bluuebunny/crossref_metadata_2025 huggingface dataset:
Wavelet-Based Multi-Fractal Spectrum for Machine Defect Identification
Authors: Yan Ruqiang , Gao Robert X.
Published: May 2009

This paper presents a technique based on the wavelet-based multi-fractal singularity spectrum for rotary machine defect identification. Specifically, vibration signals measured by accelerometers are decomposed into a series of scales, with each scale corresponding to a sub-frequency band, by means of the continuous wavelet transform (CWT). The multi-fractal spectrum is then calculated from the wavelet coefficient modulus-maxima lines. Comparing to other signal processing techniques, the inherently flexible time-frequency resolution property of the wavelet transform characterizes the scaling properties of the multi-fractal spectrum, thus is more effective in singularity identification. Experimental studies on rolling bearings and a gearbox have shown that the presented technique provides an effective tool for defect identification.
A Wide Frequency Range Tunable Vibration Energy Harvesting Device Using Magnetically Induced Stiffness
Authors: Challa Vinod R. , Prasad M. G. , Shi Yong , Fisher Frank
Published: May 2009

Although wireless sensors show extensive promise across a wide range of applications, one requirement necessary for widespread deployment is a suitable long-life power source. Self sustainable powering techniques allow for efficient use of these sensors, whose potential life is usually longer than that of the power sources. Vibration energy harvesting techniques offer to have the potential to be employed in powering these devices. The most important requirement of vibration energy harvesting devices is that they be in resonance to harvest energy efficiently. Most of the vibration energy harvesting devices built, irrespective of the mechanism involved, are based on a single resonance frequency, with the efficiency of these devices is very much limited to that specific frequency. In this paper, a frequency tunable mechanism is presented which allows the energy harvesting device to generate power over a wide range of frequencies. External magnetic forces have been used to induce additional stiffness which is variable depending on the distance between the magnets. This technique allowed us to tune the resonance frequencies to have +/− 20% of the original (untuned) resonant frequency. Further, the device can be tuned to higher and lower frequency with respect to the untuned resonance frequency by using attractive and repulsive magnetic forces, respectively. As a proof-of-concept, a piezoelectric cantilever-based energy harvesting device with a natural frequency of 26 Hz was fabricated whose resonance frequency was successfully tuned over a frequency range of 22 Hz to 32 Hz, enabling a continuous power output of 240 μW to 280 μW over the entire frequency range. The tuning mechanism can be employed to any vibrating structure.
The Influence of Non-Traditional Composite Laminates on Open-Hole Tension Strength
Authors: Stone D. P. , Smith L. V. , Kothidar A.
Published: May 2009

Composite materials are commonly used in applications with a need for increased strength or reduced weight. The composite structure is often attached using mechanical fasteners, even in cases where adhesive bonding is prevalent. The strength of the composite is typically reduced by large factors in the presence of these stress risers. The following considers the sensitivity of non-traditional layups to stress concentrations in the form of open-hole tension. The effects are described numerically and experimentally using finite element analysis and spatial strain measurements, respectively. Improvements in strength exceeding 10% from this preliminary exercise suggest that tailoring fiber orientations may have potential to minimize the effect of stress concentrations. Consideration of the strain field in the vicinity of the hole showed evidence of damage evolution within approximately 25% UTS for many of the laminates. The maximum strain failure criterion was able to describe the onset of damage or yield for the laminates considered here.
Condition Monitoring of Operating Spindle Based on Stochastic Subspace Identification
Authors: Gao Robert X. , Yan Ruqiang , Zhang Li , Lee Kang B.
Published: May 2009

Accurate identification of spindle modal parameters is critical to realizing a new generation of “smart” machine tools with built-in self-diagnosis capability. This paper describes a new approach to extracting spindle modal parameters from the output measured during operation, based upon stochastic subspace identification. The technique accounts for structural dynamic behavior, associated with the spindle rotation, that is not present when the spindle remains stationary. Experimental results conducted on a customized spindle test bed under different speed-load combinations confirm the effectiveness of the new technique for on-line spindle condition monitoring.
Development of a Laboratory Equipment for the Analysis of Mechanisms
Authors: Correa Julio C. , Va´squez Rafael E. , Va´squez Juan M. , Tamayo Sergio
Published: May 2009

This work addresses the development of an equipment for the analysis of one-degree-of-freedom planar mechanisms, used for teaching in the areas of mechanical design and dynamic systems and control at the Universidad Pontificia Bolivariana. The prototype was developed to teach fundamental topics of the Mechanical Engineering curriculum: mechanics of machines and motion control. The prototype consists of a mechanical frame with three modules: a power transmission train, a four-bar planar nechanisms module and a planar cam-follower module. The equipment has been instrumented to get measurements of the main variables associated with motion: position, velocity, acceleration, force and torque. Therefore, experimental measures can be contrasted with theoretical results in order to facilitate the students to get concepts related to the mechanics of machines in a more interactive and real way. The equipment is also useful in research projects where different kinds of state observers and motion controllers can be tested.
Microfluidics Supporting an Optical Instrument for Multimodal Single Cell Biomechanics
Authors: Ne`ve Nathalie , Lingwood James K. , Winn Shelley R. , Tretheway Derek C. , Kohles Sean S.
Published: May 2009

