A FRETTING FATIGUE NORMAL PRESSURE THRESHOLD CONCEPT

The results obtained and presented in this paper illustrate the existence of a normal pressure threshold (the value after which increasing the pressure does not affect the life) in fretting fatigue. This finding has led the authors to question the role of normal pressure and frictional stress in fretting fatigue failure. This is because at a given applied cyclic stress and below the pressure threshold, fretting fatigue failure is a function of normal pressure and the change in normal pressure, hence by the first law of friction: fretting fatigue life is a function of frictional stress and the change of frictional stress. Above the pressure threshold, fretting fatigue failure is just a function of normal pressure and frictional stress, not the increase of these two variables. In conjunction with these findings, it has been argued that a critical frictional stress might exist that causes the fretting damage to reach its threshold faster.