The reflectivity of ultrasonic wave from contacting surface between ball bearing and housing changed, when the inner ring was damaged, and echo height ratio decreased. In order to investigate the cause of this result, stress of contacting surface was calculated by CAE with shifting the position where the ball contacted with the inner ring flaw. As the result, it was clarified that the stress between outer ring and housing decreased, when the ball contacted with the flaw part. Especially, the decreasing ratio of stress between two surfaces was remarkable when flaw contacted near the sound axis of probe. However, in the case of ball contacting with flaw in the position away from the sound axis, the stress on the sound axis was almost equal to the flawless bearing. It can be concluded that the decrease of echo height ratio H was caused by the contact between ball and flaw near the sound axis.
