bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructural Modeling During Multi-Pass Rolling of a Nickel-Base Superalloy
Authors: Subramanian Kannan , Cherukuri Harish P.
Published: July 2010

Superalloys are metallic alloys used for high temperature applications such as encountered in the aircraft industry and where resistance to deformation is a primary requirement. Alloy 718 is one such Nickel-base superalloy that resists deformation at elevated temperatures and is therefore difficult to hot work. One of the major hotworking operations is multi-pass shape rolling in which Alloy 718 undergoes multiple deformations in several passes along with reheating between passes. For a given composition of alloy, the high temperature flow stress is influenced to a large extent by the grain size of the microstructure. In the case of shape rolling in which the cross section changes from circular to oval in alternate passes, the correct working forces, which relate to gauge and shape control as well as to power requirements, can be estimated accurately only if the microstructure relevant to the specific pass of rolling is known. In addition, the microstructure present at the end of the rolling and cooling operations controls the product properties. Control of grain size is an increasingly important characteristic in hotworking. The narrow temperature range (980°C and 1120°C [1]) for hotworking of Alloy 718 makes the grain size control more difficult. During hotworking, Alloy 718 undergoes microscopic and mesoscopic events such as dynamic recrystallization (DRX), metadynamic recrystallization (MDRX) and static grain growth (SGG) depending on the temperature, strain rate and retained strain. Modeling these microstructural events is important in designing the rolling process. Due to the tremendous amount of time, cost and effort associated with experiments and industrial trials, numerical methods are resorted to because of the complexity of the variables involved in multi-pass rolling. One such popular numerical technique, finite element (FE) method can predict process variables such as strain, strain rate and temperature for the deformation process. In general, microstructural modeling relates these process variables to microstructural evolution. During microstructural modeling, constitutive equations describing the microstructural evolutions are developed using experiments, which can then be readily implemented in an FE package capable of modeling rolling processes.
Aspects About Sonic Pollution and Vibrations Sources in Urban Area and Solutions for Them Suppressing
Authors: Pop Petru A. , Veres Mircea , Gordan Mircea , Ungur Petru
Published: July 2010

This paper presents some aspects about sonic pollution and vibrations sources in urban area, respectively in Oradea town with its metropolitan zone, and suppressing solutions. The noise and vibration pollution in urban area represents an actual theme of environment protection in Europe and other world’s zone. In last time, Oradea Town has known a large urban and economical development, which due to including inside of urban zone two metallic railway bridges “Oradea East” and “Oradea West”, over “Crisul Repede” River. This ambient noise level and vibration loads produced by railway bridges on passing trains must be reduce, increasing of working bridge’s age and population’s comfort. The experiments about of automotive and tram traffic influence of historical monuments and public Oradea’s buildings have been extended, such as church and hospital. The tests have emphasized the necessity of suppressing noise and vibration pollution by mounting of sonic absorbent panels near buildings from railway bridges, phonic insulation of buildings walls, hour’s restriction program of traffic in these areas, and other solutions.
Modeling of Dielectrophoresis for Myoglobin Molecules in a Microchannel With Parallel Electrodes
Authors: Naga Siva Kumar G. , Mitra Sushanta K.
Published: July 2010

Myoglobin is one of the important cardiac markers, whose concentration increases from 90 pg/ml to over 5000 pg/ml in the blood serum of heart attack patients. Separation and detection of myoglobin play a vital role in deciding the cardiac arrest in advance, which is the challenging part of ongoing research. In the present study, one of the electrokinetic approach i.e., dielectrophoresis (DEP) is chosen to manipulate the myoglobin molecule in aqueous solution. A generalized theoretical expression is developed for the dielectrophoretic force acting on an arbitrary shape of the particle. Dielectric myoglobin model is developed by approximating the shape of the molecule as sphere, oblate and prolate spheroids. Mathematical model for simulating dielectrophoretic behavior of a myoglobin molecule in a microchannel is developed. The microchannel consists of parallel array of electrodes at the bottom wall. Finite element based approach is considered to solve the problem. The variation in the Clausius-Mossotti factor with respect to the applied electric field frequency is observed for aqueous solution of myoglobin. The crossover frequency is obtained as 30 MHz for given properties, for all the shapes of molecule. Shifting of crossover frequency with conductivity of medium is observed. The simulation results indicate that, the electric field and DEP forces are maximum at the edges of the electrodes and minimum elsewhere. The results also indicate that, DEP force exponentially decayed along the height of the channel.
Cohesive Finite Element Simulation of the Impact Response of Polymer Bonded Explosives
Authors: Barua A. , Zhou M.
Published: July 2010

