ASME Conference Presenter Attendance Policy and Archival Proceedings

2015;():V001T00A001. doi:10.1115/SMASIS2015-NS1.

This online compilation of papers from the ASME 2015 Conference on Smart Materials, Adaptive Structures and Intelligent Systems (SMASIS2015) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

Development and Characterization of Multifunctional Materials

2015;():V001T01A001. doi:10.1115/SMASIS2015-8801.

In this work we discuss the design and fabrication of a cantilever that may be actuated by utilizing the martensite to austenite phase transformation of a sputtered thin film of equiatomic NiTi shape memory alloy (SMA). The cantilever devices were fabricated on a silicon wafer using standard micro fabrication techniques, and may therefore be applicable to microelectromechanical systems (MEMS) switch or actuator applications. This paper details the development of a co-sputtering process to yield a SMA film with controllable composition of Ni50Ti50 and transformation temperature around 60° C. Shape memory effects were characterized using Differential Scanning Calorimetry (DSC), for which we demonstrated martensite-austenite phase change at 57° C for 1–3 um films, annealed at 600° C. We used wafer stress versus temperature measurements as additional confirmation for the repeatable measurement of reversible phase transformation peaking at 73° C upon heating. Up to 62 MPa was available for actuation during the thermally induced phase change. After exploring multiple approaches to a frontside wafer release process, we were successful in patterning and fabricating 10 um wide freestanding Ni50Ti50 cantilevers.

Commentary by Dr. Valentin Fuster
2015;():V001T01A002. doi:10.1115/SMASIS2015-8855.

The goal of this study is to examine the theoretical capability of bimaterial lattices as thermally driven actuators. The lattices are composed of planar non-identical cells. Each cell consists of a skewed hexagon surrounding an irregular triangle; the skew angles of the hexagon and the ratio of the coefficients of thermal expansion (CTEs) of the two component materials determine the overall performance of the actuator. Such a cell has three tailorable CTEs along the lines connecting the points where adjoining cells are connected. Each individual cell and a lattice consisting of such cells can be strongly anisotropic in terms of thermal expansion. While these lattice cells have been used as stress-free connectors for components with differing CTEs, they have not been explored for their actuation capacity. This paper develops models for bimaterial lattices that can be used as mechanical actuators for valves, switches and differential motion. A general procedure for lattice design includes drawing of its skeleton, which identifies the points at which a lattice cell is connected to other cells or substrates; calculation of three CTEs in each cell depending upon the functionality desired; choosing lattice materials; and finding of the skew angles for each cell as solutions of three nonlinear algebraic equations. By changing materials and geometry, we can determine the change of their configuration when the temperature changes. This paper illustrates the concepts with several examples: a two-cell lattice that is connected to a substrate that functions as a lever in a switch; a three-cell lattice that serves as a valve; and a lattice that controls the maximum total deflection of two adjoining parts of a structure.

Commentary by Dr. Valentin Fuster
2015;():V001T01A003. doi:10.1115/SMASIS2015-8859.

This paper has explored and analyzed new routes to design new concepts of materials capable of feeling external effects and feed information back to a monitor and/or react through embedded actuators to resist any deformation. The material with its new artificial sensing property can be easily scaled-up to govern a whole structure at macro scale. The research has investigated a variety of manufacturing routes to build prototypes to be tested for the sake of characterization and performance assessment as well as cost analysis to assess effectiveness. This has included ultrasonic fiber optics embedding in thin Metals e.g. Aluminum which has shown some challenges to be discussed. The host materials included mainly layered manufacturing based materials e.g. powder based materials (Alloy Al6061) and additive process e.g. 3D printing with ABS material. This work has considered samples with concepts having embedded fiber optics in 1D, 2D and 3D. The integrity of the fiber optics and the host materials as well as the sensors performance has been investigated under several conditions of pressure, temperature and geometric placement of the fiber optics. A parametric compromise between materials standard performance and integrity of the sensors is to be found.

Topics: Sensors , Polymers
Commentary by Dr. Valentin Fuster
2015;():V001T01A004. doi:10.1115/SMASIS2015-8895.

This paper describes a new three-dimensional (3D) additive manufacturing (AM) technique in which electroactive polymer filament material is used to build soft active 3D structures, layer by layer. The proposed manufacturing process is well-suited for creating electroactive soft complex structures and devices, whereby the entire system can be manufactured from an electroactive polymer material. For the first time, the unique actuation and sensing properties of ionic polymer-metal composite (IPMC) is exploited and directly incorporated into the structural design to create sub-millimeter scale cilia-like actuators and sensors to macro-scale soft robotic systems. Because ionic polymers such as Nafion are not melt-processable, in the first step a precursor material (non-acid Nafion precursor resin) is extruded into a thermoplastic filament for 3D printing. The filament is then used by a custom-designed 3D printer to manufacture the desired soft polymer structures, layer by layer. Since, at this stage the 3D-printed samples are not yet electroactive, a chemical functionalization process follows, consisting in hydrolyzing the precursor resin in an aqueous solution of sodium hydroxide (NaOH) and dimethyl sulfoxide (DMSO, C2H6OS). Upon functionalization, metal electrodes are applied on the samples through an electroless plating process, which enables selected areas of the 3D-printed electroactive structures to be controlled by voltage signals for actuation, while other parts can function as sensors. This innovative AM process is described in detail and experimental results are presented to demonstrate the potential and feasibility of creating 3D-printed IPMC actuator samples.

Commentary by Dr. Valentin Fuster
2015;():V001T01A005. doi:10.1115/SMASIS2015-8911.

A theoretical investigation of the dynamic response of a pair of interacting carbon nanotubes (CNTs) dispersed in a liquid medium under the presence of an alternating current (AC) electric field is presented. The proposed modeling strategy is based on the dielectrophoretic (DEP) theory and classical electrodynamics, and considers the effect of an applied AC electric field on the rotational and translation motion of interacting CNTs represented as electrical dipoles. The mutual interaction between a pair of adjacent CNTs stems from the presence of DEP-induced charges on the CNTs and, as such, contributes to the rotational and translational dynamics of the system. Based on experimental evidence, the parameters which are expected to cause a major contribution to the CNTs motion are investigated for different initial configurations. Based on the obtained results, it is here predicted that high electric field frequencies, long CNTs, high values of electrical permittivity and conductivity of CNTs immersed in solvents of high polarity promote faster rotational and translational motion and therefore faster equilibrium conditions (CNT tip-to-tip contact and horizontal alignment). The results incorporate important knowledge towards a better understanding of the complex mechanisms involved in the efforts of tailoring CNT networks by electric fields.

Commentary by Dr. Valentin Fuster
2015;():V001T01A006. doi:10.1115/SMASIS2015-8915.

Structural supercapacitors are very interesting multifunctional devices combining the properties of an electrical energy storage device and a structural component simultaneously. These types of supercapacitors are mostly equipped with solid state electrolytes, instead of traditional liquid electrolytes, avoiding leakage and safety problems and supporting the mechanical performance of the composite materials. In the present study, the Lithium-ion based solid ceramic electrolyte Li1.4Al0.4Ti1.6(PO4)3 was successfully synthesized by sol-gel method. Its electrical properties were characterized by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Results show that Li1.4Al0.4Ti1.6(PO4)3 possesses a conductivity of 2.94×10−4 S/cm at room temperature and a specific capacity of 55.57 μF/g. The as-prepared samples were embedded into fiber composite material using the aviation approved resin RTM6 with an injection process making the composite structure flexible. Subsequently, the specific capacity and conductivity were tested getting values of 53.44μF/g and 2.00×10−4 S/cm respectively. The reason for electrical properties loss was investigated by computerized tomography (CT) and EIS tests and the results provide reference for the future research.

Commentary by Dr. Valentin Fuster
2015;():V001T01A007. doi:10.1115/SMASIS2015-8916.

Thermally responsive self-healing polyurethanes (1DA1T, 1.5DA1T, and 2DA1H) with shape memory property were developed and the fully reversible Diels-Alder (DA) and retro Diels-Alder (rDA) reactions were employed for the healing mechanism. The transition temperatures of the DA and rDA reactions were confirmed through a differential scanning calorimetry and the molecular level of analysis on the reversibility and the repeatability between the DA and rDA reactions were completed though a variable temperature proton nuclear magnetic resonance at the reaction temperatures. Also, compact tension specimens were made to observe the healing efficiencies. These specimens were healed without the use of external forces to close the crack surfaces after testing for the repeatable healing ability with three cycles. As a result, the average first healing cycle efficiencies of 80%, 84%, and 96% for 1DA1T, 1.5DA1T and 2DA1H, respectively, were achieved and small drops for the second and third healing cycles were observed. Then, using two of the self-healing polyurethanes as resins, continuous carbon fiber fabric reinforced polymer matrix composites (C1.5DA1T and C2DA1H) were fabricated and short beam shear testing was conducted to determine the healing capability on the delamination. Accordingly, the first healing efficiencies of 88% and 85% were measured without any additional treatments on the fibers; however, an external pressure was applied during the composite healing process.

