SYMPOSIA PAPER Published: 08 September 2020

Spall Propagation Characteristics of Life-Tested VIM-VAR M50 and Pyrowear 675 Bearing Steels


Spall propagation experiments were conducted on fatigue life-tested 208-size angular contact bearings made of vacuum induction melted, vacuum arc remelted (VIM-VAR) M50 (with both M50 and Si3N4 rolling elements) and two heat treatment variations of VIM-VAR Pyrowear 675 (P675) (with Si3N4 rolling elements). The primary focus was to study the effect of accumulated stress cycles and spall initiation method on spall propagation rate. Bearings were initially tested for rolling contact fatigue (RCF) life at maximum Hertzian contact stress values of 3.10 GPa (all-metal) and 3.56 GPa (hybrid) and at a temperature of 128°C using high thermal stability (HTS) oil conforming to MIL-PRF-23699G. Spall propagation tests were then subsequently conducted on fatigue life-tested bearings at 2.41 GPa (350 ksi) maximum Hertzian contact stress until a predetermined amount of material removal was detected. Propagation experiments were performed on both naturally occurring fatigue spalls from life testing and spalls initiated from Rockwell hardness indentations on suspended life-tested bearings. Selected life-tested bearings were investigated for alteration in microstructure and residual stress prior to spall propagation experiments. The effect of alloy, heat treatment, and stress cycling on spall propagation rate was examined. The material microstructural decay from accumulated stress cycles had a significant effect on the spall propagation time of hybrid bearings.

Author Information

Trivedi, Hitesh, K.
UES Inc. Dayton, Dayton, OH, US
Haywood, DaMari, A.
UES Inc. Dayton, Dayton, OH, US
Rosado, Lewis
Air Force Research Laboratory, Wright-Patterson AFB, OH, US
Kirsch, Mathew, S.
Air Force Research Laboratory, Wright-Patterson AFB, OH, US
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Pages: 528–550
DOI: 10.1520/STP162320190102
ISBN-EB: 978-0-8031-7693-5
ISBN-13: 978-0-8031-7692-8