Robert J. Asaro - US grants

An Institute of Mechanics and Materials (IMM) is being established at the University of California at San Diego to integrate research and industrial applications in mechanics and materials. The Institute will foster interdisciplinary communication and liaison between academia, industry and governmental organizations. The principal activities will include short courses on frontier, interdisciplinary areas; workshops on specific industrial problems and innovative materials; and short and intermediate length visits of graduate students, post-doctoral fellows, faculty members, and scientists and engineers form government laboratories and industrial organizations. The Institute will not conduct extensive research projects, per se, but will aim to serve as an intellectual forum to catalyze the formation of research groups when new areas or methods of approach are identified. This will include novel techniques for materials development, synthesis and processing; characterization and identification of properties-microstructure relations; physically-based micromechanical and computational modeling; and constitutive relations for nonlinear response and failure analysis; as well as design and performance analysis of complete structural entities. Timely topics will be discussed in think-tank-style workshops which will also be used for periodic assessments of long-term goals in mechanics and materials science and engineering. An external Board of Governors of prominent senior scientists and engineers will direct the Institute activities through action subcommittees and regularly assess the Institute's progress. The educational efforts of the Institute will include all levels of engineers and scientists in academia, industry and government (both national and international); and a strong outreach program to high school students and their teachers on a nationwide basis wherever there is interest, with a deliberate effort to reach minorities and under-represented segments of the population, as well as the gifted.

This proposal aims to gain fundamental understanding of the
deformation mechanisms that operate in nanostructured metals and
alloys, in particular in those produced by severe plastic deformation
(SPD) methods. Based on this knowledge it further aims to develop full
capability to manufacture these materials in high quality bulk forms.

The extremely attractive (and rare) combination of mechanical
properties (high strength, ductility, fatigue resistance) and
manufacturability of these materials leads to a new class of high
performance alloys for structural uses. It is understood that this
combination of properties is due to the formation of nano-scale grain
sizes in these materials, but the mechanisms responsible for the high
strength combined with high ductility are not well understood. This
presents a fundamental obstacle to the optimization of these
materials, or to predictions of the performance of these materials in
applications.

An integrated approach with strong emphasis on manufacturing is
proposed. On the theoretical side, deformation mechanisms will be
simulated with crystal-plasticity aggregate models and with detailed
models of the grains and grain boundaries. The experimental program
covers a wide a range of strain rates and temperatures, texture
development, and in situ transmission electron microscopy and atomic
force microscopy to directly verify deformation mechanisms. The
experimental results will provide validation to the theoretical
modeling and manufacturing process simulations.

Finally, simulations of the manufacturing processes will enable
process parameter optimization. A complete, miniature, yet fully
scalable, manufacturing facility will be designed and implemented.

The significant impacts of the proposed research are made possible by
the acquired fundamental understanding of the deformation mechanisms,
and include advances in manufacturing techniques to produce these
highly desirable materials in bulk. The miniature manufacturing
facility will become a source of significant quantities of
nano-structured alloys. Finally, the proposal will provide students at
the UCSD and at local K-12 schools with interdisciplinary education in
a cutting-edge area of research.

Grain Stability in Nanostructured Metals

Abstract

This project is concerned with fundamental studies of the stability of ultra-fine and nanstructured grains in metals, both with face centered cubic and hexagonal close packed crystal structures, and in metals that contain either, or both, nano-sized grains or nano-sized twins. Nano-twinned copper and nano-grain size titanium will be studied using a variety of methods, including micro-indentation, dynamic deformation, and micro-tensile testing. The dynamic deformation in titanium is designed specifically to document the tendency of titanium grain boundaries to migrate leading to instability of the ultra-fine grain structure. Complimentary theoretical studies will include atomistic simulation using our newly developed finite temperature quasi-continuum method. In these studies simulations of the deformation of nano-sized twinned structures will be performed to explore the interaction of dislocations with twins and the potential motion (that is the instability) of twin boundaries.

Educational activities include the training of graduate students and undergraduate students chosen from under represented groups; two such undergraduate students are already working on directly related topics. A web site is established to rapidly disseminate novel results and to act as a repository for others to add newly obtained data. We are participating in a program called ?Bridges to the Future?, a San Diego program designed to transition the careers of under represented minorities into science. We also participate in the California State Summer School for Mathematics and Science (COSMOS) aimed at 9th-12th graders who demonstrate interest in math and science. Our focus in this will be nanotechnology.