Brass Rings or Brass Buttons in Engineering Design*

The purpose of this paper is to point out two distinct selections for student design projects. The main decision maker is assumed to be the faculty advisor for the projects, although the students would be expected to have input. The brass ring project involves some aspect of cutting edge technology. The brass button project is one that satisfies the typical criteria of a thoroughly designed, fabricated, and documented “component.” Both types of projects have great value for the students although one is obviously more visible outside the academic community. These two philosophical approaches in engineering design projects reflect the distinction between entrepreneurial and traditional engineering education. As we move from the concept of engineers working for large companies to engineers starting companies, this distinction becomes more important. The primary example base is drawn from electrical and mechanical engineering due to our experiences. While two philosophical approaches are indicated, there are ultimately numerous methodologies and end points possible as a result of diversions along the way.     

Simulation of Fatigue Crack Propagation in Ductile Metals by Blunting and Re-sharpening

Laird and Smith [(1962). Philosophical Magazine 8, 847–857] proposed a plastic sliding-off mechanism for the stage II fatigue crack growth via striation formation. In their view, the fatigue crack extension results solely from the changing character of deformation at the crack tip during loading and unloading. In particular, the crack tip blunts during the loading stage and folds into a double notch during the unloading stage, resulting in striation formation. In order to verify Laird’s plastic blunting mechanism for ductile polycrystals as well as for ductile fcc single crystals, FE calculations were performed for a rectangular plate with an initially sharp crack under plane strain conditions. The plate was subjected to a fully reversed tension-to-pressure cyclic load perpendicular to the crack plane (Mode 1). In the single crystal case the crack propagation simulations were carried out for cracks with crack plane (001) for two different crack growth orientations [110] and [100]. No initial radius for the crack tip was assumed. The actual shape of the crack tip followed from an initially sharp crack by repeated remeshing. To model the constitutive behavior typical for polycrystalline ductile metals, J₂ hypo-elasto-plasticity model with Armstrong–Frederick kinematic hardening was used. To model the constitutive behavior typical for ductile fcc single crystals, a geometrically nonlinear version of Cailletaud’s model based on the multiplicative elasto-plastic decomposition of the deformation gradient was implemented into the FE program ABAQUS. For simplicity, only octahedral slip systems were considered. Using repeated remeshing for severely distorted elements at the advancing crack tip, deformation patterns in the sense of Laird’s mechanism for fatigue crack propagation with striation formation were obtained in the case of the polycrystal simulation as well as in the case of the single crystal simulation for [110] crack growth direction. The simulation for [100] crack growth direction with the same stress level as for [110] direction also yielded crack extension by progressive large deformations but without striation formation. The dependence of the fatigue striation formation on the crack growth direction as predicted by the simulation of crack propagation in single crystals is verified by the experimental results of Neumann [(1974). Acta Metallurgica 22, 1155–1165] on pure copper single crystals.     

无铅易切削黄铜的研究进展

随着世界各国对铅造成的污染和危害的重视,含铅黄铜的使用受到越来越多的限制,开发低成本无铅易切削黄铜迫在眉睫。本文根据无铅黄铜第三组元的选择特性,从组织结构、易切削机理、加工工艺、耐腐蚀性能四个方面综述了国内外无铅易切削黄铜合金的研究现状,并详细分析了铋、锑的凝固行为对合金显微组织和性能的影响,重点介绍了无铅易切削钙磷黄铜合金的微观组织、能谱分析结果、力学性能和切削性能,提出了当前工作中存在的问题,并对今后的研究趋势进行了展望,期待能够在无铅易切削黄铜的研究及实际应用中起到一定的指导作用。     

黄铜黑色氧化工艺

采用化学法对铸造黄铜着黑色氧化膜的方法进行了实验和分析，通过正交实验对化学着色溶液的成分进行了优选，并讨论了溶液组分对着色效果的影响。     

镁黄铜的组织与性能研究

采用熔铸、挤压的方法制备出了镁黄铜棒材.利用扫描电镜(SEM)、光学显微镜(OM)、X射线衍射仪(XRD)和差热分析仪(DSC)等手段对镁黄铜的微观组织、物相组成和相转变特征、力学性能、切削性能以及腐蚀性能进行了研究.结果表明:合金物相由α相、β相和Cu2Mg相组成,以α相为主;镁黄铜的抗拉强度为494.39MPa,屈服强度为388 56MPa,伸长率为8.78%,布氏硬度为HV140.7,优于铅黄铜;切削性能达到铅黄铜性能的78.5%.研制的镁黄铜替代铅黄铜具有可行性.     

Nucleation and migration of high angle grain boundaries in bilayer foils I: Nucleation

Thin evaporated epitaxial Cu/Ni bilayers were observed by transmission electron microscopy in order to study the modifications that occur to the initial structure during heating. Nucleation of mobile high angle grain boundaries was observed to occur from microtwins, which are present in the as-evaporated bilayers and are enlarged by reaction with the misfit dislocation arrays. A mechanism for this nucleation process is proposed and the significance of twins in the nucleation of mobile grain boundaries is discussed with reference to other work on the recrystallization of bulk materials.     

