  A new model is presented to predict hydrogen-assisted fatigue. The model
combines a phase field description of fracture and fatigue, stress-assisted
hydrogen diffusion, and a toughness degradation formulation with cyclic and
hydrogen contributions. Hydrogen-assisted fatigue crack growth predictions
exhibit an excellent agreement with experiments over all the scenarios
considered, spanning multiple load ratios, H2 pressures and loading
frequencies. These are obtained without any calibration with hydrogen-assisted
fatigue data, taking as input only mechanical and hydrogen transport material
properties, the material's fatigue characteristics (from a single test in air),
and the sensitivity of fracture toughness to hydrogen content. Furthermore, the
model is used to determine: (i) what are suitable test loading frequencies to
obtain conservative data, and (ii) the underestimation made when not
pre-charging samples. The model can handle both laboratory specimens and
large-scale engineering components, enabling the Virtual Testing paradigm in
infrastructure exposed to hydrogen environments and cyclic loading.
