Three-Dimensional Finite Element Analyses of Compact Tension Specimens of Irradiated Zr-2.5Nb Materials Using Submodeling

Abstract

In this paper, the crack tip stresses along the front of a crack in a compact tension (CT) specimen of irradiated Zr-2.5Nb material are investigated by three-dimensional finite element analyses using the submodeling technique. A parametric study on two-dimensional submodeling of a CT specimen was first conducted to determine the appropriate mesh near the crack tip of a global model and the appropriate size of a submodel. The results show that the collapsed elements should be used near the crack tip in a global model and the region of a submodel should at least enclose the plastic zone to achieve acceptable results. With the submodeling strategy, a three-dimensional finite element analysis of the CT specimen is conducted. The distributions of the opening stress and out-of-plane normal stress ahead of the front of a crack in the CT specimen are obtained. Based on the computational results with the hydride fracture stress of 750 MPa for both radial and circumferential hydrides, all radial hydrides ahead of the crack front and the circumferential hydrides in the middle portion of the specimen should fracture at the specimen load of 3,000 N. Circumferential hydrides near the free surfaces do not fracture and the size of the zone without fractured circumferential hydrides increases with the increasing radial distance to the crack front. The computational results also show the three-dimensional effects on the variation of the plastic zone size and shape along the crack front, that is different from the conventional understanding of a dog-bone shape where the plastic zone on the free surface follows that under plane stress conditions and the plastic zone near the middle portion of the crack front follows that under plane strain conditions.