PSI - Issue 13

Y. Charles et al. / Procedia Structural Integrity 13 (2018) 896–901 Yann Charles / Structural Integrity Procedia 00 (2018) 000–000

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diffusion process: the more the plastic strain, the bigger the trap density, and the slower the transport process. 5 s 15 s 20 s 30 s 40 s

T 

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(b)

Fig. 3. Trap sites occupancy, considering (a) a transient or (b) an instantaneous trapping process, for different times. ¼ of the sample is removed for visualization purpose only. 3.2. Submodelling process To perform similar computations at the polycrystal scale, a submodelling scheme is used. A synthetic 0.2 3 mm 3 cubic polycrystal based on a Voronoi tessellation is defined, made of 100 grains, defined by the Neper software [21] and reconstructed in Abaqus CAE based on python scripts. This polycrystal is meshed using 16934 quadratic tetrahedron elements, with full integration. The polycrystal location is indicated by the arrow on Fig. 2. Boundary conditions are imposed on the polycrystal faces, and set using the Abaqus ‘submodelling’ conditions: displacement or diffusive hydrogen boundary conditions applied on each external nodes of this polycrystal are extracted from the macroscopic computations results, to transpose the whole bending process at that scale. Two computations have been performed, namely for kinetic and instantaneous trapping, with the same random crystallographic texture. The resulting the hydrogen fields heterogeneities are presented on Fig. 4.

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Fig. 4. Evolution of (a-b) diffusive hydrogen concentration and (c-d) trapped hydrogen coverage fields in the polycrystal. Comparison of transient ((a) and (c)) or instantaneous trapping ((b) and (d)). To exhibit the effect of crystalline plasticity, a simulation with the macroscopic isotropic behaviour has also been made on the same Voronoi tessellation to compare at each Gauss point both maximal principal stresses and hydrogen concentration. FFig. 5 shows the distributions, for the maximum principal stress and for the hydrogen concentrations,