孔边角裂纹近门槛区疲劳裂纹扩展规律及门槛值研究

RESEARCH ON NEAR-THRESHOLD CRACK PROPAGATION AND THRESHOLD OF CORNER-CRACK AT THE HOLE

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 features of the three-dimensional crack, an experimental method was presented to measure the near-threshold fatigue crack growth rate and threshold of the corner crack at a hole. In order to get the actual crack shape variable law, this paper firstly established the “b-a” demarcated curve for the particular specimen by the marking-line method- Refer to the standrd test method on Threshold, We just directly measured the crack size of “a” direction, the crack size of “b” direction could be calculated by the demareated curve. Then we could get two set of data separately for “a” and “b” , which represent characteristic directions of the crack. Through the experimental studies for 30CrMaSiNi2A and 2024T3 material, the method used in this paper was proved available. On the basis of test data, this paper have carried out statistical comparisons between results, and concluded: 1. the near-threshold fatigue crack grouth rates and thresholds for “a” and “b”are essentially coincident; 2. different diameters of the holes make no difference to results; 3. With the same thickness, the near-threshold fatigue crack growth rate of a specimen with the coruer-crack at a hole is higher than that of a CT Specimen, but the threshold is less.