bluuebunny/crossref_metadata_2025 huggingface dataset:
Analytical and Experimental Investigation of Buckled Beams as Negative Stiffness Elements for Passive Vibration and Shock Isolation Systems
Authors: Fulcher Benjamin A. , Shahan David W. , Haberman Michael R. , Conner Seepersad Carolyn , Wilson Preston S.
Published: February 2014

The behavior of a buckled beam mechanism, which exhibits both bistability and negative stiffness, is investigated for the purposes of passive shock and vibration isolation. The vibration and shock isolation systems investigated in this research include linear, positive stiffness springs in parallel with the transverse motion of buckled beams, resulting in quasizero stiffness behavior. For vibration isolation systems, quasizero stiffness lowers the resonance frequency of the system, thereby reducing its transmissibility at frequencies greater than resonance. For shock isolation systems, quasizero stiffness provides constant-force shock isolation at tailored force levels, thereby enabling increased capacity for absorbing shock energy relative to a comparable positive stiffness system. Single- and double-beam configurations that exhibit first-mode buckling are utilized for vibration isolation, and a single beam that exhibits first- and third-mode buckling is used for shock isolation. For all cases, the static and dynamic behavior of each configuration is modeled analytically. The models are then used to design prototype vibration and shock isolation systems that are fabricated using selective laser sintering (SLS). The dynamic behavior of the systems in response to base excitations is determined experimentally, and the results are compared to model-based predictions. The vibration isolation prototypes display isolation levels that are tunable by varying the axial compression of the beams. Double-beam systems are shown to provide greater reductions in resonance frequency than single-beam systems for comparable levels of axial compression. However, low-frequency isolation capabilities are sensitive to the high levels of precision required to obtain low levels of system stiffness. The shock isolation prototype provides isolation at prespecified threshold levels of force or acceleration. In the prototype system, an input shock with a peak acceleration of approximately 7 g is reduced to a peak acceleration of the isolated mass of approximately 1 g. High levels of negative acceleration are observed in models and prototype systems when the buckled beam snaps back to its original position; however, models indicate that large negative accelerations can be mitigated using one-way dampers.
An Analytical Model for Thermoelastic Damping in Microresonators Based on Entropy Generation
Authors: Tai Yongpeng , Li Pu
Published: February 2014

This paper presents an analytical model for thermoelastic damping (TED) in micromechanical resonators, which is based on entropy generation, a thermodynamic parameter measuring the irreversibility in heat conduction. The analytical solution is derived from the entropy generation equation and provides an accurate estimation of thermoelastic damping in flexural resonators. This solution technique for estimation of thermoelastic damping is applied in beams and plates resonators. The derivation shows that the analytical expression for fully clamped and simply supported plates is similar to that for beams, but not the same as the latter due to different strain and stress fields. The present model is verified by comparing with Zener's approximation and the LR (Lifshitz and Roukes) method. The effect of structural dimensions on entropy generation corresponding to thermoelastic damping is investigated for beam resonators. The results of the present model are found to be in good agreement with the numerical and experimental results.
Shakedown Limit Load Determination of a Cylindrical Vessel–Nozzle Intersection Subjected to Steady Internal Pressures and Cyclic In-Plane Bending Moments
Authors: Abdalla Hany F.
Published: February 2014

In the current research, the elastic shakedown limit loads for a cylindrical vessel–nozzle intersection is determined via a direct noncyclic simplified technique. The cylindrical vessel–nozzle intersection is subjected to a spectrum of steady internal pressure magnitudes and cyclic in-plane bending moments on the nozzle end. The determined elastic shakedown limit loads are utilized to generate the elastic shakedown boundary (Bree diagram) of the cylindrical vessel–nozzle structure. Additionally, the maximum moment carrying capacity (limit moments) and the elastic limit loads are determined and imposed on the Bree diagram of the structure. The simplified technique outcomes showed excellent correlation with the results of full cyclic loading elastic–plastic finite element simulations.
Development of a Device for the Nondestructive Thermal Diffusivity Determination of Combustion Chamber Deposits and Thin Coatings
Authors: Hoffman Mark A. , Lawler Benjamin J. , Filipi Zoran S. , Güralp Orgun A. , Najt Paul M.
Published: February 2014

