Modelling hydrogen dragging by mobile dislocations

International audienceIn metallic materials, hydrogen atoms diffuse trough lattice sites and can be trapped on defects, as vacancy or dislocations. These traps can move, leading to an induced mobility of the trapped hydrogen, modifying the hydrogen distribution in the sample. Hydrogen dragging by moving dislocation has been observed in various materials, leading to an increase of the apparent hydrogen diffusion coefficient. While numerous experimental investigations have been conducted in the 80’s on hydrogen transport by mobile dislocation, little attention has been paid to its modelling. Recently, a revised hydrogen transport and trapping model accounting for this phenomenon has been proposed, using an extra flux term.In the present work, an alternative revision is considered, based on trap mobility. Reaction-diffusion equations are used to describe the temporal evolution of the trapped hydrogen concentration and of the trap density. A transient trapping kinetics permits to link the diffusive and the trapped hydrogen. These equations are implemented in Abaqus finite element software by using User Subroutines.This allows to describe interactions between trap creation (by plasticity), trapping process, hydrogen diffusion and hydrogen dragging by mobile traps. By using a Small-Scale Yielding (SSY) configuration, and based on literature results, this approach is proven to be an extension of the classical transport and trapping equation as initially proposed by Sofronis and latter modified by Krom. A parametric study is then conducted to illustrate the acceleration of hydrogen transport due to hydrogen dragging by mobile dislocation and, especially, the effect of trapping kinetics, hydrogen diffusion, and mechanical loading rate on the hydrogen distribution

Effect of transient trapping on hydrogen transport near a blunting crack tip

International audienceThe paper revisits the way transient trapping is introduced in the literature based on the Sofronis and McMeeking model [1] of hydrogen transport. It is shown that the direct use of the improved formulation made by Krom et al. [2] for transient trapping may lead to nonphysical results of hydrogen concentration in case of an insulated system. The use of McNabb and Foster trapping kinetic equation is more relevant, and its ability to model both trap creation and kinetic trapping is investigated on a Small Scale Yielding configuration for the sake of comparison with a reference case from the literature. A parametric study is conducted, exhibiting differences with literature, and emphasizes on the significant effect of trapping kinetics on the hydrogen distribution

Integration of the role of dislocations in macroscopic hydrogen transport modelling

2023.05.31 09:35 - 10:05International audienc

Finite element simulation of hydrogen transport coupled with various thermomechanical loadings

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Finite Element Implementation of hydrogen transport and trapping models in metallic structure under complex thermomechanical loadings

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Numerical simulation of the transient hydrogen trapping process using an analytical approximation of the McNabb and Foster equation

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Numerical simulation of the transient hydrogen trapping process using an analytical approximation of the McNabb and Foster equation. Part 2: domain of validity

International audienceIn a previous study [1], a resolution scheme called Generalized Oriani's Approximation (GOA) was proposed to solve a transient transport and trapping problem in the Abaqus Finite Element software. This proposition was motivated by the convergence of the Finite Element problem linked to the estimation of several functions during the computation (and especially the dudt one). In this study, the GOA is shown to be able to provide an accurate estimation of the trapped concentration in transient trapping processes as soon as the time increment is small enough for two configurations: hydrogen in metals and water in polymers. An estimation of the induced error is given. The GOA approach is illustrated on a simple configuration with various trapping parameters. Last, the ability of Abaqus to converge while modeling a transient trapping and transport problem is analyzed considering several dudt: it is shown especially that its estimation based on the GOA allows the solver to efficiently converge toward the solution

Identification methodology of a rate-sensitive constitutive law with mean field and full field modeling approaches for polycrystalline materials

International audienceThe present paper deals with the consideration of the rate-sensitivity mechanical behavior of metallic materials, in the framework of mean field and full field homogenization approaches. We re-examine the possibility of describing properly this rate sensitivity with a simple and widely used power law expressed at the level of the slip system, and we propose a methodology to accelerate the identification of the global material constitutive law for Finite Element (FE) simulations. For such an aim, simulations of a tensile test are conducted, using a simple homogenization model (the Taylor one, used in a relaxed constraint form) and an FE code (Abaqus), both using the same single-crystal rate-dependent constitutive law. It is shown that, provided that the identification of this law is performed with care and well adapted to the examined case (rate-sensitive or insensitive materials, static and/or dynamic ranges), the simple power law can be used to simulate the macroscopic behavior of polycrystalline aggregates in a wide range of strain rate (including both static and dynamic regimes) and strain-rate sensitivity values (up the rate-insensitive limit)