Open Access. Powered by Scholars. Published by Universities.®

Digital Commons Network

Open Access. Powered by Scholars. Published by Universities.®

Articles 1 - 28 of 28

Full-Text Articles in Entire DC Network

Guest Editorial, Yongho Sohn, Carelyn Campbell, John E. Morral, Richard D. Sisson Dec 2006

Guest Editorial, Yongho Sohn, Carelyn Campbell, John E. Morral, Richard D. Sisson

Mechanical Engineering Faculty Publications

No abstract provided.


A Simple Numerical Method Of Cycle Jumps For Cyclically Loaded Structures, D. Cojocaru, Anette M. Karlsson Dec 2006

A Simple Numerical Method Of Cycle Jumps For Cyclically Loaded Structures, D. Cojocaru, Anette M. Karlsson

Mechanical Engineering Faculty Publications

A method for accelerated numerical simulations of structures subjected to cyclic loading is investigated. Of particular interest is a class of structures where the structural properties evolve with time. The proposed method is based on conducting detailed finite element analysis for a set of cycles to establish a trend line, extrapolating the trend line spanning many cycles, and use the extrapolated state as initial state for additional FEA simulations. This includes a control function that automatically monitors the length of the cycle jump to ensure a realistic solution. We compare the proposed method to a reference calculation, where all incremental ...


A Fuzzy Logic Controller For Autonomous Wheeled Vehicles, Mohamed Trabia, Linda Z. Shi, Neil Eugene Hodge Dec 2006

A Fuzzy Logic Controller For Autonomous Wheeled Vehicles, Mohamed Trabia, Linda Z. Shi, Neil Eugene Hodge

Mechanical Engineering Faculty Publications

Autonomous vehicles have potential applications in many fields, such as replacing humans in hazardous environments, conducting military missions, and performing routine tasks for industry. Driving ground vehicles is an area where human performance has proven to be reliable. Drivers typically respond quickly to sudden changes in their environment. While other control techniques may be used to control a vehicle, fuzzy logic has certain advantages in this area; one of them is its ability to incorporate human knowledge and experience, via language, into relationships among the given quantities. Fuzzy logic controllers for autonomous vehicles have been successfully applied to address various ...


Carbon Diffusion In Steels: A Numerical Analysis Based On Direct Integration Of The Flux, Olga Karabelchtchlkova, Richard D. Sisson Jr. Dec 2006

Carbon Diffusion In Steels: A Numerical Analysis Based On Direct Integration Of The Flux, Olga Karabelchtchlkova, Richard D. Sisson Jr.

Mechanical Engineering Faculty Publications

In the early 1970s, Professor Dayananda developed a technique for the direct integration of fluxes from the concentration profiles in vapor-solid diffusion couples to determine diffusion coefficients and atomic mobilities. As part of a project to control and optimize the industrial carburization process in mild- and low-alloyed steels, a modified integration analysis was applied to determine the mass transfer coefficient in the gas boundary layer and carbon diffusivity in austenite. Because carbon flux and surface carbon content vary with time during single-stage carburizing even with a fixed carbon potential in the atmosphere, a mass balance at the gas-solid interface must ...


Mechanical Response Of Fuel Cell Membranes Subjected To A Hygro-Thermal Cycle, Ahmet Kusoglu, Anette M. Karlsson, Michael H. Santare, Simon Cleghorn, William B. Johnson Oct 2006

Mechanical Response Of Fuel Cell Membranes Subjected To A Hygro-Thermal Cycle, Ahmet Kusoglu, Anette M. Karlsson, Michael H. Santare, Simon Cleghorn, William B. Johnson

Mechanical Engineering Faculty Publications

The mechanical response of fuel cell proton exchange membranes subjected to a single hygro-thermal duty cycle in a fuel cell assembly is investigated through numerical means. To this end, the behavior of the membrane with temperature and humidity dependent material properties is simulated under temperature and humidity loading and unloading conditions. The stress-evolution during a simplified operating cycle is determined using finite element analysis for two clamping methods and two alignments of the bipolar plates. It is shown that compressive, plastic deformation occurs during the hygro-thermal loading, resulting in tensile residual stresses after unloading. These residual in-plane stresses in the ...


