Experimental full-field analysis of size effects in miniaturized cellular elastomeric metamaterials

Abstract

Cellular elastomeric metamaterials are interesting for various applications, e.g. soft robotics, as they may exhibit multiple microstructural pattern transformations, each with its characteristic mechanical behavior. Numerical literature studies revealed that pattern formation is restricted in (thick) boundary layers causing significant mechanical size effects. This paper aims to experimentally validate these findings on miniaturized specimens, relevant for real applications, and to investigate the effect of increased geometrical and material imperfections resulting from specimen miniaturization. To this end, miniaturized cellular metamaterial specimens are manufactured with different scale ratios, subjected to in-situ micro-compression tests combined with digital image correlation yielding full-field kinematics, and compared to complementary numerical simulations. The specimens global behavior agrees well with the numerical predictions, in terms of pre-buckling stiffness, buckling strain and post-buckling stress. Their local behavior, i.e. pattern transformation and boundary layer formation, is also consistent between experiments and simulations. Comparison of these results with idealized numerical studies from literature reveals the influence of the boundary conditions in real cellular metamaterial applications, e.g. lateral confinement, on the mechanical response in terms of size effects and boundary layer formation.

Finite deformations govern the anisotropic shear-induced area reduction of soft elastic contacts

“…This is far beyond the range of validity of the small-strain theory, and linear elasticity in particular, so that the finite-strain framework used here is actually essential. At those large strains, the mechanical behaviour of the elastomer used in the experiments of Sahli et al (2018Sahli et al ( , 2019 (Sylgard 184) is already well beyond its linear range (Nguyen et al, 2011;Maraghechi et al, 2020).…”

Characterization of a chiral metamaterial depending on the type of connection between unit cells

“…Their behavior strongly depends on microstructural geometry, and buckling (local damage) of the microstructure entails nonlocal effective behavior. 4 An artificially designed structure in cellular mechanical metamaterials can be of two types: (i) stochastic, as in foams where a gaseous phase is randomly dispersed in a continuous solid medium, 3 and (ii) periodic one with a highly ordered arrangement of unit cells.…”

“…Their behavior strongly depends on microstructural geometry, and buckling (local damage) of the microstructure entails nonlocal effective behavior. 4…”

Topology optimization design for buckling analysis related to the size effect

“…With the tremendous development of additive manufacturing (AM) in recent years, the high resolution and rapid prototyping features of AM have triggered extensive interest in the design of micro-structure or nano-structure. However, the size effect has been significantly observed in a series of experimental results when the feature size of the structure was reduced to the micrometer or even nanometer scale [1][2][3][4]. The mechanical behaviors of structures in such scale range cannot be explained effectively by the classical mechanics owing to the lack of microscopic parameters that characterize the microscopic properties in the constitutive model [5][6][7].…”