<p>The sharp penetration of granular materials is relevant to a variety of applications, including the locomotion of animals and robots on sandy grounds, defensive structures or civil constructions. In traditional granular materials, the grains “flow” around the advancing penetrator like a viscous liquid, which involves frictional dissipation but produces limited resistance to penetration. In this report, we explore the mechanical performance and mechanics of fully dense FCC granular crystals subjected to sharp penetration. These “granular metamaterials”, at the boundary between traditional granular materials and architected materials, are about 1000 times more resistant to penetration than traditional granular materials made of randomly distributed spheres. Using experiments and discrete element models, we show that despite the high mechanical confinement of the crystals, frictional sliding along specific slip planes is a prominent deformation mechanism up to the failure of the uppermost layer of grains. In addition, as the indenter is “wedged” between the grains, large compressive forces develop in the transverse directions, which eventually lead to the sudden buckling of the uppermost layer of grains, and to “explosive” failures involving the ejection of grains. As penetration proceeds, this loading-buckling cycle repeats, as layers are defeated in sequence. We finally show that once the surface layers of the crystal are destroyed by the penetrator, the crystal can be “healed” with vibrations and then punctured again with no loss of mechanical performance. These granular “metamaterials” can serve as a platform to develop additional strengthening strategies inspired by metallurgy, and they can find applications for rapid and versatile construction of static structures or as lightweight protective materials in a multitude of applications (e.g., buildings, body armor and vehicles).</p>