bluuebunny/crossref_metadata_2025 huggingface dataset:
Novel Technique for Measurement of Screw Bending in Bone Fixation Constructs
Authors: James Thomas P. , Dobson Benjamin J. , Saigal Anil
Published: May 2012

The focus of the present research was to develop a reliable test method and apparatus to measure bending deflection of individual surgical screws during quasi-static loading of a plate construct. It was preferable to measure screw deflection in a non-invasive manner, thus promoting clinical relevance. Significant research has been conducted in the area of axial pullout strength and failure of screws due to torsion, but little exists related to bending deflection of surgical screws and the resultant bending stress. Current test methods to predict screw failure typically require cyclical loading of plate constructs to failure. This is both costly and time consuming. The desire to develop a new method for screw deflection measurement was instigated from observed screw failures postoperative open wedge high tibial osteotomy. Screw failures have been observed prior to healing of the open wedge, resulting in partial collapse and recurring misalignment. It was hypothesized that these failures were due to high bending loads. Engineers continue to design new plate and screw systems to strengthen the tibial plate construct. Most relevant design parameters include materials, plate geometry, number and alignment of screws, and most recently various retention methods of screw heads against the plate. With such a proliferation of designs, there exists a need to develop experimental methods for measurement of screw deflections as a precursor to ultimate cyclic failure. An open wedge, medial, high tibial osteotomy was performed on a composite replica tibia. A servo hydraulic machine was used to cyclically load the tibia in compression, while a Puddu plate construct supported the open wedge osteotomy. Deflection of individual screws was determined by means of laser projection and dial indicators affixed to exposed screw heads and reference points on the bone. During the period of elastic deformation, screw deflection measurements confirmed that each screw in the plate carried a different load. The laser projection method allows engineers to test newly designed plate constructs under relatively few cycles to determine the bending load carried by each screw. This non-invasive method of measuring screw deflection was repeatable with minimal error.
Colloidal Interactions for Nanopatterned Surfaces Based on Surface Element Integration (SEI) Approach
Authors: Hosseini Amir Ehsan , Bhattacharjee Subir , Hoek Eric M. V.
Published: May 2012

In this study, van der Waals and electrostatic interaction energies on a nanopatterned rough surface was investigated. Surface element integration method (SEI) was applied to determine the interaction between a nanostructured substrate and an infinite flat plate. Hemispherical protrusions or depressions were mathematically generated on a square lattice to represent the rough surface. The size of the asperities and the pitch (separation) between their centers were varied. From the above calculations, we have analyzed the coupling between the range of the interactions and the roughness features of the substrate by comparing the ratios of the rough surface to smooth surface interaction energies per unit area. At small separations, the rough surface van der Waals interaction is seriously attenuated in the presence of protruding asperities. This attenuation is less pronounced for depressions. The attenuation of the van der Waals interaction due to asperities diminishes at large separations. In contrast, attenuation of the electrostatic interaction is independent of the separation.
Advanced Computational Modeling of Multiphase Boiling Flow and Heat Transfer
Authors: Li Huiying , Vasquez Sergio A. , Spicka Peter
Published: May 2012

Numerical simulation of boiling flow and heat transfer presents a number of unique challenges in both theoretical modeling and developing robust numerical methodology. The major difficulty arises due to the heat transfer and phase changes between heated walls and fluid (liquid and vapor). Furthermore, modeling of the liquid-vapor interfacial transfers of momentum, heat and mass proves to be equally challenging. The multiphase boiling modeling approach described in this paper has been found to be capable of addressing these issues and is therefore suitable for inclusion in an advanced general purpose CFD solver. In the present approach, boiling flows are modeled within the framework of the Eulerian multifluid model. The governing equations solved are phase continuity, momentum and energy equations. Turbulence effects can be accounted for using mixture, dispersed or per-phase multiphase turbulence models. Wall boiling phenomena are modeled using the baseline mechanistic RPI model for nucleate boiling, and its extensions to non-equilibrium boiling and critical heat flux regime. A range of sub-models are considered to account for the interfacial momentum, mass and heat transfer, and flow regime transitions. An advanced numerical scheme has been developed for solving the model equations which can handle the heat partition between heated walls and fluid, provide for wall and interfacial mass transfer source terms in phase volume fraction equations, and address the coupling between the phase change rates and the pressure correction equation. The wall boiling models and numerical algorithm have been implemented in an advanced, general-purpose CFD code, FLUENT. Validations have been carried out for a range of 2D and 3D boiling flows, including pressurized water through a vertical pipe with heated walls, R-113 liquid in a vertical annulus with internal heated walls, a 3D BRW core channel geometry with vertical heated rods, and water in a vertical circular pipe under critical heat flux and post dry-out conditions. The results demonstrate that the wall boiling models are able to correctly predict the wall temperature and vapor volume fraction distribution. The predictions in all the cases are in reasonable good agreement with available experiments. Tests also indicate that the present implementation is fast and robust, as compared to previous approaches. All the cases are able to be simulated with the use of the FLUENT steady-state multiphase solver with reasonable numbers of iterations.
Model-Based Optimization of Coupled Thermo-Electro-Magneto-Mechanical Behavior of Load-Bearing Antennas
Authors: Santapuri Sushma , Bechtel Stephen E.
Published: May 2012

