Micromechanical and macromechanical effects in grain scale polycrystal plasticity experimentation and simulation

A polycrystalline aluminum sample with a quasi-2D single layer of coarse gr ains is plastically deformed in a channel die plane strain set-up at ambien t temperature and low strain rate. The microtexture of the specimen is dete rmined by analysis of electron back scattering patterns obtained in a scann ing electron microscope. The spatial distribution of the plastic microstrai ns at the sample surface is determined by measurement of the 3D plastic dis placement field using a photogrametric pixel-based pattern recognition algo rithm. The initial microtexture is mapped onto a finite element mesh. Conti nuum and crystal plasticity finite element simulations are conducted using boundary conditions which approximate those of the channel die experiments. The experimental and simulation data are analyzed with respect to macromec hanical and micromechanical effects on grain-scale plastic heterogeneity. T he most important contributions among these are the macroscopic strain prof ile (friction), the kinematic hardness of the crystals (individual orientat ion factors), the interaction with neighbor grain, and grain boundary effec ts, Crystallographic analysis of the data reveals two important points. Fir st, the macroscopic plastic strain path is not completely altered by the cr ystallographic texture, but modulated following soft crystals and avoiding hard crystals. Second, grain-scale mechanisms are strongly superimposed by effects arising from the macroscopic profile of strain, The identification of genuine interaction mechanisms at this scale therefore requires procedur es to filter out macroscopically induced strain gradients. As an analysis t ool, the paper introduces a micromechanical Taylor factor, which differs fr om the macromechanical Taylor factor by the fact that crystal shear is norm alized by the local rather than the global von Mises strain. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.