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Articles 271 - 300 of 300
Full-Text Articles in Mechanical Engineering
Robust Shape Design Techniques For Steady-State Metal Forming Processes, Jalaja Repalle
Robust Shape Design Techniques For Steady-State Metal Forming Processes, Jalaja Repalle
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Metal forming is a process that transforms a simple shape of a workpiece into a predetermined complex shape through the application of compressive/tensile forces exerted by dies. In the design of a forming process, the only factors that are known are the final component shape and the material with which it is to be made. Then the engineer has to design a process to make defect-free product, subject to limitations of shape, material properties, cost, time, and other such factors. The design cycle can be enhanced if performance sensitivity information is available that could be used with any commercially available …
Investigation Into The Behavior Of Bolted Joints, Steven M. Page
Investigation Into The Behavior Of Bolted Joints, Steven M. Page
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Models to capture the physics of jointed structures have been proposed for over 40 years. These models approximate the behavior of the joint under carefully developed operating conditions. When these conditions change, the model has to be changed. Recent developments in numeric codes like finite elements have created interest in incorporating joint models into the design process but joint models need to represent the joined structure over a broader operating range. This work investigates the dynamic response of a structure with a joint. Isolation of a few dominant effects may give way to a model able to capture a broader …
Computational Study Of Ring-Cusp Magnet Configurations That Provide Maximum Electron Confinement, Taiwo A. Ogunjobi
Computational Study Of Ring-Cusp Magnet Configurations That Provide Maximum Electron Confinement, Taiwo A. Ogunjobi
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Enhancing the confinement of primary electrons within the plasma in a discharge chamber of an ion thruster improves plasma ionization and consequently the thruster's performance. This work computationally calculates the location, position, and orientation of the permanent magnets that provide a ring-cusp magnetic field that maximizes electron confinement in an axi-symmetric cylindrical aluminum-wall discharge chamber. Small samarium cobalt magnets are circumferentially arranged in a ring around the front, side, or back wall of the chamber. The generated ring-cusp magnetic field for any specified magnet configuration is calculated using MAXWELL2D, a two dimensional electromagnetic field simulation computer code. For various magnet …
Multi-Attribute Optimization Based On Conjoint Analysis, Hemanth K. Amarchinta
Multi-Attribute Optimization Based On Conjoint Analysis, Hemanth K. Amarchinta
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Over the last thirty years, there were tremendous advances in multidisciplinary design optimization in reducing computational cost, developing algorithms for efficient sensitivity analysis in reaching an optimum. Most of these efforts assumed a single objective (attribute) function and a multitude of constraints. Very little work has been done in including the designer's preferences as part of the optimization scheme and in addressing the ability to handle multiple attributes simultaneously. This need to develop a systematic method for including designer's preferences is the main focus of this research work. The concept of modeling preferences among multi-attribute alternatives is prevalent in consumer …
Using In-Situ Error Tracking For Mode Selection In Proper Orthogonal Decomposition Reduced Order Modelling, Michael Richard Maddux
Using In-Situ Error Tracking For Mode Selection In Proper Orthogonal Decomposition Reduced Order Modelling, Michael Richard Maddux
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Proper Orthogonal Decomposition (POD) provides a method of analyzing data and/or creating a Reduced Order Model (ROM). In this thesis, POD is used to create a ROM comprised of basis functions onto which the governing equations of a Computational Fluid Dynamics (CFD) problem are projected via Galerkin's method. The model is of reduced order since the basis functions span a space smaller than the space from which they were created. A full order simulation called the training period is conducted first to obtain data to be used for creating the ROM using POD. The dominant characteristics are extracted from the …
Method Of Reducing Internal Stress In Materials, Maher S. Amer, John F. Maguire
Method Of Reducing Internal Stress In Materials, Maher S. Amer, John F. Maguire
Mechanical and Materials Engineering Faculty Publications
