This PDF file contains the front matter associated with SPIE Proceedings Volume 12044 including the Title Page, Copyright information, and Table of Contents.

Materials that have a shape memory are capable to switch between different stable states when external stimuli are applied. This work introduces a new, multi-physical concept for shape memory in assembled composite structures. The concept is called magnetofriction and is based on magnetism, elasticity, contact and friction. In assemblies of permanently magnetized MagnetoActive Elastomers (MAE), the contact pressure is established by magnetic attraction forces. When the assembly is deformed, the contact surfaces slide over each other and the deformed shape is locked by the friction in the interface. A loosening of the contact causes the friction forces to vanish and each part of the assembly recovers its initial state due to the elastic forces in the materials. The contact is restored after the shape recovery. A test assembly, called MagnetoFriction – Shape Memory Polymer (MFSMP), is used to validate the concept experimentally. It consists of two stacked, permanently magnetized MAE beams. The assembled structure is subjected to a three-point bending test and retains a permanent deformation after the tests. The force displacement response of the MF-SMP reveals that the deformed configuration is stabilized after a first loading cycle. A digital image correlation reveals sliding in the contact interface of the assembly during the first loading. The adhesion, observed in the subsequent loading cycles, is responsible for the shape lock. When the beams are separated manually or by compressed air, the stored deformation vanishes. Magnetofriction is compared to other mechanisms to classify the new concept in the field of shape memory materials.

Process fluctuations due to changing environmental conditions, thermal loads and wear are known problems in industrial production. When accumulated, they can lead to instabilities in process chains. Paraffin wax-based phase change actuators (PCA) are an available, robust solution for stabilization and error compensation. Consisting of two deep-drawn steel cups, joined by laser welding, they enclose a paraffin wax core. Phase transformation of the paraffin wax leads to a significant volume expansion, generating the actuating force. The PCAs are suitable even for highly rigid systems with achievable actuating forces of above 85 N/mm² of effective actuator area. Additionally, the particularly compact housing offers high integration capability. Passive PCAs, activated by environmental heat, are already integrated in industrial applications. For active application, an energy supply via additional external heating elements, e.g. heating tapes, is required. This contradicts the concept of a simple and compact overall system and thus the integration capability. The overriding challenge results in implementing the PCA as an actively controllable, integrated overall system. This paper presents an approach based on printed electronics, consisting of a conductive carbon ink, applied to a corresponding substrate by means of screen-printing. Electrical connections are subsequently attached and the heating unit is integrated into the PCA. This work shows challenges within design and implementation of these high-performance heating electronics. It discusses different inks, substrates and their necessary properties for PCA usage. Concepts for electrical conduction through the sealed actuator housing are presented. Finally, the performance of these PCAs is discussed and compared with passive, externally activated PCAs.

Bistable laminates present a promising approach for shape-morphing applications due to their large deflections and low input energy required to transition between states. Recently, these engineered materials have been considered for kinetic systems in architecture. One challenge of using large bistable laminates in a building-scale application is finding proper actuation mechanisms. This paper focuses on a case study using Magneto-Active Elastomers (MAEs) as actuators of bistable flaps. More specifically, this study aims to determine adequate bistable and MAE configurations for a kinetic shading device. Our experimental approach evaluates various MAE actuation configurations and their potential to deform a bistable kinetic shading setup. In a first experiment, we identified the appropriate locations and quantities of MAE patches, although the bistable structures could not be actuated outside of the flaps' deflection path. We further determined that 1) the most promising placement is when the MAE patches are perpendicular to the flaps’ longest side, and 2) a maximum of four MAE patches are adequate for non-contact actuation. In a second experiment, we tested smaller bistable sheets and measured the magnetic field strength required to initiate actuation. Actuation outside the deflection path was successful for most sheets, with non-contact actuation achieved at a 60-80 mm distance from the bistable flaps to the magnet. The study also showed that bistable flaps with more significant length to width (L/W) ratios the flaps bounceback, which is problematic for actuation and, therefore, should be avoided. Finally, we discuss the limitations and suggest strategies for increasing the kinetic capabilities of bistable systems applied to kinetic shades, including clamping the edge of bistable flaps and combining non-bistable sections to bistable laminates.

