Multiphysical approach of the ageing of martensitic stainless steels under loading and on its consequences onto the fatigue crack growth properties – PREVISIA

This project shall permit to realise innovations in terms of mechanical behaviour prediction of engine pylon parts made out of martensitic stainless precipitate hardening steels.
It is dedicated to demonstrate that a multi-scale modelling will permit to optimise the static and damage tolerance design of structural parts in 15-5PH used at 1200MPa taking into account their highly severe in-service conditions.
It answers a more general approach on engine pylon parts made out of high strength materials as titanium or nickel based alloys and answering to severe loads under long time temperature exposure (in service temperature between 120°C et 325°C), for which designers want to adapt the predicting tools currently used for other metallic materials employed in less severe conditions.
Scientific and technical stakes concern the aging of 15-5PH under stress between 275°C and 325°C for long term use and the effects of load spectrum on the fatigue crack propagation in relationship with the aging of the material and the oxydation of the fracture because it avoids the use of this steel for the new applications.
The project is proposing to update our metallurgical and mechanical knowledge on the material used under severe thermomechanical conditions.
At first, the aging mechanisms will be studied and modelled in order to predict the evolution in service of the static and fatigue properties. Then, the fatigue crack growth mechanisms will be studied in relationship with the aging and the oxydation mechanisms to enlarge the application of various models. Finally, the results put in place during PREVISIA project will be compared to the results of a representative test of fatigue under temperature of a representative element of the aircraft.
The organisation is to put in place the understanding phases from nanometric scale, going through microscopic and macroscopic scales until testing under spectrum on representative element :
- Nanometric scale of the microstructure to characterize the aging from metallurgical observations
- Microscopic scale to characterize and model the behaviour laws as a function of the temperature and the aging to describe the fatigue crack growth mechanisms
- Millimetric scale to characterize the effects of the fatigue sprectrum in relationship with the behaviour laws, the oxydation effects and the fatigue crack mechanisms
- Part scale to validate the predicting tools.

The partnership is as follows :
- Academic partners : SIMAP, CIRIMAT, INSTITUT P’ ENSMA, LMT Cachan.
- Industrial partners : Aubert & Duval, Airbus Operation SAS, EADS IW.

The tasks are defined hereafter :
- Task 1 : Definition of the field of the study from real load cases, given by AIRBUS.
- Task 2 : Study and modeling of the microstructures aged under mechanical loading .
- Task 3 : Study and modelling of static behaviour and fatigue laws after aging under mechanical load.
- Task 4 : Characterisation and modeling of the fatigue crack growth under spectrum on aged materials.
- Task 5 : Validation on industrial part.
- Task 6 : Coordination of the project by EADS IW.