Mechanical Engineering Commons^™

Preparation Of Mesoporous Tin Oxide For Electrochemical Applications, Fanglin Chen, Meilin Liu

Faculty Publications

Mesoporous tin oxide stable up to 500 °C has been prepared for the first time using both cationic and neutral surfactants.

The Evolution Of Probability Functions In An Inelasticly Deforming Two-Phase Medium, Brent L. Adams, H. Garmestani, S. Lin

Faculty Publications

A formulation is introduced here for the evolution of correlation functions in an inelastically deforming two phase medium. Probability functions play a major role in describing the statistical distribution of different phases in a heterogeneous medium in the development of statistical continuum theory. Proper formulation of statistical continuum model for inelastic deformation requires better understanding of the evolution of the corresponding probability functions. A two point probability function representation is used to approximate the statistical correlation functions. The evolution of these functions requires the information from higher order probability functions, in this case, a three point probability function. A decomposition …

Successive Galerkin Approximation Algorithms For Nonlinear Optimal And Robust Control, Timothy Mclain, Randal W. Beard

Faculty Publications

Nonlinear optimal control and nonlinear H infinity control are two of the most significant paradigms in nonlinear systems theory. Unfortunately, these problems require the solution of Hamilton-Jacobi equations, which are extremely difficult to solve in practice. To make matters worse, approximation techniques for these equations are inherently prone to the so-called 'curse of dimensionality'. While there have been many attempts to approximate these equations, solutions resulting in closed-loop control with well-defined stability and robustness have remained elusive. This paper describes a recent breakthrough in approximating the Hamilton-Jacobi-Bellman and Hamilton-Jacobi-Isaacs equations. Successive approximation and Galerkin approximation methods are combined to derive …

Nonlinear Optimal Control Design Of A Missile Autopilot, Tim Mclain, Randal W. Beard

Faculty Publications

The application of a new nonlinear optimal control strategy to the design of missile autopilots is presented. The control approach described and demonstrated here is based upon the numerical solution of the Hamilton-Jacobi-Bellman equation by Successive Galerkin Approximation. Using this approach, feedback controllers are computed by an iterative application of a numerical Galerkin-type PDE solver. Simulation results demonstrating the application of this approach to the design of a missile autopilot are presented.

Development And Experimental Validation Of An Underwater Manipulator Hydrodynamic Model, Timothy W. Mclain, Stephen M. Rock

Faculty Publications

Hydrodynamic forces can be large and hence have a significant effect on the dynamic performance of underwater manipulation systems. this paper investigates these forces for a cylindrical single-link arm undergoing motions that are characteristics of a robotic manipulator. Based on flow visualization, theoretical analysis, and experimental measurements, a new model is developed that describes these forces. This model differs from previous models in that the drag and added-mass coefficients are state-dependent functions that depend on the distance traveled by the arm. A factor of four improvement in accuracy is demonstrated over standard constant-coefficient models.

Successive Galerkin Approximations To The Nonlinear Optimal Control Of An Underwater Robotic Vehicle, Timothy Mclain, Randal W. Beard

Faculty Publications

The application of a new nonlinear optimal control strategy to the station-keeping control of an underwater robotic vehicle is considered. The control approach described and demonstrated here is based upon the numerical approximation of solutions to the Hamilton-Jacobi-Bellman equation. These solutions are computed by an iterative application of Galerkin's method. Preliminary simulation results demonstrating the application of this approach to the control of an underwater vehicle in the horizontal plane are presented.

A Practical Algorithm For Designing H∞ Control Laws, Timothy Mclain, Randal W. Beard

Faculty Publications

We describe an approximation method for the Hamilton-Jacobi-Isaacs (HJI) equation that results in feedback control. The approximation is accomplished via a two-step successive Galerkin approximation scheme. An application of the technique to the control of the forward motion of an underwater vehicle is described.

