M. Hadfield et al., FAILURE MODES OF CERAMICS IN ROLLING-CONTACT, Proceedings - Royal Society. Mathematical and physical sciences, 443(1919), 1993, pp. 607-621
A comprehensive experimental study has been carried out to ascertain t
he prevailing mode of failure of concentrated rolling ceramic contacts
subjected to cyclic loading conditions. The findings of the studies p
resented in this paper confirm that good quality silicon nitride balls
in non-conforming contact do not fail in a catastrophic mode and thus
can be considered for important engineering applications such as roll
ing contact bearings for gas turbines. The results of extensive testin
g carried out on perfect and artificially pre-cracked balls under high
compressive cyclic stress showed that the prevailing mode of failure
is delamination. Scanning electron microscope (SEM) observations enabl
ed the delamination failures to be classified in terms of location of
crack initiation and subsequent crack propagation. By using X-ray diff
raction, residual stresses on delaminated surfaces were measured and r
esults showed that under certain conditions plastic deformation of the
ceramic can take place. Results of supplementary chemical analysis of
failure surfaces suggest that changes in the level of silicon, nitrog
en and oxygen may take place on delaminated surfaces. Experiments with
artificially pre-cracked balls revealed the role played by a lubricat
ing medium in the process of fatigue failure. All findings are illustr
ated with SEM micrographs and the physical aspects of failure mechanic
s are discussed.