The impact response of HMX/Estane, a Polymer Bonded Explosive (PBX), is analyzed under two-dimensional plane-strain conditions using a cohesive finite element method (CFEM). The framework enables the consideration of arbitrary microstructures. The binder polymer is modeled as a viscoelastic material. The dependence of elastic modulus on temperature across the glass transition temperature Tg (= 233 K) is considered in the constitutive framework. Also, the HMX crystals are assumed to be elastic under the conditions analyzed. Cohesive elements are implemented throughout the microstructure, allowing explicit tracking of arbitrary crack paths through each constituent or interfaces between the constituents. A contact algorithm used to track and account for the interactions between failed crack surfaces. The simulations capture the failure characteristics observed experimentally at temperatures ranging from below to above Tg of the polymer.
Evaporation of Nanoparticles Droplets on Nanoporous Superhydrophobic Surfaces
Authors: Leeladhar Rajesh , Xu Wei , Choi Chang-Hwan
Published: July 2010

In this paper, we experimentally studied the evaporative behavior of the nanofluid droplets (fluid containing metal nanoparticles) on nanoporous superhydrophobic surfaces. Uniformly dispersed in water, gold chloride (AuCl3) nanoparticles of varying sizes (10–250 nm) and concentrations (0.001–0.1% wt) were tested as nanofluids. Porous anodized aluminum oxide (AAO) with a pore size of 250 nm was tested as a nanoporous superhydrophobic surface, coated by a self assembled monolayer (SAM). During the evaporation in a room temperature and pressure, the evaporation kinetics (e.g., contact angle, contact diameter, and volume) of the nanofluid droplets was measured over time by using a goniometer. In the beginning, the initial droplet contact angles were significantly affected by the nanoparticle sizes and concentrations such that as the concentration increased, the initial contact angle decreased, which was more pronounced at larger particle sizes. During evaporation, despite the different particle sizes and concentrations, there were two distinct stages shown, especially for the change of contact angles, i.e., gradual decrease in the beginning, followed by rapid decrease in the end. No remarkable wetting transition from de-wetting (Cassie) to wetting (Wenzel) state was shown during the evaporation. Evaporation rate was influenced by nanoparticles such that it was significantly mitigated with the nanofluid droplet of the highest concentration (0.1% wt). The scanning electron microscope (SEM) images show that the ring-like dry-out pattern forms after the evaporation of nanofluids with lower concentrations (0.001%, 0.01% wt), whereas the one with higher concentrations (0.1%wt) forms a uniformly distributed pattern. These results demonstrate that nanoparticle sizes and concentrations make significant effects on interfacial phenomena in droplet evaporation on nanostructured surfaces, which will impact many engineering applications and system designs based on droplets such as microfluidics and heat transfer.
Finite Element Thermal Analysis for Microscale Laser Joining of Nanoscale Coatings of Titanium on Glass/Polyimide System
Authors: Mayeed Mohammed S. , Lubna Nusrat J. , Auner Gregory W. , Newaz Golam M. , Patwa Rahul , Herfurth Hans
Published: July 2010

Finite element thermal analysis and comparison with experiments of microscale laser joining of biocompatible materials, polyimide (PI) and nanoscale coating of titanium (Ti) on glass (Gl), is vital for the long-term application of bio-implants and important for the applications of nanoscale solid coatings. In this study, a comprehensive three dimensional (3D) transient simulation for thermal analysis of transmission laser micro-joining of dissimilar materials has been performed by using the finite element (FE) code ABAQUS, along with a moving Gaussian laser heat source. The laser beam (wavelength of 1100 nm and diameter of 0.2 mm), moving at an optimized velocity (100 mm/min), passes through the transparent PI, gets absorbed by the absorbing Ti, and eventually melts the PI to form the bond. The laser bonded joint area is 6.5 mm long on three different Ti coating thicknesses of 400, 200 and 50 nms on Gl surface. Non-uniform mixed meshes have been used and optimized to formulate the 3D FE model and ensure very refined meshing around the bond area. During the microscale laser heating finite element modeling shows widths of PI surface experiencing temperatures above the glass transition temperature are similar to the widths of bonds observed in experiments for coating thicknesses of 400 and 200 nms of Ti on Gl. However, for the case of 50 nm coating bond width using finite element analysis cannot produce and is lower than the bond width observed experimentally.
Design Optimization for Non-Resonant MEMS Gyroscope
Authors: Cui Wei , Chen Xiaolin , Xue Wei
Published: July 2010

Conventional capacitive MEMS gyroscopes require close matching between the resonant frequencies of drive mode and sense mode. However, the uncertainties in the microfabrication process impair the robustness of the gyroscopes and often lead to unpredictable device performance. This paper analyzes a 4 degree-of-freedom (DOF) non-resonant gyroscope which is less vulnerable to the fabrication perturbations. Unlike the conventional resonant gyroscope which has only one resonant frequency for drive and sense modes, the 4-DOF gyroscope includes two resonant frequencies for each mode. The non-resonant gyroscope design aims to reduce resonance frequency matching, namely to minimize the effect of the inevitable fabrication uncertainties as well as to increase the bandwidth with less sacrifice to the sensitivity. The device performance is analyzed and optimized by the behavior model approach in CoventorWare which significantly accelerates the simulation compared to the traditional finite element method. The optimized non-resonant gyroscope with higher fabrication tolerance as well as enhanced device performance is proven to be an effective design and can be used in a wide range of applications.
Implementation of an Efficient Algorithm for Virtual Prototyping of Dynamics of Molecular Conformation
Authors: Duan Shanzhong Shawn , Ries Andrew
Published: July 2010

