13th International Conference on Fracture June 16–21, 2013, Beijing, China -9- martensitic-ferritic phase alloy. These results show that the crack propagation within the SNDFCO is controlled by the microstructure mechanics, and the crack propagation outside the SNDFCO is controlled by elastic-plastic or linear mechanics. SNDFCO size depends on transition of crack propagation from stage I to stage II. Figure 7. Stress intensity factor ranges at the front of SNDFCO in the martensite-ferritic steel. 5. Concluding remarks In the VHCF regime, strain localization will occur in all these materials. This leads to local plasticity exhaustion the formation of local “fine grain area”. High strain localization causes dislocation accumulation of very small strain during each cyclic loading and consequently and also increases the local hardness of the material. This can cause quasi-cleavage crack origin, and finally the formation of SNDFCO. The formation of SNDFCO is controlled by the microstructure mechanics. SNDFCO size depends on transition of crack propagation from stage I to stage II. The crack propagation outside the SNDFCO is controlled by elastic-plastic or linear mechanics. Acknowledgements This paper is published by permission of Sandvik Materials Technology. The author is also indebted to the co-authors in the reference list for their contribution and collaborations. References [1] H. Mughrabi, Fat. Fract. Eng. Mater Struct, 25 (2002) 755. [2] P. Lukas and L. Kunz, Fat. Fract. Eng. Mater Struct, 25 (2002) 747.
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