bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Tools for Semi-Active Optimization of 2D Wave’s Dispersion Into Mechanical System
Authors: Collet Manuel , Ouisse Morvan , Ichchou Mohammed , Ruzzene Massimo
Published: April 2011

In the context of mid-frequency elastodynamical analysis of periodic structures, the Floquet-Bloch theorem has been recently applied. The latter allows the use of limited-size modeling of a representative cell to characterize waves dispersion properties of the assembled structure. The theorem provides a rigorous and well posed spectral problem representing waves dispersion in viscolelastic media. In particular, the wave-FEM (WFE) method and associated techniques are based on the Floquet-Bloch approach. Most of the current applications are limited either to undamped or to slightly damped systems. In this paper, the Floquet-Bloch theorem is used to set up an alternative technique in order to estimate the dispersion characteristics of a periodic structure. The approach is based on the same basic assumptions, but the generalized eigenvalue problem which has to be solved differs from the one usually considered in WFE. Instead of discretizing the k-space, the harmonic frequency and the wave heading are used to scan the k-space. Then the formulated eigenvalue problem is solved and the dispersion characteristics are obtained, including spatial attenuation terms. Some fundamentals properties of the eigensolutions are discussed, and the methodology is finally applied on a 2D waveguide application which can be found in the literature for an undamped case. The same example is considered with various damping levels, in order to illustrate the performances and specificities the efficiency of proposed approach. The proposed approach finds application in the analysis of wave propagation in the presence of damping materials or shunted piezoelectric patches, as well as in actively controlled systems, where equivalent damping terms are associated with the considered control scheme.
Electromechanical Stability of Dielectric Elastomer Using Electric Energy Density Function With Variable Dielectric Constant
Authors: Liu Liwu , Li Tiefeng , Liu Yanju , Leng Jinsong
Published: April 2011

Dielectric elastomer(DE) is a kind of promising material bearing excellent activate properties including large deformations (up to 380%), high energy densities (up to 3.4 J/g), high efficiency, high responsive speed, good reliability and durability. Thus the DE actuator, sensors and energy harvester is widely used in the field of aeronautics and smart bionics. When an electric field is applied on the compliant electrodes of the dielectric elastomers, the polymer shrinks along the electric field and expands in the transverse plane. In consequence, the electric field becomes higher. This kind of positive feedback may cause the elastomer to thin down, resulting in an electromechanical stability. An analysis on the electromechanical stability of dielectric elastomer using arbitrary free-energy function with constant dielectric constant has been presented in Suo’s papers. In many research on the electromechanical stability analysis of DE actuator, DE’s dielectric constant is assumed to be a constant. This is only the truth if the dielectric elastomer undergoing limited deformation. Actually, a typical dielectric elastomer is a kind of crosslinked polymer. The structural symmetry of the macromolecular, the crosslinking degree, along with the tensile deformation can affect the dielectric permittivity enormously. For dielectric elastomers with higher crosslinking degree, or higher degree of molecular structural symmetry, its permittivity is relatively low. In addition, stretching can guide the macromolecule to be arranged in order, this can increase the intermolecular forces and reduce the activities of polar group, as a results, the dielectric constant will decrease. However, if the crosslinking degree is low and the deformation is well below the extension limit, the molecular units in the polymers can be polarized as freely as in a polymeric liquid. In this case the corresponding permittivity is unaffected by the deformation. Recent experimental research results also proved that the dielectric permittivity of dielectric elastomer changed while undergoing large deformation. According to Pelrine, the dielectric constant of the DE film is variable and it is a function of the area increase ratio which depends on stretch ratio. In this paper, approach for the electromechanical stability of a dielectric elastomer having variable dielectric constant is developed. The critical breakdown electric field is obtained. Simulation results proved that the prestretching process can enhance remarkably the electromechanical stability of dielectric elastomer. These results agree well with the experimental data and can be used as guidances in the design and fabrication of dielectric elastomer actuators.
Experimental Study of a Self-Excited Piezoelectric Energy Harvester
Authors: Akaydın Hu¨seyin Dog˘us¸ , Elvin Niell , Andreopoulos Yiannis
Published: April 2011

In the present experimental work, we explore the possibility of using piezoelectric based fluid flow energy harvesters. These harvesters are self-excited and self-sustained in the sense that they can be used in steady uniform flows. The configuration consists of a piezoelectric cantilever beam with a cylindrical tip body which promotes sustainable, aero-elastic structural vibrations induced by vortex shedding and galloping. The structural and aerodynamic properties of the harvester alter the vibration amplitude and frequency of the piezoelectric beam and thus its electrical output. This paper presents results of energy-harvesting tests with one configuration of such a self-excited piezoelectric harvester using a PZT bimorph. In addition to the electrical voltage output, the strain on the surface of beam close to its clamped tip was also measured The measured strain and voltage output were perfectly correlated in the frequency range containing the first natural mode of vibration of the system. It was observed that about 0.24 mW of electrical power can be attained with this harvester in a uniform flow of 28 m/s.
Design and Optimization of Hybrid Compliant Narrow-Gauge Surgical Forceps
Authors: Aguirre Milton E. , Frecker Mary
Published: April 2011

