1. Context

Since the 1990s, there has been growing interest in film-like materials that can deform into 3D shapes without the application of external forces, due to the films' internal bending moment. A classic example is a bimetallic strip, consisting of two welded layers of metals with different coefficients of expansion (e.g. steel and copper). The unequal expansion of the layers, bonded together, leads to the bending moment, which is balanced by the bending stiffness of the layers. The problem was considered mathematically a century ago by Stoney , who proposed the first...