Abstract
During the initial stages of hydrogen environmentally assisted cracking (HEAC), including crack incubation, initiation and microstructurally short cracking, the geometrical configuration of the microstructure greatly influences the crack growth behaviour. Therefore, there is a big incentive to generate a model which can replicate intergranular HEAC at a microstructural scale. This report provides a general framework to implement a microstructural intergranular HEAC model by using a cohesive zone approach in Abaqus. The parameters of the phenomenological model were fitted by using in-situ synchrotron tomography observations of crack initiation and propagation during HEAC of AA7449-T7651. After fitting the parameters, the real HEAC behaviour of the aluminium alloy 7449-T7651 has been replicated accurately. Several characteristic HEAC features were achieved, including crack segmentation, preferential cracking along grain boundaries with a high resolved normal stress and cracks slowing down at grain boundary triple junctions. Comparisons with experimental observations show the suitability of this approach for the prognosis of crack initiation and propagation at a microstructural scale under HEAC conditions.
Highlights
Absorbed hydrogen can severely degrade the fracture resistance of high-strength alloys such as steel [1], titanium [2] and aluminium alloys [3,4]
It is much more likely that the Hydrogen environmentally assisted cracking (HEAC) rates for the tomography samples were limited by the surface-reaction rates
HEAC samples with nominally similar material properties subjected to equivalent loading and environmental conditions exhibit some form of statistical variability in the fracture behaviour
Summary
Absorbed hydrogen can severely degrade the fracture resistance of high-strength alloys such as steel [1], titanium [2] and aluminium alloys [3,4]. Hydrogen environmentally assisted cracking (HEAC) involves the synergistic action of mechanical stresses and surface chemical reactions [4]. For specific material–environment combinations, chemical reactions at the alloy surface produce atomic hydrogen which can be subsequently absorbed into the alloy matrix. Critical concentrations of atomic hydrogen can lead to subcritical crack growth at stress levels significantly below yield. This compromises the structural integrity of many alloys used for a broad range of engineering components. Many investigations have been performed to understand the hydrogen embrittlement mechanisms which degrade the fracture resistance of different alloys. This has led to the postulation of several mechanisms. The most popular mechanisms include: hydrogen enhanced decohesion (HEDE) [5], hydrogen enhanced localised plasticity (HELP) [6] and the adsorption-induced dislocation emission (AIDE) mechanism [7]
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