Monitoring damage by acoustic emission in bearing steels in cryogenic environment

Abstract

Fatigue is the usual type of damage occurring at heavily loaded hertzian contact zones such as those found on bearings. An in-depth knowledge of the origins and evolution of fatigue-induced damage is crucial for correctly foreseeing the life span of mechanical parts. In order to monitor crack-initiation during an extremely low-temperature (cryogenic) fatigue test, acoustic emission measurements were used. In this present study we show that the analysis of those signals emitted during testing is a reliable means of distinguishing and quantifying the first two stages of fatigue-induced damage, namely microscopic crack-initiation and crack-growth. The after-the-fact analysis of failed test specimens (their autopsy, so to speak) provides us with a detailed picture of these stages by revealing the crack-initiation zones and the way in which they grow.