were mainly the nature of fatigue, side flow, and plowing to form
grooves. Furthermore, the level of individual wear modes could be
distinctively classified by the increase of excitation intervals. Test
with short excitation intervals was generally apt to forming of
cavities, which was basically caused by material fatigue. Test with
long excitation intervals was mainly dominant with plowing wear
to form deep grooves (Fig. 11c). Analysis of the morphological
results seemed to indicate that (i) the smoothing up of wear track
was mainly due to the occurring of plastic deformation on the
plowed contact surfaces, where were also built-up with material
and frequently subjected to transient high loading; and (ii) area
under frequently varying loading tended to destroy the isotropicity
of side-flow material and to yield fatigue wear Bar
chart (Fig. 12) of the profile of cross-sectional area of the wear
tracks showed the obtainment of largest wear volume with the
40 min excitation period-implying the long excitation interval of
DHE loading likely to accelerate wear rate in running-in period.
The results of the COF and IPCA curves (Figs. 9 and 10) with various
excitation periods, together with these observed phenomena
suggest that high excitation frequency can help to (i) smoothen
wear track, (ii) reduce peak magnitudes of the COF and IPCA
values, and (iii) accelerate the completion of running-in process.
They also indicate that long excitation intervals tend to (i) deepen
plowing grooves, (ii) increase peak magnitudes of the COF and
IPCA values, and (iii) aggravate wear rate during the running-in
period.
4.3. Contact analysis by finite element analysis
Finite element analysis (FEA) was conducted to understand the
stress distribution of the contact surfaces, which facilitates preliminarily
visualizing the possible mechanics causing the damage
forms on the wear track of the disc under DHE loading. Generally,
the non-uniform material distribution around the impacting ball
resulted in unevenly circumferential stressing along the rim of
indentation. Such indented stressing adding on the shearing slide