bluuebunny/crossref_metadata_2025 huggingface dataset:
Particle Dampers for Workpiece Chatter Mitigation
Authors: Sims Neil D. , Amarasinghe Ashan , Ridgway Keith
Published: April 2008

It is well known that the chatter stability of a machining process can be improved by increasing the structural damping of the system. To date this approach has been effectively used on various components of the machining system, for example boring bars, milling tools, and the machine structure itself. Various damping treatments have been proposed, including tuned vibration absorbers, active methods, and impact dampers. However, to date there has been little or no work to investigate the issue of particle dampers for this application. This special class of damper comprises a container of thousands of small granular particles which dissipate energy by friction and impact when the container vibrates. The resulting behaviour is highly nonlinear but can provide very high levels of damping across a wide frequency range. In the present study, particle dampers were applied to a workpiece to mitigate chatter during milling, and the limiting critical depth of cut was increased by an order of magnitude. This article gives an overview of the particle damper’s behaviour and key design parameters. Cutting trials employing the device are then described.
Design and Fabrication of 2D Phononic Crystals in Surface Acoustic Wave Micro Devices
Authors: Gu Kebin , Chang Chien-Liu , Shieh Jyh-Cherng
Published: April 2008

In this paper, we present the design and fabrication of innovative phononic crystals integrated with two sets of interdigital (IDT) electrodes for frequency band selection of surface acoustic waves (SAW). The potential applications of this device include performance improvement of SAW micro-sensors, front-end components in RF circuitries, and directional receptions of high frequency acoustic waves. Analogous to the band-gap generated by photonic crystals, the phononic crystals, two dimensional repetitive structures composed of two different elastic materials, can prohibit the propagation of elastic waves with either specific incident angles or certain bandwidth. In this paper, the prohibited bandwidth has been verified by fabricating the phononic crystals between a micromachined SAW resonator and a receiver. Both the resonator and receiver are composed of IDT electrodes deposited and patterned on a thin piezoelectric layer. To confine the prohibited bandwidth on the order of hundred MHz, the diameter of the circular pores in phononic crystals is designed to be 6 micron and the aspect ratio of each pore is 3:1. To maximize the power transduction from IDT electrodes to SAW, the spacing between two inter-digits is one-fourth the wavelength of SAW. Specifically, the spacing ranges from 3.4 microns to 9.0 microns, depending on the central frequency. Both surface and bulk micromachining are employed and integrated to fabricate the crystals as well as SAW resonator and receiver altogether. Firstly, a 1.5-micron zinc oxide, which provides well-defined central frequency, is sputtered and patterned onto silicon substrate. Second, the IDT electrodes are evaporated and patterned by lift-off technique. Then the exposed silicon substrate is etched using DRIE to generate two dimensional phononic crystals. To tune the prohibited SAW bandwidth, the crystal pores are filled with copper or nickel by electroless plating. The insertion loss of the fabricated devices is characterized and is found to agree with simulation results.
Vehicle Active Suspension Control: Using AaVariable Structure Model Reference Adaptive Controller
Authors: Mohammadi Ardeshir Karami
Published: April 2008

A Variable Structure Model Reference Adaptive Controller (VS-MRAC) is proposed for Active control of vehicle suspension. One DOF quarter car model has been considered. The reference model is a one DOF vibrating system with skyhook damper. The structure of the switching functions is designed based on global exponential stability requirements, and shows perfect model following at a finite time. Sliding surfaces are independent of system parameters and therefore VS-MRAC is insensitive to system parameter variations. Simulation is presented for some road irregularities, and compares to active suspension with fixed structure MRAC, and passive suspension. VS-MRAC shows the best performance on ride and working space
Design and Fabrication of a Magnetocaloric Microcooler
Authors: Kim Sangchae , Bethala Bharath , Ghirlanda Simone , Sambandam Senthil N. , Bhansali Shekhar
Published: April 2008

Magnetocaloric refrigeration is increasingly being explored as an alternative technology for cooling. This paper presents the design and fabrication of a micromachined magnetocaloric cooler. The cooler consists of fluidic microchannels (in a Si wafer), diffused temperature sensors, and a Gd5(Si2Ge2) magnetocaloric refrigeration element. A magnetic field of 1.5 T is applied using an electromagnet to change the entropy of the magnetocaloric element for different ambient temperature conditions ranging from 258 K to 280 K, and the results are discussed. The tests show a maximum temperature change of 7 K on the magnetocaloric element at 258 K. The experimental results co-relate well with the entropy change of the material.
Density and Growth Rate Measurements in a High Atwood Number Rayleigh-Taylor Mixing
Authors: Banerjee Arindam , Andrews Malcolm J.
Published: April 2008

