Plasticity

I have attached a copy of my McMat07 talk below.  The talk is about a modified mechanical threshold stress (Follansbee-Kocks) model that can be used for strain rates > 1000 /s and high homologous temperatures.  In the model, the pressure dependence of the flow stress arises from the pressure dependence of the shear modulus.  Even after using the most accurate models for the shear modulus (and the melting temperature) we find that the pressure sensitivity of the flow stress is underestimated by our model (by quite a bit).

Recently, there have been many strain gradient theories that are used for the interpretation of size effect at the micron and submicron length scales. The basic idea of these theories is the introduction of a first, or second (or both) gradients of strain or any internal state variable in the governing equations of classical theories.

Huang et al., PRL 98, 185501 (2007)

Watch movies at: http://netserver.aip.org/cgi-bin/epaps?ID=E-PRLTAO-98-002719

We report exceptional ductile behavior in individual double-walled and triple-walled carbon nanotubes at temperatures above 2000 C, with tensile elongation of 190% and diameter reduction of 90%, during in situ tensile-loading experiments conducted inside a high-resolution transmission electron microscope. Concurrent atomic-scale microstructure observations reveal that the superelongation is attributed to a high temperature creep deformation mechanism mediated by atom or vacancy diffusion, dislocation climb, and kink motion at high temperatures. The superelongation in double-walled and triple-walled carbon nanotubes, the creep deformation mechanism, and dislocation climb in carbon nanotubes are reported here for the first time.

Recently Henry talked about software that could be used to simulate explosions and introduced CartaBlanca. Luming asked whether anyone had used the software, how good it was, and whether one needed Java to implement models into CartaBlanca.

A couple of years ago a colleague who wanted to simulate high-speed machining asked me: " Which is the best phenomenological flow stress model for metals?" I wasn't able to give an answer right away and decided to look in the literature.

What I found was, every ten years or so, a new model appears in the literature that tries to solve some of the problems of older models. However, a clear ranking of models has not been established yet.