This paper presents an O(N) algorithm and its preliminary computer simulation results for virtual prototyping of molecular systems with a simple chain structure. The algorithm is based on proper integration between an internal coordinate method (ICM) and a multibody molecular model. ICM method makes the use of recursive relations possible between two adjacent subsets within a molecular system. The multibody molecular model takes the benefits of freezing degrees of freedom of some lightly excited high frequency bonds. Because these high frequency bonds would force the use of very small integration step sizes, which severely limits the time scales for virtual prototyping of dynamics of molecular conformation over long periods of time. Thus a new multiscale model and efficient algorithm is produced to increase computational efficiency for virtual prototyping of dynamical behaviors of molecular confirmation. This paper will be initially directed towards introduction of the new model and algorithm. Then attention will be turned to the implementation of the algorithm at macro scale, which can be used to demonstrate the validity of the procedure and algorithm. Final focus will be turned to the implementation of the algorithm to a simple molecular chain at micro scale. The algorithm gives an O(N) computational performance for formation/solution of equations of motion for a molecular chain system.
Tunable Lloyd-Mirror Interferometer for Large-Area Nanopatterning
Authors: Wathuthanthri Ishan , Choi Chang-Hwan
Published: July 2010

This paper reports on a new Lloyd-mirror interference lithography system whose mirror angle is variable with respect to the substrate. We demonstrate that this tunable Lloyd-mirror interferometer significantly increases the nanopatterning area with greater controllability compared to a conventional fixed-angle system for pattern periodicity over 500 nm. The new configuration capable of the independent control of mirror angle will enhance the advantages of Lloyd-mirror interferometer for large-area nanopatterning with more flexibility.
Fatigue Analysis of Metallic Components Using Critical Distance Methods
Authors: Chattopadhyay Somnath
Published: July 2010

The high cycle fatigue strength of crack-like discontinuities in metallic structures has been investigated using the critical distance approaches. Two methods have been employed, (a) the point method, and (b) the imaginary crack method. In the point method, the stress at a critical point within the material volume is chosen as the governing fatigue criterion. The effective parameter is the distance “d” from the material surface, which is a material property and the reference parameter is the fatigue limit. The imaginary crack method involves introduction of a sharp crack at the root of a notch and the length of the crack, “l0” assumed a material constant. The point method leads to a practical design rule that uses fatigue design curves expressed in terms of equivalent strain range versus number of cycles to failure. The equivalent strain is evaluated at a distance “d” from the crack tip. In the imaginary crack method, the effective crack length is taken as the sum of the actual crack and the material parameter “l0”. It is concluded that the high cycle fatigue has a volumetric character and the proposed methods introduce the volume effect in the determination of stress and strain fields as well as the fatigue life. Using the material parameter, the number of cycles to initiate a fatigue has been determined.
Size-Specific Capture of Circulating DNA Onto a Nanotip Using Dielectrophoretic and Capillary Forces
Authors: Yeo Woon-Hong , Chung Jae-Hyun
Published: July 2010

One of the critical challenges in the fields of disease diagnostics and environmental molecular biology is detection of circulating DNA from a sample mixture. Circulating DNA is free DNA in biological solution, which can provide critical information about pathogens and toxins. Current DNA detection methods, however, are not able to directly capture circulating DNA. This paper presents a novel, size-specific concentration mechanism that captures DNA onto a nanotip using dielectrophoresis and capillary action in a size-specific way. To investigate the size-specific mechanism, the dielectrophoretic force and the capillary forces are compared. The experiment using nanospheres are performed to validate the size-specific mechanism. The size-specific concentration is also demonstrated for capturing DNA from sample mixtures. The experimental and analytical work will provide the ground work formulating the basic principles for a nanoscale concentrator in a size-specific way.
Prediction of Tensile Properties of Glass/Jute Hybrid Injection Moldings
Authors: Morii Tohru , Jumonji Nobuyuki , Ohta Tomoko , Nakai Asami , Hamada Hiroyuki
Published: July 2010

This study dealt with the effect of hybridization of jute fiber and glass fiber on the mechanical properties of fiber reinforced thermoplastics injection moldings. In the glass/jute hybrid materials the weight fraction of glass fiber was fixed at 10wt% and that of jute fiber was varied from 5wt% to 30wt%. Dumbbell-shaped specimens were prepared by injection molding, and the static tensile tests were performed with acoustic emission (AE) monitoring. AE monitoring was conducted to understand the fracture behaviors of glass/jute hybrid materials. By adding the glass fiber to jute fiber reinforced plastics the tensile strength was improved. However, too much content of jute fiber could not achieve the improvement of strength because the uniform distribution of glass fiber was restricted by too much bulky jute fiber. After tensile test the fiber distribution on the fracture surface was observed. Based on the fiber distribution of jute fiber and glass fiber the strength prediction was attempted by introducing the rule of mixture.
Mitigation of Fouling on Hollow Fibre Membrane Using Ultrasonic Transducer
Authors: Li Xu , Nnanna A. G. Agwu
Published: July 2010

