The load-carrying capacity of initially imperfect eccentrically loaded plates

Theoretical analyses of compressed plates with various loading and boundary conditions previously published by the authors are extended to include the effects of initial imperfections. Comparison of the theoretical results is made with experiment. It is shown that for plates with supports on both unloaded edges the simple criterion that collapse occurs when the maximum membrane stress reaches yield, gives accurate estimates of failure for eccentrically loaded plates. The collapse modes of plates which have one edge free are found to be rather complex in nature and vary with plate thickness and loading eccentricity.A simplified design analysis for the prediction of collapse loads of eccentrically loaded simply supported plates is formulated and shown to predict experimental results very accurately.     

A composite view on Windenburg's problem: Buckling and minimum stiffness requirements of compressively loaded orthotropic plates with edge reinforcements

This paper discusses the buckling behaviour of orthotropic composite plates under uniform uniaxial compression with one free reinforced unloaded edge. A typical application example for use of such a mechanical model is the web of stiffeners and frames attached to the fuselage skin of an aircraft. The considered plates are rectangular and simply supported at the loaded transverse edges. One of the longitudinal unloaded edges is also simply supported, while the second unloaded edge is not supported at all but is reinforced by a flange of arbitrary cross-section. At first, an exact solution for the elastic buckling problem is derived from the governing differential equation by imposing the underlying boundary conditions. Thereafter, two approximate closed-form solutions for the buckling load are derived, which can be conveniently used for practical application purposes. Generic buckling curves using characteristic non-dimensional quantities are also presented. Finally, the question of the required bending stiffness EI_min of the flange is treated, to ensure that the flange withstands buckling and provides simply supported boundary conditions to the free reinforced plate edge.     

Influence of in-plane displacements at the boundaries of rigid-plastic beams and plates

An approximate theoretical rigid-plastic study has been undertaken into the influence of small in-plane displacements at the boundaries of various laterally loaded beams. The most interesting feature of these theoretical predictions is the remarkably small in-plane displacements at the supports which can change the response from that of an axially restrained beam, with considerable reserve strengthening beyond the limit load for moderate lateral deflections, to that of a freely supported beam with no concomitant increase in strength beyond the limit load. A comparison has also been made between some theoretical predictions for a laterally loaded square plate and the corresponding experimental results obtained by Clarkson on rotationally fixed plates with edges free to slide inwards.     

Stability behaviour of arbitrarily laminated composite plates with free and elastically restrained unloaded edges

In this paper, the initial buckling loads and the corresponding buckling modes of symmetric rectangular laminated plates are investigated. The considered laminates are supposed to have a uniform thickness, are subjected to a linearly distributed inplane compressive normal load and are simply supported at the two loaded edges with one free unloaded plate edge and with one simply supported unloaded edge where elastic rotational restraints are considered. Unlike in many other investigations, the composite laminates presently under consideration may have arbitrary yet symmetric lamination schemes with bending–torsion coupling. The initial buckling loads of such plates are calculated using the RITZ-method for which some especially adjusted displacement shape functions are employed. Since a series expansion of the buckling shape is performed in the load direction only while in the perpendicular direction one single displacement function can be shown to be sufficient, the present approach is numerically very efficient when compared to approaches in which a series representation is chosen with respect to both inplane directions. Comparison with reference results and with finite element computations leads to an excellent agreement. Some new findings on the general stability behaviour of this class of laminated plates are presented as a closure.     

特高压输电系统中磁控电抗器抑制工频过电压的研究

针对我国特高压输电线路中普遍安装的不可控电抗器,显著制约线路传输功率的缺点,本文采用磁控电抗器来限制特高压输电线路在长线空载电容效应、不对称接地和突然甩负荷三种工况下产生的工频过电压.对磁控电抗器抑制工频过电压基理进行分析,随后根据我国特高压线路的实际情况,用仿真软件分别分析了不同裳设方式下磁控电抗器抑制工频电压升高的...     

