Role of Inclusions, Surface Roughness and Operating Conditions on Rolling Contact Fatigue

TLDR

The study evaluates how inclusions, surface roughness, and operating conditions affect rolling contact fatigue in AISI 52100 and M50 bearing steels using a two‑disk machine. The experiments used a two‑disk machine under jet‑engine‑typical conditions, testing up to 4.2 GPa with two surface finishes and monitoring early sub‑surface micro‑cracks via ultrasonic echography. The tests identified key parameters influencing crack initiation and propagation, revealing surface‑initiated deep spalling at 3.5 GPa for unpolished surfaces under rolling plus sliding, sub‑surface deep spalling at 4.2 GPa for polished specimens, and overall surface distress and sub‑surface damage that could lead to catastrophic failure, with results discussed relative to rolling contact fatigue theories.

Abstract

Tests have been performed on a two-disk machine in order to evaluate the role of inclusions, surface roughness and operating conditions on rolling contact fatigue of AISI 52100 and M50 bearing steels. Important parameters—such as nature and location of inclusions, small and large wavelengths of surface roughness, normal loading or sliding conditions—on crack initiation and propagation stages have been identified. The operating conditions have been selected to encompass typical jet engine applications. Tests have been carried out up to 4.2 GPa, for two different surface finishes. Surface distress and sub-surface damage which could result in catastrophic failure have been observed. Indeed, surface initiated deep spalling (observed at 3.5 GPa for unpolished surfaces and under rolling plus sliding conditions) as well as sub-surface initiated deep spalling (at 4.2 GPa for polished specimens) have been observed. Sub-surface micro-cracks were detected early and followed during some interrupted tests by the means of an ultrasonic echographic device. Results of our experiments are analyzed and discussed in relation to the rolling contact fatigue theories.