Study on magneto-sensitive solids : Experiments, Theory and Numerics

Abstract : The present work deals with the stability and post-bifurcation response of isotropic magnetorheological elastomers (MREs). MREs are elastomers comprising a finite volume fraction of magnetizable iron particles, distributed randomly in the volume. Specifically, a nonlinear magnetoelastic film/substrate system is experimentally, numerically and theoretically 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 two otherwise independent loading mechanisms--mechanical pre-compression and magnetic field--allows 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 probed successfully with full-field finite element simulations at large strains and magnetic fields. A theoretical magnetomechanical bifurcation analysis on an infinite magnetoelastic system is further employed to explore the effect of the interlayer combined properties on the critical response and is compared with the available numerical results.  With the perspective of applying the principle of surface actuation to new magnetomechanically triggered patterns, we further investigate the post-bifurcation of an entirely magnetorheological bilayer block. The underlying idea is to create different interlayer contrasts of magnetic and mechanical properties allowing us to trigger a larger range of surface patterns than that already obtained when using a MRE film on a passive (magnetically insensitive) foundation. Post-bifurcation calculations of MRE films bonded on MRE substrates allow to reveal novel patterns that lead to significant curvature localisation and crinkling.  In all cases studied, the magnetoelastic coupling allows for the reversible on/off control of surface patterning under adjustable critical magnetic and mechanical fields for a single specimen and thus, this study constitutes a first step towards realistic active haptic and morphing devices.
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Erato Psarra. Study on magneto-sensitive solids : Experiments, Theory and Numerics. Mechanics of the solides [physics.class-ph]. Université Paris-Saclay, 2018. English. ⟨NNT : 2018SACLX094⟩. ⟨tel-02060836⟩

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