This work describes a design and optimization method for developing hybrid, multi-material, compliant instruments which are expected to be useful in mini-laparoscopy and natural orifice translumenal endoscopic surgery. These two-material devices are designed specifically for Penn State’s lost mold rapid infiltration process, which is capable of fabricating hundreds of freestanding meso-scale parts in parallel. New narrow-gauge surgical procedures impose severe geometric constraints that challenge traditional compliant mechanism design methods. Since narrow-gauge constraints leave geometry optimization ineffective, new design methods are explored to improve the performance of a 1 mm diameter contact-aided compliant forceps. By considering hybrid designs, new design possibilities are enabled through material variation. The hybrid forceps has desired regions of flexibility and stiffness that can be isolated to improve tool performance. For instance, a hybrid forceps can be designed with greater flexibility in some regions to provide larger jaw openings while maintaining high stiffness in other regions to obtain large grasping forces, both vital features in a surgical forceps. Using ANSYS to model large deformation and contact, an optimization problem is formulated to maximize tool performance and to determine optimal segregation of hybrid materials considering a range of modulus ratios. Materials under consideration include nanoparticulate 3 mol% yttria partially stabilized zirconia (3YSZ) and austenitic (300 series) stainless steel. All results are compared to previously optimized homogeneous designs.
Design, Fabrication, and Testing of Meso-Scale Cellular Contact-Aided Compliant Mechanisms
Authors: Mehta Vipul , Hayes Greg , Frecker Mary , Adair James H. , Lesieutre George A.
Published: April 2011

The design and fabrication of meso-scale cellular contact-aided compliant mechanisms with micron sized features are presented in this paper. Cellular structures with internal contact mechanisms exhibit a reduction in stress during deformation and, thus, can be stretched further than they could without a contact mechanism. Fabricating such structures at a meso-scale can result in new high-strength, high-strain materials. Manufacturing at a meso-scale restrains the maximum aspect ratio and the initial contact gap of the mechanism. An analytical model is used to resolve the tradeoffs between these manufacturing constraints and to design suitable contact-aided cellular mechanisms. A lost mold rapid infiltration forming process is employed to fabricate meso-scale cellular mechanisms using either 316L stainless steel or a composite 316L stainless steel with nanoparticulate zirconia. A custom rig was developed to test meso-scale cellular mechanisms. The elastic modulus of 316L stainless steel was found to be about 110 ± 40 GPa both from tensile testing of test bars and from model-matching of cellular mechanisms. The cellular mechanisms were observed to exhibit about 1.1% of overall strain before any local permanent deformation. This study validates the efficacy of the design and fabrication methodology for the meso-scale cellular mechanisms.
Microwave Antenna Sensors for Fatigue Crack Monitoring Under Lap Joints
Authors: Erdmann Justin , Deshmukh Srikar , Huang Haying
Published: April 2011

This paper presents a microwave antenna sensor that has the ability to monitor fatigue cracks between lap joints where compressive force is present or in any other areas where a crack is hidden between two parts of a structure. The sensor is designed to be low profile, light weight, and conformal, making it ideal for aerospace applications where lap joints are a common design feature, and thus minimizing manual inspection times. The design of the fatigue sample for simulating a lap joint will be presented. The experiment results validated the microwave antenna sensor’s capability to effectively monitor fatigue cracks under lap joints.
Adaptive Resetting of SMA-Actuators
Authors: Langbein Sven , Sadek Tim , Czechowicz Alexander
Published: April 2011

Shape Memory Alloys (SMAs) have essential advantages compared to conventional actuators, in particular their high power density and their silent mode of operation. However, this material has not gained acceptance in technical applications yet. The main reasons are the missing simulation tools and a lack of knowledge of materials as well as the companies’ uncertainty how to handle SMAs. The resetting of the SMA element to generate a repeatable movement is often a defined problem. In this context reset springs made of steel are conventional solutions although their characteristics are a disadvantage. To reach a high level of power output and hence a high degree of efficiency, a reduction of the pre-load is necessary. A solution for this problem is an adaptive resetting. One main possibility to generate an adaptive resetting is given by the agonist-antagonist principle where two SMA-elements work against each other. Here the reset force can be applied if necessary. The advantage of this type of design is that a conventional return spring or a mechanical brake for clamping the position (electrically operated) is not necessary. Another possibility for adaptive resetting is to change the spring characteristics of a pseudoelastic SMA-element by heating. The aim of this study is to show the properties of the agonist-antagonist design and the other concepts. It also provides methods and the knowledge to support the development process of such resetting principles. The development of these methods is based on the analysis of different designs and requirements. Based on the results, instructions for the conception of adaptive resetting systems have been created.
Modeling Ultrasonic Guided Wave Generation From Piezoelectric Fiber Composite Strip Actuators
Authors: Li Sheng , Lissenden Cliff J.
Published: April 2011

