两种加载方式下疲劳裂纹的扩展

本文测量了在旋转弯曲加载和三点弯曲加载下，45Cr钢试样经淬火后，在200℃、400℃、500℃、600℃回火条件下的疲劳裂纹扩展速率，并用不着定量金相法，电镜观察法研究了上述两种加载方式下，疲劳裂纹扩展的微观机制。试验结果表明，在旋转弯曲加载下，500℃回火态的疲劳裂纹扩展速率比其它三个温度回火态的要低；而在三点弯曲加载下，随着回火温度的提高，裂纹扩展速率单调下降；裂纹扩展速率随回火温度变化规律与扩展机制随回火态的要低；而在三点弯曲加载下，随着回火温度的提高，裂纹扩展速率单调下降；裂纹扩展速率随回火温度变化规律与扩展机制随回火温度变化规律有密切的关系。结果表明，应该注意到加载方式对疲劳裂纹扩展的影响。

THE FATIGUE CRACK GROWTH UNDER TWO LOADING CONDITIONS

The rate of fatigue crack growth (FCG) under rotative bend loading and three-point bend loading for 45Cr steel tempered at four different temperatures (200℃, 400℃, 500℃ and 600℃)was investigated respectively. The mechanism of FCG under the above loading conditions.have been studied by. Optical microscope and electron microscopy. The experamental results show that under rotative bend loading the rate of FCG of the steelas tempered at 500℃temperature is the lowest among the rate of FCG at four different temperature But under three-point bend loading the rate of FCG decrease monotonically with the increase of the tempering temperature. These results can be explained by the different mechanism of FCG under different tempering temperatures. It is suggested that the inflence of the Ioading condition on the FCG must be noticed.