Inverted and Programmable Poynting Effects in Metamaterials

Abstract

The Poynting effect generically manifests itself as the extension of the material in the direction perpendicular to an applied shear deformation (torsion) and is a material parameter hard to design. Unlike isotropic solids, in designed structures, peculiar couplings between shear and normal deformations can be achieved and exploited for practical applications. Here, a metamaterial is engineered that can be programmed to contract or extend under torsion and undergo nonlinear twist under compression. First, it is shown that the system exhibits a novel type of inverted Poynting effect, where axial compression induces a nonlinear torsion. Then the Poynting modulus of the structure is programmed from initial negative values to zero and positive values via a pre-compression applied prior to torsion. The work opens avenues for programming nonlinear elastic moduli of materials and tuning the couplings between shear and normal responses by rational design. Obtaining inverted and programmable Poynting effects in metamaterials inspires diverse applications from designing machine materials, soft robots, and actuators to engineering biological tissues, implants, and prosthetic devices functioning under compression and torsion.

Programmable nonreciprocal Poynting effect enabled by lattice metamaterials

“…Although both phenomena involve longitudinal and transverse displacements, the displacements are driven by the normal force in the compression-twisting effect (20,21) and by the shear force in the Poynting effect (22,23). Traditionally, the Poynting effect demonstrates that the normal stress remains the same when shearing in both the left and right directions (24)(25)(26)(27), which is reciprocal and adheres to the Maxwell-Betti reciprocity theorem (1) ( F ⊥ R U = F ⊥ L U in Fig. 1A).…”

Shape Morphing of Tubular Structures with Tailorable Mechanical Properties

“…The fixed structural ends are imitated by adding solid rings of 5 mm thickness at the ends of the samples (Figure 2c and 8). It enabled to avoid clamping [ 49 ] or gluing the ends, thus simplifying the testing procedure.…”

Shear rupture mechanism and dissipation phenomena in bias-extension test of pantographic sheets: Numerical modeling and experiments

“…The research lines can be roughly classified into those devoted to the analysis of theoretical aspects [7][8][9][10][11][12], to the formulation of computational methods in discrete [13][14][15][16] and continuum framework [17][18][19][20], as well as to the investigations of experimental evidence [21][22][23][24][25][26][27]. The genesis in conceiving the pantographic sheet can be traced back in the grounding idea of non-local materials, and in particular of second or higher gradient theories [28][29][30][31][32][33][34][35][36][37], in which the constitutive law is a function also of the second or higher gradient of the displacement field. In the same context of non-local formulation, it is worth mentioning the peridynamic approach proposed, among the others, in previous studies [38][39][40][41][42].…”