Conferences, Lectures, & Seminars
Events for September
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Mode-dependent Thin Film Interfacial Property Measurement by Laser Induced Stress Waves
Wed, Sep 05, 2007 @ 03:30 PM - 04:30 PM
Aerospace and Mechanical Engineering
Conferences, Lectures, & Seminars
Junlan WangDepartment of Mechanical Engineering,
University of California, Riverside, CA AbstractThin films are crucial components in a wide range of multilayer microelectronic and optical devices. They are also desirable candidates for micro-actuators in micro-electro-mechanical systems. Due to the dissimilar nature of the constituents, large residual stress can be induced in the film during the fabrication process which leads to the subsequent failure of the thin film devices. Among the many properties, interfacial adhesion between the thin film and substrate is one of the key parameters influencing the overall reliability and durability of the integrated thin film devices. However, due to the critical dimension of thin films, conventional techniques face challenges to reliably evaluate the thin film interfacial properties.
To address the above challenge, we developed a unique set of laser-induced stress wave techniques to quantitatively investigate the intrinsic strength of a planar thin film/substrate interface. High-amplitude short-duration stress wave pulses generated by laser-pulse absorption are used to delaminate a thin film/substrate interface and the corresponding interfacial stress is calculated from the transient high-speed interferometric displacement measurement using wave mechanics. Depending on the geometry of the substrate, the thin film interfaces can be subjected to a variety of loading modes including tensile, mixed-mode and pure-shear. Systematic studies of similar interfaces failed under different loading conditions reveals that the thin film interfacial failure as well as the adhesion is highly mode-dependent. Significant wrinkling and tearing of the films happens under mixed-mode and pure-shear loading, in great contrast to blister patterns observed in similar films failed under tensile loading. This technique has been further developed to investigate the interfacial adhesion of various thin film/substrate interfaces interesting to semiconductor industry and biomedical applications as well as those under high strain-rate loading for defense applications.
Biosketch Junlan Wang received her Ph.D. in Theoretical and Applied Mechanics from the University of Illinois at Urbana-Champaign in 2002. She joined the faculty in the Department of Mechanical Engineering at the University of California, Riverside in 2003 after finishing one year post-doctoral research in the Solid Mechanics and Structures group at Brown University. Her research interest is in the mechanics of thin films and coatings, high strain rate materials behavior, size-dependent mechanical behavior of surface micro and nanostructures, and mechanical reliability of multifunctional nanoporous materials. Her recent awards include the SEM Hetenyi Award in 2004, UC Regents Faculty Fellowship in 2004, Faculty Development Award in 2006, UCR College of Engineering Excellence in Teaching Award in 2007, and ASEE Beer and Johnston, Jr. Outstanding New Mechanics Educator Award in 2007.
Location: Staufer Science Lecture (SLH) Rm 102
Audiences: Everyone Is Invited
Contact: April Mundy
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Multiscale Fluid Flow Studies with Molecular Tagging Diagnostics
Wed, Sep 12, 2007 @ 03:30 PM - 04:30 PM
Aerospace and Mechanical Engineering
Conferences, Lectures, & Seminars
Manoochehr Koochesfahani ProfessorDepartment of Mechanical Engineering Michigan State University East Lansing, MI A brief overview of molecular tagging diagnostics will be presented, along with results from studies in three different flow fields. Molecular tagging methods take advantage of molecules that can be turned into long lifetime tracers upon excitation by photons of an appropriate wavelength. Typically a pulsed laser is used to "tag" the regions of interest, and those tagged regions are interrogated at successive times within the lifetime of the tracer. This approach has been utilized for the measurement of velocity and temperature fields. The first study presented here considers unsteady flow separation from a pitching airfoil. Boundary-layer resolved measurements of this phenomenon and comparison with complementary computations will be discussed. The second study involves in-cylinder measurements in a motored IC engine. Results from flow mapping of cycle-to-cycle variation in late compression will be presented. Preliminary observations on the possibility of flow control will be discussed. The final study addresses the flow inside a microchannel driven by either a pressure differential or electroosmosis. In-situ measurements of wall friction factor in pressure-driven flow will be compared with theoretical predictions in order to assess the large discrepancies that have been previously reported. Electroosmotically-driven flows involve additional complications, e.g. presence of an electric field and a time-varying temperature field caused by Joule heating. Results will be shown from simultaneous measurements of velocity and temperature within a microchannel for different applied potentials.
