  We investigate the mechanical response of thin sheets perforated with a
square array of mutually orthogonal cuts, which leaves a network of squares
connected by small ligaments. Our combined analytical, experimental and
numerical results indicate that under uniaxial tension the ligaments buckle
out-of-plane, inducing the formation of 3D patterns whose morphology is
controlled by the load direction. We also find that by largely stretching the
buckled perforated sheets, plastic strains develop in the ligaments. This gives
rise to the formation of kirigami sheets comprising periodic distribution of
cuts and permanent folds. As such, the proposed buckling-induced pop-up
strategy points to a simple route for manufacturing complex morphable
structures out of flat perforated sheets.
