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Fundamental Studies on teh Environmental Fatigue Fracture Toughness and the Design Curve of Structural Materials

结构材料环境疲劳断裂韧性及设计曲线的基础研究

基本信息

批准号：
61550051
负责人：
SAWAKI Yozo
金额：
$ 1.22万
依托单位：
TOHOKU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1986
资助国家：
日本
起止时间：
1986 至 1987
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-61550051/
关键词：
Fatigue Fatigue Fracture Toughness Stress Ratio Cyclic Plastic Zone Grain Diameter Low Temperature Silica Glass 下限界応力拡大係数破壊靭性

项目摘要

The concept of the environmental fatigue fracture toughness proposed by the author, through the research "Basic Study on Fatigue Design for Offshore Structure", Project No.58460080, has been developed for a low temperature environment from room temperature to 77K.It is cleared that this value governs the fatigue cracking behavioru of the material at low temperature. The fatigue characteristic stress intensities Ke and Kv, can be proposed as controlling stress intensities, where the region 2 and the region 3 fatigue crack propagation starts, respectively.Since the correlations between the fatigue fracture toughness and the Ke, Kv, a method of teh estimation of the fatigue crack growth curve, covering the entrire range of stress intensity can be also presented. This method can be utilized to determine the threshold stress intensity factor in a low temperature environment.The proposed characteristic stress intensitiy Kv corresponds to the K value where the static mode of fracture begins to superimpose to the fatigue crack propagation. The other fatigue characteristic stress intensity, Ke, is the K value where the cyclic plastic zone size equals to the grain diameter of the material. This implies that both of the Ke and threshold stress intensity, Kth, are linearly related to the <delta>yROO<d>, where, <delta>y is yield stress and d grain diameter, as indicated by the experiment.The fatigue crack propagation in the brittle material, such as silica glass, is fundamentally the same as that in static loading condition. This behaviour is explained by the low value of the Kv, meaning that the crack propagation of this material mainly controlled by the region 3 crack propagation.

作者在课题“海洋结构疲劳设计基础研究”（项目编号58460080）中提出的环境疲劳断裂韧性概念，在室温至77K的低温环境中得到了发展，明确了该值控制着材料在低温下的疲劳开裂行为。提出了疲劳特征应力强度Ke和Kv分别作为2区和3区疲劳裂纹扩展起始处的控制应力强度，并根据Ke、Kv与疲劳断裂韧性的相关性，提出了一种估算疲劳裂纹扩展曲线的方法，该方法涵盖了应力强度的整个范围。该方法可用于确定低温环境下的门槛应力强度因子，所提出的特征应力强度Kv对应于静态断裂模式开始转向疲劳裂纹扩展的K值。另一个疲劳特征应力强度Ke是循环塑性区尺寸等于材料粒径时的K值。实验表明，Ke和门槛应力强度Kth与<delta>γ ROO<d><delta>（γ为屈服应力，d为晶粒直径）均呈线性关系，脆性材料（如石英玻璃）的疲劳裂纹扩展与静载条件下基本相同。这种行为可以通过Kv的低值来解释，这意味着该材料的裂纹扩展主要由区域3裂纹扩展控制。