The changes in mechanical properties that occur during plastic deformation of metals result from the complex interaction of huge numbers of mobile and immobile (trapped) line defects called dislocations. In spite of this underlying complexity, mechanical property measurements exhibit a relatively simple and consistent behavior, requiring only a few empirically determined internal state variables for reasonably accurate simulation. We have shown that a deforming metal can be described as a self-organizing critical system and that the correct internal state variables are actually statistical parameters dealing with how mobile dislocations interact with cell walls. The controlling factor is the distribution of dislocation segment lengths in the walls. With only the Burgers vector and the elastic shear modulus as inputs, and with no adjustable parameters, this model correctly predicts the formation of slip lines and slip bands, the linear and nonlinear behavior of the stress-strain curve, and the magnitude of the flow stress. Many valuable extensions of this model are possible, including the behavior of alloys and polycrystals, the influence of temperature, and the role of large local stress fluctuations that we have recently measured experimentally. Both theory and modeling approaches are needed.

 

key words

Chaos; Complex systems; Dislocations; Multiscale modeling; Percolation theory; Statistical physics;

Citizenship:  Open to U.S. citizens

Level:  Open to Postdoctoral applicants