Push–pull tests of rolled magnesium alloy AZ31 were performed with a side-notch plate specimen to examine the crack growth behavior under negative mean stress conditions in conditions of high humidity. The effects of repetition of compression on crack growth were discussed. The geometry of the fracture surface and the changes in microstructure were related to the crack growth behavior. The crack growth rate varied even when the experimental conditions were the same. When the oxidized powder appeared from the cracked surface, the crack growth rate became lower. That was related to the changes in microstructure while the crack grew with local shear plastic deformation. The variation of crack closure point was related to the local shear plastic deformation.

中文翻译：

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晶粒尺寸变化和孪晶变形对AZ31镁合金裂纹扩展行为的影响

轧制镁合金 AZ31 的推拉试验采用侧缺口板试样进行，以检查在高湿度条件下负平均应力条件下的裂纹扩展行为。讨论了重复压缩对裂纹扩展的影响。断口的几何形状和微观结构的变化与裂纹扩展行为有关。即使在实验条件相同的情况下，裂纹扩展速率也会发生变化。当氧化粉末从裂纹表面出现时，裂纹扩展速度变慢。这与微观结构的变化有关，而裂纹随着局部剪切塑性变形而增长。裂纹闭合点的变化与局部剪切塑性变形有关。