National Institute of Standards and Technology, Materials Science
and Engineering Laboratory
*Department Materials and Nuclear Engineering , University of Maryland,
College Park
An adaptive composite containing a shape memory alloy as an active component is the subject of this research. These composites utilize the unique properties of SMA, which change their crystalline structure in response to the change temperature and stress. The combination of the shape memory material as an active and the elastic material as a passive component allows one to improve the properties of the SMA itself (create two-way shape memory) and to engineer a composite material which can have superelastic properties.
In this work the thermodynamic analysis of deformation of elastically heterogeneous composite containing shape memory material as an active component is presented. It is shown that the superelastic modulus of the composite depends on the fraction of the active layer and can be negative if relative thickness of the active layer exceeds some critical value depending on the ratio between the elastic moduli of the layers and the characteristics of transformation. The negative superelastic modulus corresponds to the thermodynamic instability of superelastic deformation and results in stress-strain hysteresis. The relation between the elastic properties of the compositeâs components and relative thickness of the layers which enable stability of the superelastic deformation is obtained.