bluuebunny/crossref_metadata_2025 huggingface dataset:
A Modified Microplane Model Using Transformation Surfaces to Consider Loading History on Phase Transition in Shape Memory Alloys
Authors: Shirani Milad , Mehrabi Reza , Andani Masood Taheri , Kadkhodaei Mahmoud , Elahinia Mohammad , Andani Mohsen Taheri
Published: December 2014

In most of the existing SMA constitutive models, it is assumed that transformation starts when a thermodynamic driving force reaches a specified amount regardless of loading history. In this work, a phenomenological approach is used to develop an enhanced one-dimensional constitutive model in which loading history is directly considered as one of the main parameters affecting the transformation start conditions. To generalize the model to three-dimensional cases, a microplane formulation based on volumetric-deviatoric is employed. A free energy potential is defined at the microplane level, integrated over all orientations at a material point to provide the macroscopic free energy. Experiments are carried out on Nitinol superelastic tubes to validate the newly proposed constitutive model. In these experiments, interruptions are applied during transformations to show the effects of loading history on transformation start conditions. Numerical results are compared with the experimental data to demonstrate the accuracy of the enhanced model.
An Axially-Suspended Vibration Energy Harvesting Beam for Broadband Performance and High Versatility
Authors: Harne R. L. , Wang K. W.
Published: December 2014

It has recently been shown that negligible linear stiffness or very small negative stiffness may be the most beneficial stiffness nonlinearities for vibrational energy harvesters due to the broadband, amplified responses which result from such designs. These stiffness characteristics are often achieved by providing axial compression along the length of a harvester beam. Axial compressive forces induced using magnetic or electrostatic effects are often easily tuned; however, electrostatic energy harvesters are practically limited to microscale realizations and magnets are not amenable in a variety of applications, e.g. self-powered biomedical implants or when the harvesters are packaged with particular circuits. On the other hand, mechanically-induced pre-compression methods considered to date are less able to achieve fine control of the applied force which is typically governed by a pre-compression distance that has practical constraints such as resolution and tolerance. This notably limits the harvester’s ability to precisely obtain the desired near-zero or small negative linear stiffness and thus inhibits the favorable dynamical phenomena that lead to high energy conversion performance. Inspired by the wing motor structure of the common diptera (fly), this research explores an alternative energy harvester design and configuration that considerably improves control over pre-compression factors and their influence upon performance-improving dynamics. A pre-compressed harvester beam having an axial suspension on an end is investigated through theoretical and numerical studies and experimental efforts. Suspension and pre-loading adjustments are found to enable comprehensive variation over the resulting dynamics. It is shown that the incorporation of adjustable axial suspension into the design of pre-compressed energy harvester beams is therefore a versatile, all-mechanical means to enhance the performance of such devices and ensure favorable dynamics are retained across a wide range of excitation conditions.
Active Artificial Hair Cells Using Nonlinear Feedback Control
Authors: Joyce Bryan S. , Tarazaga Pablo A.
Published: December 2014

There is interest in developing devices that mimic the sound transduction of the cochlear hair cells. Current artificial hair cell (AHC) designs have focused on passive transduction of sound into electrical signals. However, measurements inside living cochleae have revealed that a nonlinear amplification is at work in mammalian hearing. This amplification lowers the threshold for sound detection allowing mammals to hear faint sounds. The nonlinearity results in an amplitude compression whereby a large range of sound pressure levels produces a smaller range of displacements. This compressive nonlinearity gives the ear a large dynamic range. This work seeks to develop and analyze active artificial hair cells which employ a bio-inspired amplification to improve performance. This paper examines two artificial hair cell designs. The first is an 18.5 in long aluminum cantilever beam which is excited and controlled using piezoelectric actuators along the length of the beam. The second design is a one inch piezoelectric bimorph beam subject to a base excitation. In both cases a nonlinear feedback control law is implemented which reduces the beam’s linear viscous damping and introduces a cubic damping term. Model and experimental results show the control law amplified the response of the artificial hair cell to low excitation levels near the resonance frequency. Increasing input levels produced a compressive nonlinearity at resonance similar to that observed in measurements from mammalian cochleae. This work could lead to the development of new bio-inspired sensors with a lower threshold of detection, improved frequency sensitivity, and larger dynamic range.
Design of a Self-Adjusting Terminal Connector Based on Shape Memory Alloys
Authors: Zimmermann Philipp , Pagel Kenny , Bucht André , Drossel Welf-Guntram
Published: December 2014