Interfacing a novel micron-resolution particle image velocimetry and dual optical tweezers system (μPIVOT) with microfluidics facilitates the exposure of an individual biologic cell to a wide range of static and dynamic mechanical stress conditions. Single cells can be manipulated in a sequence of mechanical stresses (hydrostatic pressure variations, tension or compression, as well as shear and extensional fluid induced stresses) while measuring cellular deformation. The unique multimodal load states enable a new realm of single cell biomechanical studies.
A Mechanical Model for Cytoskeleton and Membrane Interactions in Neuronal Growth Cones
Authors: Allen Kathleen B. , Layton Bradley
Published: May 2009

Revealing the molecular events of neuronal growth is critical to obtaining a deeper understanding of nervous system development, neural injury response, and neural tissue engineering. Central to this is the need to understand the mechanical interactions among the cytoskeleton and the cell membrane, and how these interactions affect the overall growth mechanics of neurons. Using ANSYS, the force produced by a cytoskeletal protein acting against a deformable membrane was modeled, and the deformation, stress, and strain were computed for the membrane. Parameters to represent the flexural rigidities of the well-studied actin and tubulin cytoskeletal proteins as well as the mechanical properties of neuronal growth cones were used in the simulations. Our model predicts that while a single actin filament is able to produce a force sufficient to cause membrane deformation and thus growth, it is also possible that the actin filament may cause the membrane to rupture, if a dilatational strain of more than 3–4% occurs. Additionally, neurotoxins or pharmaceuticals that alter the mechanical properties of either the cell membrane or cytoskeletal proteins could disrupt the balance of forces required for neurons to not only push out and grow correctly, but also to sustain their shapes as high-aspect-ratio structures once growth is complete. Understanding how cytoskeletal elements have coevolved mechanically with their respective cell membranes will yield insights into the events that gave rise to the sequences and quaternary structures of the major cytoskeletal elements.
Parametric Analysis of Damage Detection Using Piezoelectric Transducer and Lamb Wave Approach
Authors: Wang X. , Li Y. , Tang J.
Published: May 2009

Structural damage detection using piezoelectric transducers and the Lamb wave approach has been under intensive investigations. A commonly-pursued topic is the selection of system parameters such that the detection performance can be maximized. Previous studies have indicated that the excitation center frequency plays a critical role and suggested use the “sweet spot” frequency. This paper provides a comprehensive parametric analysis on Lamb wave propagation excited and sensed by piezoelectric transducers, where the “sweet spot” phenomenon is systematically explored by using correlated analytical, numerical, and experimental analyses. The analyses results can be used as guidelines for damage detection research.
Modeling the Size and Interface Effects in Thin Metal Film-Substrate Systems Using the Strain Gradient Plasticity
Authors: Abu Al-Rub Rashid K. , Voyiadjis George Z.
Published: May 2009

It is well-known by now through intensive experimental studies that have been performed at the micron and nano length scales that the material mechanical properties strongly depend on the size of specimen and the microstructural features. The classical continuum mechanics fails to address this problem since no material length scale exists in its constitutive description. On the other hand, nonlocal continuum theories of integral-type or gradient-type have been to a good extent successful in predicting this type of size effect. However, they fail to predict size effects when strain gradients are minimal such as the Hall-Petch effect. This problem is the main focus of this work. The effect of the material microstructural interfaces increase as the surface-to-volume ratio increases. It is shown in this work that interfacial effects have a profound impact on the scale-dependent plasticity encountered in micro/nano-systems. This is achieved by developing a higher-order gradient-dependent plasticity theory that enforces microscopic boundary conditions at interfaces and free surfaces. These nonstandard boundary conditions relate the microtraction stress at the interface to the interfacial energy. Application of the proposed framework to size effects in shear loading of a thin-film on an elastic substrate is presented. Three film-interface conditions are modeled: soft, intermediate, and hard interfaces.
2D Parametric Study of Viscous Fingering
Authors: Medici Ezequiel , Allen Jeffrey
Published: May 2009

When a low viscosity fluid is forced to displace another immiscible fluid with a higher viscosity inside of a porous media a particular flow structure called viscous fingering is generated. The study of that particular flow structure has special relevance in understanding the diffusion process and the transport characteristics of a fluid inside of a porous media. This work examined the effect of two fundamental parameters like the injected volumetric flow rate and the domain aspect ratio over the viscous fingering pattern. In order to perform that parametric study, a set of numerical simulations using the 2D network simulator model are used. A large viscosity ratio between the injected and displaced fluid is used to focus the work only on the unstable behavior state.
Performances of Silicon Micro-Flow-Passage Cold Plates From Single-Phase to Two-Phase With Water and HFE-7100 as Working Fluids
Authors: Tong Tao , Chang Je-Young , Devasenathipathy Shankar , Dirner John , Prstic Suzana , Prasher Ravi
Published: May 2009

