bluuebunny/crossref_metadata_2025 huggingface dataset:
Brush Seal Bristle Wear Analysis
Authors: Aksit Mahmut F. , Tichy John A. , Dinc O. Saim
Published: March 2009

Turbomachinery sealing applications require accommodating large rotor excursions at high surface speeds. Achieving seal compliance under such demanding conditions combined with typical high operating temperatures poses a major engineering challenge. Formed by a dense pack of bristles, brush seals have emerged as viable alternatives to conventional labyrinth seals. Being contact seals, brush seals undergo unavoidable bristle wear in operation. Rate and extent of bristle wear determines seal life and performance. Detailed understanding of brush seal contact loads is necessary to estimate seal wear performance. The complicated nature of bristle behavior under various combinations of pressure load and rotor interference requires computer analysis to study details that may not be available through analytical formulations. This work presents a summary of a 3-D computational brush seal tip force and wear analysis. The analysis models a representative brush segment with bristles formed by 3-D beam elements. Bristle interlocking and frictional interactions (interbristle, bristle-backing plate and bristle-rotor) are included to better calculate resulting seal stiffness and tip forces. Results are compared to stiffness measurements and full scale seal wear tests.
Effect of Current Polarity on Tribological Behavior of Copper-Aluminum Electrical Interface
Authors: Bansal Dinesh , Kovalchenko Andriy , Streator Jeffrey , Danyluk Steven
Published: March 2009

Wear and friction in sliding electrical contacts is affected by a multitude of factors such as contact load, current density, sliding speed, sliding distance and materials in contact [1], [2]. Very limited studies have been done to investigate the effect of current polarity on wear and coefficient of friction. In the present study, the authors investigate the effect of current polarity on the frictional response and wear of copper-aluminum interface. Copper wire mounted on a fixture is slid on aluminum flat under different current levels. Large scale melting at the interface was observed when slider (copper) was maintained as anode. Observations of the slider and flat surface made under microscope reveal material transfer of aluminum on copper even at low current levels of 60 Amperes. The results of the study can be used in the light of applying different coatings or surface design for anode and cathode in order to minimize their wear or degradation.
Parametric Studies on Dynamic Performance of Hydrostatic Flexure Pivot Tilting Pad Gas Bearing With Radial Compliance
Authors: Petro Robert N. , Kim Daejong
Published: March 2009

Flexure pivot tilting pad gas bearings are recognized as an alternative to foil gas bearing [1, 2] for high speed turbomachinery, due to their capability to provide high rotor-bearing stability and simple structure. The flexure pivot design eliminates wear problem of axial pins or sockets at the pivots which are common in traditional tilting pad bearings. Added features such as a pivot offset and pad preloads can also be optimized to further improve the stability. Hybrid flexure pivot tilting pad gas bearing have also been reported [3]. The hybrid bearing has a direct air supply to the bearing clearance through a tiny orifice. It has shown that the hybrid operation of the tilting pad gas bearing can also increase the rotor-bearing stability [3]. In many microturbomachinery applications, hollow shafts are adopted to reduce the rotor weight and increase the bending critical speeds. However, the hollow shaft has a large centrifugal growth at high speeds requiring the gas bearing to have radial compliances. However, the radial compliance within the tilting pads can compromise the rotor-bearing stability because large displacement of the pads along the radial direction can cause hydrodynamic rotor-bearing instability associated with the increased bearing clearance (i.e. decreased effective preload) if the radial stiffness is not designed properly. Analytical studies show that optimal choice of pad radial stiffness could extend operating envelope of flexure pivot tilting pad gas bearing without deteriorating rotor-bearing stability [4]. High speed operation can generate significant amount of heat and adequate heat dissipation mechanism should also be developed. Hybrid operation is considered to have added benefit of effective cooling capability. This paper presents design studies on hybrid flexure tilting pad gas bearing with radial compliance which can accommodate large rotor centrifugal growth and also provide effective cooling mechanism.
Thermomechanical Finite Element Analysis of Impact-Induced Magnetic Erasures in Magnetic Storage Thin Film Media
Authors: Yu Ning , Polycarpou Andreas A. , Hanchi Jorge V.
Published: March 2009

Oblique impact of a slider with a rotating disk in hard disk drives was analyzed using the finite element method. A three dimensional, thermomechanical, impact model was developed to study the mechanical and thermal response during the impact of a spherical slider corner with the disk. The model was validated by comparing finite element results with analytical solutions for homogeneous glass disk under simple conditions. Impact penetration, stress and incurred flash temperature were obtained for various normal impact velocities.
Elastic/Plastic Contact Mechanics-Based Analysis of Hard Disk Drive Media Damage From Slider Corner Impacts
Authors: Katta Raja R. , Polycarpou Andreas A. , Hanchi Jorge V.
Published: March 2009