In electrical engineering terminal connectors are commonly used for connecting and releasing electrical conductors. Within the clamp or contact area the conductor is clamped safely and steadily by a mechanical mechanism to ensure a connection with a consistent quality and safety during the whole period of application. Terminal connectors are used to transfer power in the low and mid voltage range and for transmitting information. The contact force can decrease and the conductor can become loose. This happens due to an inappropriate installation of the conductor in the terminal connector, vibrations, temperature changes as well as the creepage of the contact material, mostly of the conductor. This may lead to damages or fires. Conventional connectors with a self-adjusting capability are not available for all conductor diameters respectively currents and are comparatively cost-intensive. In this paper a self-adjusting terminal connector based on shape memory alloy is developed to enhance a common screw terminal by the integration of a SMA cylinder and the terminal connector is then evaluated regarding its performance and capability.
Algorithms for Rapid Development of Inherently-Manufacturable Laminate Devices
Authors: Aukes Daniel M. , Wood Robert J.
Published: December 2014

We present several algorithms suited for the generation and analysis of structures used in manufacturing laminate electro-mechanical devices. These devices may be fabricated by a family of related manufacturing processes such as printed-circuit MEMS (PC-MEMS) smart composite microstructures (SCM), or lamina emergent mechanisms (LEM), which, by utilizing multi-material laminate composites, enables kinematic motion, component embedding, and monolithic fabrication of high-precision millimeter-scale features. The presented algorithms enable rapid generation of manufacturing features such as support structures and cut files, while facilitating integration with the user’s design intent and available material removal processes. An exemplar device is presented, which, though simple in concept, could not be manufactured without the aid of an expert designer to produce the same features generated by these algorithms.
Integration of Shape Memory Alloy Wires in Fiber Reinforced Polymers for Endless Crash Absorber Structures
Authors: Nissle Sebastian , Hübler Moritz , Gurka Martin , Schmeer Sebastian , Voll Nikolai
Published: December 2014

Today in most cases crash absorber elements are made of metals. Those materials absorb the energy during a crash event by ductile plastification, as e.g. by buckling. Fiber reinforced polymers (FRP) offer due to their heterogenic structure several failure mechanisms for energy absorption under compressive load, such as fiber-break, matrix-break, delamination, fiber pull-out, fiber-matrix-interphase failure and friction processes. This in combination with the low density leads to significantly better specific energy absorption of FRP absorbers (50 J/g to 200 J/g FRP, 20 J/g steel, 40 J/g aluminum). But in case of tensile load fiber reinforced polymers break brittle and the energy absorption level is low. Today as a consequence of rising energy costs FRP with their good specific mechanic properties are used more and more also for crash relevant structures as in automobiles and aircrafts. For this applications a good crash behavior in both cases, compressive and tensile loading, is important. The integration of metal elements in FRP-structures offers the possibility to improve the tensile crash behavior of fiber reinforced polymers as the metal elements can prevent a catastrophic failure of the structure in case of FRP-break and distributes the load during tensile deformation on a larger FRP volume. The integration of shape memory alloys (SMA) with their pseudoplastic martensitic detwinning plateau allows for manufacturing of an “endless” crash absorber in case of tensile load. Required is a well dimensioned structure of shape memory alloys, e.g. a wire mesh, the FRP component and their interface. Doing so, it is possible to get huge number of breaks in the SMA reinforced FRP. The pseudoplastic detwinning plateau and the huge strain hardening of the SMA material ensure that after a FRP-break and the drop of the force level associated therewith the force level in the whole structure raises again so that another FRP-break is initiated. Also the reinforcement prevents a complete failure of the structure.

In this contribution we present a theoretical extrapolation of the behavior of these new hybrid structures under tensile loading, give an estimation of their potential and demonstrate a first experimental validation of this new concept.
MRE-Based Adaptive-Tuned Dynamic Absorber With Self-Sensing Function for Vibration Control of Structures
Authors: Komatsuzaki Toshihiko , Inoue Toshio , Iwata Yoshio
Published: December 2014

Magneto-rheological elastomer (MRE) is known as class of smart materials whose elastic property can be varied by the applied external magnetic field. For the use of semi-active vibration control, any kind of external sensor such as accelerometer or displacement sensor is usually used to monitor the real-time response of structures while leaving cost, proper installation and maintenance problems for real applications. In addition to the field-dependent stiffness change property of MRE, the electrical resistance of the composite is also changed by the induced strain within the elastomer providing a new self-sensing feature as a multifunctional material. In the present study, a novel dynamic vibration absorber having self-sensing function and adaptability using Magneto-rheological elastomer is developed. The natural frequency of the absorber is instantaneously tuned to a dominant frequency extracted from the strain signal. The damping performance of the absorber is investigated by applying the absorber to a fundamental base-excited 1-dof vibration system. Investigations show that the vibration of the target structure exposed to a non-stationary disturbance can be satisfactorily reduced by the proposed frequency-tunable dynamic absorber without the use of an external sensor, at the exceeding performance in comparison to conventional passive-type dynamic absorber.
Experimental Characterization of a Circular Diaphragm Dielectric Elastomer Generator
Authors: Righi Michele , Vertechy Rocco , Fontana Marco
Published: December 2014

