Electrical conductivity changes of bulk tin and Sn-3.0Ag-0.5Cu in bulk and in joints during isothermal aging

The changes of electrical conductivity(resistance) between Sn-3.0Ag-0.5Cu solder joints and printed circuit board(PCB) assembly during aging at 125℃were investigated by the four-point probe technique.The microstructural characterizations of interfacial layers between the solder matrix and the substrate were examined by optical microscopy and scanning electronic microscopy.Different types of specimens were designed to consider several factors.The experimental results indicate that electrical conductivitie...     

集装箱板冷弯裂纹形成分析

针对广州珠江钢铁公司生产的厚规格集装箱板易在外弧面出现微裂纹的现象,采用金相显微镜和扫描电镜对其大量冷弯裂纹试样进行了观察和分析。结果表明,冷弯裂纹试样主要存在以下3种缺陷：距表层10～30μm处的皮下微裂纹、皮下链状夹杂物和表层氧化层与基体结合部位的残余元素（Cu、Ni、As）偏析,其中以皮下微裂纹缺陷的几率居多。     

不同应力状态下铝合金变形及损伤机理的研究

利用改装的Arcan夹具对铝合金（6063）的蝶形试样进行0°，30°，45°，60°，90°的拉伸及拉伸卸载试验，研究了铝合金在不同应力状态下变形及损伤机理。结果表明：铝合金在不同应力状态下的工程应力一应变曲线明显不同。0°加载时，在蝶形中心产生微孔洞，微孔洞之间剪切，从而产生了微裂纹。随着微裂纹的扩展、连接导致试样断裂。随着试样中三轴应力度的减小，在蝶形试样中心的剪切应力不断增大，同时在蝶形试样中的剪切变形带越来越集中。显微裂纹首先在剪切带中产生，随着微裂纹的扩展导致试样的断裂。90°拉伸时，在蝶形中心形成明显的剪切变形带。90°加载时，在试样中产生的剪切带是形变剪切带而非相变剪切带。利用有限元软件ABAQUS对不同角度拉伸试验进行模拟，从而得出了不同应力状态下的塑性区的形状和大小。     

On the elasticT-term of a main crack induced by near tip microcracks

In the expansion form of the stress field near a crack tip, the nonsingular and constant stress acting parallel to the crack plane is called the elasticT-term, which is very important in fracture analysis. The elasticT-term of a main crack induced by near tip microcracks is analyzed. The original problem considered consists of a main crack accompanied by near tip microcracks, which are loaded remotely by the first three terms of the crack tip stress field expansion parameterized by stress intensity factorsK _I ,K _II , and the nonsingular stress, i.e., theT-term,. With the principle of superposition, the problem can be reduced to a system of Fredholm integral equations which can be solved numerically. After obtaining the solution, the induced elasticT-term is evaluated. Several typical numerical examples are given and the results are shown in Figures, from which some useful discussion and conclusions are obtained.     

基于微缺陷成核序列的岩石微裂纹生长和损伤演化模型

岩石在承载之初,由于微缺陷无序成核和有限生长,在材料内部形成大量分布性微裂纹。在该文中,这种演化机制被归结为：微缺陷随机、孤立成核生成最小微裂纹和微缺陷无重叠聚集成核、排列生长形成大尺度微裂纹,裂纹尺度生长是微缺陷成核数的函数。利用微裂纹尺度-频数分布分形以及微裂纹粗糙表面分形,建立基于微缺陷累计成核数序列的裂纹尺度生长模型和损伤演化模型。通过对二维岩石试件破坏过程的微裂纹尺度统计和损伤测试表明,模型的预测结果与观测值符合较好。由于微缺陷成核与声发射源机制具有相似性以及微缺陷成核数序列与声发射数序列具有相似性,所以该模型可用于通过声发射参数序列跟踪微裂纹生长和损伤演化。裂纹尺度生长对于完整认识材料宏观力学性质演化和预测材料灾变具有重要意义。     

