Uniaxial ratcheting behaviors of Zircaloy-4 tubes at 400 °C

A series of uniaxial tensile, incremental cyclic and uniaxial ratcheting tests were conducted at 400 °C on Zr-4 tubes to investigate the mechanical behaviors under various loading conditions. The experimental results show that this material features cyclic softening at room temperature (RT), and cyclic stable and hardening at 400 °C. Uniaxial ratcheting strain increases with the increase of mean stress and stress amplitude, and decrease with the increase of loading rate. Loading history has significant influence on the uniaxial ratcheting behavior. Lower stress level after a loading history with higher stress level leads to the shakedown of ratcheting. Higher loading rate after a loading history with lower loading rate brings down the ratcheting strain rate. The sequence of stress rate appears to have no effects on the final ratcheting strain accumulation. The ratcheting strain is sensitive to temperature, and the higher temperature leads to less ratcheting under same normalized stress (σ‾=σ/σ0.2).