3.4 Fracture behavior of SZs
The fractured samples of BM (315 MPa) and as-welded SZ (210 MPa) are
shown in Fig. 7 (a) and (d). During fatigue test, the load of the two
samples had an instantaneous elongation larger than 50 μm. However, the
samples did not fracture. The cross section of the BM sample is shown in
Fig. 7 (b) and (c). The crack initiated on the surface. The
instantaneous crack propagation contributed to the instantaneous
elongation. In Fig. 7 (c), the straight crack was the instantaneously
propagated crack. The crack in the as-welded SZ sample is shown in Fig.
7 (e). It was observed that the crack initiated in the SZ near the
PAZ/BM interface.