A contact mechanics-based elastic-plastic impact model which considers slider corner – head disk interaction has been proposed. This model estimates the impact contact parameters accounting for the plastic deformation effects of the realistic thin-film disk media. These properties were utilized for the elastic-plastic impact model to estimate the contact parameters. Very high impact velocities and/or small slider corner radii resulted is extremely high contact depths where the disk substrate mostly dominated the impact and the effect of layers could not be seen. At lower impact velocities and higher corner radii, the impact damage was relatively smaller. The effect of the thin-film layers, which are stiffer than the substrate, was clearly observed.
Shoe-Floor Frictional Properties for Varying Sliding Speed, Pressure and Contaminant
Authors: Beschorner K. E. , Lovell M. R. , Redfern M. S.
Published: March 2009

Injuries resulting from slips and falls are a major health concern. Current devices to measure slip resistance of shoe-floor-contaminant interfaces attempt to mimic biomechanical conditions (shoe angle, sliding speed, and normal force); however, the results are variable, depending upon the measurement methods used. Thus, an understanding of shoe-floor surface interaction from a theoretical view could provide insights into coefficient of friction (COF) of the shoe-floor interface and improve testing procedures. The purpose of this work was to provide basic measurement towards an understanding of the fundamental characteristics of shoe-floor friction. In experiment #1, the effects of nominal pressure and sliding speed on COF are examined for dry conditions using two common shoe materials. In experiment #2, effects of sliding speed on COF when a contaminant is present are examined for the same shoe materials. All experiments were conducted on a tribometer where a patch of shoe material was loaded on a rotating disc of floor material. The two shoe materials were polyurethane and polyvinyl chloride. Three load levels corresponding to nominal pressures of 4.3, 22.1 and 57.6 kPa on the polyurethane and 3.8, 19.6 and 51.2 kPa on the polyvinyl chloride and three speed levels of 16, 78 and 156 mm/sec were examined in experiment #1. In experiment #2 six levels of speed were adjusted at 16, 39, 78, 117, 156 and 195 mm/sec. COF were measured using the tribometer with a computerized data acquisition system. Nominal pressure was determined from the apparent contact area and the applied load. Three trials were recorded and averaged for each condition. In experiment #1, the COF was found to be smaller at lower speeds and nominal pressures but was independent of pressure and speed at moderate and higher speeds and pressures. At low nominal pressures, few asperities may have been in contact between the shoe and floor material, which may have caused the lower COF. In experiment #2, COF decreased with increasing sliding speed. The shape of this curve was similar to the Stribeck curve. Therefore, it was determined that as sliding speed increased, fluid thickness increased, which decreased the interaction of asperities between the shoe and floor surfaces.
Surface Analysis of Radial Lip Seals With Deterministic Micro Cavities on the Shaft
Authors: Stephens Lyndon Scott , Warren Katherine
Published: March 2009

Many approaches have been used to control the reverse pumping effect in radial lip seals. One of those is the use of oriented triangular micro-asperities on the shaft of the seal. This extended abstract presents areal surface parameter measurements from a lip seal with triangular micro-cavities oriented towards the direction of rotation. Surface parameters in the roughness, hybrid and functional groups are presented. The measurements are then discussed and placed in the context of radial lip seal performance.
Abrasive Wear Behaviour of Al-Si-Graphite Composite Under Heat-Treated Condition
Authors: Ramesh C. S. , Prasad T. B.
Published: March 2009

Composites were prepared from commercially available scrap piston by dispersing copper coated graphite particulates by stir casting, followed by heat treatment of the composite. Abrasive wear tests were conducted on the composites and the matrix alloy both before and after heat treatment. The test duration was 30min while coarse silicon carbide abrasive wheels were used. Wear was measured as weight loss of the specimen using digital weighing machine of accuracy 0.001gms. The worn surfaces were subjected to SEM analysis. Addition of graphite particulates followed by heat treatment has resulted in uniform distribution of graphite in the matrix alloy and improved abrasive wear resistance of the cast Al-Si-graphite composites.
A Kineto-Static Model for a Cracked Shaft Flexible Bearing System With Linear-Angular Coupled DOF in Bending
Authors: Alugongo Alfayo Anyika , Munda Josiah Lange
Published: March 2009

In this paper, a model for vibration of a cracked rotor shaft flexible bearing system with linear-angular coupled DOF in bending is proposed. A vector approach on the change of the system’s angular momentum at a steady state has been used to derive the equation of motion leading to a linear time-variant system. By considering the forces and moments in the kinematic pairs of the shaft and bearing, an equivalent coupled 4-DOF complex spring is analytically introduced to simulate the system at a low rotating speed with the crack as an external force. Consequently, the Kineto-static response has been obtained by restricting the system to strong parameters. Viability of the model for investigating the complex response of a shallow-crack rotor bearing system has been demonstrated by analysis and features in time history and frequency spectra explored for crack detection. Various scenarios are considered, and the presented results concur with the published literature.
Incorporation of THD Boundary Conditions for the Efficient Evaluation of Journal Bearing Performance
Authors: Keogh P. S. , Khonsari M. M.
Published: March 2009

