Fig.10 Micro fracture morphology under DP, P=50MPa, σe=400MPa.
The amplified morphologies of areas I, II, and III in Fig.10 are shown
in Fig.11;
There are obvious cracks in the CSZ, and due to the combined effect of
axial stress and torsional stress, the cracks are tortuous, as shown in
Fig.11(a). In addition to the main crack, there are multiple secondary
cracks around the main crack. The CPZ is between the CSZ and IFZ, and
fatigue striation is the main feature due to the repeated open and
closure of the cracks, therefore many grooves are formed here, as shown
in Fig.11(b). The IFZ is formed due to the instability propagation of
the crack. Since the formation of this characteristic region is
instantaneous, stairs are often formed along the crack propagation
direction on the fracture surface, as shown in Fig.11(c).