Initiation and early growth of fatigue cracks in an aerospace aluminium alloy
Initiation and early growth of fatigue cracks in an aerospace aluminium alloy
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DOI：
10.1046/j.1460-2695.2002.00482.x
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发表时间：
2002-02-01
影响因子：
3.7
通讯作者：
Clark, G
中科院分区：
文献类型：
--
作者：
Barter, SA;Sharp, PK;Clark, G
材料缺陷通常在疲劳裂纹的早期阶段起重要作用。本文介绍了7050-T7451铝合金试样和具有生产表面光洁度的全尺寸疲劳试验件中疲劳裂纹萌生缺陷和早期裂纹扩展的一些观察结果。等效初始裂纹尺寸（EIFS）的方法用于评估冶金，制造和服务引起的功能的疲劳影响进行了改进，通过使用定量断口分析，以获得详细的信息，早期裂纹扩展行为的个别裂纹;裂纹扩展的观察采用了一个简单的裂纹扩展模型，用于分析服务裂纹扩展。使用观察到的裂纹扩展行为减少了可变性，这是固有的EIFS方法依赖于模拟整个疲劳寿命，并可以主导EIFS方法。对实际初始缺陷的观察也突出了疲劳寿命决定早期疲劳增长阶段的一些重要因素，如表面处理工艺。虽然夹杂物通常被认为是最常见的初始缺陷类型，但包括蚀刻在内的工艺可能导致晶界的蚀坑，并对疲劳寿命产生重大影响。
Material imperfections usually play a substantial role in the early stages of fatigue cracking. This article presents some observations concerning fatigue crack initiating flaws and early crack growth in 7050-T7451 aluminium alloy specimens and in full-scale fatigue test articles with a production surface finish. Equivalent initial flaw size (EIFS) approaches used to evaluate the fatigue implications of metallurgical, manufacturing and service-induced features were refined by using quantitative fractography to acquire detailed information on the early crack growth behaviour of individual cracks; the crack growth observations were employed in a simple crack growth model developed for use in analysing service crack growth. The use of observed crack growth behaviour reduces the variability which is inherent in EIFS approaches which rely on modelling the whole of fatigue life, and which can dominate EIFS methods. The observations of realistic initial flaws also highlighted some of the significant factors in the fatigue life-determining early fatigue growth phase, such as surface treatment processes. Although inclusions are often regarded as the single most common type of initiating flaw, processes which include etching can lead to etch pitting of grain boundaries with significant fatigue life implications.