bluuebunny/crossref_metadata_2025 huggingface dataset:
Brake Shoe Coefficient of Friction Variation
Authors: Cummings Scott , McCabe Tom , Guelde Glenn , Gosselin Dan
Published: February 2010

A series of dynamometer tests were conducted by the Wheel Defect Prevention Research Consortium (WDPRC) to quantify the amount of expected variation in brake shoe coefficient of friction (COF) and resulting wheel temperature throughout the life of an individual brake shoe. Variations in brake shoe COF within an individual railcar are one potential source of elevated wheel temperatures and thermal mechanical shelling (TMS) damage to the wheels. High friction composition and tread conditioning brake shoes were installed in the “as manufactured” condition with no wear-in or machining at the beginning of the test matrix which consisted of seventeen stop tests and twelve grade tests. For each brake shoe tested, the average COF and maximum wheel temperature were recorded during eleven identical light grade tests interspersed throughout the test matrix.
Machine Vision Condition Monitoring of Railcar Structural Underframe Components
Authors: Hart John M. , Schlake Bryan , Todorovic Sinisa , Edwards J. Riley , Ahuja Narendra , Barkan Christopher P. L.
Published: February 2010

Monitoring the structural health of rolling stock is critical to ensuring safe and efficient railroad operation. The structural integrity of freight cars depends on the health of certain structural components within their underframes. These structural components serve two principal functions: supporting the car body and lading, and transmitting longitudinal buff and draft forces. Although railcars are engineered to withstand large static, dynamic and cyclical loads, various structural defects can still develop within their underframes. As a result, both the United States Department of Transportation (USDOT) Federal Railroad Administration (FRA) regulations and individual railroad mechanical department practices require periodic inspection of railcars to detect structural damage and defects. These inspections are conducted manually and rely heavily on the acuity, knowledge and endurance of qualified inspection personnel. Enhancements are possible through machine-vision technology, which uses computer algorithms to convert digital image data into useful information. This paper describes research investigating the feasibility of an automated inspection system capable of detecting structural defects in freight car underframes and presents an inspection approach using machine-vision techniques, including multi-scale image segmentation. Using field data from a preliminary image acquisition system, algorithms were developed to analyze images of railcar underframes and assess the condition of certain structural components. This technology, in conjunction with additional preventive maintenance systems, has the potential to provide more objective information on railcar condition, improve utilization of railcar inspection and repair resources, increase train and employee safety, and improve overall railroad network efficiency.
The Calculation of Stiffness for Semiconductor Components
Authors: Gaith Mohamed , Alhayek Imad
Published: February 2010

In this study, the correlation between macroscopic and microscopic properties of the II-IV semiconductor compounds CdX (X = S, Se, Te) is investigated. Based on constructing orthonormal tensor basis elements using the form-invariant expressions, the elastic stiffness for cubic system materials is decomposed into two parts; isotropic (two terms) and anisotropic parts. A new scale for measuring the overall elastic stiffness of these compounds is introduced and its correlation with the calculated bulk modulus and lattice constants is analyzed. The overall elastic stiffness is calculated and found to be directly proportional to bulk modulus and inversely proportional to lattice constants. A scale quantitative comparison of the contribution of the anisotropy to the elastic stiffness and to measure the anisotropy degree in an anisotropic material is proposed using the Norm Ratio Criteria (NRC). It is found that CdS is the nearest to isotropy (or least anisotropic) while CdTe is the least near to isotropy (or nearest to anisotropic) among these compounds. The norm and norm ratios are found to be very useful for selecting suitable materials for electro-optic devices, transducers, modulators, acousto-optic devices.
Exploratory Work in Fiber Optic Brush Seals for Turbomachinery Health Prognostics
Authors: Ruggiero Eric J.
Published: February 2010

Brush seals are found in aircraft engines, compressors, steam turbines, and power generators. Their design enables excellent sealing while mitigating any adverse rotor dynamics. Brush seals rely heavily on a pressure differential across their bristle pack to force the bristles to press against the rotor. This phenomenon, commonly referred to as “blow-down,” enables brush seals to seal tightly at a variety of operating conditions and transient events. The phenomenon of blow-down is rather complex. There are frictional forces between each bristle and between the bristle tips and rotor, fluid flow through the bristle pack and beneath the bristle tips, dynamic excitation of individual fibers, and even dynamic excitation of the bristle pack as a whole. These factors are also functions of operating temperature, operating pressure, and rotor speed, thus making them extremely difficult to model for reliability and life predictions. To develop a better understanding of the physics behind blow-down as well as gain further insight into the general behavior of brush seals under different operating conditions, a brush seal incorporating fiber Bragg grating sensors was fabricated and experimentally tested at GE Global Research. Fiber Bragg grating technology and brush seal technology form a synergistic relationship. The fiber Bragg grating sensor cables can be inserted within the heart of a brush seal bristle pack to interrogate the seal’s health and operating environment without limiting or interfering with the sealing capability of the brush seal. As a consequence, thermal profiles and strain levels within a brush seal can be measured directly. Multifunctional fiber Bragg grating sensors are a platform for integral turbomachinery health prognostics. In this work, a Kevlar fiber brush seal was augmented with a series of fiber Bragg grating sensors designed to measure the thermal and the dynamic strain response of the seal. A series of tests were then performed to validate the proposed concept of using fiber Bragg grating sensors to interrogate the seal. The results of the experimental work performed indicate that the local thermal transients, bristle pack dynamics, and static strain can all be extracted using fiber Bragg grating sensors.
Lightweight Actuator Structure With SMA Honeycomb Core and CFRP Skins
Authors: Okabe Yoji , Sugiyama Hiroshi , Inayoshi Toru
Published: February 2010