The evaluation of the thermohydrodynamic (THD) performance of journal bearings continues to be an important issue. This is particularly so for high speed or heavily loaded bearing designs. This paper focuses attention on the thermal boundary conditions at the lubricant-bearing interface. The solid component conduction problem is solved in advance of the main THD analysis. Boundary conditions are then imposed on the lubricant THD analysis through use of an appropriate influence coefficient matrix that incorporates the solid component conduction problem. This avoids the current practice of solving the lubricant and solid component problems separately in an iterative loop to achieve continuous temperatures and heat fluxes at the interface. Instead, only the lubricant problem needs to be solved using the boundary conditions imposed by the influence coefficient matrix.
Mechatronics Applied to Tribological Systems: Experimental Examples
Authors: Santos Ilmar Ferreria
Published: March 2009

The development of active lubricated bearings and journal bearings controlled by active chamber systems has a short history of a little more than one decade. Nevertheless, research activities have shown the potential of such new mechatronic devices and this paper is intent to give an overview of the promising field of mechatronics applied to tribological systems, with emphasis on the dynamic performance of hydrodynamic bearings. The main experimental results are summarized and the advantages and limitations of such new devices are elucidated.
On the Dynamics of Gas Lubricated Triboelements
Authors: Green Itzhak
Published: March 2009

Gas lubricated triboelements are ubiquitous in many applications, from gas turbines seals, high speed dental drills, cryogenic refrigerators, oil-free bearings for turbo chargers, to read-write self acting heads in magnetic recording. In all these application the film must be maintained sufficiently precise especially in the presence of disturbances. Hence, it is insufficient to analyze such triboelements quasi statically, where a complete dynamic analysis of the system is needed. Numerous techniques have been developed over the past five decades, some are purely numerical, and others are semi-analytical. Complete analytical methods are practically non-existent because of the non-linear nature of the Reynolds equation. This work discusses a few of the common techniques, explores their intricate, and highlights limitations and flaws in implementation. Particularly: (1) in the so called “orbit codes” the equations of motion and the Reynolds equation must be solved simultaneously (and not “side-by-side”), (2) a common representation of linearized stiffness and damping is shown to be produce unrealistic results even in the simplest application, and (3) for the first time a mathematical justification is given for the use of Prony series representation of the hereditary stiffness in the so called “step-jump” method.
Between Continuum and Atomistic Contact Mechanics: Could We Bridge the Gap?
Authors: Dini Daniele
Published: March 2009

Recently various attempts have been made to compare continuum contact mechanics to atomistic simulations. The general conclusion of these studies is that continuum mechanics is not adequate to study nanoscopic interactions. Although the use of continuum mechanics at the nanometre scale has a number of limitations, some of the results obtained at atomic level using atomistic simulations can be explained at the continuum level by modelling the interacting surfaces as idealised rough contacts. This will be explicitly proven in this paper. The interfacial contact pressure distribution is found for a sphere pressed onto an elastically similar half-space whose surface is populated by a uniform array of spherical asperities (here representing individual atoms). Details of the load suffered by asperities in the contact disk, together with the effects of the roughness on the overall tangential compliance and the frictional energy losses, are found using a recently proposed technique [1]. Results obtained at continuum level are then generalised and compared to those reported in the literature at atomic level. It is shown that the use of the rough contact idealisation described here is capable of reconciling continuum mechanics and atomistic simulations by capturing some of the features that cannot be captured by the means of conventional Hertzian theory.
Contact Moment and Friction Force in Elastic Contact of Two Rough Surfaces
Authors: Sepehri A. , Farhang K.
Published: March 2009

It is reasonable to expect that when two nominally flat rough surfaces are brought into contact by an applied resultant force, they must support, in addition to the compressive load, an induced moment. The existence of a net applied moment would imply non-even distribution of contact force so that there are more asperities in contact over one region of the nominal area. In this paper we consider the contact between two rectangular rough surfaces that provide normal and tangential contact force as well as contact moment to counteract the net moment imposed by the applied forces. The surfaces are permitted to develop slight angular misalignment and through this contact moment is derived. Through this scheme it is possible to also define elastic contribution to friction since the half-plane tangential contact force on one side of an asperity is no longer balanced by the half-plane tangential force component on the opposite side. The elastic friction force however is shown to be of a much smaller order than the contact normal force.
Leakage Prediction in Mechanical Seals Under Hydrostatic Operating Condition
Authors: Elhanafi S. , Farhang K.
Published: March 2009

This paper considers leakage in mechanical seals under hydrostatic operating condition. A contact model based on the Greenwood and Williamson contact of rough surfaces is developed for treating problems involving mechanical seals in which both the micron scale roughness of the seal face and its macro scale profile are used to obtain either a closed-form equation or a nonlinear equation relating mean plane separation to the mass flow rate. The equations involve the micron scale geometry of the rough surfaces and physical parameter of the seal and carriage. Under hydrostatic condition, it is shown that there is an approximate closed-form solution in which mass flow rate in terms of the mean plane separation, or alternatively, the mean plane separation in terms of the leakage mass flow rate is found. Equations pertaining to leakage in nominally flat seal macro profile is considered and closed form equation relating to leakage flow rate to pressure difference is obtained that contain macro and micron geometries of the seal.
Generalized Stiffness Gear-Mesh Matrix Including EHD Stiffness
Authors: Stringer D. Blake , Younan Amir , Sheth Pradip N. , Allaire Paul E.
Published: March 2009

