Matteo Pezzulla

Thermodynamically based multiphysic modeling of ionic polymer metal composites

The modeling of the complex response of the IPMC-like body to electrical and mechanical stimuli is set within the context of the 3-D theory of linear elasticity. A field of chemically induced distortions is included in the model; these mechanical distortions and the derivation of the final PDE equations of the multiphysics problem are thermodynamically consistent. Some results of the numerical experiments are revisited through an original analysis of the stress distribution along the IPMC-like body.

Morphing of geometric composites via residual swelling

Understanding and controlling the shape of thin, soft objects has been the focus of significant research efforts among physicists, biologists, and engineers in the last decade. These studies aim to utilize advanced materials in novel, adaptive ways such as fabricating smart actuators or mimicking living tissues. Here, we present the controlled growth-like morphing of 2D sheets into 3D shapes by preparing geometric composite structures that deform by residual swelling. The morphing of these geometric composites is dictated by both swelling and geometry, with diffusion controlling the swelling-induced actuation, and geometric confinement dictating the structures deformed shape. Building on a simple mechanical analog, we present an analytical model that quantitatively describes how the Gaussian and mean curvatures of a thin disk are affected by the interplay among geometry, mechanics, and swelling. This model is in excellent agreement with our experiments and numerics. We show that the dynamics of residual swelling is dictated by a competition between two characteristic diffusive length scales governed by geometry. Our results provide the first 2D analog of Timoshenkos classical formula for the thermal bending of bimetallic beams - our generalization explains how the Gaussian curvature of a 2D geometric composite is affected by geometry and elasticity. The understanding conferred by these results suggests that the controlled shaping of geometric composites may provide a simple complement to traditional manufacturing techniques.

Swelling-induced and controlled curving in layered gel beams.

We describe swelling-driven curving in originally straight and non-homogeneous beams. We present and verify a structural model of swollen beams, based on a new point of view adopted to describe swelling-induced deformation processes in bilayered gel beams, that is based on the split of the swelling-induced deformation of the beam at equilibrium into two components, both depending on the elastic properties of the gel. The method allows us to: (i) determine beam stretching and curving, once assigned the characteristics of the solvent bath and of the non-homogeneous beam, and (ii) estimate the characteristics of non-homogeneous flat gel beams in such a way as to obtain, under free-swelling conditions, three-dimensional shapes. The study was pursued by means of analytical, semi-analytical and numerical tools; excellent agreement of the outcomes of the different techniques was found, thus confirming the strength of the method.

Steady and transient analysis of anisotropic swelling in fibered gels

The swelling–induced mechanical response of homogeneous anisotropic gels under free conditions and uniaxial loading is investigated. Semi–analytical and numerical analyses show that fibers hamper solvent uptake regardless of their orientation, causing the several changes in shape that occur. Finally, we verified that fibers do not significantly alter relaxation time, which determines the steady state under free–swelling conditions.

Curvature-driven morphing of non-Euclidean shells

We investigate how thin structures change their shape in response to non-mechanical stimuli that can be interpreted as variations in the structure’s natural curvature. Starting from the theory of non-Euclidean plates and shells, we derive an effective model that reduces a three-dimensional stimulus to the natural fundamental forms of the mid-surface of the structure, incorporating expansion, or growth, in the thickness. Then, we apply the model to a variety of thin bodies, from flat plates to spherical shells, obtaining excellent agreement between theory and numerics. We show how cylinders and cones can either bend more or unroll, and eventually snap and rotate. We also study the nearly isometric deformations of a spherical shell and describe how this shape change is ruled by the geometry of a spindle. As the derived results stem from a purely geometrical model, they are general and scalable.

Actuation and buckling effects in IPMCs

In the last decade, ionic polymer–metal composites are emerged as viable intelligent materials working both as bending actuators and energy harvesting systems. Recently, the feasibility of actuation from mechanical buckling has been investigated. In the present research, we present relevant numerical experiments concerning the possible electromechanical transduction when different patterned electrodes are considered. The focus of this research is theoretical, numerical, and experimental. In particular, with reference to almost one–dimensional IPMC strips, we take into account the large influence of electrodes’ bending stiffness on the IPMC behavior. We consider an original continuous metal strip covering the ionic polymer, and the patterned electrodes with one or more gaps. The actuation response of the system to low and to high voltages is studied; a strong difference is evidenced in the two situations as, in presence of high voltage, the system shows a buckling in opposite direction which needs further investigations.

Giant Displacements in IPMC-Based Structures: A Preliminary Study

A joint preliminary study has been performed to elucidate the capability of IPMC-based structures mimicking the behavior of biological systems. The structural deformation in response to an applied voltage is described within a nonlinear physics-based model of IPMC actuators. A characteristic of the model is the varying-along-the-thickness relative permittivity of the IPMCs, which takes into account the highly heterogeneous layers resulting from electrode deposition, where charge redistribution occurs. Preliminary experiments on an IPMC-based medusoid are presented to offer some validation of the modeling approach and provide directions for further studies.

Snapping of bistable, prestressed cylindrical shells

Bistable shells can reversibly change between two stable configurations with very little energetic input. Understanding what governs the shape and snap-through criteria of these structures is crucial for designing devices that utilize instability for functionality. Bistable cylindrical shells fabricated by stretching and bonding multiple layers of elastic plates will contain residual stress that will impact the shells shape and the magnitude of stimulus necessary to induce snapping. Using the framework of non-Euclidean shell theory, we first predict the mean curvature of a nearly cylindrical shell formed by arbitrarily prestretching one layer of a bilayer plate with respect to another. Then, beginning with a residually stressed cylinder, we determine the amount of the stimuli needed to trigger the snapping between two configurations through a combination of numerical simulations and theory. We demonstrate the role of prestress on the snap-through criteria, and highlight the important role that the Gaussian curvature in the boundary layer of the shell plays in dictating shell stability.