Endommagement en fatigue oligocyclique des disques de turbomachines^*

Low cycle fatigue damage in turboenine disks

¹ Chef du service « Mécanique des Matériaux », SNECMA, Corbeil
² Chef du Département « Matériaux et Procédés », SNECMA, Corbeil

Abstract

In modem turboengines, disks are the most critical parts due to the high thermal and mechanical loadings they are submitted to. The damage processes of these parts are correlated to engine working cycles, generating low frequency and high amplitude cyclic loads: the life of disks is therefore mainly limited by low cycle fatigue, possibly associated with environment effects (time, temperature) and high frequency low amplitude cycles superimposition (due to interferences in rotating machines).

Disks designing is based on laboratory specimens tests results, which enable the quantification of damage models, used in calculations. The reliability of those methods, as well as the accurate knowledge of physical damaging mechanisms in disk alloys, allow to deliver “safe lives” to those parts, which are however checked by spin pit tests on moduli or whole engines. Nevertheless, the recent trend towards “Damage Tolerance Concepts”, in which material defects are taken in account, need more intensive studies of crack propagation and damage mechanics, including complex phenomena such as spectrum fatigue. Therefore, the improvement of more and more sophisticated laboratory mechanical tests (short crack propagation, thermo-mechanical fatigue, complex fatigue) seems mandatory to meet those requirements.