Bulk conical and surface helical acoustic waves in transversely isotropic cylinders; application to the stiffness tensor measurement

Abstract

A point-source-point-receiver technique, based on laser generation and laser detection of acoustic waves, allows determination of mechanical properties of anisotropic cylinders. The anisotropic nature of the material and the geometry of the samples make the acoustic signature difficult to interpret. In addition to multiple surface waves, quasi-longitudinal and quasi-shear bulk waves are diffracted and acoustic rays are reflected with or without mode conversion at the cylinder surface. Moreover both bulk and surface diffracted waves have a dispersive behavior. To bypass the intricacies, wave fronts are synthesized with signals provided by scanning a straight line on the cylinder with the laser point source. Conical waves propagating in the volume and helical waves propagating along the surface are then numerically produced. The recovery of the stiffness-tensor components is based on the inversion of the bulk waves, phase velocities. The method is presented and applied to signals simulated or experimentally recorded for a composite material. The five independent stiffness coefficients of the hexagonal symmetry are thus measured with waveforms provided by a single scan along the cylinder surface. The method provides a unique mean for the noncontact measurement of elastic properties of cylindrical parts.