Fig.6 Morphology of fretting region; (a) P=50 MPa, (b) P=150 MPa, (c)
P=250 MPa, DP, σe =400MPa;(d) P=150MPa, SP,
σe= 400MPa.
Under DP, when the contact stress is 50 MPa, which is a relatively low
value, the amount of deformation caused by the fretting of the sample
and the fretting pad is limited, the relative displacement is large, and
the fretting process is nearly in the slip regime, as shown in Fig.6
(a), although there are a large number of scratch marks and micro
abrasive debris, the scratch marks are shallow, and the deformation and
damage in the fretting region are not very severe; With the increase of
contact stress, the adhesion between the specimen and the fretting pad
is too close to reduce the relative displacement. Compared with low
contact stress, the fretting region has deeper scratch marks, and the
surface of the fretting region is severely worn. When the contact stress
is 150 MPa, as shown in Fig.6 (b), a partial stick area has appeared in
the center of the fretting region and there is an obvious furrow
phenomenon in the slip area; When the contact stress is further
increased to 250 MPa, the fretting region is then basically in an stick
state, as shown in Fig.6 (c), there are no furrows due to sliding. Due
to lower contact stress, the relative displacement in Fig.6 (b) is
larger compared to Fig.6 (c). During the fretting fatigue process, part
of the material in the adhesion area tears due to the large relative
displacement. As a result, the surface material of the fretting region
is torn in Fig.6(b), and a large number of pits are generated. By
compared with Fig.6 (c), Fig.6 (b) is more severely damaged due to the
severe tearing of the surface material and the coupling effect with the
fretting wear.
Under SP, as the contact stress increases, the surface wear of the
fretting zone also becomes more serious. Compared with the morphology of
the fretting zone of the DP, due to the larger amount of strain under
the same conditions under SP, there is a relatively large amount of
relative displacement. Therefore, under the same contact stress, the
adhesion of SP is lower, and surface tearing is weaker than that of the
DP. When the contact stress is 150 MPa, stick and slip regions can also
be observed on the surface of the fretting zone. There are more abrasive
debris in the slip region and a small amount of surface material tear in
the stick region.