Study of 3-D stress development in parent and twin pairs of a hexagonal close-packed polycrystal: Part II - crystal plasticity finite element modeling

Stress heterogeneity within each individual grain of polycrystalline Zircaloy-2 is studied using a crystal plasticity finite element (CPFE) model. For this purpose, the weighted Voronoi tessellation method is used to construct 3D geometries of more than 2600 grains based on their center-of-mass positions and volumes as measured by three-dimensional X-ray diffraction (3DXRD) microscopy. The constructed microstructure is meshed with different element densities and for different numbers of grains. Then a selected group of twin and parent pairs are studied. It is shown that the measured average stress for each grain from the 3DXRD experiment is within the stress variation zone of the grain modeled in the CPFE simulation. Also, the CPFE average stress calculation for each grain is in good agreement with the measured average stress values. It is shown that upon considering the stress variations within each grain, stresses in the parent and twin are quite different if they are plotted in the global coordinate system. However, if the stress tensor is rotated into the local coordinate system of the twin habit plane, all the stress components averaged over the presented population are close, except for the shear acting on the twin plane and the transverse stress. This result is significant as it provides information needed to model such parent-twin interactions in crystal plasticity codes. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

利用晶体塑性有限元（CPFE）模型研究了多晶锆 - 2中每个晶粒内的应力不均匀性。为此，采用加权沃罗诺伊剖分法，根据三维X射线衍射（3DXRD）显微镜测量的质心位置和体积构建了2600多个晶粒的三维几何形状。所构建的微观结构采用不同的单元密度以及针对不同数量的晶粒进行网格划分。然后对一组选定的孪晶和母晶对进行了研究。结果表明，3DXRD实验中每个晶粒测得的平均应力处于CPFE模拟中所建晶粒的应力变化区域内。此外，每个晶粒的CPFE平均应力计算值与测得的平均应力值吻合良好。结果显示，考虑到每个晶粒内的应力变化时，如果在全局坐标系中绘制，母晶和孪晶中的应力差异很大。然而，如果将应力张量旋转到孪晶惯习面的局部坐标系中，除了作用在孪晶面上的剪切应力和横向应力外，在所呈现的总体上平均的所有应力分量都很接近。这一结果意义重大，因为它为在晶体塑性代码中模拟此类母晶 - 孪晶相互作用提供了所需信息。（C）2015 Acta Materialia Inc.，由爱思唯尔有限公司出版。保留所有权利。