Two-field surface pattern control via marginally stable magnetorheological elastomers

Abstract

The stability and post-bifurcation of a non-linear magnetoelastic film/substrate block is experimentally exploited to obtain active control of surface roughness. The non-intuitive interplay between magnetic field and elastic deformation owes to material and geometry selection, namely a ferromagnetic particle composite film bonded on a compliant passive foundation. Cooperation of the two otherwise independent loading mechanisms-mechanical pre-compression and magnetic field-allows one to bring the structure near a marginally stable state and then destabilize it with either magnetic or mechanical fields. We demonstrate for the first time that the critical magnetic field is a decreasing function of pre-compression and vice versa. The experimental results are then probed successfully with full-field finite element simulations at large strains and magnetic fields. The magnetoelastic coupling allows for reversible on/off control of surface wrinkling under adjustable critical magnetic and mechanical fields, thus this study constitutes a first step towards realistic active haptic and morphing devices.

Programmable higher-order Euler buckling modes in hierarchical beams

“…that of the elemental beams and that of the hierarchical macroscopic beam) with a small number of sinusoidal modes or even combination of elementary functions. Finally, we note that the observed overall buckled patterns of the hierarchical beams in Fig.12c resemble remarkably the crinkle morphology Pipkin (1986) observed in graphene (Kothari et al, 2018) and magnetorheological polymer film/substrate blocks (Psarra et al, 2017).…”

“…10. This curvature localization, discussed in more detail in the following section, leads to morphological patterns that resemble the crinkling patterns observed in graphene Kothari et al (2018) and in magnetorheological polymer film/substrate blocks Psarra et al (2017).…”

Microstructurally-guided explicit continuum models for isotropic magnetorheological elastomers with iron particles

“…Both µ and v 5 are of course independent of F and H. In this last expression and for later use, we have also defined the effective susceptibility χ = µ/µ 0 −1 of the MRE. It is also noted that (48) corresponds to the well-known Maxwell-Garnett (or equivalently Hashin-Shtrikman) estimate for purely magnetic composites (Psarra et al, 2017). As a consequence, (39) may be expressed explicitly as…”

“…However, the boundary conditions, to which a magneto-active elastomer is subjected to, is usually very different from the electro-active experiments. A MRE is typically placed far from the fixed magnetic poles, which essentially creates a Eulerian background magnetic field in between them (Psarra et al, 2017;Bodelot et al, 2018). On the other hand, electrodes are typically sprayed on an electro-active soft composite to apply an electric field directly on the boundary of the composite.…”

“…The former allows us to expressB as the curl of a vector potential A, i.e.,B = CurlA, whereas the latter leads to an expression ofH in terms of the gradient of a scalar potential, such that,H = −Gradϕ. Such vector/scalar potential-based formulations are used extensively in the numerical realization of coupled magneto-mechanical boundary value problems (Lefèvre et al, 2017;Danas, 2017;Psarra et al, 2017). In fact, from a purely computational point of view, the scalar potential-based formulation is simpler to implement due to the use of a single additional scalar degree of freedom, i.e., the scalar potential.…”