The authors proposed a sandwich structure that consists of a shape memory alloy (SMA) honeycomb core and carbon fiber reinforced plastic (CFRP) skins as a shape-controllable structure. This actuator structure can be bent by heating, even though it is lightweight and has a moderate bending stiffness. First, unidirectional CFRP skins were bonded to the SMA honeycomb core made of thin SMA foils and a pre-shear-strain was applied to the SMA core. Then the ends of the upper and lower skins were fixed together to other cores. The length of the sandwich beam specimen was 18cm, and the weight was only 9.2g. When the specimen was heated, the beam was bent upward taking the form of a sigmoid curve and generated the sufficient actuation force. Then, when the specimen was cooled to the room temperature, the beam returned to the initial straight shape. Hence the two-way actuation is possible. This method has the better ability to bend skins with high in-plane stiffness, because the recovery shear force has the out-of-plane stress component and is applied uniformly to the skins from the inner core. Also the microscopic mechanism of this bending deformation could be clarified by a numerical simulation with the finite element method. Furthermore, this actuator structure has a possibility to be used as a member to suppress the resonance, because the natural frequency of the beam can be controlled owing to the increase in the elastic moduli of SMA by heating.
Fabrication Processes for Creating Micro Features in Thin Film NiTi Endovascular Grafts
Authors: Chun Youngjae , Levi Daniel S. , Mohanchandra K. P. , Carman Gregory P.
Published: February 2010

Micro features were created in thin film NiTi using a novel lift-off process to create an endovascular biomedical device. This manuscript describes fabrication problems with wet etching and introduces an effective way, named “Lift-off” process to solve undercut and nonuniform pattern issues. Two lift-off processes (i.e., lift-off I and II) are discussed. Lift-off I process has fracture issues and the film peels off the substrate due to high aspect ratio post structures. Lift-off II process use the film on the top of the Si substrate to fabricate various shape patterns (i.e., ellipse, diamond, circle, square, etc.) in the range of 5∼60μm. The lift-off II process shows smooth and well aligned micro patterns in thin film NiTi. In-vivo tests in swine were performed to evaluate the endothelial tissue growth through fabricated micro patterns. Angiography and SEM images show patency of the artery and a uniform endothelial layer covering the device without thromobosis.
Modelling Piezoelectric Actuation During Structural Flutter
Authors: Hariri M. , John S. , Trivailo P.
Published: February 2010

Aeroelasticity is a major concern in structural control. It results from the interaction between the air-stream and the structure. Wing flutter is a well known problem of the aero-elasticity. It occurs when the two lowest system eigenvalues (plunge and pitch motion) coalesce at a certain air speed known as the flutter speed. The increasing use of active material induced-strain actuation such as piezoelectric materials in the suppression of structural vibrations has seen its extension to wing flutter control. Higher flutter speed and hence, a wider operating envelope was achieved by delaying the coalescence of these two eigenvalues. This delay is obtained by adding more strain energy to the system as a result of the activation of the piezoelectric actuators. This paper models a simple beam under nominal aerodynamic loading conditions for the determination of analytically-derived onset of flutter speeds. Also shown in this paper, is the effect of orientation of actuated piezoelectric patches, on the shift of the flutter speed.
Beams and Plates Vibroacoustic Energy Diffusion Optimization by Mean of Distributed Shunted Piezoelectric Patches
Authors: Collet Manuel , Cunefare Ken A. , Ruzzene Massimo , Ouisse Morvan , Beck Benjamin , Airoldi L. , Casadei F.
Published: February 2010

The paper proposes a synthesis of different new methodologies for developing a distributed, integrated shunted piezo composite for beams and plates applications able to modify the structural vibro acoustical impedance of the passive supporting structure so as to absorb or reflect incidental power flow. This design implements tailored structural responses, through integrated passive and active features, and offers the potential for higher levels of vibration isolation as compared to current designs. Novel active and passive shunting configurations will be investigated to reduce vibrations such as distributed Resistance Inductance and Resistance with negative Capacitance circuits.
Design and Test of Adaptronic Joints With Quasi-Statical Clearance Adjustment in a Parallel Robot
Authors: Keimer Ralf , Pavlovic Nenad
Published: February 2010

