Abstract
Long-range internal stresses (LRIS) are widely suggested to exist in materials as a result of dislocation heterogeneities in plastically deformed materials. The dislocation heterogeneities include cell and subgrain walls in monotonically deformed materials and edge-dislocation dipole bundles (veins) and the edge dipole walls of persistent slip bands (PSBs) in cyclically deformed materials. Long-range internal stresses have long been suggested to be responsible for the Bauschinger effect in reversed and cyclic deformation. Evidence for long-range internal stresses (LRIS) includes stress-dip tests, dislocation pinning of loaded materials, in-situ deformation experiments, and asymmetric x-ray line broadening analysis. Other experiments, including recent dipole separation observations and convergent beam electron diffraction experiments, may be less supportive of LRIS. Most recently, long-range internal stresses were investigated by us using advanced x-ray microbeam diffraction experiments. These were accomplished using a synchrotron at the Advanced Photon Source that is able to determine the elastic strains in very small volumes within the cell interiors, and very recently, within the cell walls. These were accomplished using oriented monotonically and cyclically deformed Cu single crystals. The results suggest that long-range internal stresses are present. The magnitude and variation of these stresses with position within the microstructure will be described. These results are placed in the context of earlier experiments.
About the speaker
Michael Kassner is currently the Director of Research at the US Office of Naval Research. He assumed the position in October 2009. Prof Kassner graduated with a Bachelor in Science-Engineering from Northwestern University in 1972, and an MS and PhD in Materials Science and Engineering from Stanford University in 1979 and 1981. From 1981 to 1990, Prof Kassner worked at Lawrence Livermore National Laboratory and performed basic research on the mechanical behavior of metals, as well as a variety of defense-related projects. He was promoted to Head of the Physical Metallurgy and Welding Section and was the Thrust Leader for Physical Metallurgy Research. In 1984, he spent a year on leave at the University of Groningen in The Netherlands as a Fulbright Senior Scholar.
Prof Kassner accepted a faculty position in the Mechanical Engineering Department at Oregon State University in 1990 where he was Northwest Aluminum Professor of Mechanical Engineering and Director of the interdisciplinary PhD program in materials science. He received the College of Engineering Outstanding Sustained Research Award in 1995. While at Oregon State, Prof Kassner was detailed to Basic Energy Sciences of the US Department of Energy and a Program Manager. He was also on leave for one year at the NSF Institute of Mechanics and Materials at the University of California at San Diego, where he was an Adjunct Professor. Prof Kassner moved in 2003 to accept a position as Chairman, Mechanical and Aerospace Engineering Department and the University of Southern California (USC). He is also a Professor of Materials Science at USC. Prof Kassner is currently active in pursuing research at USC on creep, fracture, fatigue and thermodynamics.
Prof Kassner has published two books, one on the fundamentals of creep plasticity in metals and another on phase diagrams and has authored or co-authored over 200 published articles. He serves on several editorial and review boards for major scientific journals. He is a Fellow of American Society of Metals (ASM), a Fellow of the American Society of Mechanical Engineers (ASME) and a Fellow of the American Association for the Advancement of Science (AAAS).
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