bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimization of a Forward-Swept Compliant Mechanism
Authors: Calogero Joseph , Frecker Mary , Hasnain Zohaib , Hubbard James E.
Published: November 2017

A coupled 3 degree-of-freedom contact-aided compliant mechanism called the Forward Swept Compliant Mechanism (FSCM) is designed optimized for coupling orthogonal translational motion. The purpose of this mechanism is to allow desirable wing morphing passively in an ornithopter wing structure to improve free flight pitch agility via sweeping the wing tip forward during downstroke. This new contact-aided compliant mechanism design, based on the coupled three degree of freedom Bend-Twist-and-Sweep Compliant Mechanism, was developed to couple motion in bending to forward sweep during downstroke to destabilize the downstroke, and thereby increasing pitch agility. This is made possible due to an axial rotation of the mechanism, positioning the angled compliant joint such that the axis of deformation is skewed from the lifting direction. A multi-objective optimization problem was formulated and solved using a multi-objective genetic algorithm. The objectives of this optimization were to maximize forward sweep while minimizing bending, twist, peak stress, and mass. During the optimization, 3084 designs were simulated throughout 37 generations. The complete data set from the optimization was used to understand the relationship between each design variable and each objective, as well as in a random forest of regression trees to determine each variable’s importance to each objective. Two designs were chosen and compared for performance tradeoffs, where additional shape change is achieved at the expense of higher peak stress. The first design achieved the desired 2 degrees of forward sweep, and the second design achieved 5 degrees of forward sweep at the expense of larger bending and a higher peak stress.
Modeling of Bio-Inspired, Snapping Composite Shells With Magnetically Aligned Reinforcements
Authors: Riley Katherine S. , Le Ferrand Hortense , Arrieta Andres F.
Published: November 2017

Materials capable of exhibiting inherent morphing are rare and typically reliant on nanometric chemical properties. The resulting shape adaptability is thus slow and limited to specific environmental conditions. In contrast, natural composites, such as those found in carnivorous plants, have evolved hierarchical architectures displaying remarkably fast adaptation upon environmental stimuli. These biological materials have inspired the fabrication of snapping composite shells through the careful design of the internal microstructure of synthetic materials by magnetic alignment of reinforcements. The ability to accurately model such programmable materials using finite element analysis (FEA) is necessary to facilitate the design optimization of resulting structures. Using similar material parameters as explored in previous experimental studies, we employ nonlinear FEA to investigate the effects of introducing curvilinear spatially distributed micro-reinforcements on the deformation of a shell with bioinspired geometry. The FEA model is subject to a preliminary experimental validation. Comparison to a conventional [0/90] composite layup and simplified models demonstrates the advantages of magnetically aligned reinforcements to achieve complex, snapping morphing structures with tailored characteristics.
PDF Evolution of Texture in the Fabrication of Magneto-Active Elastomers
Authors: Rodriguez Manuel Aurelio , von Lockette Paris
Published: November 2017

Magneto-Active elastomers (MAEs) and magneto-rheological elastomers (MREs) are smart materials that consist of hard and soft magnetic particles, respectively, embedded in a flexible matrix. Their actuation capabilities are dependent on the arrangement of particles achieved during the fabrication process. Previous works have shown varying degrees of particle alignment and / or agglomeration as a function of fabrication process variable, most notably volume fraction of the particulates, their magnetic material type (hard vs soft), and the strength of the external field applied during curing. In this work, we simulated the dynamics of magnetic particles suspended in a fluid matrix to predict the evolution of microstructures resulting from these varying process conditions. The simulations accounted for the magnetic interaction of all particles using standard dipole-dipole interaction potentials along with dipole-field potentials developed from the Zeeman Energy. Additionally, the field local to each particle, on which magnetization depends, was determined by the sum of the external fields generated by each member of the ensemble and their demagnetizing fields. Fluid drag forces and short range particle-particle repulsion (non-overlapping) were also considered. These interactions determined the body forces and torques acting on each particle that drove the system of equations of motions for the ensemble of particles. The simulation was carried out over a nearest neighbor periodic unit cell using an adaptive time stepping numerical integration scheme until an equilibrium structure was reached. Structural parameters, related to the magnetic energy, spatial distribution, spatial alignment, and orientation alignments of the particle distributions were defined to characterize the simulated structures. The effect of volume fraction and intensity of the external magnetic field on the achieved particle distributions were studied. At low external field strengths, the particles formed long entangled chains that had very low alignment with the applied field. The remnant magnetic potential energy of these configurations was also significantly low. As the field is increased the length of the chains reduced and the alignment increased. The corresponding change in magnetic potential energy of the system with an increase in the applied field was found to follow a power law fit that spanned a wide range of magnetic field strengths. At low volume fractions the particles aligned rapidly with the field and formed short chains. As the volume fraction of the samples increased the chains grew longer and closer to each other, and magnetic potential of the structure became lower. Results of the simulations suggest that it is possible to tailor the microstructure and thus affect remanent magnetization and magnetization anisotropy, by judicious control of process parameters. This ability could have implications for newly emerging additive manufacturing techniques utilizing suspensions of magnetic particulates.
A Physical Interpretation for Broken Reciprocity in Spatiotemporal Modulated Periodic Rods
Authors: Marconi Jacopo , Cazzulani Gabriele , Ruzzene Massimo , Braghin Francesco
Published: November 2017