Commentary by Dr. Valentin Fuster
2015;():V001T01A008. doi:10.1115/SMASIS2015-8917.

Shape setting is a fundamental step in the production route of Nitinol Shape Memory Alloys (SMAs) for the fixing of the functional properties, such as the shape memory effect and the pseudo-elasticity. The conventional method for making the shape setting needs the use of furnaces.

In this work laser technology was adopted for performing the straight shape setting on commercially available Nitinol thin wires. The laser beam was moved along the wire length for inducing the functional performances. Calorimetric and pseudo-elastic response of the wires, laser annealed, were studied; high energy X-Rays diffraction was done for studying the evolution of the microstructure texture. It can be stated that the laser technology can realize the shape setting of thin SMA wires with pseudo-elastic properties; the wire performances can be modulated in function of the laser power.

Commentary by Dr. Valentin Fuster
2015;():V001T01A009. doi:10.1115/SMASIS2015-8920.

Azobenzene polymers show promising photostrictive behavior for a broad range of applications in flow control, robotics, and energy harvesting applications. The conversion of solar energy directly into mechanical work provides unique capabilities in adaptive structures; however, the energy conversion of visible light into mechanical work presents several material chemistry challenges. Azobenzene strongly absorbs ultraviolet (UV) light and blue/green light which limits the efficiency of the photomechanical response under solar irradiation. Photon upconversion — combining two or more low energy photons (longer wavelength) to generate a higher energy excited state (shorter wavelength), provides an intriguing strategy to drive these high energy photochemical reactions with low energy light. We present an experimental study showing the feasibility to drive azobenzene photoisomerization using visible light via select up-conversion molecules in the fluidic state. Multi-physics modeling is then used to predict advances in photomechanical energy conversion when up-conversion molecules are introduced within an azobenzene polymer.

Commentary by Dr. Valentin Fuster
2015;():V001T01A010. doi:10.1115/SMASIS2015-8944.

Solid state refrigeration processes, such as magnetocaloric and electrocaloric refrigeration, have recently shown to be a promising alternative to conventional compression refrigeration. A new solid state elastocaloric refrigeration process using the latent heats within Shape Memory Alloys (SMA) could also hold potential in this field. This work investigates the elastocaloric effects in Ni-Ti-based superelastic Shape Memory Alloy (SMA) systems for use in an elastocaloric cooling processes. Ni-Ti alloys exhibits large latent heats and a small mechanical hysteresis, which may potentially lead to the development of an efficient environmentally friendly solid-state cooling system, without the need for ozone-depleting refrigerants. A systematic investigation of the SMA is conducted using a novel custom-built scientific testing platform specifically designed to measure cooling process related phenomena. This testing system is capable of performing tensile tests at high rates as well as measuring and controlling the solid-state heat transfer between SMA and heat source/heat sink.

Tests are conducted following a cooling process related training cycle where the material has achieved stabilized behavior. First, a characterization of the elastocaloric material properties is performed followed by an investigation of the material under cooling process conditions.

A comprehensive monitoring of the mechanical and thermal parameters enables the observation of temperature changes during mechanical cycling of the SMA at high strain rates. These observations can be used to study the rate dependent efficiency of the elastocaloric material.

The measurement of the temperature of both the heat source/heat sink and the SMA itself, as well as the required mechanical work during a running cooling process, reveals the influence of the operating conditions on the elastocaloric effect of the material.

Furthermore investigations of the process efficiency at different thermal boundary conditions (temperature of heat source/heat sink), indicates that the process is dependent on the boundary conditions which have to be controlled in order to optimize the efficiency.

Topics: Cooling , Alloys
Commentary by Dr. Valentin Fuster
2015;():V001T01A011. doi:10.1115/SMASIS2015-8957.

Recently, NiTiHf-based HTSMAs have been shown to exhibit unique precipitation and mechanical behavior. In this study, a rolled plate of NiTiHf HTSMA was homogenized and heat treated at various times and temperatures and characterized using a barrage of analytical techniques including high-energy synchrotron X-ray diffraction (SR-XRD). Neither homogenization nor any of heat treatments studied significantly affect the austenitic or martensitic transformation temperatures. H-phase was observed to precipitate at heat treating times below 30 minutes and then to subsequently dissolve away for times of 30 minutes and above. The presence of H-phase dramatically increases the material strength by almost a factor of 2, Lastly, an over-aging effect occurs with increasing time due to the disappearance of the H-phase.

Topics: Heat
Commentary by Dr. Valentin Fuster
2015;():V001T01A012. doi:10.1115/SMASIS2015-8958.

This paper presents an analysis of optimization for multifunctional nanocomposites. A carbon nanotubeepoxy composite is optimized for maximum resistance change and minimum strain energy. Analysis uses a finite element method and includes the coupled physics of mechanics, electrostatics, and piezoresistivity. The problem is solved first for minimum strain energy, then two resistance maximization problems are solved. For all optimization, sensitivities are obtained analytically. After solving the individual problems a weighted sum approach is used in the multi-objective optimization of both minimizing the strain energy and maximizing the resistance change. Comments are made as to the effect of the topology optimization method as a design tool, on the shape of the optimized cross sections, and on the possible extensions on using the coupled physics topology optimization algorithm.

Commentary by Dr. Valentin Fuster
2015;():V001T01A013. doi:10.1115/SMASIS2015-9001.

Origami-inspired active structures have important characteristics such as reconfigurability and the ability to adopt compact flat forms for storage. A self-folding shape memory alloy (SMA)-based laminated sheet is considered in this work wherein SMA wire meshes comprise the top and bottom layers and a thermally insulating compliant elastomer comprises the middle layer. Uncertainty in various parameters (e.g. material properties) may affect the performance of the sheet, which is explored here. Different modeling approaches are studied in order to compare their accuracy and computational cost. A numerical approach based on the Euler-Bernoulli beam theory is selected due to its accuracy when compared to higher fidelity finite element simulations and its low computational cost, necessary to perform a large number of design evaluations as required for uncertainty analysis. Optimization is performed considering uncertainty in the material properties. Failure probabilities under mechanical constraints and expected values of fold curvature and blocking moment are considered during optimization of the self-folding sheet. The multiobjective genetic algorithm for technology characterization P3GA is used to obtain the Pareto dominant designs. Most designs forming the Pareto frontier have the same values for certain design parameters such as the distance between the wires in the SMA meshes non-dimensionalized by SMA wire thickness, elastomer layer thickness non-dimensionalized by SMA wire thickness, and applied temperature. The design parameter deciding the trade-off between fold curvature and blocking moment is found to be the SMA wire thickness.

Commentary by Dr. Valentin Fuster
2015;():V001T01A014. doi:10.1115/SMASIS2015-9018.

Recent studies on periodic metamaterial systems have shown that remarkable properties adaptivity and multifunctionality are often products of exploiting internal, coexisting metastable states. Yet to realize such attractive potential, effecting coexisting metastable states in material systems may require the determination of a periodic constituent which promotes a non-uniqueness when composed within the whole system, thus creating a need for costly, multiscale design. To surmount such concerns, this research first focuses on the development of adaptable, metastable modules: once assembled into modular metastructures, synergistic properties adaptation is found to be a natural byproduct of the strategic module design. Using this approach, it is seen that modularity facilitates a direct pathway to create and effectively exploit metastable states for massive, metastructure properties adaptivity, including a near-continuous variation of mechanical properties or stable topologies and adjustable hysteresis. A model is developed to understand the source of the synergistic characteristics, and theoretical findings are found to be in good agreement with experimental results. Important design-based questions are raised regarding the modular metastructure concept, and a genetic algorithm routine is developed to elucidate the sensitivities of the properties variation with respect to the statistics among assembled module design variables. To obtain target multifunctionality and adaptivity, the routine discovers that particular degrees and types of modular heterogeneity are required. Future realizations of modular metastructures are discussed to illustrate the extensibility of the design concept and broad application base.

