Characteristics and Formative Factors of Fracture Surfaces on Subsurface Initial Crack Growth in Very High Cycle Fatigue
Characteristics and Formative Factors of Fracture Surfaces on Subsurface Initial Crack Growth in Very High Cycle Fatigue
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超高周疲劳下表层初始裂纹扩展断裂面特征及形成因素
DOI：
10.2472/jsms.60.1066
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发表时间：
2011
期刊：
影响因子：
--
通讯作者：
H. Oguma
中科院分区：
文献类型：
--
作者：
Takashi Nakamura;H. Oguma
在超过 107 个循环的极高循环状态下，疲劳裂纹通常从材料的次表面开始。在地下裂缝中，已知裂缝起点周围存在一种独特的裂缝表面，具有精细的凹凸图案，称为光学暗区（ODA）。这种类型的断裂面不仅在高强度钢中观察到，而且在钛合金中也观察到。为了揭示精细凹凸图案的形成因素，本研究重点关注地下裂纹周围的独特环境。地下裂纹没有被大气包围；因此，它们周围的环境可以类似于真空。基于这一想法，在高真空中、不同条件下对高强度钢（SNCM439）和钛合金（Ti-6Al-4V）进行了疲劳裂纹扩展试验，并通过扫描电镜（SEM）分析了断口表面。其结果是，在裂纹扩展试验中得到的断口表面上观察到与表面下断口中的ODA类似的微细凹凸形貌。此外，还阐明了独特的断裂面不是在裂纹扩展过程中形成的，而是由已引发的断裂面在高真空中长期重复接触形成的。当满足以下两个条件时，无论材料如何，都可以形成精细的凹凸变形；一种是真空环境，另一种是断裂表面约 107 个循环的长期重复接触。
In the very high cycle regime over 107 cycles, a fatigue crack often initiates from subsurface of materials. In subsurface fractures, a unique fracture surface with a fine concavo-convex pattern called Optically Dark Area (ODA) is known to exist around the fracture origins. This type of fracture surface has been observed not only in high strength steel, but also in Ti alloy. To reveal the formative factors of the fine concavo-convex pattern, this study focuses on a unique environment around subsurface cracks. Subsurface cracks are not surrounded by atmosphere; therefore, the environment around them can be similar to vacuum. Based on this idea, fatigue crack growth tests using high strength steel (SNCM439) and Titanium alloy (Ti-6Al-4V) were conducted in high vacuum under various conditions, and fracture surfaces were investigated by SEM analyses. As a result, the fine concavo-convexo morph similar to ODA in subsurface fractures was observed on the fracture surfaces obtained in the crack growth tests. In addition, it was clarified that the unique fracture surface was not formed during crack growth process but formed by the long term repeating contacts of already initiated fracture surfaces in high vacuum. The fine concavo-convexo morph can be formed regardless of materials when the following two conditions are satisfied ; one is a vacuum environment and the other is a long term repeating contacts of fracture surfaces over about 107 cycles.
Ti-6Al-4V内引发疲劳断口晶粒区形成因素
DOI：
--
发表时间：
2007
期刊：
材料 56巻
影响因子：
--
作者：
中村孝;山下亮平;小熊博幸;脇田実奈;野口徹
通讯作者：
野口徹