Periodic systems have long been known for their peculiar characteristics in wave propagation and have been studied in many fields over the last century, going from electro-magnetics and optics to elastic structures, which drew an increasing interest in structural and mechanical engineering for vibration suppression and control spanning over broadband frequency ranges. Recently, on the stream of other studies conducted in different fields, spatiotemporal modulated elastic structures have been studied, showing promising results for wave control in that one-way propagation in the so called directional-bands can be achieved, constituting what may be called a mechanical diode. Despite of the fact that mathematical methods for the analysis of such structures have already been developed, often physics behind them is difficult to grasp. In this work, a simplified interpretation of the undergoing phenomena is thus given relating wave propagation in the mean to its physical characteristics as well as to modulation parameters. Exploiting Doppler effect and passive equivalent structures, it is shown that the broken reciprocity is due to the fact that opposite travelling waves effectively see two different periodic structures. To this aim the rod case is analysed for low modulation speeds and low modulation amplitudes; finally, in the light of the previous analysis, an explanation for First Brillouin Zone’s asymmetry is given.
Development of Surrogate Biomedical Knee Implants for Validation of Embedded Smart Sensors
Authors: Ponder Robert I. , Safaei Mohsen , Anton Steven R.
Published: November 2017

Total Knee Replacement (TKR) is a very common procedure in the United States, especially with the aging population. However, despite high numbers of procedures and advancing technology, about 20% of patients with TKR are unsatisfied with the level of discomfort they experience with their replacement. Prevailing theories suggest that this is due to gradual misalignment of the knee. Multiple methods have been attempted to detect the cause of mechanical failure in replacements. One possible method for performing state detection in knees is the embedding of piezoelectric transducers (PZTs) into the bearing component. Preliminary testing of PZT’s embedded in simplified plastic components has shown that this method contains promise. With this said, further testing on realistic knee implant components is still needed to solidify the method’s validity. Commercial knee implant bearings utilize medical grade Ultra-High Molecular Weight Polyethylene (UHMW) and manufacturers utilize proprietary processing technology to develop the final components. This work focuses on the development of surrogate knee implant prototypes that replicate the material and geometric properties of actual knee implants to provide a convenient and economical solution to evaluate the performance of embedded PZTs. In this work, scans of an original knee bearing are taken and used to create a 3D model. From there, a variety of processes including 3D printing and Computer Numerical Controlled (CNC) machining are used to develop surrogate prototypes that are compared for accuracy to a benchmark. This benchmark is taken as a polished CNC machined non-medical grade UHMW prototype. Standards that the prototypes must meet include cost and time effectiveness as well as similarity in geometry and material property to the benchmark. The performance of the prototypes is experimentally compared through mechanical load testing by using pressure sensitive films placed between the femoral and bearing components of the implant as well as measuring piezoelectric output. In addition, the measured voltage output is compared to predictions from an analytical model for validation of the piezoelectric performance. These two experiments help to derive information about the applied load distribution and location, allowing comparisons to be made to the benchmark. This study shows that, while some types of 3D printing, such as fused deposition modeling, provide fast and cheap prototypes, other options such as stereolithography printing produce higher quality and more replicative components. Results of this study can be used in the development of useful surrogates for the advancement of biomedical sensors.
Multifunctional NMC-Si Batteries With Self-Actuation and Self-Sensing
Authors: Ma Jun , Rahn Christopher , Frecker Mary
Published: November 2017

Among anode materials for lithium ion batteries, silicon (Si) is known for high theoretical capacity and low cost. Si changes volume by 300% during cycling, however, often resulting in fast capacity fade. With sufficiently small Si particles in a flexible composite matrix, the cycle life of Si anodes can be extended. Si anodes also demonstrate stress-potential coupling where the open circuit voltage depends on applied stress. In this paper, we present a NMC-Si battery design, utilizing the undesired volume change of Si for actuation and the stress-potential coupling effect for sensing. The battery consists of one Li(Ni1/3Mn1/3Co1/3)O2 (NMC) cathode in a separator pouch placed in an electrolyte-filled container with Si composite anode cantilevers. Models predict the shape of the cantilever as a function of battery state of charge (SOC) and the cell voltage as a function of distributed loading. Simulations of a copper current collector coated with Si active material show 11.05 mAh of energy storage, large displacement in a unimorph configuration (>60% of beam length) and over 100 mV of voltage change due to gravitational loading.
Flexural Frequency Bandgaps in a Foldable Metamaterial Structure
Authors: Nanda Aditya , Karami M. Amin
Published: November 2017