Commentary by Dr. Valentin Fuster
2015;():V001T01A015. doi:10.1115/SMASIS2015-9027.

The present work deals with the design of a fiber-reinforced composite lamina with varying fiber-volume fraction (FVF) along its thickness direction. In the available elastic analyses of this kind of composite, the elastic properties are evaluated based on the assumptions like continuous variation of FVF and existence of decoupled representative volume element (RVE) at every point along the thickness direction. In order to predict the graded material properties without any of these assumptions at present, first a micro-structure of similar graded composite is designed for the variation of FVF according to a sigmoid function of thickness coordinate. Next, a continuum micro-mechanics finite element model of the corresponding representative volume (RV) is derived. The RV is basically composed of several micro-volumes of different FVFs and the classical homogenization treatment is implemented over these micro-volumes without decoupling them from the overall volume of RV. The importance of this coupled analysis is verified through a parallel decoupled analysis. The effect of the total number of micro-volumes within a specified thickness of lamina on its graded elastic properties is presented. The characteristics of graded elastic properties according to the sigmoid function are also discussed.

Commentary by Dr. Valentin Fuster
2015;():V001T01A016. doi:10.1115/SMASIS2015-9030.

Field induced phase transformations in relaxor ferroelectric single crystals with compositions near the morphotropic phase boundary can be induced by electrical or mechanical loading above a certain threshold. Concurrent electrical and mechanical loading of [011]C cut and poled crystals drives the ferroelectric rhombohedral to ferroelectric orthorhombic phase transformation at lower threshold levels than either load alone. Likewise, electrical loading of [001]C cut and poled crystals hinders the mechanically driven ferroelectric rhombohedral to ferroelectric orthorhombic phase transformation. The current experimental technique for characterization of the large field behavior including the phase transformation requires an extensive set of measurements performed under electric field cycling at different stress preloads and stress cycling at different bias electric fields, repeated at multiple temperatures. This procedure requires specialized equipment and training, and is very time-consuming. In this work a mechanism based model is combined with a more limited set of experiments to obtain the same results. The model utilizes a work-energy criterion that calculates the work required to induce the transformation by overcoming an energy barrier. This approach reduces the number of required experiments while potentially eliminating the need of a load frame for mechanical loading of [011]C crystals. This decreases the time and resources required for characterization of new compositions. The results of the combined experiment / modeling approach are compared to the fully experimental approach and error is discussed.

Topics: Crystals , Modeling
Commentary by Dr. Valentin Fuster
2015;():V001T01A017. doi:10.1115/SMASIS2015-9034.

Deformation behavior of a capsule-type micro actuator using palladium as a hydrogen storage alloy was investigated. The capsule-type micro actuator using hydrogen storage alloys (HSA-CMA) drives by the volume change of the hydrogen storage alloy induced by the absorption and discharge of hydrogen gas. It was developed as a compact, lightweight and energy-saving actuator mounted on the super multi-link manipulator to capture space debris. In the present work, a palladium foil was used as the hydrogen storage alloy. It was confirmed that the actuator of 10 mm in diameter fabricated with palladium has deformed by the introduction and evacuation of hydrogen gas. The height change and deformation rate have increased with the cycle between hydrogen introduction and evacuation.

Commentary by Dr. Valentin Fuster
2015;():V001T01A018. doi:10.1115/SMASIS2015-9043.

Designing devices made from epoxy-based shape memory polymers is difficult because few material behavior parameters are available for these materials in the rubbery/shape changing region. This work examines the rubbery state, greater than 20° C above the glass transition temperature (Tg), as an elastomeric regime suited to characterization with simple tension and planar tension experiments. Differential scanning calorimetry (DSC) results show a 70° C Tg, which agrees with prior research. Simple tension experiments at 100° C exhibited nonlinear elastic behavior, and finite element analysis (FEA) agreed with the constitutive behavior exhibited in the experiments. Planar tension experiments exhibited novel results. The stress/strain response was sigmoidal with a significant plateau in stress followed by rising stress to failure. The typical 10:1 gage width/gage length ratio seemed to over constrain the material. The strain to failure is small, and suggests the material behavior is a hybrid of elastic and hyperelastic behavior.

Commentary by Dr. Valentin Fuster
2015;():V001T01A019. doi:10.1115/SMASIS2015-9065.

Minimizing water retention on the air side of aluminum surfaces is important in the design and operation of efficient heat exchangers for heating, ventilation, air-conditioning and refrigeration (HVAC&R) systems. Accumulation of water degrades the performance of heat exchangers by lowering the heat transfer rate and increasing the pressure drop. As a result, power consumption in such systems increases. In this work, a method of fabricating liquid-infused slippery surfaces with honeycomb-like superhydrophobic micro-/nano-structure substrate via an anodization process is developed. The slippery surface exhibits superhydrophobicity with a contact angle of 155° and a sliding angle smaller than 5°. The delay of ice formation is observed during condensation/frosting experiment. Frost-melt retention experiments show that the liquid-infused slippery surface reduces the water retention by 90% compared to an untreated specimen. The longevity of the slippery surface is also explored. The water retention ratio does not show a significant change after 60 frosting/defrosting cycles, and is still only one third that of the baseline. The slippery surface has potential in HVAC&R applications.

Commentary by Dr. Valentin Fuster
2015;():V001T01A020. doi:10.1115/SMASIS2015-9066.

Origami-based design is increasing in popularity as its benefits and advantages become better understood and explored. Surrogate folds are a means of achieving fold-like behavior, offering solutions for origami-based products in new materials. A surrogate fold is a localized reduction in stiffness in a given direction allowing the material to function like a fold. A family of surrogate folds is reviewed and the respective behaviors of the folds discussed. For a given fold configuration, the material thickness is varied to yield different sizes of surrogate folds. Constraint assumptions drive the design, and the resultant configurations are compared for bending motions. Finite element and analytical models for the folds are also compared. Prototypes are made from different materials. This work creates a base for creating design guidelines for using surrogate folds in thick sheet materials.

Topics: Sheet materials
Commentary by Dr. Valentin Fuster
2015;():V001T01A021. doi:10.1115/SMASIS2015-9067.

Thermo-responsive wettability is studied for adaptive surface, which can potentially help to enhance the performance of thermal devices under various operation conditions. Poly(N-isopropylacrylamide) or PNIPAAm polymer brush can be grafted onto solid surfaces so that at temperatures below the lower critical solution temperature (LCST), the surface is hydrophilic, while at temperatures above LCST, it automatically becomes more hydrophobic. In this study, PNIPAAm is grafted on to aluminum alloy 6061, which is a multipurpose alloy commonly used in thermal mechanical systems. It is demonstrated by water static contact angle experiment at varies temperature that, the surface is hydrophobic at temperatures above LCST, and hydrophilic below LCST. The results are compared with bare aluminum surface at similar temperatures. Grafting PNIPAAm polymer brush on roughened aluminum surface would result in the ability to automatically switch between superhydrophobic state and superhydrophilic state in response to temperature change.

Topics: Aluminum , Polymers , Water
Commentary by Dr. Valentin Fuster
2015;():V001T01A022. doi:10.1115/SMASIS2015-9085.

A novel flexible electrochemical biosensor for protein biomarker detection was successfully designed and fabricated on a nanoporous polyimide membrane using zinc oxide (ZnO). Nanostructures of ZnO were grown on microelectrode platform using aqueous solution bath. Electrochemical measurements were performed using gold, ZnO seed and nanostructured electrodes to study the influence of electrode surface area on biosensing performance. Feasibility analysis of sensor platforms was evaluated using high concentrations (in ng/mL) of troponin-T. The results showed that improved performance can be obtained on nanostructured platform by careful optimization of growth conditions. This study demonstrates the development of nanostructured ZnO flexible biosensors towards ultra-sensitive protein biosensing.

Commentary by Dr. Valentin Fuster

Mechanics and Behavior of Active Materials

2015;():V001T02A001. doi:10.1115/SMASIS2015-8823.

A sharp-interface model based on the linear constrained theory of laminates identifies eight distinct rank-2 periodic patterns in tetragonal ferroelectrics. While some of the periodic solutions, such as the herringbone and stripe patterns are commonly observed, others such as the checkerboard pattern consisting of repeating polarization vortices are rarely seen in experiments. The linear constrained theory predicts compatible domain arrangements, but neglects gradient effects at domain walls and misfit stresses due to junctions of domains. Here, we employ a phase-field model to test the stability of the periodic domain patterns with in-plane polarizations, under periodic boundary conditions which impose zero average stress and electric field. The results indicate that domain patterns containing strong disclinations are of high energy and typically unstable in the absence of external stresses or electric fields. The study also provides insight into the internal stresses developed in the various domain patterns.