Two-phase (phase-change) microchannel (MC) system is a promising technology for achieving enhanced heat removal for highdensity electronics. Yet phase-change studies in MCs with hydraulic diameters on the order of several hundred micrometers or smaller have been inconclusive. Most of earlier studies involved one specific channel design and one type of working fluid. It is thus difficult to make fair comparisons across various experimental works toward recommending the best design option for real applications under specific operating conditions. In the current work, flow boiling experiments were conducted for MC cold plates with channel widths ranging from 61 μm to 330 μm and channel height ∼ 300 μm (hydraulic diameters from ∼ 100 μm to ∼ 337 μm) and a pin-fin array cold plate with fin size and inter-spacing ∼ 150 μm. Two working fluids, deionized water at sub-atmospheric pressure (∼ 25 kPa to 45 kPa) and HFE-7100 at ambient pressure, were tested respectively. High-speed visualization facilities were employed to help understand the rapid phase-change processes inside the flow passages. Pressure drop and heat transfer characteristics of the microchannel cold plates under various heat flux and flow rate conditions were recorded and analyzed as well as boiling fluctuations. Detailed visualization results will be presented in a separate paper [Tong et al., IMECE2007-42028].
High-Speed Visualization of Phase-Change Processes in Silicon Microchannels With Water and HFE-7100 as Working Fluids
Authors: Tong Tao , Chang Je-Young , Devasenathipathy Shankar , Dirner John , Prstic Suzana , Prasher Ravi
Published: May 2009

Pumped-loop liquid-cooled system involving phase-change (two-phase) is a promising technology for removing excess heat from high-density electronics. However, no consensus has been reached so far regarding the hydraulic and heat transfer characteristics of such two-phase (TP) micro flow passages with hydraulic diameters (Dh) on the order of several hundred micrometers or smaller. In a previous paper [Tong et al., ASME IMECE2007-42027], we reported flow boiling experiments for several microchannel (MC) cold plate devices with channel widths ranging from 61 to 340 μm (hydraulic diameters from 100 to 337 μm) and a micro-pin-fin array (μPFA) device. Two working fluids, deionized water and HFE-7100, were tested respectively. In this paper, we focus on the highspeed visualization study of the phase-change phenomena inside the MC cold plates. Features of the major TP flow patterns are discussed for each MC unit with varying sizes and with the two different working fluids. From direct visualization, we report the liquid thin film evaporation rate for the pulsating annular flow regions in MCs. The observed liquid film evaporation rate is much higher than previous predictions/assumptions from a steady-state annular flow picture as assumed by most theoretical investigations so far. The local transient heat flux is thus much higher than the average heat flux provided, especially for water and small hydraulic diameter MCs.
A Review of Proper Modeling Techniques
Authors: Ersal Tulga , Fathy Hosam K. , Louca Loucas S. , Rideout D. Geoff , Stein Jeffrey L.
Published: May 2009

A dynamic system model is proper for a particular application if it achieves the accuracy required by the application with minimal complexity. Because model complexity often — but not always — correlates inversely with simulation speed, a proper model is often alternatively defined as one balancing accuracy and speed. Such balancing is crucial for applications requiring both model accuracy and speed, such as system optimization and hardware-in-the-loop simulation. Furthermore, the simplicity of proper models conduces to control system analysis and design, particularly given the ease with which lower-order controllers can be implemented compared to higher-order ones. The literature presents many algorithms for deducing proper models from simpler ones or reducing complex models until they become proper. This paper presents a broad survey of the proper modeling literature. To simplify the presentation, the algorithms are classified into frequency-, projection-, optimization-, and energy-based, based on the metrics they use for obtaining proper models. The basic mechanics, properties, advantages and limitations of the methods are discussed, along with the relationships between different techniques, with the intention of helping the modeler to identify the most suitable proper modeling method for their application.
Property Libraries for Working Fluids for Calculating Heat Cycles, Turbines, Heat Pumps, and Refrigeration Processes
Authors: Kretzschmar H.-J. , Stoecker I. , Jaehne I. , Herrmann S. , Kunick M.
Published: May 2009