This manuscript investigates the flexural wave propagation behavior of a foldable metamaterial structure. Origami-inspired foldable structures are making inroads into many engineering applications — deployable solar cell arrays, foldable telescope lenses, foldable automotive airbags, to name a few; driven primarily by some of the remarkable mechanical properties (high stiffness, negative Poisson’s ratio, bistability etc.) of these structures. The chief motivation of this research is a comprehensive analysis of flexural wave propagation in such foldable structures. The repeating unit cell of the structure consists of an Euler-Bernoulli beam and a torsion spring. Transfer Matrix (TM) method is used to analyze the vibration attenuation properties of the structure and it is shown that the structure exhibits bandgap behavior. The obtained bandgaps are validated using Finite Element Analysis (FEA). Using the characteristic equation of the transfer matrix, we derive a transcendental equation for the bandgap edge frequencies. We show that for the nth band gap, the second band edge frequency is always equal to the natural frequency of the nth modeshape of the constituent beam under the simply supported condition. This frequency, therefore, is independent of the torsion spring constant. In addition, a detailed parametric study of the variation in band edge frequencies when the geometric and material parameters of the structure (Young’s modulus of beam, torsional spring constant, width and thickness of beam etc.) are varied is conducted. It is concluded that the ratio of flexural rigidity of the beam to the torsion spring constant (EI/kt) is an important parameter affecting the width of the bandgap. For low values of the ratio, i.e., low beam flexural rigidity and high torsional stiffness, the first band edge frequency is almost equal to the second band edge and, effectively, no bandgap exists. As the stiffness ratio increases, i.e. high flexural rigidity (EI of the beam) and low torsional stiffness kt, the first band edge frequency assumes progressively lower values relative to the second band edge and we obtain a relatively large bandgap over which no flexural waves propagate. This has important ramifications for the design of foldable metamaterial structures.
Energy Harvesting From Arterial Blood Pressure for Powering Embedded Microsensors in Human Brain
Authors: Nanda Aditya , Karami M. Amin
Published: November 2017

This manuscript investigates energy harvesting from arterial blood pressure via the piezoelectric effect for the purpose of powering embedded micro-sensors in the human brain. One of the major hurdles in recording and measuring electrical data in the human nervous system is the lack of implantable and long term interfaces that record neural activity for extended periods of time. Recently, some authors have proposed micro sensors implanted deep in the brain that measure local electrical and physiological data which is then communicated to an external interrogator. This paper proposes a way of powering such interfaces. The geometry of the proposed harvester consists of a piezoelectric, circular, curved bimorph that fits into the blood vessel (specifically, the Carotid artery) and undergoes bending motion because of blood pressure variation. In addition, the harvester thickness is constrained such that it does not modify arterial wall dynamics. This transforms the problem into a known strain problem and the integral form of Gauss’s law is used to obtain an equation relating arterial wall motion to the induced voltage. The theoretical model is validated by means of a Multiphysics 3D-FEA simulation comparing the harvested power at different load resistances. The peak harvested power achieved for the Carotid artery (proximal to Brain), with PZT-5H, was 11.7 μ W. The peak power for the Aorta was 203.4 μ W. Further, the variation of harvested power with variation in harvester width and thickness, arterial contractility and the pulse rate is investigated. Moreover, potential application of the harvester as a chronic, implantable and real-time Blood pressure sensor is considered. Energy harvested via this mechanism will also have applications in long-term, implantable Brain Micro-stimulation.
Constraint Tuning of Lightweight Elastomeric Metamaterials for Structural Impact Tolerance
Authors: Song Yu , Saxena Sansriti , Bishop Justin , Harne Ryan L.
Published: November 2017

To alleviate wave and vibration transmission in automotive, aerospace, and civil engineering fields, researchers have investigated periodic metamaterials with especially architected internal topologies. Yet, these solutions employ heavy materials and narrowband, resonant phenomena that are unsuitable for the many applications where broadband frequency vibration energy is a concern, such as that injected by impact forces, and weight is a performance penalty. To overcome these limitations, a new idea for lightweight, elastomeric metamaterials constrained near critical points is recently being explored, such that improved shock and vibration damping is achieved using reduced mass than conventional periodic metamaterials. On the other hand, the internal architectures of these metamaterials have not been explored beyond classical circular designs whereas numerous engineering structures involve square or rectangular geometries that may challenge the ability to realize critical point constraints due to the lack of rotational symmetry. The objectives of this research are to undertake a first study of square cross-section elastomeric metamaterials and to assess the impact tolerance of structures into which these metamaterials are embedded and constrained. Finite element simulations guide attention to design parameters for the metamaterial architectures, while experimental efforts quantify the advantages of constraints on enhancing impact tolerance metrics for engineering structures. It is seen that although the architected metamaterial leads to slightly greater instantaneous acceleration amplitude immediately after impact, it more rapidly attenuates the injected energy when compared to the solid and heavier elastomer mass from which the metamaterial is derived.
Uncertainty Analysis of Ferroelectric Polydomain Structures
Authors: Miles Paul , Oates William , Leon Lider , Smith Ralph
Published: November 2017