Commentary by Dr. Valentin Fuster
2015;():V001T02A002. doi:10.1115/SMASIS2015-8842.

The aim of the present study was to investigate the potential of using IPMC as a flexible impact sensor to be used in typical impact protective devices like a protective headgear to estimate the severity level of head impacts. To that end, IPMC strips were embedded into two layers of protective dilatant material and several impact testings were performed. Results of output IPMC voltage and impact acceleration were captured and analyzed. IPMCs appear to present a potential as impact sensors. In so doing, small strips of either Platinum or Gold chemically-plated IPMCs were used. Results of IPMC voltage output and impact accelerations were reported. The results indicate that IPMCs can be used as flexible impact sensors.

Commentary by Dr. Valentin Fuster
2015;():V001T02A003. doi:10.1115/SMASIS2015-8846.

Viscoelasticity causes a time-dependent performance and affects the conversion efficiency of VHB-based dielectric elastomers actuator (DEA), when subject to voltage and temperature. However, few reports focus on the effect of temperature on the viscoelastic electromechanical performance on the DEA. The viscoelastic performance of a VHB film in a circular actuator configuration undergoing temperature variation is studied both theoretically and experimentally. Subjected to temperature variation and voltage, viscoelastic creep and higher deformation at higher temperature are obtained using thermodynamics models. Subsequently, an experiment was designed to validate the simulation and the results indicate that DEA creeps with time due to the viscoelasticity and a bigger deformation can be achieved at a higher temperature, which shows well consistent with the experimental results.

Commentary by Dr. Valentin Fuster
2015;():V001T02A004. doi:10.1115/SMASIS2015-8919.

A variety of models have been developed to simulate the behavior of electroactive elastomers. As with all modeling applications, there are varying levels of uncertainty associated with measurement limitations and lack of knowledge of the constitutive behavior. Methods of quantifying this uncertainty have been explored previously using Bayesian statistics under uniaxial mechanical loading. The research presented here expands prior developments to quantify constitutive model uncertainty under multi-axial mechanical loading at different electrostatic fields. Specifically, we experimentally characterize and simulate transverse loading of a pre-stretched membrane under different electrostatic fields. We also quantify the dielectric response from electric displacement versus electric field loops. Bayesian statistical methods are employed to quantify modeling uncertainties in light of the data conducted on the 3M elastomer, VHB 4910.

Commentary by Dr. Valentin Fuster
2015;():V001T02A005. doi:10.1115/SMASIS2015-8949.

This work presents the design, fabrication and testing of a comprehensive DEAP test station. The tester is designed to perform tensile tests of planar DEAPs while measuring quantities such as tensile force, stretch, film thickness and voltage/current. The work details the specimen preparation and how the specimen is placed in the clamps. While the assembly process is performed by hand features were built-in to the design of the specimen frame and clamps to enable reliable placement and specimen geometry. Test results of the pure-shear specimen demonstrated good performance of the testing device. Although the electrode surface was rough the thickness stretch was evident during the stretching/actuation of the DEAP actuator.

Commentary by Dr. Valentin Fuster
2015;():V001T02A006. doi:10.1115/SMASIS2015-8951.

Magnetoactive elastomers (MAEs) are composites made of an elastomeric matrix and a magnetizable filler material. The combination of their properties enables a MAE to undergo a change of its rheological respective damping behavior. Furthermore, it is expected that such a magnetic field can lead to an actuation of a MAE. This actuation causes actuation forces perceptible on the surfaces of MAEs. For the investigation of the induced actuation forces different MAE-probes are characterized in a first step. The resulting forces of these MAE-probes are measured by generating a variable external magnetic field in a suitable test setup. Subsequently, a finite element analysis (FEA) is carried out to investigate the behavior from a theoretical point of view by introducing an appropriate continuum mechanical model approach based on the Kelvin force. Therefore, a coupling of magnetism and structural-mechanics domain is developed and implemented using the FEA-tool Comsol Multiphyisics. Finally, the experimental and numerical results of the actuation forces are compared showing a good accordance.

Topics: Elastomers , Modeling
Commentary by Dr. Valentin Fuster
2015;():V001T02A007. doi:10.1115/SMASIS2015-8975.

The Digital Twin concept represents an innovative method to monitor and predict the performance of an aircraft’s various subsystems. By creating ultra-realistic multi-physical computational models associated with each unique aircraft and combining them with known flight histories, operators could benefit from a real-time understanding of the vehicle’s current capabilities. One important facet of the Digital Twin program is the detection and monitoring of structural damage. Recently, a method to detect fatigue cracks using the transformation response of shape memory alloy (SMA) particles embedded in the aircraft structure has been proposed. By detecting changes in the mechanical and/or electromagnetic responses of embedded particles, operators could detect the onset of fatigue cracks in the vicinity of these particles. In this work, the development of a finite element model of an aircraft wing containing embedded SMA particles in key regions will be discussed. In particular, this model will feature a technique known as substructure analysis, which retains degrees of freedom at specified points key to scale transitions, greatly reducing computational cost. By using this technique to model an aircraft wing subjected to loading experienced during flight, we can simulate the response of these localized particles while also reducing computation time. This new model serves to demonstrate key aspects of this detection technique. Future work, including the determination of the material properties associated with these particles as well as exploring the positioning of these particles for optimal crack detection, is also discussed.

Commentary by Dr. Valentin Fuster
2015;():V001T02A008. doi:10.1115/SMASIS2015-8985.

Transducers based on dielectric electroactive polymers (DEAP) gained a lot of attention within the last years. By applying an electric field, the elastomer material, coated with compliant electrodes on its opposing surfaces, deforms. Due to this electromechanical coupling DEAP transducers are predestined for generator and actuator applications. However, to increase the absolute energy gain or the actuation, multilayer DEAP transducers are used. To withstand tensile forces a reliable adhesion between the single layers of the transducer is mandatory. If the transducer is made from high-quality pre-fabricated polymer films it is preferable to laminate the layers without glue in order to keep the processing steps simple and fast. Therefore, within this publication the adhesion between the material surfaces is theoretically and experimentally investigated. For this purpose, different adhesion theories are studied based on the properties of polymers. In particular, the adsorption theory is theoretically considered in more detail and used to determine the surface energy experimentally for different elastomer materials. By using the obtained surface energies, models are derived to describe the adhesion between them. Finally, the adhesion is experimentally investigated by corresponding experiments.

Topics: Adhesion , Actuators
Commentary by Dr. Valentin Fuster
2015;():V001T02A009. doi:10.1115/SMASIS2015-8992.

This paper focuses on the actuation mechanisms of CNT-papers and CNT-arrays. CNT-papers represent architectures of CNTs which are connected by van der Waals forces or structural entanglement. In contrast CNT-arrays are vertically aligned CNTs. Single CNTs are favored for investigation of the active behavior of the hexagonal carbon structure formed by covalent C-bonds. CNT-arrays feature contiuous tubes of 3 mm length which allows the test the tubes themselves. Thus they are clamped at each end they represent samples for testing covalent bonds. Both sample types are tested within an actuated tensile test set-up under different conditions to identify the specific influence. Furthermore different electrolytes are used to investigate the influence of the ion-radius on the CNT-paper. CNT-papers are tested in water-based electrolytes CNT-arrays are tested in an ionic liquid. It was found that the performance of CNT-papers strongly depends on the conditions which indicates ion-diffusion as actuation mechanism. However, CNT-arrays are almost unaffected by the conditions, considering their active response and sample composition quantum mechanical reasons seem to be the most appropriate explanation for the array actuation.

Commentary by Dr. Valentin Fuster
2015;():V001T02A010. doi:10.1115/SMASIS2015-9040.

Shape memory alloys (SMAs), are a class of metals that possess the capability to recover substantial deformations resulting from applied mechanical loads through a solid-solid phase transformation. Typical deployment systems for solar arrays on microsats only allow for one-way deployment. However, by using an SMA actuator in place of a conventional deployment system, repeatable deployment and retraction can be achieved. Relative to conventional actuators, SMA-based solid state actuators offer a reduction in the weight, volume, and overall complexity of the system. In this study, a design of an SMA-based solar panel deployment mechanism for a typical microsat is presented. In this design, a conventional actuation system is replaced with a system of SMA torsional actuators, which allows for a deployed and stowed phase to be reached independent of environmental conditions. This design study illustrates that an SMA-based solar array deployment system can provide a viable replacement for a conventional deployment system while significantly reducing the deployment system weight, volume, and complexity.

