When 3:30 PM - 4:30 PM Apr 06, 2006
Where 1670 CSE
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Atomistic Simulation and Analysis of Plasticity in Amorphous Silicon as a Space Network Solid

Ali S. Argon - MIT

Computer simulations and experiments on the plasticity of metallic glasses and glassy polymers have clarified the mechanisms of plasticity in atomic and chain polymeric glasses. There has been comparatively little done on the space network glasses on this subject. In the present simulation to be discussed in this lecture we have explored these phenomena in amorphous silicon as a generic example of a space network glass.
In the simulation the unit plastic events have been identified to consist of discrete shear transformations triggered in fertile regions at characteristic threshold stresses where locally a fundamental normal mode vanishes. In the ensuing collapse, transformation shear strains with an average value of about 0.015 develop inside transformed inclusions.
A key observation of the simulation is that the shear transformations are facilitated by the concentration of the liquid-like environments with close to 5 coordination in the structure, while solid-like environments with close to 4 coordination primarily act as “filler”.
Based on the findings of the simulation a kinetics model of plastic flow has been developed that explains the temperature dependence of the plastic resistance and explains the evolution of a unique flow state regardless of the state of relaxation of the starting structure. It is proposed that these finding should be broadly applicable to other strongly bonded glassy covalent compounds. Comparisons will be made with the mechanisms of corresponding processes in metallic and polymeric glasses.