This paper presents a method to compute gear mesh stiffness based on the EHD behavior by combined finite element solution of the Reynolds Equation with the elastic contact model. It is shown that this solution requires iterative procedure to balance the computed pressure profile with the external nominal transmission load. This mesh stiffness is load dependent and therefore is a nonlinear phenomenon. The nominal stiffness value is utilized to model a full (12×12) gear mesh matrix for a linear dynamic model of rotor bearing systems including gears to evaluate system dynamics and coupling between lateral/torsional vibrations.
Boundary Effect on Particle Motion in the Head Disk Interface
Authors: Liu Nan , Bogy David B.
Published: March 2009

Simulation of particle motion in the Head Disk Interface (HDI) helps to understand the contamination process on a slider, which is critical for achieving higher areal density of hard disk drives. In this study, the boundary effect—the presence of the slider and disk—on particle motion in the HDI is investigated. A correction factor to account for this effect is incorporated into the drag force formula for particles in a flow. A contamination criterion is provided to determine when a particle will contaminate a slider. The contamination profile on a specific Air Bearing Surface is obtained, which compares well with experiments.
Lubrication Treatment for Stabilizing Spindle Impact Balancing Process in Hard Disk Mechanisms
Authors: Aruga Keiji , Watanabe Keiji , Kouhei Toru , Nakayama Nobuyoshi , Kotake Shigeyuki
Published: March 2009

In higher TPI and faster rpm drives, rotational spindle balancing is very vital for its performance and user amenity. We have developed impact balancing which uses piezoelectric impact hammer without additional mass. To obtain a stable yield, the friction of mechanical parts disturbed, hence we tried lubrication treatment for the mechanical parts. Using very thin fluorocarbon lubricant, the friction between mechanical parts diminished and became more stable, and the yield increased. We subsequently reported our experimental results.
Experimental Study on Effects of Contact Angle on Static and Dynamic Characteristics of a Liquid Meniscus Bridge in Macroscopic Scale
Authors: Matsuoka Hiroshige , Ishihara Kyouji , Inada Kazuki , Fukui Shigehisa
Published: March 2009

Two types of experiments with respect to a liquid meniscus bridge were performed; i) force curve measurements, ii) resonance curve measurements. The contact angle of a liquid (n-tetradecane) to a solid (glass) was controlled by concentration of an oil repellent which was coated on the glass surface by dipping method. Effects of the contact angle on the static and dynamic characteristics of a liquid meniscus bridge were clarified.
A Noble Photo-Grafting Technique of Perfluoropolyether Molecular Chains to the Carbon Overcoat
Authors: Kasai Paul H. , Wakabayashi A.
Published: March 2009

The technique of enhancing adhesion of PFPE (perfluoropolyether) lubricants to the carbon overcoat of magnetic media discs by irradiation with far-UV (185 nm) was reported some time ago.[1] It was later suggested that photoelectrons emanating from the carbon layer was responsible for the observed efficacy.[2] Capture of these low energy electrons by PFPE molecular chains would lead to detachment of a fluoride anion and formation of a radical center on the polymer backbone. Adhesion occurs when the radical center reacts with the carbon layer. Most recently this mechanism was challenged, and photo-cleavage of a CF2O unit from the molecular chain thus generating two radical chain fragments was proposed as the primary happening.[3] In either case the reaction commences at a point randomly selected on the molecular chain. The UV-curing process was not adopted into the production process until recently. The process is now being used for such lubricant mixtures as A20H/Z-dol and A20H/Z-tetraol. In these mixtures, however, an electro- or photo-chemistry involving the phosphazene moiety of A20H appears to play a major role.[4] One negative issue with the far-UV curing process is production of ozone if oxygen is present.
Experimental Investigations on Development of Rapid Die Wear Tests for Stamping of Advanced High Strength Steels
Authors: Cora O¨mer Necati , Usta Yusuf , Koc¸ Muammer
Published: March 2009

In a quest to achieve low-mass vehicles (i.e., higher fuel economy and lower emission), the automotive industry has been actively investigating the use of lightweight materials for a wide range of body panels and structural parts. Among the lightweight materials considered, Advanced and Ultra High Strength Steels (A/UHSS) hold promise as a prominent choice for the near future due to their relatively high formability and low cost compared to Aluminum and Magnesium alloys. However, due to their significantly higher strength than mild steel, in addition to the springback, blanking and joining issues, serious problems with the die wear are expected to arise during manufacturing. Although the die wear literature for the forming of conventional steels is prevalent, tribological issues of high strength steels have not been understood well yet. This study aims to develop a new, rapid and automated wear test for the die materials used in sheet metal forming operations of high strength steels (mainly DP and TRIP steels) and to investigate the wear, friction, and lubrication issues. With this test, the actual stamping conditions such as contact pressure, temperature, and sliding velocity can be represented well. Our preliminary tests on two different extreme contact conditions (soft-soft, hard-hard) indicate that this novel wear test method results in relatively reasonable wear rate estimations/measurements when compared to the results in the literature.
Constant-Temperature Embossing of Amorphous Poly(Ethylene Terephthalate) Films
Authors: Yao Donggang , Nagarajan Pratapkumar , Ramasubramani K. R. T.
Published: March 2009