Ferroelectric materials exhibit strong electromechanical behavior which has led to the production of a wide variety of adaptive structures and intelligent systems, ranging from structural health monitoring sensors, energy harvesting circuits, and flow control actuators. Given the large number of applications, accurate prediction of ferroelectric materials constitutive behavior is critical. This presents many challenges, including the need to predict behavior from electronic structures up to macroscropic continuum. Many of the structure-property relations in these materials can be accurately calculated using density functional theory (DFT). However, DFT is not necessarily conducive to the large scale computations required to solve these problems on a continuum scale. Introducing a phase field polarization order parameter is an alternative approach, which provides a means to simulate the length scale gap between nano- and microscale domain structure evolution. The introduction of the phase field approximation results in uncertainty. Bayesian statistical analysis is an ideal tool for quantifying the uncertainty associated with the continuum phase field model parameters. Analyses of monodomain structures allows for identification of Landau energy and electrostrictive stress parameters. Identifying the exchange parameters, which are proportional to the polarization gradients, requires consideration of polydomain structures. This is a nontrivial problem as domain wall structures are fully coupled between the Landau energy, electrostrictive, and exchange parameters. Accurately quantifying the uncertainty in the phase field parameters will provide insight into the nonlinear constitutive behavior.
Network Theoretic Approach to Atomistic Material Modeling Using Spectral Sparsification
Authors: Woerner Peter C. , Nair Aditya G. , Taira Kunihiko , Oates William S.
Published: November 2017

Network theory is used to formulate an atomistic material network. Spectral sparsification is applied to the network as a method for approximating the interatomic forces. Local molecular forces and the total force balance is quantified when the internal forces are approximated. In particular, we compare spectral sparsification to conventional thresholding (radial cut-off distance) of molecular forces for a Lennard-Jones potential and a Coulomb potential. The spectral sparsification for the Lennard-Jones potential yields comparable results while spectral sparsification of the Coulomb potential outperforms the thresholding approach. The results show promising opportunities which may accelerate molecular simulations containing long-range electrical interactions which are relevant to many multifunctional materials.
A Novel Chopped Pyroelectric Infrared Sensor for Detecting the Presence of Stationary and Moving Occupants
Authors: Liu Haili , Lin Hanbing , Wang Kevin , Wang Ya
Published: November 2017

Owing to the unique features of passive sensing, low cost, large detection range and wide field of view (FOV), the pyroelectric infrared (PIR) sensors are widely used for smart home applications based on motion detection, such as light control, intrusion detection. However, due to the pyroelectricity on which their sensing principles are based, PIR sensors cannot detect stationary objects, which confines their applications to advanced sensing systems, e.g. stationary occupancy sensing. To address this issue, this paper develops a novel chopped PIR (C-PIR) sensor for detecting the presence of both moving and stationary occupants, which consists of a chopper, a servo motor, a Fresnel lens, PIR sensing elements and a controller. Theoretical analysis is conducted to reveal the working principles of the proposed C-PIR sensor. A prototype of the C-PIR sensor is fabricated and experiments are conducted to find the optimal option of the chopper material, and the optimal values of the thickness, and the chopping frequency. Results show that the proposed C-PIR sensor can sense human presence no matter if the occupant is moving or not. In experiments, the preliminary prototype shows its detection range up to 4.0 m for stationary occupant sensing and 8.5 m for moving occupant sensing. Meanwhile, the C-PIR sensor maintains the same performance of the field of view as its traditional PIR sensor counterpart. Thus, the C-PIR sensor has great potential to provide accurate occupancy information for smart building energy management.
A Black Box Design Approach to Avian-Inspired SMA Coil Actuated Wearable Morphing Angel Wings
Authors: Dalton Sean , Koon Henry , O’Malley Jennifer , Abel Julianna
Published: November 2017

