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Search Publications by

Stephen Langer (Fed)

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Displaying 1 - 25 of 27

Analytical and Numerical Analyses for Two-Dimensional Stress Transfer

October 12, 2021
C H. Hsueh, P Becher, Lin-Sien H. Lum, Stephen A. Langer, W Carter
Both analytical modeling and numerical simulations were performed to analyze the stress transfer in platelet-reinforced composites in a two-dimensional sense. In the two-dimensional model, an embedded elongate plate bonded to a matrix along its length

Effects of Bond Coat Surface-Roughness on Residual Stresses of Thermal Barrier Coating Systems

October 12, 2021
C H. Hsueh, J Haynes, M Lance, P Becher, M Ferber, Stephen A. Langer, W Carter, W R. Cannon, Lin-Sien H. Lum
The adherence of plasma-sprayed thermal barrier coatings (TBCs) is dependent on mechanical interlocking at the interface between the ceramic top coat and the underlying metallic bond coat. A rough bond coat surface is required in order to establish

Simulating Thermal Response of EB-PVD Thermal Barrier Coating Microstructures

October 12, 2021
M Bartsch, U Schulz, J M. Dorvaux, O Lavigne, Lin-Sien H. Lum, Stephen A. Langer
As ceramic thermal barrier coatings (TBC) are used in more critical applications in advanced engines, knowing basic physiproperties of TBC's is essential for design and reliability assessment. In particular, knowledge of thermal conductivity is cruciin

Spatial strain correlations, machine learning, and deformation history in crystal plasticity

May 16, 2019
Andrew C. Reid, Stefanos Papanikolaou, Hengxu Song, Erik Van der Giessen, Stephen A. Langer, Michail Tzimas
Digital image correlation (DIC) is a well-established, non-invasive technique for tracking and quantifying the deformation of mechanical samples under test. While it provides an obvious way to observe incremental and aggregate displacement information, it

gtklogger: A Tool For Systematically Testing Graphical User Interfaces

August 20, 2015
Stephen A. Langer, Faical Y. Congo, Andrew C. Reid, Rhonald Lua, Valerie R. Coffman
We describe a scheme for systematically testing the operation of a graphical user interface. The scheme provides a capability for generating event logs, which are recordings of a user session with the interface. These logs can be annotated with assertion

OOF3D: An Image-Based Finite Element Solver for Materials Science

March 28, 2012
Valerie R. Coffman, Andrew C. Reid, Stephen A. Langer, Gunay Dogan
Recent advances in experimental techniques (micro CT scans, automated serial sectioning, electron back-scatter diffraction, synchrotron radiation x-rays) have made it possible to characterize the full, three dimensional structure of real materials. Such

Modeling Microstructures with OOF2

September 1, 2009
Andrew C. Reid, Rhonald Lua, R E. Garcia, Valerie R. Coffman, Stephen A. Langer
OOF2 is a program for computing the properties and behavior of material microstructures, beginning with an image of the microstructural geometry. OOF2 uses finite elements, but is designed to be used by materials scientists with little or no finite element

Velocity Fluctuations in a Steadily Sheared Model Foam

June 18, 2003
I K. Ono, S Tewari, Stephen A. Langer, A J. Liu
Numerical simulations are conducted to calculate velocity fluctuations in a simple two-dimensional model of foam under steady shear. The width of the velocity distribution increases sublinearly with the shear rate, indicating that velocity fluctuations are

Microstructure-Based Simulation of Thermomechanical Behavior of Composite Materials by Object-Oriented Finite Element Analysis

December 1, 2002
N Chawla, B V. Patel, M Koopman, K K. Chawla, R Saha, B R. Patterson, Lin-Sien H. Lum, Stephen A. Langer
While it is well recognized that microstructure controls the physical and mechanical properties of a material, the complexity of the microstructure often makes it difficult to simulate by analytical or numerical techniques. In this paper we present a

Effective Temperatures of a Driven System Near Jamming

August 26, 2002
I K. Ono, C S. O'Hern, Stephen A. Langer, A J. Liu, S R. Nagel, D J. Durian
Fluctuations in a model of a sheared, zero-temperature foam are studied numerically. Five different quantities that reduce to the true temperature in an equilibrium thermal system are calculated. All five have the same shear-rate dependence, and three have

Random Packings of Frictionless Particles

February 18, 2002
C S. O'Hern, Stephen A. Langer, A J. Liu, S R. Nagel
We study random packings of frictionless particles at T=0. The packing fraction where the pressure becomes nonzero is the same as the jamming threshold, where the static shear modulus becomes nonzero. The distribution of threshold packing fractions narrows

OOF: An Image-Based Finite Element Analysis of Material Microstructure

June 1, 2001
Stephen A. Langer, W Carter, Lin-Sien H. Lum
The determination of macroscopic properties of a material given its microscopic structure is of fundamental importance to materials science. We present an overview of two public domain programs which jointly predict macroscopic behavior, starting from an

Force Distributions Near the Jamming and Glass Transitions

January 1, 2001
C S. O'Hern, Stephen A. Langer, A J. Liu, S R. Nagel
We measure the distributions of interparticle normal forces P(F) near the glass transition in supercooled liquids and near the jamming transition in foams and compare them to those obtained in recent experiments on static granular packings. We find that

Sheared Foam as a Supercooled Liquid?

January 1, 2000
Stephen A. Langer, A J. Liu
We conduct numerical simulations on a simple model of a two-dimensional steady-state sheared foam, and define a quantity Γ that measures pressure fluctuations in the constant-area system. This quantity reduces to the temperature in an equilibrium system

Statistics of Shear-Induced Rearrangements in a Two-Dimensional Model Foam

October 1, 1999
S Tewari, D Schiemann, D J. Durian, C M. Knobler, Stephen A. Langer, A J. Liu
Under steady shear, a foam relaxes stress through intermittent rearrangements of bubbles accompanied by sudden drops in the stored elastic energy. We use a simple model of foam that incorporates both elasticity and dissipation to study the statistics of

Effect of Ordering on Spinodal Decomposition of Liquid-Crystal/Polymer Mixtures

January 1, 1999
A M. Lapena, S C. Glotzer, Stephen A. Langer, A J. Liu
Partially phase-separated liquid-crystal/polymer dispersions display highly fibrillar domain morphologies that are dramatically different from the typical structure found in isotropic mixtures. To explain this, we explore the coupling between phase

The OOF Manual: Version 1.0

November 1, 1998
W C. Carter, Stephen A. Langer, Lin-Sien H. Lum
OOF and PPM200F are programs developed at NIST to investigate the properties of microstructures. The user starts with an image of a real or simulated microstructure, assigns material properties to the features in the image, and performs virtual experiments

Effect of Interface Properties on Microcracking of Iron Titanate

January 1, 1998
A Saigal, Stephen A. Langer, W Carter, M H. Zimmerman, K T. Faber, Lin-Sien H. Lum
It has been shown both experimentally and theoretically that mechanical properties are strongly dependent on the grain size in single-phase polycrystalline ceramics with large thermal expansion anisotropy [1,2]. This dependence is related to the residual