The mechanical response of polycrystalline materials to an externally applied load and their in-service performance depend on the local load partitioning among the constituent crystals. In hexagonal close-packed polycrystals such load partitioning is significantly affected by deformation twinning. Here we report in-situ compression-tension experiments conducted on magnesium specimens to measure the evolution of grain resolved tensorial stresses and formation and annihilation of twins. More than 13000 grains and 1300 twin-parent pairs are studied individually using three-dimensional synchrotron X-ray diffraction. It is shown that at the early stages of plasticity, the axial stress in twins is higher than that of parents, yet twins relax with further loading. While a sign reversal is observed for the resolved shear stress (RSS) acting on the twin habit plane in the parent, the sign of RSS within the majority of twins stays unchanged until twin annihilation during the load reversal. The variations of measured average stresses across parents and twins are also investigated.

多晶材料对外部施加的载荷的机械响应及其使用性能取决于组成晶体之间的局部载荷分配。在六角形紧密堆积的多晶体中，这种变形变形会显着影响这种载荷分配。在这里，我们报告在镁试样上进行的原位压缩张力实验，以测量晶粒分解张应力的演变以及孪晶的形成和an灭。使用三维同步加速器X射线衍射分别研究了13000多个晶粒和1300个双亲对。结果表明，在可塑性的早期，双胞胎的轴向应力高于父母，而双胞胎随着进一步的载荷而松弛。尽管观察到作用在父母双胞胎习惯平面上的已分解剪切应力（RSS）发生符号反转，但大多数双胞胎中RSS的符号保持不变，直到负载反转期间双子twin没。还研究了父母和双胞胎之间测得的平均应力的变化。