Deformation activated negative group velocity state in soft laminates

We report the observation of deformation-induced negative group velocity (NGV) state in the non-periodic media. The phenomenon is illustrated by examples of the shear waves traveling along the non-periodic direction of pre-strained soft laminates. We show that the NGV state can be induced in absolutely stable laminates without invoking buckling. These stable composites with activated NGV states are achieved through tailored stiffening behavior of their non-Gaussian soft phases. The deformation range – for which the NGV state is activated – is multiple times higher in the proposed absolutely-stable composites than those prone to buckling. Finally, we analyze how this unusual NGV state can be induced and further tuned by variations in the material and geometric parameter spaces.