Methods are provided for adjusting and controlling the stress between layers of material in a multilayer structure. A first stress is configured in a region of stress on the substrate material. A second material is then deposited over the substrate. A second stress results between the substrate and the second material such that a net stress results where the net stress is a function of said first and second stresses. As such, the first stress can be configured to achieve a predetermined, desired net stress. For example, the first stress can be configured to cancel out the second stress such …
Slip Behavior In Liquid Films On Surfaces Of Patterned Wettability: Comparison Between Continuum And Molecular Dynamics Simulations, Nikolai V. Priezjev, Anton A. Darhuber, Sandra M. Troian
Slip Behavior In Liquid Films On Surfaces Of Patterned Wettability: Comparison Between Continuum And Molecular Dynamics Simulations, Nikolai V. Priezjev, Anton A. Darhuber, Sandra M. Troian
Mechanical and Materials Engineering Faculty Publications
We investigate the behavior of the slip length in Newtonian liquids subject to planar shear bounded by substrates with mixed boundary conditions. The upper wall, consisting of a homogenous surface of finite or vanishing slip, moves at a constant speed parallel to a lower stationary wall, whose surface is patterned with an array of stripes representing alternating regions of no shear and finite or no slip. Velocity fields and effective slip lengths are computed both from molecular dynamics (MD) simulations and solution of the Stokes equation for flow configurations either parallel or perpendicular to the stripes. Excellent agreement between the …
Vibrational Behavior Of The MN+1AxN Phases From First-Order Raman Scattering (M=Ti,V,Cr, A=Si, X=C,N), Jonathan E. Spanier, Surojit Gupta, Maher S. Amer, Michel W. Barsoum
Vibrational Behavior Of The MN+1AxN Phases From First-Order Raman Scattering (M=Ti,V,Cr, A=Si, X=C,N), Jonathan E. Spanier, Surojit Gupta, Maher S. Amer, Michel W. Barsoum
Mechanical and Materials Engineering Faculty Publications
We report on the Raman spectra of Ti3SiC2 (312), M2AlC(211) (M=Ti, V, Cr, and Nb) and Ti4AlN3 (413), as representative compounds from the family of Mn+1AXn phases. Intense and narrow first-order Raman peaks are observed, and we present an analysis of the spectra based on symmetry considerations and from results of first-principles calculations of phonon frequencies. The agreement between experimental and calculated mode energies is excellent. The identification of the modes enables application of Raman scattering as a diagnostic tool for the detailed study of the structural and physical properties of this family of compounds and their …
Unsteady Tip Leakage, Bow Shock, Igv Wake Interaction In A Compressor, Xuedong Zhou, J. Mitch Wolff
Unsteady Tip Leakage, Bow Shock, Igv Wake Interaction In A Compressor, Xuedong Zhou, J. Mitch Wolff
Mechanical and Materials Engineering Faculty Publications
Unsteady aerodynamic analysis of Inlet Guide Vane (IGV)/rotor interaction is conducted with a commercial CFD solver, STAR-CD. 12% and 26% IGV axial chord IGV/Rotor spacing configurations were examined for 100% corrected speed at choke, peak efficiency and near stall conditions to investigate bow shock/tip leakage interaction within blade rows. Comparison with IGV surface unsteady pressure experimental data indicates good agreement at the IGV trailing edge across the span for both spacing configurations; therefore, validating the modeling of the high speed, highly loaded transonic compressor. The strongest effect on the tip clearance flow physics was caused by decreasing the axial spacing. …
Large Scale Visualization Of Pulsed Vortex Generator Jets, Kenneth Jay Moore Jr.
Large Scale Visualization Of Pulsed Vortex Generator Jets, Kenneth Jay Moore Jr.
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The use of small jets of air has proven to be an effective means of flow control on low Reynolds number turbine blades. Pulsing of these jets has also shown benefits in reducing the amount of air needed to achieve the same level of flow control. An experiment using Hot Wire Anemometry and Particle Image Velocimetry (PIV) has been used to investigate how these pulsed jets interact with the boundary layer to help keep the flow attached. A 25x scaled jet in a flat plate has been utilized. The 25.4 mm diameter jet has a pitch angle of 30° and …
Studies On Yba2nbo6 And Yba2cu3-Xnbxoy Buffer Layers, S. Sathiraju, R. Wheeler, Paul N. Barnes, T. L. Peterson, Iman Maartense, A. L. Campbell, N. A. Yust, T. J. Haugan, Q. Jia, Paul Arendt, Sharmila M. Mukhopadhyay, S. Vemulakonda
Studies On Yba2nbo6 And Yba2cu3-Xnbxoy Buffer Layers, S. Sathiraju, R. Wheeler, Paul N. Barnes, T. L. Peterson, Iman Maartense, A. L. Campbell, N. A. Yust, T. J. Haugan, Q. Jia, Paul Arendt, Sharmila M. Mukhopadhyay, S. Vemulakonda
Mechanical and Materials Engineering Faculty Publications
No abstract provided.
