Short versus long crack fatigue crack growth: A new experimental approach

Abstract : Some aircraft components, such as turbine disks, are subjected to very strict certification stages. Other than the fact that the material has a non-linear behaviour (Nickel base superalloy), the complex loading it experiences makes the definition of a fatigue cycle difficult. Moreover, during operation or maintenance those components are exposed to the creation of surface anomalies such as dents or scratches. Besides creating an initial residual stress state that is multiaxial, they create micro-cracks that lead into a significant effect of T-stress. This study aims to highlight the effect of T-stress during a mode I fatigue crack propagation and link it to the short crack effect. The crack propagation under a loading in terms of stress intensity factor depends on its initial length. In fact, the crack growth rate of a short crack is greater than the one for the long crack. Assuming that the difference between short and long cracks stems from T-stress, bi-axial tests have been performed in order to propagate a long crack as if it were a micro-crack. This can be done by changing the biaxiality state, i.e. creating a (KI, T) loading specific to a micro-crack. The results about T=0 MPa to negative T-stress tests show a major potential increase. The effect of T-stress is along 40µm and lasts for 5k cycles. Those results will be compared to the one with real short cracks, the challenge here is obtaining a mechanically short crack, meaning a large crack front but a small length. The comparison of the results obtained on short and long cracks will allow us to validate the assumption that the same fatigue crack growth is obtained if the loading (KI,T) is applied. If confirmed, it will be possible to measure short crack growth using tests on long cracks.
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https://hal.archives-ouvertes.fr/hal-01903884
Contributor : Yoann Guilhem <>
Submitted on : Wednesday, October 24, 2018 - 4:45:47 PM
Last modification on : Friday, May 24, 2019 - 5:27:47 PM

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  • HAL Id : hal-01903884, version 1

Citation

Besnik Sadriji, Bumedijen Raka, Yoann Guilhem, Didier Soria, Sylvie Pommier. Short versus long crack fatigue crack growth: A new experimental approach. International Conference on Fatigue Damage of Structural Materials XII (FATDXII), Sep 2018, Hyannis, United States. 2018. ⟨hal-01903884⟩

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