Inflated Circular Diaphragm Dielectric Elastomer Generators (CD-DEGs) are a special embodiment of polymeric transducer that can be used to convert pneumatic energy into high-voltage direct-current electricity. Potential application of CD-DEGs is as power take-off system for wave energy converters that are based on the oscillating water column principle. Optimal usage of CD-DEGs requires the adequate knowledge of their dynamic electro-mechanical response. This paper presents a test-rig for the experimental study of the dynamic response of CD-DEGs under different programmable electro-mechanical loading conditions. Experimental results acquired on the test-rig are also presented, which highlight the dynamic performances of CD-DEGs that are based on acrylic elastomer membranes and carbon conductive grease electrodes.
Open Shape Morphing Honeycombs Through Kirigami
Authors: Neville Robin M. , Pirrera Alberto , Scarpa Fabrizio
Published: December 2014

This work presents an “open” and deployable honeycomb configuration created using kirigami-inspired cutting and folding techniques. The open honeycomb differs from traditional “closed” honeycomb by its reduced density and its increased flexibility. The exploitation of these characteristics for multifunctional applications is the focus of this work. Potential fields in which the open honeycomb could find application include sandwich panel manufacturing, morphing, and deployable structures.
The Effect of Laser Welds on the Thermomechanical Fatigue of NiTi Shape Memory Alloys
Authors: Panton B. , Zeng Z. , Zhou Y. N. , Khan M. I.
Published: December 2014

Welding and joining of NiTi based shape memory alloys (SMAs) is essential for their integration into an increasing variety of applications. The titanium elemental constituent significantly complicates joining, especially with dissimilar materials where brittle intermetallics are often formed. There have been a relatively small number of investigations of the welding of NiTi in similar and in dissimilar joints. Of these studies, a few have investigated the effect of similar welded joints on the pseudoelastic fatigue of NiTi. To the author’s knowledge there are no investigations on the effect of joining on the fatigue of thermally actuated NiTi. The current work investigates the physical, thermomechanical fatigue and shape memory properties of welded shape memory wires. The welded NiTi wires successfully achieved 86% of the base metal ultimate tensile strength. The cycle lives of the welded wires that underwent thermomechanical fatigue were significantly less than the base metal.
Design of a Compliant Flexure Joint for Use in a Flow Energy Harvester
Authors: Chatterjee Punnag , Bryant Matthew
Published: December 2014

This paper presents an initial experimental and computational investigation of a flow-induced vibration energy harvester with a compliant flexure mechanism. This energy harvester utilizes the aeroelastic flutter phenomenon to convert the flow energy to vibrational energy which can be converted into useful electrical power using piezoelectric transducers. However, unlike previous flutter-based flow energy harvesters [1] which require assembling multiple components to create the necessary aeroelastic arrangement, the device described here utilizes a monolithic, compact design to achieve the same. In this paper, we propose a flexure design for this device and model it using analytic methods and finite element simulations. A proof of concept energy harvester incorporating this flexure design has been fabricated and experimentally investigated in wind tunnel testing.
Adaptive Individual Blade Pitch Control to Reduce Platform Pitch Motion of a Floating Offshore Wind Turbine: Preliminary Study
Authors: Magar Kaman Thapa , Balas Mark J.
Published: December 2014

This paper presents the preliminary study on damping of platform pitch motion of floating offshore wind turbine using adaptive individual blade pitch control. The platform pitch displacement is measured and used to derive the signal to actuate pitch of each blade independently which tries to damp the platform pitch motion. This independent blade pitch control signal is then combined with collective blade pitch control signal which is responsible for regulating the generator speed. The performance of proposed controller is compared with the baseline PID collective pitch controller and adaptive collective pitch controller.
Studies With SMA Actuated Needle for Steering Within Tissue
Authors: Datla Naresh V. , Konh Bardia , Hutapea Parsaoran
Published: December 2014

Flexible needles that can be steered within soft tissues are a promising approach to precisely reach target locations, thereby can significantly benefit needle based surgical procedures such as brachytherapy and biopsy. Several design approaches have been suggested to increase needle flexibility that include bevel-tip needles, kinked needles and flexure-based needles. These needles when inserted into a soft materials takes a curved path. This curved path can be controlled while inserting by rotating the needle at its base. In this work another approach to control the curved path was explored. Here the needle body was attached with a shape memory alloy (SMA) actuator close the needle tip that when actuated bends the needle and thereby leads to a curved path inside soft tissue. A prototype of the SMA actuated needle was developed and the working principle was demonstrated in air, tissue-mimicking gel, and pig liver. Moreover, the effect of actuator wire diameter on the needle behavior were studied.
Self-Assembling Swimming Smart Boxes
Authors: Karami M. Amin , Esfahani Ehsan T. , Daghooghi Mohsen , Borazjani Iman
Published: December 2014