Black box design is a constraint driven design approach that distills essential elements of a physical process into inputs and outputs. This paper details the black box design implementation and validation of shape memory alloy (SMA) coil actuators as active members in a Watt I six bar avian-inspired wearable morphing angel wing mechanism. SMA coil actuators leverage the unique characteristics of high energy density SMA wire by providing a compact structural platform for large actuation displacement applications. The moderate force and displacement performance of low spring index coil actuators paired with their virtually silent actuation performance made them an attractive actuator solution to an avian-inspired wearable morphing wing mechanism for the University of Minnesota Department of Theatre Arts and Dance production of ‘Marisol’. The wing design constraints (extended span of 7.5 ft, a closed span of 3 ft) required a tailorable actuator system with capacity to perform at particular target force and strain metrics cyclically. A low spring index parameter study was conducted to facilitate an accelerated phase of design prototyping. The parameter study featured six SMA coil actuator prototypes made with 0.012” diameter Dynalloy Flexinol® wire of varying spring indexes (C = 2.5–4.9). The coil actuators were manufactured through a CNC winding process, shape set in a furnace at 450 °C for 10 minutes, and water quenched for hardening. A series of thermomechanical actuation tests were conducted to experimentally characterize the low spring index actuation performances. The coil actuation characterizations demonstrated increased force and decreased actuator displacement corresponding to decreased spring indexes. Scaling these results aided an accelerated design of an actuator system. The actuator system consisted of four C = 3.05 coil actuators wound with 0.02” diameter SMA that were integrated into each Watt I mechanism. The characterization of the force-displacement profiles for low index SMA coil actuators provides an effective empirical design strategy for scaling actuator performance to mechanical systems requiring moderate force, moderate displacement actuators.
Free and Forced Vibration Characteristics of Axially Graded Multifunctional Viscoelastic Beams
Authors: Heras Segura Mariona , Singh Kumar Vikram , Khan Fazeel
Published: November 2017

Variable performance characteristics in a multifunctional structure may be achieved by identifying suitable material candidates, and spatially varying, or grading, their material properties along the structures. Additive manufacturing (e.g. 3D printing) offers various possibilities to fabricate/manufacture such graded structures. The material properties of multifunctional composite structures, such as beams or plates, are often graded along their thickness (laminate/sandwich) or distributed in a material matrix (fibers/nanoparticles). In recent years, it has been demonstrated that by tailoring the materials in other directions (axially/radially), superior mechanical behavior and structural stability can be realized. In this research, the modeling and analyses of axially graded polymeric beams to maximize their vibration performance for a large bandwidth of frequencies and damping is presented. Polymeric materials have frequency and temperature dependent viscoelastic properties (complex modulus, glass transition temperature etc.) which can be leveraged for different applications. The goal is to spatially combine these materials such that desired longitudinal vibration characteristics (natural frequencies, damping and modes) can be achieved. To this end, the modeling for the free and forced vibration of beams with spatially varying properties, is carried out by a piecewise uniform continuous model. The spectral characteristics (natural frequency, damping ratios, and frequency response functions) of the axially graded beams are computed by solving associated transcendental eigenvalues problems. The parametric studies included the grading of polymers which are regularly used for additive manufacturing, such as ABS, PLA, etc. These results demonstrate that the response of the system can be manipulated by axial grading and optimal design/fabrication (3D printing) of multifunctional smart structures may be developed for vibration control applications.
Tailoring the Elastic Postbuckling Response of Thin-Walled Cylindrical Shells for Applications in Mechanical Devices and Adaptive Structures
Authors: Guo Jun , Liu Suihan , Burgueño Rigoberto
Published: November 2017

Postbuckling response, long considered mainly as a failure limit state is gaining increased interest for smart applications, such as energy harvesting, frequency tuning, sensing, actuation, etc. Cylindrical shells have received less attention as structural form to harness elastic instabilities due to their increased modeling complexity and high imperfection sensitivity. Yet, preliminary experimental and computational evidence indicates that the elastic postbuckling response of cylindrical shells can be controlled and potentially managed. Further, cylindrical shells offer desirable features for the design of mechanical devices and adaptive structures that other forms cannot attain without additional external constraints. This paper presents a study on tailoring the elastic postbuckling response of thin-walled cylindrical shells under compression by means of non-uniform wall stiffness distributions. The pattern of stiffness distribution was designed by discretizing the shell surface into cells and thickening selected cells with respect to a baseline uniform wall thickness. Diverse patterns were characterized in the way of how they affect the postbuckling response through numerical simulations using the finite element method. Results show that the elastic postbuckling response can be tailored into three response types: softening, sustaining, and stiffening; and that number, sequence/time and location/space of localized buckling events can be designed. This work provides new knowledge on the means to design the cylindrical shells with controlled elastic postbuckling behavior for applications in smart materials, mechanical devices, and adaptive structures.
Polypyrrole-Coated Carbon Nanotube-Arrays: The Missing Link Between Bucky-Paper Actuation and CNT-Array Actuation
Authors: Geier Sebastian M. , Wierach Peter , Mahrholz Thorsten , Sinapius Michael
Published: November 2017

The actuation mechanisms of cnt-based materials are still controversially discussed. It is not common sense whether it is a macroscopic volume effect caused by ion intercalation or electrostatic repulsion of equally charged cnts or a nanoscopic effect of filled electron anti-bonding orbitals of the carbon atom or interactions with ions docking on the carbon surface. In the presented paper arrays of highly aligned multi-walled carbon nanotubes (mwcnts) are used which are stabilized by a polypyrrole-coating. The samples are tested along the cnt-orientation and in perpendicular mode to analyze the influence of the structure-ion interaction. The mwcnt-arrays exhibit only a total length of approximately 2.8 mm but by coating with polypyrrole larger geometries can be tested. The actuation is analyzed using an in-plane test and an actuated tensile testing. Free strain can be detected using the first set-up, the second method is carried out to evaluate the mechanical stability of the samples. As might be expected, the material shows a strong anisotropic active behavior with the actuation along the tube axis being only half of the value detected at the perpendicular oriented samples. The findings point out that an intercalation of ions into the charged CNT-architecture seems here to be the dominating mechanism.
Design of Linear Actuators Based on Compliant Multi-Stable Structures
Authors: Anderson Aaron J. , Arrieta Andres F.
Published: November 2017