Robots based on parallel kinematic structures feature low moved masses, allowing for better dynamic performance compared to serial mechanisms, eventually resulting in shorter cycle-times in handling and assembly. A side effect of this high dynamics is a higher level of vibration which has to be addressed in order to reach the full potential for short cycle-times. Some active measures for vibration-suppression were already presented previously. Another problem of parallel robots is a small ratio between working-space to installation-space. In order to overcome the problem (e.g. by changing configurations) specific components (e.g. joints) are needed. In this paper the use of an adaptronic joint with quasi-statical clearance adjustment integrated in the five-bar parallel structure is presented, addressing both vibration-suppression and configuration changes. Dimensioning of the adaptronic joint covers two aspects. Firstly increasing of friction up to blocking the joint in order to change configuration of the five-bar-structure. Secondly friction variation is used to optimize vibration damping and thus indirectly shorten cycle-times. The design and the test-setup for use of adaptronic joints in a parallel robot is presented.
Recovery and Residual Stress of Shape Memory Alloy Wires and Its Application
Authors: Choi Eunsoo , Nam Tae-hyun , Kim Man-Cheol , Hu Jong Wan , Cho Bak-Soon , Yoon Soon-Jong
Published: February 2010

Two kinds of shape memory alloy wires, NiTiNb and NiTi, are manufactured and pre-elongated during the manufacturing process. After fixing the pre-elongated wires, heating on the wires induces recovery stress on them. Several tests to measure the recovery stress are conducted with varying initial strains. Stress-reduction of the recovery stress is observed after the temperature of the wires is cold down; the remaining stress is called residual stress that is also measured. Also, this study measures the stress-strain curves of the SMA wires under the state that the residual stress is working. The tension behavior of the wires under residual stress is very unique. The NiTi is martensitic state at room temperature, thus a residual deformation remains after applying a large strain. However, under residual stress, the tensile behavior of the wire does not remain residual deformation and return to the original position by unloading; this looks like viscoelastic behavior. The residual stress of the SMA wires can be used as active confinement for civil structures and the behavior under residual stress can be used as like an elastic spring with hysteretic damping. This study confines concrete cylinders and reinforced concrete columns using the pre-elongated SMA wires to introduce an active confinement on them. The SMA wire jackets on concrete cylinders increase the peak strength and the ductility so much comparing to the plain concrete cylinders. Also, the wires on reinforced concrete columns increase the ductility so much without the reduction of flexural strength.
Mechanical Properties of Closed Cellular Materials Containing Polymer
Authors: Kishimoto Satoshi , Naito Kimiyoshi , Shimizu Toru , Yin Fuxing
Published: February 2010

Cellular materials have unique thermal, acoustic, damping and energy absorbing properties that can be combined with their structural efficiency. Therefore, many kinds of cellular materials have been developed and tested as energy absorbing and damping materials. Particularly, closed cellular materials are thought to have many favorable properties and applications. In this study, a metallic closed cellular materials containing polymer was fabricated by the penetrating polymer into metal foam. The aluminum and stainless steel foams were selected for the metal foam and epoxy resin and polyurethane resin were selected for the penetrated polymer. The mechanical and damping properties of this material were measured. The results of the compressive tests show that this material has different stress-strain curves among the specimens that include different materials in the cells. Also, These results show that this material has high-energy absorption. The internal friction of this material was measured and the result shows that the internal friction of this material is larger than that of pure aluminum closed cellular material without any polymer and change with increasing of temperature.
Semi-Active Vibration Isolation Using Fluidic Flexible Matrix Composite Mounts
Authors: Philen Michael
Published: February 2010

Variable modulus fluidic flexible matrix composites (F2MC) are investigated for vibration isolation mounts. The fluidic flexible matrix composites are based upon flexible matrix composite tubes containing a high bulk modulus internal fluid. By tailoring the fibers (orientation, number of layers, material, etc.) and the choice of the matrix material, the F2MC tube can obtain significant changes in stiffness by simply opening or closing an inlet valve to the tubes. The objective in this research is to investigate the F2MC variable modulus system for semi-active vibration isolation. A nonlinear analytical model of an isolation mount based on the F2MC tube with a proportional valve is developed. Analysis results indicate that the F2MC based isolation mount is effective for reducing the transmission from a disturbance source to a mass. Simulation studies demonstrate that the resonant frequencies and the damping can be controlled through simple valve control, which can be effective for vibration isolation.
Shape Memory Alloy Cables: Exploratory Experiments
Authors: Reedlunn Benjamin , Shaw John , Daly Samantha
Published: February 2010

Conventional structural cables (or wire ropes) are composed of steel wires helically wound into strands, which, in turn, are wound around a core. Cables made from NiTi shape memory alloy (SMA) wires are a new structural element with promising adaptive and enhanced structural properties for a broad range of applications. Potential advantages of this form include increased bending flexibility for spooling/packaging, better fatigue performance, energy absorption and damping, reduced thermal lag, redundancy, and significant design flexibility. Exploratory thermomechanical experiments were performed on a conventional cable construction: the right regular lay 7 × 7, consisting of 7 strands with 7 wires per strand. Uniaxial tension experiments characterize the cables’ sensitivity to strain rate, temperature, and lubrication. Experiments were also performed on individual strands and wires from the cable to study the hierarchical nature of the cable construction. Special attention was paid to the propagation of phase transformation fronts, similar to that seen previously in uniaxial tension of NiTi wire.
Using Multiscale Modeling to Predict Material Response of Polymeric Materials
Authors: Beblo Richard V. , Weiland Lisa Mauck
Published: February 2010