This paper presents vibration analysis and structural optimization of a self-assembled structure for swimming. The mode shapes of the structure resemble the body waveform of a swimming Mackerel fish. The lateral deformation waveform of the body of Mackerel is extracted from literature. At higher swimming speeds fish generate the waveform at a higher frequency. Their body waveform stays the same at almost all normal swimming speeds. At the final destination, the box self-assembles using shape memory alloys. The shape memory alloys used for configuration change of the box robot cannot be used for swimming since they fail to operate at high frequencies. MFCs are actuated at the fundamental natural frequency of the structure. This excites the primary mode of resonance. The primary mode of resonance involves rotations of the joints of the robot in the desired fashion. The MFCs are therefore used to indirectly generate the body waveform. We optimize the thickness of the panels and the stiffness of the joints to most efficiently generate the swimming waveforms. Unlike eel we change the speed of the robot by changing the amplitude of the body motions. This is because the frequency of the motion is fixed to the first natural frequency of the robot. The swimming box can swim over the surface and can also swim underwater. With slight modification the boxes can crawl or slither over the land.
Dynamic Characterization of a Partially Treated MR Based Sandwich Plate: Finite Element Modeling and Experimental Study
Authors: Eshaghi Mehdi , Sedaghati Ramin , Rakheja Subhash
Published: December 2014

The dynamic characteristics of a partially treated MR sandwich plate are investigated through finite element analysis and laboratory experiments. A finite element (FE) model is developed to formulate the governing equations of motion of the multi-layer plate with a partial MR fluid core layer, while considering the slippage between the constraining top and bottom aluminum layers. A phenomenological model is further proposed to describe the complex shear modulus of the MR fluid in the pre-yield region as a function of both the applied magnetic field and the excitation frequency. The validity of the FE model is demonstrated through measurements in the laboratory under different intensities of the magnetic field. The results show important effect of the shear deformations in vibration suppression capability of the MR sandwich plate.
Experimental Analysis of Self-Folding SMA-Based Sheet Design for Simulation Validation
Authors: Powledge Aaron C. , Hartl Darren J. , Malak Richard J.
Published: December 2014

The goal of this research is to experimentally characterize the capabilities of a concept for a self-folding reconfigurable sheet for use in origami-inspired engineering design and to use this characterization to validate simulations of physics-based models of the sheet. The sheet consists of an active, self-morphing laminate that contains two shape memory alloy (SMA) mesh layers and a passive compliant medium between these layers. The SMA layers are thermally actuated, allowing bending to occur in both positive and negative directions to create soft hill and valley folds. These folds are completely reversible, allowing the structure to fold and unfold without permanent deformation. Unlike past work on self-folding structures, these sheets can have folds along any line, be subsequently unfolded, and then be folded again in a new way.

To explore the effect of changing design parameters on the performance metrics of the sheet, it is desirable to use Finite Element Analysis (FEA) simulations instead of relying on time consuming experiments. Such models have been created incorporating user material subroutines (UMATs) in an FEA solver such as Abaqus to capture material behavior, but these must now be validated against experimental data to establish how well they match experimental performance. The primary performance metric of the sheet was chosen to be the radius of curvature measured perpendicularly to the line of heating. Both experiment and simulation focus on the radius of curvature achieved by the sheet for a given set of design parameters and actuation path. The goal of validation is to achieve a desirable level of agreement and repeatability in these results.

To measure the deformation and curvature in the sheet as it actuates, a 3D Digital Image Correlation (3D DIC) system is employed to track the movement of points along the surface of the sample as it is heated to a temperature above the transformation temperature of the SMA and allowed to fully actuate. These tools are utilized for a number of samples so that validation of the sheet encompasses multiple values for each of the primary design parameters.
Ultrasonic Assembly of Biologically Inspired Anisotropic Short Fibre Reinforced Composites
Authors: Trask Richard S.
Published: December 2014

In nature, both material and structure are formed according to the principles of biologically controlled self-assembly, a process defined as the spontaneous and reversible ordering of small molecular building blocks under the influence of non-covalent, static interactions. The orientation and distribution of reinforcing entities in engineering composites is key to enabling structural efficiency, yet the architecture remains simplistic when compared to the distinctive and unique hierarchies found in Nature. These biological ‘composite’ materials achieve such configurations by accurately controlling the orientation of anisotropic nano- and micro-sized ‘building blocks’, thereby reinforcing the material in specific directions to carry the multidirectional external loads at different length scales. Capturing the design principles underlying the exquisite architecture of such biological materials will overcome many of the mechanical limitations of current engineering composites. The scientific vision for this study is the development of a novel and highly ordered complex architecture fibrous material for additive layer manufacturing. Using novel chemistry and controlled field-effect assembly, functionally graded, stiffness modulated architectures, analogous to those found in nature, are synthesised to realise enhanced mechanical performance, multi-dimensional composite structures. To achieve this, both hierarchical discontinuous fibres (glass fibres with ZnO nanrods) and a new type of ultrasonic device has been developed. The two studies reported here have been successfully employed to manufacture and mechanically characterise the fibres and aligned discontinuous fibres. A 43 % improvement in strength was observed for samples tested parallel to the direction of the fibre reinforcement over those strained normal to the fibre direction, despite the relatively low volume percentage of the reinforcement phase. This technique shows great potential for the low cost instantaneous alignment of structural reinforcement to generate the light-weight high performance structures required for the future.
Integrated Design Optimization of Dielectric Elastomer Actuators in High-Performance Switchgear
Authors: Price Aaron D. , Ask Anna
Published: December 2014