Commentary by Dr. Valentin Fuster
2015;():V001T02A011. doi:10.1115/SMASIS2015-9076.

Researchers have attempted to model the magneto-mechanical behavior of magnetic shape memory alloys (MSMAs) for over a decade, but all of the models developed to date have only been validated against experimental data generated under two-dimensional loading conditions. As efforts have been underway to develop models able to predict the most general (i.e. 3D) loading conditions for the material, there is a need for experimental data to support the calibration and validation of these models. This paper presents magneto-mechanical data from experiments where a MSMA specimen whose microstructure accommodates three martensite variants is subjected to three-dimensional magneto-mechanical loading. To the best of our knowledge, all prior experimental investigations on MSMA have been performed on samples accommodating two martensite variants and exposed to two-dimensional magneto-mechanical loads. The experimental results from the 3D loading of the three variant MSMA specimen are used to calibrate and validate a 3D model developed by this group [LaMaster et al. (2014)]. This model assumes that three martensite variants coexist in the material. The LaMaster et al. model captures the general trends seen in the experimental data, but does not predict the data with a high degree of accuracy. Possible reasons for the mismatch between experimental data and model predictions are discussed.

Commentary by Dr. Valentin Fuster
2015;():V001T02A012. doi:10.1115/SMASIS2015-9111.

The current work aims to explore the effective piezoresistive response of polymer bonded explosive (PBX) materials where the polymer medium is reinforced with carbon nanotubes (CNTs). The effective piezoresistive response of these nanocomposite bound polymer explosives (NCBX) is evaluated using micromechanics based 2-scale hierarchical model connecting the CNT-polymer nanocomposite scale (nanoscale) to the explosive grain structure scale (microscale). The binding nanocomposite medium is modeled as electromechanical cohesive zones between adjacent explosive grains which are representative of effective electromechanical response of CNT-polymer nanocomposites. The hierarchical framework developed here is used to explore key features of the NCBX microstructure, e.g. ratio of grain to nanocomposite stiffness, ratio of grain to nanocomposite conductivities etc., and related to the NCBX effective piezoresistive response. The results obtained from the current work show dependence of effective NCBX piezoresistive properties on each of these microstructural features with and without interfacial damage between the explosive grains.

Commentary by Dr. Valentin Fuster

Modeling, Simulation and Control of Adaptive Systems

2015;():V001T03A001. doi:10.1115/SMASIS2015-8803.

This paper analyses the Rolamite architecture exploiting shape memory alloys as power element to obtain a solid state actuator. The Rolamite mechanism was discovered in the late sixties, initially as precision and low friction linear bearing. The most common Rolamite configuration consists of a flexible thin metal strip and two rollers mounted between two fixed parallel guide surfaces. The system can roll back and forth without slipping guided by the plates along its so called sensing axis. The system presents another relevant advantage in addition to low friction coefficient, which is the possibility to provide force generation in a quite simple way. In the original literature works the force was provided thanks to cutouts of various shape in the strip, though this method does not allow the Rolamite to be considered a proper actuator, but only a force generator. In this paper we developed the idea of exploiting the shape memory alloy as Rolamite power element and therefore to use the shape memory effect to change the elastic properties of the strip and to provide the actuation force. The mechanical analyses and the equations where the martensite-austenite transition is modelled in a simplified way, show that this application is feasible, mainly thanks to the initial precurvature of the SMA strip. The discussion of the results highlights some important merits of this architecture such as long stroke, constant force and compactness.

Commentary by Dr. Valentin Fuster
2015;():V001T03A002. doi:10.1115/SMASIS2015-8806.

An attractive but little explored field of application of the shape memory technology is the area of rotary actuators, in particular for generating endless motion. This paper presents a miniature rotary motor based on SMA wires and overrunning clutches which produces high output torque and unlimited rotation. The concept features a SMA wire tightly wound around a low-friction cylindrical drum to convert wire strains into large rotations within a compact package. The seesaw motion of the drum ensuing from repeated contraction-elongation cycles of the wire is converted into unidirectional motion of the output shaft by an overrunning clutch fitted between drum and shaft. Following a design process developed in a former paper, a six-stage prototype with size envelope of 48×22×30 mm is built and tested. Diverse supply strategy are implemented to optimize either the output torque or the speed regularity of the motor with the following results: maximum torque = 20 Nmm; specific torque = 6.31×10−4 Nmm/mm3; rotation per module = 15 deg; free continuous speed = 4 rpm.

Topics: Wire , Design , Shapes
Commentary by Dr. Valentin Fuster
2015;():V001T03A003. doi:10.1115/SMASIS2015-8819.

Several new methods are proposed to reconfigure smart structures with embedded computing, sensors and actuators. These methods are based on heteroclinic connections between equal-energy unstable equilibria in an idealised spring-mass smart structure model. Transitions between equal-energy unstable (but actively controlled) equilibria are considered since in an ideal model zero net energy input is required, compared to transitions between stable equilibria across a potential barrier. Dynamical system theory is used firstly to identify sets of equal-energy unstable configurations in the model, and then to connect them through heteroclinic connection in the phase space numerically. However, it is difficult to obtain such heteroclinic connections numerically in complex dynamical systems, so an optimal control method is investigated to seek transitions between unstable equilibria, which approximate the ideal heteroclinic connection. The optimal control method is verified to be effective through comparison with the results of the exact heteroclinic connection. In addition, we explore the use of polynomials of varying order to approximate the heteroclinic connection, and then develop an inverse method to control the dynamics of the system to track the polynomial reference trajectory. It is found that high order polynomials can provide a good approximation to true heteroclinic connections and provide an efficient means of generating such trajectories. The polynomial method is envisaged as being computationally efficient to form the basis for real-time reconfiguration of real, complex smart structures with embedded computing, sensors and actuators.

Commentary by Dr. Valentin Fuster
2015;():V001T03A004. doi:10.1115/SMASIS2015-8830.

In the present paper we investigated the behaviour of magnetorheological fluids (MRFs) under a hydrostatic pressure up to 40 bar. We designed, manufactured and tested a magnetorheological damper (MRD) with a novel architecture which provides the control of the internal pressure. The pressure was regulated by means of an additional apparatus connected to the damper that acts on the fluid volume. The MRD was tested under sinusoidal inputs and with several values of magnetic field and internal pressure. The results show that the new architecture is able to work without a volume compensator and bear high pressures. On the one hand, the influence of hydrostatic pressure on the yield stress of MRFs is not strong probably because the ferromagnetic particles cannot arrange themselves into thicker columns. On the other hand, the benefits of the pressure on the behaviour of the MRD are useful in terms of preventing cavitation.

Commentary by Dr. Valentin Fuster
2015;():V001T03A005. doi:10.1115/SMASIS2015-8834.

Fluidic artificial muscles have the potential for a wide range of uses; from injury rehabilitation to high-powered hydraulic systems. Their modeling to date has largely been quasi-static and relied on the operator to adjust pressure so as to control force output and utilization while little work has been done to date to analyze the kinematics of the driving-systems involved in their operation. This paper establishes a combined electro-hydraulic model of a fluidic artificial muscle actuated climbing robot to establish a method for studying the relationships between muscle size, robot size and function, and system design. The study indicates a strong relationship between appropriate system component selection and not only system efficiency but individual component effectiveness. The results of the study show that robot mass, operating pressure, muscle size, and motor-pump selection have noteworthy impacts on the efficiency and thereby longevity of the robot for performing its task.

Topics: Robots , Modeling , Muscle
Commentary by Dr. Valentin Fuster
2015;():V001T03A006. doi:10.1115/SMASIS2015-8836.

This article proposes a new layout of electrical network based on two negative capacitance circuits, aimed at increasing the performances of a traditional resistive piezoelectric shunt for structural vibration reduction. It is equivalent to artificially increase the modal electromechanical coupling factor of the electromechanical structure by both decreasing the short-circuit natural frequencies and increasing the open-circuit ones. This leads to higher values of the modal electromechanical coupling factor with respect to simple negative capacitance configurations, when the same margin from stability is considered. This technique is shown to be powerful in enhancing the control performance when associated to a simple resistive shunt, usually avoided because of its poor performances.

Topics: Damping , Circuits
Commentary by Dr. Valentin Fuster
2015;():V001T03A007. doi:10.1115/SMASIS2015-8844.