A novel gas channel experiment is used to study the non-equilibrium development of high Atwood number Rayleigh-Taylor mixing. Two gas streams, one containing air-helium mixture and the other air, flow parallel to each other separated by a thin splitter plate. The streams meet at the end of a splitter plate leading to the formation of an unstable interface and initiation of buoyancy driven mixing. This set up is statistically steady and allows for long data collection times. Here, we describe initial measurements to determine the density profile and growth rate along the mix at low density differences (At ~ 0.05). The facility is however designed capable of large Atwood number studies (At ~ 0.75). Diagnostics include high resolution digital image analysis, which is used to determine the density profile across the mix. The growth parameter (α) is also estimated by a “moving window” calculation. The results are then verified with measurements of α made by a Constant temperature (CT) hot-wire probe and with the growth parameter obtained from small Atwood number experiments (At ~ 0.001). However, there were some inherent errors in the density profile measurements because of non-uniformity in the concentration of smoke. To verify that these errors were indeed measurement errors and not as a result of lack of statistical convergence, a detailed statistical convergence test was performed. It showed that convergence was a direct consequence of the number of different large 3D structures that were averaged over the duration of the run.
Modeling of Distribution Media and Vacuum Bag Properties on Permeability Variations During Vacuum Assisted Resin Transfer Molding (VARTM)
Authors: Zhang Yuhong , Lopatnikov Sergey , Heider Dirk
Published: April 2008

This paper investigates the deformation of the vacuum film into the distribution media, its effect on the change of the unit cell porosity and ultimately the reduction of permeability of the overall system in a Vacuum Assisted Resin Transfer Molding (VARTM) process. Experimental results have shown the obvious effects of the vacuum bagging penetration into the distribution media on permeability; however, there is no analytical model to explicitly characterize this phenomenon. In this paper, we proposed an analytical model to capture the vacuum film penetration into the distribution media based on an energy approach for the first time, and then we connect this analytical model with Carman-Kozeny equation to predict the permeability variations in terms of the parameters of plastic vacuum bag and distribution media. Design curves are obtained in parametric studies to predict the permeability reduction as a function of bag modulus and thickness, and distribution media geometry. These reduction factors can be used in flow simulations to accurately predict the resin filling time for a wide variety of distribution media/flexible bag systems. Simulation results are compatible with observations from the preliminary experiment results.
Visualizations of Buoyancy Driven Mixing
Authors: Kraft Wayne N. , Banerjee Arindam , Andrews Malcolm J.
Published: April 2008

A collection of visualizations that convey a basic understanding of buoyancy-driven mixing is presented. Buoyancy-driven mixing resulting from the Rayleigh-Taylor instability occurs in a unstably stratified flow when a heavy fluid rests above a light fluid. The difficulty of creating an unstable density stratification and repeatable fluid interface has made studying the Rayleigh-Taylor instability a challenging task. Our experiments utilize a water channel and most recently a gas channel (low speed wind tunnel). The experimental configuration allows unstable perturbations to develop into a mixing layer as they travel downstream. Thus resulting in a repeatable experiment and statistically steady flow. Various visualization techniques have been used to observe the development of the Rayleigh-Taylor instability. Visualizations using Nigrosene dye as a fluid marker are shown in the evolution of single and binary mode perturbations due to the Rayleigh-Taylor instability. In contrast, visualizations of the Rayleigh-Taylor instability developed from multi-mode perturbations are seen for the gas channel using both fog and smoke to visualize the flow. Together these techniques help provide an understanding for the nature and complexity of buoyancy driven mixing.
Modelling Processing of Unfilled and Long-Glass Fibre Reinforced Thermoplastics in a Screw-Barrel Unit
Authors: Moguedet M. , Balcaen J. , Be´reaux Y. , Charmeau J.-Y.
Published: April 2008

In injection moulding, long glass fibre reinforced thermoplastics (LGFT) are an attractive way to produce large parts at low cost. The strength of the part depends chiefly on the average fibre length, fibres which are subjected to considerable attrition during processing in conventional three stage screws. First of all, in this study we have coupled a melting analysis in a conventional screw to a model of fibre breakage whereby a fibre anchored at one end in the solid bed is submitted, at its other end, to the intense shear stress of the molten polymer flowing in the film close to the barrel. As the melting of the solid bed progresses, more fibres are unlayered and submitted to bending which intensity is depending on both the fibre length and orientation. When the bending is too high, the fibre breaks. Bimodal fibre length distribution are obtained and compared to existing data. The sensibility of the model to main processing parameters such as screw rotation, initial fibre length, viscosity, barrel temperature and screw geometry are also investigated. Next, we present a new analytical solution for flow of a viscous fluid in a single screw channel that takes into account the torsion and curvature of the channel. Contrary to common knowledge in polymer processing based on the Parallel Plate Model, we found that, in the case of cross-sections with large aspect ratio, torsion effects can be significant. The implication of the model on velocity field, residence time and mixing efficiency is investigated and compared to the predictions of the classical Parallel Plate Model, to finite elements calculations, and to 3D experimental measurements. Indeed, an innovating device has been developed in our laboratory to visualize the flow of a viscous fluid in the channel of a screw. It consists of a transparent barrel and of a rotating screw, pumping a transparent viscous fluid at room temperature. A particle plunged in the flow is constantly monitored by four video-cameras placed around the barrel and recording its position in a frame. The 3D path lines are then computed.
Investigation of Thermosyphon Cooling for Drilling Operation: An Experimental Study
Authors: Jen Tien-Chien , Tuchowski Fern , Chen Yau-Min
Published: April 2008