Load-bearing antennas are multi-functional sensing (actuating) and receiving (detecting) devices that are integrated with a load-bearing structure. These antennas are appealing for military applications, importantly Unmanned Aerial Vehicles (UAV). The antenna structure is subjected to mechanical forces, temperature gradients, and electromagnetic fields, giving rise to highly-coupled nonlinear thermo-electro-magneto-mechanical (TEMM) behavior. In the present work, we have developed analytical techniques and computational tools for multi-scale, multi-physics modeling of composite load-bearing antennas, specific to UAV applications. Our mathematical model, based predominantly on first principles, employs the thermomechanical governing equations (i.e., conservation of mass, momentum, angular momentum, energy and second law of thermodynamics) coupled with Maxwells equations. The macro-scale coupling terms that characterize the thermo-mechanical and electromagnetic interactions are deduced from micro-scale behavior. Our modeling has identified 92 nondimensional numbers which quantify the competition between physical effects in the operation of load-bearing antenna. Depending on the design of the structure and nature of the excitation, only a subset of physical effects are dominant, which dictates the appropriate computational model. A fixed relative ordering of all competing effects as quantified by nondimensional numbers, determines a regime of antenna/environment interaction. The mathematical structure of leading-order equations for various physical regimes is presented for use in the optimization and analysis of coupled TEMM behavior of load-bearing antennas.
A Method for the Design of Ring Dampers for Gears in Aeronautical Applications
Authors: Zucca S. , Firrone C. M. , Facchini M.
Published: May 2012

In order to reduce resonant vibration of thin walled gears used for aeronautical applications, friction ring dampers may be added to the gear. In order to design the damper geometry, engineers must be able to evaluate its effect on the dynamics of the gear. In this paper a method for the calculation of the forced response of gears with friction ring dampers for aeronautical applications is proposed for the first time. The gear and the damper are modeled by means of FEM and they are coupled by means of contact elements, characterized by tangential and normal contact stiffness. The periodical response of the system is computed in the frequency domain, by means of the harmonic balance method. The harmonic excitation is calculated by means of Fourier analysis of the periodic force profile acting on the gear teeth. The methodology is applied to a case of industrial interest. The effect of the principal design parameters of the ring damper is highlighted.
Real-Time Multi-Body Software for HIL Simulations
Authors: Righettini Paolo , Oldani Alberto
Published: May 2012

The Hardware in the Loop simulation is an useful instrument to simulate complex mechanical systems in which the subject of the test is an hardware component. The results of the simulation, closer to the real behavior of the system, are the main advantage of this approach. This application is often used during the design process to test components of a complex mechanical system before the development of the prototype (e.g. embedded systems). The literature examples show, in general, mathematical model finalized to the application. The objective of this work is focused on the development of a generic Multi-Body software for HIL applications. Some simulations examples, the dynamic of a slider-crank and of a McPherson suspension, are presented at the end of the paper.
A Novel Tactile Sensor Design for Stiffness Detection of Soft Tissues
Authors: Fath El Bab Ahmed M. R. , Ahmed Khaled I. E.
Published: May 2012

A novel tactile sensor design for stiffness detection of soft tissues is proposed aiming to get output readings uninfluenced of the contact conditions. The sensor principle is based on the concept of applying two springs, with considerably different stiffnesses, to soft tissue for stiffness detection. The sensor consists of two coaxial diaphragms with contact mesa to work as two different springs. The sensor mesas are designed in circular shape to compensate the error caused by the pushing distances between the sensor and the soft tissue. A finite element simulation model is developed to investigate the sensor performance. The results show that the sensor can successfully distinguish between different tissues with close stiffnesses independently of the pushing distance between the sensor and the tissue. Moreover the sensor shows good output linearity when measure different tissue stiffnesses.
Ballistic Heat Transfer Modelling in Semiconductor Electronic Devices: A Modified Fourier-Based Approach
Authors: Nabovati Aydin , Sellan Daniel P. , Amon Cristina H.
Published: May 2012

It is well known that continuum-based thermal transport models, such as the Fourier law, fail when the characteristic size of a system becomes comparable to the mean free path of carriers that transport thermal energy. The current work uses the lattice Boltzmann method to develop two modifications to the Fourier heat equation so that it can capture sub-continuum effects. The two modifications are: (i) a size-dependent thermal conductivity and (ii) a size-dependent temperature jump at the system boundaries.
Experimental Testing of a Wind Tunnel Model for Use in a Vertical Axis Wind Turbine
Authors: Panther Chad C. , Williams Kenny A. , Wilhelm Jay P. , Smith James E.
Published: May 2012

