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Journal of Zhejiang University SCIENCE A
ISSN 1673-565X(Print), 1862-1775(Online), Monthly
2014 Vol.15 No.11 P.873-882
Fatigue growth of a surface crack in a V-shaped notched round bar under cyclic tension
Abstract: This paper presents modeling results for fatigue crack growths of a semi-elliptical surface crack in a V-shaped notched round bar under uniform cyclic tension. All the analyses were carried out by using a software package featuring the boundary element method. The J-integral technique was used to compute the stress intensity factors (SIFs), and the NASGRO crack growth rate was chosen to simulate the fatigue crack growths. Mechanical and fracture properties of AZ-6A-T5 magnesium alloy were used for our analysis. Crack shape evolutions for different crack aspect ratios and the corresponding SIFs may be correlated to study the behavior of crack growths. An unstable crack growth was observed when the evolving crack aspect ratio was between 0.6 and 0.7. Careful consideration should be taken if the cylinder contains a defect which has a straight shape on the crack front or a smaller crack aspect ratio.
Key words: Fatigue crack growth, Crack aspect ratio, Boundary element method, Stress intensity factor (SIF)
研究方法：1. 构建V形切口圆条模型（图1），基于线性二次元将模型表面离散成一个个网格点（图2）；2. 以AZ-6A-T5镁合金为例，利用J积分计算应力强度因数，利用NASGRO裂纹增长率模拟裂纹的疲劳扩展；3. 通过研究不同的裂纹纵横比和对应的应力强度因数之间的相关性来研究裂纹的扩展。
重要结论：1. 在裂纹扩展时裂纹纵横比的初始值对断裂形状的发展有重要影响；2. 裂纹纵横比对疲劳负荷寿命的作用比缺口半径更加明显；3. 当裂纹前缘演变成一条直线形时可观察到不稳定的裂纹扩展；4. 裂纹深度一定时，断裂纵横比越小，疲劳负荷寿命越短；5. 当裂纹纵横比为0.6-0.7时，出现了不稳定的裂纹扩展。
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DOI:
10.1631/jzus.A1400042
CLC number:
TH140
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On-line Access:
2014-11-04
Received:
2014-01-28
Revision Accepted:
2014-06-09
Crosschecked:
2014-10-30