Contact fatigue in rolling-element bearings

Surface contact fatigue is a common cause of failure in rolling-element bearings. The extent of damage observed depends on the contact loads, the curvature of the rolling elements, and the relative motion between the contacting surfaces. The characteristics of the various types of contact fatigue are as follows: (a) Microscopic pits form under pure rolling contact. These may act as stress concentration sites for further damage. (b) Under rolling-sliding contact, irregular-shaped pits are formed. This type of damage is accelerated by the presence of geometric inhomogeneities such as corrosion pits, handling damage, and dents. (c) Flaking occurs as a progression of the pits formed under rolling and rolling-sliding contact fatigue, and leads to the formation of large, irregular-shaped pits. (d) Spalling refers to the formation of large, deep pits with sharp edges, steep sides, and flat bases, or to cracking at the case-core interface in case-hardened surfaces. A number of practical examples of bearing failure have been used to illustrate the various types of contact fatigue damage.