An experimental radiation chamber has been developed to nondestructively measure the thermal diffusivity of a combustion chamber deposit (CCD) layer. The accumulation of CCD shifts the operability range of homogeneous charge compression ignition (HCCI) to lower loads where the fuel economy benefit of HCCI over a traditional spark ignition strategy is at a maximum. The formation and burn-off of CCD introduce operational variability, which increases the control system burden of a practical HCCI engine. To fully characterize the impact of CCD on HCCI combustion and develop strategies which limit the CCD imposed variability, the thermal and physical properties of HCCI CCD must be determined without destroying the morphology of the CCD layer. The radiation chamber device provides a controlled, inert atmosphere absent of cyclical pressure oscillations and fuel/air interactions found within an engine. The device exposes temperature probes coated with CCD to controlled heat flux pulses generated by a graphite emitter and a rotating disk. CCD layer thermal diffusivity is then calculated based on the phase delay of the sub-CCD temperature response relative to the response of the temperature probe when clean. This work validates the accuracy of the radiation chamber's diffusivity determination methodology by testing materials of known properties. Wafers of three different materials, whose thermal diffusivities span two orders of magnitude centered on predicted CCD diffusivity values, are installed over the temperature probes to act as CCD surrogates. Multiple thicknesses of each material are tested over a range of heat flux pulse durations. Diffusivity values determined from radiation chamber testing are independent of sample thickness with each of the three calibration materials. The radiation chamber diffusivity values exhibit a slight, but consistent underprediction for all wafers due to residual contact resistance at the wafer–probe interface. Overall, the validation studies establish the radiation chamber as an effective device for the nondestructive thermal diffusivity determination of thin insulative coatings. The similarity of expected CCD diffusivity values to those of the validation specimens instills confidence that the methodology and device presented herein can be successfully utilized in the characterization of HCCI CCD layers.
Dynamics of Phononic Materials and Structures: Historical Origins, Recent Progress, and Future Outlook
Authors: Hussein Mahmoud I. , Leamy Michael J. , Ruzzene Massimo
Published: February 2014

The study of phononic materials and structures is an emerging discipline that lies at the crossroads of vibration and acoustics engineering and condensed matter physics. Broadly speaking, a phononic medium is a material or structural system that usually exhibits some form of periodicity, which can be in the constituent material phases, or the internal geometry, or even the boundary conditions. As such, its overall dynamical characteristics are compactly described by a frequency band structure, in analogy to an electronic band diagram. With roots extended to early studies of periodic systems by Newton and Rayleigh, the field has grown to encompass engineering configurations ranging from trusses and ribbed shells to phononic crystals and metamaterials. While applied research in this area has been abundant in recent years, treatment from a fundamental mechanics perspective, and particularly from the standpoint of dynamical systems, is needed to advance the field in new directions. For example, techniques already developed for the incorporation of damping and nonlinearities have recently been applied to wave propagation in phononic materials and structures. Similarly, numerical and experimental approaches originally developed for the characterization of conventional materials and structures are now being employed toward better understanding and exploitation of phononic systems. This article starts with an overview of historical developments and follows with an in-depth literature and technical review of recent progress in the field with special consideration given to aspects pertaining to the fundamentals of dynamics, vibrations, and acoustics. Finally, an outlook is projected onto the future on the basis of the current trajectories of the field.
Experimental Study of Solar-Powered Desalination Pond as Second Stage in Proposed Zero Discharge Desalination Process
Authors: Farahbod Farshad , Farahmand Sara
Published: February 2014

An experimental scale desalination pond which utilizes solar energy as a heat source is studied in this paper. The marked solar desalination pond is considered as one of the main stages in a proposed zero discharge desalination process. The effluent waste water of the desalination unit of the petrochemical complex is treated in the proposed zero discharge desalination process to produce potable water and salt. Evaporation distillation method is used in the studied solar desalination pond. Basically, this solar desalination pond is working as batch stage. At the first, the solar-powered desalination pond is introduced then the used method for distillation is discussed and the experimental results are represented in this paper, finally. The results show the feasibility of using the proposed solar-powered pond. The rate of gained distilled water by the proposed solar powered pond is compared with conventional solar pond, finally.
Structural Damage Assessment Using Output-Only Measurement: Localization and Quantification
Authors: Loh Chin-Hsiung , Tseng Min-Hsuan , Chao Shu-Hsien
Published: February 2014

One of the important issues to conduct the damage detection of a structure using vibration-based damage detection (VBDD) is not only to detect the damage but also to locate and quantify the damage. In this paper a systematic way of damage assessment, including identification of damage location and damage quantification, is proposed by using output-only measurement. Four level of damage identification algorithms are proposed. First, to identify the damage occurrence, null-space and subspace damage index are used. The eigenvalue difference ratio is also discussed for detecting the damage. Second, to locate the damage, the change of mode shape slope ratio and the prediction error from response using singular spectrum analysis are used. Finally, to quantify the damage the RSSI-COV algorithm is used to identify the change of dynamic characteristics together with the model updating technique, the loss of stiffness can be identified. Experimental data collected from the bridge foundation scouring in hydraulic lab was used to demonstrate the applicability of the proposed methods. The computation efficiency of each method is also discussed so as to accommodate the online damage detection.
Structural Damage Detection Based on an Improved Edge-Detection Technique
Authors: Chen Peng , Hu Guangda , Nazarian Soheil , Yan Guirong
Published: February 2014

