Chemical Equilibrium Fracture Mechanics—Hydrogen Embrittlement Application

Chemical Equilibrium Fracture Mechanics (CEFM) studies the effect of chemical reactions and phase transformations on crack-tip fields and material fracture toughness under chemical equilibrium. An important CEFM direction is hydrogen-induced embrittlement of alloys, due to several industrial applications, including those within the industrial value chain of hydrogen that is under development, which, according to European and international policies, are expected to contribute significantly to the replacement of fossil fuels by renewable energy sources. In the present study, the effect of hydrogen on the crack-tip fields of hydride- and non-hydride-forming alloys is examined. The crack-tip stress and hydrogen concentration distributions are derived under hydrogen chemical equilibrium, which is approached by considering the coupling of the operating physical mechanisms. In all cases, analytic relations are derived, thus facilitating integrity assessments, i.e., without the need to rely on complicated numerical methods, expected to lead to the development of respective tools in industrial applications. It is shown that, in the case of hydride precipitation, there are significant deviations from the K, HRR, and Prandtl fields, and, thus, the well-known approaches of Linear Elastic Fracture Mechanics (LEFM) and Elastic–Plastic Fracture Mechanics (EPFM) need to be accordingly modified/extended.