Michel de Billy

Theoretical and experimental studies of surface waves on solid–fluid interfaces when the value of the fluid sound velocity is located between the shear and the longitudinal ones in the solid

The existence of two surface waves propagating on a plane solid–fluid interface is demonstrated when the value of the fluid sound velocity is located between the shear and the longitudinal ones in the solid. First, the Scholte–Stoneley dispersion equation is studied analytically and numerically to find the roots corresponding to the Stoneley and the Rayleigh waves. The anatomy of each one is then described with the formalism of the evanescent plane waves: both waves are unleaky. Finally, the results are confirmed experimentally by measuring the times of flight on a Plexiglas–water interface and on a PVC–water interface.

Experimental validation of band gaps and localization in a one-dimensional diatomic phononic crystal

The propagation of compressional ultrasonic pulses through a finite one-dimensional chain of various unit cells is investigated experimentally. The chain, initially compressed by an axially applied constant force, is excited by a periodic force, which acts in line with axis of bead chain. The experimental measurements giving the eigenfrequencies of the specimen are based on a Fourier analysis of the transmitted acoustic pulse. The results are compared with the numerical calculations and it is shown that the two approaches are well correlated. A phononic band structure is observed and under certain conditions, depending on the parity of the number and on the masses of the beads in the chain, it is shown that localized modes propagating in the forbidden band are exhibited. Much attention is devoted to the existence of these localized modes according to the mass ratio between two adjacent beads constituting the unit cell.

Evaluation of friction‐welded aluminum‐steel bonds using dispersive guided modes of a layered substrate

In nondestructive evaluation the inspection of bond quality is a very important problem. In this paper we suggest an experimental method based on dispersion curve measurements for evaluating the quality of the bond between a layer and a substrate bonded by the inertia‐friction welding process. The experimental results are in good agreement with theoretical calculations which show that the behavior of the lowest velocity modes is very sensitive to the interface conditions and to the quality of the bond.

Measurements of backscattered leaky Lamb waves in plates

We have reported earlier the observation of backscattered leaky Raleigh waves from a liquid–solid interface [J. Acoust. Soc. Am. 72, 1018–1020 (1982)]. Now we have carried out experiments to observe backscattered leaky Lamb waves from a plate immersed in liquid, using a single transducer in pulse echo modes. Sharp peaks were observed at angles corresponding to backward propagating symmetrical and antisymmetrical Lamb modes. These backward propagating Lamb waves leak back at both sides of the plate.

Excitation of ultrasonic Rayleigh leaky waves at liquid‐solid interface for general angle incidence

Experimental results are presented to demonstrate the existence of ultrasonic leaky wave radiation from liquid‐solid interface. This leaky wave is generated by a finite ultrasonic beam incident at any angle (not only at Rayleigh angle) to a liquid‐solid interface and observed at the Rayleigh angle both forward and backward. It is suggested that the phenomena occurring at the Rayleigh angle incidence and producing (1) a complex reflected field and (2) a backscattered field are just two special cases of this general phenomenon.

Conical radiating waves from immersed wedges

The finite-element approach has previously been used, with the help of the ATILA code, to model the subsonic and supersonic waves in immersed waveguides [A. C. Hladky-Hennion et al., J. Sound Vib. 212, 265–274 (1998)]. This method has given a precise account of the experimental results and has shown the major effects. In this paper, a new representation of radiating waves is presented, leading to a simple understanding of the physical phenomenon: radiating waves are propagating with the same phase velocity on the surface of a cone, the axis of which is the wedge direction.

Time analysis of immersed waveguides using the finite element method

The propagation of acoustic waves in immersed waveguides has been previously studied with the help of the finite element method, using the ATILA code [A. C. Hladky-Hennion et al., J. Sound Vib. 200, 519–530 (1997)]. But this method, which is a modal analysis, essentially concerns the case of rectilinear, infinite, and uniform waveguides. Thus this paper deals with another way of solving the problem of wave propagation along waveguides, with the help of a time analysis using finite elements. First, the theoretical formulation is presented for immersed structures. Then, Plexiglas and brass wedge guides, of different apex angles, are considered. When immersed in water, these wedges generate either propagating or radiating wedge waves. The finite element results, using a time analysis, are compared to the previous finite element results, using a modal analysis and to the experiments, leading to a good agreement. Thus the approach can be easily extended to other waveguides whatever their cross sections.

Parameters affecting backscattered ultrasonic leaky‐Rayleigh waves from liquid–solid interfaces

Experiments were carried out to observe backscattered ultrasonic waves from liquid–solid interfaces. It is found that the backscattered energy is maximum at the Rayleigh angle, directly proportional to the so‐called Schoch displacement (Δs) and inversely proportional to the beamwidth. This result is in qualitative agreement with the Bertoni and Tamir [Appl. Phys. 2, 157–172 (1973)] theoretical prediction for the beam distortion of the reflected field at the Rayleigh angle. It is also suggested the backscattered phenomenon enables one to measure the Rayleigh velocity at liquid–solid interfaces.

Quantitative analysis of the vibration modes in a finite set of coupled spheres

This paper deals with the propagation of waves along a one-dimensional chain made up of welded spheres. First, a theoretical analysis allows the vibration modes of the chain to be quantitatively described. It has been validated by a comparison between numerical results, using the finite element method and experimental results, restricted to sets of two or three coupled spheres. It is numerically and experimentally verified that the peaks associated with the Rayleigh modes broaden out as the mode number increases and that the passband structure is strongly influenced by the characteristics of the welding between the cells of the periodic structure. The interest of such an approach is then illustrated by the examination of an inverse problem, in which the analytical model is used to deduce the characteristics of the welding.

Frequency analysis of the acoustic signal transmitted through a one-dimensional chain of metallic spheres

This work investigates the propagation of acoustic pulses through a chain of elastic spheres embedded in air. This study is an extension of the works realized on individual sphere by several authors for measuring elastic constant and internal friction with a monofrequential acoustic excitation. The frequency analysis of the experimental transmitted train waves exhibit maxima which were correlated to different types of free vibration modes: the Rayleigh modes (Rnl), the torsional modes (Tnl), and the spheroidal modes (Snl). These resonances may be generated separately according to the polarization of the excitation pulse.This work investigates the propagation of acoustic pulses through a chain of elastic spheres embedded in air. This study is an extension of the works realized on individual sphere by several authors for measuring elastic constant and internal friction with a monofrequential acoustic excitation. The frequency analysis of the experimental transmitted train waves exhibit maxima which were correlated to different types of free vibration modes: the Rayleigh modes (Rnl), the torsional modes (Tnl), and the spheroidal modes (Snl). These resonances may be generated separately according to the polarization of the excitation pulse.