INTERNAL FRICTION AMPLITUDE DEPENDENCE IN SILVER SINGLE CRYSTAL

A carefull investigation of the low frequency (~ 1 Hz) amplitude dependent internal friction, in high purity silver single crystals, was conducted in the 300 - 600 K temperature range. Experimental results, Q-1 versus maximal strain amplitude, at different temperatures, or Q-1 versus temperature for different amplitude, are very close to theoretical curves obtained from the theory developped by BLAIRHUTCHISON and ROGERS for the thermally assisted unpinning of very long dislocation loops. The calculated distance between pinning points, according to the B.H.R. theory, (104b), being too large for dislocation pinning by impurity atoms, an interpretation involving interactions between long dislocation segments and the trees of the forest is discussed