Mechanism of fatigue failure in ultralong life regime
Mechanism of fatigue failure in ultralong life regime
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DOI：
10.1046/j.1460-2695.2002.00576.x
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发表时间：
2002-08-01
影响因子：
3.7
通讯作者：
Nagata, J
中科院分区：
文献类型：
--
作者：
Murakami, Y;Yokoyama, NN;Nagata, J
用光学显微镜和扫描电子显微镜研究了在N=10(5)~5×10(8)循环范围内失效的热处理硬质钢试件的疲劳断口。疲劳寿命较长的试件，除了断口处的夹杂物外，还有特殊的形貌。这种特殊的形态看起来像光学上的黑暗，在之前的论文中它被命名为光学黑暗区域，oda。官方发展援助内部的粗糙度大于外部官方发展援助。随着疲劳寿命的增加，oda与断口夹杂物尺寸的相对大小也随之增大。因此，oda被认为在超长寿命疲劳破坏机制中起着至关重要的作用。给出了断口夹杂物中存在氢的直接证据。断口应力与夹杂物捕获氢气的循环应力耦合作用产生了oda。为了验证氢的影响，通过不同的热处理方法制备了含有不同氢含量的样品。这些试件的疲劳试验结果表明，夹杂物捕获的氢是导致高强度钢超长疲劳破坏的关键因素。从实验方法、样品尺寸和夹杂物尺寸的统计分布等方面对S-N双曲线进行了讨论。
The fatigue fracture surfaces of specimens of heat treated hard steels which failed in the regime of N = 10(5) to 5 x 10(8) cycles, were investigated by optical microscopy and SEM. Specimens having a longer fatigue life had a particular morphology beside the inclusion at the fracture origin. The particular morphology looked optically dark and in the previous paper it was named the Optically Dark Area, ODA. The roughness inside ODA is larger than outside ODA. The relative size of the ODA to the size of the inclusion at the fracture origin increases with increase in fatigue life. Thus, the ODA is considered to have a crucial role in the mechanism of ultra long life fatigue failure. Direct evidences of existence of hydrogen at the inclusion at fracture origin are presented. It is presumed that the ODA is made by the cyclic stress coupled with the hydrogen which is trapped by the inclusion at the fracture origin. To verify the influence of hydrogen, specimens containing different levels of hydrogen were prepared by different heat treatments. The results obtained by fatigue tests of these specimens suggest that the hydrogen trapped by inclusions is a crucial factor which causes the ultra long fatigue failure of high strength steels. Aspects of the double S-N curve are also discussed in terms of experimental methods, specimen size and statistical distribution of inclusions sizes.