Presented is a multiscale modeling method applied to light activated shape memory polymers (LASMP). LASMP are a new class of shape memory polymer (SMP) being developed for applications where a thermal stimulus is undesired. Rotational Isomeric State (RIS) theory is used to build a molecular scale model of the polymer chain yielding a list of distances between the predicted cross-link locations, or r-values. The r-values are then fit with Johnson probability density functions and used with Boltzmann statistical mechanics to predict stress as a function of strain of the phantom network. Junction constraint theory is then used to calculate the stress contribution due to interactions with neighboring chains, resulting in previously unattainable numerically accurate Young’s modulus predictions based on the molecular formula of the polymer. The system is modular in nature and thus lends itself well to being adapted for specific applications. The results of the model are presented with experimental data for confirmation of correctness along with discussion of the potential of the model to be used to computationally adjust the chemical composition of LASMP to achieve specified material characteristics, greatly reducing the time and resources required for formula development.
Dielectric Elastomers for Direct Wind-to-Electricity Power Generation
Authors: Brochu Paul , Yuan Wei , Zhang Han , Pei Qibing
Published: February 2010

We present a universal dielectric elastomer energy generator that can be scaled to match the requirements of the energy source. The design couples mechanical energy directly into an out of plane deflection that deforms the film. Cycling the generator between high and low strain states while applying a bias electric field switches the device between high and low energy states; charge that is injected at low energy can then be extracted at a higher potential. We present an analysis of the energy generation capacity and mechanical stability of the device and demonstrate its scalability via a compact, low energy/low deflection device and a larger, higher energy device. We demonstrate the capability of generating approximately 40 mJ per cycle in a single layer device with an active elastomer volume of only 0.57 cm3 and a maximum observed energy conversion efficiency of over 55%. We use recently developed advances in dielectric elastomer technology including interpenetrating polymer network films and carbon nanotube electrodes to improve operational reliability and present comparative results that demonstrate an increase in lifetime by several orders of magnitude over prestrained VHB acrylic films with carbon grease electrodes.
A Review of Scaling and Performance Considerations for Articulating Technologies
Authors: Rau Andrew C. , Frecker Mary
Published: February 2010

Mechanisms with dexterous manipulation capabilities are needed for many applications at the meso scale (1–5 mm diameter with micro scale features). Scaling down larger designs has proven to be impossible in many cases, and the manipulation forces produced by most existing meso scale designs are notably insufficient for intended applications. A review of articulating mechanisms and manipulator technologies developed within the last decade is presented, and the potential for these technologies to be implemented at the meso scale is explored. The utility of these systems is analyzed in terms of two main performance metrics: maximum range of motion and force application. Determining the miniaturization potential and performance capabilities of these mechanisms has highlighted necessary improvements for current systems and provided insight on which system types are most likely to be effective on the meso scale.
Improvements to Phenomenologically Modeled Behavior of Shape Memory Alloys
Authors: Chang-Siu Evan , Lunenburg Janno , Tomizuka Masayoshi
Published: February 2010

This paper presents improvements to phenomenological modeled behavior of Shape Memory Alloys (SMAs). The specific type of SMA analyzed is the two-way SMA wire that contracts upon heating and extends upon cooling due to an internal phase transformation. To optimally design controllers for SMAs, the proposed model accounts for varying conditions such as input supply voltages and wire diameters and at the same time exhibits attractive numerical features such as differentiability and numerical stability. The paper also analyzes some of the shortcomings of the conventional nonlinear model. For example, the conventional model is not fully able to describe the initial contraction behavior due to an artificial dead zone. The proposed improvements include a new method of approximating the phase transformation behavior, incorporating a dynamic internal resistance, and implementing a heat transfer model that accounts for changing diameter and latent heat. Nonlinear system identification is performed to show the effectiveness of the improved model.
Dynamic Testing and Modeling of Magneto-Rheological Elastomers
Authors: Usman Muhammad , Jang Dong-Doo , Kim In-Ho , Jung Hyung-Jo , Koo Jeong-Hoi
Published: February 2010

This study presents the dynamic numerical model of magneto-rheological elastomers (MREs) along with the dynamic testing of the material under various loading conditions. Primarily the loading in shear mode is considered in this study because many civil engineering structures are subjected to shear loading. Experimental tests were carried out in order to characterize the dynamic behavior of MREs. A test setup was designed and fabricated to load the MRE samples in shear mode with varying magnetic fields. A series of shear tests of MRE samples were performed under various magnetic field values, amplitudes and frequencies of loading. The test results show that the material stiffness is increased with increasing magnetic field and loading frequency within the ranges of the magnetic field and exciting frequency considered in this work. Based on the experimental results, a dynamic model was developed to capture the dynamic behavior of the MRE.
Fluidic Composite Tuned Vibration Absorbers
Authors: Lotfi-Gaskarimahalle Amir , Scarborough Lloyd H. , Rahn Christopher D. , Smith Edward C.
Published: February 2010

