Bending-induced extension in two-dimensional crystals
  According to the classical theory of elasticity, a plate subjected to a bending moment always deflects with symmetric tensile and compressive strains in its two sides, without overall deformation perpendicular to the bending moment. Here, we find by ab initio simulations that significant overall tensile strain can be induced by pure bending in a wide range of two-dimensional crystals perpendicular to the bending moment, just like an accordion being bent to open. This accordion effect is raised by asymmetric response of chemical bonds and electron density to the bending curvature, with the tensile strain being a power function of the curvature. 
Douxing Pan, Yao Li, Tzu-Chiang Wang, and Wanlin Guo
cond-mat.mtrl-sci