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We propose a magnetic field-induced asymmetric mechanical metamaterial. The tunable metamaterial integrates hard-Magnetic Active Elastomers (hMAEs) into the microstructural design combining snap-through, bi-stability, and local resonant effects. The proposed metamaterial design comprises resonating units made out of hMAE, and these units are supported by highly deformable curved beams connected with an elastomeric matrix. Activated by a magnetic field, the resonating units attain an unstable regime with dramatic configuration and stiffness variation. These controlled transformations significantly affect the elastic wave propagation. We illustrate that the proposed magnetoactive metamaterial enables bandgap tunability over a broadband low-frequency range. Thus, the proposed design allows remote and reversible control of the metamaterial performance. Moreover, the hMAE-based systems can incorporate the polarity and chirality stemming from the interaction of external magnetic fields and hMAE phases, giving rise to the unusual behavior of the metamaterial, and potentially enabling elastic cloaking.

We report the observation of deformation-induced negative group velocity (NGV) state in the non-periodic media. The phenomenon is illustrated by examples of the shear waves traveling along the non-periodic direction of pre-strained soft laminates. We show that the NGV state can be induced in absolutely stable laminates without invoking buckling. These stable composites with activated NGV states are achieved through tailored stiffening behavior of their non-Gaussian soft phases. The deformation range – for which the NGV state is activated – is multiple times higher in the proposed absolutely-stable composites than those prone to buckling. Finally, we analyze how this unusual NGV state can be induced and further tuned by variations in the material and geometric parameter spaces.

We investigate the microscopic and long-wave (or macroscopic) instabilities in fiber composites (FCs) with hyperelastic phases. To study the influence of the phase stiffening behavior, we employ the phase constitutive models that are developed based on the non-Gaussian statistics of polymeric molecular chains. These non-Gaussian models accurately predict the non-linear behavior of soft materials. Moreover, they can capture the essential soft material stiffening behavior arising due to the finite extensibility of the polymer chains. In turn, the non-linear behavior of the composite phases significantly influences the elastic instabilities and the buckling patterns. Here, we illustrate the phenomenon by the example of FCs with Gent phases. We derive an explicit closed-form expression – in terms of the phase properties and composition – for the onset of long-wave instabilities. To predict the onset of finite length scale (or microscopic) instabilities, we employ the Bloch-Floquet analysis superimposed on finite deformations. We find that the matrix stiffening behavior stabilizes the composites, and can even result in an absolutely stable scenario. Remarkably, Gent FCs with identical phase stiffening characteristics are found to be more stable than their neo-Hookean counterparts for morphologies at which the microscopic instabilities are to develop first. The stiffening behavior of the phases dictates the interplay between the long-wave and microscopic instabilities, and defines the wavelength of the buckling patterns. Thus, the pre-designed phase properties can be used in tailoring the instability-induced patterns in soft fiber composites. [ABSTRACT FROM AUTHOR]

In this work, we study the nonlinear behavior of soft photocured polymers typically used in 3D-printing. We perform experimental testing of 3D-printed samples cured at various controlled light intensities. The experimental data show the dependency of the material elasticity and rate-sensitivity on the curing light intensity. To elucidate these relations, we develop a physically-based visco-hyperelastic model in the continuum thermodynamics framework. In our model, the macroscopic viscoelastic behavior is bridged to the microscopic molecular chain scale. This approach allows us to express the material constants in terms of polymer chain physical parameters. We consider different physical mechanisms governing hyperelasticity and rate-dependent behaviors. The hyperelastic behavior is dictated by the crosslinked network; whereas, the viscous part originates in the free and dangling chains. Based on our experimental data, we illustrate the ability of the new constitutive model to accurately describe the influence of the light intensity on photocured polymer viscoelasticity.