A SIMPLE UNIFIED THEORY FOR THE CYCLIC DEFORMATION OF METALS AT HIGH-TEMPERATURE

A simple constitutive equation involving only six material constants h as been developed to describe the high temperature deformation of meta ls over a wide range of stress and temperature. The model involves a d rag stress and a back stress, along with their evolution equations. A new concept has been introduced to connect the growth behavior of thes e two internal state variables so as to reduce the number of material constants required in the description under cyclic loading conditions. It is demonstrated that this simple model can adequately describe the stress-strain behavior of a 617 Nickel-base superalloy over three dif ferent orders of strain rate, and up to 900 degrees C. It can also pro vide the cyclic hardening behavior and stable hysteresis loop under a strain-controlled loading, and the strain-ratchetting under an off-axi s, stress-controlled loading, among others. The influence of stress an d temperature on creep, and the influence of mechanical and thermal cy cling on the creep strain accumulation can all be studied with this se t of simple constitutive equations.