A New Technique for High Frequency Multiaxial Thermo-mechanical Fatigue Testing of Materials

Abstract

The proposed thermo-mechanical fatigue test rig is based on a rotating bending machine and employs a high and a low temperature sources. This permits imposing thermal and mechanical loading at relatively high frequencies on a portion of a surface generatrix of a tubular specimen. Using this rig, a series of experiments was carried out on superalloy test specimens. These tests were conducted at various mechanical loadings with the temperature cycling between 600 and 1050°C in 10 seconds. The temperature distribution on the test specimen was measured under stabilized conditions and the same was calculated using a finite element code. Good correlation was found between the experimental and simulated temperature distributions. The thermal stress field, hence calculated, enables us to identify the critical crack initiation sites of the specimen and to calculate the applied thermo-mechanical cycle. In this way, an equivalent constant temperature can be defined and fatigue life has been predicted using isothermal fatigue results only.