  We present a new mechanistic, phase field-based formulation for predicting
hydrogen embrittlement. The multi-physics model developed incorporates, for the
first time, a Taylor-based dislocation model to resolve the mechanics of crack
tip deformation. This enables capturing the role of dislocation hardening
mechanisms in elevating the tensile stress, hydrogen concentration and
dislocation trap density within tens of microns ahead of the crack tip. The
constitutive strain gradient plasticity model employed is coupled to a phase
field formulation, to simulate the fracture process, and to a multi-trap
hydrogen transport model. The analysis of stationary and propagating cracks
reveals that the modelling framework presented is capable of adequately
capturing the sensitivity to the hydrogen concentration, the loading rate, the
material strength and the plastic length scale. In addition, model predictions
are compared to experimental data of notch tensile strength versus hydrogen
content on a high-strength steel; a very good agreement is attained. We define
and implement both atomistic-based and phenomenological hydrogen degradation
laws and discuss similarities, differences and implications for the development
of parameter-free hydrogen embrittlement models.
