一次预过载对铝合金喷丸前后缺口疲劳强度的影响

 预过载拉伸可提高铝合金缺口疲劳寿命,但效果不及喷丸;过载量太大还使寿寿命趋于子下降。预过载压缩降低缺口疲劳寿命;喷丸后经过载压缩,寿命降低幅度更大,均与缺口残余应力及亚结构变化有关。

EFFECT OF OVER-PRE LOADING ON THE NOTCH FATIGUE STRENGTH OF AN ALUMINIUM ALLOY WITH AND WITHOUT SHOT PEENING

The experiments on notched specimens of an Aluminium alloy indicat that the notch fatigue life can be increased by a tensile over-pre loading but decreased by a compressive over-pre loading. It is discovered, however, that the beneficial effect of tension lies below that of shot peening and even becomes weak as the level of over-pre loading is too high, and the detrimental effect of compression appears to be more pronounced for specimens with shot peening on the root surface. The shot peening induced increment of fatigue strength can be destroyed completely by compressive over-pre loading. The results are analysed based on the calculation of residual stress and the observation of dislocation configuration around the notch root area. The increase of fatigue life lies in the fact that the crack propagation rate is reduced greatly in a compressive residual stress field. The relaxation of residual stress an the damage in microstructure incorporated with the relaxation result in the decrease of fatigue life.