The effect of hydrogen content and yield strength on the distribution of hydrogen in steel: a diffusion coupled micromechanical FEM study

In this study, we investigate the effect of the heterogeneous micromechanical stress fields resulting from the grain-scale anisotropy on the redistribution of hydrogen using a diffusion coupled crystal plasticity model. A representative volume element with periodic boundary conditions was used to model a synthetic microstructure. The effect of tensile loading, initial hydrogen content and yield strength on the redistribution of lattice (CL) and dislocation trapped (Cx) hydrogen was studied. It was found that the heterogeneous micromechanical stress fields resulted in the accumulation of both populations primarily at the grain boundaries. This shows that in addition to the well-known grain boundary trapping, the interplay of the heterogeneous micromechanical hydrostatic stresses and plastic strains contribute to the accumulation of hydrogen at the grain boundaries. Higher yield strength reduced the amount of Cx due to the resulting lower plastic deformation levels. On the other side, the resulting higher hydrostatic stresses increased the depletion of CL from the compressive regions and its diffusion toward the tensile ones. These regions with increased CL are expected to be potential damage initiation zones. This aligns with the observations that high-strength steels are more susceptible to hydrogen embrittlement than those with lower-strength.Ship Hydromechanics and StructuresTeam Poulumi Dey(OLD) MSE-7Engineering Thermodynamic

Efficient hydrogen storage in defective graphene and its mechanical stability: A combined density functional theory and molecular dynamics simulation study

A combined density functional theory and molecular dynamics approach is employed to study modifications of graphene at atomistic level for better H2 storage. The study reveals H2 desorption from hydrogenated defective graphene structure, V222, to be exothermic. H2 adsorption and desorption processes are found to be more reversible for V222 as compared to pristine graphene. Our study shows that V222 undergoes brittle fracture under tensile loading similar to the case of pristine graphene. The tensile strength of V222 shows slight reduction with respect to their pristine counterpart, which is attributed to the transition of sp2 to sp3-like hybridization. The study also shows that the V222 structure is mechanically more stable than the defective graphene structure without chemically adsorbed hydrogen atoms. The current fundamental study, thus, reveals the efficient recovery mechanism of adsorbed hydrogen from V222 and paves the way for the engineering of structural defects in graphene for H2 storage.(OLD) MSE-7Ship Hydromechanics and StructuresEngineering ThermodynamicsTeam Poulumi De