  We present a simple discrete formula for the elastic energy of a bilayer. The
formula is convenient for rapidly computing equilibrium configurations of
actuated bilayers of general initial shapes. We use maps of principal
curvatures and minimum-curvature direction fields to analyze configurations. We
find good agreement between the computations and an approximate analytical
solution for the case of a rectangular bilayer. For more general shapes (simple
polyiamonds), we find a range of typical bending behaviors: overall bending
directions along longest and shortest dimensions, inward bending at corners,
curvature intensification near boundaries, and conical bending and partitioned
bending zones in some cases.
