case of cross-sections with two axes of symmetry; to torsion and bending in the case of cross-sections with one axes of symmetry and to torsion, bending and tension in the case of general cross-sections. An illustrative example of beam with one axis of symmetry is given.     

拼接子镜力矩促动器布局优化设计

为了降低较为昂贵的镜面抛光和光机装配费用,以及应对温度、重力及其他意外因素导致的镜面低阶像差,一种在被动浮动支撑结构上施加力矩以实现面型实时校正的力矩促动器在部分望远镜上已有成熟应用。本文旨在针对我国未来的大口径地基光学望远镜,对其拼接子镜力矩促动器的分布进行优化与设计。首先根据工程经验和参考文献初步确定力矩促动器所需校正能力,通过三维建模软件对拼接子镜及镜室进行建模,最后通过有限元仿真和最小二乘法拟合对力矩促动器的布局进行优化设计。计算结果表明,采用18个力矩促动器的分布方案能够对离焦、像散、彗差、三叶像差进行良好的校正。对于具有数百面子镜的拼接望远镜来说,18个力矩促动器的方案在满足光学设计需求的同时,有效节约了建设经费并降低了工艺的复杂性。     

四腿机器人步态的稳定性研究

对四腿动物走路姿态进行分析，通过对比一种国际上机器人比赛中普遍采用的典型步态，提出了一种新的走路步态，从动力学特性角度分析说明了这种新的步态的稳定性，并定义了一个衡量稳定性能指标的量，谈性能指标是利用机器人受到的三维的合力大小来定义的，这个性能指标具有衡量稳定性的特点，并通过实验说明该步态的稳定性能。     

我校工业设计教育改革初探

针对目前市场对工业设计人才的需求,本文论述了我校在工业设计教育方面的改革措施,着重介绍了我校工业设计教育在软件和硬件方面所进行的一系列的改革。     

平面度误差测量及数据处理研究

介绍了平面度误差的评定方法及平面度误差常用的几种测量方法,提出了采用旋转法处理数据,使之符合最小条件,从而计算出平面度误差。     

Reconstruction of the rose of directions from a digital microhologram of fibres

Digital holography makes it possible to acquire quickly the interference patterns of objects spread in a volume. The digital processing of the fringes is still too slow to achieve on line analysis of the holograms. We describe a new approach to obtain information on the direction of illuminated objects. The key idea is to avoid reconstruction of the volume followed by classical three-dimensional image processing. The hologram is processed using a global analysis based on autocorrelation. A fundamental property of diffraction patterns leads to an estimate of the mean geometric covariogram of the objects projections. The rose of directions is connected with the mean geometric covariogram through an inverse problem. In the general case, only the two-dimensional rose of the object projections can be reconstructed. The further assumption of unique-size objects gives access with the knowledge of this size to the three-dimensional direction information. An iterative scheme is suggested to reconstruct the three-dimensional rose in this special case. Results are provided on holograms of paper fibres.     

气缸低摩擦力测量方法的研究

为了测量新型金属密封气缸的低摩擦力,设计了间测法和直测法两种测量系统。比较实验表明,直测法测量精度高、数据一致性好、动摩擦力测量时可预设速度值,因此更适合于气缸低摩擦力的测量。在此基础上,采用直测法获得了新型金属密封气缸静摩擦力和不同速度下的气缸动摩擦力,为该型气缸的使用提供了基础数据。     

Finite-element simulation of hole-flanging process of circular sheets of anisotropic materials

A hole-flanging operation on a flat circular sheet with a hole in the center is simulated by an incremental elasto-plastic finite-element method, which incorporates strain-hardening and anisotropy in the direction normal to the sheet, with care taken to describe the boundary conditions of penetration, separation and the alternation of the sliding—sticking state of friction. The simulation clearly demonstrates the processes of generation of deformation shape until unloading. The calculated sheet geometries and the relationship of punch load to punch stroke are in good agreement with the experimental data.The stress at the hole periphery in the flange is assumed to a state of circumferential uniaxial tension, in order to simplify the fracture mode as a simple tension test. By making use of the instability of uniaxial tension, an approximate relationship to determine the onset of necking of the hole periphery in the hole-flanging process is derived and it is found to be influenced by the process geometry and the plastic properties of the material, such as the stress-concentration factor K, strain-hardening n and normal anisotropy R, and the estimated value, being obtained by the derived equation, agrees well with the experimental data.It is noted that the derived relationship for estimating the instability of the hole-flanging process can be combined into the developed finite-element model to simulate the critical condition of the limiting deformation of the hole-flanging process. This combined method could possibly be applied towards improving both the manufacturing process and the design of tools for the hole-flanging operation.