Location: Staufer Science Lecture Hall, Rm 102 (SLH)
Audiences: Everyone Is Invited
Contact: April Mundy
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Homogeneous Microcombustion Studies: Progress and Observations
Wed, Sep 19, 2007 @ 03:30 PM - 04:30 PM
Aerospace and Mechanical Engineering
Conferences, Lectures, & Seminars
Mark A. Shannon James W. Bayne Professor of Mechanical Engineering Department of Mechanical Science and Engineering University of Illinois at Urbana-Champagne Urbana IL, 61801-2906 ABSTRACT:In the past few years, there has been an intense interest in building very small engines, power plants, and high temperature microchemical reactors, all running on the combustion of hydrocarbon fuels (due to their high inherent energy densities). While most systems employ catalytic and heterogeneous combustion processes, we wished to create and study high-temperature flames confined within burners with the smallest gap below 1 mm in length. The problem we immediately confronted is that flames either could not be created within narrow confined structures, or quenched quickly, similar to that which occurs in flame arrestors. We hypothesized that if we could have hot enough walls with low enough radical recombination probabilities, we could create and sustain homogeneous combustion in burners with sub-millimeter gaps. Therefore, we investigated a number of different wall materials and burner configurations, and found that flames of hydrogen, methane, propane, butane, and acetylene mixed with oxygen can be sustained in cavities as small as 100 microns, provided that the walls are sufficiently "quenchless." In addition, we have observed unusual flame structures at this scale, and flame dynamics that strongly vary with changes in temperature profiles. Homogeneously burning hydrocarbons in air at this scale has proved to be more difficult, requiring even higher wall temperatures and better thermal management. In this talk, I will present the experiments that we have conducted towards developing microcombustion-based systems, some of the observations I find interesting, what we now know is happening within the structures, and the many open questions that remain to be answered (hopefully!) by many of the excellent researchers working in combustion studies throughout the U.S. and world.
Location: Stauffer Science Lecture Hall, Rm 102
Audiences: Everyone Is Invited
Contact: April Mundy
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Numerical Simulation and Modeling of Complex Turbulent Flows
Wed, Sep 26, 2007 @ 03:30 PM - 04:30 PM
Aerospace and Mechanical Engineering
Conferences, Lectures, & Seminars
Professor Kyle D. SquiresMechanical and Aerospace Engineering DepartmentArizona State UniversityTempe, AZ 85287 USAAbstract:Numerical simulation and modeling of the turbulent flows encountered in aerodynamics applications are challenging for several reasons, including the fact that the Reynolds numbers are usually large and the flows often exhibit significant effects of separation. These and other features challenge simulation strategies and have constrained the application of Computational Fluid Dynamics as a tool for analysis and design.
Simulation strategies have typically relied on Reynolds-averaged Navier-Stokes (RANS) approaches that are computationally feasible and often sufficient in attached flows though are unable to accurately account for the complex effects characteristic of flow separation.
Large Eddy Simulation (LES) is a technique that offers greater fidelity and is a powerful approach away from solid surfaces. Near the wall, however, the computational cost of LES is prohibitive, a fact that will constrain its widespread at high Reynolds numbers for the foreseeable future. These and other considerations have motivated development of
hybrid methods, the most popular of these approaches being Detached-Eddy Simulation (DES). DES combines the most favorable elements of RANS and LES models in a single simulation. In this seminar, development and applications of the method aimed at advancing DES will be reviewed. In natural applications of the technique, attached boundary layers are treated by RANS, exploiting the computational efficiency and relative accuracy of RANS models in attached shear layers. The method becomes an
LES in regions away from the wall provided the grid density is sufficient. The range of DES applications to date include an array of ``building block'' test cases such as the flow over a cylinder, sphere, aircraft forebody, and missile base. In addition, the technique has
been applied to complex geometries, including the flows around fighter aircraft. The developing experience base is encouraging expansion of the method beyond the originally intended class of massively separated flows and a brief description of some of the challenges and recent advances will be presented. These include improvements to the method that modify the DES length scale to overcome errors that can arise from the interface between the RANS and LES regions and development of strategies for seeding turbulent fluctuations in boundary layers.
Location: Stauffer Science Lecture Hall, Rm 102
Audiences: Everyone Is Invited
Contact: April Mundy