The nonlinearity parameters, which are combinations of third-order elastic constants, of neutron-irradiated copper single crystals were determined at room temperature by measuring quantitatively the harmonic distortion of pulsed MHz ultrasonic waves propagating in three crystallographic directions. For this purpose, a capacitive detector was used with which ultrasonic displacement amplitudes of the order of ${10}^{-10\mathrm{}}$ cm can be detected and measured absolutely. Using the nonlinearity parameters in combination with other data, a complete set of third-order elastic constants for copper is calculated. The experiments represent a new technique for determining third-order elastic constants which is of special interest for measurements on easily deformed metal crystals.

• Received 3 November 1967

DOI:https://doi.org/10.1103/PhysRev.168.655