New Developments in Understanding Long-Range Internal Stresses in Materials

CHEMS Seminar

Featuring Michael E. Kassner, Ph.D.
Professor, Aerospace and Mechanical Engineering
Viterbi School of Engineering
University of Southern California

Location:  Donald Bren Hall (DBH) Room 1500

Abstract:
Long-range internal stresses (LRIS) are widely suggested to exist in materials as a result of dislocation heterogeneities in plastically deformed microstructures. 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 stress has often 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 ambiguous. Most recently, long-range internal stress was investigated by us using advanced x-ray microbeam diffraction experiments. These were accomplished using a synchrotron at the Advanced Photon Source at Argonne National Laboratory that is able to determine the elastic strains in very small volumes (e.g. 0.1 cubic micron) within the cell interiors, and very recently, within the cell walls. These were accomplished using oriented monotonically 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.