In the standard hot embossing process for thermoplastic polymers, thermal cycling is needed in order to soften and subsequently cool and solidify the polymer. This thermal cycling, however, not only results in long cycle times but also deteriorates the quality of embossed features. A new embossing method based on slowly crystallizing polymers was investigated to eliminate thermal cycling. Poly(ethylene terephthalate) was used as a model system for demonstration. Due to its slow crystallization, amorphous PET film can be made by casting a PET melt onto a chill roll. The amorphous PET film was embossed at a constant temperature of 180°C for a period of time comparable to or longer than PET’s half-time of crystallization. During constant-temperature embossing, the film first liquefies, caused by rubber softening of the amorphous phase, and then solidifies, resulting from the crystallization of the amorphous phase. Since the embossed film is hardened under the constant mold temperature, no cooling is needed. Selected micro features, including circular microchannels and high aspect ratio rectangular microchannels, were successfully embossed using a total cycle time about 40 s.
Internal Model Control Using EWMA for a Wedge-Type Piezoelectric Motor
Authors: Ting Yung , Feng Hui-Yi , Hsieh Han-Chih , Wang Li-Yen , Li Chun-Chung , Kang Yuan , Wang Shihming
Published: March 2009

Wedge-type piezoelectric motor is easily subject to disturbance such as friction, preload and temperature change, which influences the performance significantly and reduces the positioning accuracy and reliability. In this study, Exponentially Weighted Moving Average (EWMA) method is considered to use for the velocity-feedback loop, which is included in an Internal Model Control (IMC) to achieve a Run-to-Run IMC (RtR-IMC) control structure. Such control scheme is able to adapt the control command following a changing system dynamics so that it can improve the tracking accuracy and robustness. Friction is also a problem of generating dead-zone area and causes serious nonlinear phenomenon especially while moving direction is changed. A feedforward controller is designed based on the friction model. Moreover, temperature increase appears in long-time operation, which is another factor influential to piezoelectric motor’ performance. Instead of using the Single EWMA method, which cannot efficiently deal with such environmental drift problem, a Double EWMA algorithm is developed. Practical experiment is carried out to verify the performance by using these proposed methods. It concludes that the Double EWMA associated with the friction-model-based feedforward controller is superior to the other methods.
An On-Machine Error Measurement System for Micro-Machining
Authors: Wang Shih-Ming , Yu Han-Jen , Liu Yi-Hung , Chen Da-Fun
Published: March 2009

Technology development trends towards the ability to manufacture ever smaller parts and feature sizes with increased precision and decreased cost. Micro machining is one of the important manufacturing methods to fulfill the requirements from the industry. The objective of this paper is to develop an on-machine error measurement system that can identify the micro machining errors for error compensation so that the machining accuracy of a meso-scale machine tool (mMT) can be enhanced. Because of the difficulty in handling and repositioning the miniature workpiece, the error measurement system should be non-contact and on-machine executable. To meet this requirement, a vision-based error measurement system integrating image re-constructive technology, camera pixel correction, and model comparison algorithm error was developed in this study. The proposed measurement system consists of a CCD with CCTV lens, a precision 3-DOF platform, image re-construction sub-system, and contour error calculation sub-system. By adopting Canny Edge Detection algorithm and camera pixel calibration method, the contour of a machined workpiece can be identified and compared to the pixel-based theoretical contour model of the workpiece to determine the micro machining errors. Because the system does not have to remove the machined workpiece from the CNC machine tool, errors due to re-installing and re-positioning can be avoided. To prove the feasibility of the developed algorithm and system, measurement results obtained from the vision-based measurement system were compared with the measurements of CMM, and error compensation experiment conducted on a 3-DOF mMT was also conducted. The results have shown the good feasibility and effectiveness of the developed system.
Micromilling Process Planning and Modeling for Micromold Manufacturing
Authors: Dhanorker Atul , Liu Xinyu , O¨zel Tug˘rul
Published: March 2009

