INTERNAL-FRICTION AND DISLOCATION COLLECTIVE PINNING IN DISORDERED QUENCHED SOLID-SOLUTIONS

We introduce the collective pinning of dislocations in disordered quen ched solid solutions and calculate the macroscopic mechanical response to a small de or ac applied stress. This work is a generalization of the Granato-Lucke string model, able to describe self-consistently sho rt and long range dislocation motion. Under de applied stress the long distance dislocation creep has at the microscopic level avalanche fea tures, which result in a macroscopic nonlinear ''glassy'' velocity-str ess characteristic. Under ac conditions the model predicts, in additio n to the anelastic internal friction relaxation in the high frequency regime, a linear internal friction background which remains amplitude- independent down to a crossover frequency to a strongly nonlinear inte rnal friction regime. (C) 1997 American Institute of Physics.