搅拌摩擦焊接加筋板轴压稳定性研究

运用半经验公式对采用搅拌摩擦焊接技术的加筋板轴向压缩局部屈曲临界应力进行工程计算,并应用有限元软件ABAQUS对该型结构的稳定性进行数值计算,得到结构的失稳屈曲临界载荷;参考工程计算和有限元计算值,对加筋板进行轴向压缩试验,对其屈曲形式、失稳及破坏载荷进行试验研究,并考虑侧边支持条件对结果的影响。试验分析表明,非承载边的约束条件对试件的屈曲载荷有一定的影响,而对试件的承载能力影响较小;搅拌摩擦焊加筋板具有一定的后屈曲承载能力;有限元计算结果与试验结果较吻合,说明模拟方法可以用来对该型结构的稳定性能进行分析,从而为该型结构的优化设计及工程应用提供分析参考。     

Relative movements between Kinemax Plus tibial inserts and the tibial base-plates

Tests were performed on six large Kinemax Plus knee bearings (snap-fit design) to evaluate the amount of movement between 10- and 15-mm-thick tibial inserts and the tibial base plates. The knee bearings were tested up to 1 x 10(6) cycles on the Durham six-station knee wear simulator which subjected the bearings to similar motion and loading profiles that would be experienced by the natural knee during walking. Although passive internal/external (I/E) rotation was allowed, no active I/E rotation was applied. The movement of the tibial inserts was measured with dial gauges (accuracy +/-0.01 mm) before and after the bearings were tested on the simulator, when unloaded, and throughout the tests while the bearings were being dynamically loaded in the simulator. Movement occurred between the tibial insert and the tibial base plate after initial assembly due to the snap-fit mechanism used to locate the tibial insert within the tibial base plate. However this decreased appreciably when the bearings were loaded in the simulator. The amount of movement did not change with time when the bearings were continuously loaded in the simulator. However, after each test the amount of movement of the tibial inserts, when unloaded, was only 65 per cent (anterior-posterior) and 46 per cent (medial-lateral) of the values before the test. This was thought to be due to creep of the ultra-high molecular weight polyethylene (UHMWPE) inserts. The movement between the tibial insert and tibial base plate in situ is likely to be much less than that observed by a surgeon at the time of assembly due to loading of the knee bearing in the body. However, the amount of movement when the tibial inserts are loaded may still be great enough to produce a second interface where wear of the tibial insert may take place.     

水路集装箱运输机械环境条件研究

介绍了水路集装箱运输机械环境条件的特点和分类,分析了集装箱在港口装卸和水路运输过程中振动冲击值,并结合振动冲击等环境条件对货物的影响,提出了安全防护的几点措施,为水路集装箱安全运输提供理论依据。     

Point mass identification in rods

The possibility of applying the acoustic free-vibration method to diagnose rods with localized masses is considered. Calculation data of vibration frequencies of loaded and unloaded rods that were obtained using the proposed model and other author’s models are compared.     

车床卡盘安全保护系统的设计

根据普通卧式车床在实际操作过程中安全隐患最为突出的卡盘扳手而设计出一套车床卡盘安全保护系统.针对普通卧式车床在实际操作装卸工件时存在的安全隐患,提出安装车床卡盘安全保护系统的必要性,详细说明了所设计的安全保护系统的结构和工作原理,并对车床卡盘安全保护系统的安全保护性能进行了分析.     

Natural frequencies of stepped thickness rectangular plates

This paper presents the natural frequencies of stepped thickness square and rectangular plates together with the mode shapes of vibration. The transverse deflection of a stepped thickness plate is written in a series of the products of the deflection functions of beams parallel to the edges satisfying the boundary conditions, and the frequency equation of the plate is derived by the energy method. By use of the frequency equation, the natural frequencies (the eigenvalues of vibration) and the mode shapes are calculated numerically in good accuracy for square and rectangular plates with edges simply supported or elastically restrained against rotation, having square, circular or elliptical stepped thickness, from which the effects of the stepped thickness on the vibration are studied.     

基于小波变换和形态学的图像边缘检测方法

提出了一种基于小波变换和形态学的图像边缘检测方法。对源图像进行小波分解,用数学形态学法对低频子图像进行边缘检测,用小波变换法提取高频图像的边缘,采用一定的融合规则将两个边缘图像融合在一起得到一幅完好的边缘图像。这种边缘检测方法结合了小波变换法和数学形态学法的优点,对用这两种方法得到的边缘信息进行融合,有效地抑制了噪声,且边缘连续、清晰。实验结果表明,提出的这种结合方法优于单独使用数学形态学法或小波变换法。     

连续式超临界流体萃取进卸料装置

概括了超临界流体萃取技术和包括连续式操作在内的超临界流体萃取装置的研究现状 ,提出了一种通过球形进、卸料器完成固相物料超临界流体萃取连续化进卸料的装置 ,介绍了该装置的结构和工作原理 ,给出装置中各主要部件的计算方法。     

