A cohesive zone framework for environmentally assisted fatigue

Susana del Busto, Covadonga Betegón, Emilio Martínez Pañeda

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    Abstract

    We present a compelling finite element framework to model hydrogen assisted fatigue by means of a hydrogen- and cycle-dependent cohesive zone formulation. The model builds upon: (i) appropriate environmental boundary conditions, (ii) a coupled mechanical and hydrogen diffusion response, driven by chemical potential gradients, (iii) a mechanical behavior characterized by finite deformation J2 plasticity, (iv) a phenomenological trapping model, (v) an irreversible cohesive zone formulation for fatigue, grounded on continuum damage mechanics, and (vi) a traction-separation law dependent on hydrogen coverage calculated from first principles. The computations show that the present scheme appropriately captures the main experimental trends; namely, the sensitivity of fatigue crack growth rates to the loading frequency and the environment. The role of yield strength, work hardening, and constraint conditions in enhancing crack growth rates as a function of the frequency is thoroughly investigated. The results reveal the need to incorporate additional sources of stress elevation, such as gradient-enhanced dislocation hardening, to attain a quantitative agreement with the experiments.
    Original languageEnglish
    JournalEngineering Fracture Mechanics
    Volume185
    Pages (from-to)210-226
    ISSN0013-7944
    DOIs
    Publication statusPublished - 2017

    Keywords

    • Hydrogen embrittlement
    • Cohesive zone models
    • Hydrogen diffusion
    • Finite element analysis
    • Fatigue crack growth

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