A dislocation-based constitutive model for hydrogen—deformation interactions and a study of hydrogen-induced intergranular fracture

This thesis presents two models of the effect of hydrogen on materials. Both models are intended to link experimental observations of material microstructure with macroscopically observable results. The first model creates a continuum, rate dependent plasticity model that incorporates the effect of hydrogen on dislocation generation, motion, and annihilation; the transient motion of hydrogen through the material is considered in a complete thermodynamic framework which determines the chemical potential of the diffusing hydrogen. The behavior of several austenitic stainless steels is considered, both in comparison with uniaxial tension experiments and in comparison with a rate independent model of plastic deformation ahead of a crack tip. The second model is a framework for describing the effect of hydrogen on a weakest-link statistical fracture model by combining the two hydrogen embrittlement mechanisms usually thought of as mutually exclusive, hydrogen enhanced localized plasticity, and hydrogen induced decohesion. The model is developed, implemented in a finite element analysis program, and verified against experiment and previous statistical fracture models. The model is used to predict the failure load of a high strength, low alloy steel, and sets a basis for the prognosis of structural steel components in a hydrogen environment