A Study on Applicability of Microscopic Approach to clear the Fracture Behavior of Materials

显微方法清除材料断裂行为的适用性研究

基本信息

批准号：
10450383
负责人：
YOSHINARI Hitoshi
金额：
$ 8.77万
依托单位：
University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B).
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 2000
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-10450383/
关键词：
fatigue crack propagation Scanning Electron Microscope Molecular Dynamics Cu single cystal active slip plane 3%Si Steel Neumann's model Laird model 疲労き裂伝播活動すべり系結晶粒界多重すべり銅単結晶材微視的メカニズム疑似疲労シミュレーション

项目摘要

We studied on essential aspects of fatigue crack propagation behavior from a microscopic view by means of Scanning Electoron Microscope (SEM) and Molecular Dynamics (MD). Fatigue tests of Cu single cristals (fcc material) and 3%Si steels (bcc material) were conducted using CT specimens. Combinations of crystallographic orientation and pre-crack direction are varied systematically for each specimens. It is shown that fatigue crack of both materials propagates microscopically on the active slip plane which is characteristic of each crystal system, but not on the mechanical principal stress plane. This mechanism can not be explained by the Laird model, which is thought to be appropriate in continuum mechanics, and can be explained by the modefied Neumann model. In these materials an active slip system interferes intricately with the others, and fatigue crack propagation rates depend much on this mechanism, therfore Paris law are not useful in these cases. In MD simulations corresponding to test conditions, it is shown that the propagation behavior of fatigue crack of both materials is similar to tests resuls and SEM observations of fractured surfaces. Changes of atomcs under cyclic loading are also simulated and represent the irreversible changes of atoms (fatigue damages). In case of 3%Si steels, we investigated effects of grain boundary on fracture behavior and comperared with test resuls. When a crack across the grain boundary, fracture behavior will be changed largely upon the crystallographic direction of two adjoining grains. It can be said that MD method may be a useful tool for analyzing a microscopical mechanism of fracture in metals.

我们通过扫描选举显微镜（SEM）和分子动力学（MD）研究了从显微镜视图的疲劳裂纹传播行为的基本方面。使用CT样品进行了CU单晶鼠（FCC材料）和3％Si钢（BCC材料）的疲劳测试。对于每个样品，晶体学取向和前裂动方向的组合是系统的。结果表明，两种材料的疲劳裂纹均在每个晶体系统的特征上的活性滑动平面上传播，但在机械主应力平面上不进行。该机制无法通过LAIRD模型来解释，LAIRD模型被认为在连续力学中是合适的，并且可以通过模态的Neumann模型来解释。在这些材料中，主动滑动系统与其他材料复杂地干扰了其他材料，并且疲劳裂纹的传播速率在很大程度上取决于这种机制，因此在这些情况下，巴黎定律并不是有用的。在与测试条件相对应的MD模拟中，这表明两种材料的疲劳裂纹的传播行为类似于测试的重新脉冲和骨折表面的SEM观测值。还模拟了循环载荷下的原子量的变化，并表示原子的不可逆变化（疲劳损害）。如果有3％的Si钢，我们研究了晶界对断裂行为的影响，并通过测试重新调查。当跨晶界的裂纹裂纹时，断裂行为将在两个相邻晶粒的晶体学方向上发生改变。可以说，MD方法可能是分析金属裂缝微观机制的有用工具。