Light-weight, compact actuators capable of delivering large linear stroke based compliant structures offer interesting potential for adaptive structures and robotics given their capability to carry a load and to be geometrically scalable. Furthermore, the utilization of compliant structures replacing mechanisms and moving parts offers the possibility for reducing losses due to friction. Solid state actuators have been proposed as a means to attain such capabilities with particular success for smart systems based on piezoelectric, shape memory, and electroactive polymer materials. Despite this success, smart material systems do not concurrently offer large strokes, high blocking force and wide response bandwidth. Recently, a new class of multi-stable structures that generate large linear strokes from twisting have been introduced. Furthermore, the snap-through action characterizing the changes between stable states of multi-stable systems has been shown to be a viable mechanism for inducing controlled actuation at high rates. In this paper, the novel design of a linear actuator adapted from twisting multi-stable structures is tailored to have geometric instability that is exploited to achieve large axial strokes under the action of small deformations from a single structural component. Finite element modeling is used for analysis of the structure, where parameter studies of composite layup and structure geometry are conducted to adjust equilibrium positions and stroke length of the actuator design. Different smart actuator topologies demonstrating the ability for compliant multi-stable systems are coupled with smart materials to produce large linear deformations and wide actuation bandwidth. The herein presented unconventional design serves as a useful linear actuator, as well as a load carrying component. The introduced multi-functional light-weight load-carrying actuators relevant for aerospace and robotics applications.
Analysis of Microstructure-Based Network Models for the Nonlinear Electrostriction Modeling of Electro-Active Polymers
Authors: Erol Anil , Ahmed Saad , von Lockette Paris , Ounaies Zoubeida
Published: November 2017

Relaxor ferroelectric polymers are a unique branch of electro-active polymers (EAPs) that generate high electromechanical strain with relatively low hysteresis and high nonlinearity. Polyvinylidene fluoride-based EAPs possess these qualities due to the semicrystalline nature of their microstructure. The interactions of electric dipoles within the microstructure of the material generate large strains under an external electric field, and the reduced crystalline domain sizes yield a relaxor effect by exhibiting low hysteresis and hyperelastic properties. This phenomenon has been partially modeled by previous works, but micro-electro-mechanisms for electrostriction in the microstructure have been largely ignored. This study focuses on the effects of various microstructural frameworks on the nonlinear dielectric behavior of dipole-based, semicrystalline EAPs. The Helmholtz free energy function of a microscopic representative volume element (RVE) is composed of an electrostatic energy and an elastic energy. The dipole-dipole interaction energy is prescribed for the electrostatic forces observed among the crystalline regions, and the elastic component attributed to the relaxation of the amorphous phase is modeled by the hyperelastic eight-chain model, which is microstructure-based. The RVE of the system is modeled by a central dipole surrounded by dipoles whose relative spatial locations are determined by a probability distribution function (PDF). The hyperelastic amorphous phase constitutes the volume separating the central and surrounding dipoles. The free energy of the RVE is implemented into a continuum description of the equilibrium of the system to obtain electromechanical relations. Additionally, this electromechanical response data is applied to a 1D structural mechanics model for simulating the large deformation of a multi-layered beam. The effects of microstructure on electrostrictive coupling are explored by varying the centers and deviations of dipole locations within the PDF. Discrete microstructural arrangements representing 3-chain network averaging schemes may be studied alongside more continuous ellipsoidal or random models of dipole spatial arrangements. The simulation results of the PDF-based networks are in good agreement with experimental data. The results indicate that the electrostrictive behavior of EAPs is strongly dependent on (1) the relative dipole spatial locations and (2) the extent of the regions containing dipoles, which represent crystalline domains. The model finds that adding extra crystalline domains in the network averaging schemes generates a better characteristic behavior due to a broader averaging of spatial orientations. These results offer a gateway to predicting microstructurally-dependent dipole-based behavior that can lead to the predictive theoretical tailoring of microstructures for desired electromechanical properties.
Development of 3D Impact Self-Sensing Composites Using Fracto-Mechanoluminescent EuD4TEA
Authors: Holguin Brandon , Allison James , Ryu Donghyeon , Alvarez Zachary , Hernandez Francisco , Kimberley Jamie
Published: November 2017

