The fatigue crack propagation (FCP) rate is an important performance index in the aerospace industry for the safe lifespan evaluation. In this study, the FCP anisotropy of an Al–Zn–Mg–Cu super-thick rolled plate was analyzed. The results show that as the depth increases, the FCP anisotropy gradually becomes significant especially in the low ΔK region. The specimens tested along the transverse direction exhibit lower FCP rate than those tested along the rolling direction in the low ΔK region, which is related to the difference in the grain shape and grain orientation. More specifically, the crack is easy to deflect along the grain boundaries in the deformed grains when loading along the transverse direction. Meanwhile, more obvious grain orientation deviation on both sides of the crack can cause larger angle deflection, longer FCP path, and lower FCP rate. In the Paris region, the FCP anisotropy is not obvious regardless of thickness. The reason is that the main influencing factor is controlled by strength in this region, while the strength anisotropy is very limited leading to this similarity.

中文翻译：

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Al-Zn-Mg-Cu超厚板的疲劳裂纹扩展各向异性


疲劳裂纹扩展（FCP）速率是航空航天工业中评估安全寿命的重要性能指标。在本研究中，分析了 Al-Zn-Mg-Cu 超厚轧制板的 FCP 各向异性。结果表明，随着深度的增加，FCP各向异性逐渐变得显着，尤其是在低ΔK区域。在低ΔK区域，沿横向测试的试样表现出比沿轧制方向测试的试样更低的FCP率，这与晶粒形状和晶粒取向的差异有关。更具体地说，当沿横向加载时，裂纹很容易沿变形晶粒的晶界偏转。同时，裂纹两侧晶粒取向偏差越明显，会导致较大的角偏转、较长的FCP路径和较低的FCP速率。在巴黎地区，无论厚度如何，FCP各向异性都不明显。原因是该区域的主要影响因素受强度控制，而强度各向异性非常有限，导致了这种相似性。