This paper investigates using a thermosyphon in the center of a drill (thermosyphon drill) to remove the heat generated at the cutting tip and transfer it to the drill chuck, which acts as a heat sink, in an effort to reduce the temperature at the drill tip. This study compared the heat transfer performance of a thermosyphon drill to the performance of a solid drill and a heat pipe drill under simulated and actual drilling conditions. Results show that when using a drill with a thermosyphon the temperature of the drill tip was almost 60% lower than a solid drill for 45 and 55-volt power inputs and 37% lower for 35-volt power input. Compared to a heat pipe drill the maximum temperatures were reduced 18% to 36%. It was also shown that higher speed has an adverse effect on the operation of the thermosyphon, but in the worst case, the drill tip temperature was only 16% higher than that of the stationary thermosyphon drill.
Application of Minimum Amount of Fluid by Spray in Turning of AISI 316 Stainless Steels
Authors: Gennari Walter , Pereira Alexander A. , Santos Henrique L. A.
Published: April 2008

Methods of near dry machining (NDM) are becoming a suitable alternative to reduce costs and eliminate, significantly, high amounts of fluid which would be rejected at the end of its life. This work presents a comparison between conventional fluid application (by gravity and high volume ~ 150 liters/hr) and the method of NDM (applying cutting fluid by spray ~ 60 ml/hr). Considering that investigation was carried out by turning a low machinability material like AISI 316 stainless steels, severe cutting temperatures made possible the evaluation of the efficiency of fluid spray in lubrication. Results suggest that only in a few conditions of severe heating, conventional method presented slightly better tool life and, for most of the investigated conditions, method of NDM showed good lubrication in tool-workpiece interface and enough cooling, determining an excellent performance of tool life and integrity of cutting edge.
Estimation of Clutch Parameters for Online Diagnostics and Control Applications
Authors: Joshi S. , Liu J. , Ananthakrishnan S.
Published: April 2008

The primary goal of this research was to identify the role of non-linear parameter estimation in clutch torque estimation for automotive applications. The benefit of this approach in estimating parameters of a system defined by a set of differential algebraic equations (DAEs) that represents, say, clutch torque profile is investigated. In addition, online implementation, albeit at a slow rate compared to control loop rates is demonstrated. This method of analytical DAE based estimation has significant advantages over purely empirical methods in that it directly identifies the relationships between system problem variables, such as, engine speed, cross shaft angle to variable of interest, say, clutch torque, unlike, indirect approaches [1]. In addition, in contrast with time series evolution of discrete system models based on ARMAX models, this approach allows a designer to know the relationship between system parameters such as friction coefficient, clutch engagement angle, etc and the estimation process leading to better design of clutch control algorithms. However, unlike, the direct digital control methods, DAE based approaches are computationally more intensive resulting in a need for additional onboard processing. One of the goals of this initial research is to study this to identify practical analytical and numerical approaches that will lead to onboard implementation of these algorithms for truck applications, specifically in automated mechanical transmissions (AMTs) [2, 3].
A Learning Module for Increasing Ethical Awareness of Students
Authors: Kulkarni Anil K. , Wise John C.
Published: April 2008

A learning module was introduced in a required Mechanical Engineering undergraduate course with the goal of increasing the ethical awareness of students. Specifically, the students were supposed to understand the basic theories of ethics and an engineering code of ethics, apply this understanding to differentiate between ethical and unethical engineering practices, and be able to suggest ethical solutions. The course was junior level Measurements and Instrumentation, taken by 120 students in six sections of about 20 each. In each section, a two-and-a-half-hour “Ethics workshop” was conducted during a lab period which included several interactive student activities such as discussion of theories of ethics, engineering case-studies and guidelines to solve an engineering “problem”, short video clips, a quiz, and an in-depth analysis of a hypothetical situation. At the conclusion of the module, students were asked to prepare a short report on an ethical solution of that situation. A survey was administered several days before and again several days after the workshop with identical questions. Based on the chi-square test, statistically significant increase in the ethical awareness of students was evident. Similar modules were also presented in freshman seminars courses. Although the above survey involved primarily junior students, it appears that the introduction of material on topics of academic integrity would be helpful to first-year students, and the introduction of engineering professional ethics would be useful at the beginning of their major in the first semester in the junior year.
Concepts for Power and Energy Analysis in Nastic Structures
Authors: Giurgiutiu Victor , Matthews Luke , Leo Donald J. , Sundaresan Vishnu Baba
Published: April 2008

