Fig. 8 Crack in as-welded SZ
The SZ sample with a thickness of 4 mm under a maximum load of 315MPa is
show in Fig. 9 (a). It also had an instantaneous elongation during
fatigue test. The cross section of the SZ sample with a thickness of 4
mm is shown in Fig. 9 (b). It was observed that the crack initiated and
propagated in the SZ region. The crack initiation region is marked in
Fig. 9 (c). The crack initiation relied on the debonding of lamellar
structure as shown in Fig. 9 (d) and (e). The instantaneous crack
propagation is indicated in Fig. 9 (c), (d), and (e) which contributed
to the instantaneous elongation during fatigue test.