Experimental testing was performed on a circulation controlled airfoil with upper and lower trailing edge blowing slots, controlled by span wise pneumatic valves. The augmented blade was designed for application to a circulation controlled vertical axis wind turbine. The design is based upon a conventional NACA0018 shape, replacing the sharp trailing edge with a rounded Coanda surface and blowing slots. A scale model with a chord of 8 inches and span of 16.5 inches was created using an ABS plastic rapid prototyping machine. In the past, circulation control wind tunnel models have been constructed with a separate blowing slot and trailing edge using conventional machining methods. The slot must be tediously aligned along the span for a consistent height which ultimately affects the uniformity and performance of the circulation control jet in combination with the flow rate. The rapid prototyping machine eased fabrication as a modular trailing edge section was printed which includes the Coanda surface, blowing slot, and diffuser all in one piece. Pressure taps were integrated by the prototyping machine into both the printed skin and trailing edge module. This method left additional space inside the model for circulation control valving components and eliminated the need for machining pressure ports. This paper will outline the model building procedures, wind tunnel test rig, and experimental results. Aerodynamic forces were determined by both load cells and surface pressure measurements; the agreement between the two methods will be analyzed and addressed. Test conditions include various angles of attack (±20°) at Cμ = 0, 0.02, 0.06, and 0.10; the test Reynolds number was kept constant at 300K. The results indicate that the blade performed at ΔCl/Cμ near 30 for Cμ = 0.02.
Study of Blade Wear in Reciprocating Sawing
Authors: James Thomas P. , Domblesky Joseph P.
Published: May 2012

Previous work has resulted in an analytical model for linear sawing processes which incorporates key process parameters and is capable of predicting cutting rate. While this provides useful information to guide saw design and cutting, rapid blade wear has a pronounced effect. It is necessary to characterize this effect of cutting edge wear on sawing rates. In the present study, work was conducted using the reciprocating sawing process to assess geometric changes of individual blade teeth and how this affects cutting rate. Geometric changes resulting from blade wear were analyzed and an expression was developed that allows the edge radius to be predicted as a function of cutting conditions and time. The cutting rate model predicts that as edge radius increased, cutting rate would fall exponentially and this was confirmed by experiment. Predicted edge radius values in conjunction with the cutting model were found to provide good agreement with experimentally obtained cutting rate results.
Design of a PZT Sensor Network Based on Guided Lamb Waves for Structural Health Monitoring of Metallic Structures
Authors: Rocha Bruno , Silva Carlos , Suleman Afzal
Published: May 2012

A Structural Health Monitoring (SHM) system of metallic structures based on guided Lamb waves is presented. Lamb waves are reflected on discontinuities in material properties and geometries such as damage. Lamb waves present advantages when applied on thin structures due to their low amplitude damping which enables them to travel longer distances. The selection of transducers, their size and selected locations in the structure are described. Additionally, the design, development and implementation of a new signal generation and data acquisition systems is presented in detail. The requirements leading to the development and selection of these systems are explained and particularly the selection of the actuation signal is discussed. A damage detection algorithm based on the comparison between the damaged structural state and a healthy reference state is used to detect damage based on reflected Lamb waves. Subsequently, the detection algorithm based on discrete signals correlation was further improved by incorporating statistical methods. Tests performed on a plate with multiple surface cuts, through the thickness cuts, loosened rivets and cuts originating from rivets resulted in repeatable detections of 1 mm damages with a probability of detection greater that 95%. New tests are currently being performed on composite panels with embedded Fiber Bragg Grating (FBG) optical sensor network to detect the fast propagating Lamb waves.
Size Effects in Green-Kubo and Direct Method Molecular Dynamics Predictions of Thermal Conductivity
Authors: Sellan Daniel P. , Landry Eric S. , Turney Joseph E. , McGaughey Alan J. H. , Amon Cristina H.
Published: May 2012

The bulk thermal conductivity of Lennard-Jones argon and Stillinger-Weber silicon is predicted using the Green-Kubo (GK) and direct methods in classical molecular dynamics simulations. While system-size independent thermal conductivities can be obtained with less than 1000 atoms for both materials using the GK method, the linear extrapolation procedure [Schelling et al. Phys. Rev. B 65, 144306 (2002)] must be applied to direct method results for multiple system sizes. It is found that applying the linear extrapolation procedure in a manner consistent with previous researchers can lead to an underprediction of the GK thermal conductivity (e.g., by a factor of 2.5 for Stillinger-Weber silicon at a temperature of 500 K). To understand this discrepancy, phonon properties are predicted from lattice dynamics calculations, and from these, length-dependent thermal conductivities. These results show that the linear extrapolation procedure is only accurate when the minimum system size used in the direct method simulations is comparable to the largest mean free paths of the phonons that dominate the thermal transport. This condition has not typically been satisfied in previous works.
Novel Morphing Wing Design Using Antagonistic Shape Memory Alloy Actuation
Authors: Sofla A. Y. N. , Meguid S. A. , Tan K. T.
Published: May 2012

