University of Minnesota
Aerospace Engineering and Mechanics
Spring 2000 Seminar Series



Rethinking Plasticity: deformation and fracture in noncrystalline solids


Dr. Michael Falk

Division of Engineering and Applied Sciences, Harvard University


Abstract


The microscopic processes that underlie plasticity in crystalline solids are relatively well understood in terms of dislocations. Nonetheless, making a connection between these dislocation dynamics and theories of macroscopic plasticity in order to understand phenomena such as the brittle/ductile transition in fracture remains elusive. Meanwhile, the micromechanics that give rise to a nearly identical range of phenomena in noncrystalline materials are relatively poorly understood. This route to understanding plasticity may prove simpler and could shed light on phenomena in both types of solids. Molecular dynamics investigations of fracture in model noncrystalline systems reveal that the relative ductility, ie fracture toughness, is sensitive to the particulars of the interatomic potential. Similar investigations of the inelastic shear response of this model system reveal analogous time and history dependent behavior to that seen in actual materials. Examination of the rearrangements underlying these phenomena leads to the conclusion that the basic unit of inelastic shear can be understood as a microscopic two-state system. A theory of the dynamics of inelastic deformation under shear is developed from this assumption and compared to the simulation results. The implications for fracture are discussed.

Friday, January 21, 2000
209 Akerman Hall
2:30-3:30 p.m.


Refreshments served after the seminar in 227 Akerman Hall.
Disability accomodations provided upon request.
Contact Kristal Belisle, Senior Secretary, 625-8000.