The objective of this study is to develop three dimensional (3D) impact self-sensing composites capable of localizing impact damage in through-the-thickness direction. The 3D impact self-sensing composites (3D-ISSC) are designed by embedding fracto-mechanoluminescent (FML) crystals in cells of honeycomb-cored fiber reinforced polymer (FRP) structural composites. FML crystals were shown to emit light resulting from cleavage of crystalline structures due to external mechanical stimuli. Unlike other conventional sensor networks, without supplying external electrical source, the 3D-ISSC is envisioned to monitor impact occurrences and detect damage. Instead, the emitted light will be utilized for informing severity of impact occurrences and 3D locations of the impact damage. First, FML europium-doped dibenzoylmethide triethylammonium (EuD4TEA) crystals are synthesized. Second, the synthesized EuD4TEA crystals are embedded in the honey-cored FRP structural composites to fabricate 3D-ISSC. Third, to validate its 3D self-sensing capability, Kolsky bar is employed to apply high strain-rate compressive loading to simulate impact occurrences while taking high-speed video footage for quantifying intensity of FML light emission through image processing technique.
Cost-Effective Monitoring of Railroad Bridge Performance
Authors: Liu Bideng , Ozdagli Ali I. , Moreu Fernando
Published: November 2017

Railroads carry 40% of the U.S.’ freight tonnage. Railroad bridges are the most critical component of this network. Measuring transverse displacement of railroad bridges under train-crossing load is essential for the safe and cost-effective operation of railroad network. However, bridge displacement is difficult to collect in the field with traditional sensors due to the lack of fixed reference frame. Although reference-free sensors provide flexibility overcoming the aforementioned challenge, they often fail to capture pseudo-static components observed in timber bridges. This study proposes a novel reference-free sensing system to measure the total displacements of railroad bridges under train-crossing loads. A novel passive-servo electro-magnetic-induction (PSEMI) sensing technology provides accurate direct reference-free dynamic displacement measurement. Furthermore, researchers utilize two reference-free accelerometers to record inclination measurement and transform to pseudo-static displacement. Total bridge displacement is obtained by adding dynamic and pseudo-static responses together. Shake table experiments employing a bridge pier model excited by bridge displacements measured in the field has validated the effectiveness and accuracy of the novel sensing system.
Bowden Tube NiTi Actuators With Linear Parameter Varying Model and Sliding Mode Control
Authors: Gurley Austin , Kubik Kyle , Lambert Tyler Ross , Beale David , Broughton Royall
Published: November 2017

One of the primary difficulties to implementing NiTi shape memory alloys as robotic actuators is reliably amplifying their low linear strain to large effective displacements. Bowden tubes, called “push-pull cables” in other industries, allow a long length of Shape Memory Alloy (SMA) wire to fit in a small space; this provides a method for increasing effective SMA actuator strain without compromising space or complexity of the entire mechanism. The mechanical advantage of the Bowden tube provides faster actuation speeds, but comes at a cost of increased thermal capacitance resulting in higher power consumption. A feedback control system has been formed comprising the Bowden tube actuator, a rotary platform, and a microcontroller. The controller heats the SMA by passing current through the SMA wire using pulse-width-modulation. After describing the creation of the electro-mechanical system, its capabilities and limitations are discussed. Linear Parameter Varying (LPV) models of SMA are used to determine the range of characteristics the inherently nonlinear SMA system will exhibit. A sliding mode controller is designed based on these characteristics, and implemented in the prototype. Sliding-mode control is shown to be a powerful tool for SMA control even when system parameters are uncertain.
Stick-Slip Energy Harvesting: A Preliminary Study
Authors: Masuda Arata , Sawai Chisato
Published: November 2017

In this paper, a design of an energy harvesting device which converts a translational relative motion to an oscillatory motion via stick-slip phenomenon is presented. In this design, an L-shape cantilever is used as an energy converter, the tip of which is rubbed by a linearly moving rubber pad. The induced stick-slip motion produces a relatively high frequency oscillation in the middle part of the cantilever during the stick phase, which is then converted to the electrical energy via a piezoelectric element attached on the cantilever surface. Testing of a proof-of-concept prototype reveals how the linear relative motion induces the stick-slip motion and the high frequency oscillation of the cantilever. The dependence of the stick-slip frequency on the design parameters is preliminary studied. Then, the load resistance optimization and the maximum output power are discussed, and the energy efficiency which is defined as the ratio of the output electrical energy to the input mechanical work during the rubbing motion is evaluated.
Microsecond State Monitoring of Nonlinear Time-Varying Dynamic Systems
Authors: Dodson Jacob , Joyce Bryan , Hong Jonathan , Laflamme Simon , Wolfson Janet
Published: November 2017

Reliable operation of next generation high-speed complex structures (e.g. hypersonic air vehicles, space structures, and weapons) relies on the development of microsecond structural health monitoring (μSHM) systems. High amplitude impacts may damage or alter the structure, and therefore change the underlying system configuration and the dynamic response of these systems. While state-of-the-art structural health monitoring (SHM) systems can measure structures which change on the order of seconds to minutes, there are no real-time methods for detection and characterization of damage in the microsecond timescales.