To localize small damage from mode shapes, the polynomial annihilation edge detection method has been proposed and demonstrated its effectiveness on different types of structural components [7]. However, much computational effort involved in this approach lowers the damage detection speed. To alleviate this difficulty, in this paper, we improve the approach by first using the divided difference approach to identify the region(s) in which jump discontinuities are located, and then only applying the polynomial annihilation method to points in the identified region. In this way, the computational burden of this approach is significantly relieved, while the accuracy is still maintained. The improved approach has been validated by numerical simulations on a cable-stayed bridge model. This approach only requires post-damage mode shapes.
Aeroelastic Suppression of Wind Turbine Blade Using Trailing-Edge Flap
Authors: Li Nailu , Balas Mark J.
Published: February 2014

The variation of aeroelastic system dynamics is treated as the change of time-varying aerodynamic loads along the operation trajectory of a spinning wind turbine. An Adaptive Control scheme is introduced to suppress flutter based on the proposed model. The robustness and effectiveness of Adaptive Control is shown by simulation results. For stability analysis, Adaptive Stability Theorem is proved theoretically by Kalman-Yacubovic Lemma and demonstrated numerically by certain cases.
Experimental Implementation of Opposed SMA Wires for Actuator Control
Authors: Kolansky Jeremy , Tarazaga Pablo , Ohanian John
Published: February 2014

Shape Memory Alloys (SMA) have shown their potential as linear actuators. The study conducted here investigates the use of SMA wires as linear actuators for the control of a rotational actuator. The SMA wires are attached to the sides of the actuator to generate opposing forces which are used to control the position of the actuator. In this study the capabilities of this mechanism are demonstrated through tracking of a control path. This mechanism also serves to highlight many effects of SMA wires not commonly discussed: the interaction of opposing hysteresis curves and their effects on the trajectory of the system, the effects of accelerated cooling rates on the hysteresis curves of SMA wires, and the benefits to response time because of the opposing SMA wires.
Design Optimization of a Twist Compliant Mechanism With Nonlinear Stiffness
Authors: Tummala Yashwanth , Frecker Mary , Wissa Aimy , Hubbard James E.
Published: February 2014

A contact aided compliant mechanism called twist compliant mechanism is presented in this paper. This mechanism has nonlinear stiffness when it is twisted in both directions along its axis. The inner core of the mechanism is responsible for its flexibility in one twisting direction. The contact surfaces of the cross-members and compliant sectors are responsible for its high stiffness in the opposite direction. A twist compliant mechanism with desired twist angle and stiffness can be designed by choosing the right thickness of its cross-members, thickness of the core and thickness of its sectors. A multi-objective optimization problem with three objective functions is proposed in this paper, and used to design an optimal twist compliant mechanism with desired deflection. The objective functions are to minimize the mass and maximum von Mises stress observed, while minimizing or maximizing the twist angles under specific loading conditions. The multi-objective optimization problem proposed in this paper is solved using an ornithopter flight research platform as a case study, with the goal of using the twist compliant mechanism to achieve passive twisting of the wing during upstroke, while keeping the wing fully extended and rigid during the downstroke. Prototype twist compliant mechanisms have been fabricated using a waterjet cutter and will be tested as part of future work.
Comprehensive Investigations on Magnetic Field Distribution in a Solenoid
Authors: Gu Xiaoyu , Li Yancheng
Published: February 2014

Finding engineering applications for a new class of smart material, magnetorheological elastomer (MRE), has been a major task for researchers in this field. Novel MRE devices, such as vibration absorbers and vibration isolators, have been proposed and fabricated to pioneer its engineering applications. In civil engineering, the author has proposed a novel MRE based isolator to be used in the base isolation system for mitigating the devastating effects of earthquakes on civil structures. For any MRE-based device, electromagnetic coil is evitable involved to provide magnetic field for the MRE materials. Comparing with magnetic circuit design in magnetorheological fluid (MRF) device, i.e. MR damper, MRE devices normally need a larger coil to energize the MRE materials, particularly for a large-scale MRE device. Therefore, investigation of the solenoid on the magnetic field distribution is of great importance for the design and development of MRE based device. In particular, provision of sufficient and uniform magnetic field is essential towards the success in designing MRF/MRE devices. To understand the mechanism of magnetic field generation in a solenoid is the key for device design and optimization. The main objective of this paper is to analytically investigate and experimentally validate the magnetic field distribution in a solenoid. The theoretical investigation starts from the analysis on an ideally thin cylindrical solenoid in order to obtain analytical results. To stimulate the coil which can be used in the design of MRE device, theoretical investigation is to conduct on a thick-wall cylindrical solenoid. Finite element analysis is also used to examine the magnetic field distribution in the solenoid. In order to verify the theoretical findings, experimental testing is conducted to acquire the magnetic field distribution in a sample solenoid. Results from analytical solution, finite element analysis and experimental testing agree very well. The findings provide valuable information for the design and optimization of the MRE device in which a solenoid is inevitably involved.
An Advanced Energy Relaxation Scheme for the Modeling of Displacive Phase Transformations
Authors: Bartel Thorsten , Buckmann Karsten , Kiefer Björn , Menzel Andreas
Published: February 2014

