Burst Ductility of Zirconium Clads: The Defining Role of Residual Stress

Closed end burst tests, using room temperature water as pressurizing medium, were performed on a number of industrially produced zirconium (Zr) clads. A total of 31 samples were selected based on observed differences in burst ductility. The latter was represented as total circumferential elongation or TCE. The selected samples, with a range of TCE values (5 to 35 pct), did not show any correlation with mechanical properties along axial direction, microstructural parameters, crystallographic textures, and outer tube-surface normal (σ ₁₁) and shear (τ ₁₃) components of the residual stress matrix. TCEs, however, had a clear correlation with hydrostatic residual stress (P _h), as estimated from tri-axial stress analysis on the outer tube surface. Estimated P _h also scaled with measured normal stress (σ ₃₃) at the tube cross section. An elastic–plastic finite element model with ductile damage failure criterion was developed to understand the burst mechanism of zirconium clads. Experimentally measured P _h gradients were imposed on a solid element continuum finite element (FE) simulation to mimic the residual stresses present prior to pressurization. Trends in experimental TCEs were also brought out with computationally efficient shell element-based FE simulations imposing the outer tube-surface P _h values. Suitable components of the residual stress matrix thus determined the burst performance of the Zr clads.