Samuel Forest, Mines ParisTech CNRS, France
Crystal plasticity of polycrystalline aggregates under cyclic loading : 3D experiments and computations, size effects and fatigue cracking
BIO: Samuel Forest, 48 year old, is CNRS Research Director at Centre des Materiaux Mines ParisTech and continuum mechanics professor at Mines ParisTech. He is working on mechanics of materials focusing on crystal plasticity modelling and mechanics of generalized continua. He has been the PhD advisor of 35 PhD students on these scientific topics, each of them corresponding to a contract with industrial partners (SAFRAN, RENAULT, EDF, Arcelor-Mittal, Michelin, CEA, EDF, etc.) or with the state and EU. He got the Bronze and Siver medals of CNRS INSIS and the Plumey prize of the Academie des Sciences. He published more than 120 papers in peer-reviewed international journals. He is associate editor of 5 international journals including Int. J. Solids Structures and Phil. Mag. He is leading the CNRS Federation of Mechanics labs in the Paris Region, promoting cooperation between 14 mechanics labs in the Paris region.
Abstract: The mustiscale approach to the plasticity and fracture of crystalline metals and alloys is based nowadays on large scale simulations of representative volume elements of polycrystalline aggregates. The deformation modes inside the individual grains are described by continuum crystal plasticity models involving dislocation densities and suitable interface conditions at grain boundaries . Recent 3D experiments performed under synchrotron radiation at ESRF reveal the plastic events in the grains like slip banding and development of crystal lattice curvature . These results are compared to finite element simulations involving millions of degrees of freedom for a detailed description of intragranular mechanical fields. The cyclic loading of such samples leads to the initiation and propagation of fatigue cracks going through the grains and stopping at or overcoming grain boundaries. This damage process can also be observed by 3D images and simulated by corresponding finite element simulations .
The constitutive laws for crystal plasticity and damage incorporate gradient plasticity and gradient damage contributions in order to account for size effects in the material behaviour [3,4,5]. These effects include the size-dependent piling-up of dislocations during cyclic loading and the description of finite width localization bands and cracks. The provided examples deal with cubic aluminum, titanium and nickel-based alloys.
 S. Forest, Some links between Cosserat, strain gradient crystal plasticity and the statistical theory of dislocations , Philosophical Magazine, vol. 88, pp. 3549-3563, 2008. doi:10.1080/14786430802154815  H. Proudhon, J. Li, P. Reischig, N. Gueninchault, S. Forest and W. Ludwig, Coupling Diffraction Contrast Tomography with the Finite Element Method, Advanced Engineering Materials, vol. 18, pp. 903-912, 2016. doi:10.1002/adem.201500414  H. Proudhon, J. Li, F. Wang, A. Roos, V. Chiaruttini and S. Forest, 3D simulation of short fatigue crack propagation by finite element crystal plasticity and remeshing, International Journal of Fatigue, vol. 82, pp. 238-246, 2016. doi:10.1016/j.ijfatigue.2015.05.022  S. Forest and N. Guéninchault, Inspection of free energy functions in gradient crystal plasticity, Acta Mechanica Sinica, vol. 29, pp. 763-772, 2013. doi:10.1007/s10409-013-0088-0  S. Wulfinghoff, S. Forest and T. Böhlke, Strain gradient plasticity modelling of the cyclic behaviour of laminate microstructures, Journal of the Mechanics and Physics of Solids, vol. 79, pp. 1-20, 2015. doi:10.1016/j.jmps.2015.02.008  O. Aslan, S. Quilici and S. Forest, Numerical Modeling of Fatigue Crack Growth in Single Crystals Based on Microdamage Theory , International Journal of Damage Mechanics, vol. 20, pp. 681-705, 2011. doi:10.1177/1056789510395738