A shape memory polymer (SMP), the tBA/PEGDMA, is elaborated and characterized. The dynamic mechanical characterization of this SMP highlights promising damping properties. The frequency and temperature dependency of the SMP is represented by a viscoelastic model allowing the introduction of the material in the design process of complex structures. A composite sandwich is developed by coupling the SMP with aluminum skins. A finite element model is developed for modeling the behavior of the SMP when integrated in a sandwich structure. The damping performances obtained by the numerical approach are validated experimentally using modal analysis. The experimental results are found to be in good agreement with the predictions of the finite element model. Furthermore, it is found that the controlled heating of the SMP core allows damping the structure over a wide frequency range. The SMP core temperature is tuned from the time-temperature superposition through a calibration curve to correspond to optimal values of damping ratio in the frequency range of interest; a vibration attenuation of about 20dB is observed.

Commentary by Dr. Valentin Fuster
2015;():V001T03A008. doi:10.1115/SMASIS2015-8857.

This work addresses the optimization of the geometry of smart sensors and actuators on cantilever beams. Three transduction principles are studied and compared in term of efficiency: piezoelectric, electrostatic and dielectric. For the piezoelectric transduction, an active layer of a shorter length than the one of the beam is added on its surfaces. For the electrostatic transduction, the beam is made of a conducting material and it is faced with a fixed electrode at a distance called the gap. This architecture is widely used for M/NEMS (Micro/Nano ElectroMechanical Systems). The last transduction principle, new and promising, is based on the use of dielectric layers on the beam surface. In this case, the excitation is based on electrostatic forces between the charged electrodes, causing transverse deformation of the dielectric film and bending of the multilayer structure; the detection of the vibration is capacitive, based on the fluctuation of the capacitance due to the deformation of the dielectric film. This work presents the optimization of the length and the thickness of the piezoelectric/dielectric layers and, for the electrostatic case, the optimization of the length and the gap of the electrostatic cavity. The study is based on an analytic model for a laminated beam and closed-form formula of the optimization parameters (coupling factor, driving efficiency, sensing efficiency) are obtained. The application of those three transduction principles mainly focus on resonating M/NEMS sensors, whereas the case of piezoelectric transduction is also useful for vibration control of macro-structures, especially with passive shunt techniques. General results on the comparison of the transduction efficiency, as a function of the device size and of the material properties, are also derived.

Commentary by Dr. Valentin Fuster
2015;():V001T03A009. doi:10.1115/SMASIS2015-8866.

Phenomenological model on thermo-mechanical response of shape memory alloy (SMA) strip is presented in this paper. Thermal response and transformation accompanied deformation are described by the proposed model. Newly transformation expansion tensor is defined to describe the relationship between the transformation-induced deformation of the strip and the temperature. The model is then implemented into ABAQUS by using the user-defined subroutine. Finally, the proposed model is verified by the comparison between the finite element simulation and experiment.

Commentary by Dr. Valentin Fuster
2015;():V001T03A010. doi:10.1115/SMASIS2015-8872.

A direct adaptive control approach is used to track the tip speed ratio of wind turbine to maximize the power captured during the below rated wind speed operation. Assuming a known optimum value of tip speed ratio, the deviation of actual tip speed ratio from the optimum one is mathematically expressed as tip speed ratio tracking error. Since the actual tip speed ratio is not a measurable quantity, this expression for tip speed ratio tracking error is linearized and simplified to express it in terms of wind speed and rotor speed, where rotor speed can easily be measured whereas an estimator is designed to estimate the wind speed.

Important results from stability and convergence analysis of the proposed adaptive controller with state estimation and state feedback is also presented. From the analysis it was observed that the adaptive disturbance tracking controller can be combined with adaptive state feedback to achieve other control objectives such as reducing the wind turbine structural loading. Hence, an adaptive state feedback scheme is also proposed to reduce wind turbine tower fore-aft and side-side motions.

Commentary by Dr. Valentin Fuster
2015;():V001T03A011. doi:10.1115/SMASIS2015-8874.

Active Vibration Control (AVC) and Active Structural Acoustic Control (ASAC) gained much attention in all kind of industries in the past. Promising results have been achieved in controlling the vibration and the noise emission/transmission of single panel structures. Especially for aircraft applications, concepts for the reduction of the turbulent boundary layer, rotor or jet noise are presented in the literature. In most cases the contributed work is focused on a single panel or a section of the fuselage/lining. However, an AVC/ASAC system can only be effective for the passengers when it is expanded to the entire fuselage structure. This expansion inevitably leads to a large number of sensors and actuators and thus to a controlled plant of high dimensions. For model-based control approaches especially, the system identification and the proof of stability would be challenging and probably not realizable.

In this paper a strategy for such large-scale problems is investigated. A decentralized control approach with collocated actuator-sensor pairs is proposed. Since adjacent control loops are highly coupled by the underlying structure, special attention has to be given to the global stability of the entire control system. Instead of proving local stability and setting a global master gain, a method for the tuning of the single collocated control loops is developed that takes the cross-couplings into account. Based on data of DLR’s experimental aircraft Dornier 728, it can be shown that the new method increases the performance of the control system compared to the master-gain method.

Topics: Stability
Commentary by Dr. Valentin Fuster
2015;():V001T03A012. doi:10.1115/SMASIS2015-8875.

The paper presents a new constitutive model for iron-based shape memory alloys (Fe-SMAs) adapted from the ZM model initially proposed for Nitinol by Zaki and Moumni [JMPS2007]. The model introduces nonlinear hardening terms to account for interactions between the grains, martensite variants and slip systems that may exist within a volume element of the material. The expressions used for the hardening terms are similar to those in (Khalil et al. [JIMSS2012]). The equations of the model are derived from the expression of a Helmholtz free energy potential, with complementary loading conditions obtained within the framework of generalized standard materials with internal constraints. A detailed derivation of the implicit algorithm used for the integration of the model is provided and used for numerical simulations that are shown to agree with experimental data.

Commentary by Dr. Valentin Fuster
2015;():V001T03A013. doi:10.1115/SMASIS2015-8882.

In this study, the primary response of an Euler-Bernoulli beam resting on nonlinear elastic foundation is investigated. The beam is subjected to thermal and magnetic axial loads. The nonlocal Eringen’s elasticity theory is used to derive the mathematical model to account for the scale effect of the beam. A simply supported beam is considered in the analysis, and the multi-mode approach is used to obtain the reduced nonlinear temporal equations of motion that contain quadratic and cubic nonlinear terms. The method of multiple-scales is applied to obtain approximate analytical solutions for the nonlinear natural frequencies in addition to the primary resonance response curves. Moreover, the effective nonlinearity is obtained as a function of the natural frequencies and the coefficients of the elastic foundation. The results reveal that the scale parameter has a significant effect on the frequencies and amplitudes of the beam. The obtained results are presented over a selected range of physical parameters such as the scale effect parameter, foundation parameters, thermal and magnetic loads, and the excitation level. Time responses, phase planes and Poincaré maps are generated for the beam under consideration.

Commentary by Dr. Valentin Fuster
2015;():V001T03A014. doi:10.1115/SMASIS2015-8893.

The principle of a magnetorheological elastomer (MRE) dynamic vibration absorber (DVA) is proposed and the corresponding configuration is designed in this paper. The MRE DVA is composed of a vibration absorbing unit and a passive vibration isolation unit. The vibration absorbing unit can be utilized to mitigate the kinetic energy acting on the primary system (i.e., the system of which the vibration will be mitigated) and the passive vibration isolation unit utilized to support the primary system. The vibration absorbing unit consists of magnetic conductor, shearing sleeve, bobbin core, electromagnetic coil winding, and vulcanized MRE between the shearing sleeve and the bobbin core. The magnetic field produced by the electromagnetic coil winding starts from the bobbin core, and passes through the magnetic conductor and the shearing sleeve, then goes through the MRE and forms a closed loop. The shear storage modulus of the MRE could be tuned continuously by varying the applied current, which results in natural frequency shift of the MRE DVA. The optimal parameters of the electromagnetic circuit of the MRE DVA are calculated based on Kirchoff’s law. The finite element method is employed to validate the electromagnetic circuit of the MRE DVA and to obtain the corresponding electromagnetic characteristics. The mathematical model of the MRE DVA is also derived. In order to analyze how the parameters of the MRE DVA influence the effectiveness of the vibration control and to validate the flexibility of the control systems, the MRE DVA is employed in a powertrain mount system to replace the conventional passive mount. A single-degree-of-freedom (SDOF) dynamic model for the semi-active powertrain mount system is established. A varied step optimum algorithm is adopted to realize the vibration control of the powertrain mount system based on the MRE DVA.

