Multiscale Modeling of Hydrogen Embrittlement for Multiphase Material

摘要

ABSTRACTHydrogen Embrittlement (HE) is a very common failure mechanism induced crackpropagation in materials that are utilized in oil and gas industry structural componentsand equipment. Considering the prediction of HE behavior, which is suggestedin this study, is one technique of monitoring HE of equipment in service. Therefore,multi-scale constitutive models that account for the failure in polycrystalline BodyCentered Cubic (BCC) materials due to hydrogen embrittlement are developed. Thepolycrystalline material is modeled as two-phase materials consisting of a grain interior(GI) phase and a grain boundary (GB) phase. In the rst part of this work, thehydrogen concentration in the GI (Cgi) and the GB (Cgb) as well as the hydrogen distributionin each phase, were calculated and modeled by using kinetic regime-A andC, respectively. In the second part of this work, this dissertation captures the adversee ects of hydrogen concentration, in each phase, in micro/meso and macro-scale modelson the mechanical behavior of steel; e.g. tensile strength and critical porosity. Themodels predict the damage mechanisms and the reduction in the ultimate strengthpro le of a notched, round bar under tension for di erent hydrogen concentrations asobserved in the experimental data available in the literature for steels. Moreover, thestudy outcomes are supported by the experimental data of the Fractography and HEindices investigation. In addition to the aforementioned continuum model, this workemploys the Molecular Dynamics (MD) simulations to provide information regarding45bond formulation and breaking. The MD analyses are conducted for both single grainand polycrystalline BCC iron with di erent amounts of hydrogen and di erent size ofnano-voids. The simulations show that the hydrogen atoms could form the transmissionin materials con guration from BCC to FCC (Face Centered Cubic) and HCP(Hexagonal Close Packed). They also suggest the preferred sites of hydrogen for eachcase. The connections between the results for di erent scales (nano, micro/meso andmacro-scale) were suggested in this dissertation and show good agreements betweenthem. We nally conclude that hydrogen-induced steel fracture and the change offracture mode are caused by the suppression of dislocation emission at crack tip andchanging in the material structure due to accumulation of hydrogen, which is drivenby the stress elds. This causes the brittle fracture to occur as inter-granular in theGB and trans-granular in the GI.