Titanium-Nickel Based Shape Memory Alloys Under Cyclic Loading Experimental Investigations and Thermomechanical Modeling
Pseudoelastic shape memory alloys come into use to an increasing degree e.g. in medical technology and the building industry. Topic of this thesis is the specific material behaviour of pseudoelastic Nickel-Titanium shape memory alloys subjected to cyclic loads. The decrease of the transformation stresses due to repeated cyclic loading is investigated and the reversibility of this process is researched. As micromechanical reason for the specific material behaviour, the creation and back-formation of residual martensite is identified. The findings of the experimental investigations form the basis for a thermodynamically consistent material model. Starting from the second law of thermodynamics, a continuum-mechanics based phenomenological constitutive model is derived that reflects the decrease of the transformation stresses and the different material properties of austenite and martensite in Nitinol.