Although the performance of stacked dielectric elastomers has been demonstrated experimentally, improved simulation tools are required to accurately predict their dynamic performance in demanding applications in the power and automation industries. This investigation presents an integrated design optimization system that elucidates the relationship between various design variables and resulting electromechanical system performance in the context of a dielectric elastomer actuator driven electrical contactor.

The system comprises several specially developed software modules that interact to automatically determine an optimal design. The core module consists of a user material subroutine that models electro-viscoelastic elastomers, the development of which is presented herein. This material behavior is then integrated within a coupled multi-body simulation implemented in the ABAQUS commercial finite element software. This module captures the mechanical dynamics of the switchgear for a given actuator design candidate. Finally, a fully-integrated multi-objective optimization workflow that automatically generates and evaluates design candidates is presented.
A Hydrogel-Based Droplet Interface Lipid Bilayer Network
Authors: Edgerton Alex , Najem Joseph , Leo Donald
Published: December 2014

In this work, we present a process for the fabrication of meso-scale hydrogel-based lipid bilayer arrays. The hydrogels support lipid monolayers at an oil-water interface, and when brought together, form stable bilayers. The substrates are formed using 3D printed molds and include built-in, customizable circuits patterned with silver paint. The system can be adapted to varying network sizes and circuit designs, and new arrays are fabricated quickly and inexpensively using common laboratory techniques. An enclosed 3×3 array with 3 mm spacing between neighboring hydrogels and electrodes to individually examine each bilayer has been created using this method. An alternative test setup was also developed to better observe the formation of bilayers in a small array. Using this setup, two bilayers were formed simultaneously, demonstrating the feasibility of this type of system and providing valuable information for expanding and improving the enclosed network. Many of the design concepts presented here can be adapted for use at smaller scales using microfabrication techniques.
Micro-Encapsulation and Tuning of Biomolecular Unit Cell Networks
Authors: Nguyen Mary-Anne , Sarles Stephen A.
Published: December 2014

The goal of our research is to fabricate an autonomic material system that provides compartmentalization and multi-bilayer networks for enabling collective biomolecular functionality, as is found in living cells and tissues. The material system is based on biomolecular unit cells, which consist of synthetic lipid bilayers formed at the interfaces of lipid-coated aqueous droplets submerged in oil and contained in a solid material. This paper focuses on microfluidic encapsulation of unit cells within a solid material and tuning the amount of contact between droplets, two approaches aimed at increasing the functional density of the droplet-based material system. Hydrodynamic traps within microfluidic platforms have shown to be a promising method to capture single droplets within microfluidic devices. Herein, we develop a resistive flow model to design hydrodynamic traps for collecting pairs of droplets in a direct trapping mode to form unit cells. We also compare to the model the results of droplet trapping in a prototype microfluidic device fabricated prior to model development. In addition to flow techniques for assembling unit cells in solid materials, we examine the use of mineral oil as the hydrophobic oil phase that surrounds the droplets to increase the area of the lipid membrane formed between neighboring droplets. Compared to hexadecane, mineral oil produces larger contact areas between droplets and more-tightly packed multi-bilayer networks. The total free energies of formation for droplet arrays in mineral oil and hexadecane indicate that connected droplets in mineral oil exhibit a greater decrease in free energy upon formation (i.e. they exist at a lower energy state compared to those in hexadecane) and that hexagonal packing provides the maximum amount of decrease in free energy per droplet for droplets in large arrays. Electrical measurements of unit cells formed in mineral oil initially show gigaohm resistances typical of unit cells, however these unit cells exhibit increasing values of conductance as the bilayer areas grow.
Characterization and Modeling of Thermo-Mechanical Fatigue in Equiatomic NiTi Actuators
Authors: Wheeler Robert W. , Hartl Darren J. , Chemisky Yves , Lagoudas Dimitris C.
Published: December 2014

