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           COLLOQUIUM OF THE COMPUTATIONAL MATERIALS SCIENCE CENTER
                              College of Science
                       (CDS Department CSI 898-Sec 001)
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    Fracture and plasticity in thin films and small volumes
    
                      Dylan J. Morris

          Materials Science and Engineering Laboratory
National Institute of Standards and Technology, Gaithersburg, MD

Instrumented indentation (or as is commonly called, âœnanoindentationâ) is used to probe the mechanical properties of small volumes and thin films. Nanoindentation is essentially a hardness test that can record forces and displacements during a contact cycle between a target material and a mechanical probe. However it has been realized that much more than hardness can be studied. Two unconventional applications of nanoindentation will be described.

The first application is the study of brittle fracture in thin (~ 1 micrometer) films for microelectronic applications. Nanoporous low-dielectric-constant (low-κ) films constitute a class of materials that are plagued by fracture concerns and are not amenable to traditional fracture toughness measurement techniques. We look at the generation and interpretation of flaws that are on the scale of the film thickness. Although the fracture behavior changes with film thickness in a complex way, the fracture toughness can be estimated with a combined contact and fracture mechanics model.

The second application is the point of first yield in metals. Nanoindentation can probe small volumes of metallic crystals that are initially dislocation-free. The point of first yield is associated with homogeneous dislocation nucleation, which can be used to define a rule for dislocation nucleation in dislocation-dynamics simulations. The Hertzian equations are typically used to interpret the experiment in terms of a critical shear stress. A combination of experiment and finite-element simulation shows that this may not always be appropriate. 

collaborators: 
Stefhanni Jennerjohn, David Bahr (Washington State University)
Li Ma, Lyle Levine (NIST Metallurgy Division)
Robert Cook (NIST Ceramics Division)

                        Monday, November 17, 2008
                                  4:30 pm
                     Room 301, Research I, Fairfax Campus

Refreshments will be served at 4:15 PM.
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Find the schedule at www.cmasc.gmu.edu/seminar/schedule.html
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