The program libraries developed for calculating the thermophysical properties of working fluids can be used by engineers who routinely calculate heat cycles, steam or gas turbines, boilers, heat pumps, or other thermal or refrigeration processes. Thermodynamic properties, transport properties, derivatives, and inverse functions can be calculated. Today gas turbines are being developed for higher and higher temperatures and pressures. However, the calculation of the combustion gas as an ideal gas mixture will be inaccurate at high pressures. For this reason, a property library has been developed for humid combustion gases calculated as an ideal mixture of real fluids. The advanced adiabatic compressed air energy storage technology requires very accurate algorithms for the thermodynamic and transport properties of humid air at low temperatures and high pressures. At these parameters, humid air cannot be calculated as an ideal gas mixture. For this reason, a property library with real gas algorithms has been developed. The following properly libraries will be presented: LibHuGas for humid combustion gas mixtures at high pressures calculated as an ideal mixture of real fluids. The library also includes mixtures of steam and carbon dioxide. The dissociation at high temperatures, the poynting effect, and the condensation of water are considered as well. LibHuAir for humid air at high pressures calculated as an ideal mixture of the real fluids dry air, steam and water or ice. The dissociation at high temperatures and the poynting effect are taken into consideration. LibAmWa for mixtures of ammonia and water in the Kalina cycle and in absorption refrigeration processes. LibWaLi for mixtures of water and lithium bromide in absorption refrigeration processes. LibldGas for combustion gas mixtures calculated as an ideal mixture of ideal gases using the VDI-Guideline 4670. LibIdAir for humid air calculated as an ideal mixture of the ideal gases dry air and steam using the VDI-Guideline 4670. LibIdGasMix for 25 ideal gases and their mixtures. LibIF97 for water and steam calculated from the Industrial Formulation IAPWS-IF97 and all new backward equations of the four supplementary releases adopted by IAPWS between 2001 and 2005. LibCO2 for carbon dioxide. LibNH3 for ammonia. LibR134a for the refrigerant R134a. LibPropane for propane. LibButane_Iso and LibButane_n for Iso- and n-butane. LibHe for helium. LibH2 for hydrogen. The libraries contain the most accurate algorithms for thermodynamic and transport properties. The following software solutions will also be presented: - DLLs for Windows® applications. - Add-In FluidEXL for Excel®. - Add-On FluidLAB for MATLAB®. - Add-On FluidMAT for Mathcad®. - Properly libraries for HP, TI, and Casio pocket calculators. Student versions of all programs are available.
Simulation-Based Analysis of 3D Flow Inside a Micropump With Passive Valves
Authors: Tabak A. F. , Solak A. , Erdem E. Y. , Akcan C. , Yesilyurt S.
Published: May 2009

It is expected that chemical, biological and environmental applications of microdevices will increase with new developments in micromachining techniques. In this work, a micropump design that utilizes passive valves and an actuated diaphragm is presented. The flow rate is controlled by the deflection and the frequency of the diaphragm’s displacement. Passive valves are used for directing the flow. Poiseuille flow analogy is used to generate the equivalent pressure drop and flow rate via modifying the viscosity in the valve-channel in order to replace the variation of the channel width due to valve movement. Overall flow in the micropump is governed by three-dimensional time-dependent Navier Stokes equations. Deformation of the domain due to moving boundaries that coincide with the diaphragm motion is handled with the arbitrary Lagrangian-Eulerian method. Flow rate, hydraulic power and the efficiency of the micropump are obtained with respect to driving frequency and displacement of the diaphragm.
Effect of Ammonia Treatment on Pt Catalyst Used for Low-Temperature Reaction
Authors: Hyland Patrick , Lee Jungmin , Lin Chien Shung , Ahn Jeongmin , Ronney Paul D.
Published: May 2009

Platinum based catalysts are well known as the most active ones among noble metals for oxidation of hydrocarbons as well as hydrogen. Microcombustion experiments using bare Pt foil catalyst have shown that hydrocarbon fuels (e.g. propane) can be oxidized at low-temperature (< 60 °C) and ignited (< 90 °C) by treating the catalyst surface by burning propane-air mixtures with ∼ 5% of the propane replaced by ammonia for half an hour. This NH3 pre-treatment etches the catalyst surface and creates surface structures on the scale of few μms, completely unlike those without NH3 treatment. This change in structure with NH3 treatment is noteworthy in that it increases the performance of the catalyst by a factor of 3, but only for low Re, corresponding to conditions with low maximum reaction temperatures characteristic of microcombustors. However, no similar such low-temperatures were found without NH3 pre-treatment, even for catalytic reactions. This is not merely a surface area effect, since increasing bulk catalyst area had almost no effect on combustion performance. Nevertheless, it may be possible to further extend reaction and ignition to even lower temperatures by examining alternative hydrocarbon fuels and catalysts. Self-starting fuels and catalysts are highly desirable, especially for the micro-combustors used for MEMS (Micro Electro-Mechanical Systems) power generators, because it would eliminate the need for glow plugs, supplemental battery, electronics, etc. associated with active ignition systems.
Approximate Dynamic Similitude in Energetic Multi-Domain Systems: Quantification and Use in Multiobjective Scaling
Authors: Kittirungsi Burit , Fathy Hosam K. , Stein Jeffrey L.
Published: May 2009

