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This paper investigates the fatigue performance of Nitinol thin-film devices used in medical applications. Freestanding films are fabricated and structured by microsystem technology processes (magnetron sputtering, UV lithography and wet chemical etching). A test rig is developed to address the requirements of Nitinol thin-film samples in terms of force, stroke and precision and also allows the multiplication of test rigs due to its inexpensive components. Hence, several samples can be tested simultaneously at different parameters in order to obtain a thorough characterization within reasonable test duration. Finite element analysis (FEA) is used to derive maximum principle strains of test specimen during cycling loading. Therefore, a superelastic, multiaxial material model with two different kinetic transformation mechanisms being capable of considering tension/compression asymmetry and temperature effects is realized and implemented using the FEA software Comsol Multiphysics. Good agreement between simulation and experimental tensile tests is shown. An excellent fatigue resistance with a high fatigue safety limit of 1.75% pulsatile strain amplitude for mean strains up to 2.5% with sputtered Nitinol diamond specimen is observed. [ABSTRACT FROM AUTHOR]

In situ measurements are a pivotal extension of conventional transmission electron microscopy (TEM). By means of the shape memory alloy NiTi thin film Functional Grids were produced for in situ straining as alternative or at least complement of expensive commercial holders. Due to the martensite-austenite transition temperature straining effects can be observed by use of customary heating holders in the range of 50 to 100   °C. The grids can be produced in diversified designs to fit for different strain situations. Micro tensile tests were performed and compared with finite element simulations to estimate the applied forces on the sample and to predict the functionality of different grid designs. As a first example of this Functional Grid technology, we demonstrate the impact of applying a strain to a network of ZnO tetrapods. [ABSTRACT FROM AUTHOR]

The elastocaloric effect that occurs during the stress-induced martensitic transformation in shape memory alloys is a promising mechanism in view of solid state cooling applications. It also allows for downscaling to feature sizes in the μm range, thus, being attractive for micro-cooling applications using thin film materials. In this study, elastocaloric properties of TiNi and TiNiCu films and their relation to functional fatigue were investigated. Both materials show similar effect sizes, their fatigue behavior is however different. While the temperature change in TiNi degrades by a factor of two within 150 cycles, no significant elastocaloric fatigue was found in TiNiCu. [ABSTRACT FROM AUTHOR]