The influence of localized stresses and strains on the iodine scc behavior of Zircaloy-2 tubing

Abstract

The segmented expanding mandrel test is modified to provide additional information on the localized stresses and strains during ramp-hold tests. A chamfered specimen is designed with four flats on the outer diameter for the purpose of creating sectors of variable wall thickness which establishes a more nearly plane strain state in the thinnest-gauge sections. Ramp-hold tests conducted in 40 MPa of iodine at 325[deg]C show that at a measured diametral strain of 0.8%, chamfered specimens fail while regular tubing specimens require diametral strains of 2% or greater for failure. Calculations made with a two-dimensional, finite elements code show that at a measured diametral strain of 0.8%, the local strains in the clad ID over the segment interfaces are nearly identical for the regular and chamfered samples while the local stress in the chamfered sample is 15% greater. Results suggest that the smaller diametral failure strain of the chamfered specimen at low measured diametral strains is mainly due to its near plane strain condition and the higher hoop stresses resulting therefrom.