AMPLITUDE-DEPENDENT INTERNAL-FRICTION, MICROPLASTIC STRAIN AND RECOVERY OF LEAD AT AMBIENT-TEMPERATURE

Damping properties and the influence of plastic prestrain on microplas tic behaviour of polycrystalline lead have been studied by internal fr iction. Measurements were performed in the infra-and ultrasonic ranges . Infrasonic tests were combined with high-resolution registration of the microplastic strain. The strain amplitude dependence of internal f riction shows two stages characterized by different recovery times. Th ese stages are attributed to different mechanisms: dislocation - point defect interaction at moderate oscillatory strain amplitudes and disl ocation - dislocation interaction at high amplitudes. A pronounced and nonmonotonic dependence of the amplitude-dependent internal friction (ADIF) and elastic limit on prestrain is revealed. Prestraining up to 10% suppresses the ADIF in the ultrasonic range and causes a considera ble increase of the elastic limit in the infrasonic range. A further p restrain up to 30% is accompanied by a drastic increase of the ultraso nic ADIF and a pronounced fast softening of lead in the micro-and macr oplastic ranges. The conclusion has been drawn that ortho-and metareco very occur intensively in lead after high prestrain. These processes a re ascribed, respectively, to a decrease in net dislocation density an d to a transition from a relatively homogeneous dislocation distributi on to an inhomogeneous one. (C) 1997 Elsevier Science S.A.