This paper examines the scaling of an energetic system to meet new design requirements while satisfying dynamic similitude. The literature defines such similitude discretely, in terms of whether the scaled design satisfies monomial scaling laws derived via the Pi Theorem (or its group-theoretic extensions). Previous work adds flexibility to this approach by using activity analysis to (i) assess the relative importance of scaling laws and (ii) neglect less important ones. Difficulties still arise when scaling laws deemed important cannot be followed exactly (e.g., due to design constraints), thus precluding exact similitude. To address these difficulties, this paper proposes the first continuous measure of approximate similitude, namely, the activity-weighted deviation of a system design from exact similitude. The paper then presents a multiobjective scaling framework that trades approximate similitude off versus other scaling requirements and constraints. Two examples, pertaining to quarter-car and fuel cell air supply scaling, demonstrate the proposed approach.
Wetting Effects on Two-Phase Flow in a Microchannel
Authors: Herescu Alexandru , Allen Jeffrey S.
Published: May 2009

In the recent years there has been an increasing interest in the study of two-phase flows in low Bond number systems (where capillary forces are important relative to gravitational forces). Such systems include capillary tubes and microchannels as well as the gas flow channels of a PEM fuel cell. At the capillary scale, surface tension forces play an important role in two-phase flow regime transitions, pointing out the need to take into account the geometry of the cross section and the surface properties (wettability). Surface tension is generally considered in flow transitions, but the wetting properties of the fluid-surface material pairs (contact angle) are rarely given any importance. The researchers investigating two-phase flows should take extreme care when choosing the material of the test sections, as the flow morphology and the the pressure drop accordingly can vary widely with contact angle. In order to show these morphological changes high speed visualization experiments of air-water flow through 500 μm square and round microchannels were conducted. For the round channels, contact angles of less than 20° (wetting) and 105° (non-wetting) were investigated. For the square section, things are complicated by the presence of the corners. According to the Concus-Finn criterion, the liquid will wick into (wet) the corner if the contact angle is less then 45°, or will de-wet the corner if the contact angle is above 45°. A new case not previously mentioned in the literature arises for a contact angle of 45° ≤ θ ≤ 90°, for which the liquid is wetting the walls but dewetting the corners. Three contact angles of less than 20°, 80° and 105° are considered to investigate the possible morphologies in the square geometry. Images aquired with a high speed camera depicting the different flow morphologies that exist at the same air-water flow rates for each of the considered contact angle and geometry are presented.
Resonance Induced by Bounded Noise
Authors: Zhu Jinyu , Xie W.-C. , So Ronald M. C.
Published: May 2009

Dynamic stability of a two degrees-of-freedom system under bounded noise excitation with a narrow band characteristic is studied through the determination of the moment Lyapunov exponent. The partial differential eigenvalue problem governing the moment Lyapunov exponent is established using the theory of stochastic dynamical system. For weak noise excitations, a singular perturbation method is employed to obtain second-order expansions of the moment Lyapunov exponents. The case when the system is in combination additive resonance in the absence of noise is considered and the effect of noise on the parametric resonance is investigated.
Stability Analysis of Robotic Swarm With Limited Field of View
Authors: Etemadi Sh. , Alasty A. , Vossoughi G. R.
Published: May 2009

This paper presents an analytical study of swarm motion in static environments, in which, motion of the swarm is modeled as a quasi static model. Motion of each member is being affected by interactive forces and environmental effects. Interactive effects on each member could be attractive or repulsive due to being far from or close to other members respectively. Environmental effects also could be attractive or repulsive or a combination of both. The method is based on Lyapunov analysis. Two objectives are investigated through the analysis; one is to preserve the unity of swarm i.e. not losing any member through motion, and the other is to move toward attractant areas and away from repellant environmental zones. It is also considered that the visibility of members to each other and to environmental objects will fade due to the increasing distance; which is the most important characteristic of this work. Simulations of swarm motion show behaviors similar to natural swarms which verifies the vision model considered in this paper.
Design Optimization Using Genetic Algorithms of Web Handling Systems: The Case of the Pendulum Dancer Mechanism
Authors: Vedrines Marc , Knittel Dominique
Published: May 2009

Web systems handling elastic webs are very common in industry. The plant considered in this paper is an industrial winding system with pendulum dancer mechanism. Such a studied dancer moves along an arc of circle. Its utility is double: it imposes the web tension (in steady state operation) and filters the variations of tension mechanically. It is actuated by an air jack with adjustable pressure and has a stiffness and viscous dynamic behavior. Pendulum dancers have been rarely presented and studied in publications. The non-linear model built in Matlab software environment is used as a simulator. Moreover, the state space model useful for modern controller computing can be found thanks to linearization around an operating point. In order to improve the unwinder-winder control performances, the mechanical parameters of the pendulum dancer have to be optimized. The more constant the dynamic behavior over a large frequency band will be, the better the performance of a linear time invariant controller will be obtained. This is the main objective in desensitizing the dancer. The optimization is achieved by using genetic algorithms. The obtained results are discussed and the benefits of this design optimization for industry applications are presented.
Stability of SDOF Nonlinear Viscoelastic System Under the Excitation of Wide-Band Noise
Authors: Huang Qinghua , Xie Wei-Chau
Published: May 2009