In this paper, a model-based micro-end milling process planning guideline for machining micro mold cavities was proposed. The goal is to facilitate proper selections of the process parameters. Specifically, the axial depth of cut, the feed per tooth are critical in achieving performance objectives in terms of cutting forces, surface accuracy, tool life, etc. To this end, the finite element modeling was used to provide a comprehensive understanding of the underlying science base for the micro-machining (e.g., chip formation mechanisms, minimum chip thickness effect, material deformation flows, stress, strain and temperature distributions). Further, a mechanistic time-domain simulation model was utilized to provide predictive capability in practical machining performance, such as cutting forces, tool vibrations, surface accuracy, and surface roughness. The generalized process planning strategy consists of two steps: roughing and finishing. In roughing, the objective is to control the cutting force within a predefined threshold to prevent premature tool breakage and to maximize the material removal rate. In finishing, the primary objective is to control the form error within the tolerance and to obtain satisfactory surface roughness. The proposed process planning strategy was applied for micro-milling of a mold cavity in AL2024-T6.
Micro-Feature Replication via Polymer Molding at Ambient Pressure
Authors: Thakur Varun , Mosaddegh Peiman , Angstadt David C.
Published: March 2009

The study focuses on the ability of a polymer to replicate micro-features when processed at an elevated mold temperature without externally applied pressure. Replication is performed using four different polymers—High Density Polyethylene (HDPE), Polypropylene (PP), Polystyrene (PS), and Poly (Methyl Methacrylate) (PMMA) on a silicon mold containing surface features as small as 500nm. Feature replication is assessed using scanning electron microscopy (SEM) and atomic force microscopy (AFM) to compare feature dimensions of the mold to those of the replicated parts. Shrinkage in dimensions is observed to be anisotropic in the molded parts and its extent of varies among the different polymers. Crystalline HDPE shows a higher degree of shrinkage relative to amorphous polymers such as PS and PMMA. These results verify the theoretical value of shrinkage calculated from the coefficient of volumetric shrinkage values and density. By increasing the mold temperature well above the melting point of the polymer, a depth ratio of 70–80% can be achieved in parts having aspect ratios of around 0.5. The result is comparable to the values achieved by similar studies. Varying aspect ratios are fully replicated by all four polymers at elevated mold temperature. This clearly shows that increasing mold temperature results in significant improvement in depth ratios for micro-featured parts. The amorphous materials provide better feature replication and lower surface roughness than the semi-crystalline polymer.
An Experimental Study on the Relationship Between Heat Transfer Rate During Fabrication and 3D Pore Architecture of Alginate Scaffolds
Authors: Parks W. M. , Guo Y. B.
Published: March 2009

The fabrication of 3-dimensional tissue scaffolds is an essential prerequisite to engineered tissues. A polymer processing technique has been developed in this study to cast the 3D pore architecture of alginate tissue scaffolds. The alginate/calcium gluconate hydrogel was quenched in a mold and freeze dried to form a spongelike architecture whose tiny pores retain the shape of the ice crystals during quenching. Knowing that the water in the alginate hydrogel would form ice crystals if frozen and that different drying might dramatically influence the sublimation of the ice crystals, and therefore the pore architecture, we examined the speed and direction of the heat transfer out of the hydrogel as it freeze dries with regard to pore size and orientation. The pore architecture at the different locations of the fabricated scaffolds was characterized using scanning electron microscopy. It has been found that the pore size, orientation, and uniformity are significantly affected by the condition of heat transfer during freeze drying. Tailoring the pore architecture of the scaffolds is feasible by controlling the heat transfer rate. This study provides an insight on pore architecture formation and control by altered process parameters to improve the mechanical integrity.
The Synergistic Effect of Tool Geometry and Hard Turning vs. Grinding Processes on 3D Surface Micro Topography
Authors: Waikar R. A. , Guo Y. B.
Published: March 2009

Surface topography induced by precision machining is critical for component performance. This paper is to study the synergistic effects of work materials, machining processes, and tool geometry on the geometrical surface quality. Four representative surface topographies of turned and ground surfaces were prepared at “extreme” machining conditions (gentle and abusive) and compared in terms of 3-dimensional (3D) surface features of amplitude, area and volume, spatial, and hybrid parameters. The 3D surface topography maps revealed the anisotropic and repeatable nature of a turned surface which was in sharp contrast with the random and isotropic nature of a ground surface. In general, a gentle turned surface has higher values of amplitude parameters (arithmetic mean, root mean square, maximum height of summits, maximum depth of valleys, and ten-point height) than an abusively turned surface, whereas the opposite was true for the ground counterparts. Only the gentle ground surface has a negative skewness which means that the topography distribution is more biased towards the valley side. The larger kurtosis value of the abusively ground surface implies a more peaked surface topography. The gentle ground and abusively turned surfaces have a much larger bearing area ratio and therefore better bearing capacity than the gentle turned and abusively ground ones. The abusively ground surface has higher fluid retainability than other surfaces in terms of mean void volume.
Numerical and Analytical Modeling of Laser Deposition With Preheating
Authors: Fan Zhiqiang , Stroble Jacquelyn K. , Ruan Jianzhong , Sparks Todd E. , Liou Frank
Published: March 2009