A wing shear concept is adopted here to design and fabricate morphing wing for an unmanned aerial vehicle. The concept uses a parallelogram wing-box that consists of several composite rib shells that are hinged to two active spars. Antagonistic shape memory actuation is used to flex the spars and consequently shape morph the wing between straight and curved shapes.
Measuring Ignition Temperature and Heat Generation From Moist Propane-Oxygen Mixtures on Platinum
Authors: Leichliter Katie , Steciak Judi , Budwig Ralph , Beyerlein Steve
Published: May 2012

The surface temperature and heat generation from reactions of propane-water-oxygen-nitrogen mixtures on a platinum wire catalyst were determined using microcalorimetry. A 127 micron diameter, 99.95% pure Pt coiled wire was placed crosswise in the quartz tube of a plug flow reactor. A precision sourcemeter with a four-lead technique allowed the platinum wire to measure its average temperature by serving as a resistance thermometer, and enabled us to determine the amount of heat generated from surface reactions. Ignition temperatures varied from 450 to 500 K and heat generation from 0.8 to 11.5 W/cm2 depending on the absolute amounts of propane and oxygen, the propane:water ratio, and the fuel-oxygen equivalence ratio. As propane:water molar ratios reached 70:30, the temperature required to initiate surface reactions was as much as 6K higher. No clear effect of water addition on the release of energy due to surface reactions was observed; values were within 2% to 3% agreement between wet and dry experiments. These experimental results aid in understanding the heat transfer processes of catalytic igniters used to ignite fuel-lean mixtures.
Experimental Testing of Periodic Roughness Elements on a Small Scale Wind Turbine Blade
Authors: Gregg Jason R. , Van Treuren Kenneth W.
Published: May 2012

When studied in large wind turbines, roughness on wind turbine blades has been shown to decrease wind turbine performance by up to 50%. However, during wind turbine testing in the Baylor University Subsonic Wind Tunnel, roughness effects that were an artifact of the blade manufacturing process led to a significant power increase over smooth blades at the design wind speed of 10 mph. These results have led to an investigation of the effects of roughness on wind turbine performance under a flow condition with local Reynolds numbers ranging from 14,200 to 58,800. It was found that under these flow conditions the roughness can improve measured power output by up to 126% when compared with a smooth blade. This paper examines the conditions where roughness can positively affect the operation of a wind turbine by testing a 500 mm diameter, horizontal axis, three blade, fixed pitch wind turbine system in a wind tunnel. The experiments have been carried out on a single direct-drive wind turbine model and a single blade design using the NREL designed S818 airfoil. The design point for the blades tested is 10 miles per hour, with a tip speed ratio of 7. Roughness can be an effective treatment when used at or near the stall speed of the wind turbine blade for lower Reynolds number conditions. The roughness elements tested were both perpendicular to and along the flow lines. These blades were then compared to a blade configuration without roughness elements.
Explosively Driven Fragmentation Experiments for Continuum Damage Modeling
Authors: Lambert David E. , Weiderhold Joseph , Osborn John , Hopson Michael V.
Published: May 2012

The explosively loaded right-circular tube geometry is used as the basis for dynamic fracture and fragmentation modeling. Details of the cylinder configuration are investigated to prescribe controlled loading conditions of uniaxial stress and plane strain. Earlier works by Goto et al [1] had used thin-walled tubes to provide plane strain loading and shorter “rings” to establish uniaxial stress conditions. This paper extends on that work to look at alternative cylinder dimensions and metals of interest. A tungsten alloy, Aero-224, and a high strength steel, Eglin Steel (ES-1), are the subject metals. Transient continuum-mechanics simulations evaluated whether the stress triaxiality conditions were being met as design parameters of cylinder material, cylinder wall-thickness, cylinder length, and initiation configuration were varied. Design analysis shows that the thin cylinders of ES-1 steel do establish the desired plane strain conditions as it expands to failure. Ultra-high speed photography experiments verify the time of fracture and correlate casewall expansion and velocity measurements. Synchronization of the code and diagnostics measurements is presented as a valuable analysis method. On the other hand, rings (i.e. uniaxial stress) of the Aero-224 tungsten alloy were failing just short of uniaxial stress approximating conditions. Analysis of the Aero-224 rings indicated it must be capable of achieving at least a 25% strain to failure in order to have the triaxiality condition satisfied. Strain to failure measurements directly from recovered fragments were less than 14%. Nevertheless, a Weibull distribution was fit to the empirical data set and used to drive a statistically compensated fracture model. Results and discussion of the failure strain distribution and the ability for continuum codes to adequately conduct such simulations are presented.
Implementation of Robots Competition Into a Freshman Level Course
Authors: Joo Sung-Hwan
Published: May 2012

