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"Dislocation avalanches, strain bursts, and the problem of plastic forming"

Relatore: Stefano Zapperi- CNR - Modena

Aula Feyman
09 Dicembre 2008 ore 15.30

Under stress many crystalline materials exhibit irreversible plastic deformation caused by the motion of lattice dislocations. In plastically deformed microcrystals, internal dislocation avalanches lead to jumps in the stress-strain curves (strain bursts) whereas in macroscopic samples plasticity appears as a smooth process. By combining three-dimensional simulations of the dynamics of interacting dislocations with statistical analysis of the corresponding deformation behavior, it is possible to determine the distribution of strain changes during dislocation avalanches and establish its dependence on microcrystal size. Our results suggest that for sample dimensions on the micron and sub-micron scale large strain fluctuations may cause problems in controlling the resulting shape in a plastic forming process.