On the effects of reorientation and shear transfer during twin formation: Comparison between high resolution electron backscatter diffraction experiments and a crystal plasticity finite element model

The effects of reorientation and twin shear transfer on the load sharing between twin and parent pairs in hexagonal closed-pack (HCP) polycrystals have been examined by combined experimental and numerical methods. A highly textured Zircaloy-2 sample was uniaxially strained in a direction that favours twin formation and then unloaded to measure variations in residual elastic strains, lattice rotations, and stresses within twin and parent grains by the use of high resolution electron backscattered diffraction (HR-EBSD). The measured grain structures were imported into a finite element solver to study local stresses within each grain and their evolution as twins form. A crystal plasticity finite element code was modified to integrate the effect of twin shear strain into the constitutive equations. Results show that between reorientation and twin transformation strain, the later plays the more important role on determining the state of the stress in the parent, twin and the surrounding environment. The elastic energy of the parent grain was shown to reduce upon twin formation but then stay constant after the early stages of twin shear transfer. This can promote the formation of the next twin in preference to increasing the size of the current one. Comparison of the model with HR-EBSD measurements took into account that the residual stress variations were measured relative to the (unknown) stress state at the reference point within each grain. (C) 2016 The Author(s). Published by Elsevier Ltd.

通过实验和数值相结合的方法，研究了重新定向和孪晶剪切传递对六方密堆积（HCP）多晶体中孪晶与母相之间载荷分配的影响。一个具有高度织构的锆 - 2合金样品在有利于孪晶形成的方向上进行单轴拉伸，然后卸载，通过高分辨率电子背散射衍射（HR - EBSD）测量孪晶和母相晶粒内残余弹性应变、晶格旋转和应力的变化。将测量得到的晶粒结构导入有限元求解器，以研究每个晶粒内的局部应力及其在孪晶形成过程中的演变。对晶体塑性有限元代码进行了修改，将孪晶剪切应变的影响纳入本构方程。结果表明，在重新定向和孪晶转变应变之间，后者在确定母相、孪晶及其周围环境的应力状态方面起着更重要的作用。母相晶粒的弹性能在孪晶形成时降低，但在孪晶剪切传递的早期阶段之后保持不变。这可能有利于下一个孪晶的形成，而不是增加当前孪晶的尺寸。将模型与HR - EBSD测量结果进行比较时，考虑到残余应力变化是相对于每个晶粒内参考点（未知的）应力状态进行测量的。（C）2016作者。由爱思唯尔有限公司出版。