In this contribution, a micro-mechanically motivated constitutive model for phase transformation, martensite reorientation and twin formation in shape memory alloys is proposed. The formulation builds on an effective parametrization of the austenite-twinned martensite microstructure through first- and second-order laminates. To define the effective energy density of the phase mixture, the concept of energy relaxation is applied. The values of the dissipative internal state variables that describe the microstructure evolution are computed via constrained incremental energy minimization. This work also suggests a first step towards the continuous modeling of twin formation embedded into the concept of energy relaxation and can be viewed as a generalization of earlier models suggested in [1–3]. More specifically, in the current model the orientation of martensitic variants in space is not pre-assigned. Variants are rather left free to arrange in an energy-minimizing fashion and are only distinguished by their rotation in reference to a master variant. Finally, macro-homogeneous uniaxial strain and pure shear loading cases are analyzed to demonstrate the capabilities of the proposed modeling framework.
Adaptive Elastic SMA Elements for Damping Applications
Authors: Czechowicz Alexander , Dültgen Peter , Langbein Sven
Published: February 2014

Shape memory alloys (SMA) are smart materials, which have two technical usable effects: While pseudoplastic SMA have the ability to change into a previously imprinted actual shape through the means of thermal activation, pseudoelastic SMA show a reversible mechanical elongation up to 8% at constant temperature. The transformation between the two possible material phases (austenite and martensite) shows a hysteretic behavior. As a result of these properties, SMA can be used as elastic elements with intrinsic damping function. Additionally the electrical resistance changes remarkably during the material deformation. These effects are presented in the publication in combination with potential for applications in different branches at varying boundary conditions. The focus of the presented research is concentrated on the application of elastic elements with adaptive damping function. As a proof for the potential considerations, an application example sums up this presentation.
A Multi-Purpose Method for SMA Actuator Development
Authors: Langbein Sven , Czechowicz Alexander
Published: February 2014

Shape memory alloys (SMA) are thermally activated smart materials. Due to their ability to change into a previously imprinted actual shape through the means of thermal activation, they are suitable as actuators for mechatronical systems. Despite of the advantages shape memory alloy actuators provide, these elements are only seldom integrated by engineers into mechatronical systems. Reasons are the complex characteristics, especially at different boundary conditions and the missing simulation- and design tools. Also the lack of knowledge and empirical data are a reason why development projects with shape memory actuators often lead to failures. Therefore, a need of developing methods, standardized testing of empirical properties and computer aided simulation tools is motivated. While computer-aided approaches have been discussed in further papers, as well as standardization potentials of SMA actuators, this paper focuses on a developing method for SMA actuators. The main part of the publication presents the logical steps which have to be passed, in order to develop an SMA actuator, considering several options like mechanical, thermal, and electrical options. As a result of the research work, the paper proves this method by one example in the field of SMA-valve technology.
Photocurrent Response of Composite Perovskite Oxide Thin Films With Specific Semiconducting and Ferroelectric Properties
Authors: Shieh Jay , Chen Szu-Wei , Fang Chia-Yu
Published: February 2014

The goal of this study is to investigate photocatalytic semiconductor systems which are layered thin film composites built from perovskite oxide materials with characteristics such as small and large band gaps and/or ferroelectricity. In order to improve the efficiency of photocatalysis, semiconductor heterojunctions within the developed composites have been designed to possess electronic band offsets favoring the separation of photo-induced electron and hole (e−/h+) pairs. Furthermore, the remanent polarization of the ferroelectric component within the composites has been utilized to induce favorable band bending at the material interface, lowering the potential barrier for electron transfer. The band offsets and ferroelectric polarization could be considered as built-in electric fields; how they interact with photo-induced e−/h+ would greatly affect the photocatalytic properties of the composites. In this study, various perovskite oxide thin film materials — large band gap strontium titanate (SrTiO3), small band gap silver niobate (AgNbO3) and ferroelectric lead lanthanum titanate (PLT) — were combined to form layered thin film composites. The composites were then adopted as photoanodes in a photoelectrochemical cell and detailed characterization of their photocurrent response was carried out under different light irradiation and ferroelectric polarization conditions. Electronic band offsets at the material interface (i.e., heterojunction) were determined by ultraviolet-visible spectrophotometry and ultraviolet photoelectron spectroscopy. Electric field poling of the ferroelectric component was achieved by non-contact corona charging.