Joining Challenges In The Packaging Of Biomems, Hans Herfurth, Reiner Witte, S. Heinemann, Golam Newaz, Ahsan Mian, Daniel Georgiev, Greg Auner
Joining Challenges In The Packaging Of Biomems, Hans Herfurth, Reiner Witte, S. Heinemann, Golam Newaz, Ahsan Mian, Daniel Georgiev, Greg Auner
Mechanical and Materials Engineering Faculty Publications
Micro-joining and hermetic sealing of dissimilar and biocompatible materials is a critical issue for a broad spectrum of products such as micro -electronical, micro -optical and biomedical products and devices. Novel implantable microsystems currently under development will include functions such as localized sensing of temperature and pressure, electrical stimulation of neural tissue and the delivery of drugs. These devices are designed to be long-term implants that are remotely powered and controlled. The development of new, biocompatible materials and manufacturing processes that ensure long-lasting functionality and reliability are critical challenges. Important factors in the assembly of such systems are the small …
Cfd Analysis Of Unsteady Separated Transonic Oscillation Cascade Aerodynamics, Xuedong Zhou, J. Mitch Wolff
Cfd Analysis Of Unsteady Separated Transonic Oscillation Cascade Aerodynamics, Xuedong Zhou, J. Mitch Wolff
Mechanical and Materials Engineering Faculty Publications
With an improved algebraic mesh-deforming algorithm, STAR-CD, a commercial computational fluid dynamics (CFD) solver is employed for the numerical analysis of a transonic oscillating linear cascade of advanced design blades. The center blade oscillates 0.6-degrees about the middle cord. The numerical simulation is conducted for a frequency range from 200 Hz to 500 Hz. A hybrid grid, which utilizes a structured O-grid around the airfoil and an unstructured grid everywhere else is employed. The Spalart-Allmaras (S-A), one equation turbulence model, along with other two equation k-ε models, are also utilized for the steady state simulation. The S-A turbulence …
External And Intrinsic Anchoring In Nematic Liquid Crystals: A Monte Carlo Study, Nikolai V. Priezjev, G. Skacej, R. A. Pelcovits, S. Zumer
External And Intrinsic Anchoring In Nematic Liquid Crystals: A Monte Carlo Study, Nikolai V. Priezjev, G. Skacej, R. A. Pelcovits, S. Zumer
Mechanical and Materials Engineering Faculty Publications
We present a Monte Carlo study of external surface anchoring in nematic cells with partially disordered solid substrates, as well as of intrinsic anchoring at free nematic interfaces. The simulations are based on the simple hexagonal lattice model with a spatially anisotropic intermolecular potential. We estimate the corresponding extrapolation length b by imposing an elastic deformation in a hybrid cell-like nematic sample. Our estimates for b increase with increasing surface disorder and are essentially temperature independent. Experimental values of b are approached only when both the coupling of nematic molecules with the substrate and the anisotropy of nematic-nematic interactions are …
Optomechanical Properties Of Stretched Polymer Dispersed Liquid Crystal Films For Scattering Polarizer Applications, Iciro Amimori, Nikolai V. Priezjev, Robert A. Pelcovits, Gregory P. Crawford
Optomechanical Properties Of Stretched Polymer Dispersed Liquid Crystal Films For Scattering Polarizer Applications, Iciro Amimori, Nikolai V. Priezjev, Robert A. Pelcovits, Gregory P. Crawford
Mechanical and Materials Engineering Faculty Publications
A scattering polarizer is created by subjecting a polymer dispersed liquid crystal (PDLC) film to tensile strain. The optomechanical properties of the film are investigated by simultaneously measuring the stress-strain and polarization dependent optical transmission characteristics. The correlation between transmittances of two orthogonal polarizations and the stress-strain curve reveals that the polymer orientation as well as the droplet shape anisotropy influences the liquid crystal alignment within the droplets. A Monte-Carlo simulation based on the Lebwohl-Lasher model is used to explain the subtle influence of polymer orientation on liquid crystal alignment.