Nastic structures are potentially high-energy density smart materials that will be capable of achieving controllable deformation and shape change due to internal microactuation that functions on principles found in the biological process of nastic motion. In plants, nastic motion is accomplished through osmotic pressure changes causing a respective increase or decrease in cell volume, thereby causing net movement. In nastic structures, osmotic pressure is increased by moving fluid from low concentration to high concentration areas by means of active transport, powered by adenosine triphosphate (ATP) hydrolysis. Power analysis involves calculating possible ranges of actuation as a result of interior pressure exchanges and hydraulic flux rates which will determine the speed of actuation. Because pressure inside the actuating cylinder is uniform, the cylinder undergoes deformation in all the three dimensions. Predicting the work-energy balance involves considering the factors that determine the total volumetric change, including cylinder wall expansion, surface bulging and stretching, and outside forces that oppose the actuation. The hydraulic flux rates determine both the force magnitude and the actuation speed. Energy analysis considers the pressure variation range needed to accomplish the desired actuation deflection, and the energy required for active transport mechanisms to move the volume of fluid into the nastic actuator. Nonlinear effects are present, as the pressure inside the actuation cylinder increases, it takes more energy for active transport to continue moving fluid into it. The chemical reaction of ATP hydrolysis supplies the energy for active transport, which is related to the ratio of the reactants, to the products, as well as to the pH level. As the pH lowers, more energy is released through ATP hydrolysis. Therefore, as pH decreases, ATP Hydrolysis releases more energy, enabling active transport to move more fluid into the actuation cylinder, thereby increasing the internal osmotic pressure and causing material deformation work and actuation.
A New Magnetic Energizer for Enhancement of Refrigeration and Heat Pumping Equipment
Authors: Sami Samuel
Published: April 2008

This paper is concerned with ENERGIZER MHD technology. The test results of the performance of some new alternative refrigerant mixtures such as; 410A, R-507, R-407C, and R-404A under various conditions of magnetic field are discussed, analysed and presented. The test results were obtained using an air-source heat pump set up with enhanced surface tubing under various magnetic field conditions. Performance tests were conducted according to the ARI/ASHRAE Standards. The test results demonstrated that as magnetic force increases evaporator performance increases as well as coefficient of performance. The use of magnetic field on refrigeration systems was optimised and results were discussed.
Palm Power: Using Combustion at Small Scales and a Free Piston Stirling Engine to Replace Batteries
Authors: Gomez Alessandro , Berry Jonathan , Roychoudhury Subir , Huth James
Published: April 2008

A critical parameter to compact and portable power generation is gravimetric energy density (energy per unit weight), in terms of which fuels fare much better than conventional batteries. As a result, there has recently been a flurry of, sometimes questionable, activities on micro/meso-scale fuel-based power generation. This article discusses an approach to mesoscale electric power production relying on a clean and efficient combustor coupled with a free-piston Stirling engine. First, the design and development of a catalytic burner will be reviewed. Its main components are: a multiplexed electrospray to disperse jet propulsion fuel (JP-8), a stack of catalytically coated grids through which fuel conversion and heat release is achieved cleanly and efficiently, and a recuperator to improve the system thermodynamic efficiency. The combustor has a volume of tens of cm3 and operates at JP-8 flow rates on the order of tens of g/hr, and equivalence ratios varying in the 0.35-0.70 range. The combustor was interfaced with the 35 We Sunpower (Athens, OH) free-piston Stirling engine to achieve power generation with a gross fuel-electric efficiency of 21%. With design optimization, 21% efficiency net of parasitic losses should be achievable, with an energy density on the order of 1,000–2,000 W-hr/kg, depending on fuel autonomy.
Investigation of the Effects of Sliding on Wheel Tread Damage
Authors: Talamini Brandon , Gordon Jeff , Perlman A. Benjamin
Published: April 2008

Wheel tread spalling is the main source of damage to wheel treads and a primary cause for wheel removals from service. Severe frictional heating of the wheel-rail contact patch during sliding causes the formation of martensite, a hard, brittle microstructure. The martensite patches break away from the more resilient bulk of the wheel tread when subjected to contact loads, resulting in spall formation. Prolonged sliding allows a greater volume of wheel tread material to reach extremely high temperatures, which will lead to material ablation and the formation of a slid flat. Such flats are the cause of wheel impact loads, which are extremely damaging to truck components and rail. This paper outlines an approach developed to estimate the effects of sliding on wheel flat formation and the potential severity of spalling. The methodology is described and preliminary results are presented using an intentionally simplified idealization of the wheel-rail contact geometry. Material characterization (temperature-dependent properties and failure criteria) and management of model size are of equal importance to geometric fidelity and are the focus in the early stages of the development of the qualitative model present here.
Relaxation in Nanoscale Freestanding Gold Films Using MEMS
Authors: Samuel B. S. , Desai A. V. , Haque M. A.
Published: April 2008

