Theory and computation for the microstructure near the interface between twinned layers and a pure variant of martensite

We report results on a finite element simulation of a needle-like martensit ic microstructure observed in biaxial loading experiments conducted by Chu and James on single crystals of the shape-memory alloy Cu-14 at.% Al-3.9 at .% Ni. This microstructure was observed near an interface between twinned l ayers of two variants and a pure variant of martensite. We used a geometric ally nonlinear theory of martensite to model and compute the complex micros tructure by energy minimization with a boundary condition that is compatibl e with the microstructure. Our computational model has yielded multiple met astable states that depend on the initial state of our energy-minimizing it eration. The simulated twinned layers form branches and bend as they approa ch the laminate-single variant interface in good agreement with the experim ent of Chu and James. (C) 1999 Elsevier Science S.A. All rights reserved.