Deformation

Dislocations 2000:An International Conference on the Fundamentals of Plastic Deformation, June 19-22, 2000

Objectives

Predict mechanical response of plastically deformed metals from theoretical models of the underlying dislocation structures which evolve during deformation.

Problems/Issues/Challenges Addressed

Current finite element simulations of metal forming use empirical models of mechanical behavior.  These models are very inaccurate, increasing the time and cost of designing dies.  Developing new models based upon the underlying deformation physics requires a new statistical-physics based theory of deformation, extensive computer simulations of deformation microstructural changes, and input from recently developed experimental techniques using NIST's materials science X-ray synchrotron beam lines at Brookhaven and Argonne.

Deliverables

• A dislocation-based model for changes in mechanical properties during plastic deformation.
• A computer subroutine called a "materials module" for industrial finite element method computer codes that are used to model metal forming operations.

Likely Impacts/Consequences

• Accelerate the development of new materials with superior mechanical properties.
• Greatly reduce time and cost of all metal forming operations.
• Enable increased use of Al alloys and high-strength steels in automobiles resulting in decreased weight and increased fuel economy.

Accomplishments and Highlights

• Developed initial theoretical model of strain percolation through dislocation wall structures during plastic deformation of metals.  We showed that a deforming metal is a self-organizing critical system, and have related the mechanical characteristics to internal parameters of the system.  See Robb Thomson and L. E. Levine, PRL, 81, 3884 (1998).
• Completed theoretical work on small-angle-scattering (SAS) from dislocation structures and confirmed model using computer simulations and experimental measurements.  This model allows NIST's unique X-ray synchrotron beam line to be used for measurements of dislocation structure evolution.  Data from these experiments is now being used as input into the strain percolation theory and the corresponding computer simulations. Accepted by Acta Cryst A (Robb Thomson, L. E. Levine, and G. G. Long).
• Developed a general theory for Bragg scattering by dislocations in crystals and applied this theory to the specific case of screw dislocations.  This work will allow quantitative parameters to be obtained from future neutron diffraction experiments to be conducted at the NIST Center for Neutron Research.  See L. E. Levine and Robb Thomson, Acta Cryst, A53,  590 (1997).
• The above theoretical work is synergistic with a comprehansive NIST experimental program being conducted by L. E. Levine, G. G. Long, D. R. Black,  R. J. Fields, and J. Fink.

People

Nist Researchers: L. E. Levine, Robb Thomson (Emeritus), G. G. Long, R. J. Fields, R. deWit
Industrial Collaborators: O. Richmond, R. Becker, M. Glazov (ALCOA), B. Maker (LSTC)
Laboratory Collaborators: M. A. Khaleel, J. S. Vetrano, S. Zhou (LANL)
University Collaborators: J. Hirth, H. M. Zbib (WSU), G. Daehn (OSU)