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Cyclic behavior and fatigue of shape memory alloys

le 16 novembre 2017
à 13h30

Ziad Moumni, Professeur à l'IMSIA (ENSTA ParisTech), interviendra lors d'un séminaire.

Shape memory alloys (SMAs) exhibit interesting properties when subjected to mechanical or thermal loadings. For instance, they can accommodate large recoverable strains, or recover their shape by simple heating after being inelastically strained. In many applications, shape memory alloys are subjected to cyclic loadings, which could induce failure of the SMA structure by fatigue. A better understanding of fatigue in SMAs thus seems important in order to further promote the use of these materials. Among the available literature, some studies suggest that the fatigue of SMA wires varies with the loading frequency,  and explained it by temperature variations. Indeed, the occurrence of the martensitic transformation during a thermal and/or mechanical loading, is accompanied with a production of entropy and heat; this results in a strong thermomechanical coupling, the mechanical response of SMAs being highly dependent on temperature. Thermomechanical coupling can explain the dependence of SMA behavior on strain rate. In this regard, experimental evidence shows that the dissipated energy evolves non monotonically with the strain rate.     
Our aim is to link together those two observations (namely the dependence of fatigue lifetime on the loading frequency and the strong thermomechanical coupling) to build a global approach for fatigue design of SMAs structures. This approach consists into two steps: first, the development of a simple but accurate model to predict the stabilized thermomechanical state of a SMA structure under cyclic loading; then the extension of a fatigue criterion to take into account the main features which can be experimentally observed and particularly the dependence on the loading frequency.           
Type :
Séminaires - conférences
Lieu(x) :
Campus de Cachan
Bâtiment Léonard de Vinci
Amphi E-media

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