DETERMINATION OF THE ELASTIC-CONSTANTS OF ISOTROPIC SOLIDS BY OPTICAL HETERODYNE INTERFEROMETRY

An experimental method based on the application of speckle interferometry is proposed in order to determine the dynamic elastic constants of an isotropic material. A broad frequency spectrum impact is applied to a cylindrical sample and, when this vibrates freely, a heterodyne laser interferometer is used to detect the displacement of a point of the material. Once the sample is suitably excited, the displacement component of interest, either in-plane or out-of-plane, is detected in order to determine its frequency content. A spectral analysis allows the determination of the longitudinal, transverse, and torsional natural frequencies. From this the elastic constants are calculated. The measurement precision is checked experimentally using the same method by means of a third detection.