ELASTIC CONSTANTS AND LOSSES IN NICKEL 



983 



should increase linearly with the frequency. The indicated maximum for this 

 rod is below 120 kilocycles. 



In order to obtain the first part of the decrement vs frequency curve, a 

 rod of 46.05 cm length and 0.637 cm diameter was next used. This rod was 

 annealed at 1050°C and presumably has a smaller average domain size than 

 the first one, so that the important variations occur in a more favorable 

 frequency range. 



The changes in elastic constant and the decrement for this rod are shown 

 by Fig. 12 for frequencies from 5 kilocycles to 96 kilocycles. At the lower 

 frequencies the decrement increases in proportion to the frequency in 



0.22 



20 



■^0.,8 



^0.6 



Q 



< 0.14 



h- 0.12 



z 

 u 



^0.10 



a. 



o 



LJ 08 



o 



3 0.04 



0.02 



20 



40 60 80 100 120 140 160 



FREQUENCY IN KILOCYCLES PER SECOND 



Fig. 12 — Fractional change in Young's modulus, and the decrement, plotted as a 

 function of frequency for rod No. 2. 



agreement with the simple theory. By extending this curve down to zero 

 frequency it is seen that a micro-hysteresis effect (which is independent of 

 the frequency) gives an initial decrement of about 0.010. The decrement 

 rises to an indicated maximum at somewhat more than 100 kilocycles and 

 the change in elastic constant with saturation decreases with frequency. 

 The data on these two rods taken together indicate that there is a fre- 

 quency of maximum decrement and for frequencies above and below this 

 the decrement is smaller. The A£ change in the elastic constant decreases 

 as the frequency increases and for very high frequencies the A£ effect be- 

 comes very small. As shown by the discussion in the next section, the fre- 



