Fretting has been the subject of numerous experimental investigations. It occurs when two surfaces rub against each other at very low amplitude (some tens of microns of sliding distance). If the tangential force Q is lower than the product of the friction coefficient μ and the normal force P, two different zones can be observed within the contacting zone. At the center, both surfaces are sticked to each other while they have a relative motion in the annular zone. This is the partial slip regime. The corresponding dominant failure is crack initiation located at the edges of the contact area.

Fretting is present in a blade-disc attachment of a turboshaft engine. It is due to the superimposition of two fatigue stresses: a low frequency loading (LCF), induced by the centrifugal force from the rotation of the disc, and a high frequency loading (HCF), which is a sinusoidal force induced by vibrations. It's a difficult phenomenon to model and industries are not capable of predicting it with good accuracy yet. Instead, they are forced to use huge safety factors. Therefore, the prediction of the lifetime of a blade disc assembly under fretting has now become a major issue in the field of turboshaft engineering.

A major difficulty of providing such a prediction comes from the complication of determining the stress and strain fields in the vicinity of the contact. The finite element parameters needed to compute the intense stress gradient in this zone have been found out using a simplified 2D finite element model of a classical fretting test device. This model was also used for a sensitivity analysis of the damage using the Dang Van fatigue criterion. An important set of results was obtained. These results provide a better understanding of the mechanism of fretting damage, and enriching information for decision support concerning future experimental campaigns.

The second step of our work was to set up a calculation process to compute the stress field under a fretting contact induced by a superimposed LCF + HCF solicitation in a fir-tree root. The combination of this process with the Dang Van fatigue criterion allows the calculation of a criticality parameter related to the life cycle. This modeling process was first applied on a model representing an innovative test device, designed at Safran Helicopter Engines, allowing the superimposition of a static and a vibratory loading on a dovetail test specimen. The model reproduces experimental observations with a very good accuracy. This modeling process was then applied to the model representing a real fir-tree root geometry. The results correlate with the feedback from in-service engines. The simulation results from the test device and the fir-tree root models were compared. This comparison made possible the determination of the dovetail geometry and the experimental conditions to apply that are most representative of the phenomenon that induces fretting failure in a blade-disc attachment.