The stochastic stability of a single degree-of-freedom (SDOF) nonlinear viscoelastic system under the excitation of wide-band noise is studied in this paper. An example of such a system is the transverse vibration of a viscoelastic column under the excitation of stochastic axial compressive load. The equation of motion is an integro-differential equation with parametric excitation. The stochastic averaging method and averaging method for integro-differential equations are applied to reduce the system. The largest Lyapunov exponents and stochastic bifurcation are studied after the averaged sytem is obtained.
Effect of Heat-Treatment and Reinforcement With Silicon Carbide on the Microstructure and Mechanical Properties of AlFeVSi Alloy
Authors: Arhami M. , Sarioglu F. , Kalkanli A.
Published: May 2009

The aging response of Al-Fe-V-Si composite was compared with the un-reinforced alloy. The effects of solutionizing time, alloying element and SiC reinforcement on the age hardening response, microstructure and mechanical properties of these alloy and its composites was also investigated. The study was performed by T6 heat treatment at three different solutionizing times. Room temperature tensile testing was conducted for peak aged specimens to determine the effect of this heat treatment on the strength of squeezed cast un-reinforced and reinforced Al-Fe-V-Si alloy with SiC particles. The presence of SiC particles accelerated the aging kinetics of the composites compared to the unreinforced alloys. The time to reach peak age hardness was decreased by addition of SiCp. Mainly two different Fe-intermetallics; small α-Al7(Fe, V)3Si and large β-Al18Fe11Si phases were present in the system studied. The fracture surfaces of composites revealed decohesion of SiC particles from the matrix and cracking of needle like-β intermetallics was observed.
Micro-Damage Constitutive Modeling and Numerical Simulation of Perforation of Targets by Projectiles
Authors: Abu Al-Rub Rashid K. , Voyiadjis George Z. , Palazotto Anthony N.
Published: May 2009

The effective use of existing Finite Element Codes in the direct simulation of hypervelocity impacts by projectiles is limited by the dependence of the size of localized failure regions on the mesh size and alignment. This gives rise to a non-physical description of the penetration and perforation processes. A micromechanical constitutive model that couples the anisotropic thermo-viscodamage mechanism with the thermo-hypoelasto-viscoplastic deformation will be presented as a remedy to this situation. Explicit and implicit microstructural length scale measures, which preserve the well-posed nature of the differential equations, are introduced through the use of the viscosity and gradient localization limiters. Simple and robust numerical algorithms for the integration of the constitutive equations will be also presented. The proposed unified integration algorithms are extensions of the classical rate-independent return mapping algorithms to the rate-dependent problems. A simple and direct computational algorithm is also used for implementing the gradient-dependent equations. This algorithm can be implemented in the existing finite element codes without numerous modifications as compared to the current numerical approaches for integrating gradient-dependent models. Model capabilities are preliminarily illustrated for the dynamic localization of inelastic flow in adiabatic shear bands and the perforation of Weldox 460E steel plates with various thicknesses by a deformable blunt projectile at various high impact speeds.
Identification of Gyroscopic System With Complex Variable Coordinates
Authors: Suk Jae Hyeuk , Fabien Brian C.
Published: May 2009

This paper presents a use of the complex coordinates (z = x + iy) for identifying a linear dynamic model of a flywheel energy storage system (FESS). The complex coordinate system transformation yields a compact linear system model, and eliminates the skew-symmetric gyroscopic elements in equation of motion. The paper presents some basic results from linear systems theory using states that are represented by complex variables. In particular, it is shown that the concepts such as controllability and observability can be applied to this system representation. In addition, it is shown that the Eigensystem Realization Algorithm (ERA) can also be applied to these systems. The paper also demonstrates the efficacy of the proposed identification technique by application to an actual FESS.
Experimental Verification of Water Ingress in a Void by Quick Diffusion at High Reflow Temperature
Authors: Park Seungbae , Zhang Haojun , Jang Changsoo
Published: May 2009

The pop-corning failure is known to result from high vapor pressure generation inside cavities at defective interfaces of the electronic package. In order to study the phenomenon, vapor pressure inside a void at high temperature is measured using a specific specimen configuration developed for this purpose. The specimen incorporates a volume-controllable cavity at a polymer-metal interface. A pressure sensor is used to monitor pressure evolution inside the void at high temperature. An underfill material used in the configuration is characterized in terms of hygroscopic properties. The phenomenon is also simulated on a finite element model based on these properties and specimen geometry. The prediction by the numerical model well matches the measurement by pressure sensor. This corroborates the validity of the hypothesis of high vapor pressure employed in numerous existing studies that simulated the pop-corning failure.
Producing a Composite Surface Using Friction Stir Processing
Authors: Qu Jun , Feng Zhili , Xu Hanbing , Frederick D. Alan , Jolly Brian C. , David Stan A.
Published: May 2009

