Transcending dissipative force proportional to velocity in internal friction and in crack propagation: the role of phonon emission

After summarizing simple models of (a) internal friction and (b) crack prop agation, in which essential input is a dissipative force which is a constan t times velocity (u)overdot, where u is the displacement, their consequence s are brought into contact with processes (a) and (b) when it is known from experiment that phonon emission constitutes a major damping mechanism. Sam e experiments on both (a) and (b) are noted, where such radiation force is important. One must expect then that it becomes essential to transcend damp ing which is assumed to be proportional to (u)overdot. (C) 2000 Elsevier Sc ience Ltd. All rights reserved.