13th International Conference on Fracture June 16–21, 2013, Beijing, China -7- Figure 7 exhibits the fracture morphology on the etched cross sections just beneath the fracture surfaces. In the non-charged specimens (left-hand side), most of the graphites coalesced with each other leading to a typical ductile behavior, regardless of CHS. On the other hand, in the hydrogen-charged specimens (right-hand side), the fracture process was accompanied with the interconnecting cracks between adjacent graphites. This tendency appeared prominently at lower CHS (cf. Figure 7(c)). Figure 8 illustrates two distinct fracture modes in the non-charged and the hydrogen-charged specimens, which were based on the observation of fracture processes. As illustrated for the hydrogen-charged specimen, in the presence of the interconnecting cracks between graphites, less graphite nodules tend to appear on the fracture surface. (a) Ductile dimple fracture (Non-charged specimen) (b) Cracking in local hydrogen gas environment (Hydrogen-charged specimen) Figure 8. Two typical fracture processes in the non-charged and the hydrogen-charged specimens
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