Innovative Forced Response Analysis Method Applied To A Transonic Compressor, Timothy M. Hutton
Innovative Forced Response Analysis Method Applied To A Transonic Compressor, Timothy M. Hutton
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A set of inlet guide vane (IGV) unsteady surface pressure measurements of a transonic compressor is presented. Using a flexible pressure sensor array, unsteady IGV suction-surface and pressure-surface pressures are acquired for six spanwise by five chordwise locations for various speed lines and throttle settings. Measurements from this sensor array are used to investigate unsteady vane/blade interaction aeromechanical forcing functions in a modern, highly loaded compressor stage. A significant effect is shown on the unsteady forced response of the IGV with changes in compressor operating point and IGV/rotor axial spacing for various span and chord locations. In particular, variations in …
Plastic Dissipation Energy In Mixed-Mode Fatigue Crack Growth On Ductile Bimaterial Interfaces, Jeremy S. Daily
Plastic Dissipation Energy In Mixed-Mode Fatigue Crack Growth On Ductile Bimaterial Interfaces, Jeremy S. Daily
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A new theory of fatigue crack growth in ductile solids has recently been proposed based on the total plastic energy dissipation per cycle ahead of the crack. This and previous energy-based approaches in the literature suggest that the total plastic dissipation per cycle can be closely correlated with fatigue crack growth rates under Mode I loading. The goal of the current study is to extend the dissipated energy approach to steady-state crack growth under mixed-mode loading conditions, with application to cyclic delamination of ductile interfaces in layered materials. The total plastic dissipation per cycle is obtained by 2-D elastic-plastic finite …
Coarsening Dynamics Of Biaxial Nematic Liquid Crystals, Nikolai V. Priezjev, Robert A. Pelcovits
Coarsening Dynamics Of Biaxial Nematic Liquid Crystals, Nikolai V. Priezjev, Robert A. Pelcovits
Mechanical and Materials Engineering Faculty Publications
We study the coarsening dynamics of two- and three-dimensional biaxial nematic liquid crystals, using Langevin dynamics. Unlike previous work, we use a model with no a priori relationship among the three elastic constants associated with director deformations. Biaxial nematics possess four topologically distinct classes of defects, three of which have half-integer charge, while the fourth, which plays a minor role in coarsening, is of integer charge. We find a rich variety of coarsening behavior, including the presence of one, two, or three of the half-integer classes at late times, depending on the relative values of the elastic constants and the …
Virtual Surfaces, Director Domains And The Freedericksz Transition In Polymer Stabilized Nematic Liquid Crystals, Pavel A. Kossyrev, Jun Qi, Nikolai V. Priezjev, Robert A. Pelcovits, Gregory P. Crawford
Virtual Surfaces, Director Domains And The Freedericksz Transition In Polymer Stabilized Nematic Liquid Crystals, Pavel A. Kossyrev, Jun Qi, Nikolai V. Priezjev, Robert A. Pelcovits, Gregory P. Crawford
Mechanical and Materials Engineering Faculty Publications
The critical field of the Freedericksz transition and switching dynamics are investigated for polymer stabilized nematic liquid crystals as a function of polymer concentration. A simple phenomenological model is proposed to describe the observed critical field and dynamic response time behaviors as a function of concentration. In this model the polymer fibrils form director domains, which are bounded by virtual surfaces with a finite anchoring energy. The Freedericksz transition occurs independently within each of these domains.
