Straining
Our research means to investigate the properties of strained thin films on nitinol substrate. To strain our material we used two different methods: axial and bending.
Axial strain was performed using an Instron 5500, which clamps either end of a thin, flat sample and pulls upward at one end while remaining stationary at the other.
Bending strain was performed by laying the sample over a cylinder with a very well-defined radius. It is likely that, due to the properties of this material, that this method of strain may not be able to produce a phase change.
A fair amount of research has been done to characterize the behavior of nitinol under axial strain. In these instances it has been shown that the material undergoes a solid-state phase change when placed under a measurable amount of strain. These phase changes have been shown to form (or “nucleate”) at the clamps (points of localized stress) and propagate toward the center of the sample (points of lower stress). The reflexivity of the material changes at these nucleation sites, so the phase change and propagation is a dramatic visual event, as illustrated by these graphics.
Very little research has been done regarding the phase-change properties of nitinol under bending stress (which is both tensile and compressive). This means that our research is very-nearly cutting edge!
Go back to homepage, or move on to References and Acknowledgements