FATIGUE CRACK PROPAGATION IN Al-Li ALLOY 8090
8090Al—Li合金的疲劳裂纹扩展

Fatigue crack growth rates of 8090 type Al-Li alloy in air were found to be strongly dependent upon the aging conditions. The naturally aged and underaged specimens showed the highest resistance to the fatigue crack propagation. The fatigue crack growth re- sistance of the overaged specimen is the lowest and that of the peakaged specimen in between. As compared to air, 3.5%NaCl solution did not change the effect of aging conditions on the fatigue crack growth, but caused a decrease of the resistance to the fatigue crack growth un- der the same aging condition. Both short cracks from notch and physically short cracks showed much higher rates of fatigue crack propagation in comparison with long cracks under the same aging condition and stress intensity level. The growth behavior of the short crack depends on its type. The growth rate of short crack from notch decreases first to a minimum and then increases with increasing AK. However, the physically short crack grows at a progressively increasing rate. The effects of aging conditions were explained in terms of the slip planarity of dislocations and the cyclic slip reversibility. The observed short crack behav- ior was considered to be dependent on the crack closure and the local plasticity near the crack