This paper presents a novel Tuned Vibration Absorber (TVA) using Fluidic Flexible Matrix Composites (F2MC). Fiber reinforcement of the F2MC tube kinematically links the internal volume with axial strain. Coupling of a fluid-filled F2MC tube through a fluid port to a pressurized air accumulator can suppress primary mass forced vibration at the tuned absorber frequency. 3-D elasticity model for the tube and a lumped fluid mass develops a 4th-order model of an F2MC-mass system. The model provides a closed form isolation frequency that depends mainly on the port inertance, orifice flow coefficient, and the tube parameters. A small amount of viscous damping in the orifice increases the isolation bandwidth. With a fully closed orifice, the zero disappears and the system has a single resonant peak. Variations in the primary mass do not change the isolation frequency, making the F2MC TVA robust to mass variations. Experimental results validate the theoretical predictions in showing a tunable isolation frequency that is insensitive to primary mass variations, and a 94% reduction in forced vibration response relative to the closed-valve case.
Experiments and Modeling of the Magneto-Mechanical Response of Magnetic Shape Memory Alloys
Authors: Feigenbaum Heidi P. , Ciocanel Constantin
Published: February 2010

Magnetic shape memory alloys (MSMAs) are relatively new materials that exhibit a magnetic shape memory effect as a result of the rearrangement of martensitic variants under the influence of magnetic fields. Due to the MSMAs newness there is limited understanding of their magneto-mechanical behavior. This work presents experimental and modeling results of MSMAs for cases in which the material is loaded and unloaded in uniaxial compression in the presence of a constant magnetic field. The experiments are performed with the magnetic field applied perpendicular and at an angle to the mechanical loading axis. During the loading and unloading process, the evolution of the magnetic flux density is monitored to assess the potential of these materials for power harvesting applications. The modeling is based on the thermodynamic approach proposed by Kiefer and Lagoudas [1]. This model was modified and calibrated to reproduce material response under biaxial constant magnetic field and variable uni-axial compressive stress. Comparing the experimental and simulated results, one can recognize that further work is needed to improve the model.
Active Vibration Attenuation of Smart Material Systems With Model-Based and Nonlinear Multispectral Controllers
Authors: Kim Byeongil , Washington Gregory N. , Singh Rajendra
Published: February 2010

Many efforts have been concentrated on the active noise and vibration control with smart material systems. However, previous studies are limited to the reduction of a single frequency. Thus, more investigations are needed on multispectral control, which deals with multiple frequency components simultaneously. The main objective of this research is to establish a model-based and nonlinear multispectral controller by integrating the least mean squares (LMS) algorithm with model-based controllers. It is expected that multispectral signals are managed appropriately by model-based controls and nonlinear control covers the nonlinearity, model uncertainty, and other unexpected conditions. Performances of the proposed algorithms are validated with simulations and experiments in various cases. Novel methodologies developed in this research are expected to be employed for numerous applications in active vibration and noise control studies such as structural vibration attenuation, vehicle vibration and noise reduction, and active struts for aircrafts, helicopters, and other vibrating platforms.
Topology Optimization of Contact-Aided Compliant Cellular Mechanisms
Authors: Mehta Vipul , Frecker Mary , Lesieutre George A.
Published: February 2010

Applications of topology optimization to design compliant cellular mechanisms with and without a contact mechanism are presented in this paper. A two-step procedure is developed. For cellular structures without contact, the inverse homogenization method is employed using ‘Solid Isotropic Material with Penalization’ approach. The compliant mechanism is optimized to yield prescribed elasticity coefficients. The structure is also required to undergo a large overall strain without exceeding the allowable local strain. Results including a honeycomb similar structure and a negative Poisson’s ratio structure are presented. To implement a contact mechanism in the second step, the continuum model of a non-contact structure is converted into a frame model. Such a model is investigated for a contact pair which would reduce the maximum local strain. The scheme demonstrates that stress relief can be obtained.
Self-Charging Structures Using Piezoceramics and Thin-Film Batteries
Authors: Anton Steven R. , Erturk Alper , Kong Na , Ha Dong S. , Inman Daniel J.
Published: February 2010

This paper presents the investigation of a novel concept involving the combination of piezoelectrics and new thin-film battery technology to form multifunctional self-charging, load-bearing energy harvesting devices. The proposed self-charging structures contain both power generation and energy storage capabilities in a multilayered, composite platform consisting of active piezoceramic layers for scavenging energy, thin-film battery layers for storing scavenged energy, and a central metallic substrate layer. Several aspects of the design, modeling, fabrication, and evaluation of the self-charging structures are reviewed. A focus is placed on the evaluation of the load-bearing capabilities of the fabricated self-charging structures through both classical static failure testing as well as dynamic vibration failure testing.
Experimental Implementation of Negative Impedance Shunts on Periodic Structures
Authors: Beck Benjamin , Cunefare Kenneth A. , Ruzzene Massimo , Collet Manuel
Published: February 2010