This paper presents the design and implementation of the 6 week-long robotics competition project at Grand Valley State University, MI. This particular course is named as “EGR-101” and this course is the first engineering course that all freshmen are required to take. Described are the infrastructure used to run the competition, course topics, the educational outcomes, and student responsibilities that make this competition an excellent opportunity for freshman student educational growth without too much load for students. This robot competition provides a foundation for students to experience the first real design process while working on the team-based project that simulates the real industrial project. With faculty supervision, the students have full responsibilities for developing the initial concepts, manufacturing a robot and competing at the competition. Each semester, a new set of the competition that results in the development of new robots. Also, methods to improve the competition will be presented and discussed. The key student learning possibilities that are presented in the paper include: a) team-based learning; b) communication skills; c) leadership skills; d) organization and management skills; e) manufacturing skills. Four examples of real competition are presented and discussed in the paper include: a) catching the falling balls competition,; b) air-hockey competition; c) mars rock competition; d) robot world cup competition.
Electro-Thermal Icing Mitigation System for Polymeric Composite Airfoil
Authors: Mohseni Maryam , Mertiny Pierre , Amirfazli Alidad
Published: May 2012

Polymer composite materials are widely used in aircraft and wind turbine industries due to their high specific stiffness and strength. In this study the concept of an electro-thermal anti-icing system is developed using composite material. Controlling temperature distribution and minimizing energy consumption can be the main benefits of such an anti-icing system. The thermal behavior of a composite material, power consumption and the type of thermal system were characterized for designing the icing mitigation system. Constantan wires as thermal elements were embedded inside fiberglass/epoxy composite laminates, and the thermal characteristics of the system at specific power levels were investigated using thermocouples in a wind tunnel under room temperature and cold room conditions. When applying power, the surface temperature reached 50% of its final steady-state value in 20s. To obtain a relatively uniform temperature distribution and prevent the formation of cold spots on the surface, the maximum distance between the thermal elements was 1cm. The temperature of different points on the surface increased with increasing power, and its trend was the same in room temperature and cold room tests. In cold room tests, a surface temperature above 5°C was reached at the thermal elements and between them at 0.42 W/cm, which is sufficient to prevent ice formation in icing condition. This power did not cause thermal degradation of the composite material.
Enhancing Engine Operations in Off-Grid Renewable Energy Applications Through the Additional Use of Hydrogen
Authors: Robbins Curtis , Jacobson Roger , Purcell Rick , Collier Kirk , Wagner Ralph , Mahderekal Isaac
Published: May 2012

The current renewable energy transformation taking place around the world has led to drastic advances in technology that relates to the issue of climate change. Although many solutions have been found and/or created, there has yet to be one that can, on its own, solve the problem of finding an environmentally friendly energy source. This leads to the challenge of creating an integrated system which relies on several components with different types of energy. It has been the goal of this study to further enhance an off-grid renewable energy power system to supply economical, secure, and continuous electrical power, in an environmentally conscious way, for various types of loads. The previous power system consisted of a mobile unit with inverters, batteries, hydrogen generator, hydrogen storage, propane storage and an internal combustion engine generator that was connected to photovoltaics and wind turbines while being controlled and monitored by a single computer unit. The only pollutants emitted from this power system were the result of the use of propane as a backup fuel, when renewable energy was insufficient. Even though propane is a fossil fuel, its use in this study allowed the system to be simpler and more cost effective. With the assistance of Southwest Gas Corporation, a more efficient and reliable internal combustion engine was acquired. The three cylinder engine, with a 10,000 hour maintenance interval, was converted from natural gas to combust either hydrogen or propane. The engine provides mechanical power to a belt driven alternator supplying electricity to the load and other components of the system. Initial testing of the engine achieved engine dynamometer efficiency of over 40% using propane at wide open throttle and 45% using hydrogen at wide open throttle. The output under these conditions was roughly 20 HP using propane and 10 HP using hydrogen. The current system is not mobile but has the potential to be mobile by using an existing KOH electrolyzer for hydrogen generation with a larger output and hydrogen storage capacity.
A Heat Recovery Study: Application of Intercooler as a Feed-Water Heater of Heat Recovery Steam Generator
Authors: Shukla P. , Izadi M. , Marzocca P. , Aidun D. K.
Published: May 2012

