Calculation of turbine rotors in secondary creep range

Turbine rotors in power plants are exposed to triaxial stresses by centrifugal forces at high temperatures which induce long time creep effects. In the first step, we implemented an algorithm for centrifugal volume forces in ADINA. In the next step, we tested the numerical behaviour of the modified Newton-algorithm in ADINA within the long time secondary creep range for simplified examples. Isotropie strain hardening was assumed in most cases of creep calculations.

The estimate of creep properties is based on the minimum least square method. The numerical stability in creep calculations is dependent on the magnitude of time step size and on a good fit between creep law properties and the real experimental material data.

In the examples of turbine rotor models with rotational symmetry we were able to estimate the state of stress and strain under creep conditions for life time periods up to 2 × 10⁵ hr.