有限长主裂纹与微裂纹的相互作用

利用一种新的边界元方法来研究有限长主裂纹与微裂纹的相互作用.该边界元方法由Crouch与Starfield建立的常位移不连续单元和裂尖位移不连续单元构成.考虑了两个模型:有限长主裂纹与一个共线微裂纹的相互作用;有限长主裂纹与一对共线微裂纹的相互作用.在分析计算中取微裂纹与主裂纹的长度之比为0.05~0.4.数值结果表明,本数值方法对研究此类有限长主裂纹与微裂纹相互作用是非常有效的,可以揭示微裂纹尺寸的相对大小对有限长主裂纹与微裂纹相互作用的影响性.     

成膜温度对AZ80镁合金磷酸盐转化膜微裂纹形成及耐蚀性的影响

目的通过不同成膜温度下转化膜上的微裂纹宽度和面积的统计以及电化学测试,研究成膜温度对镁合金磷酸盐转化膜微裂纹形成及耐蚀性的影响。方法采用扫描电子显微镜观察不同成膜温度所得转化膜的微裂纹形貌,使用Image-pro-plus软件测量转化膜的微裂纹宽度和面积。采用极化曲线和电化学阻抗研究转化膜的耐蚀性。结果微裂纹统计结果表明,成膜温度为50℃时,所得转化膜的微裂纹宽度和面积最小,分别为2.68μm和1067μm2;而30℃所得的转化膜的微裂纹宽度和面积最大,分别为3.14μm和1391μm2;70℃所得的转化膜的微裂纹宽度和面积分别为2.74μm和1170μm2。电化学测试表明,成膜温度为50℃时,转化膜的自腐蚀电流最小,Jcorr=20.3μA/cm2,且交流阻抗图谱中的容抗弧半径最大。结论随着成膜温度的升高,转化膜中的微裂纹变窄并减少,但温度更高时,转化膜上的微裂纹略有变宽增多。当成膜温度为50℃时,转化膜上的微裂纹较少且窄,转化膜的耐蚀性最好。     

Tensile strength of plasma-sprayed alumina and/or zirconia coatings on titanium

The heat treatment effect on the characteristics and tensile strength of plasma-sprayed alumina, yttria-stabilized zirconia (YSZ), and mixtures of alumina and YSZ coatings on titanium was investigated. The as-sprayed structures of alumina and YSZ coatings consists of a and y alumina phases, and cubic and tetragonal zirconia phases, respectively. The tensile strength of the coatings containing a large amount of YSZ is increased from 25 to 50 MPa by heat treatment at 800 °C. The 60% YSZ-AI₂O₃ coating showed the highest tensile strength. The tensile strength increase of the YSZ-containing coating by heat treatment is caused by formation of 10 to 100 nm wide microcracks. The interface adhesion strength between the heat-treated titanium substrate and the alumina-containing coating is increased by chemical reaction at the in-terface. Thus, a heat-treated alumina and zirconia mixture coating may be favorable in obtaining high tensile strength due to microcrack formation in the coating and the chemical reaction at the interface. During this work, S. Baba was a graduate student at Kyushu Institute of Technology, Sumitomo Metal Ind. Ltd., Osaka, Japan.     

PDC刀具切削花岗岩过程的微裂纹扩展

采用偏光显微镜观察ＰＤＣ（聚晶金刚石复合片）刀具切削花岗岩的微观过程，研究切削过程微裂纹产生和扩展的规律。分析了矿物特性如矿物成份、晶粒大小及初始裂纹等对微观裂纹扩展路径的影响。研究结果表明：在切削深度较小时，矿物特性对花岗岩微裂纹的产生与扩展过程起主导作用。     

X65Q钢级管线管焊接缺陷的成因分析

在X65Q钢级管线管的焊接过程中,焊缝出现显微裂纹和缩孔缺陷,为此,对管体的化学成分和显微组织进行了检测,并对焊缝的凝固过程进行了分析。分析表明,焊接线能量强度偏高和焊后冷却强度偏低是产生上述焊接缺陷的主要原因,在此基础上,提出相应的改进措施。