Optical-Acoustic Spectroscopy of Structural Changes in Metals Under Shock Loading

Z.A.Sazhko, Yu.V.Sudenkov (St. Petersburg State University, St. Petersburg, Russia)

e-mail: spm@unicorn.math.spbu.ru; yuri.sudenkov@pobox.spbu.ru

The results of experimental investigations of metal structure changes by a optical.acoustic spectroscopy method are submitted. Iron and nickel samples subjected to vacuum annealing at different temperatures were investigated. The grain sizes were about 25-30 microns (annealing at 700C) and 250-300 microns (1000C). The samples were loaded by sub-microsecond shock pulses. The frequency dependences of the longitudinal sound speed and the attenuation outside and inside of shock loading zone were measured. In samples with the different grain size the plastic deformation in a loading zone leads to reorganization of structure completed at different scale levels. For fine-grained samples the twinning results in reorganization of grains crystallographic orientation. Intergranular, rotational mechanism with characteristic scale of changes ~1E-5 m become determinative factor. For coarse-grained samples the change of grains crystallographic orientation does not occur, so the twining remains by the determinative mechanism of plastic yielding (characteristic scale ~1E-8 m). The results of investigations of metals by a optical-acoustic method have shown an opportunity of confident monitoring of structure change at a level 1E-5 - 1E-6 m. Evidently the using of the laser with smaller pulse duration will allow to increase considerably the resolution of a method (up to scales about 1E-7 - 1E-8m).


Section : 9