Shunt damping of structures has been heavily researched, both passively and actively. Negative capacitance shunts actively control vibration on a structure and have been shown to obtain significant broadband suppression. The use of smaller piezoelectric patches, implemented in a periodic array, can alter the behavior of the control. Assorted shunt arrangements as well as circuit configurations will be investigated. Experimental results will be compared to theoretical predictions of shunt performance.
2-D Directional Phased Array Using Piezoelectric Paint to Detect Damages in Isotropic Plates
Authors: Yoo Byungseok , Pines Darryll J. , Purekar Ashish S.
Published: February 2010

Research interests in structural health monitoring have increased due to in-situ monitoring of structural components to detect damage. This can secure personal safety and reduce maintenance effort for mechanical systems. Conventional damage detection techniques known as nondestructive evaluation (NDE) have been conducted to detect and locate damaged area in structures. Ultrasonic testing, using ultrasonic transducers or electromagnetic acoustic transducers, is one of the most widespread NDE techniques, based on monitoring changes in acoustic impedance. Although the ultrasonic testing has advantages such as high sensitivity to discontinuities and evaluation accuracy, it requires testing surface accessibility, close location to the damaged area, and decent skill and training of technicians. In recent years, modal analysis techniques to capture changes of mode shapes and natural frequency of structures have been investigated. However, the technique is relatively insensitive to small amount of damage such as an initial crack which can rapidly grow in structures under cyclic loadings. In addition, structural health monitoring based on guided waves has become a preferred damage detection approach due to its quick examination of large area and simple inspection mechanisms. There are many techniques used to analyze sensor signals to bring out features related to damage. A phased array coupled with the guided wave approach has been introduced to effectively analyze complicated guided wave signals. Phased array theory as a directional filtering technique is usually used in antenna applications. By using phased array signal processing, virtually steering the array to find the largest response of source, the desired signal component can be enhanced while unwanted information is eliminated.
Damage Characterization of Composite Wing Subjected to Impact Loading: An Experimental Study
Authors: Hiche Cristobal , Coelho Clyde K. , Moncada Albert , Yekani Fard Masoud , Chattopadhyay Aditi
Published: February 2010

Damage on woven composites is a phenomenon that is difficult to characterize due to complex weave geometry. A woven composite wing structure adds to the complexity of characterizing damage through Fiber Bragg Grating (FBG) sensors. The present paper studies the FBG response and damage characterization of foam core and hollow composite wings. Plain and twill weave wings were manufactured and subjected to low energy (52.5J) and high energy (150J) impacts. Damage was assessed using FBG sensors, flash thermography, and visual inspection of the wings. Two FBG sensors were placed along the chord length and the spanwise direction at equal distances from the impact site to measure the axial strain as a function of time. The main failure modes of foam core wings were fiber breakage and foam crushing for high energy impacts, while core crushing and delamination between the core and the composite wing was found for low energy impacts. The hollow wings had a significant reduction in stiffness, resulting in a ripple effect where the wing would go into tension, then compression. This phenomenon varied depending on the location of the sensors on the wing. Although the impact zone was near the middle of the chord length of the wing, the resulting stress has caused large damage at the leading edge and significant debonding at the trailing edge of the hollow wing. An FE model was created to validate the experimental results and showed good correlation between the high stress areas in the model, the FBG response, and the damage sites on the wing.
Low-Power Control Strategies for Thin-Film Piezoelectric Micro-Robotic Actuators
Authors: Oldham Kenn , Edamana Biju , Hahn Bongsu
Published: February 2010

Three low-power control strategies for piezoelectric actuators based on on-off or related switching control approaches are described. These strategies are targeted for leg actuation in autonomous micro-robots, where available power is severely constrained, below the power level that more conventional analog or pulse-width-modulation drive circuitry, switching rates, and/or sampling frequency would require. The first strategy optimizes the sequence of ‘on’ and ‘off’ transitions over a finite number of steps to minimize actuator energy while ensuring that a system moves to a desired set of final states. Transitions are selected via convex optimization by binary programming. The second strategy optimizes a set of commands to a drive circuit including charge recovery components to improve both power consumption and positioning accuracy, with optimal transitions chosen using mixed integer quadratic programming. The third strategy is proposed to account for modeling error using step to step adaptation of input sequences with limited sensor measurements.
Electro-Mechanical Analysis of a Biased Dielectric EAP Actuator
Authors: York Alexander , Hodgins Micah , Seelecke Stefan
Published: February 2010

