Mechanism of superlong fatigue failure in the regime of N>107 cycles and fractography of the fracture surface
Mechanism of superlong fatigue failure in the regime of N>107 cycles and fractography of the fracture surface
复制标题
N>107次循环超长疲劳失效机理及断口断口形貌
DOI：
10.1299/kikaia.66.311
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发表时间：
2000
期刊：
影响因子：
--
通讯作者：
Y. Murakami
中科院分区：
文献类型：
--
作者：
Y. Murakami;T. Ueda;T. Nomoto;Y. Murakami
为了阐明N> 107循环的超长疲劳失效机理，采用光学显微镜、扫描电镜和原子力显微镜对热处理硬质钢、SCM 435和0.46%中碳钢试样的断口进行了观察。结果表明，寿命较长的试样，除了断裂处的夹杂物外，还具有特殊的形貌。通过光学显微镜观察，这种特殊的形态看起来是光学暗区，并将其命名为光学暗区（ODA）。在SEM和AFM的观察中，ODA看起来是一个粗糙的区域。随着疲劳寿命的增加，ODA相对于断裂处夹杂物尺寸的相对尺寸增加。因此，ODA对超长疲劳失效机理的研究具有重要意义。据推测，ODA是由循环应力引起的疲劳与氢结合而产生的，氢被夹杂物捕获在断裂起源处。为了验证该假设，制备在300 ° C真空中退火的样品（VA样品）和在真空中淬火的样品（VQ样品）以解吸被夹杂物捕获的氢。试样VA和VQ具有比常规热处理试样小得多的ODA。因此，夹杂物中的氢是导致高强钢超长疲劳失效的关键因素。
In order to elucidate the mechanism of superlong fatigue failure in the regime of N>107 cycles, the fracture surfaces of specimens of heat treated hard steel, SCM 435 and 0.46% medium carbon steel were investigated by optical microscope, SEM and AFM. It has been revealed that specimens having longer life have a particular morphology beside the inclusion at fracture origin. The particular morphology looks optically dark by the observation of optical microscope and it has been named the optically dark area, ODA. The ODA looks a rough area in the observation by SEM and AFM. The relative size of ODA to the size of inclusion at fracture origin increases with increase in fatigue life. Thus, ODA has a crucial importance for the mechanism of superlong fatigue failure. It has been assumed that ODA is made by the fatigue due to cyclic stress coupled with hydrogen which is trapped by the inclusion at fracture origin. To verify the hypothesis, specimens annealed at 300°C in a vacuum (VA specimens) and quenched in a vacuum (VQ specimens) are prepared to desorp the hydrogen trapped by inclusions. The specimens VA and VQ, had a much smaller ODA than conventionally heat treated specimens. Thus, it has been concluded that hydrogen trapped by inclusion is the crucial factor which causes superlong fatigue failure of high strength steels.