Structural health monitoring (SHM) and condition based maintenance (CBM) are keys to shifting the paradigm from schedule based maintenance to cost effective operation and maintenance of reliable systems. Continuous comb transducer strips have the potential to generate ultrasonic guided waves for structural health monitoring of plate and shell structures (pipelines, pressure vessels, storage tanks, airframes). A theoretically driven approach, based on the application of wave mechanics principles, is used to research and design a network of strip sensor. Fibrous piezoelectric composites are considered for the comb elements, widely expanding the design space of these elements to include fiber orientation and volume fraction in addition to size, configuration, and location of the electrodes. Piezoelectric and mechanical properties for these innovative sensor designs are estimated through micromechanical modeling. Specifically, micromechanics enables us to consider different fiber orientations and constituent properties and provides the composite properties for input to finite element analysis of wave propagation. Finite element simulations of ultrasonic guided wave generation and propagation using Abaqus Explicit-Standard Co-Simulation are conducted in order to design the sensory system.
Wave Propagation in Rib-Stiffened Structures: Modeling and Experiments
Authors: Reynolds Whitney , Doyle Derek , Brown Jacob , Arritt Brandon
Published: April 2011

This work focuses on the analysis of wave propagation in rib-stiffened structures as it is related to Structural Health Monitoring (SHM) methods. Current satellite validation tests involve numerous procedures to qualify the satellite for the vibrations expected during launch, and for exposure to the space environment. SHM methods are being considered in an effort to truncate the number and duration of tests required for satellite checkout. The most promising of these SHM methods uses an active wave-based method in which an actuator propagates a Lamb wave through the structure, which is then received by a sensor. The received waves are evaluated over time to detect structural changes. Thus far, this method has proven effective in locating structural defects in a complex satellite panel; however, the attributes associated with the first wave arrival change significantly as the wave travels through ribs and joining features. Complex isogrid reinforcements within the satellite panel significantly affect any conclusions that can be made about the arriving waves. For this purpose, an experimental and numerical study of wave propagation within rib-reinforced plates has been undertaken. Wave propagation was modeled using finite element software. These results were analyzed for an understanding of dispersion within the structure, particularly how the group velocity and mode conversion are affected by the rib interaction. Experiments were carried out to validate the model and gain further insight into the wave propagation phenomena in the structure. The analysis indicates that mode conversion plays a significant role in the first wave arrival, although this can be accounted for through proper frequency selection, and signal analysis. A range of excitation frequencies which are most appropriate for the structure are presented.
Analysis of Wrinkled Membranes Bounded With Macro-Fiber Composite (MFC) Actuators
Authors: Doosthoseini Alireza , Salehian Armaghan , Daly Matthew
Published: April 2011

In this paper we focus on a study which involves quantifying the effects of Macro Fiber Composite (MFC) actuators on the pattern and magnitude of wrinkles in a membrane when exposed to various loadings. An ABAQUS finite element code is employed for this research. The membrane in this study has a rectangular shape which is clamped at one edge and is free to move in the horizontal direction at the other edge. MFC actuators are bounded to the membrane to make a bimorph configuration.
A Rod-Shaped Ionic Polymer-Metal Composite for Use as an Active Catheter-Platform
Authors: Kim Seong Jun , Pugal Deivid , Jung Youngsoo , Wong Johnson , Kim Kwang J. , Yim Woosoon
Published: April 2011

“Catheterization” is becoming one of the important medical operations since it engages minimally invasive medical procedures. It is a common practice that a catheter is inserted into body-cavities to administrate diversified medical functions such as diagnosis and surgery. Current method to deal with catheters is based upon the manual mechanisms that are time consuming and, sometimes, involving high risk to the patient. In this work, we explore the use of a promising electroactive polymer (EAP), called ionic polymer-metal composite (IPMC) as a material for use in active catheter-platforms. The configuration of our interest is a rod-shaped IPMC with 2-DOF electromechanical actuation capability. The desired functionality was achieved by fabricating inter-digitated electrodes. Firstly, the 3-D Finite Element (FE) model was introduced as a design tool to optimize the important parameters including electrode configurations. The FE model is based upon the physical transport processes — field induced migration and diffusion of ions. Secondly, based upon the FE modeling we fabricated an initial prototype exhibiting desired electromechanical output. The prototype of rod-shaped IPMC has a diameter of 1 mm and a 20 mm length. We have successfully demonstrated that the 2-DOF bending of the fabricated IPMC is feasible.
Modeling of Inhomogeneous Deformation in a Dielectric Elastomer Generator for Energy Harvesting
Authors: Li Tiefeng , Keplinger Christoph , Liu Liwu , Baumgartner Richard , Qu Shaoxing
Published: April 2011