This paper evaluates the possibility of combining an intercooled gas turbine power cycle with a steam turbine cycle and the application of the intercooler as a feed-water heater for the heat recovery steam generator. In advance gas turbines the intercooler is used to improve the overall efficiency of the simple cycle but a noticeable amount of heat is wasted to the atmosphere. However, this energy can be recovered by using the proposed method in the current study. Accordingly, a thermodynamic study is done to investigate the improvement in efficiency achieved by feed-water heating. First the effect of intercooler parameters on the outlet condition of the water is studied. The bottoming cycle is then studied in details for the effect of feed-water temperature. An estimate of the energy saving by using the proposed method will be reported. The results show that less heat input will be required for the same amount of steam generation. The current study provides a theoretical support for waste heat recovery from the intercooler.
Stress Intensity Incubation Periods for the Al-Hg Coupled Subjected to LME
Authors: Keller Scott G. , Gordon Ali P.
Published: May 2012

When in the presence of liquid metal environments, structural materials can potentially lose the ability to deform and plastically flow. In the case of a ductile material, the result of this reduction in flow ability is a transition from ductile to brittle behavior, resulting in a brittle-like failure. This phenomenon is known as liquid metal embrittlement (LME) and is a subset of the more commonly known family of environmentally assisted cracking (EAC). Both EAC and LME have a significant negative impact on structural materials that are designed to behave elastically. Previous research in all facets of EAC, including stress corrosion cracking (SCC), corrosion fatigue (CF) and LME, has revealed that structural materials subjected to loading will generate and propagate cracks at stresses and stress intensities well below the critical values for that material. Additionally, crack tip velocities have been predicted and observed to be orders of magnitude greater than in ambient environments, with velocities in the range of tens to hundreds of centimeters per second. A variety of experimental routines have been used to characterize the interaction and develop microstructural failure mechanism in LME; however, uncertainty still surrounds the true failure mechanism. In a novel experimental approach, the dependence of the stress intensity factor (SIF) on crack propagation in the presence of a liquid metal was observed. Fracture mechanics specimens machined from Al7075-T651 in the S-L orientation were fatigue pre-cracked and incubated under load while submersed in liquid mercury. The result was the observation of rupture times over a range of stress intensity factors. It was noted that any stress concentration could provide the necessary criterion for crack initiation and propagation, regardless of the presence of a crack. Critical stresses and critical microstructural orientations dictated rupture paths more so than a pre-formed fatigue crack. Further experimentation, involving original and novel methods, has been conducted to determine the relationship between the stress intensity factor, stress concentration and microstructural orientation. Ultimately, the goal to confirm, extend or reject current microstructural failure mechanisms can be achieved through continued experimental routines.
A Physically-Based Anisotropic Discrete Fiber Model for Fibrous Soft Tissues
Authors: Flynn C. , Rubin M. B. , Nielsen P. M. F.
Published: May 2012

Physically-based fibrous soft tissue models often consider the tissue to be a collection of fibers with a continuous distribution function to represent their orientations. This study proposes a simple model for the response of fibrous connective tissues in terms of a discrete number of fiber bundles. The proposed model consists of six weighted fiber bundles orientated such that they pass through opposing vertices of an icosahedron. A novel aspect of the proposed model is the use of a simple analytical function to represent the undulation distribution of the collagen fibers. The mechanical response of the elastin fiber is represented by a neo-Hookean hyperelastic equation. A parameter study was performed to analyze the effect of each parameter on the overall response of the model. The proposed model accurately simulated the uniaxial stretching of pig skin with an 8% error-of-fit for stretch ratios up to 1.8. The model also accurately simulated the biaxial stretching of rabbit skin with a 10% error-of-fit for stretch ratios up to 1.9. The stiffness of the collagen fibers determined by the model was about 100 MPa for the rabbit skin and 900 MPa for the pig skin, which are comparable with values reported in the literature. The stiffness of the elastin fibers in the model was about 2 kPa.
An Innovative Non-Petroleum Rhizobium Tropici Biopolymer Salt for Soil Stabilization
Authors: Larson Steven , Ballard John , Griggs Christopher , Newman J. Kent , Nestler Catherine
Published: May 2012

Construction site soils are a significant source of sediment, and pollutants carried by sediment, to surface water runoff. Currently, silt fences/barriers, petroleum-derived polymers, and re-vegetation are the primary tools to prevent sediment loss from construction areas. Even with these methods in place, the U. S. Environmental Protection Agency estimates that 20 to 150 tons of soil per acre is lost to storm water runoff from construction sites each year. A low-cost, environmentally friendly soil amendment that reduces erosion from construction sites would improve surface water quality. An extracellular polymeric substance (EPS) is produced naturally by the symbiotic soil bacterium Rhizobium tropici. A dry, easily transportable salt of this biopolymer, when mixed with soil at low levels (0.01 to 0.5% by mass) substantially increases the soil strength for load bearing, decreases surface erosion and suspended solids in surface water runoff. Re-vegetation is also assisted by biopolymer application, since drought resistance and seed germination rates can be increased by 30% to 40% using the biopolymer. Results of mesoscale rainfall lysimeter system demonstrations of soil amendment with biopolymer documents reduced soil erosion, reduced transport of suspended solids in surface water runoff, and increased establishment success of vegetative cover under simulated drought conditions in biopolymer amended soils.
Stand-Up Forklift Acceleration
Authors: Railsback Ben T. , Ziernicki Richard M.
Published: May 2012

