Paris von Lockette

Multi-Field Responsive Origami Structures: Preliminary Modeling and Experiments

The use of origami principles to create 3-dimensional shapes has the potential to revolutionize active material structures and compliant mechanisms. Active origami structures can be applied to a broad range of areas such as reconfigurable aircraft and deployable space structures as well as instruments for minimally invasive surgery. Our current research is focused on dielectric elastomer (DE) and magneto active elastomer (MAE) materials to create multi-field responsive structures. Such multi-field responsive structures will integrate the DE and MAE materials to enable active structures that fold/unfold in different ways in response to electric and/or magnetic field. They can also unfold either as a result of eliminating the applied field or in response to the application of an opposite field. This concept is demonstrated in a folding cube shape and induced locomotion in the MAE material. Two finite element models are developed for both the DE and MAE materials and validated through physical testing of these materials. The models are then integrated to demonstrate multi-field responses of a bi-fold multi-field responsive structure. The bifold model is designed to fold about one axis in an electric field and a perpendicular axis in a magnetic field. Future modeling efforts and research directions are also discussed based on these preliminary results.Copyright

Bistable compliant mechanism using magneto active elastomer actuation

One of the challenges in the emerging field of origami engineering is achieving large deformations to enable significant shape transformations. Bistable compliant mechanisms provide a means to achieve this, and the goal of this research is to investigate the feasibility and design of a compliant bistable mechanism that is actuated by magneto active elastomer material. When exposed to an external field, magneto active elastomer material deforms to align embedded magnetic particles with the field. We investigate a case study using magneto active elastomer actuation through the development of finite element analysis models to predict the magnetic field required to snap the device from its first stable position to its second for various geometries and field strengths. The finite element analysis model also predicts the displacement of the mechanism as it moves from one position to the other to determine whether the device is in fact bistable. These results can be used to understand the relationship between the substrate properties and the bistability of the device. The experimental results validate the finite element analysis models and demonstrate the functionality of active magneto active elastomer materials to be used as actuators for such devices and applications of origami engineering.

Differentiating Bending From Folding in Origami Engineering Using Active Materials

Origami engineering — the use of origami principles in engineering applications — provides numerous opportunities to revolutionize the way we design, manufacture, assemble, and package products and devices. By combining origami principles with active materials, we can create reconfigurable products and devices that can fold and unfold on demand. In origami, the folded medium is paper, yet many engineering applications require materials with finite thickness to provide the necessary strength and stiffness to achieve the desired functionality. In such applications, it is important to distinguish between bending and folding so that we understand the differences in material behavior when actuated. In this paper, we propose definitions for bending and folding for materials used in engineering applications. The literature is reviewed in detail to provide context and support for the proposed definitions, and examples from our own research with active materials, specifically, magneto-active elastomers (MAE) and dielectric elastomers (DE), are used to illustrate the subtle, yet important, differences between bending and folding in materials with finite thickness.Copyright

Folding Actuation and Locomotion of Novel Magneto-Active Elastomer (MAE) Composites

Magneto-active elastomers (also called magnetorheological elastomers) are most often used in vibration attenuation application due to their ability to increase in shear modulus under a magnetic field. These shear-stiffening materials are generally comprised of soft-magnetic iron particles embedded in a rubbery elastomer matrix. More recently researchers have begun fabricating MAEs using hard-magnetic particles such as barium ferrite. Under the influence of uniform magnetic fields these hard-magnetic MAEs have shown large deformation bending behaviors resulting from magnetic torques acting on the distributed particles and consequently highlight their ability for use as remotely powered actuators. Using the magnetic-torque-driven hard-magnetic MAE materials and an unfilled silicone elastomer, this work develops novel composite geometries for actuation and locomotion. MAE materials are fabricated using 30% v/v 325 mesh barium ferrite particles in Dow Corning HS II silicone elastomers. MAE materials are cured in a 2T magnetic field to create magnetically aligned (anisotropic) materials as confirmed by vibrating sample magnetometry (VSM). Gelest optical encapsulant is used as the uniflled elastomer material. Mechanical actuation tests of cantilevers in bending and of accordion folding structures highlight the ability of the material to perform work in moderate, uniform fields of . Computational simulations are developed for comparison. Folding structures are also investigated as a means to produce untethered locomotion across a flat surface when subjected to an alternating field similar to scratch drive actuators; geometries investigated show promising results.

