Optimization of the simulation of stress-assisted hydrogen diffusion for studies of hydrogen embrittlement of notched bars

Abstract

The stress-strain assisted hydrogen diffusion in metals under variable loading is concerned as a key element of elucidation of hydrogen embrittlement (HE). The suitability of simplified treatments of hydrogen diffusion in notched solids under monotonic loading is addressed comparing various 1D and 2D modeling approaches with the purpose to assess if generated approximate solutions can provide acceptable results along the diffusion depth towards prospective rupture sites, so that quite more expensive simulations may be eluded. For different geometry-and-loading cases, respective time-depth domains are revealed where certain simplified procedures can be fairly suitable to carry out calculations of metal hydrogenation for the purposes of HE analysis and control, while the choice of the optimum strategy for the stress-strain assisted diffusion simulations in notched members is case-and purpose-dependent. Key words: hydrogen embrittlement, hydrogen-assisted fracture, stress-strain assisted diffusion.Hydrogen embrittlement (HE) of metals has been the long-standing problem of physicochemical mechanics of materials [1][2][3][4]. The process of hydrogen-assisted fracture (HAF) of metals consists of several stages [4][5][6], one of which is hydrogen transport from the harsh environment towards certain locations within metal where hydrogen assisted damage takes place. Diverse studies [5][6][7][8] argued that hydrogen transport inside metals could proceed by two different mechanisms: via the movement by dislocations during continuing plastic straining and via the lattice diffusion affected by stressstrain state in the material. It has been repeatedly substantiated [5,[8][9][10]] that hydrogen diffusion in metal can be the dominating mode of hydrogen supply to prospective microstructural fracture sites under a broad range of circumstances. Then, evaluation of the stress-and-strain assisted hydrogen diffusion is of great interest for rationalization of HE manifestations and gaining the HAF predictive capability, e.g. via assessment of the local critical hydrogen concentrations in the fracture sites on the basis of dedicated experimentation, and afterwards, their use to predict the HAF susceptibility of structural parts under diverse loading-environmental conditions in service, as it has been suggested elsewhere, see, e.g. [11][12][13][14][15]. These tasks require efficient procedures of solution of specific boundary value problems of the stress-strain assisted diffusion.Concerning this in the general case non-linear and non-steady state coupled problem of mechanics and mass transfer, various analysis procedures have been developed including one-and two-dimensional (1D and 2D) linearised and nonlinear formulations for different cases of solid geometry and loading [11][12][13][15][16][17][18][19][20]. Obviously, the multidimensional approach is usually more realistic when irregularities of geometries and of associated stress-strain states in solids, e.g. when cracks and notches are present, can make diffusion trajectories to be...

Influence of Loading Rate on the Hydrogen-Assisted Micro-Damage in Bluntly Notched Samples of Pearlitic Steel

“…Local fracture event in the particular steel takes place at a certain locus (x) when hydrogen concentration, C, reaches a critical value which is itself time dependent: C(x, t) = C cr (σ(x, t)) [6,36]. According to the model of hydrogen diffusion assisted by the stress field in the material, Equation (1), two driving forces govern hydrogen diffusion towards prospective damage places: the gradient of hydrogen concentration and the gradient of hydrostatic stress.…”

“…Under such environmental conditions, hydrogen diffuses towards the internal regions of the material sample and can reach a critical concentration dependent on the stress-stain state at a given point and at a specific time [6].…”

Formation Criterion of Hydrogen-Induced Cracking in Steel Based on Fracture Mechanics

“…The equation of state for an ideal gas can be used to solve the problem of elasticity theory for the crack opening under gas pressure as well as the theory of gas diffusion into the crack cavity [12]. Due to the stress-strain concentration effect around the crack tip, the process of hydrogen diffusion in the crack is affected [13][14][15].…”

Influence of the Stress-Strain State on the Distribution of Hydrogen Concentration in the Process Zone

“…In [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16], the influence of the stress-strain state on the distribution of hydrogen in the process zone was investigated in various specific cases.…”