By using ultrasonic resonance spectroscopy, measurements were made of the elastic constants and internal friction of isotropic polycrystalline 6N-purity material, with a grain size of about 75, which contained large numbers of twins. It was found that the measured elastic constants agreed with published values, whereas the internal friction was much lower than that found by using pulse-echo methods. By comparing the present internal friction data with the predictions of the Koehler-Granato-Lücke model, it was possible to estimate the dislocation loop length. The shear internal friction exceeded the longitudinal internal friction by a factor of about 1.5.

H.Ledbetter, C.Fortunko, P.Heyliger: Journal of Materials Research, 1995, 10[6], 1352-3