We present experimental results to describe the stress relaxation behavior of thin (125 nm) freestanding gold films at room temperature. The experiments were performed inside a field emission scanning microscope using a MEMS-based test bed which is only 3mm × 10mm in size. The effect of stress relaxation on the young’s modulus of gold thin films is observed. The thin film specimen used in the experiment is co-fabricated with the micromechanical loading device and hence eliminates problems of alignment and gripping. Freestanding thin films provide us with information about the mechanical behavior of thin films in the absence of substrate effects.
Dynamic Model of Mechanisms With Highly Compliant Members
Authors: Lan Chao-Chieh , Lee Kok-Meng
Published: April 2008

The dynamic model for links in most mechanisms has often based on small deflection theory without considering geometrical nonlinearity. For applications like light-weight links or high-precision elements, it is necessary to capture the large deflection caused by bending forces. A complete dynamic model is presented here to characterize the motion of a compliant mechanism capable of large deflection with shear and axial deformation. We derive the governing equations from Hamilton’s principle along with the essential geometric constraints that relate deformation and coordinate variables, and solve them using a semi-discrete method based on the Newmark scheme and shooting method. The dynamic model has been validated experimentally. We also extend the model for analyzing compliant mechanisms. It is expected that the dynamic model will serve as a basis for analyzing a wide spectrum of compliant multi-link mechanisms.
Boiling in Enhanced Surface Microchannels
Authors: Kuo Chih-Jung , Kosar Ali , Jensen Michael K. , Peles Yoav
Published: April 2008

An experimental investigation is presented on flow boiling of de-ionized water in 227-μm hydraulic diameter microchannels with reentrant type cavities. Key features of nucleate boiling are discussed. Active nucleation site density, bubble frequency and departure diameter, and flow patterns over mass velocities ranging from 41 kg/m2-s to 302 kg/m2-s and heat fluxes ranging from 28 to 445 W/cm2 are studied. Similarities and differences with results obtained on large-scale systems and unenhanced microchannels are discussed.
New AAR Procedure Permitting Freight Car Life Beyond 50 Years
Authors: Dawson Richard W. , Iler Darrell , Koch Kevin
Published: April 2008

The Interchange Rules of the Association of American Railroads (AAR) limit the life of freight cars to 50 years from the date originally built. Recently, however, the AAR has instituted a new provision under Interchange Rule 88 that permits cars to operate for up to 65 years since their built date. The procedure incorporates two basic portions; demonstrating that the carbody has the structural integrity to last for a total life of 65 years and upgrading specific components on each car. After applying to the AAR Equipment Engineering Committee (EEC) requesting that ILS be granted to a particular group of cars, the car owner has two optional methods to demonstrate the structural integrity of the selected cars. The first option is to perform structural inspections on a specified number of representative cars and to perform a full-scale fatigue test on a test car. In place of the fatigue test, the second option is to perform structural inspections on a larger number of cars and conduct follow-up inspections every five years after receipt of approval. The physical fatigue test incorporates modern engineering best practices by utilizing finite element modeling and full-scale accelerated fatigue testing (AFT). Following the creation of a representative model, several load conditions, both real and worst-case, are then applied to determine the high-stress locations. Using instrumentation at the high-stress locations, a full-scale test is conducted with the car operating in a typical service environment. The objective of full-scale testing is to obtain real strain data and input loads produced by typical environment conditions. AFT enables the required load cycles to be applied to the test car in a dynamic test fixture in weeks or months versus years of actual service. A rapid accumulation of fatigue-damaging cycles representative of the remaining years necessary to bring the total life of the test car to 65 years are applied to the car. The requirements for the components to be replaced or upgraded under Rule 88 are similar to those for new cars and for rebuilt cars. Some components, such as air brake control valves, are to be upgraded to more recent standards. Others are to be replaced in kind with reconditioned parts. Even though the carbody is permitted to operate beyond 50 years, components must still comply with existing AAR and Federal Railroad Administration (FRA) age limits. In addition to obtaining Increased Life Status (ILS) from the AAR, the car owner must also apply to the Federal Railroad Administration for authorization to operate the cars beyond the 50-year limit of the FRA Freight Car Safety Standards. This paper will demonstrate the approval process, including AFT testing, as applied to two groups of flat cars in auto rack service, and a group of 60-foot flat cars.
Improved Heat Dissipation Capability on Electronic Motor Control Devices
Authors: Tong Wei
Published: April 2008

Heat sinks have been widely used in electronic industry to maintain the operation temperatures of electronic devices lower than their allowable values and thus are often critical to the device performance and life. However, it is difficult to design heat sinks to satisfy all design specifications optimally under complex heat transfer phenomena. The present work discloses a new design of heat sinks to improve heat dissipation capability for electric motor control devices. The heat sink contains a plurality of raindrop-shaped pin fins, acting as vortex generators to increase the rate of heat transfer and in turn, to increase the cooling efficiency of the heat sinks. Numerical results have shown that with the new designed heat sinks, the maximum temperature can reduce about 30% over the conventional heat sinks.
Nanoscale Measurements of Coupled Mechanical Electrical and Thermal Properties Using a Novel Characterization Tool
Authors: Singh Utkarsha , Abramson Alexis , Prakash Vikas
Published: April 2008

