bluuebunny/crossref_metadata_2025 huggingface dataset:
Target Shape Optimization of Functionally Graded Shape Memory Alloy Compliant Mechanism
Authors: Jovanova Jovana , Frecker Mary , Hamilton Reginald F. , Palmer Todd A.
Published: November 2016

Nickel Titanium (NiTi) shape memory alloys (SMAs) exhibit shape memory and/or superelastic properties, enabling them to demonstrate multifunctionality by engineering microstructural and compositional gradients at selected locations. This paper focuses on the design optimization of NiTi compliant mechanisms resulting in single-piece structures with functionally graded properties, based on user-defined target shape matching approach. The compositionally graded zones within the structures will exhibit an on demand superelastic effect (SE) response, exploiting the tailored mechanical behavior of the structure. The functional grading has been approximated by allowing the geometry and the superelastic properties of each zone to vary. The superelastic phenomenon has been taken into consideration using a standard nonlinear SMA material model, focusing only on 2 regions of interest: the linear region of higher Young’s modulus of elasticity and the superelastic region with significantly lower Young’s modulus of elasticity. Due to an outside load, the graded zones reach the critical stress at different stages based on their composition, position and geometry, allowing the structure morphing. This concept has been used to optimize the structures’ geometry and mechanical properties to match a user-defined target shape structure. A multi-objective evolutionary algorithm (NSGA II - Non-dominated Sorting Genetic Algorithm) for constrained optimization of the structure’s mechanical properties and geometry has been developed and implemented.
Design Optimization of a Magneto-Rheological Fluid Brake for Vehicle Applications
Authors: Shamieh Hadi , Sedaghati Ramin
Published: November 2016

The magnetorheological Brake (MRB) is an electromechanical brake in which smart magnetorheological (MR) fluids have been utilized to generate the required braking torque. The purpose of this study is to design optimize a real-size MRB for automobile applications considering geometrical, material and magnetic circuit parameters. The mathematical equations governing the system’s braking torques are derived. The dynamic range of a disk-type MRB expressing the ratio of generated toque at on and off states has been formulated as a function of the rotational speed, geometrical and material properties, and applied electrical current. The magnetic circuit analysis of the proposed MRB is performed to find the relation between magnetic field intensity and the applied electrical current as a function of the MRB geometrical and material properties. Finally, a multidisciplinary design optimization problem has been formulated to identify the optimal brake geometrical parameters to maximize the dynamic range of the MRB under weight, size and magnetic flux density constraints. The optimization problem has been solved using combined Genetic Algorithm and Sequential Quadratic Programming techniques. The optimal design is then compared with those available in the literature.
Inflatable Octet-Truss Structures
Authors: Robertson M. G. , Haseltine J. , Tawfick S.
Published: November 2016

The development of variable-stiffness systems is key to the advance of compact engineering solutions in a number of fields. Rigidizable structures exhibit variable-stiffness based on external stimuli. This function is necessary for deployable structures, such as inflatable space antennas, where the deployed structure is semi-permanent. Rigidization is also useful for a wide range of applications, such as prosthetics and exoskeletons, to help support external loads. In general, variable-stiffness designs suffer from a tradeoff between the magnitude of stiffness change and the ability of the structure to resist mechanical failure at any stiffness state.

This paper presents the design, analysis, and fabrication of a rigidizable structure based on inflatable octet-truss cells. An octet-truss is a lattice-like configuration of elements, traditionally beams, arranged in a geometry reminiscent of that of the FCC lattice found in many metals; namely, the truss elements are arranged to form a single interior octahedral cell surrounded by eight tetrahedral cells. The interior octahedral cell is the core of the octet-truss unit cell, and is used as the main structure for examining the mechanics of the unit as a whole. In this work, the elements of the inflatable octet truss are pneumatic air muscles, also called McKibben actuators. Generalized McKibben actuators are a type of tubular pneumatic actuator that possess the ability to either contract or expand axially due to an applied pressure. Their unique kinematics are achieved by using a fiber wrap around an isotropic elastomeric shell. Under normal conditions, pressurizing the isotropic shell causes expansion in all directions, like a balloon. The fiber wrap constrains the ability of the shell to freely expand, due to the fiber stiffness. The wrap geometry thus guides the extensile/contractile motion of the actuator by controlling its kinematics. It is their ability to contract under pressure that makes McKibben actuators unique, and consequently they are of great interest presently to the robotics community due to their similitude to organic muscles. Kinematic analysis from constrained maximization of the shell volume during pressurization is used to obtain relations between the input work due to applied pressure and the resulting shape change due to strain energy. Analytical results are presented to describe the truss stiffness as a function of the McKibben geometry at varying pressures.
Emergency Communication and Quick Seismic Damage Investigation Based on Smartphone
Authors: Han Ruicong , Yu Yan , Zhao Xuefeng , Peng Deli , Guan Quanhua , Li Mingchu , Ou Jinping
Published: November 2016

