Yield and Fracture of Biaxially Stressed Zircaloy-4 Cladding Tubes at Room Temperature and at 400°C

Abstract

Zircaloy-4 cladding tubes differing in texture only (Materials I and II were loaded simultaneously by internal pressure and axial forces at different stress ratios, α = axial stress, σa, and tangential stress, σt. Each stress ratio a was kept constant during the whole test, that is, from the beginning of elastic deformation to the fracture of specimens. At room temperature the axial and tangential strains ϵa and ϵt, respectively, were measured as a function of σa and σt respectively (α = constant). These stress-strain diagrams were used to determine the apparent Young's moduli and the yield loci. At 400°C the yield locus was measured for Material I. Furthermore, for each stress ratio, α, those stresses σa and σt were measured at which fracture occurred. These “fracture” loci were determined for both materials at room temperature and 400°C. Although the uniaxial data (stress ratio α = ∞) were very similar for both materials, a marked difference in yield and fracture behavior at a α ≠ ∞ was observed. Therefore, the criteria valid for isotropic materials turned out to be unsuitable for a satisfactory description of the measured data and relations.