Our results have shown that the band offsets at the SrTiO3-AgNbO3 heterojunction were about 1.0 eV in conduction band edge and 0.4 eV in valence band edge, promoting the rapid separation of photo-induced charge carriers; i.e., the flow of e− from SrTiO3 to AgNbO3 and the flow of h+ from AgNbO3 to SrTiO3. It was found that ferroelectric PLT could be used as a seeding layer for the low-temperature (500 °C) growth of SrTiO3/AgNbO3 thin film composites on ITO/glass substrates, forming a layered structure of SrTiO3/AgNbO3/PLT/ITO. In addition, the photocurrent density of the composites could be increased by depositing gold nanoparticles at the PLT-ITO interface. When the polarization of the PLT layer was poled toward the AgNbO3 layer, the potential barrier associated with the flow of e− to the ITO electrode was reduced by favorable band bending created at the AgNbO3-PLT interface. This resulted in a significant increase in photocurrent density.
A Load-Bearing Structural Element With Energy Dissipation Capability Under Harmonic Excitation
Authors: Pontecorvo Michael E. , Barbarino Silvestro , Gandhi Farhan S. , Bland Scott , Snyder Robert , Kudva Jay
Published: February 2014

This paper focuses on the design, fabrication, testing and analysis of a novel load-bearing element with good energy dissipation capability over a decade of variation in frequency and harmonic load amplitude. A single layer of the compact sandwiched-plate-like element is comprised of two von-Mises trusses (VMTs) between an upper and lower plate, connected to two dampers which stroke in the in-plane direction as the VMTs cycle between the two stable equilibrium states. The elements can be assembled in-plane to form a large plate-like structure or stacked with different properties in each layer for improved load-adaptability. Also introduced in the elements are pre-loaded springs (PLSs) that provide very high initial stiffness and allow the element to carry a design static load even when the VMTs lose their load carrying capability under harmonic disturbance input. Simulations of the system behavior using the Simscape environment show good overall correlation with test data. Good energy dissipation capability is observed over a frequency range from 0.1 Hz to 2 Hz. While the VMT parameters of a single layer can be optimized to a particular harmonic load amplitude, having two layers with softer and stiffer VMTs allow the system to show good energy dissipation characteristics at different harmonic load amplitude levels. The test and simulation results show that a two layer prototype can provide good energy dissipation over a decade of variation in harmonic load amplitude, while retaining the ability to carry static load on account of the PLSs. The paper discusses how system design parameter changes affect the static load capability and the hysteresis behavior.
Impact Load Mitigation With Bi-Stable von-Mises Trusses
Authors: Pontecorvo Michael E. , Barbarino Silvestro , Gandhi Farhan S. , Bland Scott , Snyder Robert , Kudva Jay
Published: February 2014

This paper examines the potential of a bi-stable von-Mises truss (VMT) connected to viscous damping elements in absorbing impact loads, and reducing loads and accelerations transmitted to the base. A compact sandwich-panel-like element is designed, fabricated and tested in an impact testing machine which comprises of a top plate, a bottom plate, and VMTs in-between that stroke the dashpot as they snap through. The loads transmitted to the bottom plate showed reductions of over 70% for lower drop heights, while reductions approaching 50% were seen for larger drop heights. The introduction of pre-loaded springs in parallel to the VMTs resulted in the prototype not snapping through, except at the largest drop heights tested. The reductions in the transmitted loads were modest for small drop heights but improved as the drop heights increased and snap through occurred. Accelerations transmitted to the bottom plate also showed reductions of 83–88% relative to the upper plate accelerations. A Simscape model of the system showed good overall agreement with tests for loads transmitted to the bottom plate when using the measured loads on the top plate as an input.
Testing of Vibrational Energy Harvesting on Flying Birds
Authors: Shafer Michael W. , MacCurdy Robert , Garcia Ephrahim
Published: February 2014

Discrete animal-mounted sensors and tags have a wide range of potential applications for researching wild animals and their environments. The devices could be used to monitor location, metabolic output, or used as environmental monitoring sentinels. These applications are made possible by recent decreases in the size, mass, and power consumption of modern microelectronics. Despite these performance increases, for extended deployments these systems need to generate power in-situ. In this work, we explore a device that was recently deployed to test the concept of vibrational piezoelectric energy harvesting on flying birds. We explain the development of the device and introduce test results conducted on flying pigeons (Columba livia). The 12 g testing device consisted of a miniature data acquisition system and a piezoelectric energy harvester. The system recorded both the harvested power and the in-flight accelerations of the bird. The energy harvester included a wireless receiver, battery and linear servo. By remotely actuating the linear servo, we were able to arrest the energy harvester for portions of the flight. In doing so, we will be able to compare flight accelerations of a bird with a simple proof mass and with a dynamic mass without having to stop the flight of the bird. The comparison of these two cases allows for the assessment of the feasibility of employing vibrational energy harvesting on a flying bird. We present the initial results of this testing with regard to the harvested power and the in-flight acceleration profiles.
Piezoelectric Actuators With Active and Passive Frames
Authors: Tolliver Laura , Jiang Xiaoning , Xu Tian-Bing
Published: February 2014