The ability of residents and professional emergency responders to exchange information during an emergency is necessary to provide a more efficient rescue following major disasters. Simultaneously, the quick seismic damage evaluation is significant to provide guidance for emergency response and rescue after disaster. However, traditional field investigation needs immense cost in money, manpower and time to accomplish house-to-house investigation, which results in an inefficient work. Towards this, an emergency communication and quick seismic damage investigation method based on smartphone is proposed and realized with the assistant of an application E-Explorer. First, in emergency communication module, the communication is available by using the multipeer connectivity technology even without external network, which can help to deliver important information for personal survival. Second, in damage investigation module, E-Explorer integrates the functions of questionnaire and picture collection for damage phenomenon recording and image acquisition. Last, a big data sharing platform is built, to provide guidance for rescue workers, and collect damage information for quick intensity evaluation.
Adaptive Tracking Control for Linear Infinite Dimensional Systems
Authors: Balas Mark J. , Frost Susan A.
Published: November 2016

Tracking an ensemble of basic signals is often required of control systems in general. Here we are given a linear continuous-time infinite-dimensional plant on a Hilbert space and a space of tracking signals generated by a finite basis, and we show that there exists a stabilizing direct adaptive control law that will stabilize the plant and cause it to asymptotically track any member of this collection of signals. The plant is described by a closed, densely defined linear operator that generates a continuous semigroup of bounded operators on the Hilbert space of states. There is no state or parameter estimation used in this adaptive approach. Our results are illustrated by adaptive control of general linear diffusion systems.
Thermally Adaptive Building Coverings Inspired by Botanical Thermotropism
Authors: Barrett Ronald M. , Barrett Ronald P.
Published: November 2016

This paper covers the new field of thermally adaptive building coverings, their inspiration, basic operational characteristics, analytical modeling and coupon testing. Inspiration for thermally adaptive building coverings come quite notably from various families of thermotropic plant structures. Certain plant cellular structures like those in Mimosa Pudica (Sensitive Plant), Rhododendron leaves or Albizia Julibrissin (Mimosa Tree), exhibit actuation physiology which depends on physical manipulation and/or thermal loading as a function of solar radiation. The paper draws parallels between the differential actuation via cellular turgor pressure manipulation. A parallel with these structures can be seen in the new field of thermally adaptive building coverings which use various forms of cellular foam to aid or enable actuation much in the same way that plant cells are used to move leaves. When exposed to high solar loading, the structures curve upwards and outwards. When cold, these same structures curve back towards the building forming convex pockets of dead air to insulate the building. The paper shows the basic classical laminated plate theory models comparing theory and experiment of such coupons. The study concludes with a basic description of the effectiveness of thermally adaptive building coverings.
Dynamic Simulation of Dielectric Elastomer Actuated Multibody Systems
Authors: Schlögl T. , Leyendecker S.
Published: November 2016

A three-dimensional electro-mechanically coupled finite element model for dielectric elastomers is used to actuate multibody systems. This setting allows exploring the complex behavior of humanoid robots that are driven by artificial muscles instead of electrical drives. The coupling between the finite element muscle model and the rigid bodies is formulated at configuration level, where Lagrange multipliers account for constraint forces, leading to differential algebraic equations of index-3. A well-chosen set of redundant configuration variables for the multibody system avoids any rotational degrees of freedom and leads to linear coupling constraints. As a result, the coupling between the artificial muscles and the multibody system can be formulated in a very modular way that allows for easy future extension. The applied structure preserving time integration scheme provides excellent long time energy behavior. In addition, the index-3 system is solved directly with numerical accuracy, avoiding index reduction approximations.
Sensorless Method for Switching Energy Harvester Based on Self-Sensing Approach
Authors: Yamamoto Y. , Asahina K. , Yoshimizu K. , Makihara K.
Published: November 2016

Vibration energy harvesting extracts electrical energy from vibrating structures. The past studies of vibration energy harvesting suggest that the efficiency can be improved by switch regulation in the harvesting circuit. The switch-regulation is carried out depending on the motion of the target structure with the use of vibration sensors such as displacement sensor or accelerometer. This paper proposes a new vibration self-sensing method for switching energy harvesters that do not use those vibration sensors. In this method, the voltage of the piezoelectric transducer is measured, and the structural vibrational status is estimated from the measured voltage. The transducer voltage is not smooth and does not maintain the sinusoidal wave even when the structure vibrates in a sinusoidal wave because the switch energy harvesting method inverses the transducer voltage at every period. Thus, we establish a state observer based on a Kalman filter to estimate three state values of the target harvesting system: modal displacement, modal velocity, and electric charge in the transducer.