Particle mixtures in magnetorheological elastomers (MREs)

Magnetorheological elastomers (MREs) are state-of-the-art elastomagnetic composites comprised of magnetic particles embedded in an elastomer matrix. MREs offer enormous flexibility given that elastomers are easily molded, provide good durability, exhibit hyperelastic behavior, and can be tailored to provide desired mechanical and thermal characteristics. MRE composites combine the capabilities of traditional magnetostrictive materials with the properties of elastomers, creating a novel material capable of both highly responsive sensing and controlled actuation in real-time. This work investigates the response of MRE materials comprised of varying mixtures of 40 and 10 micron iron particles. Samples are tested in compression yielding a compressive modulus and measure of the shear stiffness via Mooney plots. Samples are also tested using a tunable vibration absorber (TVA) designed specifically for this experiment. The TVA loads the samples in oscillatory shear (10-100Hz) under the influence of a magnetic field. In all samples, results show increases in the materials stiffness under the application of a magnetic field as evidenced by the frequency response function of the TVA system. Increases in stiffness of 50% at 0.15T were achieved with samples containing 30%-40 micron particles and 30%-40micron + 2%-10 micron particles. This yields a ratio of over 300%/T. The two-particle MRE appeared not to have reached saturation suggesting further stiffness enhancement was possible beyond the saturated single-particle 40 micron sample. However, this may be a result of the larger iron content. Results also suggest variation in the behavior of two-versus single-particle MRE behavior as evidenced by the shear modulus found in compression, but results are inconclusive. MRE materials made with nanoparticles of hard magnetic barium ferrite show stiffness increases of 70%/T which is comparable to MREs having larger iron particles.

Role of Magnetization Anisotropy in the Active Behavior of Magnetorheological Elastomers

Magnetorheological elastomers (MREs) are a re-emerging class of smart materials whose novel behavior stems from their response to magnetic fields. Historically comprised of soft-magnetic carbonyl (spherical) iron particles embedded in highly compliant matrix materials, MRE research has focused on their apparent change in shear modulus (in excess of 60%) under a magnetic field. Recent work by the authors has departed from the experimental and theoretical focus on MREs made from soft-magnetic particles (S-MREs) to investigate MREs having hard-magnetic particle inclusions (H-MREs). While H-MRE materials do not perform well in dynamic shear stiffness applications when compared to the traditional S-MREs, H-MREs provide remotely powered, fully reversible actuation capabilities that S-MREs are unable to achieve. In addition, in the same dynamic shear stiffness applications these H-MREs provide a measure of active control of which S-MREs are also incapable. This work examines the role that particle magnetization, developed due to shape anisotropy, plays in the actuation response S-MREs in contrast to H-MREs. H-MRE response is predicated on the response of the hard-magnetic particles to the external magnetic field and to neighboring particles. Since hard-magnetic particles have an internal preferred magnetic orientation, they are able to generate torques at the particle level, T = M × B , where T is the torque density, M is the magnetization, and B is the local magnetic flux density. In contrast, soft-magnetic particles may develop an induced magnetization when exposed to an external field if the particles exhibit shape anisotropy. This induced magnetization is also capable of producing torque at the particle level, however, spherical particles like those historically used in MREs are geometrically isotropic and therefore do not develop induced magnetization either and consequently the widely studied MREs comprised of soft-magnetic spherical particles generate no torque at the particle level. Shape anisotropy further complicates the mechanical response by inducing Eshelby-type shape-dependent effects on the mechanical stresses developed local to the particle. These effects vary the local particle rotation, resulting from a given macroscopic loading, and in turn affect the local magnetic field by changing the particle’s magnetization axis with respect to the external field. The result is a material system whose elastomagnetic response depends on particle shape and orientation as well as on particle magnetization. In previous works the authors used barium hexaferrite (a hard magnetic material) and carbonyl iron powders to generate MRE materials having varying particle alignment and magnetization permutations. These materials were examined in cantilever bending modes to assess and differentiate their abilities as bending actuators. In this work, finite element studies mirroring the bending tests are performed to determine the role of particle/magnetization anisotropy on the behavior. Results show strong dependence on particle shape anisotropy.Copyright

