TOTAL ASSESMENT OF THE CHARACTERISTICS OF SMALL CRACK PROPAGATION IN THE MATERIAL FOR STRUCTURAL USE

结构用材料中小裂纹扩展特性的总体评估

基本信息

批准号：
62420024
负责人：
SHIMIZU Masao
金额：
$ 18.69万
依托单位：
Keio University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (A)
财政年份：
1987
资助国家：
日本
起止时间：
1987 至 1989
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-62420024/
关键词：
FATIGUE STRENGTH SMALL CRACK CARBON STEEL ALUMINUM ALLOY MANSON-COFFIN LAW MINER'S RULE NON-METALLIC INCLUSION MICROSTRUCTURE 低サイクル疲労高サイクル疲労マイナー則

项目摘要

Reassessment of the structural integrity of the machine-structure system has revealed that there are still critical problems to be solved for the total safety of the system. Total assesment of the behavior of small crack initiation and propagation in structural steel under low and high cycle fatigue regime is among these problems. In the series of present research project, special attention was paid to the following three topics. (1) Characteristics of near threshold propagation of small crack. (2) Microdefects and the nature of fatigue process in high hardened steel. (3) Fatigue fracture under extremely low cycle fatigue.Results obtained are summarized in the followings. (1) Near threshold propagation behavior of small crack in dual phase microstructure of unnotched specimen can be under the control of not only the crack growth resistance of the second phase microstructure during the process of conventional growth of single crack but also the condition of coalescence of multiple crack … More s near by the main crack. In addition, this coalescence becomes the causes of high structure sensitivity during crack propagation of relatively large crack. (2) Fatigue fracture of high hardened steel can be characterized by the concept that the matrix material can be regarded as the material having a number of small pits corresponding to small non-metallic inclusion. The level of fatigue strength can be under the control of the maximum sized inclusion in the surface layer of specimen so that the upper limit of the fatigue strength of material can be attained by the inclusion free microstructure. Furthermore, a reduction of fatigue strength of nitrided titanium can be explained to be due to possible defects in the hardened layer of the specimen. (3) Fatigue life of structural steel in extremely low cycle fatigue range can be under the control of two fracture criteria which are related to the difference of crack nucleation site in the material, i.e., the internal cracking and surface cracking, respectively.This is typical phenomenon for dual phase microstructure having relatively large brittle second phase and ductile matrix. Less

对机器结构系统的结构完整性的重新评估表明，对于系统的总安全，仍然存在关键问题。在低周期和高周期疲劳状态下，小裂纹倡议和在结构钢中的繁殖的总体评估是这些问题。在本系列研究项目中，特别关注以下三个主题。（1）小裂纹接近阈值的特征。（2）高硬化钢中的微降挡和疲劳过程的性质。（3）在极低循环疲劳下疲劳性断裂。（1）在未注明的标本的双相微观结构中，小裂纹的接近阈值传播行为不仅可以控制单个裂纹的常规生长过程中第二相微观结构的裂纹生长抗性，而且还可以控制多个裂纹的合并状态……更多的S近距离裂纹接近主裂纹。另外，这种合并成为在裂纹相对较大的裂纹裂纹传播期间高结构灵敏度的原因。（2）高硬化钢的疲劳断裂的特征是，可以将基质材料视为具有许多小凹坑的材料，这些小凹坑对应于小型非金属包容。疲劳强度的水平可以在标本表面层中最大尺寸包含的控制之下，因此材料的疲劳强度的上限可以通过无包含微结构来连接。此外，可以解释硝化钛的疲劳强度的降低是由于试样硬化层中可能存在的缺陷。（3）在极低循环疲劳范围内结构钢的疲劳寿命可以在两个断裂标准的控制之下，这与材料中裂纹成核位点的差异有关，即内部裂纹和表面裂纹较少。这是具有相对较大的脆性第二相和延性基质的双相微结构的典型现象。