Press-fit disk pressure on the aperture wall of a plate loaded over its external edges

The problem on radial contact stress that appears if the press-fit disk presses to an aperture wall made in the rectangle plate loaded over its external edges by an arbitrary set of forces in the plate's plane has been solved. The general solution is transformed into formulas for solving different problems by setting different forces at the plate edges. The results of calculations carried out according to the presented procedure are compared with theoretical and experimental results and they are in good agreement. The results of the present work can be used for strength calculation for bolt and rivet joints.     

小型载货汽车后钢板弹簧的设计

通过对小型载货汽车后钢板弹簧进行设计计算,确定了钢板弹簧的总长、片厚、片宽、片数、检验刚度、装配刚度,以及自由状态下的弧高、曲率半径,并进行了相应的强度校核.最后通过生产实践证明,相关设计参数能满足汽车在空、满载条件下对行驶平顺性、操纵稳定性和安全方面等要求.     

Testing and calibration of coordinate measuring arms

Portable coordinate measuring arms with rotational axes have found their place in many industrial areas. To establish and confirm the accuracy of these measuring devices, related test methods and appropriate devices are needed. After an introduction, a new high precision measuring device for testing and calibration of portable coordinate measuring arms is presented. Analysis showed that the best results can be obtained with a device for measuring along a straight line adjusted in various spatial directions. We discuss the design and construction of this measuring system and provide a theoretical calculation of its measurement accuracy, which was confirmed by experiments carried out on a prototype of a high precision measuring device in both unloaded and loaded conditions.     

特殊专用工装夹具

介绍为提高劳动生产率和降低加工成本,在进行各类机械加工时有效地利用特殊离心式专用夹具的方法。零件旋转时产生的离心力,既能夹紧又可固定零件;停止旋转后随着离心力的消失,零件处于自由状态,可轻松装卸零件。采用特殊专用工装夹具既保证了工件的加工精度,又稳定了产品质量,还可改善工人劳动条件,保证安全生产,进而扩大机床工艺范围。     

On the explosive hardening of one end of a metallic block

Aluminium and mild steel plates were subjected to shock loading on one end by detonating Metabel explosive sheet. The residual stresses in the principal directions were measured using the X-ray, back reflection method, through the specimen thickness.Macro- and micro-structural analyses and micro-hardness surveys of the unloaded specimens were made to examine how the influence of explosive thickness decays with distance from the loaded surface. A central fracture under explosive loading is explained by reference to unloading waves.     

The biophysical effects of a single impact load on human and bovine articular cartilage

Impact injury to a joint is a known risk factor for the subsequent development of secondary osteoarthritis. An in vitro model, employing a drop-tower loading machine, was used to examine the effect of an impact load on isolated articular cartilage explants from human and bovine femoral heads. Two different types of impact experiment were performed. In the first, 4 mm diameter explants were loaded using a plane-ended impactor. In the second, a modified impactor was developed that had a central 4 mm diameter plane-ended indentor which was used to load the centre of 8 mm diameter explants. This enabled the unloaded outer ring of each explant to be compared with the loaded central core. The modulus values measured using the impactor were found to be higher, compared with the indentor in both species. Scanning electron microscopy showed that cartilage surrounding the loaded central region of the 8 mm explants protected the indented tissue, and these explants showed less damage than the 4 mm samples that were fully impacted. In addition, human cartilage was found to be less damaged than bovine, possibly as a consequence of the different structure as well as of a greater thickness. Both the source of the tissue and the nature of the impact affected the type of damage observed.     

Experimental study of a potential weakening effect in spheres with thin hard coatings

A potential weakening effect caused by very thin hard coatings on spherical substrates is investigated experimentally. This weakening effect reduces the resistance of the coated system to onset of plasticity. Half-coated spheres are prepared using an ion beam assisted deposition system. The coated and uncoated portions of these half-coated spheres are loaded by a rigid flat into their elastic–plastic regime of deformation and then unloaded. The resulting maximum interference after loading and residual interference at the completion of unloading are measured and used in an elastic–plastic loading index model to evaluate the plasticity levels of both the uncoated and coated portions on each sphere. The experimental results validate qualitatively the potential weakening effect, which was predicted theoretically in previous publications.