This paper describes the construction processes for the observer. The observed value is the transducer voltage. We also show an electric circuit for measuring the transducer voltage. Finally, we confirm the efficiency of the proposed state observer for switch harvesting with numerical simulations.
Flight Test of a Shape Memory Alloy Actuated Adaptive Trailing Edge Flap
Authors: Calkins F. T. , Mabe J. H.
Published: November 2016

The Boeing Company has a goal of creating aircraft that are capable of continuous optimization for all flight conditions. Recent advances in SMA actuation and a detailed understanding of wing design were combined to design, build, and safely demonstrate small trailing edge flaps driven by SMA actuation. As part of a 2012 full-scale flight test program a lightweight and compact Shape Memory Alloy (SMA) rotary actuator was integrated into the hinge line of a small flap on the trailing edge of a commercial aircraft wing. This Adaptive Trailing Edge program was part of a Boeing and Federal Aviation Administration (FAA) collaboration. Aerodynamic studies of these small trailing edge flaps show that improved performance requires multiple flap configurations that vary with flight regime. Configurations include small angles of deployment for reduced fuel burn and emissions during high speed cruise and larger angles of deployment for increased lift and lower noise during takeoff and approach. SMA actuation is an ideal compact solution to position these small flaps and increase aircraft performance by simply and efficiently altering the wings aerodynamic characteristics for each flight segment. Closed loop control of the flap’s position, using the SMA actuator, was demonstrated at multiple flight conditions during flight tests. Results of the successful flight test on a 737–800 commercial airplane and the significantly improved performance benefits will be presented. This is the first flight test of an SMA rotary actuator system, which was matured from TRL 4 to TRL 7 during the program.
Design and Experimentation of a Tunably-Compliant Robotic Finger Using Low Melting Point Metals
Authors: Joo Heon , Swensen John P.
Published: November 2016

In this paper, we describe the fabrication and testing of a tunably-compliant tendon-driven finger implemented through the geometric design of a skeleton made of the low-melting point Field’s metal encased in a silicone rubber. The initial prototype consists of a skeleton comprised of two rods of the metal, with heating elements in thermal contact with the metal at various points along its length, embedded in an elastomer. The inputs to the systems are both the force exerted on the tendon to bend the finger and the heat introduced to liquefy the metal locally or globally along the length of the finger. Selective localized heating allows multiple joints to be created along the length of the finger.

Fabrication was accomplished via a multiple step process of elastomer casting and liquid metal casting. Heating elements such as power resistors or Ni-Cr wire with electric connections were added as an intermediate step before the final elastomer casting. The addition of a tradition tendon actuation was inserted after all casting steps had been completed. While preliminary, this combination of selective heating and engineered geometry of the low-melting point skeletal structure will allow for further investigation into the skeletal geometry and its effects on local and global changes in device stiffness.
Parametric Analysis of Piezoelectric Metamaterial With LC Shunt Circuit
Authors: Xu Jiawen , Li Shilong , Tang J.
Published: November 2016

Piezoelectric metamaterials with LC shunt circuits have potential in acoustic wave attenuation and guiding. This type of metamaterial takes advantages of the electro-mechanical coupling and local resonance from LC circuit. A unit cell of the metamaterial consists of the host medium and a piezoelectric transducer attached onto the host plate, while an LC shunt circuit is connected to the transducer. In this research, we present theoretical modeling to analyze the piezoelectric metamaterial. The influences of electro-mechanical coupling and system parameters with respect to bandgap characteristics are presented. Moreover, the unique feature of such an electro-mechanical coupling system, the online tenability, is discussed and analyzed.
Design and Prototyping of a Wearable Assistive Tool for Hand Rehabilitation Using Shape Memory Alloys
Authors: Hadi A. , Alipour K. , Kazeminasab S. , Amerinatanzi A. , Elahinia M.
Published: November 2016

Disability to move hands perfectly is one of the most severe human physical disabilities, and it is mostly common among adults or those who have experienced serious accidents. It is desired to find a methodology to restore the motion of the hand. To this aim, we proposed and evaluated the use of wearable robots (i.e., a smart glove) for clinical therapy that is equipped with shape memory alloy (SMA) actuators. The developed robotic tool, which is a smart glove, uses the structure of human hand as a base mechanism. This glove compensates the weakness of the hand muscles utilizing the forces produced by SMA actuators. The attractive property of high force to weight ratio in SMAs makes this glove a good candidate to be used as a wearable system.

The glove actuation mechanism is tendon driven. For every finger, two active Degrees Of Freedom (DOFs) are supported in design. Consequently, four tendons are considered for activating each DOF in order to complete opening and closing phases of the fingers. Totally, twenty tendons are used for rehabilitation of a hand through the glove. Using kinematic relations between tendon length and finger movement, the required deflection of each tendon is extracted. Since a short length of SMA wires cannot provide an enough displacement of tendons in the glove, therefore, an extra mechanism was embedded to the developed glove to support the required length of SMA wires. The SMA actuators were selected and mounted on the system to support the tendons of the mechanism effectively. Moreover, the gripping force provided by the developed glove was also studied. To this end, an analysis was accomplished to extract the relationship between tendon actuation and gripping force of the glove.

