  Oriented block copolymers exhibit a buckling instability when submitted to a
tensile test perpendicular to the lamellae direction. In this paper we study
this behavior using a coarse grained molecular dynamics simulation approach.
Coarse grained models of lamellar copolymers with alternate glassy rubbery
layers are generated using the Radical Like Polymerization method, and their
mechanical response is studied. For large enough systems, uniaxial tensile
tests perpendicular to the direction of the lamellae reveal the occurrence of
the buckling instability at low strain. The results that emerge from molecular
simulation are compared to an elastic theory of the buckling instability
introduced by Read and coworkers. At high strain rates, significant differences
are observed between elastic theory and simulation results for the buckling
strain and the buckling wavelength. We explain this difference by the strain
rate dependence of the mechanical response. A simple model that takes into
account the influence of the strain rate in the mechanical response is
presented to rationalize the results at low and moderate strain rates. At very
high strain rates, cavitation takes place in the rubbery phase of the sample
and limits the validity of the approach.