Fuel Equalized Retargeting For Separated Spacecraft Interferometry, Timothy Mclain, Randal W. Beard, Fred Y. Hadaegh

Faculty Publications

Motivated by NASA's proposed Deep Space 3 interferometer mission, the paper considers the problem of reorienting a constellation of spacecraft such that the total fuel distributed across the constellation is both conserved and expended uniformly. The spacecraft constellation is controlled to reorient as if it were a rigid body. Two approaches to fuel equalization are investigated. The first approach picks a point of rotation a priori that optimizes an objective function that trades off minimum-fuel maneuvers and maneuvers that equalize the fuel. Since the point of rotation is selected a priori and is fixed during the rotation, this approach is …

Determination Of The Asymmetry Parameter And Scattering Coefficient Of Turbid Media From Spatially Resolved Reflectance Measurments, Matthew R. Jones, Yukio Yamada

Faculty Publications

We present a technique for determining the asymmetry parameter and scattering coefficient of turbid media from spatially resolved reflectance measurements. This technique will contribute to the development of medical applications in which it is necessary to predict the distribution and propagation of light in tissue. Based on Monte Carlo simulations, we derived correlations which relate the reduced scattering coefficient and the asymmetry parameter to the relative reflectance curve. Initial estimates of the optical properties are obtained from these correlations. Final values are obtained by adjusting the optical parameters and repeating the Monte Carlo simulations until the simulated reflectance pattern matches …

Sr‐ And Ni‐Doped Lacoo3 And Lafeo3 Perovskites: New Cathode Materials For Solid‐Oxide Fuel Cells, Kevin Huang, Hee Y. Lee, John B. Goodenough

Faculty Publications

An improved cathode material for a solid‐oxide fuel cell would be a mixed electronic and oxide‐ion conductor with a good catalytic activity for oxygen reduction at an operating temperature T _op ≥ 700°C and a thermal expansion matched to that of the electrolyte and interconnect. We report on the properties of Sr‐ and Ni‐doped LaCoO₃ and LaFeO₃ perovskites that meet these criteria. Single‐phase regions were determined by X‐ray diffraction, and thermogravimetric analysis measurements were used to obtain the temperatures above which oxygen loss, and hence oxide‐ion conductivity, occurs. The conductivity and Seebeck measurements indicate the coexistence of both …

Statistical Continuum Theory For Inelastic Behavior Of A Two-Phase Medium, Brent L. Adams, H. Garmestani, S. Lin

Faculty Publications

This work was supported in part (B.L. Adams) by the MRSEC Program of the National Science Foundation under Award no. DMR-9632556. Further support was provided by the Center for Materials Research and Technology (MARTECH at FSU) and Center for Nonlinear and Nonequilibrium Sciences (CENNAS at FAMU). A statistical contiuum mechanics formulation is presented to predict the inelastic behavior of a medium consisting of two isotropic phases. The phase distribution and morphology are represented by a two-point probability function. The isotropic behavior of the single phase medium is represented by a power law relationship between the strain rate and the resolved …

Nonlinear Optimal Control Of A Hydraulically Actuated Positioning System, Timothy Mclain, Randal W. Beard

Faculty Publications

In this paper, the nonlinear optimal control problem is formulated for the position control of an electrohydraulic servo system. The optimal control is given by the solution to the Hamilton-Jacobi-Bellman equation, which in this case cannot be solved explicitly. An alternative method, based upon successive Galerkin approximation, is used to obtain an approximate optimal solution. Preliminary simulation results, demonstrating the application of this approach to the position control of a hydraulically actuated device, are presented.

Extracting The Relative Grain Boundary Free Energy And Mobility Functions From The Geometry Of Microstructures, Brent L. Adams, D. Kinderlehrer, W. W. Mullins, Anthony D. Rollett, Shlomo Ta'asan

Faculty Publications

This work was supported primarily by the MRSEC Program of the National Science Foundation under Award Number DMR-9632556. This paper describes a method for extracting, from measurements of a polycrystal, the relative excess free energy and the relative mobility of the grain boundaries as functions of the crystallographic type (five degrees of freedom) and relevant thermodynamic variables. The method requires the simultaneous measurement of both the geometry and the crystallography of a large number of grain boundary intersections; the crystallographic information may be obtained from orientation imaging microscopy (OIM). For simplicity, the intersections will be assumed to be triple junctions …

Robotic Tcf And Rigid-Body Calibration Methods, Edward Red, Xuguang Wang

Faculty Publications

For off-line programming to work, systematic methods must be developed to account for non-ideal performance of the parts and devices in the manufacturing cell. Although much of the literature focuses on robot inaccuracy, this paper considers practical methods for the tool control frame (TCF) calibration and rigid-body compensation required to close the inverse kinematics loop for target driven tasks.

