I. Molinero

Wave reflection at a mixed interface between two solid half‐spaces

The reflectivity of incident longitudinal and transversal waves at the interface between two solid half‐spaces is studied for different degrees of bonding. Numerical calculations based on Murty’s assumptions [G. S. Murty, Geophys. J. R. Astron. Soc. 44, 388 (1976)] are compared with experimental measurements. The agreement between theory and experiments is reasonably good for RHHTT and RLL coefficients. The plots obtained for RVVTT reveal the existence of an interface wave, the theoretical angular position of which coincides with the critical angle calculated by assuming that this interface wave is a type of Rayleigh wave or interface wave, depending on the acoustical parameters.

On the nonobservance of nonspecular bounded beam reflection effects of Lamb modes

Reflection and transmission effects are investigated for angles of excitation of Lamb waves that are near the longitudinal critical angle. It will be shown that, for this particular angle, the coupling at the interfaces liquid/solid/liquid is such that the leaky‐surface‐wave‐radiation effect does not occur because of the weak coupling between the two media. This result affects only the symmetrical Lamb modes Si (i≠0).

Identification of Rayleigh and breathing modes for a cylindrical wire

We describe an experimental confirmation of the existence of Rayleigh and ‘‘breathing’’ modes in the case of an infinite elastic wire immersed in water. The resonance isolation and identification method initiated by G. Maze and J. Ripoche [Rev. Phys. Appl. 18, 319 (1983)] is used. The different parameters related to the use of this method are adjusted to take into account the dimensions of the target and the attenuation of each mode. The polar diagrams of the amplitude of the resonating part of the received signal confirm the existence of (n,1) and (0,1) modes.

Excitation of leaky guided waves in infinite cylinders by obliquely incident acoustic waves

The scattering of a bounded acoustic beam by elastic infinite cylinders is investigated for oblique incidence. The nonspecular effects and the frequency analysis confirm the existence of dispersive leaky guided waves propagating along the axis of the cylinder. In the present work the nongeometrical effects and the resonance phenomena are used to measure the phase velocity dispersion curves. The experimental measurements obtained with a stainless‐steel cylinder immersed in water are in good agreement with the theoretical calculations. The experiments are limited to the values of ka<16 (k is the wave vector and a designates the radius of the cylinder).

Characterization of guided waves propagating in infinite cylinders for oblique insonification

The present study confirms that in oblique incidence, leaky guided waves propagate in isotropic elastic cylinders. The various longitudinal and flexural modes of propagation are characterized by phase velocity dispersion curves. From leaking properties and resonance effects, the frequency dependence of phase velocity is experimentally measured in case of an infinite stainless‐steel cylinder for values of the dimensionless parameter ka<15. The plots, which are limited to the flexural modes (n=1, m=1–6) and to the longitudinal modes (n=0, m=1–4), are compared to the theoretical calculations based on the Pochhammer–Chree frequency equation.

Prompt Observation of Elastic Resonance Spectra Via the Use of Short Ultrasonic Pulses

It has been shown by L.R. Dragonette, S.K. Numrich and L.J. Frank [1,2] that the echo scattered by an elastic body can be considered as t he superposition of the elastic response of the target superimposed to the response o f a rigid body having the same shape. T his result has b eenused to analyse t he insonification of long cylindrical wires by short ultrasonic pulses. We show that the F ourier transform o f the elastic contribution alone g ives directly the resonance spectrum of the cylinder. This method has been checked on wires of different materials the v alues of ka involved were less than 50. The positions of the resonances in ka are in good agreement with theoretical predictions 131 as it will be verified by Regges trajectories [41.

Dispersion Curves Analysis for Bonded Plates at Low Fd

Today the use of adhesive bonds is more developed in many industries and more specifically in Space Industries. Its development is limited by the possibility to make a non-destructive evaluation of the quality of the bond. Up to now, the inspection of the cohesion and the thickness of the glue are well controlled. With regard to the adhesion, the problem is not yet solved.

OPTIMISATION OF ULTRASOUND ADHESIVE BOND TESTING METHODS USING NUMERICAL MODELING

This paper presents a method which permits the optimum conditions to test adhesive bonds by ultrasound to be evaluated using a numerical model. The model calculates the propagation of ultrasonic waves in a multilayer medium for various boundary conditions (perfect and imperfect) which simulate a good or bad adhesive bond. It is used to establish the dispersion curves of Lamb waves for the multilayer medium. The parameters for which there is a difference between good and bad conditions permit the bond to be evaluated. A practical application of the method and experimental results is presented.

EXPERIMENTAL INVESTIGATION OF THE RESONANT BEHAVIOUR OF THE TRANSMISSION COEFFICIENT OF A. FLUID-LOADED ELASTIC PLATE

An experimental study of the overlapping resonance concept is described for a fluid-loaded elastic plate. The results confirm the validity of the resonance theory and of the interference effects between neighbour modes. The case of the resonant interaction effect between the A o and S o modes is investigated in the angular variable. Additional examples are given in the frequency domain to illustrate the F.M.U. (Fiorito, Modigosky and uberall) theory. The agreement between theory and experiments is good in both domains.

Comparative Analysis of the Non - Specular Effects Observed in L/S and L/S/L Systems

When a bounded acoustic beam is incident on an in- terface liquid/solid non geometrical effects are found at the Rayleigh critical angle. S imilar ef- fects are observed in case of a liquid - solid - liquid system. We describe experimental results related to reflection and transmission coefficients and to beam profiles. A comparison of the experi- mental c urves w ith theoretical plots calculated by Ngoc and Mayer is done. A discussion about the nonobservance of non - specular effects of symme- tric Lamb modes is presented and the features of backscattered and backstransmitted variations of amplitude are a lso considered.