Shape memory alloys (SMAs) are a group of metallic alloys capable of sustaining large inelastic strains that can be recovered when subjected to a specific process between two distinct phases. Advantages of SMAs - reasonable strain, high energy density, mechanical simplicity, and long work-life render them ideal for actuator applications. Especially, Self-folding origami require high angular motion ranges and low-profile actuators within limited space. Current applications demonstrated the capacity of millimeter-sized torsional SMAs (T-SMAs) for bi-directional rotational motion, but no comprehensive design method for such actuator can be found in the existing literature. To broaden applications of actuator designs, we introduce an inverse design model according to a geometrico- static demand. We couple the geometrical and mechanical properties of torsional SMAs considering assembly and working conditions to construct the design model. We also illustrate a comprehensive mechanical performance characterization for millimeter-sized torsional SMAs and BRM actuators.

Magnetoelectric (ME) composites, composed of magnetostrictive and piezoelectric constituents, are a class of multifunctional smart materials that facilitate the coexistence of ferromagnetic and ferroelectric ferroic orders. This article presents temperature-dependent experimental quasi-static magnetoelectric (ME) studies conducted on a set of recently proposed novel distributed disc structured (DDS) ME composite configurations. A comparison of the normalized ME response at various temperatures reveals the effectiveness and versatility of epoxy-free DDS configurations over their epoxy-bonded counterparts in aggravated thermal environment. Additionally, it is observed that the fall in ME response with respect to temperature decreases with an increase in the number of discs.

The triboelectric effect is utilized in energy generators to convert ambient mechanical energy to electrical energy with potential to enable self-powered electronics. However, the fundamental mechanism behind the triboelectric effect is still unclear making it difficult to optimize the properties of the material pairs in the generator. In order to maximize the performance of triboelectric generators, the relationship between the triboelectric output and the mechanical properties of materials is investigated using polydimethylsiloxane (PDMS) as a model material. The bulk mechanical properties of PDMS were tuned by varying thermal treatment. Specifically, the tensile and compressive elastic modulus of PDMS heated for 48 hours increased by 4.4 folds and 2 folds respectively compared to PDMS without additional thermal treatment. In addition, the contacting surface of the PDMS samples were examined by measuring the surface roughness and contact angle. The results showed that the effect of thermal treatment on the mechanical properties is more significant than on the surface roughness. Interestingly, the triboelectric output polarity of the thermally treated PDMS samples is different from that of the PDMS without thermal treatment. The reversal of triboelectric polarity is surmised to result from bond breaking, and thus material transfer, between the two contacting materials. These findings confirm that the triboelectric output is not only affected by the chemical composition of the material, but also by the mechanical properties, which should be considered in the design and development of triboelectric devices.

Recently we employed entropy dynamics, a statistical inference tool that facilitates quantifying posterior probabilities of likely particle positions, to create material models relating fractal polymers networks to their constitutive behaviors.1 This methodology is applicable to classical mechanics, electromagnetic field theory, and quantum mechanics, thus offering new opportunities to expand our understating of functional materials. The entropy dynamics approach usually starts by maximizing Shannon entropy of possible particle locations with added constraints to account for particle interactions or motion. Here, we take a broader approach and use the Renyi entropy, a generalization of the Shannon entropy, to build our constitutive models for multi-functional polymers. The Renyi entropy allows us to derive wide-ranging material constitutive models that consolidate other entropy approaches such as max-entropy, min-entropy, and collision entropy. Furthermore, we investigate material properties using fractional moment constraints instead of the widely used integer moment constraints. Finally, we show how our approach provides a way to building models relevant to a broad class of smart materials and structures.

