Amplitude-dependent internal friction calculations for dislocations in alloys

Abstract

The amplitude-dependent internal friction produced by the dissipative motion of dislocations in alloys has been calculated. The dislocations were modeled in terms of a known string analogy and the alloy was represented by a random planar distribution of weak obstacles of finite interaction range. The equation of motion describing the dislocation behavior (including inertial and viscous forces) was integrated using a numerical method recently developed by Labusch and Schwarz. The results show that the flow stress and other important alloy properties can be derived from the general shape and asymptotic behavior of the decrement vs stress-amplitude curves, without the need to subject them to detailed analytical study. The present calculations were found to be in good agreement with measurements in freshly deformed crystals in which solute atoms had not been able to segregate to dislocations. On the other hand, when these crystals were annealed, the measurements were better described by the Granato-Lücke theory (based on a linear distribution of obstacles). The calculations also showed good agreement with previous measurements in superconducting materials, in which the viscous drag is low and the dislocations exhibit inertial effects.