Shape Memory Materials

Shape memory materials exhibit pseudo-elastic behaviors and shape memory properties.  They can be deformed 'elastically' up to 7-8% or even higher strain which will completely recover upon unloading.  If deformed at a low temperature, they will also recover their original shapes when heated to above a certain critical temperature.  A lot of energy is dissipated in one pseudo-elastic loading/unloading cycle, making shape memory materials excellent candidates for mechanical damping applications.  What is more, the coupling between thermal and mechanical fields enables these materials to be used as actuators or components in multifunctional composites and devices.  Our group is investigating the pseudo-elastic and shape memory properties of Cu-Al-Ni shape memory alloys.  Cu-based alloys are relatively inexpensive compared to other alloys, and have good thermal and electrical conductance.  We are making fine structures of these alloys and studying the size effects of the damping capabilities and shape memory properties.

Black curves represent two macroscopic compression tests on bulk single crystals (S-X) at 363 K and 305 K respectively.  The red curve represents the nano compression on a nano pillar at 295 K.  The very large area of the closed loading/unloading loop in the nano pillar experiment represents the much larger amount of energy dissipated compared to bulk materials.

Published Articles:

A size-effect on superelasticity: Ultra-high mechanical damping at the nano-scale
San Juan J, No ML, Schuh CA; Nature Nanotechnology, 4, 415, 2009 (PDF)

Superelasticity and shape memory in micro- and nanometer-scale pillars
Juan JMS, No ML, Schuh CA; ADVANCED MATERIALS 20 (2):272-278 JAN 2008 (PDF)