Internal friction and dislocation collective pinning in disordered quenched solid solutions

We introduce the collective pinning of dislocations in disordered quenched 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 short and long range dislocation motion. Under de applied stress the long distance dislocation creep has at the microscopic level avalanche features, which result in a macroscopic nonlinear "glassy" velocity-stress characteristic. Under ac conditions the model predicts, in addition 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 internal friction regime. (C) 1997 American Institute of Physics.