Dielectric elastomer transducers promise to combine high energy density at low cost and lightweight when used as actuators or for energy harvesting generators. A cornucopia of possible applications have been demonstrated over the last years including soft matter based actuators for robotics, tunable optics, medical devices, space robotics and energy harvesters. Prestretch effects and the electromechanical instability have been shown to highly influence the performance of dielectric elastomer transducers. Nevertheless only sparse research has been done on instability and prestretch effects of dielectric elastomer membranes under inhomogeneous deformation. Dielectric elastomer transducers consist of an elastomer membrane sandwiched between a pair of compliant electrodes and can be considered as deformable capacitors with variable capacitance. Here we focus on a specific experimental setup well suited to study the performance of dielectric elastomer materials for energy harvesting. In this setup an elastomer membrane is equibiaxially prestretched and fixed on top of an air chamber which is connected to a compressed air reservoir, the source of mechanical energy for thegenerator. From the electrical point of view the compliant electrodes on the elastomer membrane can be connected to both a high and low voltage charge reservoir. Thus the change in capacitance during deformation can be used to boost charges from the low voltage reservoir to the high voltage reservoir. Experimentally, different constant voltages are applied to the elastomer membrane during inflation and the air chamber pressure is recorded together with the shape and the volume of the balloon for different initial prestretches. The usual instability in the pressure-volume curves of ballon inflation experiments are shown to be influenced by applied voltage and prestretch. Theoretically, the setup is modeled as a thermodynamic system, with static electric and mechanical load where quasi-static equilibrium states can be achieved. To describe the inhomogeneous deformation and to correctly account for the hyperelastic behavior of the material over the whole deformation range an asymmetric model is built based on the Arruda-Boyce material model. The results of the numerical simulation are fitted to the experimental data to obtain significant material parameters in order to predict the optimal operation regime of the dielectric elastomer generator. The experimental results accompanied by the theoretical analysis may be used as a benchmark for the applicability of dielectric elastomer generators and pave ways for understanding the dielectric elastomer behavior under inhomogeneous deformation.
Precision Extrusion Deposition With Integrated Assisting Cooling to Fabricate 3D Scaffolds
Authors: Hamid Qudus , Sun Wei , Gu¨c¸eri Selc¸uk
Published: April 2011

As the field of Tissue Engineering advances to its ultimate goal of engineering a fully functional organ, there’s an increase need for enabling technologies and integrated system. Important roles in scaffold guided tissue engineering are the fabrication of extra-cellular matrices (ECM) that have the capabilities to maintain cell growth, cell attachment, and ability to form new tissues. Three-dimensional scaffolds often address multiple mechanical, biological and geometrical design constraints. With advances of technologies in the recent decades, Computer Aided Tissue Engineering (CATE) has much development in solid freeform fabrication (SFF) process, which includes but not limited to the fabrication of tissue scaffolds with precision control. Drexel University patented Precision Extrusion Deposition (PED) device uses computer aided motion and extrusion to precisely fabricate the internal and external architecture, porosity, pore size, and interconnectivity within the scaffold. The high printing resolution, precision, and controllability of the PED allows for closer mimicry of tissues and organs. Literatures have shown that some cells prefer scaffolds built from stiff material; stiff materials typically have a high melting point. Biopolymers with high melting points are difficult to manipulate to fabricate 3D scaffold. With the use of the PED and an integrated Assisting Cooling (AC) device; high melting points of biopolymer should no longer limit the fabrication of 3D scaffold. The AC device is mounted at the nozzle of the PED where the heat from the material delivery chamber of the PED has no influence on the AC fluid temperature. The AC has four cooling points, located north, south, east, and west; this allows for cooling in each direction of motion on a XY plane. AC uses but not limited to nitrogen, compressed air, and water to cool polymer filaments as it is extruded from the PED and builds scaffolds. Scaffolds fabricated from high melting point polymers that use this new integrated component to the PED should illustrate good mechanical properties, structural integrity, and precision of pore sizes and interconnectivity.
Space Application of Piezoelectric Wafer Active Sensors for Structural Health Monitoring
Authors: Giurgiutiu Victor , Santoni-Bottai Giola , Lin Bin , Cuc Adrian
Published: April 2011

Piezoelectric wafer active sensors (PWAS) are lightweight and inexpensive enablers for a large class of structural health monitoring (SHM) applications. This paper presents and discusses the challenges and opportunities related to the use of PWAS in the structures specific to space applications. The challenges posed by space structures are often different from those encountered in conventional structures. After a review of PWAS principles, the paper discusses the multi-physics power and energy transduction between structurally guided waves and PWAS; predictive modeling results using a simplified analytical approach are presented. Experimental results on space-like specimen structures are presented. Survivability of PWAS transducers under cryogenic space-like conditions are experimentally verified. The paper ends with conclusions and suggestions for further work.
Enhanced Piezoelectric Multilayered Beam: Modelling, Experimental Validation and Application to Actuation
Authors: Fernandes A. , Pouget J.
Published: April 2011