Aluminum alloys would have much wider usage in bearing applications if their wear-resistance could be significantly improved. This investigation developed a solid-state surface engineering process to form an aluminum-alumina composite surface by friction stirring ceramic particles into an aluminum surface to improve the surface hardness and wear-resistance without sacrificing the bulk ductility and conductivity. Composite layers have been successfully processed on pure aluminum (Al 1100) surfaces that have a relatively uniform particle distribution with a concentration up to 25 vol% of alumina. Microscopic examination showed that particles were severely fractured during friction stir processing and, accordingly, the particle size decreased from the original 10–50 μm to 1–5 μm in the friction stir processed composite layer. The microindentation hardness of the aluminum surface was increased from 0.33 to 0.70 GPa (HV) and the wear-resistance was improved by 30X when rubbing against a bearing steel. It has been demonstrated that powder placement methods and process parameters can be tailored to improve particle dispersion and surface hardness. Unlike most other surface engineering techniques, this process can form very thick layers, up to centimeters in thickness, avoiding delamination because of the inherent material continuity.
Application of a Transition-Sensitive Two-Equation Turbulence Model to CFD Simulations of Missile Nose-Cone Geometries
Authors: Jones J. M. , Walters D. K.
Published: May 2009

This paper presents results from an ongoing effort to develop and validate a two-equation eddy-viscosity turbulence model for computational fluid dynamics (CFD) prediction of transitional and turbulent flow. The new model is based on a k-ω model framework, making it more easily implemented into existing general-purpose CFD solvers than other recently proposed model forms. The model incorporates inviscid and viscous damping functions for the eddy viscosity, as well as a production damping term, in order to reproduce the appropriate effects of laminar, transitional, and turbulent boundary layer flow. The new model has been implemented into a Mississippi State University (MSU) Computational Simulation and Design Center (SimCenter) developed flow solver (U2NCLE), as well as a commercially available CFD code (FLUENT). For model validation, comparisons were made to experimental data for an incompressible, zero-pressure gradient, flat plate geometry over a range of freestream turbulence quantities, using both of the flow solvers. Additional test cases were performed with the in-house flow solver and compared to experimental data for two sharp-cone geometries. The Mach number for the cone cases ranged from 0.4 to 2. The results presented in this document show that the new model performed well for the 2-D test cases and showed agreement with the experimental data of the 3-D geometries. The results illustrate the ability of the model to yield reasonable predictions of transitional flow behavior using a very simple modeling framework, including an appropriate response to freestream turbulence quantities.
A Vibration and Wave Propagation Based Methodology for Near Real-Time Damage Monitoring of Composite Structures
Authors: Banerjee Sauvik , Ricci Fabrizio , Mal Ajit
Published: May 2009

This paper presents a novel approach to achieve near real-time damage monitoring whereby ultrasonic wave propagation and vibration data are analyzed to determine the location and degree of damage, requiring minimal operator intervention. An improved test setup, consisting of high fidelity sensor arrays, laser scanning vibrometer, data acquisition boards, signal conditioning and dedicated software has been implemented. The collected data are analyzed using a statistical damage index approach to determine the degree of damage to the structure as a function of time with a high confidence level. The statistical damage index approach is designed to overcome the complexity and variability of the signals in the presence of damage as well as the geometric complexity of the structure. It relies on the fact that the dynamical properties of a structure change with the initiation of new damage or growth of existing damage. Using measurements performed on an undamaged or partially damaged structure as baseline, the damage index is evaluated by comparing the changes in the frequency response of the monitored structure as a new damage occurs or an existing damage grows. The proposed algorithm does not require extensive rigorous signal processing, but it computes a single statistical damage parameter (statistic t) with a high confidence level (> 95%), which makes it very fast and automatic. The damage parameter vanishes if there is no change in the structure and its value increases with the severity and proximity of damage to the sensor locations. Thus if damage is initiated at a location within or near the sensor array, then its location and severity can be determined in real-time by the autonomous scheme. The method is applied to identify low velocity impact damage in stiffened composite panels for different arrangements of the source and the receivers.
Effect of Thermal Processing on the Dissolution of Micro/Nano-Size Metal Particles in Lead-Free Composite Solders
Authors: Faizan Mohammad , Wang Guo-Xiang
Published: May 2009

The ever increasing miniaturization of electronic devices has pressed the need to find the alternate solders that can deliver the necessary strength and reliability of the solder joints. In this view the development of composite solders seems a promising option and has become the focus for many researchers in recent years. An assessment of terminal size of embedded metal particles in a composite solder after reflow process is critical to evaluate the quality and strength of the solder joint. During the actual reflow process the heating phase, holding time and cooling phase are parts of the necessary thermal cycle of the process. These thermal variations have critical effect on the terminal size of the particles and growth of intermetallic compound (IMC) around them during the process. This paper presents a mathematical model to simulate the dissolution behavior of metal particles in composite solders during reflow process. The mathematical model is based on basic mass diffusion process and involves the actual physical properties of various species (particle, IMC, solder etc) of the system. Thermal effects and related thermodynamic constraints together with the non-equilibrium interface kinetics of dissolving micro-size particles are also considered. Dissolution behavior of micro-size Cu particles in lead-free, Sn-Ag-Cu (SAC) alloy solder was studied as a representative example. The growth of IMC and terminal size of embedded particles for various reflow conditions were analyzed using the model. The end particle size and the thickness of the IMC layer around the particles are presented for various reflow conditions. Effects of heating rate, holding time and cooling rate on the dissolution of copper particles and growth of IMC are also investigated. Results from the model show the interesting behavior of micron-size particle dissolution in liquid solders. In addition to the holding time, cooling rate of the solder was also seen to play an important role in the dissolution of copper particles.
Turbulent Forced Convection in a Plane Asymmetric Diffuser: Effect of Diffuser Angle
Authors: Lan H. , Armaly B. F. , Drallmeier J. A.
Published: May 2009