Due to their high actuation energy density and ability to recover large deformation, Shape Memory Alloys (SMAs) have many promising engineering applications. However, applications are sometimes limited to non-structural or non-critical components due to the lack of fatigue characterization standards and general understanding of the actuation fatigue process. The purpose of this study was to characterize the actuation fatigue response of equiatomic Nickel Titanium (NiTi) with various heat treatments and loading paths and utilize the characterization data collected to calibrate a previously developed constitutive damage model for multiple loading paths. Dogbone actuators were processed from heat treated NiTi sheets; heat treatments ranged from 350°C to 400°C for one to three hours. The actuators were subjected to actuation fatigue via mechanical loading, resistive heating, and convective cooling. Two mechanical loading schemes were utilized: a constant load initially set at 200MPa and a linear or spring load ranging from 150MPa (fully martensite) to 250MPa (fully austenite), thus maintaining a similar work per cycle for each loading scheme. Linear loading schemes were introduced in order to better simulate actuation in an aerospace application, such as the morphing of semi-rigid surfaces. Specimens were thermally cycled to full actuation with a feedback (displacement and temperature) control scheme developed in LabVIEW. The observed fatigue responses varied widely as a result of different heat treatments and, to a lesser extent, loading schemes. For actuators with higher temperature heat treatments, the main observed failure mechanism was strain localization (necking). Data resulting from these experiments were used to calibrate a previously developed fatigue damage model, which is formulated such that the damage accumulation rate is general in terms of its dependence on current stress and actuation strain states. This allows the model to be fit to data from specimens subjected to variable loading paths described herein. Agreement between experiments and simulations is discussed.
Sensing Interfacial Damage Initiation, Evolution and Accumulation in Carbon Nanotube-Polymer Nanocomposites Under Cyclic Loading: A Computational Micromechanics Approach
Authors: Chaurasia Adarsh K. , Seidel Gary D.
Published: December 2014

The current 2-scale computational multiscale micromechanics based exploration of sensing capabilities in carbon nanotube (CNT)-polymer nanocomposites focuses on the macroscale piezoresistive response when the nanocomposite is subjected to cyclic loading conditions. It has been shown that electron hopping at the nanoscale is the primary mechanism behind the observed macroscale piezoresistivity for such nanocomposites. A novel continuum description of the non-continuum electron hopping effect used in the current work enables the use of multiscale continuum micromechanics based approaches to study nanocomposite piezoresistivity. The focus of the current work is on the interfacial separation/damage initiation, evolution and accumulation when subjected to cyclic loading. Interfacial separation/damage is allowed at the nanoscale CNT-polymer interface using electromechanical cohesive zones to account for electron hopping across the separated interface. The mechanical response of the CNT-polymer interface is obtained in terms of normal/tangential traction-separation behavior from atomistic scale Molecular Dynamics based models. The coupled electrostatic response is based on evolving interfacial resistance through the electron hopping induced current density across the separated interface. Such coupled electromechanical description allowing for current density across the separated interface in addition to normal/tangential tractions is unique in its implementation to the best of the authors knowledge. It is observed that the effective macroscale piezoresistive response obtained from the current modeling framework captures interfacial separation/damage state and shows sensitivity to damage accumulation over several cycles. Such exploration of the governing physical mechanisms starting at the smallest scale of influence and transitioning into macroscale effective properties provides key insights into the multiscale problem.
Model Development for Dynamic Energy Conversion in Post-Buckled Multi-Stable Slender Columns
Authors: Borchani Wassim , Lajnef Nizar , Burgueño Rigoberto
Published: December 2014

Broadband piezoelectric energy harvesting solutions from ambient loading have been extensively studied with the purpose of increasing the efficiency of vibration-based harvesters. Most of the previously developed methods focus on the transducer’s properties and configurations, and require vibration input excitations. In contrast, we have previously experimentally shown a mechanical energy concentrator system that exploits the quasi-static input deformations (strains) generated within the structure and induces an amplified amplitude and frequency up-converted response. The tested energy converting devices transform low-amplitude and low-rate service strains into an amplified vibration input to the piezoelectric transducer. The snap-through behavior of bilaterally constrained columns was used as the mechanism for energy concentration. This paper presents a theoretical model, based on energy method, for the post-buckling behavior of a bilaterally constrained slender column under quasi-static axial loadings. The total potential energy of the buckled elastic element is the sum of the potential energies due to bending, compression and external applied force. The transverse deflection is limited by the lateral constraints. Therefore a constrained minimization problem of the total potential energy is solved to determine the equilibrium configurations. Equilibrium transitions are correlated to the changes in the magnitude of the weight coefficients that define the contribution of buckling modes to the deflected shape. Transition states are defined in terms of the axial displacements, axial forces, column shape, and energies stored in the system.
An Experimental Assessment of the Thermo-Elastic Response in Acrylic Elastomers and Natural Rubbers for Application on Electroactive Polymer Transducers
Authors: Berselli Giovanni , Vertechy Rocco , Fontana Marco , Pellicciari Marcello
Published: December 2014

Dielectric Elastomers (DEs) are deformable dielectrics, which are currently used as active materials in mechatronic transducers, such as actuators, sensors and generators. Nonetheless, at the present state of the art, the industrial exploitation of DE-based devices is still hampered by the irregular electro-mechanical behavior of the employed materials, also due to the unpredictable effects of environmental changes in real world applications. In many cases, DE transducers are still developed via trial-and-error procedures rather than through a well-structured design practice, one reason being the lack of experimental data along with reliable constitutive parameters of many potential DE materials.

