The fretting fatigue life gradually decreases with increasing contact
stress under SP and DP. The study by Liu et al.24showed multiaxial fretting fatigue life of 35CrMoA steel had a trend of
decreasing first, then increasing and finally decreasing with increasing
contact stress. With the same contact stress range, the same trend of
fretting fatigue life was achieved in this paper. Compared with plain
fatigue, the contact stress was added between the fretting pad and the
specimen during the fretting fatigue, which caused the fretting wear on
the surface of the specimen. The larger the contact stress, the more
severe the surface damage of the specimen, and the stress concentration
was more obvious in this situation, which accelerated the initiation and
propagation of microcracks and reduced the fretting fatigue
life.23,31 As the contact stress of 35CrMoA steel
increased, the equivalent strain also increased, indicating that the
sample had undergone severe plastic deformation during the fretting
fatigue process. At this situation, serious fretting wear occurred, so
the greater the contact stress, the more serious the surface damage of
the sample, the more obvious the stress concentration phenomenon, which
led to a faster crack initiation rate, and greater plasticity also
accelerated crack propagation; In addition, at the beginning of fretting
fatigue, there was adhesive wear between the specimen and the fretting
pad. When the adhesive part was torn due to fretting, fine metal debris
was generated.32 This process gone on and the debris
continued to increase, which caused the change of fretting wear from
adhesive wear to abrasive wear. After the fretting surface was wiped by
the abrasive wear, the surface microcracks may be erased, thereby
reducing the source of cracks and improving the fretting fatigue
life.33,34 The greater the contact stress, the lower
the relative displacement between the specimen and the fretting pad,
which reduced the wiping effect of abrasive wear on microcracks,
resulting in a low fretting fatigue life. Combining the above two
reasons, the fretting fatigue life of 35CrMoA steel under SP and DP
showed a downward trend with increasing contact stress. Under the same
contact stress and equivalent stress, the fretting fatigue life of DP
was slightly lower than the fretting fatigue life of SP. The fretting
fatigue damage of the 35CrMoA steel was greater under DP.
Analysis of fretting region