Evolution Of Surface Morphology Of Thermo-Mechanically Cycled Nicocraly Bond Coats, J. Shi, Anette M. Karlsson, B. Baufeld, M. Bartsch Oct 2006

Evolution Of Surface Morphology Of Thermo-Mechanically Cycled Nicocraly Bond Coats, J. Shi, Anette M. Karlsson, B. Baufeld, M. Bartsch

Mechanical Engineering Faculty Publications

We investigate morphological surface instabilities on bond coat surfaces of thermal barrier coatings, induced due to thermo-mechanical loading. Experimental results of hollow circular cylindrical specimens, consisting of a directionally solidified superalloy (IN 100 DS) coated with a NiCoCrAlY bond coat, show that the morphological instabilities are strongly dependent on the load conditions. In particular, the morphological instabilities develop during thermal cycling with a thermal gradient over the cylinder wall, whereas the surface remains smooth for thermal cyclic conditions without a gradient. Furthermore, if a cyclic, axial tensile force is applied (synchronized with the thermal cycling), the morphological instabilities become aligned ...


Task-Driven Multi-Formation Control For Coordinated Uav/Ugv Isr Missions, Herbert G. Tanner Oct 2006

Task-Driven Multi-Formation Control For Coordinated Uav/Ugv Isr Missions, Herbert G. Tanner

Mechanical Engineering Faculty Publications

The report describes the development of a theoretical framework for coordination and control of combined teams of UAVs and UGVs for coordinated ISR missions. We consider the mission as a composition of an ordered sequence of subtasks, each to be performed by a different team. We design continuous cooperative controllers that enable each team to perform a given subtask and we develop a discrete strategy for interleaving the action of teams on different subtasks. The overall multi-agent coordination architecture is captured by a hybrid automaton, stability is studied using Lyapunov tools, and performance is evaluated through numerical simulations.


An Initial Non-Equilibrium Porous-Media Model For Cfd Simulation Of Stirling Regenerators, Roy C. Tew, Terry Simon, David Gedeon, Mounir B. Ibrahim, Wei Rong Oct 2006

An Initial Non-Equilibrium Porous-Media Model For Cfd Simulation Of Stirling Regenerators, Roy C. Tew, Terry Simon, David Gedeon, Mounir B. Ibrahim, Wei Rong

Mechanical Engineering Faculty Publications

The objective of this paper is to define empirical parameters for an initial thermal non-equilibrium porous-media model for use in Computational Fluid Dynamics (CFD) codes for simulation of Stirling regenerators. The two codes currently used at Glenn Research Center for Stirling modeling are Fluent and CFD-ACE. The codes’ porous-media models are equilibrium models, which assume solid matrix and fluid are in thermal equilibrium. This is believed to be a poor assumption for Stirling regenerators; Stirling 1–D regenerator models, used in Stirling design, use non-equilibrium regenerator models and suggest regenerator matrix and gas average temperatures can differ by several degrees ...


Transient Response Of Rotor On Rolling-Element Bearings With Clearance, David P. Fleming, Brian T. Murphy, Jerzy T. Sawicki, J. V. Poplawski Oct 2006

Transient Response Of Rotor On Rolling-Element Bearings With Clearance, David P. Fleming, Brian T. Murphy, Jerzy T. Sawicki, J. V. Poplawski

Mechanical Engineering Faculty Publications

Internal clearance in rolling element bearings is usually present to allow for radial and axial growth of the rotor-bearing system and to accommodate bearing fit-up. The presence of this clearance also introduces a “dead band” into the load-deflection behavior of the bearing. Previous studies demonstrated that the presence of dead band clearance might have a significant effect on synchronous rotor response. In this work, the authors investigate transient response of a rotor supported on rolling element bearings with internal clearance. In addition, the stiffness of the bearings varies nonlinearly with bearing deflection and with speed. Bearing properties were accurately calculated ...