Ultrasound based on-line cleaning for hollow fiber (HF) membrane filtration of synthetic wastewater was studied. An ultrasonic transducer was submerged into a filtration system in order to get an efficient cleaning of HF membranes in fouling conditions. An ultrafiltration (UF) HF membrane with the pore size at 10,000 NMWC is employed to purify waste water. The focus of this study is on the effects of temperature, ultrasonic frequency, ultrasonic power intensity and caviation micro-bubbles as well as the transmembrane pressure (TMP) performance. Experimental evidence reveals that the permeate flux increased with the application of ultrasound after fouling by sullage solution for one hour. The micro-bubble size measured by laser PDA system shows a decreased tendency with the increase of ultrasonic frequencies, and larger micro-bubbles have greater contribution to the increase of permeate flux. Results futher shows that the permeate flux measured with lower ultrasonic frequency or higher power intensity maintained higher value in general as feeding sullage water and maintain a higher risk to extend membrane pore size. In addition, the rise of the temperature around filtration system has less impact on permeate flow rate in online ultrasound system when the temperature of feed solution maintained constant.
Capacitive Tilt Sensor Using Metallic Ball
Authors: Lee Chang Hwa , Lee Seung S.
Published: July 2010

A new capacitive type of tilt sensor using metallic ball is proposed primarily to get over the contact problem in measurement of tilt angle. Its structure and fabrication process are simpler than other previous sensors. Capacitive sensing type has many advantages such as simplicity, non-contact measurement of angle, long-throw linear displacement, and sub-micron plate spacing comparing to other types. The dimension of this prototype sensor is 20mm × 20mm and the diameter of the polystyrene tube is 5mm and the thickness of the tube is 0.15mm. The test result shows the linear relationship between tilt angles and capacitances.
Computational Analysis of Input-Shaping Control of Torsional Microelectromechanical Mirrors
Authors: Thomas Starling , Daqaq Mohammed F. , Li Gang
Published: July 2010

Input-shaping is an open-loop control technique for dynamic control of electrostatic MEMS. In MEMS applications, open-loop control is attractive as it computes a priori the required system input to achieve desired dynamic behavior without using feedback. In this work, a 3-D computational electromechanical analysis is performed to preshape the voltage commands applied to electrostatically actuate a torsional micromirror to a desired tilt angle with minimal residual oscillations. The effect of higher vibration modes on the controlled response is also investigated. We show that, depending on the design of the micromirros, the first bending mode of the micromirror structures can have significant effect on the dynamic behavior of the system, which is difficult to suppress by using the step-voltage open-loop control. We employ a numerical optimization procedure to shape the input voltage from the real time dynamic response of the mirror structures. The optimization procedure results in a periodic nonlinear input voltage design that can effectively suppress the bending mode effect.
The Influence of a Two-Stage Valve Stem on an SFEMV System
Authors: Ho H. C. , Chiang W. S. , Chen H. P. , Tsay D. M.
Published: July 2010

In the shear force electromechanical valve (SFEMV) system, to unify and simplify the assembling process, a two-stage valve is employed. Three factors, mass distribution between the two sub-valves, the valve lash, and the direction of starting stimulation, are concerned for valve dynamic performance in the two-stage valve SFEMV system. With multi-domain modeling, eighteen cases are simulated to survey the impact of these three factors. Besides, experiments for interpretation of proper energy from the actuator are shown. To keep the energy from the actuator only used in overcoming friction, the results show that the current injection period should be precisely given, the mass of two valve stems should be the same as much as possible, and the actuator should turn to the valve closing direction at the beginning.
Biodegradable Micro- and Nanofibers Fabricated Through Electrospinning for Tissue Engineering and Controlled Release Applications
Authors: Kang Jia-Chen , Wang Min , Yuan Xiao-Yan
Published: July 2010

Electrospinning is a simple and versatile technique for producing micro- and nanofibers. It has been shown that electrospun tissue engineering scaffolds mimic the structure of the extracellular matrix of human body tissues. These scaffolds can improve cell attachment behavior and subsequent cell proliferation and differentiation. On the other hand, due to their large surface area to volume ratio and porous morphology, electrospun micro- and nanofibers are potentially useful for the controlled release of therapeutic agents (drugs and therapeutic biomolecules) in human bodies. In this study, electrospinning of poly(L-lactic acid) (PLLA) nonwoven micro- and nanofibrous membranes was investigated. It is known that the morphology and size of a drug carrier could play very important roles in the drug release behavior. Therefore, in the present investigation, a comprehensive study on the fabrication parameters that could affect the morphology and diameter of PLLA fibers was conducted. For electrospinning, several parameters were associated with intrinsic properties of the polymer solution, such as PLLA intrinsic viscosity, polymer solution concentration and solvent used, while other parameters were related to the experimental setup and electrospinning environment, including applied voltage, working distance, needle size, feeding rate, etc. Among these parameters, some solution related factors were important for controlling the fiber diameter. The average fiber diameter decreased from 3.2 μm to 0.6 μm when N,N-dimethylformamide (DMF) was added into a solvent system. While using dichloromethane (DCM) as the solvent, the fiber diameter could vary between 1 μm to 8 μm using different PLLA solution concentrations. Different solvent systems could also affect the morphology of PLLA fibers. On the other hand, most of the apparatus and environment related parameters could help to improve the fiber morphology, but not very significantly. It was also found that the stability of electrospinning conditions may improve the uniformity of PLLA fiber diameter. When lower voltage was applied, although the average fiber diameter increased, the range of variation of fiber diameters decreased. This study shows that PLLA fibrous membranes with a controllable average fiber diameter ranging from 600 nm to 8 μm could be fabricated via electrospinning. These fibrous membranes have the potential as vehicles for the controlled release of therapeutic agents in tissue engineering.
A Compact Nanostructure Integrated Pool Boiler for Microscale Cooling Applications
Authors: S¸es¸en Muhsincan , Akkartal Cem Baha , Khudhayer Wisam , Karabacak Tansel , Kos¸ar Ali
Published: July 2010