This paper presents the design and development of a nano-mechanical, electrical and thermal (NMET) characterization tool for coupled measurements of one-dimensional nanostructures. The device is designed to operate inside an environmental scanning electron microscope (ESEM) to facilitate in-situ imaging, positioning and testing. The design includes a custom nanomanipulator system, which assists in controlled placement of individual one-dimensional nanostructures (specimens) between two probes. Sample straining and unique direct force and displacement measurements are achieved by the use of a commercially available actuator. The “next generation” tool is also discussed.
Electrospun Magnetic Nanofibers With Anti-Counterfeiting Applications
Authors: Barrera Carola , Gould T. , Hyde K. , Montero G. , Hinestroza J. P. , Rinaldi C.
Published: April 2008

Polyethylene oxide (PEO) nanofibers containing discrete magnetic domains have been produced using both parallel plate and syringe-plate electrospinning configurations. Magnetite nanoparticles from a commercial ferrofluid (MSG W11, Ferrotech Corporation) were suspended in 1–2 wt% PEO-in-water solutions and electrospun to produce fibers with diameters as small as 150 nm. Transmission electron microscopy was used to study particle agglomeration in the resulting nanofibers as a function of particle loading and electrospinning conditions. Magnetic measurements using a SQUID magnetometer were used to characterize the DC and AC magnetic response of the fibers. Applications to anti-counterfeiting in the textile industry are discussed.
Jatropha and Pongamia Straight Vegetable Oils as an Alternative to Diesel as a Fuel
Authors: Deshpande N. V. , Thombre Shashikant , Meshram Manish G. , Naresh T. , Sharma Yogesh P.
Published: April 2008

With the fossil fuel depleting very fast, researchers have concentrated on developing new agro-based alternative fuels, which will provide sustainable solution to the energy crisis. Presently, bio-diesels, which are obtained from trans-esterification of straight vegetable oil (SVO), are being used along with diesel in blends. The transesterification process, which is a costly, time consuming and oil quality dependent process is eliminated in the present study. The straight vegetable oils, namely, Jatropha and Pongamia have been analyzed in details. The trial was conducted on a 4-stroke, single cylinder diesel engine, having compression ratio 17.5:1. The experiments were carried out for fuel consumption and emission levels at various loads and without any engine modifications. The results obtained were comparable to and better than diesel. The CO and NOx emission was found less for Jatropha as well as for Pongamia. The specific fuel consumption (SFC) was found to be low for both Jatropha and Pongamia oil at moderate loads. The brake thermal efficiency was also found to be better for both Jatropha and Pongamia oil as compared to diesel
Numerical Simulation of a Supersonic Three-Phase Cavitating Jet Flow Through a Gaseous Medium in Injection Nozzle
Authors: Lagumbay Randy S. , Vasilyev Oleg V. , Haselbacher Andreas , Wang Jin
Published: April 2008

A new multiphase mathematical model based on a mixture formulation of the laws of conservation for a multiphase flow is used to simulate a supersonic three-phase cavitating jet flow through a gaseous medium. The model does not require an adhoc closure for the variation of mixture density with regards to the attendant pressure and yields a thermodynamically accurate value for the acoustical propagation generated by the process. A source term for cavitation is added into the equations of the mixture formulation and the resultant cavitation is mathematically modeled accordingly. The new numerical formulation has been incorporated into a multi-physics unstructured code “RocfluMP” that solves the modified three-dimensional time-dependent Euler/Navier-Stokes equations for a multiphase framework in integral form. A modified form of the Harten, Lax and van Leer approximate Riemann equations are used to resolve the isolated shock and contact waves. The newly developed multiphase flow equations provide a general framework for analyzing coupled incompressible-compressible multiphase flows that can be applied to a variety of supersonic multiphase jet flow problems such as fuel injection systems and liquid-jet machining. Preliminary results for three-phase cavitating jet flow through a gaseous medium in injection nozzle are presented and discussed.
Development of Conformal PDMS and Parylene Coatings for Microelectronics and MEMS Packaging
Authors: Lee Hyungsuk , Cho Junghyun
Published: April 2008