Therefore, in order to provide the practicing engineer with some essential information, an open-access database for DE materials has been recently created and presented in [1]. Following the same direction, this paper addresses the temperature effect on the visco-hyperelastic behavior of two DE candidates, namely a natural rubber (ZRUNEK A1040) and a well-known acrylic elastomer (3M VHB 4905). Measurements are performed on pure shear specimens placed in a climactic chamber. Experimental stress-strain curves are then provided, which makes it possible to predict hyperelasticity, plasticity, viscosity, and Mullins effect as function of the environmental temperature. Properties of these commercial elastomeric membranes are finally entered in the database and made available to the research community.
Adaptive Damage Detection Using Tunable Piezoelectric Admittance Sensor and Intelligent Inference
Authors: Zhou K. , Shuai Q. , Tang J.
Published: December 2014

The piezoelectric impedance/admittance-based damage detection has been recognized to be sensitive to small-sized damage due to its high frequency measurement capability. Recently, a new class of admittance-based damage detection schemes has been proposed, in which the piezoelectric transducer is integrated with a tunable inductive circuitry. The present research focuses on exploiting the tunable nature of the piezoelectric admittance sensor for the effective identification of damage. In particular, we incorporate the Bayesian inference network into the damage detection process which can intelligently guide the accurate identification of damage location and severity by taking full advantage of the baseline model and measurement as well as the online measurement. As the tunable sensor can provide greatly enriched measurement information, the Bayesian inference can adequately utilize such information and furthermore directly and continuously update the structural model until the model prediction matches with the measurement results. This new approach takes into account the model uncertainty, measurement error, and incompleteness of measurements. Extensive numerical analyses and experimental studies are carried out on a panel structure for methodology demonstration and validation.
Marine Energy Harvesting Using Magnetohydrodynamic Power Generation
Authors: Morgan Eric R. , Shafer Michael W.
Published: December 2014

Energy harvesting is widely used in terrestrial and aerial sensor applications but is conspicuously absent in the marine environment despite several possible harvesting modalities and numerous applications. One such energy harvesting modality is to use magnetohydrodynamic (MHD) power generators to directly produce electricity from flowing seawater. Fundamentally, MHD generators convert the kinetic energy of a conductive fluid directly into electricity by separating charged particles, thereby generating an electric field transverse to the direction of fluid flow and the magnetic field. The electric field is then accessed with an external circuit to provide power to a load. Since the power output from an MHD generator is linearly related to the conductivity of the flowing fluid and to the square of both the magnetic field strength and the fluid velocity, strong magnets and high fluid velocity are desirable. Thus, there are a myriad of possible MHD generator configurations available to maximize power output under various conditions and constraints. These include configurations of permanent magnets that offer localized high magnetic fields or geometries of the fluid duct that can be used to increase the fluid velocity through the magnetic field. One novel application for MHD generators is to power sensors and bio-loggers used in marine animal telemetry. The animal sensors are designed to take time-series measurements and store the data on the logger for transmission to satellite networks or human retrieval. These sensors and loggers are often battery-limited which constrains either the data fidelity or the longevity, or both. An MHD generator attached to a marine animal can help to supplement some of the sensor or bio-logger power requirements, thereby increasing sensor lifetimes and data fidelity. Thus, MHD generators will enable new research in the marine sciences, climatology, and biology, among others. The MHD generator can be positioned above the fluid boundary-layer so that the fluid flow around the animal is channeled through the MHD generator, producing electricity. In this work, we will develop some of the fundamental equations that describe the physics of an MHD generator and use them to make estimates of the potential power outputs that could be expected from various marine animals. We will also investigate several electrical configurations of the MHD to determine the most suitable MHD generator for different flow regimes. Initial studies suggest that MHD generators are viable power sources in the marine environment and can easily supplement the entire energy budget of a bio-logger under certain conditions.
A Modeling of Fe-Ga Magnetostrictive Shunt Damper
Authors: Yoo JinHyoeng
Published: December 2014