Commentary by Dr. Valentin Fuster
2015;():V001T03A015. doi:10.1115/SMASIS2015-8923.

The paper presents a numerical implementation of the Large Time Increment (LaTIn) method for the integration of the ZM model [1] for SMAs in the pseudoelastic range. LaTIn was initially proposed as an alternative to the conventional incremental approach for the integration of nonlinear constitutive models [2]. It is adapted here for the simulation of pseudoelastic SMA behavior and is shown to be especially useful in situations where the phase transformation process presents little to no hardening. In these situations, a slight stress variation during a load increment can result in large variation of the volume fraction of martensite within a representative volume element of the SMA. This can lead to difficulty in numerical convergence if the incremental method is used. LaTIn involves two stages: in the first stage a solution satisfying the conditions of static equilibrium is obtained for each load increment without considering the consistency with the phase transformation conditions, then in the second stage consistent increments of the local state variables are determined for the entire loading path. The two stages take place sequentially, in contrast to the incremental method that requires satisfying the global equilibrium and local consistency conditions simultaneously at a given load increment before proceeding to the next. The numerical integration algorithm consists of the following steps: 1. Division of the loading path into a finite number of increments, 2. Solution for all the load increments of the static equilibrium problem in which the local consistency conditions are relaxed, 3. Update of the state variables in accordance with the consistency conditions for all the load increments. Steps 2 and 3 are repeated until a solution is reached that satisfies simultaneously the equilibrium and consistency requirements. An algorithm is presented for the implicit integration of the time-discrete equations. The algorithm is used for finite element simulations using Abaqus, in which the model is implemented by means of a user material subroutine. The simulation results are discussed in comparison with those obtained using conventional step-by-step incremental integration.

Commentary by Dr. Valentin Fuster
2015;():V001T03A016. doi:10.1115/SMASIS2015-8991.

Smart hydrogel micro-valves are essential components of micro-chemo-mechanical fluid systems. These valves show a transistor-like behavior and are based on phase-changeable polymers. They can open and close micro-fluidic channels depending on chemical concentrations in the fluid. These highly complex systems are challenging to engineer and their development will advance faster if proper simulations take place beforehand.

A concept of how to simulate concentration-triggered, phase-changeable hydrogels is proposed. A simplified flow simulations will be presented to demonstrate the feasibility of this approach and to highlight geometrical problems. Based on the results, structurally more advanced models will be introduced with implemented multi-field solver interactions including thermal, mechanical and fluidic domains. The results of these models show the closing behavior of a micro-valve. The computed parameters of such valves are implemented into a circuit representation, which is capable of efficiently computing large scale micro-fluidic systems using an electric circuit simulator. These methods will help to predict, visualize and understand polymeric swelling behavior and demonstrate the performance of large-scale chip applications before any complex experiment is performed.

Commentary by Dr. Valentin Fuster
2015;():V001T03A017. doi:10.1115/SMASIS2015-8996.

Hydrogels consist of a network of cross-linked polymers that swell when put into water. For temperature-sensitive smart hydrogels the equilibrium hydrogel size depends on the temperature of the liquid. These hydrogels are used to build temperature-controlled fluidic valves. Here we present an equivalent circuit model of such a hydrogel valve. The transient behavior is based on the model by Tanaka with three additional assumptions: 1. Only the fundamental mode of the deformation field, i.e. the slowest-decaying exponential temporal behavior, is relevant. 2. There are distinct equilibrium sizes for the swollen and the de-swollen state. 3. As observed in experiment, the swollen gel and the de-swollen gel have different elastic moduli, which affect the time constants of swelling vs. de-swelling. The resulting network model includes three physical subsystems: the thermal subsystem, the polymeric subsystem and the fluidic subsystem. The thermal subsystem considers the temperature of the heater, of the adhesive and of the hydrogel. It is assumed that adhesive, housing and hydrogel act as heat capacities in combination with heat resistors. The modeled polymeric subsystem causes in addition time delays for swelling and de-swelling of first order with different delay constants. The fluidic subsystem basically includes the fluidic channel between hydrogel and housing with time varying cross section, which is modeled as controlled source. All subsystems are described and coupled within one single circuit. Thus the transient behavior of the hydrogel can be calculated using a circuit simulator. Simulation results for an assumed hydrogel setup are presented.

Topics: Valves , Circuits , Hydrogels
Commentary by Dr. Valentin Fuster
2015;():V001T03A018. doi:10.1115/SMASIS2015-9002.

Negative stiffness systems have been widely studied for their seismic response reduction characteristics and have been found to be very effective in reducing seismic responses in structures. Based primarily on the concept of introducing flexibility in the structure, they bring about seismic response reduction by reversing the force–deformation behaviour of the structure-device assembly. While some negative stiffness devices alter the physical behaviour of the structure to deformation, some devices show “pseudo negative stiffness” behaviour by means of a control algorithm. To have the best possible reduction of seismic response in structures, it is essential that an optimal combination of dampers is used. The present work studies the performance of true negative system (TNS) and an adaptive negative stiffness system (ANSS) on a 5 degree of freedom shear structure. The optimal values of parameters and optimal number of dampers are studied based on the response such as inter-storey drifts, accelerations, displacements and base shear obtained from MATLAB analysis.

Topics: Damping , Stiffness
Commentary by Dr. Valentin Fuster
2015;():V001T03A019. doi:10.1115/SMASIS2015-9016.

Vibration control in smart structures is discussed in this paper using an approach based on connecting collocated control elements to one another via a network with certain topology. Consensus method is implemented to force disagreements between the control agents of the structure to zero, where each control agent consists of a multi-mode Positive Position Feedback (PPF) second-order compensator. Multi-agent state-space representation of actuator/sensor elements is used, accompanied with an optimal state-estimator. The consensus law is embedded in the dynamics of the PPF control elements. Required conditions for stability of the closed-loop multi-agent system are then extracted. Performance of the controller is numerically investigated, and synchronization of controller agents is examined. Significant advantage of the decentralized consensus-based vibration controller over centralized forms is in robustness to failure of components or an entire agent, and obtained synchronized performance of the whole control system.

Commentary by Dr. Valentin Fuster
2015;():V001T03A020. doi:10.1115/SMASIS2015-9019.

This paper discusses a new nonlinear controller for vibration reduction in nonlinear vibrating smart structures. Nonlinear Integral Resonant Controller (NIRC) applies additional damping to the closed-loop system of a nonlinear vibrating system, and reduces the vibration amplitude in a wide range of frequency domain. An approximate solution is obtained using a multi-layer implementation of the Method of Multiple Scales, steady-state amplitude-frequency response is obtained and closed-loop stability is examined. Effects of different controller parameters on system response are investigated, in addition to numerical simulation results. In contrast to the Positive Position Feedback approach, the closed-loop response of the controlled system via NIRC does not show any high-amplitude peak in the neighborhood of the suppressed resonant frequency. This makes the closed-loop system robust to variations in excitation frequency.

Commentary by Dr. Valentin Fuster
2015;():V001T03A021. doi:10.1115/SMASIS2015-9020.

The focus of this study is to understand traveling wave generation and propagation in reduced order 2D plate models. A plate with all clamped (C-C-C-C) boundary conditions was selected to be the medium through which the wave propagation occurs. The plate is excited at multiple locations by point forces which generates controlled oscillations resulting in net traveling waves. A finite element model is developed and the traveling wave response is simulated. The numerical model is complex with a large number of degrees-of-freedom making a parametric study computationally intensive. In order to overcome this computational burden, balanced truncation based and interpolation-based model reduction techniques are employed to reduce the total number of degrees-of-freedom. The capabilities of these reduction techniques to capture the steady-state frequency-domain characteristics and the steady-state time-domain response have been compared in this paper.

Topics: Traveling waves
Commentary by Dr. Valentin Fuster
2015;():V001T03A022. doi:10.1115/SMASIS2015-9023.

The problem of second harmonic guided wave generation in transversely isotropic plates is investigated from a theoretical and numerical standpoint. The strain energy function of transversely isotropic materials is written down using five invariants in terms of the Green-Lagrange strain tensor and contains five linear terms and nine nonlinear terms.

