CLARIFICATION OF ROLLING-CONTACT FATIGUE INITIATION USING ACOUSTIC-EMISSION TECHNIQUE

Test bearings, simulating a 51205 thrust ball bearing were run in a mineral oil bath with maximum contact stresses of 3.0 and 3.3 GPa at a rotational speed of 660 rpm. In the tests, sources of acoustic emissions were located by an AE source location system as position on a raceway of a housing washer. The rolling contact fatigue rests were stopped automatically when the number of acoustic emissions during a prescribed lime period reached a prescribed value at ang one position on the raceway. Each of the washers was cut and polished at the source position of acoustic emissions and each cross section was observed wing a scanning electron microscope. In the cross sections, fatigue cracks initiating from inclusions were discovered below the raceway surfaces. Moreover,, clearance between inclusion and matrix, and scratch patterns which were thought to be due to rolling contact fatigue were found in the mai, iu surrounding the inclusions.