Electromechanical actuators that generate large displacements, have large load capabilities, and demonstrate strong resonance characteristics are in great demand in the areas of precision positioning, active vibration control, and energy harvesting. Piezoelectric materials have been widely investigated for these applications because of their high energy density, quick response time, and relatively low driving voltages, but they demonstrate very small strain, typically about 0.1%. We present experimental and finite element results for two designs that use active and passive frames, respectively, to enhance the small strain in piezoelectric multilayer stacks. The first design, stacked-HYBATS, employs the synergetic contribution of d33 and d31 mode piezoelectric material. Finite element results show that this structure can generate over 50 microns of displacement and nearly 40 N of blocking force in a 36 mm × 22 mm × 10 mm footprint. The second design employs frames made from passive materials to form two stages of strain amplification in a 42 mm × 30 mm × 20 mm footprint. This two-stage design can produce over 600 microns of displacement and has a blocking force of 27 N. The active and passive materials of both designs can be varied to maximize displacement and/or blocking force. The stacked-HYBATS and the two-stage amplification system display favorable force-displacement capabilities and are promising for a variety of manufacturing and space technology applications.
An Investigation of Process Parameters on Selective Laser Melting of Nitinol
Authors: Walker Jason , Elahinia Mohammad , Haberland Christoph
Published: February 2014

Nitinol’s superelastic and shape memory effects can be used in passive or active actuation systems. Often used in the aerospace industry, the use of Nitinol for actuation is also growing in the biomedical fields and elsewhere. However, the industry currently lacks the ability to produce complex Nitinol actuators, which is strictly limiting its potential. The extreme difficulty of machining Nitinol complicates manufacturing processes. Furthermore, the transformation temperatures which drive Nitinol’s unique behavior are extremely sensitive to the relative concentrations of nickel and titanium. Therefore, exceptionally tight compositional control during production is necessary to guarantee ideal material behavior. Additive manufacturing (AM) is a near-net-shaping technology which allows for the direct fabrication of complex metallic components. In this way, the (lack of) machinability of Nitinol is no longer an issue because no traditional machining is required during fabrication. Using AM also enables production of 3D geometries that are not possible using traditional techniques. Features such as engineered porosity, hollow parts, curved holes and filigree structures are suddenly realizable. Furthermore, direct CAD fabrication reduces the timescale of the concept-to-prototype transition. A major breakthrough in additive manufacturing came with the development of fiber laser technology in the mid-1990’s, which enables direct melting of manufacturing grade metals into fully dense parts. This technology became known as selective laser melting (SLM). Despite its huge potential, SLM of Nitinol has received little attention from the engineering world. In the present work, two different SLM machines (Realzier SLM 100 and Phenix Systems PXM) are used to develop Nitinol components directly from powder. Adjustment and optimization of the process parameters on the product are analyzed and compared.
Multi-Purpose Avionics Core Element: Using Digital Materials and Advanced Manufacturing to Rapidly Develop Cube Satellite Subsystems and Components
Authors: Hartney Christopher , Agasid Elwood , Hovsepian Sarah
Published: February 2014

The NASA Ames Research Center (NASA Ames) Center Chief Technologist (CCT) Office sponsors the Advanced Digital Materials and Manufacturing for Space (ADMMS) Initiative, which focuses on advanced manufacturing technologies for space, including identifying several target products, areas and applications, approaches for advanced manufacturing, mechanisms for collaboration, and complementary facilities. The pilot project for this initiative is the Multi-Purpose Avionics Core Element (M-PACE). The primary goal of M-PACE is to demonstrate advanced manufacturing techniques, such as additive manufacturing and Digital Materials, to minimize the cost of cube satellites and increase their modularity. M-PACE will be designed and built at the NASA Ames’ SpaceShop, which is a state-of-the-art advanced manufacturing facility built for NASA researchers to formulate ideas for projects.

The final products of M-PACE are several completed side panels of a one-unit (1U) (10 cm cube) cube satellite prototype built using commercial off-the-shelf (COTS) components, which will show the basic functionality of the internal payload by connecting it to the side panels for power and other subsystem capabilities. Within the structure, we are investigating the use of Digital Materials, which are universal building materials with the ability to increase precision and ease of assembly and disassembly of three dimensional (3D) objects. M-PACE will use COTS power systems and open-source hardware and software to distribute data through Ethernet through the use of snap-fit card connectors. Similar to Peripheral Component Interconnect (PCI) Express cards, we envision the spacecraft subsystems and payloads to be on a PC104-like board that will slide into the side panel connectors to enable distribution of power and data. This design has the potential to greatly reduce the cost of Cube Satellite testing and integration due to the absence of wires and ease of access to internal boards for any necessary modifications.
Wave Rich Laser Ultrasonic Wavenumber Imaging for Laser Ultrasonic Propagation Imaging System With Air-Coupled Transducer
Authors: Sunuwar Nitam , Lee Jung-Ryul
Published: February 2014

Interest in ultrasonic guided wave based Structural Health Monitoring and a nondestructive evaluation system has grown in recent years, especially to monitor thin plate like structures. However, an effective signal processing and imaging algorithms are essential to achieve necessary performance. This paper describes wave rich laser ultrasonic wavenumber imaging method (UWI) method for damage visualization. Ultrasonic waves were generated by a scanning laser source and acquired using a capacitance air coupled transducer (ACT). However, the inherent existence of multiple Lamb wave modes in signal makes it harder for effective damage evaluation. This is further complicated if the reflections from the boundaries are present in the signal. The use of an ACT with an in-line programmable filter helps to isolate lower order Lamb wave modes (Ao and So), since the dispersive waves radiate at certain angle from the specimen governed by Snell’s law. By comparing the results from the ultrasonic wavefield image obtained using the ACT and a PZT contact sensor under the same experimental condition, mode isolation phenomena was verified.