A coupled Euler-Bernoulli model of laminated piezoelectric beam is proposed. The enhanced model accounts for the effects of 3D distribution of mechanical stress and strain and the induced electric potential. The model is tested by means of numerical simulations and static and dynamical experimental tests. Applications to the distributed actuation of bistable devices by piezoelectric elements is reported as well. The model consists in an elastic buckled beam equipped with piezoelectric actuators. The model is mainly based on extensible elastica for a piezoelectric sandwich beam. The stability of the snap-through phenomenon is then controlled by two paramerters of actuation (electric potentials).
Microstructures of Constrained Shape Memory Alloy Nanowires Under Thermal Effects
Authors: Dhote Rakesh P. , Melnik Roderick V. N. , Zu Jean W. , Wang Linxiang
Published: April 2011

In this paper, martensitic transformations in constrained Fe-Pd nanowires are studied using a mesoscopic model analyzed in detail numerically in our earlier papers. The dynamics of square-to-rectangular transformation is modeled by using the modified Ginzburg-Landau theory. The simulations are performed accounting for the thermal effects using the coupled equations of non-linear thermoelasticity. Up to date, these effects have typically been neglected in modeling microstructures at the scales of interest considered here. Nanowires of length 2000 nm and widths ranging from 200 nm to 50 nm are simulated to study the effect of size on the microstructure evolution. There exists a critical width below which the size effect is prominent. We present a series of numerical results demonstrating this phenomenon. We also have carried out the study of variations in values of bulk, shear, and Landau constants to understand the difference in evolved microstructure in the coupled and uncoupled physics.
Sensor Behavior of Magneto-Rheological Elastomers
Authors: Faidley LeAnn , Tringides Christina , Hong Wei
Published: April 2011

Magneto-Rheological Elastomers (MREs) are composite materials of an elastomer matrix with a magnetic, micron-sized, powder filler. These materials have gained notoriety because they change stiffness substantially when exposed to a magnetic field giving them the capability of acting as a variable spring for numerous applications. Magnetic field induced strain has also been measured in these materials making them feasible as future actuator materials. However, the inverse effect involving a mechanically induced change in the magnetic properties of these materials has yet to be studied in great detail. This paper presents the results of an experimental study of this sensor behavior. Sheets of 5 mm thick MRE are synthesized from silicone rubber (RTV6186) and carbonyl iron power with a diameter of 9 micrometers. The application of a magnetic field during the silicone curing process allows for the creation of samples with particles aligned along the length, width, and thickness of the sample as well as unaligned samples. These samples are then strained up to 100% of their test length while exposed to various constant bias fields. The change in the internal magnetic properties of the sample as it is strained induces a voltage in a pickup coil that surrounds the sample. This voltage is found to closely track the applied strain-rate making these materials promising for large strain, non-contact strain-rate sensors. In this paper this effect is described in detail experimentally and a theoretical mechanism is proposed to describe this sensing ability. The experimental results for testing MRE samples of 4 alignments in 3 bias fields and at 3 frequencies are presented for cyclic input and the sensitivity, linearity, and repeatability are discussed. Additionally, the results of tests with random inputs are also shown.
The Effect of Numerical Solution Procedure on the Simulation of Shape Memory Alloy Actuators
Authors: Williams Eric , Tadesse Yonas , Priya Shashank , Hong Dennis
Published: April 2011

The numerical simulation of shape memory alloy actuators requires the solution of the coupled thermo-mechanical, phase transformation, and constitutive relationship equations. Simulation results are highly affected by parametric values as well as modeling equations. Specifically, the martensite fraction affects the simulation results of the actuator significantly for various input excitation as fraction of martensite is often modeled with a switching function. Depending on the assumed model this may cause changes in other properties of the system. Therefore in this study, we investigate the modeling of NiTi shape memory alloy based on the available phenomenological models and study the effects of integration step, numerical solver parameters and code formulation in Matlab/SIMULINK. To emphasis on the numerical solving procedure a simple spring biased SMA actuator configuration is chosen. Simulation results from multiple available models are provided and discussed.
A Probabilistic Model Updating Algorithm for Fatigue Damage Detection in Aluminum Hull Structures
Authors: Kurata Masahiro , Kim Jun-Hee , Lynch Jerome P. , Law Kincho H. , Salvino Liming W.
Published: April 2011

The use of aluminum alloys in the design of naval structures offers the benefit of light-weight ships that can travel at high-speed. However, the use of aluminum poses a number of challenges for the naval engineering community including higher incidence of fatigue-related cracks. Early detection of fatigue induced cracks enhances maintenance of the ships and is critical for preventing the catastrophic failure of the hull. Furthermore, monitoring the integrity of the aluminum hull can provide valuable information for estimating the residual life of hull components. This paper presents a model-based damage detection methodology for fatigue assessment of hulls that are instrumented with a long-term hull monitoring system. At the core of the data driven damage detection approach is a Bayesian model updating algorithm enhanced with systematic enumeration and pruning of candidate solutions. The Bayesian model updating approach significantly reduce the computational effort by systematically narrowing the search space using errors functions constructed using the estimated modal properties associated with the condition of the structure. This study proposes the use of the Bayesian model updating technique to detect damage in an aluminum panel modeled using high-fidelity finite element models. The performance of the proposed damage detection method is tested through simulation of a progressively growing fatigue crack introduced in the vicinity of a welded stiffener element. An experimental study verifies the accuracy of the proposed damage detection method using an aluminum plate excited with a controlled excitation in the laboratory.
Metal-Matrix Composite Metamaterials With Smart Switches Embedded by Ultrasonic Consolidation
Authors: Hopkins C. D. , Foster D. , Dapino M. J. , Zhang L.
Published: April 2011

