Investigation of multiaxial fatigue in the context of turboengine disc applications

Multiaxial fatigue is investigated on two alloys commonly used for compressor and turbine discs. With the objective to assess current design methodologies for discs, the present study involves both experimental and theoretical aspects. Several experimental facilities are used in order to cover a large range of multiaxial stress states, namely tension–compression torsion, tension–internal pressure and biaxial loads applied on a specially designed cruciform specimen. Some results with crack observations are discussed here within a thermo-elastic approach. Further, multiaxial fatigue criteria based on results of cylic viscoplastic calculations are analysed. Different multiaxial fatigue criteria, including those based on octahedral shear stress amplitude combined with hydrostatic pressure, and more recent models based on the critical plane approach are evaluated. The analyses reveal that none of them is able to deliver a correct life time estimation of all the considered uniaxial and multiaxial conditions. A new combined criterion is then proposed that offers a possible compromise and seems to significantly improve the assessments.