Levich Institute Seminar Announcement, 04/13/2010
Tuesday, 04/13/2010
2:00 PM
Steinman Hall, Room #312
(Chemical Engineering Conference Room)

Dr. Rekha Rao
Sandia National Laboratories
Thermal and Fluid Processes
"Structural Epoxy Foams: Modeling, Experiments, and Novel Formulations"


ABSTRACT


Foams are ubiquitous low density materials used for a variety of applications including shock, thermal, and vibration isolation. At Sandia National Laboratories*, we use a variety of foams, both physically and chemically blown, as encapsulants to protect sensitive electronic components. Despite their many uses, foams are still not well understood at a fundamental level. In order to better understand foam expansion, we combine experimental observations with finite element model development for several foams of interest to Sandia. A series of experiments have been performed to help characterize the materials and elucidate the foaming process, including reaction kinetics, time-dependent rheology, wetting behavior, nucleation, foam generation, and flow visualization. The continuum-modeling capability is based on a finite element discretization of the self-expansion that occurs during foam blowing; coupling the equations of motion with the movement of the free surface represented using the level set method. This continuum model uses a homogenized description of foam, which does not include the gas in the foam cells explicitly but instead tracks an evolving density equation. The current model is an engineering design tool that will allow us to study processing variables such as temperature, as well as the effect of gate and vent location for optimizing the foam encapsulation process. Comparison of the model against validation experiments is also shown. A brief discussion will be given of another project that has undertaken the development of novel epoxy foams that may eliminate the difficulties encountered in the past such as insufficient filling, density gradients, and potentially high residual stresses.

* Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under Contract DE-AC04-94AL85000.

BRIEF ACADEMIC/EMPLOYMENT BACKGROUND:

  • 1986 B.S. Chem. Engr. University of California, Berkeley
  • 1990 Ph.D. Chem. Engr. University of Washington
  • 1997 Principal Member of Technical Staff Sandia National Laboratories
  • 1990 Senior Member of Technical Staff Sandia National Laboratories

CURRENT RESEARCH INTERESTS:

Rekha is a finite element software developer and analyst for multiphysics applications including free and moving boundary problems and non-Newtonian fluid mechanics. Her research interests include viscoelastic fluid flow, suspension rheology, solid-fluid interactions and level set methods. Applications of interest include manufacturing flows such as mold filling, polymeric encapsulation with hard encapsulant, foams processing, and coating flows. Her current projects include development of models for nuclear waste reprocessing, understanding the bottle-filling flows of viscoelastic fluids, modeling coextrusion for manufacturing of capacitors, and developing foam transport and process models.