Investigation of Deformation Behavior of Ring-Tensile Specimens Machined from Pressure Tubes of Indian PHWR

Abstract

Specimens machined in the form of circular rings directly from the nuclear reactor pressure tubes and tested in a ring-tension test-setup offer great simplicity in evaluating the transverse mechanical properties of the as-manufactured as well as those of the service-exposed tubes. However, the state of stress in the specimen cross-section is not purely uni-axial due to the effect of bending and the presence of lateral pressure due to the loading mandrel. This requires the use of 3-D finite element (FE) analysis for simulation of deformation behavior of the specimens in the ring-tension test-setup. In this work, we have analyzed the deformation behavior of ring-tension specimens machined from two different types of zirconium alloy pressure tubes as used in the Indian pressurized heavy water reactors. The effect of geometry of the loading mandrel (i.e., 2-piece vs. 3-piece type of mandrel) on the load-deformation behavior of the test-setup has been studied. It was observed that the values of maximum load as well as the deformation behavior in the post-necking region differ significantly when only the geometry of the loading mandrel is changed keeping all the other parameters same. FE analysis has been able to correctly predict these variations as it takes into account of the effect of geometry, material properties as well the interaction between the mandrel and the specimen. Hence, the use of FE method is essential in the inverse analysis procedure where the material properties can be determined from these complex test-setups.