which subsequently resulted in the detachment of more and larger
wear particles from the contact surfaces. Consequently, sharp
increase in IPCA values occurred at the commencement of each
excitation period (cf. Fig. 6a and c). However, the scanning of
cross-sectional profiles of the wear tracks on disk specimens
(Fig. 7) allowed the worn area to be calculated and plotted in
Fig. 8d, which further facilitated the calculation of: (i) the wear
volume for test L1 with steady load of 30 N to be approximately
32% less than that for test L2 with steady load of 35 N, and (ii) the
wear volume for test L3 with steady load of 40 N to be approximately
7% less than that for test L2 because of shorter running
time for test L3. Further correlation of the aforementioned to the
IPCA plots in Fig. 6 suggested that (a) the values of IPCA peaks
seemingly signified the rapid increase in wear rate at the time of
application of transient loading, which was followed with a rapid
reduction of wear corresponding to the attenuation process of the
DHE loading, and (b) the total wear volume of the impacted and
slid disks generally depended on the magnitude of average loading
level – although the high transient load tended to generate horizontally
dilated V-shaped groove features on the impacted surface,
it was only sustained in a number of very short-durations
between the friction pairs.
Morphological profiles (Fig. 7) and SEM images (Fig. 8) of the
disc wear track were analyzed by a TR200 profilometer and taken
by a JSM-6460 microscope. At higher spring-connecting load, the
peaky and dense asperities seemed to be distributed closer to the
center of the bottom region and within a narrow bound across the
cross-sectional area of wear track. Furthermore, the plowed
groove formed by wear track was normally wider and deeper with
smoother side walls in larger depth (cf. Fig. 7). As seen in Fig. 3c,
these phenomena could be resulted in by the two-level loading:
(i) transient high loading, and (ii) steady loading. The transient
high loading would be the main factor leading to abrasive wear
and causing the plowing grooves. SEM images (Fig. 8) illustrated
the appearance of some side flows of materials on the damaged
surface, as reported by Zhou et al. [21] and Kishway et al. [22].
Furthermore, sight of fatigue and built-up debris due to squeezing
was also observed on the disc wear track under DHE loading.
These observations suggested when the contact surfaces of disks
were subjected to DHE loading and under transient high loading,
plastic deformation firstly took place, and abrasive/plowing wear
to produce grooves with certain level of building-up of debris was
subsequently followed. The side and front flowing material in the
direction perpendicular to sliding was apt to detach from the disc
surface to form wear particles. In the subsequent DHE loading,
severer fatigue occurred and grooves on the track parallel to the
sliding direction were further widened (Fig. 8a and b). Hence,
experimental results under a spring-connecting load of 35 N tended
to lead to severest plastic deformation of contact surfaces and
highest contact pressure to indent the surface squeezing side way
of material from the wear track, subsequently sliding resulted in
those front/side flow material to detach. The detached material
was assessed and/or monitored using an OLVF system (Fig. 2). The
sharp increase of the IPCA values (Fig. 6) generally meant the
morphology of a wear track to be suffered from a dramatic change
in loading or of influentially detrimental setting condition(s).