13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- 2.3. Main text Fig. 3.a shows the fractured surface from tested specimen where it can be seen the notch, pre-fatigue crack, ductile crack extension. As the out-of-plane constraint is highest at the centre of the specimen, accordingly the delamination is most severe. Secondary delaminations are concentrated at the 1/4 thickness points from the free surfaces and similar to the main delamination [19, 20]. Fig. 3.b shows the P x CMOD curve from the unloading compliance method indicating the occurrence of delamination on the curve. It is possible to notice load-displacement curve a degree or register sequence failure. This feature is associated to the occurrence delamination phenomenon. Ductile Extension notch precrack a) b) 200 µm RD TD ND a) b) Figure 2. Microstructure of API X70 steel: a) three-dimensional view of the API X70 steel microstructure b) banded microstructure in the delamination region. Figure 3. a) Fractured surface of sample from the fracture toughness test showing the notch, pre-fatigue and ductile extension, b) PxCMOD curve from the unloading compliance method indicating the occurrence of delamination on the curve.
RkJQdWJsaXNoZXIy MjM0NDE=