An efficient cooling system consisting of a plate, on which copper nanorods (nanorods of size ∼100nm) are integrated to copper thin film (which is deposited on Silicon substrate), a heater, an Aluminum base, and a pool was developed. Heat is transferred with high efficiency to the liquid within the pool above the base through the plate by boiling heat transfer. Near the boiling temperature of the fluid, vapor bubbles started to form with the existence of wall superheat. Phase change took place near the nanostructured plate, where the bubbles emerged from. Bubble formation and bubble motion inside the pool created an effective heat transfer from the plate surface to the pool. Nucleate boiling took place on the surface of the nanostructured plate helping the heat removal from the system to the liquid above. The heat transfer from nanostructured plate was studied using the experimental setup. The temperatures were recorded from the readings of thermocouples, which were successfully integrated to the system. The surface temperature at boiling inception was 102.1°C without the nanostructured plate while the surface temperature was successfully decreased to near 100°C with the existence of the nanostructured plate. In this study, it was proved that this device could have the potential to be an extremely useful device for small and excessive heat generating devices such as MEMS or Micro-processors. This device does not require any external energy to assist heat removal which is a great advantage compared to its counterparts.
Vibration Analysis of a Rotating FGM Cantilever Arm
Authors: Rahaeifard M. , Moeini S. A. , Kahrobaiyan M. H. , Ahmadian M. T.
Published: July 2010

Functionally graded materials (FGMs) are inhomogeneous composites which are usually made of a mixture of metals and ceramics. Properties of these kinds of materials vary continuously and smoothly from a ceramic surface to a metallic surface in a specified direction of the structure. The gradient compositional variation of the constituents from one surface to the other provides an elegant solution to the problem of high transverse shear stresses that are induced when two dissimilar materials with large differences in material properties are bonded. FGMs have attracted much attention as advanced structural materials in recent years. In this paper, free vibration of a rotating FGM cantilever arm is studied. The arm is modeled by an Euler-Bernoulli beam theory in which rotary inertia and shear deformation are neglected. The cross section area of the beam is rectangular with properties varying through the thickness following a simple power law exponent (n). This variation is a function of the volume fraction of the beam material constituents. The beam is composed of a mixture of aluminum and alumina. The deformation of the beam is considered to be in the plane of rotation. The equations of motion are derived using Hamilton’s principle and assumed mode method. Ten lowest polynomial functions are considered as mode shapes of the rotating beam. Natural frequencies of the arm are obtained and compared with the literature and verification is presented. Finally effects of various parameters on the natural frequencies and mode shapes are investigated.
Dynamics Modeling of Nanoparticle in AFM-Based Manipulation Using Two Nanoscale Friction Models
Authors: Babahosseini Hesam , Mahboobi Seyed Hanif , Meghdari Ali
Published: July 2010

Application of atomic force microscope (AFM) as a manipulator for pushing-based positioning of nanoparticles has been of considerable interest during recent years. Nevertheless comprehensive researches has been done on modeling and the dynamics analysis of nanoparticle behavior during the positioning process. The development of dynamics modeling of nanoparticle is crucial to have an accurate manipulation. In this paper, a comprehensive model of pushing based manipulation of a nanoparticle by AFM probe is presented. The proposed nanomanipulation model consists of all effective phenomena in nanoscale. Nanoscale interaction forces, elastic deformation in contact areas and friction forces in tip/particle/substrate system are considered. These effects are utilized to derive governing dynamics of the lumped model of AFM and nanoparticle during the manipulation process. The utilized friction models are a modified Coulomb approach and Lund-Grenoble (LuGre) model. The former is a combination of both normal force and contact surface area. The latter is dependent on the velocity of the nanoparticle and leads to stick-slip behavior of the nanoparticle. Finally, the compatibility and effectiveness of the two proposed models are simulated and compared.
Development and Testing of a Low-Cost Rapid-Cycle Hot Embossing System for Manufacturing Microscale Parts
Authors: Hale Melinda , Hardt David E.
Published: July 2010