Electrode Performance Test On Single Ceramic Fuel Cells Using As Electrolyte Sr‐ And Mg‐Doped Lagao3, Kevin Huang, Man Feng, John B. Goodenough, Christopher Milliken

Faculty Publications

The electrode performance of a single solid oxide fuel cell was evaluated using a 500 μm thick La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85 (LSGM) as the electrolyte membrane. Comparison of La_0.6Sr_0.4CoO_3-δ (LSCo) and La_0.9Sr_0.1MnO₃ (LSM) as cathodes showed LSCo gave an exchange current density two orders of magnitude higher than that of LSM. Comparison of CeO₂/Ni and LSGM/Ni as anodes showed a degradation of the latter with time, and studies of the anode‐electrolyte interface and the reactivity of NiO and LSGM suggest better anode …

On-Line Cartesian Trajectory Control Of Mechanisms Along Complex Curves, Edward Red, Zhaoxue Yang

Faculty Publications

New methods have been developed to control a mechanism's realtime Cartesian motion along spatially complex curves such as Non-Uniform Rational B-splines (NURBS). The methods dynamically map the critical trajectory parameters between parameter space, Cartesian space, and joint space. Trajectory models that relate Cartesian tool speeds and accelerations to joint speeds and accelerations have been generalized so that they can be applied to most classes of robots and CNC mechanisms.

Chemical Stability Study Of Bace0.9Nd0.1O3−Α High Temperature Proton-Conducting Ceramic, Fanglin Chen, O. Toft Sorensen, Guangyao Meng, Dingkum Peng

Faculty Publications

BaCe_0.9Nd_0.1O_3−a (BCN) ceramic is known to be an excellent high-temperature proton conductor and is a candidate electrolyte for use in solid oxide fuel cells, hydrogen or steam sensors and steam electrolysers. In this work, the chemical stability of BCN was investigated systematically by combining XRD and DTA–TG techniques to study its processing compatibility and its feasibility in potential applications. It was found that above 1200 °C, BCN reacted with alumina or zirconia, leading to the loss of barium and an excess of cerium. In cold water, both sintered BCN disks and powder samples had very …

Preparation Of Nd-Doped Baceo3 Proton-Conducting Ceramics By Homogeneous Oxalate Coprecipitation, Fanglin Chen, Ping Wang, O. Toft Sorensen, Guangyao Meng, Dingkum Peng

Faculty Publications

Nd-doped BaCeO₃ have been obtained from homogeneous coprecipitated oxalates when calcined at temperatures T≥1000 °C. Ball-milling of the calcined powders well disperses the agglomerates and consequently has a beneficial effect in the densification process. The calcination temperature has a major influence on the sintering process and powders calcined at 1100 °C possess good sinterabilities. The pressure applied to press the green pellets has no apparent influence on the sintered density at sintering temperatures of T≥1400 °C. By controlling the processing variables it was possible to obtain near fully dense Nd-doped BaCeO₃ ceramics with homogeneous microstructure at a sintering …

Extracting The Grain Boundary Character/Free Energy Relationship From The Microstructure: Pure <100> And <111> Tilt Boundaries, Brent L. Adams, S. Costiner, D. Kinderlehrer, W. W. Mullins, Shlomo Ta'asan

Faculty Publications

This work was supported primarily by the MRSEC Program of the National Science Foundation under Award Number DMR-9632556. Analysis is described to extract the excess free energy of grain boundaries from the mesotexture of well-equilibrated polycrystalline samples. The approach is based upon the force and torque balances at triple junctions described in the classical work of Herring. The main advantage of the approach is that the free energy function is obtained over the full fundamental zone of grain boundary types. For the purposes of exposition, the method is described for specified two-parameter hypersurfaces in the fundamental zone for cubic polycrystals …

Characterization Of Sr‐Doped Lamno3 And Lacoo3 As Cathode Materials For A Doped Lagao3 Ceramic Fuel Cell, Kevin Huang, Man Feng, John B. Goodenough, Michael Schmerling