This research deals with the development of metal-matrix composite metamaterials with embedded electrical switches made of shape memory nickel-titanium (Ni-Ti) for use in broad-band radio frequency (RF) antennas. We have created an experiment that illustrates how a Ni-Ti ribbon can form an electrical contact that opens and closes depending on the Ni-Ti phase being austenite or martensite. We have conducted finite element analyses that describe the thermal gradients in the ribbon required for effecting the phase change. Since part of the embedded Ni-Ti has to be electrically insulated from the aluminum matrix, we have investigated various insulation techniques and selected one that is both effective and straightforward to implement. In order to realize multiband/broadband metamaterials, it is necessary to seamlessly embed the Ni-Ti switches into the metamaterial for active reconfiguration of the electromagnetic response. To achieve this reconfiguration we utilize ultrasonic consolidation (UC), a new manufacturing technology that uses solid state ultrasonic metal welding (UMW) to create metal parts at relatively low temperatures. Consideration of the proposed RF switch for load-carrying antennas requires an aluminum matrix with structural-grade strength; we have conducted mechanical testing which quantifies the longitudinal tensile, transverse tensile, and shear strength of the UC matrix. Preliminary tests have been completed to evaluate the performance of an antenna device with integrated Ni-Ti switch.
A Design Method for Shape Memory Alloy Actuators Accounting for Cyclic Shakedown With Constrained Allowable Strain
Authors: Kim WonHee , Barnes Brian M. , Luntz Jonathan E. , Brei Diann E.
Published: April 2011

The high energy density actuation potential of SMA wire is tempered by conservative design guidelines set to mitigate complex factors such as functional fatigue (shakedown). Shakedown causes problems of stroke loss and interface position drift between the system and the SMA wire under higher stress levels if the wire does not undergo a pre-installation shakedown procedure. Limiting actuation strain has been reported as reducing shakedown as well as increasing fatigue life. One approach to limit actuation strain is using a mechanical strain limiter which sets a fixed Martensite strain position — useful for the development of in-device shakedown procedures which eliminates time consuming pre-installation shakedown procedures. This paper presents a new graphical design approach for SMA wire actuators which accounts for shakedown with the use of mechanical strain limiters to enable higher stress designs to maximize actuator performance. Experimental data on the effect of strain limiters along with stroke and work density contours form the basis for the new graphical design method. For each independent mechanical strain limiter, the maximum of the individual post-shakedown austenite curves at a range of applied stress are combined into a conglomerate stabilization design curve. These curves over a set of mechanical strain limiters provide steady state performance prediction for SMA actuation, effectively decoupling the shakedown material performance from design variables that affect the shakedown. The use and benefits of this new design approach are demonstrated with a common constant force actuator design example. This new design approach, which accounts for shakedown, supports design of SMA actuators at higher stresses with more economical use of material/power, and enables the utilization of strain limiters for cost saving in-device shakedown procedures.
Mitigation of Biodynamic Response to Shock Loads Using Semi-Active Vertically Stroking Crew Seats
Authors: Singh Harinder J. , Wereley Norman M.
Published: April 2011

This study addresses mitigation of biodynamic response due to an initial velocity impact of a vertically stroking crew seat using an adaptive magnetorheological energy absorber. Under consideration is a multiple degree-of-freedom detailed lumped parameter model of a human body falling with prescribed initial crash velocity (sink rate). The lumped parameter model of the human body consisted of four main parts: pelvis, upper torso, viscera and head. The governing equations of motion of a vertically stroking crew seat incorporating a human body were derived using parameters such as available damper stroke as well as MR yield force. The control algorithm for smooth landing of a rigid occupant was examined for compliant occupant and was modified accordingly. Four MR yield force models were analyzed to shape decelerations experienced by human body and an appropriate model was selected for comprehensive analysis. The simulated responses were analyzed with selected MR yield force model for a crew seat with an occupant corresponding to 90th percentile male at sink rates varying from 8 to 12 m/s. In addition, the mitigation of injuries to the human body parts due to load transmissions corresponding to crash velocities was also evaluated for the selected MR yield force model along with terminal conditions necessary for smooth landing.
Prognostics of Embedded Planar Capacitors Under Temperature and Voltage Aging
Authors: Alam Mohammed A. , Azarian Michael H. , Osterman Michael , Pecht Michael
Published: April 2011

