In rolling bearing analysis, Hertzian contact theory is used to compute local contact stresses. Hertz's analysis is applied only to surface stresses caused by a concentrated force applied perpendicular to the surface. Experimental evidence indicates that failure of rolling bearings in surface fatigue as caused by the aforementioned load emanates from points below the surfaces. Therefore, it is of interest to determine the magnitude of the subsurface stresses. The initiation and the propagation of the crack are mainly effected by the stress distribution below the surfaces, especially the shear stress distribution. Therefore, it is also important to analyze the stress condition below a contact surface and the depths where the shear stress is the maximum. Hence, in the present work, a complete numerical analysis is carried out for the calculation of subsurface stresses induced in the cylindrical roller bearing. Also a program is developed in MATLAB to understand the distribution of stresses under the surface.

Operation of a rolling bearing causes fatigue cracks within the subsurface material of highly stressed roller-raceway contacts. The subsurface cracks propagate and coalesce causing the removal of a portion of the contacting surface. This phenomenon is known as fatigue spalling. When a bearing generates a fatigue spall, the contact stresses, vibratory loads and heat generation rates are increased. This in turn causes more fatigue cracks within the unfailed subsurface material of the contacts. The propagation of existing subsurface cracks and the creation of new subsurface cracks cause continued deterioration of the contact surface, as shown in Figure 1. Repeated operation of the bearing progresses the fatigue spall until the entire contact area has been roughened. The increased heat generation rates and vibratory loads within a spalled bearing can lead to catastrophic failure of the mechanism. If the heat dissipation is such that it causes internal clearances within the bearing to disappear, the bearing could seize. Alternatively, the internal clearances could increase. This would lead to larger roller loads and possibly component fracture. Finally, the increased vibratory loads may be too high for the mechanism or the system surrounding the bearing. Again, this could lead to a catastrophic failure (Michael and Tedric, 2001).

It is generally accepted that when two solid bodies of curved shape are brought into contact, the maximum orthogonal shear stresses are developed somewhere beneath the contact spots. The depth of these stresses is dictated by the magnitude of applied loads and the elastic properties of the contacting bodies. It has been postulated that fatigue failures or pits should originate at depths where maximum shear stresses develop. Dislocation entanglement around inclusions, second-phase precipitates and other types of volume defects that are located at depths where maximum shear stress develops are thought to act as stress concentration points and hence initiate subsurface microcracks, resulting in failure (Ali, 1999).

Rolling contact fatigue is manifested as flaking of metallic particles from the surface of the raceways and/or rolling elements. For well lubricated, properly manufactured bearings, this flaking usually commences as a crack below the surface and is propagated to the surface eventually forming a pit or spall in the load-carrying surface (Tedric, 2001). Subsurface cracks propagate to the surface and also connect with surface cracks to form a network. The volume enclosed by this network crumbles, thus producing a spall or fatigue failure (Shelley and Erwin, 1963).

Mechanical Engineering Journal, Cylindrical Roller Bearing, Catastrophic Failure, Shear Stress Distributions, MATLAB, Subsurface Stress Trajectories, Crack Propagation, Photoelasticity, Principal Contact Stresses, Rolling Contact Fatigue, Hertzian Contact Theory.