This study presents mechanical energy dissipation with a proof-of-concept prototype magnetostrictive (Fe-Ga alloy, galfenol) based shunt circuit using passive electrical components. Magneto strictive material can harvest electricity out of the structural vibrations based on the Villari effect using permanent magnet and pickup coil configuration. The device in this study consists of a polycrystalline galfenol strip bonded to a brass cantilever beam. Two brass pieces, each containing a permanent magnet, are used to mass load at the end of the beam and to provide a magnetic bias field through the galfenol strip. The voltage induced in an induction coil closely wound around the cantilever beam captures the time rate of change of magnetic flux within the galfenol strip as the beam vibrates. To dissipate the electrical voltage output from the pickup coil and/or to change the phase of eddy current from the magnetic flux density fluctuation, a shunt circuit is attached. The effective mechanical impedance for the magnetostrictive shunt circuit is derived in a model. The effectiveness of a series L-R and L-C shunt circuit is demonstrated theoretically and experimentally. The non-linear model parameters, which include the mechanical-magnetic coupling factors, α and αT, and the permeability of galfenol, β, are extracted from experimental measurement. The shunted magnetostrictive damping model of both resistive and capacitance shunt cases compare well with the experimental results.
Guided Wave Delamination Detection and Quantification With Wavefield Data Analysis
Authors: Tian Zhenhua , Leckey Cara A. C. , Seebo Jeffrey P. , Yu Lingyu
Published: December 2014

Unexpected damage can occur in aerospace composites due to impact events or material stress during off-nominal loading events. In particular, laminated composites are susceptible to delamination damage due to weak transverse tensile and interlaminar shear strengths. Developments of reliable and quantitative techniques to detect delamination damage in laminated composites are imperative for safe and functional optimally-designed next-generation composite structures. In this paper, we investigate guided wave interactions with delamination damage and develop quantification algorithms by using wavefield data analysis. The trapped guided waves in the delamination region are observed from the wavefield data and further quantitatively interpreted by using different wavenumber analysis methods. The frequency-wavenumber representation of the wavefield shows that new wavenumbers are present and correlate to trapped waves in the damage region. These new wavenumbers are used to detect and quantify the delamination damage through the wavenumber analysis, which can show how the wavenumber changes as a function of wave propagation distance. The location and spatial duration of new wavenumbers can be identified, providing a useful means not only for detecting the presence of delamination damage but also for estimation of the delamination size. Our method has been applied to detect and quantify real delamination damage with complex geometry (grown using a quasi-static indentation technique). The detection and quantification results show the location, size, and shape of the delamination damage.
A Constitutive Model for Magnetic Shape Memory Alloys That Includes a Tilted Magnetic Easy Axis
Authors: Dikes Jason L. , Feigenbaum Heidi P. , Ciocanel Constantin , Nelson Isaac D.
Published: December 2014

Magnetic shape memory alloys (MSMAs) are materials commonly used for actuation, sensing, and/or power harvesting applications. While the actuation response of MSMAs can be fairly accurately predicted by currently available constitutive models, the power harvesting and/or sensing performance is not predicted as well. This suggests that current models lack features related to the change in magnetization. One such feature that is known to exist, but is not present in any current model, is the natural offset of the magnetic easy axis from the short axis of the tetragonal martensitic unit cell of MSMAs. Experimentally, Scheerbaum et al. [1] observed that this offset angle is in the range of 2° to 6°. While this is a relatively small angle, it is expected to make a dramatic difference in the evaluation of the power harvesting output, as it creates favorable domains even when the field is applied perpendicular to the short axis of the unit cell. Therefore, to facilitate the design of MSMA based sensing and power harvesting devices, a continuum model for the magneto-mechanical response of MSMAs, that accounts for the magnetic easy axis offset from the short side of the unit cell is derived from thermodynamic requirements and evaluated in this work.
20 Years of Adaptive Aerostructures in Flying Missiles, Munitions and UAVs
Authors: Barrett Ron
Published: December 2014

In September of 1994 a small uninhabited aerial vehicle took to the air. While the flight of this lightweight powered glider was unremarkable, its 3 minutes aloft represented a turning point in adaptive aerostructures technology as it was the first man-made craft to stay aloft while using only adaptive materials for all flight control. This paper celebrates and summarizes two decades of flying adaptive aerostructures controlling missiles, munitions and UAVs. The paper starts with an historical review of the technologies which underpinned the first adaptive flight vehicles. Twist-active piezoelectric plates are shown beside the earliest flightweight stabilators they were integrated into. A brief description of the 120cm wingspan UAV “Mothra” which took to the air 20 years ago is given. The earliest hard-launched adaptive actuators were designed and developed just a year after Mothra took to the air. The paper summarizes the resulting (unrestricted) adaptive actuator configurations which have come around since that time, including actuator assemblies for guided bullets and cannon shells from 5.56mm through 155mm. A decade ago, the first post-buckled precompressed (PBP) piezoelectric flight control mechanisms debuted as enabling technologies in a unique class of aircraft: “hovering missiles” flew at international airshows, guided rounds hit targets on gunnery ranges and entered serial production with PBP actuator assemblies. More modern incarnations of these actuators and others have been designed into GPS-guided grenade, mortar and artillery shells. Today, some of the world’s most active and highest work energy density actuators are built with ultra-high strain adaptive materials and have been shown to dramatically cut CEP of gravity weapons, cruise missiles and glide shells. The paper concludes with a chart showing which classes of adaptive actuators have been flown in what types of weapon systems and UAVs over the past 20 years.