Correlation Between The Xps Peak Shapes Of Y1bu2cu3o7-X And Film Quality, Paul N. Barnes, Sharmila M. Mukhopadhyay, Timothy J. Haugan, Swaminathan Krishnaswami, Justin C. Tolliver, Iman Maartense
Correlation Between The Xps Peak Shapes Of Y1bu2cu3o7-X And Film Quality, Paul N. Barnes, Sharmila M. Mukhopadhyay, Timothy J. Haugan, Swaminathan Krishnaswami, Justin C. Tolliver, Iman Maartense
Mechanical and Materials Engineering Faculty Publications
X-ray photoelectron spectroscopy (XPS) depth profiling was used to investigate the compositional and chemical profile of a typical YBCO coated conductor architecture. Results of the process revealed that the Y(3d) photoelectronic peak shape in these films is very different from bulk YBCO. To investigate this, several samples of Y i Ba2Cu307_„ thin films were intentionally created of varying quality. The films were deposited on LaA10 3 by pulsed laser deposition with ./c. values ranging from poorly conducting up to several MA/cm2. Initial results indicated a potential correlation between the Y(3d) XPS peak shape (full-width-half-maximum) of the YBCO and the film …
Simulations Of Nematic Liquid Crystals: Confined Geometries, Phase Transitions And Topological Defects, Nikolai V. Priezjev
Simulations Of Nematic Liquid Crystals: Confined Geometries, Phase Transitions And Topological Defects, Nikolai V. Priezjev
Mechanical and Materials Engineering Faculty Publications
The physics of liquid crystals is an exciting field of research with important practical applications. In this dissertation we present the results of simulation studies of nematic liquid crystals using Monte Carlo and molecular dynamic techniques. In our first project we performed Monte Carlo Simulations of the Lebwohl-Lasher (LL) model of nematic liquid crystals confined to cylindrical cavities with perpendicular anchoring. In this particular geometry one has an interesting interplay between bulk and surface energies, which results in different director configurations inside the cylinder. Our work reconciled the apparent contradictions between the results of earlier simulations and approximate analytics theories. …
Strongly Screened Vortex Lattice Model With Disorder, C. Giardina', Nikolai V. Priezjev, J. M. Kosterlitz
Strongly Screened Vortex Lattice Model With Disorder, C. Giardina', Nikolai V. Priezjev, J. M. Kosterlitz
Mechanical and Materials Engineering Faculty Publications
The three dimensional XY model with quenched random disorder and finite screening is studied. We argue that the system scales to model with λ≃0≃T and the resulting effective model is studied numerically by defect energy scaling. In zero external field we find that there exists a true superconducting phase with a stiffness exponent θ≃+1.0 for weak disorder. For low magnetic field and weak disorder, there is also a superconducting phase with θ≃+1.0 which we conjecture is a Bragg glass. For larger disorder or applied field, there is a non superconducting phase with θ≃−1.0. We estimate the critical external field whose …
Disclination Loop Behavior Near The Nematic-Isotropic Transition, Nikolai V. Priezjev, Robert A. Pelcovits
Disclination Loop Behavior Near The Nematic-Isotropic Transition, Nikolai V. Priezjev, Robert A. Pelcovits
Mechanical and Materials Engineering Faculty Publications
We investigate the behavior of disclination loops in the vicinity of the first-order nematic-isotropic transition in the Lebwohl-Lasher and related models. We find that two independent measures of the transition temperature, the free energy, and the distribution of disclination line segments, give essentially identical values. We also calculate the distribution function D(p) of disclination loops of perimeter p and fit it to a quasiexponential form. Below the transition, D(p) falls off exponentially, while in the neighborhood of the transition, it decays with a power-law exponent approximately equal to 2.5, consistent with a “blowout” of loops at the transition. In a …
Cluster Monte Carlo Simulations Of The Nematic--Isotropic Transition, Nikolai V. Priezjev, Robert A. Pelcovits
Cluster Monte Carlo Simulations Of The Nematic--Isotropic Transition, Nikolai V. Priezjev, Robert A. Pelcovits
Mechanical and Materials Engineering Faculty Publications
We report the results of simulations of the three-dimensional Lebwohl-Lasher model of the nematic-isotropic transition using a single cluster Monte Carlo algorithm. The algorithm, first introduced by Kunz and Zumbach to study two-dimensional nematics, is a modification of the Wolff algorithm for spin systems, and greatly reduces critical slowing down. We calculate the free energy in the neighborhood of the transition for systems up to linear size 70. We find a double well structure with a barrier that grows with increasing system size. We thus obtain an upper estimate of the value of the transition temperature in the thermodynamic limit.
