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Extending near-threshold fatigue crack growth mesoscopic model-application to case of high vacuum

扩展近阈值疲劳裂纹扩展细观模型——在高真空情况下的应用

基本信息

批准号：
18560074
负责人：
MESHII Toshiyuki
金额：
$ 2.41万
依托单位：
University of Fukui
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2006
资助国家：
日本
起止时间：
2006 至 2007
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-18560074/
关键词：
Fracture mechanics Fatigue crack growth Threshold stress intensity factor range Static fracture mechanism Maximum stress intensity factor Environmental effect Mesoscopic model Crack closure

项目摘要

In this research, we assessed the contribution of the environment on the decrease in threshold stress intensity factor (SIF) range ΔKth due to high maximum SIF Kmax," that is observed for several materials in the Kmax-constant fatigue crack growth (FCG) tests, under i) closure-free and non-corrosive atmosphere conditions are realized. We ran the following tests for 0.55% carbon steel JIS S55C, which is known to experience the phenomena. The tests were: i) static sustained load cracking (SLC) test (load held constant at Kmax, after running Kmax-constant ΔKth test) in air, dynamic SLC tests (constant ΔK below ΔKth with constant Kmax) in air, and iii) Kmax-constant ΔKth test in high vacuum. No crack growth was observed in tests and The decrease in ΔKth due to high Kmax in vacuum was negligible. The results of the Charpy impact tests indicated that the material was in the brittle-ductile transition range at room temperature. From these results, we concluded that the decrease in ΔKth due to high Kmax was mainly due to the brittleness of the material, which can be excluded in high vacuum. The results support the validity of our model for the phenomena, that microscopic crack growth in a grain due to static mode failure (brittle) accelerated the expected cyclic crack growth, considering that high vacuum excluded the possibility of static failure mode.

在这项研究中，我们评估了环境对由于高最大应力强度因子Kmax而导致的门槛应力强度因子范围ΔKth的降低的贡献，这是在Kmax-恒定疲劳裂纹扩展试验中观察到的，在i)无闭合和无腐蚀的气氛条件下实现。我们对已知有这种现象的0.55%碳素钢JIS S55C进行了以下测试。这些试验是：i)空气中的静态持续载荷开裂试验(运行Kmax-ConstantΔKth试验后，载荷在Kmax处保持恒定)，空气中的动态SLC试验(常量ΔK低于ΔKTh，且Kmax恒定)，以及III)高真空下的Kmax-ConstantΔKTh试验。在试验中没有观察到裂纹扩展，真空中高K_(Max)对Δ_(Kth)的影响可以忽略不计。夏比冲击试验结果表明，该材料在室温下处于脆-韧转变区。根据这些结果，我们得出结论，高K_(Max)引起的ΔK_(Th)的降低主要是由于材料的脆性，这在高真空下是可以排除的。考虑到高真空排除了静态破坏模式的可能性，结果支持了我们的模型的有效性，即由于静态模式破坏(脆性)导致的微观裂纹扩展加速了预期的循环裂纹扩展。