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Research on Fatigue Fracture Mechanisms of Micro Materials

微材料疲劳断裂机理研究

基本信息

批准号：
10650090
负责人：
NAKAI Yoshikazu
金额：
$ 2.24万
依托单位：
Kobe University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 1999
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-10650090/
关键词：
Micro material Fatigue Micro machine Fractography Crack initiation き裂発生クラフトグラフィー

项目摘要

Fatigue test systems with electrolic-polishing apparatus were developed to study the size effect on the fatigue strength of the micro-materials. This system has an electro-dynamic actuator to load small amplitude cyclic force. Fatigue tests were conducted after manufacturing small cross-sectional specimens by the electrolic-polishing apparatus without removing specimens from the system. Commercially pure aluminum and iron wires of 1.0 mm diameter were employed for the fatigue tests. The minimum diameter of each specimen was from 0.20 to 0.60 mm. To remove the effect of stress gradient, cyclic axial force was applied. The frequency of the cyclic force was 50 Hz with the stress ratio of 0.1. In both materials, the fatigue strength was almost independent of the specimen diameter, and the variations in the fatigue life from specimen to specimen at the same stress amplitude were large, and the crack initiation life is dominant to total fatigue life.The slip-band formation and fatigue crack-initiation processes in balk material of 70-30 brass were observed by means of atomic-force microscopy (AFM). The slip-band angle relative to the stress-axis at the specimen surface varied from 15 to 90°, and it appeared most frequently around 60°. The depth of the intrusion drastically increased with its outgrowth to a crack, and with coalescence of cracks, the width of cracks increased rapidly. The critical value of the intrusion depth for crack initiation was given as a function of the slip-band angle through a geometrical model for the slip-direction and the slip-step, and the critical value was independent of stress amplitude. From precise observations of slip-band tips, slip-bands had steep slope when they were blocked by grain boundaries, and the slip-bands descended by gradual slopes to plain surfaces when they terminated within grains.

研制了电抛光疲劳试验系统，研究了尺寸效应对微细材料疲劳强度的影响。该系统有一个电动执行器来加载小幅度的循环力。在不将试件从系统中取出的情况下，通过电抛光装置制作小截面试件后进行疲劳试验。疲劳试验采用直径为1.0 mm的工业纯铝丝和铁丝。每个标本的最小直径为0.20~0.60 mm。为了消除应力梯度的影响，施加了循环轴向力。循环力的频率为50赫兹，应力比为0.1。两种材料的疲劳强度几乎与试件直径无关，相同应力幅值下各试件的疲劳寿命差异较大，裂纹萌生寿命在总疲劳寿命中占主导地位。用原子力显微镜(AFM)观察了70-30黄铜板材的滑移带形成和疲劳裂纹萌生过程。试件表面相对应力轴的滑移带角度在15°~90°之间变化，在60°附近出现最多。随着裂隙的扩展，侵入深度急剧增加，并且随着裂隙的合并，裂隙的宽度迅速增加。通过滑移方向和滑移台阶的几何模型，给出了裂纹萌生的侵入深度作为滑移带角度的函数的临界值，该临界值与应力幅值无关。从滑移带尖端的精确观察可以看出，滑移带在被晶界阻挡时具有陡峭的坡度，当滑移带在晶界内终止时，滑移带以渐变的坡度下降到平坦的表面。