Fabrication and Performance of Magneto-Active Elastomer Composite Structures

This works discusses the use of magneto-active elastomer (MAE) as an active material for use in origami engineering and other applications where transformation of a composite structure between target shapes is desired. Magneto-active elastomer, as the name implies, consists of magnetic powders dispersed in an elastomer (polymer) fluid which is subsequently cured in the presence of a magnetic field to produce a net remanent magnetization in the cured solid. Having their own internal magnetization, MAE materials are affected by both magnetic forces, due to gradients in local field, as well as magnetic torques resulting from the cross product of the field and the magnetization. In this fashion, patches of MAE material, distributed throughout a non-magnetic elastomeric structure, act as distributed actuators producing deformed shapes. The use of rare-Earth magnets as the magnetic actuation elements is also investigated. The work highlights experimental efforts to develop structures with integrated MAE patches and rare-Earth magnets of varying magnetization orientations using multi-step casting processes and 3D printing techniques. Initial results show success at generating active structures having locally oriented MAE patches and magnets in accordion, water bomb and and Miru fold patterns.Copyright

A Dynamic Model of Magneto-Active Elastomer Actuation of the Waterbomb Base

Of special interest in the growing field of origami engineering is self-folding, wherein a material is able to fold itself in response to an applied field. In order to simulate the effect of active materials on an origami-inspired design, a dynamic model is needed. Ideally, the model would be an aid in determining how much active material is needed and where it should be placed to actuate the model to the desired position. A dynamic model of the origami waterbomb base, a well-known and foundational origami structure, is developed using Adams, a commercial dynamics software package. Creases are approximated as torsion springs with stiffness and damping. The stiffness of an origami crease is calculated, and the dynamic model is verified using the bistability of the waterbomb. An approximation of the torque produced by magneto-active elastomers (MAE) is calculated and is used to simulate MAE-actuated self-folding of the waterbomb.Copyright

On the electric and magnetic alignment of magnetoactive barium hexaferrite-PDMS composites

This study demonstrates how to judiciously use two different external fields to engineer a polymer- based composite that responds to both electric and magnetic fields. Specifically, we demonstrate the electric and magnetic alignment of M-type Barium Hexaferrite (BF) in polydimithylsiloxane (PDMS) to obtain a multifunctional composite whose electrical and magnetic properties depend on the orientation of the BF. First, the BFs are electrically aligned in the polymer matrices by applying an AC electric field. From optical microscopy (OM) imaging, the optimal electrical alignment conditions are determined, and those parameters are used to fabricate the composites. After the composite is electrically aligned and partially cured, magnetic field is then applied. Under the magnetic field, BFs are further aligned in-plane and out-of-plane along their magnetic c-axis within the chains that formed during electrical aligning. Following complete cure, the microstructures from the OM image show parallel chain formation. Vibrating Sample Magnetometry (VSM) and XRD results confirm BFs are crystallographically aligned along their magnetic c-axis. The textured BF-PDMS composites are found to have anisotropic magnetic and dielectric properties. The possibility of electrical alignment of magnetic particles will open up new doors to manipulate and design particle-modified polymers for different applications.

Characterization of Self-Folding Origami Structures Using Magneto-Active Elastomers

Magneto-active elastomers (MAEs) are polymers with magnetic particles that are capable of aligning with an external magnetic field; this self-alignment ability is one reason why MAEs can be used as actuators for folding or bending in origami engineering. The focus of this paper is on experimental characterization and finite element modeling of an MAE folding accordion structure. The goal is to understand the relationships among the applied magnetic field, displacement of the structure during actuation, and the resultant reaction force generated. This relationship is important for applications where force generation caused by the actuation of MAE structures is required.Data show that force increases with increasing magnetic field, and the work done by the structure can also be calculated by integrating the force. Good agreement between the finite element analysis and experimental data is shown. Future methods for improving experimentation and modeling are discussed based on the results.Copyright