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Research on Fatigue Crack Arrest Assessment Criteria under Cyclic Thermal Stresses

循环热应力下疲劳止裂评价标准研究

基本信息

批准号：
12650078
负责人：
MESHII Toshiyuki
金额：
$ 0.9万
依托单位：
Fukui University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2001
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-12650078/
关键词：
Fracture Mechanics Stress Intensity Factor Fatigue Crack Arrest Thermal Stress Threshold Stress Intensity Factor Range

项目摘要

This year, we made both analytical and experimental approach to the subject. First, we made a study of the crack arrest depth under cyclic thermal shock for an inner-surface circumferential crack in a finite-length thick-walled (R_m/W =1) cylinder with rotation-restrained edges. The inside of the cylinder is cooled from a uniform temperature distribution. The effects of heat transfer conditions on the maximum transient SIF for the problem were investigated with formerly developed systematical evaluation methods. Then, a tentative value of the threshold stress intensity range ΔK_<th> was assumed together with the Paris law and the evaluation of the crack arrest length under cyclic thermal stress was carried out. The results suggest the existence of an upper limit for the normalized crack growth depth, independent of the cylinder material. And the dominating parameters for this were concluded as the structural ones.Finally, crack propagation tests under equivalent thermal shock loads were conducted to confirm the validity of the criterion ΔK_<max> 【less than or equal】 ΔK_<th> for fatigue crack arrest. The result obtained was that the threshold stress intensity range corresponding to a thermal shock equivalent load was approximately equal to the intrinsic ΔK_<th>. The validity of applying ΔK_<max> 【less than or equal】 ΔK_<th> for crack arrest analysis under cyclic thermal shock was confirmed.

今年，我们对这个问题进行了分析和实验。本文首先研究了有限长厚壁圆筒（R_m/W =1）内表面环向裂纹在循环热冲击下的止裂深度。气缸内部由均匀的温度分布冷却。利用已有的系统评价方法，研究了传热条件对瞬态应力强度因子的影响。在此基础上，结合巴黎定律，提出了门槛应力强度范围ΔK的一个暂定值<th>，并对循环热应力作用下的裂纹止裂长度进行了估算。结果表明，存在一个上限的归一化裂纹扩展深度，独立的圆柱体材料。最后，通过等效热冲击载荷下的裂纹扩展试验，验证了ΔK ≤ <max>ΔK<th>的疲劳裂纹止裂判据的有效性。结果表明，热冲击等效载荷所对应的阈值应力强度范围近似等于本征应力强度因子ΔK<th>。验证了在循环热冲击下采用ΔK <max>[小于或等于] ΔK<th>进行裂纹止裂分析的有效性。