Theory and Computation for the MicrostructureNear the Interface Between Twinned Layers and aPure

We report results on a nite element simulation of a needle-like martensitic microstructure observed in biaxial loading experiments conducted by Chu and James on single crystals of the shape-memory alloy Cu-14at.%Al-3:9at.%Ni. This microstructure was observed near an interface between twinned layers of two variants and a pure variant of martensite. We used a geometrically nonlinear theory of martensite to model and compute the complex microstructure by energy minimization with a boundary condition that is compatible with the microstructure. Our computational model has yielded multiple metastable states that depend on the initial state of our energy-minimizing iteration. The simulated twinned layers form branches and bend as they approach the laminate-single variant interface in good agreement with the experiment of Chu and James. 1 2 Fig. 1. Photomicrograph of a needle-like microstructure near a laminate-single variant interface (Chu and James). Field of view: 2.5 mm 1.6 mm.