The obtained results offered a proper model for such a tendon driven glove. Coupling the model of the SMA actuators to that of the tendon driven glove, a composite model of smart glove was extracted. The aforementioned model was simulated numerically. Furthermore, the results were compared with those of the real-world prototype. The obtained results revealed the accuracy of the developed model which will be then employed for both system optimization and model-based control design.
Dynamic Modeling and Analysis of an Origami-Inspired Optical Shield for the Starshade Spacecraft
Authors: Bowen Landen , Trease Brian , Frecker Mary , Simpson Timothy
Published: November 2016

The Starshade is a future exoplanet discovery mission consisting of a satellite and a 34 meter diameter starshade used to block the light of a star of interest, enhancing visualization of the orbiting planets. The starshade itself is composed of a number of 7 meter long petals surrounding a 20 meter diameter optical shield. A critical design requirement of the optical shield is stowage in a 3 meter diameter area during launch. Origami has been investigated as a means of collapsing the optical shield, specifically a family of action origami models known as “flashers.”

In this paper a dynamic model of an optical shield design candidate based on a flasher pattern is created in Adams 2014. As these patterns can have many parts and joints, a method for the automatic creation of dynamic models using information about the geometry of the crease pattern is utilized. As the fabricated optical shield panels will be somewhat flexible, each quadrilateral panel is modeled as two rigid triangles connected with a joint. The effect of joint stiffness on the forces and torques developed during deployment is investigated.

It is found that the optical shield design is rigid foldable if the panel flexibility is taken into account by additional joints, which are found to bend from 10° – 40°. Joint forces are predicted over the deployment, and maximum and average joint forces are tabulated. These and other insights gained from the dynamic model can help guide future Starshade design decisions, and similar analyses can be performed for other origami-inspired deployable structures.
Superelastic Shape Memory Alloy Fiber-Reinforced Polymer Composites
Authors: Daghash Sherif M. , Ozbulut Osman E.
Published: November 2016

Fiber reinforced polymer (FRP) composites have been increasingly used in engineering applications due to their lightweights, high strength, and high corrosion resistance. However, the conventional FRPs exhibits brittle failure, low toughness, limited fatigue strength, and relatively low ultimate tensile strains. Shape memory alloys (SMAs) are a class of metallic alloys that can recover large strains upon load removal with minimal residual deformations. Besides their ability to recover large deformations, SMAs possess excellent corrosion resistance, good energy dissipation capacity, and high fatigue properties. This study explores the use of superelastic SMA fibers to reinforce a thermoset polymer matrix to produce a polymer composite with enhanced mechanical properties. Nickel-Titanium wires with a diameter of 495 micrometer are used as fibers. SMA coupons with different reinforcement ratios are fabricated using a special-made mold and following a modified hand lay-up technique. The uniaxial tensile tests are conducted under cyclic loading protocols. The results of the tests are assessed in terms of ultimate strength, ultimate strain, residual strain, and failure modes of the composites.
Carbon Fiber Composite Beam Damage Model Identification
Authors: Pesch Alexander H. , Madden Ryan J. , Martin Richard E. , Sawicki Jerzy T.
Published: November 2016

The technique of model-based identification is proposed to extract a model for damage in composite materials from experimental data. The proposed method is demonstrated on a unidirectional carbon fiber reinforced polymer (CFRP) beam. Impact damage is seeded in the CFRP beam using a spherical punch, causing localized damage. The specimen is evaluated through modal testing before and after the damage is seeded, with the healthy case modeled using the FEM. Finally, a virtual controller is found which eliminates error in response between the healthy model and damaged experimental system. The virtual controller, being in feedback with the healthy model at the FE node where the damage occurs, reflects the effect of the localized damage.

It is found that the seeded impact damage reduces stiffness and is a source of damping inside the composite beam. Interpretation of the local damage is made through the curve fitting of the identified dynamics. To confirm the efficacy of the fit, a closed-loop is made with the healthy model which is then compared to the data from the damaged system.
Origami Metastructures for Tunable Wave Propagation
Authors: Thota M. , Li S. , Wang K. W.
Published: November 2016