Faculty Publications

Energy dispersive spectrometry line scan and ac impedance spectroscopy were used in this study to investigate the chemical reactions between two cathode materials, La_0.84Sr_0.16MnO₃ (LSM), La_0.5Sr_0.5CoO_3-δ (LSC), and the electrolyte La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85 (LSGM). Significant interdiffusions of Co into LSGM and Ga into LSC were found at an LSC/LSGM interface even at relatively low fabrication temperatures. In contrast, only small interdiffusions of Mn into LSGM and Ga into LSM were detected at the LSM/LSGM interface even though it was fired at 1470°C. The …

Bounding Elastic Constants Of An Orthotropic Polycrystal Using Measurements Of The Microstructure, Brent L. Adams, M. J. Beran, T. A. Mason, Ted Olsen

Faculty Publications

We show how information about the elastic stiffness and compliance of an orthotropic polycrystal may be obtained from measurements of the statistical properties of the microstructure. We begin by discussing the statistical properties of the governing equations and the hierarchy that results when the equations are averaged. Perturbation solutions are obtained in terms of low-order statistical information. Using methods previously developed, we derive bounds for the elastic stiffnesses and compliances. A heirarchy of bounds is derived using the statistical information obtained from measurements of the microstructure. We discuss the methods used to obtain the correlation functions of the microstructure and …

Characterization Of The Si/Sio2 Interface Formed By Remote Plasma Enhanced Chemical Vapor Deposition From Sih4/N2O With Or Without Chlorine Addition, Young-Bae Park, Xiaodong Li, Shi-Woo Rhee

Faculty Publications

The Si/SiO₂interface formed by remote plasma enhanced chemical vapor deposition (RPECVD) at low temperature with SiH₄/N₂O or SiH₄/N₂O/Cl₂ was studied and compared with thermal oxidation. The interface of the CVD SiO₂ without chlorine addition is rougher than that with chlorine addition. But the surface roughness of CVD SiO₂ films increases with chlorine addition. The thermal oxidation induces strong interface strains, and the strains generated by the CVD SiO₂ without chlorine addition are stronger and are distributed more nonuniformly than those by the chlorinated SiO₂. …

Microstructure And Deposition Rate Of Aluminum Thin Films From Chemical Vapor Deposition With Dimethylethylamine Alane, Byoung-Youp Kim, Xiaodong Li, Shi-Woo Rhee

Faculty Publications

Deposition of aluminumfilm from DMEAA in the temperature range of 100–300 °C has been studied. In this temperature range, there is a maximum deposition rate at around 150 °C. The film deposited at 190 °C has elongated blocklike grain shapes, which are ∼600 nm in width and 930 nm in length. Grains in the film deposited at 150 °C showed an equiaxed structure with grain size in the range of 100–300 nm in a film with 600 nm thickness. Aluminum oxide particle inclusion was observed especially at high deposition temperature. Plausible reaction pathways of DMEAA dissociation were suggested to explain …

Grain-Boundary Structure Effects On Intergranular Stress Corrosion Cracking Of Alloy X-750, Brent L. Adams, Ted Olsen, N. Panayotou, Y. Pan

Faculty Publications

This work was supported by the Department of Energy under Grant No. DE-FG02-88ER 45355. TO was supported by the National Science Foundation during her 1993-94 stay at the Institute for Advanced Studies (Princeton) under grant DMS-9304580. The authors wish to acknowledge helpful discussion with Carol Nichols, John Hack, Gino Palumbo, Karl Aust, and Gary Was. It is well known that the properties and behavior of grain boundaries are strongly affected by local chemistry and atomic structure. This paper focuses on the mesoscale description of grain boundary structure (i.e. the five crystallographic degrees of freedom) and correlations with intergranular stress corrosion …

Experiments In The Coordinated Control Of An Underwater Arm/Vehicle System, Timothy W. Mclain, Stephen M. Rock, Michael J. Lee

Faculty Publications

The addition of manipulators to small autonomous underwater vehicles (AUVs) can pose significant control challenges due to hydrodynamic interactions between the arm and the vehicle. Experiments conducted at the monterey Bay Aquarium Research Institute (MBARI) using the OTTER vehicle have shown that dynamical interactions between an arm and a vehicle can be very significant. For the experiments reported in this paper, a single-link "arm" was mounted on OTTER. Tests showed that for 90-degree, two-second repetitive slews of the arm, the vehicle would move as much as 18 degrees in roll and 14 degrees in yaw when no vehicle control was …