This paper will examine the accelerations present during the operation of stand-up forklifts. Forklifts, or powered industrial trucks, are typically operated from 1 of 2 postures. Forklifts are either operated from a seated posture or a standing posture. Previous research has focused on the threshold of acceleration at which a standing forklift operator will be unable to maintain postural stability, but did not detail peak and average accelerations generated by forklifts during typical turning maneuvers. This paper will detail the accelerations generated by stand-up forklifts during typical operation from a theoretical examination of vehicle dynamics and present experimental data acquired during stand-up forklift testing. This paper will further examine performance required by consensus and industry standards, industry practice and the safety implications of stand-up forklift acceleration. The record of serious lower leg injury associated with stand-up forklifts, reports of ejection or loss of balance from the operator and data regarding acceleration present in the operator compartment support the use of a door for stand-up forklifts.
Novel Flexure Design for a High-Temperature Thermal Storage Vessel Coupled to a Free-Piston Stirling Engine
Authors: Qiu Songgang , Yang Bozhi , Galbraith Ross
Published: May 2012

This paper presents the design and simulation of a novel flexure structure to potentially support a thermal energy storage (TES) salt vessel that is mounted on a solar dish Stirling Engine. During operation, the TES vessel expands significantly due to the elevated salt temperature leading to large deformation (thus high thermal stress) and large temperature change on the flexures. The flexure design consists of two sets of stacked flexures (∼100 mm in distance), each having eight stacked L-shaped flexures symmetrically distributed around the salt vessel. The axial and circumferential section of each flexure allows the radial and axial vessel expansion respectively. The stacking concept is expected to provide sufficient lateral rigidity (to avoid sag under gravity) while still allows the desired axial flexibility. Super Alloy Inconel 625 is selected as the flexure material due to its desired properties at elevated temperatures. A simplified model and a system model (including flexures, dummy engine, and salt vessel) of the design were analyzed using Finite Element Analysis (FEA). Analysis shows that the design meets the stress, deformation, and fatigues requirements. Test will be conducted to verify the simulation results. The flexure design is compact, simple, and low-cost to fabricate, and the concept can potentially be used for other applications that involve support of structures with large thermal expansion.
AFM Investigation of Avian Influenza Viruses
Authors: Srinivasan Balaji , Rokadia Husein , Tung Steve , Wang Ronghui , Li Yanbin
Published: May 2012

The present paper describes a direct label-free diagnostic method that uses atomic force microscopy (AFM) to identify avian influenza virus strains through their electrical properties. In this method, a single virus particle is sandwiched between a rigid, conductive substrate and a conductive AFM tip (radius ∼ 8nm). Electrical characterization is achieved by probing the complex impedance spectrum of the sandwiched virus while mechanical characterization is achieved through nanoindentation. A total of three virus strains (inactivated) with different combinations of glycoprotein subtypes (H2N2, H3N5 and H4N6) were tested. Results from the electrical characterization indicate that the impedance spectra of different virus strains are indeed different. While the average electrical capacitance of a virus particle is about 17pF, the variation from one strain to another can be as high as 70%. A COMSOL Multiphysics™ simulation was carried out to estimate the electrical properties of the glycoproteins on the virus particle by comparing the simulated capacitance to the experimentally obtained values. The result indicates that the electrical conductivity of the glycoproteins is in the range of 9 to 14 mS and the dielectric constant value is around 2. The present results strongly suggest the possibility of using AFM as a diagnostic tool for direct recognition of avian influenza virus strains.
Position Domain PD Control for Contour Tracking
Authors: Ouyang P. R. , Dam Truong
Published: May 2012

For multi-axis motion control applications, contour tracking is one of the most common control problems encountered by industrial manipulators and robots. In this paper, a position domain PD control method is proposed for the purpose of improving the contour tracking performance. To develop the new control method, the multi-axis motion system is viewed as a master-slave motion system where the master motion is sampled equidistantly and used as an independent variable, while the slave motions are described as functions of the master motion according to the contour tracking requirements. The dynamic model of the multi-axis motion system is developed in the position domain based on the master motion by transforming the original system dynamic equations from the time domain to the position domain. In this control methodology, the master motion will yield zero tracking error for the position as it is used as reference, and only the slave motion tracking errors will affect the final contour tracking errors. The proposed position domain PD controller is successfully examined in a Cartesian robotic system for linear motion tracking and circular contour tracking.
Modeling and Simulation of PV Arrays
Authors: Sayed Khairy , Abdel-Salam Mazen , Ahmed Mahmoud , Ahmed Adel A.
Published: May 2012

