A novel method for coupling fluid pressure and crack deformation for the purpose of
analysing rolling contact fatigue (RCF) cracks in lubricated, hydrodynamic and
elastohydrodynamic, contacts is presented. The model addresses some of the
simplifying assumptions applied to existing models presented in the literature such
as: (i) using an imposed fluid pressure gradient inside the crack, (ii) using an
imposed fluid pressure at the crack mouth, and (iii) adopting a surface contact
pressure, Hertzian or EHL, that does not account for the fluid flow in and out of the
crack during loading. The model has been used to model the effect of
lubricant/crack interaction in various RCF configurations as the rolling element
passes over the pre-formed crack; which has direct application to bearings and
rail/wheel contacts. The results of the simulations performed with the fully-coupled
fluid/solid solver developed by the author suggest that the cracked
component/lubricant interaction contributes significantly to accelerate the rate of
surface breaking crack growth in rolling element bearings and wheel/rail type
contacts. It is shown through simulations that the lubricant works as a catalyst inside
the crack to convert the compressive contact load into a crack opening, tensile
fatigue mechanism, through the effect of fluid pressurisation inside the crack. The
results obtained using such a model suggest that the opening associated with the
fluid action within the crack induces large mode I stress intensity factors. This has
been shown to be the principal factor that promotes and influences the rate of rolling
contact fatigue crack growth in lubricated contacts. In addition to the modelling work, an experimental method of analysing RCF
cracks in real time has been developed. The technique is based on laser induced
fluorescence that allows the penetration of the fluid within the crack to be observed.
Though the method would require development to be used to provide results that
could be used for quantitative comparisons with crack models, some encouraging
preliminary results have been obtained: the technique has been shown to be suitable
for measuring, at least qualitatively, the real time evolution of the film thickness in
RCF cracks.