An experimental investigation of white layer on rolling contact fatigue using acoustic emission technique

Hard turning has being used to make various mechanical components. Under certain cutting conditions, a white layer (WL) may form on the machined surface that could drastically affect a component's service life. The presence of WL causes great concerns in machining industry just because the WL effects on component life are not yet understood. This study presents a novel real-time acoustic emission (AE) based rolling contact fatigue (RCF) testing system to study the WL effects on component life. AISI 52100 bearing steels were machined to generate two distinct surfaces: free of white layer (NOWL) and with WL. The real life loading of contact pressures and rolling speeds was applied to the test specimens. The applied load throughout the experiment was in-process monitored using a load cell which enabling the record of a Hertzian pressure history during rolling contact. It was found that the RCF testing system is simple and inexpensive, but very sensitive to fatigue crack initiation and propagation. Compared with AE count rate, AE parameters such as energy, RMS, and amplitude are more sensitive to fatigue crack initiation and propagation in rolling contact. The NOWL samples are more resistive to fatigue crack initiation/propagation and, therefore, have a longer life when compared to the WL samples with equivalent surface finish.