  In layered materials, a common mode of deformation involves buckling of the
layers under tensile deformation in the direction perpendicular to the layers.
The instability mechanism, which operates in elastic materials from geological
to nanometer scales, involves the elastic contrast between different layers. In
a regular stacking of "hard" and "soft" layers, the tensile stress is first
accommodated by a large deformation of the soft layers. The inhibited Poisson
contraction results in a compressive stress in the direction transverse to the
tensile deformation axis. The hard layers sustain this transverse compression
until buckling takes place and results in an undulated structure. Using
molecular simulations, we demonstrate this scenario for a material made of
triblock copolymers. The buckling deformation is observed to take place at the
nanoscale, at a wavelength that depends on strain rate. In contrast to what is
commonly assumed, the wavelength of the undulation is not determined by defects
in the microstructure. Rather, it results from kinetic effects, with a
competition between the rate of strain and the growth rate of the instability.
http://www.pnas.org/content/early/2011/12/23/1111367109.abstract
