Internal-friction measurements of dislocation inertial effects in dilute alloys of lead

The temperature dependence of the yield stress of pure lead and lead containing 3000 ppm of tin was measured using amplitude-dependent internal-friction measurements. The results are used to distinguish between models for the effect. It is shown that the temperature dependence of the stress drop is not consistent with existing rate theories, but is as expected from the inertial model. However, the low-temperature dependence of the yield stress is characteristic of a thermally-activated rate process and indicates that a mechanism combining thermal activation and inertial effects is required. It is concluded that the effect is initiated by the thermal overcoming of obstacles by dislocations, followed by inertial overcoming of subsequent obstacles.