Modeling of PV generator represents very important goal. Such modeling will allow conducting measurements without the constraints of environmental conditions. In addition it will save the use of an actual PV array, other related equipments and time. The objective of this research work is to develop an accurate and simplified photovoltaic source model. The developed model considers most of environmental variables such as: ambient temperature, solar radiation incident angle, radiation intensity, wind velocity and partial shading. Results of PV array model characteristics are easily obtained by connecting variable resistance across the PV arrays. The simulated characteristics are in good agreement with those obtained from the available experimental data; model can be used to achieve optimal choice and design of the power converter interfacing the PV generator to the utility. Further more, the model will allow choosing the suitable power converter control methods.
A Novel Undergraduate Combustion Teaching Approach Using Three-Dimensional Combustion Surfaces
Authors: Costarell Michael David
Published: May 2012

Presently, mechanical engineering thermodynamic classes discuss the individual boiler, reciprocating engine, and gas turbine cycles, while other courses mention the combustion of individual natural gas, oil and coal fuels. Though these processes and fuels have different working fluids and air-to-fuel ratios they have predictable and comparable flue gas oxygen and carbon dioxide. Presented is a curriculum supplement that allows students to model three-dimensional plots of oxygen and carbon dioxide both as varied by hydrogen-to-carbon ratio and air-to-fuel ratio. The typical operating areas are then superimposed on these three-dimensional plots for industrial boilers (3 to 25 MW), power generation boilers (25 to 1,000 MW), reciprocating engines (0.1 to 5 MW), and gas turbines (0.1 to 100 MW). As power generation and transportation fuels become scarce and more expensive, future engineering employees must know how to minimize energy consumption and cost for a variety of fuels and combustion systems. This new teaching approach provides students a concise overall combustion curriculum that predicts the theoretical flue gas mole fraction of any common combustion process used with the major fuel sources.
Investigation of the Effectiveness and Efficiency of the Exact Closure: Comparison With Industrial Closures and Spherical Harmonic Solutions
Authors: Agboola Babatunde O. , Jack David A. , Montgomery-Smith Stephen , Smith Douglas E.
Published: May 2012

For stiffness predictions of short fiber reinforced polymer composites, it is essential to understand the orientation during processing. This is often performed through the equation of change of the fiber orientation tensor to simulate the fiber orientation during processing. Unfortunately this approach, while computationally efficient, requires the next higher ordered orientation tensor, thus requiring the use of a closure approximation. Many efforts have been made to develop closures to approximate the fourth-order orientation tensor in terms of the second order orientation tensor. Recently, Montgomery-Smith et al (2010) developed a pair of exact closures, one for systems with dilute suspensions and a second for dense suspensions, where the later works well for a variety of diffusion models. In this paper we compare the fiber orientation results of the Fast Exact Closure (FEC) for dense suspensions to that of the Spherical Harmonic solution, which although considered to be numerically exact does not readily lend itself to implementations in current industrial processing CFD codes. This paper focuses on a series of comparisons of material stiffness predictions between the FEC, current fitted closure models, and the spherical harmonics solution for a thin plate subjected to pure shear. Results for the select flows considered show the similarities between the current class of orthotropic fitted closures and that of the FEC. Although the results are similar between the fitted closures and the FEC, it is important to recognize that the Fast Exact Closure is formed without a fitting process. Consequently, the results are anticipated, in general, to be more robust in implementation.
Comparison of Multiaxial Fatigue Criteria to Evaluate the Life of Crankshafts
Authors: Rodrigues Minucci Frederico , dos Santos Auteliano Antunes , Lima e Silva Rafael A.
Published: May 2012

Crankshafts are subject to multiaxial fatigue because of the complex stress distribution caused by the loads when this engine component is in service. So far there is no universally accepted approach to multiaxial fatigue; each theory is used for a determined application. Among the many high-cicle fatigue criteria, two have been largely accepted to be used with mechanical components, the one based on the critical plane and the one based on the stress invariant. This work presents the comparison of the safety factors calculated with those criteria for a conventional crankshaft. As critical plane criteria we chose those known as Matake, McDiarmid, and Dang Van, each one with a different approach. Same way we chose the Sines, Crossland, and Kakuna-kawada criterias as the stress invariant approaches. First, the work describes the basic concepts and the fatigue criteria listed. Following that the loads over the crankshaft are estimated from the loads flowing through the conrods and from the dynamic of the movement for critical points of the crankshaft. The third step was to apply the criteria to evaluate the safety when the component is working at 1700, 2100, and 3050rpm, which are the speeds where the engine is subjected to the maximum torque, maximum power, and at the maximum speed conditions. The results showed that the engine analyzed did not fail, that the critical plane criteria is more conservative, and that the safety factor is not smaller than 1.77.