Fig.11 Amplified morphologies of the CSZ, CPZ and IFZ under DP, P=50MPa, σe=400MPa;(a) CSZ; (b) CPZ; (c) IFZ.
Fig.12 shows the amplified morphologies of the CSZ, CPZ and IFZ under SP; It can be found that the crack source is located at the subsurface of fretting region from the CSZ, as shown in Fig.12(a). Similarly, the crack is tortuous, and multiple secondary cracks are around the main crack. In the CPZ, the steady propagation of cracks has appeared, and a number of small secondary cracks have also extended on the main crack, as shown in Fig.12(b). These secondary cracks have a small size due to the large propagation resistance. The IFZ is shown in Fig.12(c), the morphological features are significantly different from the IFZ under DP. Under SP, a radial cross section appeared in the IFZ. Radial cross-section is formed by the intersection of crack fronts when the cracks rapidly expand at different heights, and there are also obvious dimple patterns in the IFZ, as shown in Fig.13.