Obtaining Mode Mixity For A Bimaterial Interface Crack Using The Virtual Crack Closure Technique, A. Agrawal, Anette M. Karlsson Sep 2006

Obtaining Mode Mixity For A Bimaterial Interface Crack Using The Virtual Crack Closure Technique, A. Agrawal, Anette M. Karlsson

Mechanical Engineering Faculty Publications

We review, unify and extend work pertaining to evaluating mode mixity of interfacial fracture utilizing the virtual crack closure technique (VCCT). From the VCCT, components of the strain energy release rate (SERR) are obtained using the forces and displacements near the crack tip corresponding to the opening and sliding contributions. Unfortunately, these components depend on the crack extension size, Δ, used in the VCCT. It follows that a mode mixity based upon these components also will depend on the crack extension size. However, the components of the strain energy release rate can be used for determining the complex stress intensity ...


Output Feedback Adaptive Variable Structure Control Of A Smart Projectile Fin, Smitha Mani, Sahjendra N. Singh, Woosoon Yim Aug 2006

Output Feedback Adaptive Variable Structure Control Of A Smart Projectile Fin, Smitha Mani, Sahjendra N. Singh, Woosoon Yim

Mechanical Engineering Faculty Publications

No abstract provided.


Fatigue Crack Growth Mechanisms At The Microstructure Scale In Al-Si-Mg Cast Alloys: Mechanisms In Regions Ii And Iii, Diana A. Lados, Diran Apelian, J. Fred Major Aug 2006

Fatigue Crack Growth Mechanisms At The Microstructure Scale In Al-Si-Mg Cast Alloys: Mechanisms In Regions Ii And Iii, Diana A. Lados, Diran Apelian, J. Fred Major

Mechanical Engineering Faculty Publications

The fatigue crack growth behavior in Regions 11 and III of crack growth was investigated for hypoeutectic and eutectic Al-Si-Mg cast alloys. To isolate and establish the mechanistic contributions of characteristic microstructural features (dendritic α-Al matrix, eutectic phases, Mg-Si strengthening precipitates), alloys with various Si content/morphology, grain size level, and matrix strength were studied; the effect of secondary dendrite arm spacing (SDAS) was also assessed. In Regions 11 and III of crack growth, the observed changes in the fracture surface appearance were associated with changes in crack growth mechanisms at the microstructural scale (from a linear advance predominantly through ...


Viscoelastic Flow In Rotating Curved Pipes, Yitung Chen, Huajun Chen, Jinsuo Zhang, Benzhao Zhang Aug 2006

Viscoelastic Flow In Rotating Curved Pipes, Yitung Chen, Huajun Chen, Jinsuo Zhang, Benzhao Zhang

Mechanical Engineering Faculty Publications

Fully developed viscoelastic flows in rotating curved pipes with circular cross section are investigated theoretically and numerically employing the Oldroyd-B fluid model. Based on Dean’s approximation, a perturbation solution up to the secondary order is obtained. The governing equations are also solved numerically by the finite volume method. The theoretical and numerical solutions agree with each other very well. The results indicate that the rotation, as well as the curvature and elasticity, plays an important role in affecting the friction factor, the secondary flow pattern and intensity. The co-rotation enhances effects of curvature and elasticity on the secondary flow ...


Fluidized Bed Heat Treatment Of Cast Al-Si-Cu-Mg Alloys, S. K. Chaudhury, Diran Apelian Jul 2006

Fluidized Bed Heat Treatment Of Cast Al-Si-Cu-Mg Alloys, S. K. Chaudhury, Diran Apelian

Mechanical Engineering Faculty Publications

The effects of fluidized bed heat treatment on the microstructural and mechanical properties of Al-SiCu-Mg cast alloys, namely, 354 and 319, were studied. The heating rate in fluidized beds (FBs) is greater vis-a-vis conventional electrical resistance furnaces (CFs). The high heating rate in FBs increases the kinetics of metallurgical phenomena such as Si fragmentation and spherodization during solution heat treatment, as well as the precipitation rate of phases such as Al5Cu2Mg8Si6 and Al2Cu during aging. It is observed that the dissolution rate of phases such as Mg2Si and A15Cu2Mg8Si6 takes place very rapidly. The solution heat treatment of 319 alloy ...


