阳极氧化膜对铝合金疲劳裂纹萌生的影响

Effect of anodic oxide film on fatigue crack initiation of aluminum alloy

首先基于晶体塑性有限元理论选取有自由表面的统计体积单元建立晶粒聚集体,并在晶粒聚集体的自由表面上覆盖不同厚度的弹性各向同性介质,以表示阳极氧化形成的氧化膜;然后借助Fatemi-Socie疲劳指示参数来表征疲劳裂纹萌生驱动力,对3种应力水平下覆盖不同厚度氧化膜的晶粒聚集体的裂纹萌生驱动力极值进行统计分析。结果表明,低应力水平下氧化膜的约束作用会普遍降低铝合金基体的裂纹萌生驱动力,但随着应力水平的提高,覆盖氧化膜的晶粒聚集体的最高裂纹萌生驱动力逐渐超过了无氧化膜的晶粒聚集体。氧化膜厚度增大时,铝合金基体的裂纹萌生驱动力有所降低。当应力水平低于弹性极限时,由于氧化膜的约束作用,不仅铝合金基体的裂纹萌生驱动力会降低,铝合金基体的疲劳热点比例也会减小。

Firstly,based on the crystal plastic finite element theory,the statistical volume elements with free surfaces were selected to establish grain aggregates,and the free surfaces of grain aggregates were covered with elastic isotropic media with different thicknesses to represent the oxide film formed by anodic oxidation.Then,the fatigue crack initiation driving force was characterized by the Fatemi-Socie fatigue indicator parameter,and the extreme values of the crack initiation driving force of grain aggregates covered with different thicknesses of oxide film under three stress levels were statistically analyzed.The results show that the crack initiation driving force of aluminum alloy substrate is generally reduced by the restraint of oxide film at low stress level,but with the increase of stress level,the maximum crack initiation driving force of grain aggregates covered with oxide film gradually exceeds that of grain aggregates without oxide film.When the thickness of oxide film increases,the crack initiation driving force of aluminum alloy substrate decreases.When the stress level is lower than elastic limit,not only the crack initiation driving force of the aluminum alloy substrate decreases,but also the fatigue hot spots ratio of the aluminum alloy substrate decreases due to the restraint effect of the oxide film.