This study examines the mechanical behavior of a novel class of mechanical metamaterialsudalternating pentamode lattices and stiffening plates. The unit cell of such lattices consists of audsub-lattice of the face cubic-centered unit cell typically analyzed in the current literature onudpentamode materials. The studied systems exhibit only three soft deformation modes in theudinfinitesimal stretch-dominated regime, as opposed to the five zero-energy modes of unconfinedudpentamode lattices. We develop analytical formulae for the vertical and bending stiffnessudproperties and study the dependence of such quantities on the main design parameters: theudlattice constant, the solid volume fraction, the cross-section area of the rods, and the layerudthickness. A noteworthy result is that the effective compression modulus of the analyzedudstructures is equal to two thirds of the Young modulus of the stiffest isotropic elastic networksudcurrently available in the literature, being accompanied by zero-rigidity against infinitesimaludshear and twisting mechanisms. The use of the proposed metamaterials as novel seismicisolationuddevices and impact-protection equipment is discussed by drawing comparisons withudthe response of alternative devices already available or under development.
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