Blade life in the hot section of the gas turbine is most affected by the high operating temperatures, constant centripetal loading, and thermally induced stresses during startup and shutdown. High temperatures and constant loading result in material creep that limits the blade operating duration under steady conditions. Transient operation of the gas turbine, such as start-up and shut-down cycles result in thermally induced stresses in the blades that can cause local plastic yielding while also contributing to material creep.
In conducting a detailed transient or steady-state analysis of a gas turbine blade, an accurate representation of the blade material is required to estimate creep strain and transient strains that contribute to thermo-mechanical fatigue (TMF) life. Custom material models are typically defined for the greatest accuracy of blade material models. However, these models are expensive and time-consuming to generate. As an alternative, the material models currently available in commercial codes can be calibrated to produce the measured material response.
In this paper, a methodology is provided to calibrate complex material models in a commercial finite element (FE) code for single-crystal (SX) and directionally solidified (DS) alloys. The material model calibration relies on available test data in the literature and is used to define the material elasticity, plasticity, creep, and yield strength. Because the materials are anisotropic, the material properties are defined using orthotropic material definitions that define different material responses in the global coordinate directions. To demonstrate the accuracy of the material models, the predicted material TMF response is compared directly to test data.