Abstract

Today's and future parameters of stationary gas turbines and aircraft engines require intensive and highly efficient cooling of hot gas path components. High temperature and thermally induced stress gradients with impact on fatigue life are the consequence. Regarding the contribution and evaluation on damage, the influence of thermal gradients as a characteristic feature in turbomachinery is currently not fully understood. Therefore, a unique radiation heating has been developed allowing very high heat fluxes of q = 1.5 MW/m 2 for testing of hollow cylindrical specimens. The conventional cast nickel-base alloy Mar-M247 has been chosen to study the influence of thermally induced stress gradients on fatigue life. Low-cycle fatigue tests of hollow cylindrical specimens have been conducted both with and without superimposed stationary temperature gradients. In addition, Complex Low-Cycle Fatigue (CLCF) have been performed to provide the necessary database for the adaptation of a viscoplastic deformation model. To calculate the local stress-strain field and service life of the test specimens, linear elastic and viscoplastic finite element studies have been performed and were assessed by means of a fracture mechanicsbased lifetime model. The test results show the considerable influence of the temperature gradient on the low-cycle fatigue life for the investigated material. Both the radial temperature variation over the specimen wall with a hot outer surface and a cooled inner surface as well as the thermally induced stresses are stated to be the main drivers for the change in low-cycle fatigue life.

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