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基于三维裂纹特征,本文提出了一种测量孔边角裂纹近门槛区疲劳裂纹扩展速率及门槛值的实验方法。为了得到真实的裂纹形状变化规律,首先针对具体试样用勾线方法建立其“b-a”标定曲线。参照门槛值的标准测试方法,本文仅需测量“a”方向裂纹尺寸,然后用标定曲线换算共相应的“b”方向尺寸。这样我们就可以得到关于“a”和“b”的两组数据,而这两个方向代表孔边角裂纹特征方向。通过分别对30CrMaSiNi2A和2024T3材料的实测研究,证明本文提出的测试方法是可行的。在实验数据基础上,进行了结果的统计对比,得出:1.“a”和“b”方向的近门槛区疲劳裂纹扩展速率及门槛值基本一致;2.孔径大小对实验结果没有影响。;3.同样厚度情况下,孔边角裂纹试样的近门槛区疲劳裂纹扩展速率编高,而门槛值相应较小。
Based on the characteristics of three-dimensional crack, this paper presents an experimental method for measuring the fatigue crack growth rate and the threshold value near the threshold area of corner cracks. In order to get the real change rule of the crack shape, the “b-a” calibration curve of the concrete sample is firstly established with the hook-line method. With reference to the standard test method of threshold value, we only need to measure the crack size in “a” direction, and then use the calibration curve to calculate the corresponding “b” direction size. So that we can get two sets of data about “a” and “b” which represent the orientation of the hole corner crack. By measuring the 30CrMaSiNi2A and 2024T3 materials respectively, it is proved that the proposed method is feasible. Based on the experimental data, the statistical comparison of the results shows that: 1. The near-threshold fatigue crack growth rate and the threshold value in the “a” and “b” directions are basically the same; 2. The pore size has no effect on the experimental results. ; 3. Under the same thickness, the fatigue crack growth rate in the near-threshold area of hole corner cracks is high, and the threshold value is correspondingly smaller.