Study on Elastic-Plastic Fracture of Materials

材料弹塑性断裂研究

基本信息

批准号：
59460064
负责人：
SHIOYA Tadashi
金额：
$ 5.18万
依托单位：
University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1984
资助国家：
日本
起止时间：
1984 至 1986
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-59460064/
关键词：
Elasto-Plasticity Ductile Fracture Steel Void Stress Triaxiality Ductile-Brittle Transition ディンプル

项目摘要

The fracture of solid materials generally involves elastic and plastic deformations the magnitudes of which depend on the materials and the loading conditions. This project is aimed at the understanding in microscopic aspects of the fracture, mainly from the ductile side which accompanies large plastic deformation towards the ductile-brittle transition. The microscopic process of the ductile fracture consists of the stages of voids nucleation, growth and their coalescences. The void nucleation and growth process is considered to be affected by the population of the impurities or second phase particles which can be the void nucleation sites and the stress-strain state which influences the nucleation and growth conditions of the voids.In this project, tensile fracture experiments of steel specimens were conducted changing the chemical components concentration and the stress-strain conditions. The void nucleation and growth process was indirectly examined through the dimple distributions on the fracture surface. The observation of the fracture surface was performed by the use of the electron microscope. The results were shown as the relation between the area portion of the main dimples on the fracture surface and the stress tri-axiality of the specimen at the fracture. It was cleared that the area portion of the main dimples generally increases with the stress-triaxiality and approaches to a constant value, however, in the high purity materials, this approach to a limited value has not been seen. In the materials with increased inpurity phase, the cleavage fracture patterns were also observed besides the dimple patterns indicating that the transition to the brittle fracture occurs. This has been supported by the fact that the scale effect exists macroscopically as well as microscopically.Simple theoretical modellings are proposed in this project concerning the void nucleation and growth process, showing the qualitative coincidence with the experimental results.

固体材料的断裂通常涉及弹性和塑性变形，其大小取决于材料和载荷条件。该项目旨在从微观角度理解断裂，主要是从伴随着大塑性变形的延性侧向延性-脆性转变。韧性断裂的微观过程由空洞成核、生长及其合并阶段组成。空洞的形核和生长过程被认为受到杂质或第二相粒子的数量的影响，这些杂质或第二相颗粒可以是空洞的形核位置，以及影响空洞的形核和生长条件的应力应变状态。在这个项目中，拉伸改变化学成分浓度和应力应变条件，进行钢试样的断裂实验。通过断裂表面上的韧窝分布间接检查空洞的形核和生长过程。断裂面的观察使用电子显微镜进行。结果以断裂面上主韧窝面积部分与试样断裂时应力三轴度的关系表示。可以看出，主凹坑的面积部分通常随着应力三轴度的增加而增加并接近恒定值，然而，在高纯度材料中，尚未发现这种接近极限值的情况。在杂质相增加的材料中，除了韧窝图案外，还观察到解理断裂图案，表明发生了脆性断裂的转变。尺度效应在宏观和微观上都存在这一事实也支持了这一点。本项目提出了关于空洞成核和生长过程的简单理论模型，显示了与实验结果的定性吻合。