Hot embossing is an effective technology for replicating micro-scale features in polymeric materials, but large-scale adoption of this method is hindered by high capital costs and longer cycle times relative to other technologies. This paper details a hot embossing machine design strategy motivated by maximum production speed with minimal capital cost. Innovative design aspects include the choice of new ceramic substrate heaters for electrical heating, design of a moveable heat sink to minimize heat load during the heating cycle, and the careful design of the thermal elements to minimize the heating and cooling cycle times. The hot embossing equipment fabricated from this design has a capital cost estimated to be an order of magnitude less than currently available options. The minimum cycle time is two minutes, and microstructures are replicated within a maximum area of 25mm by 75mm. The hot embossing machine has been tested to characterize the process variability. Runs of polymethylmethacrylate (PMMA) parts manufactured using this equipment are measured to have submicron variation under a variety of processing conditions.
FEM Stress Analysis and Evaluation of the Sealing Performance in Flexible Box-Shape Bolted Flange Gasketed Joints Subjected to Internal Pressure
Authors: Tenma Kentaro , Kurosawa Ryou , Sawa Toshiyuki
Published: July 2010

Bolted joints inserting gaskets such as box-shape flange connections have been widely used in mechanical structures, nuclear and chemical industry, and so on. In automobile industry, box-shape connections are applied in oil-pan structure. They are usually used under internal pressure as well as other loadings such as thermal, impact loadings and so on. In designing the box-shape flange connections with gaskets, it is important to evaluate the sealing performance of connections under internal pressure. An important issue is how to evaluate the sealing performance in the connections by using the contact gasket stress distributions at the interfaces and how to determine the initial clamping bolt force (preload) for preventing leakage. In this paper, the stresses of box-shape flange connection with gaskets subjected to an internal pressure are analyzed using the finite element method (FEM), taking into account a hysteresis in the stress-strain curves of the gasket. The contact gasket stress distributions of the connections under the internal pressure are analyzed. The leakage tests were conducted using an actual box-shape flange connection with a gasket. Using the contact gasket stress distributions at the interfaces under an internal pressure (Helium gas was used) and the amount of the leakage measured in the experiment, the sealing performances are evaluated experimentally and numerically. Furthermore, the effect of the nominal bolt diameter, the bolt pitch and flange cover seating types (raised face / flat face) is examined on the sealing performances of box-shape flange connections. Discussion is made on the sealing performance in the above connections.
Generating Near-THz Surface Acoustic Waves Using Picosecond Ultrasonics
Authors: Lee J. H. , Sadhu J. S. , Sinha S.
Published: July 2010

We present here a technique to generate high frequency SAW in non-piezoelectric substrate with nanostructure grating of period less than 100 nm fabricated on it. A short pulse laser (with rise time less than 100fs) incident on this structure creates a periodic thermal stress due to the differential absorption in the substrate and the grating. We show that this stress sets up a surface acoustic wave on the substrate that can be detected optically. Modeling the generation process and analysis of SAW spectrum reveals the critical parameters to be controlled for obtaining SAW of high frequency. We show that the grating period less than 50 nm, a laser pulse of rise time less than 100fs and substrate properties like high optical absorption and high Rayleigh velocity are necessary for generating surface acoustic waves in near-THz range. This work provides quantitative guidelines on the design of near THz phononics.
Development of Roof-Bolting Machine Bit and Chuck Isolators for Drilling Noise Reductions
Authors: Peterson Jeffrey Shawn , Kovalchik Peter G. , Yantek David
Published: July 2010

Among underground coal miners, hearing loss remains one of the most common occupational illnesses. In response, the National Institute for Occupational Safety and Health (NIOSH) conducts research to reduce the noise emission of various underground coal mining equipment, an example of which is a roof bolting machine (RBM). After the removal of coal or rock, the remaining strata may be subject to fall, either from overhead (the roof) or from the side (the rib). One method used in underground coal-mines to prevent failures requires the installation of roof bolts. The roof bolting machine operator trams the machine to the required location, drills a hole into the strata, and then installs a roof bolt, supporting the roof or the rib, as the case may be. Field studies support the premise that, on average, drilling noise is the loudest noise that a roof bolting machine operator would be exposed to and contributes significantly to the operators’ noise exposure. NIOSH has determined that the drill steel radiates a significant amount of noise during drilling. NIOSH is developing bit and chuck isolators to reduce vibration, and thus noise radiation of the drill steel, with the longer-term goal of reducing roof bolting machine operator noise exposure. Laboratory testing has shown that operator ear sound pressure levels may be reduced by 3 to 7 dB(A), depending upon the test configuration and drilling media.
Perforated Micro- and Nanopores in Free-Standing Polymer Membranes Fabricated by Nanoimprint Lithography and Pressed Self-Perfection Method
Authors: Choi Junseo , Park Sunggook
Published: July 2010