Wave propagation inside a host media with periodically distributed inclusions can exhibit bandgaps. While controlling acoustic wave propagation has large impact on many engineering applications, studies on broadband acoustic bandgap (ABG) adaptation is still outstanding. One of the important properties of periodic structure in ABG design is the lattice-type. It is possible that by reconfiguring the periodic architectures between different lattice-types with fundamentally distinct dispersion relations, we may achieve broadband wave propagation tuning. In this spirit, this research pioneers a new class of reconfigurable periodic structures called origami metastructures (OM) that can achieve ABG adaption via topology reconfiguration by rigid-folding. It is found that origami folding, which can enable significant and precise topology reconfigurations between distinct Bravais lattice-types in underlying periodic architecture, can bring about drastic changes in wave propagation behavior. Such versatile wave transmission control is demonstrated via numerical studies that couple wave propagation theory with origami folding kinematics. Further, we also exploit the novel ABG adaptation feature of OM to design structures that can exhibit unique tunable non-reciprocal behavior. Overall the broadband adaptable wave characteristics of the OM coupled with scale independent rigid-folding mechanism can bring on-demand wave tailoring to a new level.
Graphene Nanoplatelets-Based Self-Sensing Cementitious Composites
Authors: Jiang Zhangfan , Ozbulut Osman E. , Harris Devin K.
Published: November 2016

Over the past two decades, numerous research studies have been conducted to explore behavior of self-sensing cementitious composites with different functional fillers. Most of these studies investigated the use of fillers such as carbon nanofiber (CNF), carbon black, and carbon nanotubes (CNTs) in cement composites to develop a multifunctional material. Since its discovery in 2004, graphene has also raised significant attention as 2D nanoscale reinforcement for composite materials. The planar structure of graphene sheets provides more contact area with the host material. However, high cost and dispersion difficulties are among the drawbacks of graphene. More recently, graphene nanoplatelets (GNPs), which have very thin but wide aspect ratio, are drawing the graphene market due to their advantages such as ease of processing and excellent material properties at a very low cost. The application of two-dimensional graphene nanoplatelets in cementitious composites has yet to gain widespread attention.

This paper investigates the self-sensing capabilities of GNP-reinforced hydraulic Portland cement composites. In particular, the effects of GNP content on the electrical properties and piezoresistive characteristics of mortar specimens are explored. In addition, a simple fabrication method that does not require special treating procedures such as ultrasonication and chemical (covalent) treatments for the dispersion of GNPs is pursued. The GNPs used in this study have an average thickness of 8 nanometers and a diameter of 25 microns. Standard prismatic mortar specimens containing different GNP concentrations are prepared using three different mixing procedures. The resistivity of the specimens is measured using a four-point probe method. The piezoresistive response of GNP-reinforced cement composites is evaluated under cyclic compressive loads.
Wave Power Generation Using Nonlinear Roll-Pitch Coupling in a Ship
Authors: Ansari M. H. , Yerrapragada Karthik , Karami M. Amin
Published: November 2016

When there is a two to one internal resonance ratio between the natural frequencies of the pitch motion and the roll motion of a ship, a nonlinear energy transfer occurs between the modes. If the ship is excited near the pitch natural frequency and at a large enough excitation amplitude, the pitch mode transfers energy to the roll mode. We use this interesting phenomenon to develop a wave power device for off-shore purposes. In this paper, we experimentally show that we can use a horizontal pendulum and use the quadratic nonlinear coupling between the pitch and the roll mode to get full rotation of the pendulum inside the ship. A rotating pendulum will generate orders of magnitude more power than a locally oscillating one when connected to a DC generator. This article measures the angle of the pendulum at the pitch frequency excitation of the ship to experimentally confirm the expected theoretical results on this phenomenon.
Multiple Scattering of Acoustoelastic Waves in Thin Plates for Enhanced Energy Harvesting
Authors: Darabi Amir , Leamy Michael
Published: November 2016

Harvesting of acoustoelastic wave energy in thin plates and other structures has recently gained attention from the energy harvesting community. To enhance the wave power generated, researchers have investigated metamaterial-inspired concepts to include funnels, mirrors, and defect-based resonators introduced in the metamaterial’s bandgap. Many of these concepts have been demonstrated experimentally using arrangements of cylindrical stubs mounted on the surface of a thin plate, where such stubs scatter plane and cylindrical waves in such a way as to focus mechanical energy. To support these studies, the authors have recently introduced an experimentally-verified analytical framework for investigating the coupled electromechanical response of a single circular piezoelectric harvester adhered to an infinite plate and excited by a distant harmonic point source. This paper extends these ideas to consider a similar physical system with the addition of multiple cylindrical inclusions. These additions require development of an electromechanically-coupled, multiple scattering formulation of significantly increased complexity. The formulation also includes an electrical circuit model for generating electrical current from incident waves interacting with the piezoelectric domain. Following development, the formulation is applied to the determination of optimal arrangements of scatterers which maximize the electrical power generated. Specifically, an optimization study is carried-out in which twenty-five scatterers are first placed in a semi-elliptical arrangement with the aim of focusing wave energy from one elliptical focus (i.e., source location) onto the other. It is known from past studies that additional side lobes are generated due to truncation of the ellipse, and thus not all of the energy can be focused at single point, as desired. To improve upon this situation, an optimization study is performed in which the aspect ratio of the ellipse is varied, with the goal of optimizing the power harvested from the focal point. Results from the optimization studies show conclusively that the side lobes can in fact be minimized, and that harvested power can be significantly improved.
Characterization of Adaptive Magnetoelastic Metamaterials Under Applied Magnetic Fields
Authors: Harne Ryan L. , Deng Zhangxian , Dapino Marcelo J.
Published: November 2016

