Viscoelastic Snapping Metamaterials

Abstract

Mechanical metamaterials are artificial composites with tunable advanced mechanical properties. Particularly interesting types of mechanical metamaterials are flexible metamaterials, which harness internal rotations and instabilities to exhibit programmable deformations. However, to date such materials have mostly been considered using nearly purely elastic constituents such as neo-Hookean rubbers. Here we explore experimentally the mechanical snapthrough response of metamaterials that are made of constituents that exhibit large viscoelastic relaxation effects, encountered in the vast majority of rubbers, in particular in 3D printed rubbers. We show that they exhibit a very strong sensitivity to the loading rate. In particular, the mechanical instability is strongly affected beyond a certain loading rate. We rationalize our findings with a compliant mechanism model augmented with viscoelastic interactions, which captures qualitatively well the reported behavior, suggesting that the sensitivity to loading rate stems from the nonlinear and inhomogeneous deformation rate, provoked by internal rotations. Our findings bring a novel understanding of metamaterials in the dynamical regime and opens up avenues for the use of metamaterials for dynamical shape-changing as well as vibration and impact damping applications.

Material characterisation of additively manufactured elastomers at different strain rates and build orientations

“…The mechanical flexibility of PolyJet elastomers have made them particularly useful for applications including soft robotic active hinges and actuators [14,17,18], shape memory '4D materials' and composites [14,[19][20][21][22][23][24]. Other applications included wearable electronics [25], compliant systems and metamaterials [15,26].…”

Oligomodal metamaterials with multifunctional mechanics

“…Our approach is broadly applicable for the design of flexible metamaterials with low-energy strain pathways. In particular, our approach could be further generalized to other types of unit cells, to other lattices, and to 3D tilings and applied to more types of functionalities such as chiral responses ( 31 – 33 ), shape morphing ( 4 , 11 , 34 ), enhanced energy absorption ( 26 , 35 ) and nonlinear wave propagation ( 36 , 37 ). In particular, we expect the switchable nature of oligomodal metamaterials to enable the control of deformation pathways, which could be potentially useful for dissipation of energy.…”

“…3 O ) with the top set of indenters. To quantify the deformations of each unit cell, we use particle tracking (OPENCV [a computer vision library] and Python) and custom-made tracking algorithms to quantify the flattening and orientation with respect to the horizontal of each pore and calculate the polarization ( 26 ) , where ( ) is the unit cell’s column (row). Using this protocol, we observe that we can actuate either the rotating-squares mode ( Fig.…”

“…To achieve this goal, we leave the realm of static responses and harness viscoelastic dissipation to tune the dynamical response of our metamaterial ( 26 – 28 ), previously applied to alter the direction of a mechanical mode ( 26 , 28 ). Instead, we now harness viscoelasticity to switch between modes altogether.…”

Mechanical Metamaterials on the Way from Laboratory Scale to Industrial Applications: Challenges for Characterization and Scalability

“…The vast majority of published metamaterials are made out of polymers as they can generally accommodate larger deformations [2,3,16,27,37,[41][42][43]. However, it is important to remember that polymers can exhibit viscoelastic properties that will influence the overall mechanical properties, especially under loading conditions [44].…”