On the suitability of slow strain rate tensile testing for assessing hydrogen embrittlement susceptibility

Abstract

The onset of sub-critical crack growth during slow strain rate tensile testing (SSRT) is assessed through a combined experimental and modeling approach. A systematic comparison of the extent of intergranular fracture and expected hydrogen ingress suggests that hydrogen diffusion alone is insufficient to explain the intergranular fracture depths observed after SSRT experiments in a Ni-Cu superalloy. Simulations of these experiments using a new phase field formulation indicate that crack initiation occurs as low as 40% of the time to failure. The implications of such sub-critical crack growth on the validity and interpretation of SSRT metrics are then explored.

Applications of phase field fracture in modelling hydrogen assisted failures

“…where χ is a hydrogen damage coefficient, a material parameter that can be estimated by calibrating with experiments [18] or inferred from atomistic calculations [14]. We adopt the latter approach and assume a value of χ = 0.89 throughout our calculations, this magnitude provides the best fit to atomistic calculations on iron [14,42].…”

“…Martínez-Pañeda et al [14] have recently extended the phase field fracture method to predict hydrogen assisted failures and the approach has quickly gained popularity as a framework for incorporating various hydrogen embrittlement models [15][16][17][18][19][20]. The main experimental trends have been captured and advanced fracture features such as crack merging, nucleation from arbitrary sites and branching are predicted without convergence problems or the need for remeshing.…”

A phase field model for elastic-gradient-plastic solids undergoing hydrogen embrittlement

“…Hydrogen atoms enter the material, diffuse through the crystal lattice and are attracted to regions of high hydrostatic stress, where damage occurs through mechanisms that are still being debated (Harris et al, 2018;Lynch, 2019;Robertson et al, 2015;Shishvan et al, 2020;Tehranchi and Curtin, 2019;Yu et al, 2019). By accounting for the degradation of the fracture energy with hydrogen content, multi-physics phase field fracture models capture the trends shown in the experiments (see, e.g., Martínez-Pañeda et al, 2020), while establishing a computational framework capable of dealing with the complex scenarios relevant to engineering practice. Phase field models are bringing a paradigm change to the hydrogen assisted cracking commu-nity, where modeling efforts were focused on discrete methods.…”

Effect of Natural Aging on the Stress Corrosion Cracking Behavior of A201-T7 Aluminum Alloy

“…Extending the aging time further had no additional benefit. We would also like to remind the reader that the slow strain rate testing (SSRT) might not be suitable to determine the SCC behavior of alloys in the latest research due to the sub-critical cracking and to invalidate the SSRT results [ 25 , 26 ].…”