A lexis Mion

Abstract

The hottest parts of turbojet engines are exposed to high thermomechanical stresses, particularly of the vibratory type. The improvement of the efficiency of aeronautical engines (obtained with an increase in operating temperatures), as well as the need to reduce mass, mean that the parts have to withstand ever more severe mechanical and thermal loadings. It therefore seems particularly important to improve the fatigue design methods of these parts, especially in the High Cycle Fatigue (HCF) and Very High Cycle Fatigue (VHCF) domains. However, fatigue property determination is time-consuming as the fatigue behavior depends on many parameters (nature of loading, microstructure, manufacturing process, temperature, etc.).

The self-heating method, which is based on the measurement of the temperature evolution of a specimen during cyclic loadings, makes it possible to considerably reduce characterization times. The effectiveness of this method has been demonstrated over a wide range of metallic materials at various temperatures.

High temperature self-heating tests at different load ratios are conducted on two nickel-based superalloys: INCONEL 718, a polycrystalline alloy, and AM1, a single crystal alloy. The first focus is on self-heating tests in the HCF range, performed at a frequency of 20 Hz. Then, in a second step, a protocol of self-heating tests on AM1 specimens in the VHCF domain at 20 kHz and at 1000°C on a gigacyclic machine is set up. Different models are then proposed to describe each experimental result. The link between the self-heating measurements and the fatigue properties for each configuration is also discussed.

Session