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Directivity patterns of an acoustic source generated by the absorption of a laser pulse at the interface between a transparent epoxy-resin half-space and an opaque CFRP isotropised half-space have been calculated using the reciprocity theorem. Longitudinal and shear radiation patterns of acoustic field emitted in the CFRP are compared in respect with the loading surface condition. [ABSTRACT FROM AUTHOR]

A non-contact laser-ultrasonic technique is applied to the nondestructive measurement of the stiffness properties of cylindrical rods. Acoustic waves generated in a cylinder by a laser line source under thermoelastic regime are identified by the comparison between experiment and theory. Two stiffness coefficients c11 and c12 are determined by measuring the arrival time of the reflected longitudinal wave (LL) and that of the head wave (HW). The effects of laser beamwidth and time duration on the measurement are found by numerical simulations. For such an application, a radius of 0.3 mm appears as a minimum limit for the sample size using a laser source of 0.1 mm beamwidth and 20 ns time duration. Stiffness coefficients of three aluminum rods are experimentally measured with good accuracy. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

A non-contact laser-ultrasonic technique is described that allows the determination of stiffness properties of an anisotropic layer bounded to a substrate. The method requires access to only one side of the structure. Plane waves are synthesized by scanning the surface with a laser line source at judiciously chosen intervals. By doing so, the intricacies associated with the reflection of an acoustic ray off the interface between the anisotropic media are avoided. The identification of the stiffness-tensor components is based on the inversion of the phase velocities of these reflected plane waves. [ABSTRACT FROM AUTHOR]

An inverse method is proposed for the determination of the viscoelastic properties of material plates from the plane-wave transmitted acoustic field. Innovations lie in a two-step inversion scheme based on the well-known maximum-likelihood principle with an analytic signal formulation. In addition, establishing the analytical formulations of the plate transmission coefficient we implement an efficient and slightly noise-sensitive process suited to both very thin plates and strongly dispersive media. [ABSTRACT FROM AUTHOR]

Extension to the cuspidal edges of wave surfaces in a plane of material symmetry of anisotropic solids is proposed via three different approaches. Two of the possible extensions stem from the definition of wave arrival used in the stationary phase approximation and the Cagniard-de Hoop technique for the calculation of the line source (2D) Green’s function. The third one is based on ray theory generalized to complex values of the group velocity. The stationary phase method yields an extension but only near to the cusp points. Concerning the two others methods, an extension for any angle of propagation can be obtained and it leads to a closed wave surface. The three methods are compared with experimental data and the extension given by the Cagniard technique best matches experimental measurements. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

When a laser beam is focused on the surface of a composite material, anisotropy gives rise to folded ray curves in which the acoustic rays are more concentrated in some directions than in others. In particular, the energy density can be very high at the cuspidal edge. The propagation in such media gives rise to internal diffraction by which waves are observed in directions that are not included in the cusp sector. These waves are not explained by ray theory. The measurement of the stiffness tensor of an anisotropic material by means of laser generated ultrasound is a nontrivial matter for essentially two reasons. First, the recovering of the coefficients from the group velocities is a double iterative numerical process that requires a high accuracy in the velocity measurement. Second, internal diffraction is not taken into account by such an algorithm and it provides undesired velocity data which induces a shift of the identified stiffness coefficients. In this paper, it is shown both numerically and experimentally that phase velocities can be measured using signals generated by a line source. The measurement of the stiffness coefficients from such velocities avoids the aforementioned difficulties. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]