Phase field modelling of hydrogen-assisted fatigue

Phase field fracture modelling has emerged as a promising and robust variational approach to capture complex cracking phenomena, such as nucleation from multiple sites or the coalescence of numerous defects, in general geometries [1]. The method has very recently been extended to fatigue damage[2], showing that features such as S-N curves or fatigue crack growth rate curves can be predicted without little prior assumptions. However, most structural failures often occur due to the synergistic effects of fatigue damage and environment. One example is known as hydrogen embrittlement [3].Hydrogen is ubiquitous and it significantly reduces the ductility, strength, toughness and fatigue crack growth resistance of metallic materials.

In this work, we present the first multi-physics phase field-based model for hydrogen-assisted fatigue. The modelling framework builds upon the success of recent phase field fracture formulation for hydrogen assisted cracking under static loads [4]. The model is employed to obtain fundamental insight and provide a mechanistic rationale for the trends observed in fatigue experiments in hydrogenous environments. We show that the modelling framework presented can be used to predict the impact of the environment on fatigue crack growth rate curves and S-N curves, paving the way for optimising design and maintenance through Virtual Testing, as well as planning efficient and targeted experimental campaigns.