There is a growing demand in the development of small-scale devices in microelectronics and microelectromechanical systems (MEMS). Packaging and reliability of such devices are of great concern as they introduce a number of unique packaging issues that are distinct and different from typical electronic packaging applications. In addition, the packaging or encapsulation materials are often exposed to harsh environments, for which their performance is drastically degraded. Importantly, such devices become lighter and smaller, precluding the use of conventional packaging materials and schemes. Given that, surface protective coatings can provide an innovative solution for some of the aforementioned issues. Polymers have indeed shown such a potential for use either as a standalone coating, or an intermediate layer for the subsequent harder, stiffer coatings. In this study, we explore processes and properties of the three coating systems: i) PDMS, ii) Parylene (para-xylylene), iii) Parylene/PDMS. In particular, parylene coating on PDMS is a focus of this study. The parylene coating having much higher mechanical properties than PDMS provided a way to enhance the surface properties of this PDMS. Proper surface modification of PDMS via oxygen plasma seemed to be essential to generate desirable microstructures of parylene coating. Mechanical properties of such coatings are systematically examined via a nanoindenter. The dynamic nanoindentation is also employed to assess viscoelastic properties, as well as depth-dependent mechanical properties. While characterizing the films using the nanoindentation, the substrate effect influenced the indentation data. In addition, extensive surface characterizations are carried out using atomic force microscope (AFM), scanning electron microscope (SEM), and optical microscopy.
Modeling of Contact Area, Contact Force, and Contact Stiffness of Mechanical Systems With Friction
Authors: Abdo Jamil , Shamseldin Elhanafi
Published: April 2008

It is well recognized that the contact stiffness, true contact area, and the contact force are among the key features in the study of friction system behavior. This paper presents the development of formulae for the mechanical component of dry-friction at the interface of two microscopic rough surfaces. Elastic deformation under the influence of the contact forces is considered. The elastic contact model formulation between interacting asperities is not assumed to occur only at asperity peaks, thus allowing the possibility of oblique contacts wherein the local contact surfaces are no longer parallel to the mean planes of the mating surfaces. It is shown that the approach enables the separation of the contact area into its normal and tangential projections and the contact force into its normal and tangential components. The mathematical model of contact is utilized to develop formulae for normal and tangential contact stiffness. The analytical method is used to estimate contact stiffness components. Contact parameter values for the sample are derived from the surface profile data taken from a 1.0-mm by 10-mm test area. The profile is measured using a Mahr profilometer. A computer program is written and used to analyze the profile data. The analysis yields the asperity density, average asperity radius, and the standard deviation for each test area.
Van Der Waal’s Elastica
Authors: Mockensturm Eric , Mahdavi Arash
Published: April 2008

Experimental investigations of carbon nanotubes have revealed that they can collapse into nanoribbons that have a dumb-bell shape cross-section. Due to the extreme exibility of single-atom thick graphene sheets, if the tube is large enough self-induced Van der Waals forces acting on the at surfaces of the ribbon will be large enough to hold the nanotube in the collapsed (ribbon) configuration. Energetically, the additional strain (bending) energy stored in the collapsed state is offset by the decrease in energy of the Van der Waals interactions. Because Van der Waals forces are short ranged, one nds that tubes of great enough diameter are bistable. Here we investigate the natural of this bistability by investigating how the energy stored in the tube changes as it is compressed by at rigid indenters of various widths. The nanotube is assumed to deform uniformly along its length and the cross-section is modeled using inextensible, non-linear beam theory (Euler’s Elastica). We nd that the in ated (tube) conguration is always stable but that the energy barrier against decreases with increasing tube radius. Additionally, the energy difference between the in ated and collapsed states decreases nearly linear with increasing radius and for tubes with radius greater than 26 A the collapsed state is energetically favored.
On Determining Reference Stresses for High Temperature Thin/Thick Tube Bends
Authors: Basu Abheek , Zarrabi Khosrow , Ng Lawrence
Published: April 2008

It is well known that tube/pipe bends have some degree of ovality caused during their manufacture. For the first time, based on limit analysis, the authors previously presented an explicit expression for calculation of the reference stress of tube/pipe bends with varying degrees of ovality that are subjected to uniform internal pressure. The present paper assesses this expression using an elastic-creep finite volume analysis. This is due to availability of an in-house finite volume code. It is shown that the references stresses predicted by proposed expression correlate well with those computed using elastic-creep analyses for tube/pipe bends with various degrees of ovality.
Effects of Annealing on Dynamic Behavior of a Bulk Metallic Glass
Authors: Sunny George P. , Prakash Vikas , Lewandowski John J.
Published: April 2008

Bulk metallic glasses are excellent candidate materials for integral armor because of their high strength and large elastic strain. Also, annealed glasses exhibit higher yield strengths than their fully amorphous counterparts. Therefore, the dynamic behavior of an annealed bulk metallic glass, Zr41.25Ti13.75Ni10Cu12.5Be22.5, was investigated in this study. A Split-Hopkinson Pressure Bar (SHPB) was employed to determine the stress-strain response at strain rates varying from 500/s-2000/s for the annealed glass. Also, a high-speed camera was utilized to obtain in-situ video of the specimen during the deformation process. These results were then compared to similar tests on the fully amorphous material. Finally, a new specimen design and experimental setup was proposed to promote accurate measurements from SHPB tests. During dynamic loading, the strain to failure increased as the strain-rate was increased, and the changes in strain-rate produced a larger effect than that of the annealing treatment on the failure strain. Maximum stresses were generally higher for the annealed glass, although there was some scatter. Finally, while an instability formed a dominant shear band for the as-received material, extensive fragmentation characterized the deformation after formation of an initial crack.
Enhancement of In-Plane Thermal Conductivity of Thin Films via Surface Phonon-Polaritons
Authors: Chen Dye-Zone A. , Narayanaswamy Arvind , Chen Gang
Published: April 2008