An Initial Non-Equilibrium Porous-Media Model For Cfd Simulation Of Stirling Regenerators, Roy Tew, Terry Simon, David Gedeon, Mounir B. Ibrahim, Wei Rong Jun 2006

An Initial Non-Equilibrium Porous-Media Model For Cfd Simulation Of Stirling Regenerators, Roy Tew, Terry Simon, David Gedeon, Mounir B. Ibrahim, Wei Rong

Mechanical Engineering Faculty Publications

The objective of this paper is to define empirical parameters (or closwre models) for an initial thermai non-equilibrium porous-media model for use in Computational Fluid Dynamics (CFD) codes for simulation of Stirling regenerators. The two CFD codes currently being used at Glenn Research Center (GRC) for Stirling engine modeling are Fluent and CFD-ACE. The porous-media models available in each of these codes are equilibrium models, which assmne that the solid matrix and the fluid are in thermal equilibrium at each spatial location within the porous medium. This is believed to be a poor assumption for the oscillating-flow environment within Stirling ...


An Experimental Investigation Of Humidity And Temperature Effects On The Mechanical Properties Of Persfluorosulfonic Acid Membrane, Y. L. Tang, Anette M. Karlsson, Michael H. Santare, Michael Gilbert, Simon Cleghorn, William B. Johnson Jun 2006

An Experimental Investigation Of Humidity And Temperature Effects On The Mechanical Properties Of Persfluorosulfonic Acid Membrane, Y. L. Tang, Anette M. Karlsson, Michael H. Santare, Michael Gilbert, Simon Cleghorn, William B. Johnson

Mechanical Engineering Faculty Publications

The mechanical properties of a perfluorosulfonic acid (PFSA) membrane have been investigated at different humidities and temperatures in a custom-designed environmental chamber. Tensile tests were conducted to determine Young’s modulus, the proportional limit stress (“yield strength”), break stress, and break strain. In-plane dimensional changes of the membrane at different temperature and humidities were also determined. The results indicate that Young’s modulus and the proportional limit stress of the PFSA membrane decrease as humidity and temperature increase. Higher temperature leads to lower break stress and higher break strain. However, humidity has little effect on the break stress and break ...


Determination Of Uniaxial Residual Stress And Mechanical Properties By Instrumented Indentation, Manhong Zhao, Xi Chen, Jin Yan, Anette M. Karlsson Jun 2006

Determination Of Uniaxial Residual Stress And Mechanical Properties By Instrumented Indentation, Manhong Zhao, Xi Chen, Jin Yan, Anette M. Karlsson

Mechanical Engineering Faculty Publications

We propose an improved technique to determine the uniaxial residual stress, elastic modulus, and yield stress of a linear elastic, perfectly plastic bulk material from the force–displacement curve of one conical indentation test. Explicit relationships between the indentation loading–unloading parameters, material properties, and residual stress are established through extensive finite element analyses. Good agreement is found between the input material parameters used in numerical indentation tests and the properties identified from the reverse analysis, with an error of less than 10% in most cases. The technique is applied to a nanoindentation experiment on the crosssection of a thermal ...


Stresses In Proton Exchange Membranes Due To Hygro-Thermal Loading, Yaliang Tang, Michael H. Santare, Anette M. Karlsson, Simon Cleghorn, William B. Johnson May 2006

Stresses In Proton Exchange Membranes Due To Hygro-Thermal Loading, Yaliang Tang, Michael H. Santare, Anette M. Karlsson, Simon Cleghorn, William B. Johnson

Mechanical Engineering Faculty Publications

Durability of the proton exchange membrane (PEM) is a major technical barrier to the commercial viability of polymer electrolyte membrane fuel cells (PEMFC) for stationary and transportation applications. In order to reach Department of Energy objectives for automotive PEMFCs, an operating design lifetime of at least 5000 h over a broad temperature range is required. Reaching these lifetimes is an extremely difficult technical challenge. Though good progress has been made in recent years, there are still issues that need to be addressed to assure successful, economically viable, long-term operation of PEM fuel cells. Fuel cell lifetime is currently limited by ...