X荧光能谱法测定黄铜中的铜

通过对黄铜标样及样品的测试,建立了X荧光能谱仪测定黄铜中铜含量的方法。本方法采用能谱仪中定量分析软件;选择适当工作条件,测定黄铜中钢元素。其准确度,精密度,均能满足分析要求。     

Role of Crack Tip Blunting in Stress Corrosion Cracking of High-strength Steels

This paper analyzes the role of crack tip blunting in stress corrosion cracking by localized anodic dissolution of high-strength eutectoid steel. The results of the tests show an apparent improvement of fracture resistance in aggressive environment — measured in terms of critical stress intensity factor - in relation to its reference value in an inert (air) environment. The explanation can be sought in the effects of crack tip blunting, i.e., of the increase of crack tip radius as a consequence of the dissolution process. This revised version was published online in July 2006 with corrections to the Cover Date.     

Nucleation in Quantum Liquids

In order to understand how nucleation proceeds in quantum liquids such as ⁴He and ³He, and the peculiarities of such quantum systems, I present a review of nucleation in condensed matter. By describing successive experiments, I first illustrate the interest and use of the elementary "standard theory" of nucleation. Then I consider its limitations and the existence of "spinodal" and instability limits, possibly in the frame of "density functional" methods. When finally discussing nucleation at low temperature, I consider a further improvement of the standard theory, namely the possibility of nucleation by quantum tunneling. The main emphasis is on crystallization and cavitation in liquid helium, but I also consider water, liquid hydrogen, wetting, the nucleation of steps on crystal surfaces, vortices etc.     

黄铜镀液中铜的光度测定

黄铜镀液中铜的测定常用ＥＤＴＡ滴定法 ,但此法只能测定铜锌合量 ,且许多常见的金属离子如钙、镁等均有干扰。本文用Ｃｕ ＥＤＴＡ光度法测定 ,方法具有良好的选择性 ,且简便快速。1　试剂和仪器铜标准溶液 :准确称取 1.9647ｇ优级纯ＣｕＳＯ4·5Ｈ2 Ｏ溶于水中 ,移入 2 50ｍｌ容量瓶 ,定容并混匀。此液含铜 2ｍｇ/ｍｌ。显色液 :称取 4ｇＥＤＴＡ二钠盐和 7ｇ氯化铵溶于 57ｍｌ氨水中 ,用水稀释至 10 0ｍｌ,混匀备用。分光光度计 :72 1型 (上海第三分析仪器厂出品 ) ,2ｃｍ光程比色皿。2　分析方法( 1)待测液的制备　准确吸取镀液 2 .0 0…     

黄铜镀液中锌的快速测定

研究了二甲酚橙与锌形成配合物的条件及其光度性质.结果表明,在pH值为5.7～6.0的醋酸-醋酸盐缓冲介质中,锌(Ⅱ)与二甲酚橙形成紫红色配合物,其最大吸收波长位于570 nm,锌浓度介于0～2 μg/mL,遵守比尔定律,表观摩尔吸光系统ε'570=1.48×104 L/(mol·cm).用硫代硫酸钠作掩蔽剂,大量铜(Ⅱ)共存无干扰,应用于黄铜镀液中锌的测定,方法简便快速,准确度和精密度高,能满足生产要求.     

Investigation on Structure and Properties of Brass Casting

In this work, alpha (α) brass was poured in green sand mould and metallic chill mould at about 1050℃. Sand casting method and metallic chill casting method are representing the slow and fast cooling rates of the castings, respectively. The slow cooling rate in the sand mould produces larger grains, while the metallic chill mould produces smaller grains in the castings. As the grain size decreases, the strength of the cast brass increases; micro-porosity in the casting decreases and the tendency for the casting to fracture during solidification decreases. Thus, the faster cooling rate casting offers higher strength, density and hardness compared to the slow cooling rate casting.     

凝汽器铜管腐蚀研究

某电厂凝汽器铜管在抽查中发现管内壁发生不均匀腐蚀,腐蚀区呈裂纹状,沿管轴向或沿与轴向45度方向扩展.对腐蚀后凝汽器黄铜管进行了成分分析、力学性能及残余应力测试、织构测试;用金相显微镜和扫描电镜进行观察及能谱分析;并用该黄铜管在实验室中进行了疲劳模拟试验.结果表明,凝汽器黄铜管内壁出现的裂纹状损伤是由于疲劳腐蚀引起的.     

Blunting of cracks of intermediate states of stress by scanning electron microscopy

A study of ductile blunting edge cracks in tensile specimens was undertaken in this paper by detecting the forms of different stages of blunting of the cracks under conditions of mode-l deformation as the loading progressed. All three main types of blunting were detected, with identical specimens and cracks, that is, the rounded off, the multicornered and the pointed type, depending on the particular accidental instabilities appearing in the vicinity of the crack tip as the blunting process is progressing. It was shown that an intermediate type of blunting was detected on the surfaces of the specimens by the scanning electron microscope (SEM) and this was explained by the fact that at the surfaces of specimens possessing a significant thickness to width aspect ratio the state of stress at the surface is strongly influenced by the plane stress conditions prevailing at the lateral faces of the specimens.     

Nucleation in glass and differential thermal analysis

The crystal nucleation of Li₂O-2SiO₂ glass is studied by differential thermal analysis. A simple method, based on the shift of the differential thermal analysis (DTA) crystallization-peak temperature, for evaluating the influence of temperature and time of heat-treatments on bulk nucleation, is described. The experimental results are in good agreement with results obtained by other workers.     

CdSe 在玻璃中的核化过程

用高分辨电镜、X-射线衍射研究了 CdSe 在玻璃中的成核和生长过程.首次观察到,伴随着这种成核和生长过程,玻璃的光吸收限、光吸收限的温度系数,以及光吸收系数和光子能量的依从关系都发生变化.