This paper presents the application of model-based and data-driven approaches for prognostics and health management (PHM) of embedded planar capacitors under elevated temperature and voltage conditions. An embedded planar capacitor is a thin laminate that serves both as a power/ground plane and as a parallel plate capacitor in a multilayered printed wiring board (PWB). These capacitors are typically used for decoupling applications and are found to reduce the required number of surface mount capacitors. The capacitor laminate used in this study consisted of an epoxy-barium titanate (BaTiO3) composite dielectric sandwiched between Cu layers. Three electrical parameters, capacitance, dissipation factor, and insulation resistance, were monitored in-situ once every hour during testing under elevated temperature and voltage aging conditions. The failure modes observed were a sharp drop in insulation resistance and a gradual decrease in capacitance. An approach to model the time-to-failure associated with these failure modes as a function of the stress level is presented in this paper. Model-based PHM can be used to predict the time-to-failure associated with a single failure mode, consisting of a drop in either insulation resistance or capacitance. However, failure of an embedded capacitor could occur due to either of these two failure modes and was not captured using a single model. A combined model for both these failure modes can be developed but there was a large variance in the time-to-failure data of failures as a result of a sharp drop in insulation resistance. Therefore a data-driven approach, which utilizes the trend and correlation between the parameters to predict remaining life, was investigated to perform PHM. The data-driven approach used in this paper is the Mahalanobis distance (MD) method that reduces a multivariate data set to a single parameter by considering correlations among the parameters. The Mahalanobis distance method was successful in predicting the failures as a result of a gradual decrease in capacitance. However, prediction of failures as a result of a drop in insulation resistance was generally challenging due to their sudden onset. An experimental approach to address such sudden failures is discussed to facilitate identifying any trends in the parameters prior to failure.
Onset of Self-Excited Oscillations of Traveling Wave Thermo-Acoustic-Piezoelectric Energy Harvester
Authors: Aldraihem O. , Baz A.
Published: April 2011

The onset of self-excited oscillations is developed theoretically for a traveling wave thermo-acoustic-piezoelectric (TAP) energy harvester. The harvester is intended for converting thermal energy, such as solar or waste heat energy, directly into electrical energy without the need for any moving components. The thermal energy is utilized to generate a steep temperature gradient along a porous stack. At a specific threshold of the temperature gradient, self-sustained acoustic waves are generated inside an acoustic resonator. The resulting pressure fluctuations excite a piezoelectric diaphragm, placed at the end of the resonator, which converts the acoustic energy directly into electrical energy. The pressure pulsations are amplified by using an acoustic feedback loop which introduces appropriate phasing that make the pulsations take the form of traveling waves. Such traveling waves render the harvester to be inherently reversible and thus highly efficient. The behavior of this class of harvesters is modeled using the lumped-parameter approach. The developed model is a multi-field model which combines the descriptions of the acoustic resonator, feedback loop, and the stack with the characteristics of the piezoelectric diaphragm. A new method is proposed here to analyze the onset of self-sustained oscillations of the traveling wave engine using the classical control theory. The predictions of the developed models are validated against published results. Such models present invaluable tools for the design of efficient thermo-acoustic-piezoelectric (TAP) energy harvesters and engines.
Electric Field Manipulation of Cellulose Whiskers in Polyvinyl Acetate
Authors: Kalidindi Sanjay V. , Ounaies Zoubeida , Kaddami Hamid
Published: April 2011

Cellulose whiskers as inclusions have shown a lot of promise due to their potential to enhance mechanical and piezoelectric response of polymers. In addition, CWs are high aspect ratio particles; by aligning them in polymers, improved and anisotropic physical properties could be achieved. In this study, we investigate the effect of AC electric field on the alignment of CWs in a solution of PVAc and DMF. CWs were dispersed as small bundles (<10μm). Alignment and chain formation was found to be a function of electric field magnitude, frequency and time. Dielectric constant of the solutions was studied as a function of applied electric field magnitude, frequency and duration. Significant improvements in dielectric constant were observed for the aligned cases as compared to random case. Optimum properties were achieved at 100 – 200 Vpp/mm and 50 KHz for duration of 20 minutes. Future work will focus on processing thin films with individually dispersed CWs, and improving their alignment to further increase the electrical and mechanical properties.
Customer Tailored Active Weatherstrip Design
Authors: Nagesh Shishira , Luntz Jonathan E. , Brei Diann , Alexander Paul W. , Browne Alan L. , Johnson Nancy L.
Published: April 2011

