挤压变形量对铝合金钉孔试样疲劳性能的影响

Effects of different interference values on fatigue properties of aluminum alloy specimens with fastener holes

采用冷挤压强化工艺对2×××铝合金钉孔试样进行不同挤压变形量的强化试验和疲劳验证试验,研究了合金孔挤压强化挤压变形量、残余应力和疲劳寿命三者之间的内在关系,并分析不同挤压变形量下疲劳断口形貌特征的差异性。结果表明,挤压后孔周向残余应力分布较不均匀、形成残余压应力强化层,可以延缓裂纹的萌生和扩展,有效提高试样的疲劳寿命。随着挤压变形量的增加,最大残余应力和疲劳寿命都随之增加,但是当挤压变形量超过最佳强化范围时,在疲劳应力作用下,强烈变形区域即强化层产生应力集中现象,导致微裂纹的产生,使试样的疲劳寿命并不随着最大残余应力继续增加而增加。采用4%挤压变形量可达到最佳强化效果,其安全疲劳寿命是未强化的3.38倍。

Expansion and fatigue experiments were carried out on 2 ××× Al-alloy speci- mens with fastener holes that are cold expanded with different interference values. The inves- tigation on how interference values influence residual stress, fatigue life and the fatigue frac- ture morphology shows that the residual compressive stress layer which is formed due to the uneven distribution of the circumferential residual stress around the hole can slow down the initiation and expansion of fatigue cracks and remarkably increase the fatigue life. The maxi- mum residual stress and fatigue life increase with interference values rising. But when the in- terference values exceed the best expansion scope, stress concentration phenomenon appears in the strong deformation zone （ i. e. compressive layer） under fatigue stress and micro cracks appear after that. As a result the fatigue life of the specimen does not increase with the in- crease of the maximum residual stress. Thus 4% interference values lead to optimal expan- sion effect and the fatigue life of the specimen with 4% interference values is 3.38 times that of the non-expanded holes.