Theoretical investigations reveal that second harmonics in a weakly nonlinear transversely isotropic plate are cumulative only when the phase matching and nonzero power flux criteria are satisfied. Also, only cumulative secondary symmetric Lamb wave modes can be generated — a conclusion in line with what is observed for isotropic plates. Finally, numerical simulations are carried out to examine the cumulative second harmonic generation from the S0 mode and the results obtained are discussed in the light of the theory.

Commentary by Dr. Valentin Fuster
2015;():V001T03A023. doi:10.1115/SMASIS2015-9044.

Transducers based on dielectric electroactive polymers (DEAP) offer an attractive balance of work density and electromechanical efficiency. For example in automation and haptic applications, especially multilayer transducers are used to scale up their absolute deformation and force. Depending on the application different transducer controls have to be realized to match the specifications of the particular application. However, analogous to conventional electromechanical drive systems an inner sensor-less force control can be realized for DEAP transducers, too. For this force control the nonlinear relations between voltage and electrostatic pressure as well as the electromechanical coupling have to be considered. The resulting open-loop force control can be used for superimposed motion controls, such as position, vibration and impedance controls. Therefore, within this contribution the authors propose a model-based feedforward force control based on an overall model of the transducer that does not require any force measurement. Finally, the derived open-loop force control interface is experimentally validated using in-house developed DEAP stack-transducers and driving power electronics.

Commentary by Dr. Valentin Fuster
2015;():V001T03A024. doi:10.1115/SMASIS2015-9050.

Axially-compressed columns, or strips, with bilateral continuous rigid constraints (CRC) are known to be able to attain multiple snap-through buckling events in their elastic postbuckling response that lead to the sudden release of strain energy from the system. This feature allows this structural prototype to be used as energy concentrators for smart applications. However, the parameters controlling the postbuckling response for such system are limited. The structural prototype discussed in this paper is that of an axially compressed strip provided with discrete rigid constraints (DRC), whereby the layout of the lateral constrains provides increased design freedom to control the strip’s postbuckling features. The study is based on numerical simulations using the finite element method. Using a previously characterized CRC strip as a baseline, two DRC design groups were considered in symmetric and asymmetric layouts for a total of 15 different arrangements. Results show that DRC strips can attain elastic postbuckling responses with distinct characteristics and that the far postbuckling response can be controlled by modifying the number and the location of the constraints. Compared to CRC strips, some DRC patterns allow attaining higher mode transitions and larger kinetic energy release after the first buckling event. The ability to design for such postbuckling response features can be potentially used for energy harvesting and other sensing and actuation applications.

Topics: Strips
Commentary by Dr. Valentin Fuster
2015;():V001T03A025. doi:10.1115/SMASIS2015-9051.

Piezoelectric transducers have been used for semi-active vibration reduction in structures by altering the stiffness state and dissipating electrical energy. Common approaches include state switching, synchronized switch damping on a resistor (SSDS), and synchronized switch damping on an inductor (SSDI). Each of these methods requires four switches per vibration cycle, so any delay in the switch from the ideal moment could have a significant effect on the vibration reduction. An experimental investigation into the effect of switch delays on these techniques reveals that the abrupt change in piezoelectric voltage from the switch has the effect of a step input on the structure, which may excite higher order modes and increase the peak strain. This non-ideal switching of boundary conditions has implications towards the design and performance of these state switching techniques. Switching at the peak is classically considered the ideal switch time, but the influence of the switch on the local strain may actually result in a higher peak strain for the structure than with a delayed switch. This paper will examine switch times that lead and lag the ideal case for state switching, SSDS, and SSDI to quantify the level of vibration reduction achieved under non-ideal peak sensing.

Topics: Vibration , Delays , Switches
Commentary by Dr. Valentin Fuster
2015;():V001T03A026. doi:10.1115/SMASIS2015-9053.

This paper presents a novel Magentorheological (MR) brake with permanent magnets. The proposed MR brake can generate a braking torque at a critical rotation speed without an external power source, sensors, or controllers, making it simple and cost-effective device. The brake system consists of a rotary disk, permanent magnets, springs and MR fluid. Permanent magnets are attached to the rotary disk via springs, and they move outward through grooves with two different gap distances along the radial direction of the stator due to centrifugal force. Thus, the position of the magnets is dependent on the spin speed, and it can determine the magnetic fields applied to MR fluids. Proper design of the stator geometry gives the system unique torque characteristics. To show the performance of an MR brake system, the electromagnetic characteristics of the system are analyzed, and the torques generated by the brake are calculated using the result of the electromagnetic analysis. After the simulation study, a prototype brake system is constructed and its performance is experimentally evaluated. The results demonstrate the feasibility of the proposed MR brake as a speed regulator in rotating systems.

Topics: Fluids , Safety , Rheology , Brakes
Commentary by Dr. Valentin Fuster
2015;():V001T03A027. doi:10.1115/SMASIS2015-9086.

In the last two decades it has been proposed to use actuation forces of shape memory alloy wires to develop an active needling tool to facilitate the conventional needle-based procedures. In these procedures it is always desired to guide the needle though an accurate trajectory reaching the target location. In some cases it is also desired to maintain a curved path to avoid obstacles and prevent damage to sensitive organs. Therefore, it is of a great importance to investigate the interactions of needle within tissue and understand the mechanics of the needle insertion procedure. The nonlinear properties of the deforming tissue while needle is inserted make the prediction of the needle tip placement difficult. Previous studies include experimental and analytical investigations based on a particular tissue properties and needle shape. In this work mechanics of a bevel-tipped needle inserted into soft tissue has been investigated via numerical simulation. The nonlinear properties of the tissue have been implemented in the model. This model has been generated in LS-DYNA software using Arbitrary-Eulerian-Lagrangian formulation for the solid-fluid interactions. Total insertion depth of 150mm of a 0.5mm diameter needle has been modeled. The small stiff element sizes of the needle dictate an expensive computational time. In order to have reasonable computational costs many assumptions were made such as decreasing the Young’s Modulus of the needle and tissue by the same factor. Needle insertion tests have also been performed to evaluate the accuracy of the simulations. The error of less than 10% was found and therefore validated our simulation approach. Using this model it would be possible to predict the steerability of different configurations of the needle inside the tissue. It can also be used for surgical simulation and training purposes and path planning.

Commentary by Dr. Valentin Fuster
2015;():V001T03A028. doi:10.1115/SMASIS2015-9113.

The use of laminated composite materials in aircraft or automobile structures, though very common due to various advantages of these materials, often escalates the overall noise and vibration level. An active structural acoustic control (ASAC) strategy based on a frequency weighted optimal H2 controller is developed in the present work to attenuate the transmitted sound into an enclosure surrounded by laminated composite panels. A state-space model based on a two-way coupled fluid-structure interaction analysis using Green’s theorem is proposed to include the influence of the flexible panels on the enclosed fluid (air) and vice-versa. Few points within the cavity are identified as the observer locations based on the maximum sound pressure level (SPL) within the enclosure due to external mechanical excitation. The SPL averaged over these locations is used as the performance vector for the proposed H2 controller. A feedback control strategy is then developed using surface bonded collocated IDE-PFC actuators and PVDF sensors while optimizing the quadratic H2 norm between the external excitation and the performance vector with a limit on the actuation voltage. Numerical simulation shows a maximum of 11.4 dB of averaged SPL reduction achieved inside the enclosure for a particular configuration.

Commentary by Dr. Valentin Fuster
2015;():V001T03A029. doi:10.1115/SMASIS2015-9119.

This paper deals with active vibration isolation of unbalance-induced oscillations in rotors using gain-scheduled H-controller via active bearings. Rotating machines are often exposed to gyroscopic effects, which occur due to bending deformations of rotors and the consequent tilting of rotor disks. The underlying gyroscopic moments are proportional to the rotational speed and couple the rotor’s radial degrees of freedom. Accordingly, linear time-varying models are well suited to describe the system dynamics in dependence on changing rotational speeds. In this paper, we design gain-scheduled H-controllers guaranteeing both robust stability and performance within a predefined range of operating speeds. The paper is based on a rotor test rig with two unbalance-induced resonances in its operating range. The rotor has two discs and is supported by one active and one passive bearing. The active support consists of two piezoelectric stack actuators and two collocated piezoelectric load washers. In addition, the rig is equipped with four inductive displacement sensors located at the discs. Closed-loop performance is assessed via isolation of unbalance-induced vibrations using both simulation and experimental data. This contribution is the next step on our path to achieving the long-term objective of combined vibration attenuation and isolation.

Commentary by Dr. Valentin Fuster

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