This paper presents preliminary analysis addressing the need for microsecond detection of state and parameter changes. A background of current SHM methods is presented, and the need for high rate, adaptive state estimators is illustrated. Example observers are tested on simulations of a two-degree of freedom system with a nonlinear, time-varying stiffness coupling the two masses. These results illustrate some of the challenges facing high speed damage detection.
Wave characteristics of a cylinder with periodic ribs
Authors: Jung Byung-kyoo , Hong Chinsuk , Ryue Jungsoo , Jeong Weui-bong , Shin Ku-Kyun
Published: November 2017

This paper deals with wave characteristics of a cylinder with periodic ribs. The equation of motion of the stiffened cylinder is first derived using a receptance coupling method. The dispersion diagrams of the stiffened cylinder are then obtained in order to figure out the effects of the ribs on the wave propagation. Due to the effect of the ribs, the dispersion curves are found to be repeated along the axis of the wavenumber with the repetition period of 2π/d, where d is the rib distance. Also, dispersion curves are found to show a pass and stop band of the waves. The stop bands appeared at the wavenumber of half of the wavenumber periodicity. The stop band becomes wider as the increase of the circumferential order. The waves in the pass bands are propagating well through the ribs without decay. In contrast, the waves in the stop bands are not propagating, but decaying the magnitudes. The decay of the responses in the stop band increases as the circumferential order increase. The change of the rib stiffness causes the cut-on frequency to change and the modal order to jumble. The change of the rib stiffness also leads to generate a wave whose phase velocity is positive, while group velocity is negative.
Cross-beam coherence of infrasonic signals at local and regional ranges
Authors: Alberts W. C. Kirkpatrick , Tenney Stephen M.
Published: November 2017

Signals collected by infrasound arrays require continuous analysis by skilled personnel or by automatic algorithms in order to extract useable information. Typical pieces of information gained by analysis of infrasonic signals collected by multiple sensor arrays are arrival time, line of bearing, amplitude, and duration. These can all be used, often with significant accuracy, to locate sources. A very important part of this chain is associating collected signals across multiple arrays. Here, a pairwise, cross-beam coherence method of signal association is described that allows rapid signal association for high signal-to-noise ratio events captured by multiple infrasound arrays at ranges exceeding 150 km. Methods, test cases, and results are described.
Rapid, directed transport of DC-SIGN clusters in the plasma membrane
Authors: Liu Ping , Weinreb Violetta , Ridilla Marc , Betts Laurie , Patel Pratik , de Silva Aravinda M. , Thompson Nancy L. , Jacobson Ken
Published: November 2017

Very rapid, directed movement of pathogen receptors in the plasma membrane is associated with MT close to the inner leaflet.
Webinar | Deciphering cancer: Investigating cell death mechanisms
Authors: Strasser Andreas , Letai Anthony G.
Published: November 2017

Cell death, including autophagy, necroptosis, and apoptosis, is a physiological process critical for normal development and function of multicellular organisms. Many of the signals that elicit cell death converge on mitochondria, which regulate cell death by a pivotal process called mitochondrial outer membrane permeabilization (MOMP). In apoptosis, MOMP is tightly regulated by the Bcl-2 family of proteins, composed of both proapoptotic (Bax, Bak, Bid, Bim) and antiapoptotic (Bcl-2, Bcl-xL, Bcl-W) members, which act in part by governing mitochondrial death signaling through cytochrome C release and subsequent activation of caspases. Irrespective of caspase activity, MOMP can lead to cell death by causing a progressive decline in mitochondrial function. Under certain circumstances, however, a cell can survive cell death; its survival may have pathophysiological consequences leading to cancer, autoimmunity, neurodegeneration, and resistance to cancer therapies. This webinar will examine how identification of dysregulated cell-death mechanisms underpinning various pathologies can be exploited to develop novel treatments for cancer and neurodegenerative diseases that directly activate the cell-death machinery.

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Properties and potential optoelectronic applications of lead halide perovskite nanocrystals
Authors: Kovalenko Maksym V. , Protesescu Loredana , Bodnarchuk Maryna I.
Published: November 2017

Semiconducting lead halide perovskites (LHPs) have not only become prominent thin-film absorber materials in photovoltaics but have also proven to be disruptive in the field of colloidal semiconductor nanocrystals (NCs). The most important feature of LHP NCs is their so-called defect-tolerance—the apparently benign nature of structural defects, highly abundant in these compounds, with respect to optical and electronic properties. Here, we review the important differences that exist in the chemistry and physics of LHP NCs as compared with more conventional, tetrahedrally bonded, elemental, and binary semiconductor NCs (such as silicon, germanium, cadmium selenide, gallium arsenide, and indium phosphide). We survey the prospects of LHP NCs for optoelectronic applications such as in television displays, light-emitting devices, and solar cells, emphasizing the practical hurdles that remain to be overcome.