Measurement and modeling of micro residual stresses in zirconium crystals in three dimension

Abstract

The performance of the zirconium alloys used in nuclear reactors can be affected by the state of the residual stresses that develop during manufacturing of the reactor core components. In this paper, residual stresses within individual grains of a textured α-zirconium polycrystal are studied. For this purpose, three-dimensional synchrotron X-ray diffraction is used to measure elastic strain tensor, center-of-mass (COM), orientation, and stress tensor of more than 11,000 grains in a zirconium sample. The grain measured COMs and orientations are used to reconstruct the 3D microstructure of the sample using the weighted Voronoi tessellation technique. The microstructure is subsequently imported into Abaqus to simulate the experiment using a crystal plasticity finite element model. The state of the thermal residual stresses that develop during slow cooling from 700 °C, and those that develop after unloading from 1.2% applied tensile strain are discussed. It is shown that both thermal and mechanical micro residual stresses, and their variations within a grain, are correlated with grain size. Also, due to strong anisotropy of the single crystal, residual stresses are significantly affected by the configuration of local grain neighborhood.