Such isolated wave mode was processed using a proposed wave rich UWI algorithm where a wave rich field was generated by superposing the wavefields. The mode filtered measurements were arranged in 3D space-time domain where each slice in time domain represents 2D wavefield image. A 2D Fast Fourier Transform (FFT) was applied to this spatial information in time domain which transformed it to a wavenumber domain. A wavenumber filter is then applied and inverse Fourier transformed to get back to the wavenumber filtered measurement. However, instead of applying filter to every 2D slice in time domain, certain frames were selected and merged to replicate wave propagation in total scan-area. This wave rich field not only saves time and space but also reduce computational complexity during post-processing. This method was tested successfully in an aluminum plate with milled area damage and a composite fiber-reinforced plastic (CFRP) wing skin with two impact damages.
Comparison of Three-Dimensional Shape Memory Alloy Constitutive Models: Finite Element Analysis of Actuation and Superelastic Responses of a Shape Memory Alloy Tube
Authors: Zhu Pingping , Brinson L. Catherine , Peraza-Hernandez Edwin , Hartl Darren , Stebner Aaron
Published: February 2014

Many three-dimensional constitutive models have been proposed to enhance the analysis and design of shape memory alloy (SMA) structural components. Phenomenological models are desirable for this purpose since they describe macroscopic responses using internal variables to govern the homogenized material response. Because they are computationally efficient on the scale of millimeters to meters, these models are often the only viable option when assessing the response of full-scale SMA components for engineering applications. Thus, many different 3D SMA constitutive models have been developed. However, for their intended user, the application engineer, a clear and straightforward methodology has not been established for selecting a model to use in a design process. A primary goal of the Consortium for the Advancement of Shape Memory Alloy Research and Technology (CASMART) modeling working group has been establishment of model selection methodology. One critical step in this process is the development of benchmark problems that clearly illustrate the capabilities and efficiencies of models. In this paper, we propose a set of benchmark problems centered on an SMA tube component. These problems have been selected to demonstrate both uniaxial and multiaxial, actuation and superelastic capabilities of 3D SMA models. We then use finite element simulations of these benchmark problems to compare and contrast both the material modeling and implementation of three unique SMA constitutive models.
Control of Strain Characteristics of SMA Wires Using Seebeck Voltage
Authors: Malladi V. V. N. Sriram , Tarazaga Pablo A.
Published: February 2014

Shape Memory Alloys (SMAs), as a branch of smart material actuators, are widely researched in the areas of control applications. These actuators exhibit considerable hysteresis between the supply voltage (conventionally used in resistive heating) and position characteristics of the SMA. Unless a model matches the actuator’s nonlinearities, the control of an SMA would result in an error between the desired and actual strain. An Adaptive Neuro-Fuzzy Inference System (or ANFIS) model is proposed to model the hysteresis of the system. The hysteresis of an SMA is path dependent, thus controlling the SMA in real-time requires a time series forecasting a nonlinear model. The input parameters for such an ANFIS model would be a physical variable at time t and at a time t-n, where n is a time delay. The present work studies the effect of time delay on the actuator nonlinearities for two ANFIS models. One of the models studies the relationship between the desired displacement of an SMA and the supply voltage across the SMA, while the other model predicts the actual displacement of an SMA from the feedback temperature.
Development of a SMA-Based, Slat-Cove Filler for Reduction of Aeroacoustic Noise Associated With Transport-Class Aircraft Wings
Authors: Turner Travis L. , Kidd Reggie T. , Hartl Darren J. , Scholten William D.
Published: February 2014

Airframe noise is a significant part of the overall noise produced by typical, transport-class aircraft during the approach and landing phases of flight. Leading-edge slat noise is a prominent source of airframe noise. The concept of a slat-cove filler was proposed in previous work as an effective means of mitigating slat noise.

Bench-top models were developed at 75% scale to study the feasibility of producing a functioning slat-cove filler. Initial results from several concepts led to a more-focused effort investigating a deformable structure based upon pseudoelastic SMA materials. The structure stows in the cavity between the slat and main wing during cruise and deploys simultaneously with the slat to guide the aerodynamic flow suitably for low noise.