Structural Characterization Of Aluminum Films Deposited On Sputtered-Titanium Nitride/ Silicon Substrate By Metalorganic Chemical Vapor Deposition From Dimethylethylamine Alane, Xiaodong Li, Byoung-Youp Kim, Shi-Woo Rhee

Faculty Publications

Alfilmsdeposited on sputtered‐TiN/Si substrate by metalorganic chemical vapor deposition(MOCVD) from dimethylethylamine alane (DMEAA) were characterized using x‐ray diffraction(XRD),Auger electron spectroscopy(AES),atomic force microscopy(AFM), and transmission electron microscopy (TEM). The TiN filmsputtered on the Si has a preferred orientation along the growth direction with the 〈111〉 of the film parallel to the Si〈111〉. Sputtering of the TiN film on the Si induced strains at the interface. The TiN/Si interface is flat while the Al/TiN interface is rough. There exist many dislocations at the Al/TiN interface. The Al₂O₃ phase was formed at the Al/TiN interface during the early stages of …

Otter: A Testbed Submersible For Robotics Research, Tim Mclain, H H. Wang, R L. Marks, S D. Fleischer, D W. Miles, G A. Sapilewski, S M. Rock, M J. Lee, R C. Burton

Faculty Publications

Untethered, unmanned submersibles (UUSs) have the potential of becoming useful tools in nuclear reactor inspection and repair and waste-site cleanup and survey, in addition to subsea exploration. Classical "hand-in-glove" control methods used currently by tethered, remotely-operated vehicles (ROVs) are unsuitable for UUS systems which have, at best, limited communications. The Stanford Aerospace Robotics Laboratory (ARL) has joined with the Monterey Bay Aquarium Research Institute (MBARI) in a program to develop new methods of controlling UUS systems.

As a part of this effort, a submersible testbed has been built to test and develop new technologies that will make UUSs useful tools …

Characterization Of The Near-Interface Region Of Chemical Vapor Deposited Diamond Films On Silicon By Backscatter Kikuchi Diffraction, Brent L. Adams, K. Kunze, S. Geier, R. Hessmer, M. Schreck, B. Rauschembach, B. Stritzker

Faculty Publications

The lattice orientations near the interface of chemical vapor deposited diamond films on Si(001) have been studied by orientation imaging microscopy. This technique is based on the automated analysis of electron backscatter Kikuchi diffraction patterns. The electron beam has been scanned in discrete steps over the reverse side of the diamond film after having removed the substrate. The obtained data have allowed us to determine the texture and to visualize quantitatively the orientational arrangement of and among individual diamond crystallites in the near-interface region. A comparison with the orientation of the substrate has proved the existence of epitaxially nucleated grains. …

Characterization Of The Near-Interface Region Of Chemical Vapor Deposited Diamond Films On Silicon By Backscatter Kikuchi Diffraction, Brent L. Adams, K. Kunze, S. Geier, R. Hessmer, B. Rauschembach, M. Schreck, B. Stritzker

Faculty Publications

B.L.A. and K.K. gratefully acknowledge support under a Materials Research Group Award by the National Science Foundation No. DMR-9001278. Also the software support by Th. Bollmeier is greatly appreciated. The lattice orientations near the interface of chemical vapor deposited diamond films on Si(001) have been studied by orientation imaging microscopy. This technique is based on the automated analysis of electron backscatter Kikuchi diffraction patterns. The electron beamhas been scanned in discrete steps over the reverse side of the diamond film after having removed the substrate. The obtained data have allowed us to determine the texture and to visualize quantitatively the …

The Asymptotic Structure Of Transient Elastodynamic Fields At The Tip Of A Stationary Crack, Xiaomin Deng

Faculty Publications

The asymptotic structure of the transient elastodynamic near-tip fields around a stationary crack is investigated for all three fracture modes. The transient fields are obtained as the sum of their quasi-static counterparts and corresponding transient correction terms, in terms of variable-separable expansions. By allowing the coefficients of terms in the quasi-static expansion to deviate from their quasi-static restrictions, the correction terms are shown to be the particular solutions of a set of first order (for mixed mode I and II) or second order (for mode III) ordinary differential equations with constant coefficients and non-homogeneous terms involving only sine and cosine …