Whether serving as mounts, isolators, or dampers, elastomer-based supports are common solutions to inhibit the transmission of waves and vibrations through engineered systems and therefore help to alleviate concerns of radiated noise from structural surfaces. The static and dynamic properties of elastomers govern the operational conditions over which the elastomers and host structures provide effective performance. Passive-adaptive tuning of properties can therefore broaden the useful working range of the material, making the system more robust to varying excitations and loads. While elastomer-based metamaterials are shown to adapt properties by many orders of magnitude according to the collapse of internal void architectures, researchers have not elucidated means to control these instability mechanisms such that they may be leveraged for on-demand tuning of static and dynamic properties. In addition, while magnetorheological elastomers (MREs) exhibit valuable performance-tuning control due to their intrinsic magnetic-elastic coupling, particularly with anisotropic magnetic particle alignment, the extent of their properties adaptation is not substantial when compared to metamaterials. Past studies have not identified means to apply anisotropic MREs in engineered metamaterials to activate the collapse mechanisms for tuning purposes. To address this limited understanding and effect significant performance adaptation in elastomer supports for structural vibration and noise control applications, this research explores a new concept for magnetoelastic metamaterials (MM) that leverage strategic magnetic particle alignment for unprecedented tunability of performance and functionality using non-contact actuation. MM specimens are fabricated using interrelated internal void topologies, with and without anisotropic MRE materials. Experimental characterization of stiffness, hysteretic loss, and dynamic force transmissibility assess the impact of the design variables upon performance metrics. For example, it is discovered that the mechanical properties may undergo significant adaptation, including two orders of magnitude change in mechanical power transmitted through an MM, according to the introduction of a 3 T free space external magnetic field. In addition, the variable collapse of the internal architectures is seen to tune static stiffness from finite to nearly vanishing values, while the dynamic stiffness shows as much as 50% change due to the collapsing architecture topology. Thus, strategically harnessing the internal architecture alongside magnetoelastic coupling is found to introduce a versatile means to tune the properties of the MM to achieve desired system performance across a broad range of working conditions. These results verify the research hypothesis and indicate that, when effectively leveraged, magnetoelastic metamaterials introduce remarkably versatile performance for engineering applications of vibration and noise control.
Dramatic Enhancement of Elastic Wave Energy Harvesting Using a Gradient-Index Phononic Crystal Lens
Authors: Tol Serife , Degertekin F. Levent , Erturk Alper
Published: November 2016

In this paper, we explore structure-borne elastic wave energy harvesting, both numerically and experimentally, by exploiting a Gradient-Index Phononic Crystal Lens (GRIN-PCL) structure. The proposed GRIN-PCL is formed by an array of blind holes with different diameters on an aluminum plate where the orientation and size of the blind holes are tailored to obtain a hyperbolic secant gradient distribution of refractive index guided by finite-element simulations of the lowest asymmetric mode Lamb wave band diagrams. Under plane wave excitation from a line source, experimentally measured wave field successfully validates the numerical simulation of wave focusing within the GRIN-PCL domain. A piezoelectric energy harvester disk located at the first focus of the GRIN-PCL yields an order of magnitude larger power output as compared to the baseline case of energy harvesting without the GRIN-PCL on the uniform plate counterpart for the same incident plane wave excitation. The power output is further improved by a factor of five using complex electrical load impedance matching through resistive-inductive loading as compared to purely resistive loading case.
Model Development for PZT Bimorph Actuation Employed for Micro-Air Vehicles
Authors: Crews John , Bravo Nikolas , Smith Ralph
Published: November 2016

In the paper, we discuss the development of a model for PZT bimorph actuators used to power micro-air vehicles including Robobee. Due to highly dynamic drive regimes required for the actuators, models must quantify the nonlinear, hysteretic, and rate-dependent behavior inherent to PZT in these regimes. We employ the homogenized energy model (HEM) framework to model the actuator dynamics and numerically we illustrate the capability of the model to characterize the inherent hysteresis. This provides a comprehensive model, which can be inverted and implemented for certain control regimes.
Freeform Extrusion Fabrication of Advanced Ceramic Components With Embedded Sapphire Optical Fiber Sensors
Authors: Ghazanfari Amir , Li Wenbin , Leu Ming C. , Watts Jeremy , Zhuang Yiyang , Huang Jie
Published: November 2016