Dielectric Electro-Active Polymers (DEAP’s) can achieve substantial deformation (>300% strain) while, compared to their ionic counterparts, sustaining large forces. This makes them attractive for various actuation and sensing applications such as light weight and energy efficient valve and pumping systems. This paper provides a systematic experimental investigation of the quasi-static and dynamic electro-mechanical properties of a commercially available dielectric EAP actuator. In order to completely characterize the fully coupled behavior force vs. displacement measurements at various constant voltages and force vs. voltage measurements at various fixed displacements are conducted. The experiments are conducted with a particular focus on the hysteretic and rate-dependent material behavior. These experiments provide insight into the viscoelastic and electrostatic behavior inherent in DEAP material. Typical operating conditions of the actuator require it to have a biased force, such as a spring. Experiments are conducted to observe the actuators performance under these conditions. The force and stroke capabilities are investigated while the actuator is loaded with different springs and at a variety of pre-stretch levels. The resulting behavior of the spring loaded actuator is then correlated to the viscoelastic effects observed during the electro-mechanical characterization.
Piezoelectric Controlled Pulsed Microjet Actuation
Authors: Liu Fei , Hogue Josh , Oates William , Solomon John , Alvi Farrukh
Published: February 2010

A piezohydraulic actuator has been designed and tested for broadband flow control of a microjet actuator. This actuator is under development to understand fundamental flow characteristics near a pulsed flow microjet for active flow control on a number of aircraft structures including impinging jets, cavities, and jet inlets. Recent research has shown substantial reductions in flow separation and noise reduction using steady blowing microjets. This approach often leads to inefficiencies due to excessive mass flux that is typically bled off of an aircraft compressor. Reductions in mass flux without performance losses are desired by actively pulsing the microjet. A piezohydraulic actuator design is presented to investigate this concept. The actuator includes a piezoelectric stack actuator and hydraulic circuit to achieve sufficient displacement amplification to throttle a 400 μm diameter microjet. This system is shown to provide broadband pulsed flow actuation up to 900 Hz. Key parameters contributing to dynamic actuation are shown to include hydraulic fluid behavior, biased microjet air pressure, and voltage inputs to the stack actuator.
On the Use of the Posterior Crame´r-Rao Lower Bound for Damage Estimation in Structural Health Management
Authors: Zhang Jun Jason , Zhou Wenfan , Kovvali Narayan , Papandreou-Suppappola Antonia , Chattopadhyay Aditi
Published: February 2010

The use of the posterior Crame´r-Rao lower bound (PCRLB) as a lower bound for the mean-squared estimation error (MSEE) of progressive damage is investigated. The estimation problem is formulated in terms of a stochastic dynamic system model that describes the random evolution of damage and provides measurement uncertainty. Based on whether the system is linear or nonlinear, sequential Monte Carlo techniques are used to approximate the posterior probability density function and thus obtain the damage state estimate. The resulting MSEE is compared to the lower bound offered by the PCRLB that is obtained from the implied state transition probability density function and the measurement likelihood function. The progressive estimation results and the PCRLB are demonstrated for fatigue crack estimation in an aluminum compact-tension (CT) sample subjected to variable-amplitude loading.
Multiple Resonances Piezoelectric Energy Harvesting Generator
Authors: Qi Shaofan , Shuttleworth Roger , Oyadiji S. Olutunde
Published: February 2010

Energy harvesting is the process of converting low level ambient energy into usable electrical energy, so that remote electronic instruments can be powered without the need for batteries or other supplies. Piezoelectric material has the ability to convert mechanical energy into electrical energy, and cantilever type harvesters using this material are being intensely investigated. The typical single cantilever energy harvester design has a limited bandwidth, and is restricted in ability for converting environmental vibration occurring over a wide range of frequencies. A multiple cantilever piezoelectric generator that works over a range of frequencies, yet has only one Piezo element, is being investigated. The design and testing of this novel harvester is described.
ON THE LONG TIME BEHAVIOR OF FREE STOCHASTIC SCHRÖDINGER EVOLUTIONS
Authors: BASSI ANGELO , DÜRR DETLEF , KOLB MARTIN
Published: February 2010

We discuss the time evolution of the wave function which is the solution of a stochastic Schrödinger equation describing the dynamics of a free quantum particle subject to spontaneous localizations in space. We prove global existence and uniqueness of solutions. We observe that there exist three time regimes: the collapse regime, the classical regime and the diffusive regime. Concerning the latter, we assert that the general solution converges almost surely to a diffusing Gaussian wave function having a finite spread both in position as well as in momentum. This paper corrects and completes earlier works on this issue.
DEFINITION AND APPLICATIONS OF THE ASCENT-PROBABILITY DISTRIBUTION IN ONE-DIMENSIONAL MAPS
Authors: LIVADIOTIS GEORGE
Published: February 2010

