Phase field modelling of hydrogen assisted fracture and fatigue

Talk delivered at the 2021 Annual Conference of the UK Association for Computational Mechanics (UKACM 2021).

PHASE FIELD MODELLING OF HYDROGEN ASSISTED FRACTURE AND FATIGUE
Emilio Martínez-Pañeda
Lecturer (US Asst. Professor) & 1851 Research Fellow. Imperial College London
https://www.empaneda.com/
https://www.imperial.ac.uk/mechanics-...

ABSTRACT
Metallic materials experience a dramatic reduction in ductility and fracture toughness in the presence of hydrogen - of up to 90%. This phenomenon, so-called hydrogen embrittlement, is pervasive across the transport, defence, energy and construction sectors, due to the ubiquitousness of hydrogen and the higher susceptibility of modern, high-strength alloys. Moreover, hydrogen embrittlement is one of the biggest threats to the future of hydrogen as a clean energy carrier. The development of models for predicting hydrogen assisted failures has long been considered a daunting task. Hydrogen embrittlement is a complex multi-scale and multi-physics phenomenon that is still not fully understood. From the computational side, there is a need for coupled deformation-diffusion-fracture models that can capture the underlying micro-scale physical mechanisms while delivering predictions over large time and space scales. In this talk, I will present our efforts in developing a computational framework that can achieve such elusive goal. Our model contains the following ingredients. First, to accurately characterise crack tip stresses at
the critical distance for hydrogen cracking, a strain gradient plasticity model is used for the constitutive behaviour [1, 2]. Secondly, hydrogen transport is captured, including both the influence of microstructural traps and suitable boundary conditions to resolve the electrochemical-diffusion
interface [3]. Thirdly, an atomistically-inspired phase field fracture (and fatigue) formulation is used to capture the nucleation and propagation of cracks [4, 5]. The predictions delivered by the model reveal an unprecedented agreement with laboratory experiments. Moreover, the model is employed to predict hydrogen assisted failures in large scale components, opening the door for the use of Virtual Testing in hydrogen-sensitive applications for the first time.

Keywords: Hydrogen embrittlement; Phase field fracture; Finite element analysis

References
[1] E. Martínez-Pañeda, V.S. Deshpande, C.F. Niordson, N.A. Fleck (2019): The role of plastic strain gradients in the crack growth resistance of metals. J. Mech. Phys. Solids 126, 136-150.
[2] P.K. Kristensen, C.F. Niordson, E. Martínez-Pañeda (2020): A phase field model for elastic gradient-plastic solids undergoing hydrogen embrittlement. J. Mech. Phys. Solids 143, 104093.
[3] E. Martínez-Pañeda, A. Díaz, L. Wright, A. Turnbull (2020): Generalised boundary conditions for hydrogen transport at crack tips. Corros. Sci. 173, 108698.
[4] E. Martínez-Pañeda, A. Golahmar, C.F. Niordson (2018): A phase field formulation for hydrogen assisted cracking. Comput. Methods Appl. Mech. Eng. 342, 742-761.
[5] P.K. Kristensen, C.F. Niordson, E. Martínez-Pañeda (2020): Applications of phase field fracture in modelling hydrogen assisted failures. Theor. Appl. Fract. Mech. 110, 102837.