Uniaxial deformation of an adaptive material which can change its microstructure due to a phase transformation is considered. At fixed temperature and fixed surface displacement the phase transformation results in an equilibrium two-phase mixture. A typical equilibrium two- phase microstructure of an initial and a product phase is an alteration of the plane-parallel layers of the phases with a special crystallographic orientation of interfaces between layers. The relative fractions of the phases are determined by the external conditions. The two-phase free energy is a non-convex function of constrained strain. Therefore, the stress-strain relation at displacement controlled deformation of the transforming two-phase mixture is characterized by a negative Young's modulus. If deformation proceeds under stress control, a hysteretic stress-strain curve on loading and unloading should be observed instead of a negative stress-strain slope.

Date Published: 13 June 1997
PDF: 12 pages
Proc. SPIE 3039, Smart Structures and Materials 1997: Mathematics and Control in Smart Structures, (13 June 1997); doi: 10.1117/12.276563

Published in SPIE Proceedings Vol. 3039:
Smart Structures and Materials 1997: Mathematics and Control in Smart Structures
Vasundara V. Varadan; Jagdish Chandra, Editor(s)