Restraint of fatigue crack growth by wedge effects of fine particles

This paper presents some experimental results which demonstrate restraint of fatigue crack growth in an Al–Mg alloy by wedge effects of fine particles. Fatigue test specimens were machined from a JIS A5083P‐O Al–Mg alloy plate of 5 mm thickness and an EDM starter notch was introduced to each specimen. Three kinds of fine particles were prepared as the materials to be wedged into the fatigue cracks, i.e. magnetic particles and two kinds of alumina particles having different mean particle sizes of 47.3 μm and 15.2 μm. Particles of each kind were suspended in an oil to form a paste, which was applied on the specimen surface covering the notch zone prior to the fatigue tests. In order to make some fracture mechanics approaches, in situ observations of fatigue cracks were performed for the two cases using a CCD microscope, with a magnification of ×1000. The crack length and the crack opening displacement (COD) at the notch root, δ, were measured. First it was ensured by control tests that the wedge effect of the oil itself was negligible. Then it was found that the large size alumina particles were not effective in restraining crack growth because the paste was difficult to make due to the large particle size and the particles could not enter the cracks properly. However, both of the magnetic particles and the small size alumina particles effectively restrained crack growth, especially the latter which produced 143–350% increase in the lifetime to failure. From the in situ observations, in the case of the small size alumina particles, a pronounced retardation of crack growth was observed immediately after the crack length exceeded 0.4 mm, and this is considered to be due to the range of COD value, δ_max ? δ_min , being strongly affected by the wedge effects of the particles. The crack retardation effect continues almost through the entire lifetime if the alumina paste is re‐applied at specified intervals, while the effect is apparently lost after the crack length exceeds ～2 mm when such re‐painting is not continued. After the fatigue tests, some macro‐ and microfractographic analyses were performed using a CCD microscope, a SEM and an EPMA (electron probe microanalyser), in order to examine the mechanism of fatigue crack restraint by the wedge effects of the fine particles. From those analyses, it was reasoned that the fine particles that entered a fatigue crack are subjected to cyclic pressures between the crack faces and then form a kind of wedge which causes significant levels of crack closure that restrain crack growth.     

闸板防喷器液压锁紧装置现状及发展研究

对国内外液压锁紧装置发展现状进行了分析,介绍了几种不同液压锁紧装置的结构和优、缺点。国外主要以楔面自锁结构和单向棘齿结构为主,国内主要以楔面自锁结构为主。分析了国内液压锁紧装置在设计、制造、现场使用及检测维护方面存在的问题,提出了解决这些问题的建议。最后指出,国内应大力开展液压锁紧装置的可靠性优化设计、特殊环境用液压锁紧装置的研制、标准的统一制定、手动锁紧进行液压改装和现场应用反馈信息的收集等工作,以提高我国井控装置的自动化水平,实现我国油气田钻井的安全生产。     

宝珠寺水电站左岸高边坡处理综述

宝珠寺电站左岸边坡开挖垂直高度２００余ｍ，地质情况复杂，存在多处断层及夹泥层，构成１０余组不稳定楔形岩体。施工中，根据不同的地质情况，分别采取了混凝土抗剪置换洞，锚筋桩，系统锚杆及爆破控制等综合处理措施。确保了施工期间的稳定及安全，保证了施工工期。本文以该工程为例，简要介绍了边坡处理的施工方法，以供借鉴。     

Analysis of Bimaterial Wedges Using a New Singular Finite Element

This paper is concerned with the singular stress field at the vertex of a bimaterial wedge under in-plane loading. The boundary value problem is initially formulated in terms of the complex function method. The eigenequations are obtained using the continuity conditions along the interface and the traction-free conditions along the free edges, leading to the development of explicit expressions for the singular stress and displacement fields for a general bimaterial wedge. These expressions are then used to develop a new singular finite element. This element enables the determination of the singular stress field and the associated stress intensity factors reliably and efficiently. To establish the validity of the method, test cases are examined and compared with existing solutions. The method is then applied to evaluate the effect of the wedge geometry and the elastic mismatch upon the resulting stress intensity factors.     

A Conservative Integral for Determining Stress Intensity Factors of a Bimaterial Strip

Both conservative line and area integrals are derived from the Betti reciprocal principle to determine the stress intensity factor for a bimaterial strip. Numerical results are presented to demonstrate the accuracy of the methods. Several mesh types have been exploited to examine the effect of meshing on the results. Stress intensity factors obtained by means of the line integral vary somewhat between paths. Those found by means of the area integral have the same value on different paths. This revised version was published online in August 2006 with corrections to the Cover Date.     

基于ANSYS的氧传感器夹紧套模具设计

针对汽车氧传感器夹紧套的质量问题,对氧传感器及夹紧套的结构特点进行了研究,设计出了一套能将氧传感器的敏感元件与夹紧套通过冲压成形固定在一起的夹紧套冲压模具。先利用夹紧套的径向塑性变形特点,确定夹紧套周向压缩加工的工艺方式;再由模具要将压力机的竖直运动转变为夹紧套径向塑性变形所需的水平运动,从而设计出了压盖式斜楔结构的模具结构;再对模具进行了冲压载荷校核,符合模具冲压载荷不超过冲压设备公称压力这一设计规范;选择模具中压块与连接螺杆做ANSYS应力分析,以施加载荷及约束并求解,获得了应力与应变等值线图。研究结果表明,压块与连接螺杆的强度及刚度均满足使用条件且具有较高的安全裕度。     

一种新型级进模具结构设计和工作过程分析

通过对导轨锁定器零件的级进模设计的介绍,阐述了一种新型级进模具结构设计及工作的全过程。具体从制件的冲压工艺出发,进而设计排样方案,确定模具结构,论述了模具的设计过程及冲裁模具结构和运作原理。介绍了该种模具关键部位的结构设计,浮动抬料块、杠杆结构、抽芯式弯曲结构、斜楔驱动滑动式弯曲成形机构。实践证明,此种模具结构设计新颖、模具后期维修快捷,生产操作方便,效率高,冲制的产品质量精度高。     

基于包装机械的超声焊接技术研究及应用

研究超声焊接技术在三角袋原茶包装设备中的应用。分析了压电换能器、频率跟踪发生器、变幅杆等超声焊接核心部件的工作原理及作用,剖析了它们在设计及应用中的关键影响因素;论述了超声焊接系统工作稳定性,研究了系统谐振匹配和调试技术,总结分析了应用中的常见故障及质量缺陷,给出了相应解决措施。实践表明：超声焊接技术能较好完成 PET 纱、玉米纤维、尼龙滤布及食品应用级无纺布的无缝焊接,满足原茶包装设备的需要。     

冷连轧机组轧线调整与控制

针对鞍钢莆田酸洗-冷连轧联合机组轧线调整装置采用的西门子控制系统S7400,介绍了系统中实现轧线调整控制的几个重要功能块的基本功能和参数设置情况,对参数设置调整要点作了说明,对调试过程中出现的问题进行了分析,制定出相应解决方法,实施后将轧线定位误差控制在0.28 mm以内,满足了生产要求。     

轧机中下置斜楔调整装置的结构设计与分析

介绍了轧机中下置斜楔调整装置的结构,分析了楔块受力,选取了合适的斜面自锁角度和驱动马达。最后比较了各种轧线调整装置,总结了下置斜楔调整的优点。