Characterization of martensitic transformation in shape memory wires by resistivity measurementsTuesday (18.06.2019) 20:03 - 20:04
This research work investigates on the feasibility and opportunities offered by resistivity measurements to access the martensitic phase transformation in Ni-Ti shape memory (SM) wires. The most established methods to observe phase transformations are either recording the heat flow by differential scanning calorimetry (DSC) or measuring the deformation in mechanical tests. However, these methods are restricted in sample dimension and test set-up, e.g. it is not possible to measure stressed material in DSC and mechanical tests are commonly designed for specific sample geometries. In addition, both tests suffer from a relative high inertia in tracing the phase change due to the inherent delay between spontaneous transformation and measuring signal. Exploiting the differences in specific resistivity of austenite and martensite for determining the phase transformation could be a useful approach for the characterization of SM wires by reducing the signal response time. The need of lower material quantities compared to DSC measurements could in particular improve the accuracy in the case of investigating thin structures. Furthermore, it allows for testing of wires under quasi zero stress conditions in a non-destructive method. This study compares resistivity measurements of Ni-Ti wires with conventional methods for characterizing the martensitic phase transformation and discusses advantages, opportunities and limits.