This study presents a stable and flexible method for fabricating a free-standing polymer membrane with perforated micro- and nanopores using an imprint lithography combined with a pressed self-perfection method and a sacrificial layer technique. For the fabrication, micropores were initially patterned on a double resist layer: the upper SU-8 resist layer as an active membrane layer and the lower life-off resist used as a sacrificial layer. The membrane with micropores was then pressed with a flat quartz wafer to reduce pore size down to sub-micrometer. Finally, a free-standing SU-8 membrane with perforated micro- and nanopores was successfully lifted-off from the substrate by dissolving the sacrificial layer.
Stochastic Modeling of the Bulk Thermal Conductivity for Dense Carbon Nanotube Networks
Authors: Ashtekar Nikhil A. , Jack David A.
Published: July 2010

A computational, physics-based, bulk thermal conductivity model of a neat carbon nanotube network at room temperature is developed using classical finite element techniques. The model is based on experimentally available stochastic distributions of length, diameter, chirality, and orientation, and uses theoretical results for thermal contact resistance from the literature and molecular dynamics simulations for the stochastic nature of tube separation distance. Understanding the thermal transport properties of carbon nanotube networks at various operating temperatures is crucial for the industrial acceptance of these materials in aerospace and electrical applications. Mechanisms of thermal transport are discussed including; thermal conductivity along the tube and inter-contact resistance between the tubes, where the later is considered the dominating factor. The effect of variations of several of the aforementioned stochastic factors influencing the bulk conductivity is investigated, and results demonstrate that changes in the nanotube length play a significant role in improving the bulk conductivity of the network. In addition, a brief study into localized power flow is presented and lends insight into a possible cause of premature network failure.
Modeling the Temperature-Dependence of Tertiary Creep Damage of a Directionally Solidified Ni-Base Superalloy
Authors: Stewart Calvin M. , Hogan Erik A. , Gordon Ali P.
Published: July 2010

Directionally solidified (DS) Ni-base superalloys have become a commonly used material in gas turbine components. Controlled solidification during the material manufacturing process leads to a special alignment of the grain boundaries within the material. This alignment results in different material properties dependent on the orientation of the material. When used in gas turbine applications the direction of the first principle stress experienced by a component is aligned with the enhanced grain orientation leading to enhanced impact strength, high temperature creep and fatigue resistance, and improve corrosion resistance compared to off axis orientations. Of particular importance is the creep response of these DS materials. In the current study, the classical Kachanov-Rabotnov model for tertiary creep damage is implemented in a general-purpose finite element analysis (FEA) software. Creep deformation and rupture experiments are conducted on samples from a representative DS Ni-base superalloys tested at temperatures between 649 and 982°C and two orientations (longitudinally- and transversely-oriented). The secondary creep constants are analytically determined from available experimental data in literature. The simulated annealing optimization routine is utilized to determine the tertiary creep constants. Using regression analysis the creep constants are characterized for temperature and stress-dependence. A rupture time estimation model derived from the Kachanov-Rabotnov model is then parametrically exercised and compared with available experimental data.
Hybrid Control System for Spacecraft Antenna Boom
Authors: Taylor Anastasia M. , Khatri Rajan , Dhainaut Jean-Michel , Gangadharan Sathya N. , Subramanian Chelakara , Abdelkhalik Ossama
Published: July 2010

Sensitive equipment utilized in aerospace applications experience vibrations from mechanical and thermal disturbances. Without proper vibration suppression systems, the delicate equipment can be severely damaged. A comparison between passive, active and hybrid control of light weight boom structure for space vehicles is carried out. Numerical and experimental analyses using NASTRAN finite element software are performed. Different control methods are applied, and a PID controller is implemented in the experiment. The main target of this research is to study the dynamic response of sensitive and light spacecraft structure like a boom antenna. In this experiment, the source of vibration disturbance is the force applied to one end of the structure and the response signal is captured by an accelerometer sensor at the free end of the beam. Piezoelectric Translator (PTS30 nanopositioning stage) (which is a linear actuator suitable for static and dynamic applications) is used for the reducing the vibration characteristics and thus damping out the vibrations. The maximum displacement provided by this actuator is +/− 15 mm and they provide pushing or pulling force of up to 30 N. The linear speed range of the PTS30 is 0 to 500 micrometer per second. The input to the actuator is provided by the accelerometer sensor through a power amplifier which is connected through a computer. The measured acceleration is integrated to obtain the corresponding velocities. Effectiveness of the control system highly depends on the position of the actuators. The average energy level taken over a frequency bandwidth of 4 Hz to 8 Hz will be considered as a parameter to be minimized. This research focuses on the reduction of vibration behavior of satellite boom structures over a wide frequency bandwidth using hybrid vibration control system. Here we present the results of damping effectiveness for different excitation amplitudes.
Processing and MWNT Composition Effects on the Thermal, Electrical and Mechanical Properties of PLA-MWNT Composites
Authors: Rizvi Reza R. , Kim Jae K. , Naguib Hani E.
Published: July 2010

