A new experimental method to investigate hydrogen assisted cracking is presented in this paper. By combining electrochemical pre-charging, fracture mechanics and neutron imaging it is possible to get large experimental data which can give insight into the local fracture process zone. Furthermore, it can be used to calibrate FEM-models which considers crack propagation, embrittlement, and H diffusion from a moving stress field.
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In the current work, using tensile tests, we evaluate the hydrogen embrittlement behavior of a 1.5 GPa dual-phase (DP) steel consisting of ~75% martensite. Contrary to previous studies of DP steel with ultimate tensile strength (UTS) ≤1.2 GPa, a predominant brittle fracture is observed in the DP steel in the absence of hydrogen. Conventionally, in the absence of hydrogen, ferrite is reported to arrest cracks, resulting in a ductile fracture. However, ferrite undergoes {100} brittle cleavage cracking. Furthermore, the morphology of the martensite crack is found to have an influence on ferrite {100} cleavage cracking. The micro-mechanisms are presented in detail. Subsequently, we investigated the effect of hydrogen on the degradation of tensile properties. Hydrogen caused a significant deterioration of UTS, from 1.5 GPa to 0.9 GPa. The damage mechanisms of hydrogen-induced fracture are discussed in detail.
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Spent nuclear fuels are stored after their use in reactors. Dry storage can favor the appearance in the fuel rod cladding of a mechanical-chemical phenomenon referred to as Delayed Hydride Cracking (DHC). DHC is divided into three iterative steps: (i) diffusion of hydrogen in solid solution; (ii) precipitation of this hydrogen into hydrides; (iii) brittle fracture of hydrides. To assess the risk of occurrence of this phenomenon, the fracture toughness is determined by calculating the stress intensity factor below which DHC is not observed (KIDHC) based on an experimental procedure and a numerical model.
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