Laser deposition allows quick fabrication of fully-dense metallic components directly from CAD solid models. This work uses both numerical and analytical approaches to model the laser deposition process including actual deposition and preheating. The numerical approach is used to simulate the coupled, interactive transport phenomena during actual deposition. The numerical simulation involves laser material interaction, free surface evolution, and melt-pool dynamics. The analytical approach is used to model heat transfer during preheating. The combination of these two approaches can increase computational efficiency with most of the phenomena associated with laser deposition modeled. The simulation is applied to Ti-6Al-4V and simulation results are compared with experimental results.
Stochastic Flow Model-Based Representation of System-Level Manufacturing Quality
Authors: Graton Guillaume , Guay Martin , Egbunonu Patrick , Arinez Jorge
Published: March 2009

This paper describes the application of the stochastic-flow-modeling (SFM) approach to represent the quality behavior of a manufacturing system. The paper extends the basic one-product type SFM to that of a multiple-product manufacturing system. This quality SFM-based model has aggregation by machine, product, and operational shift. The paper also describes potential supervisory control architectures that could be used in conjunction with this quality-based SFM. The distribution parameter fitting is handled with static and adaptive approaches and a comparison between these two approaches is given. Finally, results are presented for different system examples that show the accuracy of the SFM modeling approach.
Design and Fabrication of Micro Photonic Sensors for Manufacturing
Authors: Zhang Xugang , Li Xiaochun
Published: March 2009

Micron-sized subwavelength structured photonic sensors could allow critical thermo-mechanical phenomena in manufacturing processes to be monitored, while offering opportunities for fundamental understanding and better control of manufacturing processes. To implement these novel sensors into real manufacturing processes, the micro photonic sensors can be embedded at critical locations in metallic structures, which are still heavily used in hostile manufacturing environments. This paper presents the study of design, fabrication, and testing of integrated microring sensors. Various thin film optical materials were studied. Single ring resonators were designed. A new approach to fabricate metal embedded microring sensors was developed. Sensors fabricated on silicon wafers were tested and the Q factor was measured to be around 2000, the free spectrum range (FSR) was about 5 nm. Preliminary results of metal embedded sensors are also presented.
Effect of Oxygen-Radio Frequency Plasma Treatment on Three Dimensional Poly(ε-Caprolactone) Scaffolds
Authors: Yildirim Eda D. , Gu¨c¸eri Selc¸uk , Sun Wei
Published: March 2009

In the present study, the effect of oxygen-based plasma treatment on the three dimensional poly (ε-caprolactone) (PCL) was analyzed in terms of surface wettability, surface energy, and surface biocompatibility. The surface treatment was carried out for 1, 3, and 5 minutes durations on three dimensional PCL scaffolds at atmospheric pressure using a radio frequency (RF) plasma treatment system. The solid surface energies of the modified and unmodified PCL scaffolds were calculated by using the Owens-Wendt’s method. To examine the effect of oxygen plasma treatment on cell-scaffold interaction, mouse osteoblast cell line (7F2) was used. Oxygen plasma treatment contributed in decreasing the hydrophobicity of PCL for the 1-min treatment. A change in the surface energy from 39.98 mN/m for untreated to 52.54 mN/m for 1-min treated was observed by the increment in the polar component of surface energy. However, with the extended treatment times (3-min, and 5 min), the hydrophilicity, and the surface energy remained unaffected. The highest mouse osteoblast cells proliferation rate was observed for the 1-minute treated sample.
Design Analysis of a Spherical Magnetic Bearing for Multi-DOF Rotational Stage Applications
Authors: Lee Kok-Meng , Son Hungsun , Park Jong-Kweon
Published: March 2009

This paper presents an analytical method to facilitate design of a spherical magnetic bearing (SMB) for a multi-DOF rotational stage. Both passive and active regulations of the SMB are considered. We formulate the SMB dynamic model along with the method of computing the magnetic force and torque required to null any deviation of the rotor, which requires solving the magnetic field. For this, we introduce and validate a general method, referred to here as distributed-multi-pole (DMP) modeling method which requires only a limited set of known (numerical or experimental) field solutions, to derive closed-form solutions for precise calculation of the magnetic field around a permanent magnet (PM). The DMP method has been validated by comparing its modeled potential field and flux density against analytical solutions, as well as the computed force (using DMP modeled field) against published experimental data; both show excellent agreement. Finally, we demonstrate the concept feasibility of the spherical magnetic bearing, and analyze its dynamics and control performance using the DMP modeled field and computed force/torque.
Developing Strategies for Maintaining Tank Car Integrity During Train Accidents
Authors: Tyrell David , Jacobsen Karina , Talamini Brandon , Carolan Michael
Published: March 2009

