Expanding copper mandrel test evaluation of yielding and strain aging behavior of zircaloy-4 PWR fuel clad tube

Abstract

Expanding copper mandrel tests were carried out on Zircaloy-4 tube over a temperature range of 573-873 K at $&εgrave;$ =2.0×10^{-6}s^{-1}$ and 573-723 K at $&εgrave;$=1.4×10^{-5}s^{-1}$. More rigorous measurements and exact analysis of test results were made to improve the accuracy and reliability of the expanding copper mandrel tests. Yield pressures at different strain rates and temperatures were calculated from test measurements of diametral plasti c expansion and used to determine activation parameters such as yield stress, shear modulus corrected shear stress, strain rate sensitivity, activation energy and etc. The shift in yield stress peak from 612 K at $&εgrave;$=2.0×10^{-6}s^{-1}$ to 623 K at $&εgrave;$=1.4×10^{-5}s^{-1}$ can be explained in terms of dynamic strain aging due to oxygen atoms, and lower yield stress peak on 698 K at both strain rates is considered to be due to dynamic strain aging by iron atoms atmosphere locking of mobile dislocations. The test results are in good agreement with other previously published test data. The expanding copper mandrel test is proved to be a reliable and quantitative source of testing method with simple devices for yielding and strain aging behavior study for thin-walled tube materials.