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Spring 2012 Seminars

Thursday, May 24th, 2012
Inverse Problems Seminar
Speaker: Professor Antoinette Maniatty, Mechanical, Aerospace and Nuclear Engineering
Title: Large Strain Stabilized Finite Element Formulation
Location: IPRPI Conference Room (Amos Eaton 436)
Time: 1pm - 2pm

Abstract: A stabilized finite element formulation for nearly incompressible finite deformations in hyperelastic, and elastic-viscoplastic solids will be presented.
An updated Lagrangian finite element formulation is developed where mesh dependent terms are added to enhance the stability of the mixed finite element formulation. This formulation circumvents the restriction on the displacement and pressure fields due to the Babuska-Brezzi condition and provides freedom in choosing interpolation functions in the nearly incompressible limit. Moreover, it facilitates the use of low order simplex elements (i.e. P1/P1), reducing the degrees of freedom required for the solution for nearly incompressible behavior when stable elements are necessary.
Linearization of the weak form is derived for implementation into a finite element code. Numerical experiments with P1/P1 elements show that the method is effective in nearly incompressible conditions and can be advantageous.

Friday, April 6th, 2012
Inverse Problems Seminar
Speaker: Professor Antoinette Maniatty, Mechanical, Aerospace and Nuclear Engineering
Title: An Inverse Approach to Interpreting X-Ray Microbeam Diffraction Measurements of Electromigration Induced Strains        
Location: IPRPI Conference Room (Amos Eaton Rm 436)
Time: 2:00-3:00 PM

Electromigration is a mass transport process that occurs in metal interconnects when a high electrical current density is applied. If the interconnect line is not sufficiently confined, the diffusion process may continue until a void forms at the cathode end, eventually leading to failure of the line. If the line is confined, the mass transport due to electromigration eventually leads to a build-up of a stress gradient with a diffusion driving force that is equal and opposite to that due to the high current density, and the mass transport is arrested. The push for increased performance and continued miniaturization in microelectronic devices leads to higher current densities that are more likely to cause electromigration induced failure. Understanding and being able to model this phenomena is important for electronic package design. An inverse problem solving approach combining modeling and simulation coupled with X-ray microbeam studies, where local elastic strains are measured, can be used to resolve some of the challenging questions regarding the physics of electromigration. This talk provides an introduction to the prevalent electromigration modeling methodology and key issues that are currently unresolved. An inverse problem formulation, using the finite element method, is presented and used with two X-ray microbeam data sets, exhibiting opposing trends, to demonstrate how some key questions about electromigration may be answered.


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