We predict theoretically that the effective in-plane thermal conductivity of crystalline and amorphous thin films can be increased by surface phonon-polaritons significantly beyond their intrinsic bulk values. We show that the thermal conductivity due to surface phonon-polaritons increases with decreasing film thickness. In particular, for a 40 nm thick film of amorphous silicon dioxide, we calculate a total thermal conductivity of 4 W m−1 K−1 at 500 K, which is an increase of ~100% over the intrinsic phonon thermal conductivity.
Impact Resistance of Rail Vehicle Window Glazing and Related Safety Issues
Authors: Tsai Tom , Lamond James H. , Liao Sam S. C.
Published: April 2008

This paper summarizes the research conducted since 1999 to support proposed new Federal Railroad Administration (FRA) testing standards for impact resistance of glazing in windows on passenger rail vehicles. This paper focuses on tests for “small object” impact, which are intended to primarily simulate the effects of vandals throwing ballast rocks at the side windows of a passing train. The speed of rocks being thrown by a group of human subjects was first evaluated. Subsequently, impact tests with ballast rocks and a 0.41 lb (2-inch diameter) aluminum ball were performed. The aluminum ball impacting at 55 mph is currently the object proposed for use in the new FRA testing standards under development. Tests were conducted using various types of glass, including specimens having spall or vandal shields consisting of a layer of protective plastic backing. Analysis techniques for evaluating pass/fail criteria were also developed.
The Surface Roughness Effect on the Hydrostatic Thrust Spherical Bearings Performance: Part 2 — Clearance Type of Bearings
Authors: Yacout A. W. , Ismaeel A. S. , Kassab S. Z.
Published: April 2008

The clearance type of bearings, where the sphere radius is smaller than that of the seat, provides a great divergence in results compared with the fitted type. The study deals with the surface roughness and the predominant centripetal inertia terms due to the shaft rotation. The solutions are presented for the un-recessed clearance type of bearings, hemispherical and partial hemispherical seats, with capillary tube and orifice restrictors. On the basis of the stochastic theory, Reynolds equation is developed. Unlike the solution of Dowson and Taylor for this type of bearings, the well known Sommerfeld substitution of journal bearings hasn't been used in this study. Expressions for the pressure distribution, load carrying capacity, volume flow rate, frictional torque, friction factor, power losses and stiffness factor are obtained. The research studies the combined effects of the centripetal inertia and the surface roughness on the bearing performance. An optimum design based on the minimum power losses, minimum flow rate and the optimal restrictor dimensions is theoretically examined. The conventional four cases of this type of bearings, dependant on the eccentricity ratio in the previous studies, have been reduced to three cases only. In addition, a unified solution for this type is developed. Finally, a general solution for the hydrostatic thrust spherical bearing is obtained where it could be applied to the, un-recessed hemispherical and partial hemispherical, clearance and fitted types of bearings.
Stability of Gravity Driven Convection in a Cylindrical Porous Layer Subjected to Vibration
Authors: Govender Saneshan
Published: April 2008

In both pure fluids and porous media, the density gradient becomes unstable and fluid motion (convection) occurs when the critical Rayleigh number is exceeded. The classical stability analysis no longer applies if the Rayleigh number is time dependant, as found in systems where the density gradient is subjected to vibration. The influence of vibrations on thermal convection depends on the orientation of the time dependant acceleration with respect to the thermal stratification. The problem of a vibrating porous cylinder has numerous important engineering applications, the most important one being in the field of binary alloy solidification. In particular we may extend the above results to understanding the dynamics in the mushy layer (essentially a reactive porous medium) that is sandwiched between the underlying solid and overlying melt regions. Alloyed components are widely used in demanding and critical applications, such as turbine blades, and a consistent internal structure is paramount to the performance and integrity of the component. Alloys are susceptible to the formation of vertical channels which are a direct result of the presence convection, so any technique that suppresses convection/the formation of channels would be welcomed by the plant metallurgical engineer. In the current study, the linear stability theory is used to investigate analytically the effects of gravity modulation on convection in a homogeneous cylindrical porous layer heated from below. The linear stability results show that increasing the frequency of vibration stabilizes the convection. In addition the aspect ratio of the porous cylinder is shown to influence the stability of convection for all frequencies analysed. It was also observed that only synchronous solutions are possible in cylindrical porous layers, with no transition to sub harmonic solutions as was the case in Govender (2005a) for rectangular layers or cavities. The results of the current analysis will be used in the formulation of a model for binary alloy systems that includes the reactive porous medium model.