This paper introduces the discrete distribution of ascent probabilities [Formula: see text], generalizing the concept of rotation number ω, already being defined in one-dimensional unimodal maps. The map domain is partitioned into subintervals [Formula: see text], each one containing orbits with their route characterized by a specific number of n successive ascents before a descent occurs. Then, Pnis defined as the probability to have an orbit performing n successive ascents, and equals the portion of the invariant measure within In. The rotation number is found to be equal to ω = P0= P1, that is the portion of invariant measure within I0or I1. Some significant applications of this relation concern (i) the rotation number dependence on the nonlinear parameter p, (ii) the analytical derivation of the rotation number, given the invariant density explicit expression, (iii) an easy computation of the rotation number that characterizes a periodic window. Moreover, the dependence of the ascent probabilities on the nonlinear parameter p is examined. Emphasis is placed on the discrete distribution of the ascent probabilities [Formula: see text] within the chaotic zone. A particular set of nonlinear parameter values [Formula: see text] is affiliated to the concept of ascent probabilities: For each probability Pn, n = 0, 1, 2, …, there is a lower limit of the nonlinear parameter values, p(n+1), so that, Pn= 0 ∀ p ≤ p(n+1). The set [Formula: see text] is analytically determined, and its specific arrangement in the chaotic zone is studied. Finally, the "u-S-P equivalence" between the triplet of the set of the fixed point and its preimages, [Formula: see text], of the invariant density S, and of the set of the ascents probabilities, [Formula: see text], is formulated. In particular, we show that each component of this triplet can be estimated whenever the other two components are given. Applications in the case of Logistic map are thoroughly examined.
ZETA FUNCTIONS FOR HIGHER-DIMENSIONAL SHIFTS OF FINITE TYPE
Authors: HU WEN-GUEI , LIN SONG-SUN
Published: February 2010

This work investigates zeta functions for d-dimensional shifts of finite type, d ≥ 3. First, the three-dimensional case is studied. The trace operator Ta1,a2;b12and rotational matrices Rx;a1,a2;b12and Ry;a1,a2;b12are introduced to study [Formula: see text] -periodic patterns. The rotational symmetry of Ta1,a2;b12induces the reduced trace operator τa1,a2;b12and then the associated zeta function ζa1,a2;b12= ( det (I-sa1a2τa1,a2;b12))-1. The zeta function ζ is then expressed as [Formula: see text], a reciprocal of an infinite product of polynomials. The results hold for any inclined coordinates, determined by unimodular transformation in GL3(ℤ). Hence, a family of zeta functions exists with the same integer coefficients in their Taylor series expansions at the origin, and yields a family of identities in number theory. The methods used herein are also valid for d-dimensional cases, d ≥ 4, and can be applied to thermodynamic zeta functions for the three-dimensional Ising model with finite range interactions.
CHAOS OF DYNAMICAL SYSTEMS ON GENERAL TIME DOMAINS
Authors: BOYARSKY ABRAHAM , GÓRA PAWEŁ
Published: February 2010

We consider dynamical systems on time domains that alternate between continuous time intervals and discrete time intervals. The dynamics on the continuous portions may represent species growth when there is population overlap and are governed by differential or partial differential equations. The dynamics across the discrete time intervals are governed by a chaotic map and may represent population growth which is seasonal. We study the long term dynamics of this combined system. We study various conditions on the continuous time dynamics and discrete time dynamics that produce chaos and alternatively nonchaos for the combined system. When the discrete system alone is chaotic we provide a condition on the continuous dynamical component such that the combined system behaves chaotically. We also provide a condition that ensures that if the discrete time system has an absolutely continuous invariant measure so will the combined system. An example based on the logistic continuous time and logistic discrete time component is worked out.
A GENERALIZED 3-D FOUR-WING CHAOTIC SYSTEM
Authors: WANG ZENGHUI , QI GUOYUAN , SUN YANXIA , VAN WYK MICHAËL ANTONIE , VAN WYK BAREND JACOBUS
Published: February 2010

In this paper, several three-dimensional (3-D) four-wing smooth quadratic autonomous chaotic systems are analyzed. It is shown that these systems have similar features. A simpler and generalized 3-D continuous autonomous system is proposed based on these features which can be extended to existing 3-D four-wing chaotic systems by adding some linear and/or quadratic terms. The new system can generate a four-wing chaotic attractor with simple topological structures. Some basic properties of the new system is analyzed by means of Lyapunov exponents, bifurcation diagrams and Poincaré maps. Phase diagrams show that the equilibria are related to the existence of multiple wings.
CONTINUOUS FIRST ORDER LOGIC FOR UNBOUNDED METRIC STRUCTURES
Authors: YAACOV ITAÏ BEN
Published: February 2010

We present an adaptation of continuous first order logic to unbounded metric structures. This has the advantage of being closer in spirit to C. Ward Henson's logic for Banach space structures than the unit ball approach (which has been the common approach so far to Banach space structures in continuous logic), as well as of applying in situations where the unit ball approach does not apply (i.e. when the unit ball is not a definable set).

We also introduce the process of single point emboundment (closely related to the topological single point compactification), allowing to bring unbounded structures back into the setting of bounded continuous first order logic.

Together with results from [4] regarding perturbations of bounded metric structures, we prove a Ryll–Nardzewski style characterization of theories of Banach spaces which are separably categorical up to small perturbation of the norm. This last result is motivated by an unpublished result of Henson.