Traditionally, sensors to be integrated into a structural component are attached to or mounted on the component after the component has been fabricated. This tends to result in unsecured sensor attachment and/or serious offset between the sensor reading and the actual status of the structure, leading to performance degradation of the host structure. This paper describes a novel extrusion-based additive manufacturing process that has been developed to enable embedment of sensors in ceramic components during the part fabrication. In this process, an aqueous paste of ceramic particles with a very low amount of binder content (< 1 vol%) is extruded through a moving nozzle to build the part layer-by-layer. In the case of sensor embedment, the fabrication process is halted after a certain number of layers have been deposited. The sensors are placed in their predetermined locations, and the remaining layers are deposited until the part fabrication is completed. Because the sensors are embedded during the fabrication process, they are fully integrated with the part and the aforementioned problems of traditional sensor embedment can be eliminated. The sensors used in this study were made of sapphire optical fibers of 125 and 250 micro-meters diameter and can withstand temperatures up to 1600 °C. After the parts were built, two different drying processes (freeze drying and humid drying) were investigated to dry the parts. The dried parts were then sintered to achieve near theoretical density. Scanning electron microscopy was used to observe the embedded sensors and to detect any possible flaws in the part or embedded sensor. Attenuation of the sensors was measured in near-infrared region (1500–1600 nm wavelength) with a tunable laser source. Raman spectroscopy was performed on the samples to measure the residual stresses caused by shrinkage of the part and its slippage on the fibers during sintering and mismatch between the coefficients of thermal expansion of the fiber and host material. Standard test methods were employed to examine the effect of embedded fibers on the strength and hardness of the parts. The result indicated that the sapphire fiber sensors with diameters smaller than 250 micrometers are able to endure the freeform extrusion fabrication process and also the post-processing without compromising the part properties.
First Steps in Modeling Thermal Actuation of Twisted Polymer Actuators Using Virgin Material Properties
Authors: Shafer Michael W. , Feigenbaum Heidi P. , Pugh Daniel , Fisher Matthew
Published: November 2016

Artificial muscle systems have the potential to impact many technologies ranging from advanced prosthesis to miniature robotics. Recently, it has been shown that twisting drawn polymer fibers such as nylon can result in torsional or tensile actuators depending on the final fiber configuration. The actuation phenomenon relies on the anisotropic nature of the fibers moduli and thermal expansion. They have high axial stiffness, low shear stiffness, and expand more radially when heated than axially. If a polymer fiber is twisted but not coiled, these characteristics result in a torsional actuator that will untwist when heated. During the fabrication process, these twisted polymers can be configured helically before annealing. In this configuration, the untwisting that occurs in a straight twisted fiber results in a contraction or extension depending on relative directions of twist and coiling. In these ways, these materials can be used to create both torsional or axial actuators with extremely high specific work capabilities. To date, the focus of research on twisted polymer actuators (TPAs) and twisted-coiled polymer actuators (TCPAs) has been actuator characterization that demonstrates the technologies capabilities. Our work focuses here on applying a 2D analysis of individual layers of the TPAs to predict thermally induced twisting angle and fiber length based on virgin (untwisted) material properties and actuator parameters like fiber length and inserted twist. A multi-axis rheometer with a controlled thermal environmental chamber was used to twist, anneal, and test thermally induced actuation. Experimentally measured angle of untwist and axial contraction after heating are compare the the model. In comparing the experimental results with the two dimensional model, it appears that the difference between the 2D model and experimental results can be explained by the longitudinal stresses that develop inside the material. Future work will aim to include these effects in the model in order to be able to use this model in the design of TPAs.
The Effect of Porosity Type on the Mechanical Performance of Porous NiTi Bone Implants
Authors: Amerinatanzi Amirhesam , Shayesteh Moghaddam Narges , Ibrahim Hamdy , Elahinia Mohammad
Published: November 2016

NiTi has been shown to be of great interest for bone implant applications. Introducing porosity to NiTi bone implants is an effective technique to tune their equivalent modulus of elasticity in order to acquire similar value to that of cortical bone. Moreover, such porous implants allow for better tissue ingrowth due to the interconnecting open pore structure. The effect of porosity percentage on the NiTi equivalent modulus of elasticity is well understood. However, the effect of porosity type on NiTi bone implant’s performance, in terms of the geometrical structure and other mechanical properties, has not yet been investigated. To this end, we simulated three porous structures made of shape memory Ti-rich Ni50.09Ti alloy. The effect of porosity type on the NiTi implant’s geometrical structure and mechanical properties was studied using numerical tests. The purpose is to compare three NiTi implants with different kinds of porosities, at a similar level of porosity (i.e., 69 %). The assigned porosity types in this study are Schwartz-type, Gyroid-type, and Diamond-type.