Providing quality sealing to automobile doors is a challenging problem due to the inherent design tradeoffs between a) small closing effort for high customer satisfaction and quality perception, and b) large sealing forces to ensure effective water and noise isolation. A new paradigm to overcome this tradeoff is active seals using smart materials which provide two separate operational states; thus, decoupling closing effort and sealing force allowing for simultaneous improvement. While engineering functionality dictates that the sealing force should be high, the closing effort is governed by the human/seal interaction; making the optimal load profile harder to identify. This paper describes a methodology to synthesize active seals with closing force profiles customizable to the customer preferred feel of door closure while increasing the sealing force for improved water and noise isolation. To identify preferred closing force profiles, a formal customer behavioral study was conducted with an on-vehicle closing force profile emulator which allowed subjects to experience and select different profiles. While there are many possible embodiments to achieve the preferred load profiles, in this paper an active mechanism insert is presented which provides two operational states by leveraging a Shape Memory Alloy actuated five-bar-mechanism customized to a customer preferred closing force profile in the martensite phase and high sealing force when heated to the austenite phase. For this SMA mechanism, a model based genetic algorithm optimization method is described for synthesis generalized for any customer closing load profile. This method was utilized to design, fabricate and experimentally characterize an SMA mechanism-based active seal capable of producing the most popular closing force profile determined by the behavioral study, and when activated, generating high sealing force. The described synthesis process is applicable to a wide range of closing profiles and can be used to tailor active seal closing profiles to target groups of customers on individual vehicle platforms improving customer satisfaction and perceived qualitywhile simultaneously improving sealing performance.
Control of a Shape Memory Alloy Actuator for Mirror Positioning
Authors: Williams Eric , Shaw Gordon , Elahinia Mohammad
Published: April 2011

Shape Memory Alloy actuators offer solutions to many common actuation problems especially where space or weight is limited. However, practical applications for SMA actuators in the automotive industry are still relatively few. The design of a novel automotive mirror actuator is outlined. The actuator utilizes a spherical joint and a passive friction brake to translate the linear motion of SMA wires into the angular rotation required for the mirror. A simple and effective variable structure controller is developed for the control of the mirror actuator and experimental results are obtained showing the controller is effective with small perturbations.
Hysteresis Identification of Shape Memory Alloy Actuators Using a Novel Artificial Neural Network Based Presiach Model
Authors: Zakerzadeh Mohammad R. , Firouzi Mohsen , Sayyaadi Hassan , Shouraki Saeed Bagheri
Published: April 2011

In systems with hysteresis behavior like Shape Memory Alloy (SMA) actuators and Piezo actuators, an accurate modeling of hysteresis behavior either for performance evaluation and identification or controller design is essentially needed. One of the most interesting hysteresis none-linearity identification methods is Preisach model which the hysteresis is modeled by linear combination of hysteresis operators. In spite of good ability of the Preisach model to extract the main features of system with hysteresis behavior, due to its numerical nature, it is not convenient to use in real time control applications. In this paper a novel artificial neural network (ANN) approach based on the Preisach model is presented which provides accurate hysteresis none-linearity modeling. It is shown that the proposed approach can represent hysteresis behavior more accurately in compare with the classical Preisach model and can be used for many applications such as hysteresis non-linearity control, hysteresis identification and realization for performance evaluation in some physical systems such as magnetic and SMA materials. It is also greatly decrease the extremely large amount of calculation needed to numerically implement the Preisach hysteresis model. For evaluation of the proposed approach an experimental apparatus consists of one-dimensional flexible aluminum beam actuated with a SMA wire is used. It is shown that the proposed ANN based Preisach model can identify hysteresis none-linearity more accurately than the classical Preisach model besides to its reduction in the simulation and computation time.
Structural Damage Identification Based on Information Fusion Techniques
Authors: Li Hui , Bao Yuequan
Published: April 2011

With the aim to decrease the uncertainties of structural damage detection, two fusion models are presented in this paper. The first one is a weighted and selective fusion method for combing the multi-damage detection methods based on the integration of artificial neural network, Shannon entropy and Dempster-Shafer (D-S) theory. The second one is a D-S based approach for combing the damage detection results from multi-sensors data sets. Numerical study on the Binzhou Yellow River Highway Bridge and an experimental of a 20-bay rigid truss structure were carried out to validate the uncertainties decreasing ability of the proposed methods for structural damage detection. The results show that both of the methods proposed are useful to decrease the uncertainties of damage detection results.
Growth and optical properties of InP nanowires formed by Au-assisted metalorganic chemical vapor deposition: Effect of growth temperature
Authors: Guo Jingwei , Huang Hui , Ren Xiaomin , Yan Xin , Cai Shiwei , Wang Wei , Wang Qi , Huang Yongqing , Zhang Xia
Published: April 2011

Vertical indium phosphide nanowires (NWs) were grown at different temperatures by metalorganic chemical vapor deposition via a gold (Au)-assisted vapor-liquid-solid mechanism. At a low growth temperature (420 °C), the lengths of the NWs were diameter independent, which indicated that the NWs were grown with significant contributions from the direct impingement of the precursors onto the alloy droplets. In this process, the droplet acts as a catalyst rather than an adatom collector. However, at a high growth temperature (480 °C), the lengths of the NWs were inversely diameter dependent. The wurtzite percentage of NWs increases with the growth temperature. Room temperature photoluminescence properties of NWs grown under different temperatures were investigated.