Sheet metal forming processes involve multi-axial strain paths. For the numerical simulation of such processes, an appropriate constitutive model that properly describes material behavior at large strain is required. For accurate and time-effective simulations, it is crucial to use plasticity models based on physics, as material macroscopic behavior is closely related to the evolution of the associated microstructures. Accordingly, a large strain work-hardening phenomenological model that incorporates the intragranular microstructure evolution through a dislocation density approach is proposed. The model is defined by a yield criterion and hardening laws that are all grain-size dependent. The classical Hill criterion in which grainsize dependency was introduced is proposed. Hardening laws are given by a combination of kinematic and isotropic contributions that respectively take into account the evolution with strain of cell blocks formed by geometrically necessary boundaries (GNBs) and individual dislocation cells delineated by incidental dislocation boundaries within cell blocks (IDBs). On the one hand, IDBs evolution contribution is described by a modified Rauch et al. isotropic model, which is able to describe work-hardening stagnation and work-softening. On the other hand, GNBs evolution contribution is described by a grain-size dependent tensorial backstress expression proposed by Aouafi et al. [2007] to describe the plastic anisotropy and Bauschinger effect. Moreover, the proposed model aims to accurately predict steel behavior through an innovative approach by only changing few "simply measurable" microstructure data (e.g. chemical composition, grain size…). The predictive capabilities of the model are assessed for interstitial free (IF) and dual phase (DP) steels with grain sizes varying respectively in the 8-40 µm and 1-10 µm value range. Different loading paths are analyzed, namely the uniaxial tensile test, reversal simple shear and orthogonal tests.

Tel: +33 1 45 68 18 35 2 18 Abstract 22 The links between climate variability, depicted by times series of oceanic indices, and changes in 23 total water and groundwater storage are investigated across nine large aquifer basins of the 24 African continent. The Gravity Recovery and Climate Experiment (GRACE) mission's 25 observations represent a remarkable tool that can provide insight into the dynamics of terrestrial 26 hydrology in areas where direct in-situ observations are limited. In order to evaluate the impact 27 of inter-annual and multi-decadal climate variability on groundwater resources, this study 28 assesses the relationship between synoptic controls on climate and total water storage estimates 29 from (i) GRACE from 2002 to 2013 and (ii) a two-variables climate-driven model that is able to 30 reconstruct past storage changes from 1982 to 2011. The estimates are then compared to time 31 series of groundwater levels to show the extent to which total water storage covaries with 32 groundwater storage. Results indicate that rainfall patterns associated with the El Niño Southern 33 Oscillation (ENSO) are the main driver of inter-annual groundwater storage changes, whereas 34 the Atlantic Multi-Decadal Oscillation (AMO) plays a significant role in decadal to multi-35 decadal variability. The combined effect of ENSO and AMO could trigger significant changes in 36 recharge to the aquifers and groundwater storage, in particular in the Sahel. These findings could 37 3 help decision-makers prepare more effective climate-change adaptation plans at both national 38 and transboundary levels. 39 40 NOTE TO COPYEDITOR -PLEASE INSERT THE FOLLOWING AS A FIRST-PAGE 41 FOOTNOTE: 42This article is part of the topical collection "Determining groundwater sustainability from long-43 term piezometry in Sub-Saharan Africa" 44 45 46 47