Experimental And Finite Element Analysis Of Preloaded Bolted Joints Under Impact Loading, Brendan O'Toole, Kumarswamy Karpanan, Masoud Feghhi May 2006

Experimental And Finite Element Analysis Of Preloaded Bolted Joints Under Impact Loading, Brendan O'Toole, Kumarswamy Karpanan, Masoud Feghhi

Mechanical Engineering Faculty Publications

One of the primary parameters in analyzing bolted joints is preload in the bolt. We have considered several possible preload modeling techniques to analyze the effect of preload on the dynamic response of the bolted joints. Five different methods of applying preload in the nonlinear finite element analysis are evaluated. These methods are “force on bolt and nut”, “force on bolt shank”, “interference fit”, “thermal gradient” and “initial stress method”. Explicit and implicit analyses are used for transient response and preload generation in bolt respectively. Time history and shock response spectrum are used to compare experimental and simulation results. Simulation ...


Authors' Reply To Reply Of Discussion On "Nucleation Mechanism Of Eutectic Phases In Aluminum-Silicon Hypoeutectic Alloys", S. Shankar, Makhlouf M. Makhlouf Apr 2006

Authors' Reply To Reply Of Discussion On "Nucleation Mechanism Of Eutectic Phases In Aluminum-Silicon Hypoeutectic Alloys", S. Shankar, Makhlouf M. Makhlouf

Mechanical Engineering Faculty Publications

No abstract provided.


Thermodynamically Consistent Relations Involving Plasticity, Internal Energy And Thermal Effects, Howard Schreyer, Paul Maudlin Mar 2006

Thermodynamically Consistent Relations Involving Plasticity, Internal Energy And Thermal Effects, Howard Schreyer, Paul Maudlin

Mechanical Engineering Faculty Publications

Experimental data associated with plastic deformations indicate that the temperature is less than that predicted from dissipation based on plastic work. To obtain reasonable correlation between theoretical and experimental results, the plastic work is often multiplied by a constant β. This paper provides an alternative thermodynamic framework in which it is proposed that there is an additional internal energy associated with dislocation pile-up or increase in dislocation density. The form of this internal energy follows from experimental data that relates flow stress to dislocation density and to equivalent plastic strain. The result is that β is not a constant but ...


Increasing The Accuracy Of Cooperative Localization By Controlling The Sensor Graph, Deepti Kumar, Herbert G. Tanner Mar 2006

Increasing The Accuracy Of Cooperative Localization By Controlling The Sensor Graph, Deepti Kumar, Herbert G. Tanner

Mechanical Engineering Faculty Publications

We characterize the accuracy of a cooperative localization algorithm based on Kalman Filtering, as expressed by the trace of the covariance matrix, in terms of the algebraic graph theoretic properties of the sensing graph. In particular, we discover a weighted Laplacian in the expression that yields the constant, steady state value of the covariance matrix. We show how one can reduce the localization uncertainty by manipulating the eigenvalues of the weighted Laplacian. We thus provide insight to recent optimization results which indicate that increased connectivity implies higher accuracy and we offer an analysis method that could lead to more efficient ...


Effects Of Rapid Heating On Solutionizing Characteristics Of Al-Si-Mg Alloys Using A Fluidized Bed, S. K. Chaudhury, Diran Apelian Mar 2006

Effects Of Rapid Heating On Solutionizing Characteristics Of Al-Si-Mg Alloys Using A Fluidized Bed, S. K. Chaudhury, Diran Apelian

Mechanical Engineering Faculty Publications

Effects of rapid heat transfer using a fluidized bed on the heat-treating response of Al-Si-Mg alloys (both unmodified and Sr modified) were investigated. The heating rate in the fluidized bed is greater than in conventional air convective furnaces. Particle size analyses of eutectic Si showed that the high heating rate during fluidized bed solution heat treatment causes faster fragmentation and spherodization of Si particles compared to conventional air convective furnaces. The mechanism of Si fragmentation through fluidized bed processing is through both brittle fracture and neck formation and its propagation. In contrast to this, the mechanism of Si fragmentation using ...


