M. Schlaegel, University of the Federal Armed Forces Munich, Neubiberg, Germany
Superelastic Nickel-Titanium (NiTi) alloys subjected to cyclic loads exhibit two distinctive phenomena: A steady decrease of the transformation (martensite-austenite) and reverse transformation (austenite-martensite) stresses and an increase of the residual deformation in the load-free state.
At our institute, numerous test series with superelastic Nitinol wires were carried out. The aim was to quantify the effect of degradation due to the cyclic loading and to gain a deeper insight into the micromechanical causes of this effect. Ultimately, these experiments provided a basis upon which a phenomenological model for the description of the material behavior of superelastic Nitinol was created.
The main focus of the talk will be the discussion of the experimental results. For this purpose, it will be partitioned in three sections: First of all, the basic effects of cyclic loading on nitinol wires will be introduced by means of some selected experiments. Furthermore, several micromechanical explanations for the material behavior will be introduced; these explanations will then be narrowed down by means of the experimental observations. Finally, the consequences of the experimental investigations on the material modeling of superelastic NiTi shape memory alloys will be discussed.
Summary: Superelastic Nickel-Titanium (NiTi) alloys subjected to cyclic loads exhibit two distinctive phenomena:
A steady decrease of the transformation (martensite-austenite) and reverse transformation (austenite-martensite) stresses and an increase of the residual deformation in the load-free state.
At our institute, numerous test series with superelastic Nitinol wires were carried out. The aim was to quantify the effect of degradation due to the cyclic loading and to gain a deeper insight into the micromechanical causes of this effect. Ultimately, these experiments provided a basis upon which a phenomenological model for the description of the material behavior of superelastic Nitinol was created.
The main focus of the talk will be the discussion of the experimental results. For this purpose, it will be partitioned in three sections: First of all, the basic effects of cyclic loading on nitinol wires will be introduced by means of some selected experiments. Furthermore, several micromechanical explanations for the material behavior will be introduced; these explanations will then be narrowed down by means of the experimental observations. Finally, the consequences of the experimental investigations on the material modeling of superelastic NiTi shape memory alloys will be discussed.
