Compliant Hexagonal Meso-Structures Having Both High Shear Strength and High Shear Strain

Motivated by the authors’ previous study on flexible honeycomb design with negative Poisson’s ratio (NPR) often called ‘auxetic’ [1], more geometric options of hexagonal honeycomb meso-structures are explored with various ratios of the vertical cell length, h to the inclined length, l. While designing an effective shear modulus, e.g., G₁₂* of 10MPa, of hexagonal honeycombs, we are searching honeycomb geometries. Using an aluminum alloy (7075-T6) as the constituent material, the in-plane linear elastic honeycomb model is employed to get effective shear moduli, effective shear yield strengths and effective shear yield strains of hexagonal honeycombs. The numerical parametric study based on the linear cellular theory is combined with honeycomb design to get the optimal cell geometry associated with a manufacturing limitation. The re-entrant geometry makes 7075-T6 NPR honeycombs flexible, resulting in an effective shear yield strength, (τ_pl*)₁₂ of 1.7MPa and an effective shear yield strain, (γ_pl*)₁₂ of 0.17 when they are designed to have a G₁₂* of 10MPa.