Elastic constants determination of anisotropic materials from phase velocities of acoustic waves generated and detected by lasers

Abstract

This paper describes a method which allows the synthesis of acoustic plane waves by means of laser ultrasonic techniques. When a laser line source radiates at the surface of an anisotropic material, intricate effects are observed on signals obtained by transmission experiments. The material characterization from such a set of signals is not a trivial task since it requires correctly selecting the data necessary for the elastic constants determination, by distinguishing them from all the parasitic phenomena. In the present paper, it is shown that a judicious sum of signals obtained for various positions of the line source at the surface of a sample leads to the synthesis of an acoustic plane wave for which the odd phenomena disappear. Moreover, by applying a constant delay between the various signals, acoustic plane waves can be synthesized with varied refracted angles. One of the advantages of this technique is to offer convenient access to the phase velocity, providing an easier determination of the elastic constants. This method is successively applied to recover the stiffness coefficients of a silicon crystal and of a composite material. The good agreement between the so-recovered elastic constants and values given by other processes shows the contribution of such a method in the field of material characterization.

Tomographic Reconstruction of Elastic Constants in Composite Materials Using Numerical and Experimental Laser Ultrasonic Data

“…Each TOF measurement contributes in correcting many pixels lying on the path. It is quite different from the elastic constants determination from the phase or group velocities in the carefully chosen few directions along the desired symmetric or nonsymmetric directions in a homogeneous composite material [16][17][18][19][20][21][22][23][24]. In contrast, the tomography needs the scanning of the specimen from the possible views in order to reconstruct inhomogeneities and defects present in the specimen.…”

Numerical analysis of bulk conical waves in anisotropic cylinders; application to stiffness tensor measurement

“…Accordingly to Snell's law the incident and the refracted waves at a plane interface have the same projected wave number along the direction z. Therefore, in this direction, the source slowness dt/dz fixes the projection of wave vectors [2]. Thus, whatever the polarization, all the synthesized bulk waves have same wave vector projection in direction z. Owing to the symmetry of the phase slowness surfaces, i.e., isotropy in the plane (x 1 , x 2 ), projection of the wave vector in this plane holds a unique value for each mode.…”

“…For convenient sampling conditions [2], the so synthesized signal is the signal that would have been recorded if the source had travelled along the surface with the slowness dt/dz. Accordingly to Snell's law the incident and the refracted waves at a plane interface have the same projected wave number along the direction z.…”

Phased array compaction cell for measurement of the transversely isotropic elastic properties of compacting sediments

“…Here, we recover c 13 from the phased array transmission measurements through synthetic phasing of the common-receiver data generated by the N = 32 element source array to form the plane wave transmission data (Reverdy et al, 2000). This synthesis of the plane wave response is accomplished by time shifting and summing the traces in the common-receiver gather,…”