A qualitative parametric study of SMA-enabled, slat-cove filler designs was performed on the bench-top. Computational models were developed and analyses were performed to assess the displacement response under representative aerodynamic load. The bench-top and computational results provide significant insight into design trades and an optimal design.
Analysis-Driven Design Optimization of a SMA-Based Slat-Cove Filler for Aeroacoustic Noise Reduction
Authors: Scholten William , Hartl Darren , Turner Travis
Published: February 2014

Airframe noise is a significant component of environmental noise in the vicinity of airports. The noise associated with the leading-edge slat of typical transport aircraft is a prominent source of airframe noise. Previous work suggests that a slat-cove filler (SCF) may be an effective noise treatment. Hence, development and optimization of a practical slat-cove-filler structure is a priority. The objectives of this work are to optimize the design of a functioning SCF that incorporates superelastic shape memory alloy (SMA) materials as flexures that permit the deformations involved in the configuration change. The goal of the optimization is to minimize the actuation force needed to retract the slat-SCF assembly while satisfying constraints on the maximum SMA stress and on the SCF deflection under static aerodynamic pressure loads, while also satisfying the condition that the SCF self-deploy during slat extension. A finite element analysis model based on a physical bench-top model is created in Abaqus such that automated iterative analysis of the design could be performed. In order to achieve an optimized design, several design variables associated with the current SCF configuration are considered, such as the thicknesses of SMA flexures and the dimensions of various components, SMA and conventional. Design of experiment (DOE) studies are performed to investigate structural response to an aerodynamic pressure load and to slat retraction and deployment. DOE results are then used to inform the optimization process, which determines a design minimizing actuator forces while satisfying the required constraints.
Microplane Modeling of Shape Memory Alloys in an Alternative Formulation
Authors: Mehrabi Reza , Kadkhodaei Mahmoud , Elahinia Mohammad
Published: February 2014

In this work, a volumetric-deviatoric split in microplane formulation is considered for modeling of shape memory alloys. In the microplane theory, macroscopic stress tensor is projected into the microplane stresses that are decomposed to either Volumetric-Deviatoric-Tangential (V-D-T) split or Volumetric-Deviatoric (V-D) split. Then 1D constitutive laws are defined between associated microplane stress and microplane strain on any plane. The homogenization process is used according to which macroscopic strain tensor is obtained by integration strains on all orientations at a point. The constitutive formulation based on V-D-T split uses the principle of complementary virtual work (PCVW) to derive macroscopic strain tensor. It is shown that in the microplane models based on V-D-T split — which are derived from the PCVW — the thermodynamic consistency cannot be guaranteed in all loading conditions and the second thermodynamic law might violate. It is shown that a special case of V-D-T split, known as the V-D split, is an effective approach to remedy violation from the second law of thermodynamics. Numerical comparison of the microplane formulation based on V-D-T split and V-D split shows that alternative splits predict the same result in some different loadings. The efficiency of the V-D split is its thermodynamic consistency.
Principles of Biomolecular Network Design
Authors: Freeman Eric C. , Philen Michael K. , Leo Donald J.
Published: February 2014

Networks of biomolecular unit cells are proposed as a new type of biologically inspired intelligent materials. These materials are derived from natural cellular mechanics and aim to improve current biologically-inspired technologies by recreating the desired systems from the basic building block of the natural world; the cell. The individual biomolecular unit cell is able to replicate natural cellular abilities through a combination of lipid bilayer membranes containing embedded proteins and peptides. While individual unit cells offer an ideal testing environment for demonstrating proofs of concept, more advanced abilities require larger networks, utilizing cell-to-cell interactions.

The cell-to-cell interactions often involve multiple modes of communication, which have been identified for this paper as primarily electrical, chemical, and mechanical phenomenon. Previous modeling efforts have incorporated the electrical portion through equivalent circuit models, but these lack the ability to fully explain some of the network characteristics. A new formulation is presented here to illustrate how these three classes of phenomenon may be coupled to achieve various engineering design goals.
An Adaptive Tuned Mass Damper Using Friction Bars
Authors: Neubauer Marcus , Wallaschek Jörg
Published: February 2014

This publication presents a novel realization of a Tuned Mass Damper (TMD) using friction bars. Because of the friction forces in the contact, they dissipate energy similar to a dry friction contact. Because of the nonlinear, amplitude depending damping behavior, it is possible to have the pure absorbing effect combined with broadband damping, which cannot be achieved by the classical, viscousely damped TMD.

Special focus is layed on the modeling aspects. The friction contact is modeled using the Harmonic Balance method, and with help of the replacement parameters the system behavior is studied.
Performance of Galloping Piezoelectric Energy Harvesters With Square Bluff Body
Authors: Ewere Felix , Wang Gang
Published: February 2014

In this paper, we investigate a galloping piezoelectric energy harvester (GPEH) with a square bluff body. Comprehensive wind tunnel tests are conducted and experimental data are used to validate our analytical approximate solutions, which are derived from a coupled aero-electro-mechanical model. In addition, the effects of impact disturbances using a bump are investigated. The goal is to improve the performance of baseline GPEH. We expect to collect physical insight to design an optimal nonlinear GPEH configuration by placing bumps accordingly. Lessons learnt from this study will be used to improve the performance of future nonlinear GPEHs and lead to a practical device.