This paper investigates the processing and its effects and the effect of multiwall carbon nanotube (MWNT) composition on the thermal, electrical and mechanical properties of polylactide (PLA)-MWNT composites. The composite films were prepared by a solvent casting process using two solvents, chloroform and 1,4-dioxane. The dispersion of the MWNTs in PLA was examined using a scanning electron microscope and was found to be more improved when 1,4-dioxane was used as the solvent as compared to chloroform. The thermal characteristics of the composites were examined on Differential Scanning Calorimetry and Thermo-gravimetric Analysis. Composites prepared using 1,4-dioxane had greater improvements in composite decomposition temperature, glass transition temperature and displayed faster crystallization kinetics. The mechanical properties of the composites were tested in uniaxial tension. Composites prepared using chloroform had a lower modulus than composites prepared using 1,4-dioxane. The electrical AC conductivity of the composites was measured over a broad frequency spectrum. Composites prepared using 1,4-dioxane displayed electrical percolation at 0.5 wt.% MWNT in PLA while percolation was absent in 0.5 wt.% MWNT composites prepared using chloroform.
An Integrated Acoustic Evaluation of Engineering Materials
Authors: Bedford Michael W. , Farrell Adrian A. , Rene´ Dukens Q. , Lados Diana A. , Norton Robert L. , Gillis Charlie
Published: July 2010

Sound propagation characteristics of various materials have been investigated. A methodology to evaluate and compare the acoustic responses of metallic and non-metallic materials was developed and validated. Various materials were acoustically examined under impact loading using a test set-up consisting of a solenoid-driven hammer, a microphone, and software to record, Fourier transform, and analyze the sound response. Materials studied for acoustic behavior included steel, cast and wrought aluminum, gray cast iron, titanium, and various composites. All materials were ranked based on their reduction of sound pressure compared to a reference material of hardened tool steel. Test data were normalized on an A-weighted scale to account for the enhanced sensitivity of the human ear at certain frequencies. The effects of specimen geometry and material composition on the resulting sounds were also incorporated in the investigation. A complete microstructural analysis was conducted on each material to relate its acoustic behavior to intrinsic material characteristics. The experimental and analytic tools and knowledge developed in this study were further applied in a manufacturing setting to redesign an impact stop for noise reduction. The proposed prototypes were tested in the industrial environment, and the results compared to the findings from the study. These developments will be systematically presented and discussed.
On the Effects of Edge Scalloping for Collapsible Spokes in a Non-Pneumatic Wheel During High Speed Rolling
Authors: Ramachandran Maya , Bezgam Shashank , Thompson Lonny L. , Ziegert John C. , Rhyne Timothy B. , Cron Steven M.
Published: July 2010

The acoustic signature produced by non-pneumatic wheels with collapsible spokes is a critical design criterion for automotive and other mobility applications. During high speed rolling, acoustic noise may be produced by the interaction of vibrating spokes with a shear deformable ring as they enter the contact region, buckle and then snap back into a state of tension. In order to identify and help understand the causes of acoustic noise for a rolling non-pneumatic wheel, a two-dimensional finite element model with geometric nonlinearity has been utilized. The model consists of a shear ring modeled as two relatively inextensible membranes with high circumferential modulus separated by a hyper-elastic material. The temporal variation in spoke length as the spoke passes through the contact zone is extracted and used as input to a three-dimensional (3-D) model of a single spoke. The 3-D spoke model is able to capture out-of-plane vibration modes of the spoke which may contribute as a source of acoustic excitation and allows for modeling of edge scalloping. Natural frequencies and mode shapes of the various spoke design strategies are computed and correlated with the frequency response of the out-of-plane spoke vibrations. Results indicate that scalloping the edges of the spoke can dramatically reduce the amplitude of vibration, but does not have a strong effect on location of frequency peaks in a FFT of the time-signal. An optimal amount of scalloping was determined which reduces maximum vibration amplitude to an asymptotic value.
Tension-Compression Asymmetry of Solid, Shape Recovered “Bulk” Nitinol
Authors: Fonte Matthew , Saigal Anil
Published: July 2010

As the shape memory material Nitinol (55% Nickel – 45% Titanium alloy) emerges to find more and more applications in engineered products, understanding the effects of material processing becomes increasingly important. Its mechanical behavior is highly non-linear and is strongly dependent on alloy composition, heat treatment history and mechanical work. Published Nitinol literature is almost exclusively related to processing and testing of thin wall, very small diameter tubing and wire devices, usually exhibiting superelastic characteristics. In strain-controlled tension-compression testing of pseudoelastic Nitinol shape memory wires, compression recovery forces were found to be markedly higher than tension forces. However, most experimental studies of the thermomechanical behavior of Nitinol (NiTi) to date have been conducted in uniaxial tension on wire devices. There is a dearth of information in the literature regarding the compression recovery of solid blocks of Nitinol. Questions exist on whether or not solid, “bulk” Nitinol products when deformed in compression will exhibit shape recovery characteristics? The potential for shape recovery of compressed solid blocks of Nitinol products, which could have large stress-strain outputs, can enable the design of novel devices in many industries. The motivation for this research is to provide the first characterization of the shape recovery effects of “bulk” Nitinol material under compressive deformation modes versus the often practiced and well understood tensile loading of wire and thin wall tubing.