Three triply periodic minimal surface (TPMS) models (9mm×9mm×9mm) with the assigned fixed level of porosity (69 %) were designed as CAD files using Solidworks. Each model was meshed, and the convergence study was conducted. The three models were then imported into a finite element package (ABAQUS). A UMAT code developed by IUT (Isfahan University of Technology) group was used to simulate the mechanical behavior of the shape memory NiTi alloy. All boundary conditions and loading conditions were applied to the models. Compressive mechanical tests were simulated in the finite element, and the resultant equivalent modulus of elasticity, elongations, stress, and strain was estimated.

The results show anisotropic behavior within the three different porous structures. With the same level of porosity (i.e., 69 %), equivalent modulus of elasticity was observed to be 48.9, 34.8, and 30.2 GPa for Schwartz-type, Gyroid-type, and Diamond-type, respectively. Moreover, the Schwartz-type scaffold was seen to offer the highest stress at plateau start and the lowest residual strain after unloading, in comparison with the other two types of structure.
On the Optimal Piezoelectric Material Distribution in Energy Harvesting From a Nonlinear Beam Under Axial Flow
Authors: De Marqui Junior Carlos , Tan David , Erturk Alper
Published: November 2016

The recent literature of energy harvesting has shown growing interest in nonlinear aeroelastic systems for wind energy harvesting. Among other configurations, electrical power extraction from limit cycle oscillations of nonlinear beams and plates combined with a transduction mechanism in axial flow (inspired by flapping flags) have been pointed out as an alternative to traditional horizontal axis wind turbines if implemented on a large scale. Although the literature presents several works on the modeling and experimental verification of cantilevered plates in axial flow using piezoelectric transduction mechanism, the investigation of piezoelectric material distribution along the body length for proper electrode configuration to avoid cancelation of electrical outputs has not been covered. To address this problem, in this work, a fluid-structure interaction model that couples nonlinear beam equation with a lumped vortex-lattice potential flow model is implemented. The nonlinear model of the beam in axial flow is verified against wind tunnel experimental results and a numerical energy flow analysis is employed to determine the distribution of piezoelectric material along the body length. Dynamic strain distribution analysis is then performed to determine the electrode configuration to avoid cancelation of the electrical output.
Improving Durability of a Vibration Energy Harvester Using Structural Design Optimization
Authors: Nezami Saman , Lee Soobum , Kang Kiweon , Kim Jaehoon
Published: November 2016

This paper presents design optimization of an electromagnetic vibration energy harvester to improve durability and increase life cycle. The energy harvester discussed in this paper has been developed by the Korean Railroad Research Institute, as a maintenance-free power supply for a wireless sensor module that monitors rail bogie axles and bearings. Our research team realized a durability issue in the leaf spring in this harvester because of high stress concentration and the corresponding fatigue failure when the harvester experiences high impact loading in rail operation. The topology optimization method has been applied in this research to design the shape of the leaf spring with a lower stress concentration magnitude while satisfying the multiple functional requirements on vibration amplitude and natural frequency. For fast and effective design search, we firstly identified several initial models from literature. These models have been carefully chosen to minimize any unnecessary parasitic motions. The topology optimization is then applied to produce the new leaf spring structure. The results of this research showed that topology optimization method could reduce the magnitude of stress concentration while satisfying required vibration amplitude and natural frequency of the spring structure.
Systematic Design of a Piezo-Electric Stack Energy Harvester From Walking Locomotion
Authors: Balasubramanian Siddharth , Liu Haili , Wang Ya
Published: November 2016

This paper presents a systematic design of a piezoelectric stack energy harvester from human walking locomotion. The proposed footstep energy harvester is a mobile energy harvesting device that comprises of four sets of piezo-electric stack with force amplification frame assembly with associated power electronics. The objective of this work is to optimize the output power from each piezo-electric stack for which a high-efficiency force amplification frame was developed. Considering the nature of the application, High-Strength A514 Alloy Steel was chosen as the frame material and SONOX SP 505 as the piezo-electric stack in d33 configuration. The mathematical formulation of real-time human walking force excitation was also vital in the study. In this paper, a real-time equation of human Vertical Ground Reaction Forces (VGRF) was used for the systematic modeling and simulation process. Following the success of piezoelectric electro-mechanical modeling and simulation, a prototype of four sets of force-amplification frames each with a piezoelectric stack installed inside were fabricated and assembled into a unique constrainer box — such an assembled device was fit into the heel of a 12″ Field and Stream® boot to effectively convert kinetic energy from walking locomotion to electricity and therefore, to power a wireless sensor. The uniqueness of the work is to develop an easy-fit footstep energy harvester with much higher power density than similar design in the literature. In particular, the developed energy harvesting device is not visible externally and does not affect the walking gait pattern of the user. Moreover, our design only adds 0.25 kg to the self-weight of 0.85 kg of the boot. A peak power of 130 mW and peak Voltage of 118 V was recorded for an 80 kg person walking. This type of energy harvester will find its application in clean-energy generation in remote areas without electricity access.