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Abstract: According
to fracture modes, the S-N curve obtained from cantilever-type rotary
bending fatigue tests using hourglass shaped specimens of high
carbon-chromium bearing steel is clearly classified into two groups of
different crack origin. One is called the S-N curve of surface fracture
mode. It is governed by a crystal slip on the specimen surface, which
occurs in the region of short fatigue life and high stress amplitude
level. The other is called one of internal fracture mode. It is governed
by nonmetallic inclusion at subsurface, which occurs in the region of
long fatigue life and low stress amplitude. Because fatigue fractures of
internal fracture mode occurs in a wide range of stress amplitude not
only below the Fatigue limit defined as the threshold of fracture due
to the slip governed mode but also above the fatigue limit, the shape of
the S-N curve for the material used in this study is different from a
step-wise one reported in previous literature and is characterized as
duplex S-N curves. Through the detailed observation of fatigue crack
origin and calculation of crack initial size parameter, mechanisms for
internal fracture mode are discussed and fatigue life prediction
procedure is indicated based on crack initial size parameter.
Key words: Bearing steel Super-long life fatigue S-N curve
Surface crack Internal crack Nonmetallic inclusion Fisheye
CLC No: TG113
国家自然科学基金资助项目(50471047，50323003).
Received 20041120, received in revised form 20050326
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