Surface Extrapolation Length And Director Structures In Confined Nematics, Nikolai V. Priezjev, Robert A. Pelcovits
Surface Extrapolation Length And Director Structures In Confined Nematics, Nikolai V. Priezjev, Robert A. Pelcovits
Mechanical and Materials Engineering Faculty Publications
We report the results of Monte Carlo simulations of the Lebwohl-Lasher model of nematic liquid crystals confined to cylindrical cavities with homeotropic anchoring. We show that the ratio of the bulk to surface couplings is not in general equal to the corresponding parameter K/W used in elastic theory (where K is the Frank elastic constant in the one-constant approximation and W is the surface anchoring strength). By measuring the temperature dependence of K/W (which is equivalent to the surface extrapolation length) we are able to reconcile the results of our simulations as well as others with the predictions of elastic …
Three-Dimensional Dynamic Analysis Of Wheelchair Propulsion, Mary M. Rodgers, Srinivas Tummarakota, Junghsen Lieh
Three-Dimensional Dynamic Analysis Of Wheelchair Propulsion, Mary M. Rodgers, Srinivas Tummarakota, Junghsen Lieh
Mechanical and Materials Engineering Faculty Publications
A three-dimensional (3-D) inverse dynamic model of wheelchair propulsion was developed using the Newton-Euler method based on body coordinate systems. With this model, the arm was assumed to be three rigid segments (hand, forearm, and upper arm) connected by the wrist, elbow, and shoulder joints. A symbolic method was adopted to generate the equations of motion. The model was used to compute the joint forces and moments based on the inputs obtained from a 3-D motion analysis system, which included an instrumented wheelchair, video cameras, and a data acquisition system. The linear displacements of markers placed on the joints were …
Optimization Of Microstructure Development During Hot Working Using Control Theory, James C. Malas Iii, W. Garth Frazier, S. Venugopal, Enrique A. Medina, Steven Madeiros, Raghavan Srinivasan, R. Dennis Irwin, W. M. Mullins, Anil Chaudhary
Optimization Of Microstructure Development During Hot Working Using Control Theory, James C. Malas Iii, W. Garth Frazier, S. Venugopal, Enrique A. Medina, Steven Madeiros, Raghavan Srinivasan, R. Dennis Irwin, W. M. Mullins, Anil Chaudhary
Mechanical and Materials Engineering Faculty Publications
A new approach for controlling microstructure development during hot working processes is proposed. This approach is based on optimal control theory and involves state-space type models for describing the material behavior and the mechanics of the process. The effect of process control parameters such as strain, strain rate, and temperature on important microstructural features can be systematically formulated and then solved as an optimal control problem. This method has been applied to the optimization of grain size and process parameters such as die geometry and ram velocity during the extrusion of plain carbon steel. Experimental results of this investigation show …
Window-On-Europe, S. R. Leclair, A. G. Jackson
Window-On-Europe, S. R. Leclair, A. G. Jackson
Mechanical and Materials Engineering Faculty Publications
This report covers a three week visit to the following locations: 1.) A.A. Baikov Institute of Metallurgy of the Russian Academy of Science, Moscow, Russia; 2.) Institute for Applied Informatics, of the Ukrainian Academy of Science, Kiev, Ukraine; 3.)Engineering Design Center.Cambridge University, Cambridge, England- and 4) Artificial Intelligence Department, University of Edinburgh, Edinburgh, Scotland. The visits involved sites whose current research involved either empirical methods for the design of materials and resultant products and/or the development of empirical methods of potential benefit in automating empirical research of materials and/or processing. The report address, for each site, 1) a brief overview …
Relationship Of The Second Order Nonlinear Optical Coefficient To Bandgap In Inorganic Non-Centrosymmetric Crystals, A. G. Jackson, M. Ohmer, S. R. Leclair
Relationship Of The Second Order Nonlinear Optical Coefficient To Bandgap In Inorganic Non-Centrosymmetric Crystals, A. G. Jackson, M. Ohmer, S. R. Leclair
Mechanical and Materials Engineering Faculty Publications
The purpose of this paper, is to provide a means of estimating and comparing the wavelength conversion efficiency (figure of merit, FOM) of new nonlinear materials knowing only their bandgap. The approach for the estimates is trend analysis of existing data1-28 for the second order nonlinear coefficient, x(2)ijk, or dij =x(2)ijk/2, the index of refraction n, and the bandgap E. No underlying physical basis for the result will be presented. The result of this trend analysis, in the form of plots of x(2) vs E and FOM vs E …
Measurement Of Neck Development In Tensile Testing Using Projection Moire, Raghavan Srinivasan, C. S. Hartley, C. Raju, J. Clave
Measurement Of Neck Development In Tensile Testing Using Projection Moire, Raghavan Srinivasan, C. S. Hartley, C. Raju, J. Clave
Mechanical and Materials Engineering Faculty Publications
The projection moire technique affords an accurate method of measuring the geometry of the necked region in a tensile specimen. Corrections to the measured stress, necessary to account for the triaxiality introduced by the neck, require values for the radius of curvature of the specimen at the minimum section. The spacing of fringes resulting from the interference between a grating projected on the specimen surface and a master grating not only provide information which permits calculation of the radius but also demonstrates any changes in symmetry resulting from plastic deformation. Results obtained by testing specimens of copper and mild steel …