Development of plastic strain heterogeneities on cold-rolled aluminium alloys during in situ shear tests inside an SEM

Shear tests inside an SEM were performed to study plastic localisation phenomena on cold rolled aluminium alloys 1200, 3004 and 5182. Strain distribution was obtained by image analysis of micro-grids deposited on the sample surface prior to the tests. Macroscopic shear bands initiate from the samples ends and close to the grips after the load maximum. Their spreading through the whole sample occurs by nucleation and propagation of microscopic shear bands, and depends on the alloy and on the direction of shear. The link between the different scales are discussed, from the dislocation microstructures to the rnacroscopic scale. The global boundary conditions govern the distribution of spatial heterogeneities, but the local hardening behaviour controls the localisation sharpness

Piégeage transitoire de l'hydrogène dans les matériaux métalliques

National audienc

Effect of temper rolling on the mechanical behaviour of thin steel sheets under monotonous and reverse simple shear tests

International audienceTemper rolling is performed on ferritic steel thin sheets after cold rolling and annealing, in order to increase the material strength and to obtain the correct roughness and a good flatness. However, depending on the thickness reduction and on the material composition, this operation may induce specific strain-path changes effects during subsequent forming processes. This paper focuses on the analysis of the hardening behaviour during simple shear tests. The results are discussed in relation with the material compositions, the initial anisotropy and the macroscopic strain heterogeneities

Numerical simulation by finite element modelling of diffusion and transient hydrogen trapping processes in plasma facing components

International audienceIn order to simulate hydrogen charging and discharging cycles of mechanically loaded structures full 3D Macroscopic Rate Equation (MRE) modelling is proposed based on a finite element method (FEM). The model, implemented in the 3DS Abaqus software, uses a generalized transport equation, which accounts for mechanical fields, hydrogen transport and trapping, and their evolution with time. The influence of a-priori known thermal field has also been included. To ensure the solution convergence and the numerical stability, the trapping kinetic is introduced by using an approximation of the analytical solution the McNabb and Foster equation. Comparisons with a relevant 1D MRE code and with thermal programmed desorption (TPD) experimental results are performed on a 1D configuration to validate the model. Next, the model is used to simulate the tritium diffusion and trapping in a 2D geometry of interest in the upper plug of ITER tokamak, and results of tritium inventory are compared with an equivalent 1D calculation

Phenomenological Analysis of the Kinematic Hardening of HSLA and IF Steels Using Reverse Simple Shear Tests

International audienc

Contribution des champs mécaniques à l'échelle du polycristal à l'amorçage de fissures de corrosion sous contrainte

National audienc

Experimental and numerical analysis of the Lüders phenomenon in simple shear

International audienceThe Lüders phenomenon is investigated in a low carbon ferritic steel under simple shear loading. Tensile and shear experiments are carried out associated with digital image correlation (DIC) measurements of the local strain field. An elastoviscoplastic constitutive law is identified with special attention paid to the choice of the equivalent stress measure in the yield function. It is then used to simulate the shear experiment using finite element analyses. Several mesh types and sizes are used to illustrate some mesh sensitivity observed in the finite element results. A regularized model based on strain gradient plasticity is then proposed to ensure fully mesh insensitive simulations and properly describe the finite thickness of the Lüders band front. The additional internal length introduced in the regularized model is identified from the DIC strain measurements. Finally, the boundary conditions best–suited for an accurate description of the shear experiment are discussed

Effet du trajet de chargement sur l'amorçage de fissures de corrosion sous contrainte dans les aciers inoxydables écrouis

National audienc

Effect of microstructure on the diffusion property of polycrystals

International audienc

Effect of loading mode on blistering in iron submitted to plastic prestrain before hydrogen cathodic charging

International audienceTensile tests and simple shear tests have been performed on Armco iron sheets before hydrogen cathodic charging, in order to study the effect of loading mode on blistering of plastically prestrained samples. The experimental results from surfometry and image analysis show the decrease of the blisters size with prestrain increase, and quantitative differences between tensile or shear prestrain are exhibited. Phenomenological modeling of blister initiation is proposed, based on void expansion increase under internal pressure, and considering both plastic strain and pores as traps during hydrogen transport. Finite element simulations of material expansion due to hydrogen induced void growth lead to qualitative agreement with experimental tendencies