Accidents that lead to rupture of tank cars carrying hazardous materials can cause serious public safety hazards and substantial economic losses. The desirability of improved tank car designs that are better equipped to keep the commodity contained during impacts is clear. This paper describes a framework for developing strategies to maintain the structural integrity of tank cars during accidents. The target of this effort is to design a tank car capable of surviving impacts without loss of lading at twice the impact speed of current equipment (or, equivalently, is capable of absorbing four times the impact energy). The methodology developed breaks down the process into three steps: 1. Define the impact scenarios of concern. 2. Choose strategies to mitigate failure modes present in each scenario. 3. Design and select technology and tactics to implement the mitigation strategies. The railroad accidents involving tank cars that occurred in Minot, ND, in 2002, and Graniteville, SC, in 2005, are examined to define the impact scenarios. Analysis of these accidents shows that two car-to-car impact scenarios are of greatest concern: head impact, where railroad equipment impacts the end of a tank car and possibly overrides it, and shell impact, where the tank car is impacted on its side, possibly off center. A conceptual design that can protect its lading at twice the impact speed of current equipment in the car-to-car impact scenarios is being developed. The conceptual design includes four functions to meet the impact requirements: blunts the impact loads, absorbs collision energy, strengthens the tank, and controls the load path to assure that loads are blunted and that energy is absorbed before the tank is loaded. Preliminary studies of available weight and space, strategies for increasing energy absorption, and strategies for strengthening the head and shell are ongoing; this paper describes the current results of these studies. Additional studies are also ongoing. The steps required to complete this effort are also described.
Dynamic Behavior of Different Wheel Profiles and Their Sensitivities to Track Characteristics
Authors: Nasr Asghar , Mehrgou Mahdi
Published: March 2009

Wheel/rail interaction and the relevant phenomena have been of much concern to many railways and researchers during last two or three decades. On going research is being conducted for optimizing interaction between wheel and track. Safety, comfort and economical aspects in rail transportation systems are the very most common research interests in rail transportation systems. The attempts made to increase both the speed and axle load of new railroad vehicles have been the main incentives of the current progressive research in rail industries. Several strategies have been implemented and are still in use by railroad agencies to control the wear of wheels and rails and to enhance safety and ride comfort. Optimizing contact characteristics of wheel and rail using the most compatible wheel and rail profiles is an important issue concerning dynamic interaction of wheel and rail. In this paper, the effect of S1002, IR1002 and P8 wheel profiles on the interaction of wheel and rail for similar track conditions are considered.
A Novel Method for Estimating the Neutral Temperature of Continuously Welded Rail
Authors: Shust William , Read David , Jury F. Brent
Published: March 2009

Traditionally, railroad track is installed so that rails that are welded together into strings longer than 400 feet experience no longitudinal thermal force at rail temperatures of 90 to 115 degrees °F. This rail temperature at which the thermal force is zero is commonly referred to as the rail’s neutral temperature. Rail at temperatures higher than the neutral temperature are in a state of compression, and in cooler temperatures are in tension. Except for the textbook case of a perfectly straight rail, these longitudinal forces must be reacted along the length of the rail via friction and the rail fasteners. A new device is designed to exploit changes in vibration of the rails within these fastenings and yield a non-destructive estimate of the installed neutral temperature. This paper will report on various on-track tests conducted at the Transportation Technology Center, Inc. (TTCI) in Pueblo, CO. This behavior was first noted empirically, without a background engineering mechanics outline. Similarly, this paper will follow the same evolution. After presentation of test data, engineering explanations will follow using theory and mechanical modeling.
Genetic Contribution to Variation in Cognitive Function: An fMRI Study in Twins
Authors: Koten Jan Willem , Wood Guilherme , Hagoort Peter , Goebel Rainer , Propping Peter , Willmes Klaus , Boomsma Dorret I.
Published: March 2009

Little is known about the genetic contribution to individual differences in neural networks subserving cognition function. In this functional magnetic resonance imaging (fMRI) twin study, we found a significant genetic influence on brain activation in neural networks supporting digit working memory tasks. Participants activating frontal-parietal networks responded faster than individuals relying more on language-related brain networks. There were genetic influences on brain activation in language-relevant brain circuits that were atypical for numerical working memory tasks as such. This suggests that differences in cognition might be related to brain activation patterns that differ qualitatively among individuals.
Visualizing Antigen-Specific and Infected Cells in Situ Predicts Outcomes in Early Viral Infection
Authors: Li Qingsheng , Skinner Pamela J. , Ha Sang-Jun , Duan Lijie , Mattila Teresa L. , Hage Aaron , White Cara , Barber Daniel L. , O'Mara Leigh , Southern Peter J. , Reilly Cavan S. , Carlis John V. , Miller Christopher J. , Ahmed Rafi , Haase Ashley T.
Published: March 2009

In the early stages of viral infection, outcomes depend on a race between expansion of infection and the immune response generated to contain it. We combined in situ tetramer staining with in situ hybridization to visualize, map, and quantify relationships between immune effector cells and their targets in tissues. In simian immunodeficiency virus infections in macaques and lymphocytic choriomeningitis virus infections in mice, the magnitude and timing of the establishment of an excess of effector cells versus targets were found to correlate with the extent of control and the infection outcome (i.e., control and clearance versus partial or poor control and persistent infection). This method highlights the importance of the location, timing, and magnitude of the immune response needed for a vaccine to be effective against agents of persistent infection, such as HIV-1.