Selective Laser Sintering (SLS) is a branch of powder bed fusion additive manufacturing (AM) technique in which laser is used as a power source to sinter polymer powder materials. The laser targets the points in space defined by a 3D computer model and binds the material together to create a solid structure. Although thermoplastic materials (PA12, PA6, et) have been successfully demonstrated in SLS, printed 3D objects from these materials exhibit a lack of polymer interchain connection in print direction, resulting in poor mechanical properties and poor fatigue behavior. This deficiency of thermoplastics has encouraged to print high-performance thermosets using SLS. In this research, bismaleimide (BMI) resin thermoset powder was successfully printed using SLS with a two-step melting and post curing process. Dimensional and thermal stability of printed thermosets after curing is proved in this research for the very first time. Almost zero-dimensional change (0.033% increment in length, 0.23% increment in width, and 0.317% decrement in thickness) after curing of SLS printed thermoset part was presented. The thermomechanical property of printed BMI was characterized by dynamic mechanical analysis. Polymer crosslinking mechanism during curing process through FTIR as well as the thermal and mechanical stability of printed thermoset through compression tests have been analyzed in this research. The feasibility study demonstrates the feasibility of using SLS for printing high temperature tehermoset for variety energy and defense related applications.

Photoresponsive polymers are commonly used for applications such as controlled drug delivery, patterned thin films of hydrogels and polymer brushes, photodegradable materials, and liquid crystal actuators.1 Photoresponsive polymers are unique as they can change shape when exposed to a certain wavelength, intensity, or polarization of light while not requiring an electrical circuit or tethered power supply. However, the majority of photoresponsive polymers are based on the azobenzene moiety and the conversion of light into mechanical work is often inefficient. This work summarizes the relaxation behavior of a novel photopolymer film derived from stilbene and its unsensitized analog. Experiments are conducted quantifying the relaxation behavior of the films. The relaxation behavior of the photopolymer is analyzed by comparing fractional order and integer order Maxwell models. All results are statistically validated using Bayesian uncertainty methods to obtain posterior densities for the model parameters. It is shown that the fractional order Maxwell model is superior based on errors that are an order of magnitude lower than the integer order Maxwell model.

We propose a new composite that uses xerogel to bind sand particles to be used as the building materials for the Mars base. As the xerogel can be made by mixing minor polymer into water (available as ice), the xerogel-based building material (XBM) can maximize the in-situ resource utilization (ISRU). XBM cubes, after being cured under terrestrial environment (room temperature and approximately 1 atm.) or Mars-like environment ( -55°C and 0.00001 atm.), can achieve adequate mechanical properties for sustaining an apartment-size dome under the lower gravity on Mars (1/3 g). DEM is used to simulate the failure of XBM.

Validation is a key component of model development; for models seeking to represent complex and coupled physics, comparison to carefully considered experimental assessments is necessary. In particular, models describing multifunctional materials, in this case materials designed to resist fluid flow and then dissolve, require validation cases that adequately represent the physics involved while inducing the desired material behavior. This paper seeks to develop a representative experiment for use in validating a two-dimensional model which examines the coupled physics of fluid dynamics, structural mechanics, and a changing reference outer mold line (OML) due to material loss. The proposed experiment examines a dissolvable baffle under flow in a water tunnel. The baffle spans the width of an open channel test section, minimizing 3D effects, and is made of water-soluble PVA. Two idealized cases affecting the structural response are studied: in one, a thick, “rigid” baffle is affixed to a torsional spring, and all structural response is assumed to be captured by spring rotation (θ); in the other case, a flexible baffle is fixed rigidly, and structural response is described via cantilevered beam bending. The OML changes, resulting from both deformation and material loss, the baffle experiences during the study are captured optically and analyzed via edge tracking. The expected fluid loads are approximated using measured flow velocity at a given point in the closed loop water tunnel. Observations of baffle profile and deformation in time under a constant flow condition are presented.