A cohesive zone framework for environmentally assisted fatigue

Journal article

We present a compelling finite element framework to model hydrogen assisted fatigue by means of a hydrogen- and cycle-dependent cohesive zone formulation. The model builds upon: (i) appropriate environmental boundary conditions, (ii) a coupled mechanical and hydrogen diffusion response, driven by chemical potential gradients, (iii) a mechanical behavior characterized by finite deformation J2 plasticity, (iv) a phenomenological trapping model, (v) an irreversible cohesive zone formulation for fatigue, grounded on continuum damage mechanics, and (vi) a traction-separation law dependent on hydrogen coverage calculated from first principles. The computations show that the present scheme appropriately captures the main experimental trends; namely, the sensitivity of fatigue crack growth rates to the loading frequency and the environment. The role of yield strength, work hardening, and constraint conditions in enhancing crack growth rates as a function of the frequency is thoroughly investigated. The results reveal the need to incorporate additional sources of stress elevation, such as gradient-enhanced dislocation hardening, to attain a quantitative agreement with the experiments.

Authors: del Busto, S; Betegón, C; Martínez-Pañeda, E

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Elsevier
• Journal: Engineering Fracture Mechanics
• Volume: 185
• Pages: 210-226
• Publication date: 2017-05-27
• Acceptance date: 2017-05-16
• DOI: 10.1016/j.engfracmech.2017.05.021
• EISSN: 1873-7315
• ISSN: 0013-7944
• Language: English
• Keywords: fatigue crack growth; cohesive zone models; hydrogen embrittlement; finite element analysis; hydrogen diffusion