Simulation of two-dimensional turbulent forced convection in a plane asymmetric diffuser is performed and the effect of diffuser angle on the flow and heat transfer is reported. This geometry is common in many heat exchanging devices and the convective heat transfer in it has not been examined. The flow field in this geometry, however, has received significant attention already and the results show that the υ2–f turbulence model provides a better comparison with measured velocity distributions than the k–ε turbulence models. This improvement in predictions is due to selecting different turbulent velocity scale and time scale for the eddy viscosity than what is used in conventional two-equation turbulence models. The results show that the diffuser angle influences significantly the flow field (separation and reattachment) and consequently, it must influence significantly the heat transfer. The υ2–f type turbulence models have been shown to provide good heat transfer results for separated flow, and for that reason a k-ε-ζ (or υ2–f type) turbulence model is used in this study. FLUENT 6.2.16 is used as the platform for these simulations and User Defined Functions (UDF) are developed to incorporate this turbulence model (which is not included in the commercial version of the FLUENT code at this time) into this CFD code. The UDF for the k-ε-ζ turbulence model is validated by comparisons with available measured velocity data in an asymmetric diffuser and with available measured heat transfer and velocity data in a backward facing step flow, and with heat transfer data for a normally-impinging jet flow with very good agreement between simulated and measured results.
Design of a Magnetic Field-Based Multi Degree-of-Freedom Orientation Sensor Using the Distributed-Multiple-Pole Model
Authors: Lee Kok-Meng , Son Hungsun
Published: May 2009

Precision control of a tiltable spinning shaft requires real-time measurement of the inclination. Conventional single-axis encoders, though capable of providing high-resolution (linear or angular) measurements, rely on mechanical linkages (that often introduce frictions, backlashes, and singularities) to constrain the device so that the three-DOF motion can be deduced from the individual orthogonal measurements. Vision-based sensors, which have the attractive features of being non-contact, are limited to low speed measurements. We present here an efficient method for designing a magnetic field-based orientation sensor for devices where orientation control of a rotating shaft under the influence of a magnetic field is required. The ability to characterize the magnetic fields and forces in addition to orientation sensing can offer a number of advantages in real-time computation and control.
Transient Simulations for Economical Analysis of Energy Systems in Industry and Buildings
Authors: Wischhusen Stefan , Schmitz Gerhard
Published: May 2009

In this paper, criteria which indicate the usage of transient models and dynamic simulation environments for such energy systems are presented. A complex energy system for heating and cooling of industrial facilities and industrial processes is presented as a reference model. A model of a hot water storage tank is presented, which is optimized for the simulation in whole years, in which a very accurate transient response at much quicker simulation times compared to conventional geometric models can be delivered. The model was validated with measurement data from a large cogeneration plant. In addition, the economical impact of system simulation is emphasized on by an optimization study carried out on a large industrial system. Furthermore, the impact of a transient system model is compared to that of a steady state approach of the same system.
Self-Cleansing Flexible Stent for Prevention of Clogging of Blood Vessels
Authors: Leung Solomon W. , Ebrahimpour Arya , Schoen Marco P. , Lai James C. K.
Published: May 2009

Different types of stents are available to be implanted into blood-vessels (e.g., cardiovascular stent) or organs to maintain unobstructed blood flow or flow of tissue fluid through ducts (e.g., biliary and uretic stents and others). On the one hand, it is imperative to use smart material such that its mechanical and elastic properties meet those of the ideal stent. A smart stent can change the orientation of the material(s) either by sensing control, temperature, or blood pressure, thus alter the overall shape of the stent (wiggling). These wiggling motions can prevent or reduce the deposit of cholesterol inside the stent’s lumen. On the other hand, there is a need for a better physiological model of how the tensile and shear stresses of a blood vessel are altered as the blood pressure changes along a defined length of that vessel and how the shape changes of the blood vessel could prevent the deposits of lipid material on the vessel wall thereby possibly decrease the likelihood of stenosis. However, the design of an ideal stent is complicated by the lack of proper materials and modeling studies, and difficulties to have an optimized design because of complexities of environmental factors. In this literature review, we therefore propose that an optimal stents design should incorporate the use of highly biocompatible material(s) of well characterized properties and with an adequately modeled mechanical design. We have discussed the importance and relevance of these issues for future stent design and fabrication.