Abstract
Plastic zones near bulk hydrides and fracture paths in representative volume elements (RVEs) with bulk hydrides in hydrided irradiated Zr-2.5Nb pressure tube materials are investigated by two-dimensional finite element analyses under plane strain conditions. Three RVEs with different distributions of bulk hydrides are selected from the micrographs of the radial-circumferential cross section of a hydrided irradiated Zr-2.5Nb pressure tube specimen. The bulk hydrides are assumed to be separated from the pressure tube material in the early stage of the loading and are assumed as cracks. The RVEs are subjected to high stress triaxiality loading conditions similar to those ahead of the front of an axial crack in a pressure tube specimen under internal pressure. The elastic-plastic stress-strain relation for the matrix materials in the RVEs follows that of a tensile test of a transverse tensile specimen cut from an irradiated Zr-2.5Nb pressure tube specimen. The computational results indicate that due to close proximity of bulk hydrides, narrow plastic zones emanating from the tips of bulk hydrides connect either to the tips of other neighboring bulk hydrides or to the neighboring fractured bulk hydride surfaces as the loading increases. Possible fracture paths are identified and presented by connecting the fractured bulk hydrides and the narrow plastic zones emanating from the tips of bulk hydrides. The features of the fracture surfaces of the RVEs based on these possible fracture paths are generally consistent with those ahead of the front of a crack in a curved compact tension specimen cut from a hydrided irradiated Zr-2.5Nb pressure tube specimen. The computational results also show that the macroscopic elastic modulus and maximum stress of the RVE increase as the net section percentage of the possible fracture path increases.