On The Determination Of Residual Stress And Mechanical Properties By Indentation, Xi Chen, Jin Yan Yan, Anette M. Karlsson Jan 2006

On The Determination Of Residual Stress And Mechanical Properties By Indentation, Xi Chen, Jin Yan Yan, Anette M. Karlsson

Mechanical Engineering Faculty Publications

Residual stresses are of practical importance in bulk materials and coatings, which critically affects their mechanical integrity and reliability. Comparing with traditional techniques, the depth-sensing indentation technique provides a quick and effective method of measuring the residual stress field. In this study, we have used the finite element method to investigate the effect of in-plane residual stress on hardness and stiffness measurements of a bulk material/thick coating. It is found that the contact hardness, stiffness, and indentation work are sensitive to the residual stress, in particular for materials with a relatively high yield strain. Based on the reverse analysis ...


Application Of An Hp-Adaptive Finite Element Method For Thermal Flow Problems, Xiuling Wang, Darrell Pepper Jan 2006

Application Of An Hp-Adaptive Finite Element Method For Thermal Flow Problems, Xiuling Wang, Darrell Pepper

Mechanical Engineering Faculty Publications

Numerical results are presented for a set of convective thermal flow problems using an hp-adaptive finite element technique. The hp-adaptive model is based on mesh refinement and spectral order incensement to produce enhanced accuracy while attempting to minimize computational requirements. An a-posteriori error estimator based on the L2 norm is employed to guide the adaptation procedure. Example test cases consisting of natural convection in a differentially heated enclosure, flow with forced convection heat transfer over a backward facing step and natural convection within an enclosed partition are presented. Numerical results are compared with published data in the ...


The Effect Of Residual Stress On The Fatigue Crack Growth Behavior Of Al-Si-Mg Cast Alloys - Mechanisms And Corrective Mathematical Models, Diana A. Lados, Diran Apelian Jan 2006

The Effect Of Residual Stress On The Fatigue Crack Growth Behavior Of Al-Si-Mg Cast Alloys - Mechanisms And Corrective Mathematical Models, Diana A. Lados, Diran Apelian

Mechanical Engineering Faculty Publications

The fatigue crack growth (FCG) behavior of various types of alloys is significantly affected by the presence of residual stress induced by manufacturing and post-manufacturing processes. There is a qualitative understanding of the effects of residual stress on fatigue behavior, but the effects are not comprehensively quantified or accounted for. The difficulty in quantifying these effects is largely due to the complexity of residual-stress measurements (especially considering that parts produced in similar conditions can have different residual-stress levels) and the lack of mathematical models able to convert experimental data with residual stress into residual-stress-free data. This article provides experimental, testing ...


Reza Abbaschian - 2006 President Of, Asm International, Diran Apelian Jan 2006

Reza Abbaschian - 2006 President Of, Asm International, Diran Apelian

Mechanical Engineering Faculty Publications

No abstract provided.


Cracking Of Martensitic Alloy Ep-823 Under Controlled Potential, Ajit K. Roy, M. K. Hossain Jan 2006

Cracking Of Martensitic Alloy Ep-823 Under Controlled Potential, Ajit K. Roy, M. K. Hossain

Mechanical Engineering Faculty Publications

The susceptibility of martensitic Alloy EP-823 to stress corrosion cracking was evaluated with and without an applied cathodic potential using the slow-strain-rate (SSR) testing technique. The magnitude of the applied potential was based on the corrosion potential determined by cyclic polarization. The cracking susceptibility in an acidic environment at different temperatures was expressed in terms of the true failure stress (ơf), time to failure (TTF), and ductility parameters, including percent elongation (%El) and percent reduction in area (%RA). The data indicate that the magnitudes of ơr, TTF, %El, and %RA were reduced due to cathodic charging. The scanning ...