Effect of Temperature Dependent Mechanical Properties on Thermal Stress in Cooled Turbine Blades

Abstract

Finite element analyses show that maximum thermal stresses in a typically cooled turbine blade are approximately 40 percent larger than they are if calculated assuming constant, average temperature material properties—even though the local-to-average properties vary only 2 to 3 percent. An error of this size in stress leads to an order of magnitude over prediction of cyclic life. This surprisingly large effect is explained by means of the solution for thermal stress in a flat plate with a thermal gradient through its thickness. In general, finite element computer codes allow for temperature dependency of properties, but some do not permit this dependency within an element. It is shown that this can be a serious limitation with higher-order elements.