Gilles Despaux

Ultrasonic study of UO2: effects of porosity and grain size on ultrasonic attenuation and velocities

Abstract Ultrasonic techniques applied to nuclear fuel characterisation are developed in our group since 1996. Before applying our methods to irradiated fuel, we are searching sensitive parameters which could give interesting information. That is the reason why only results concerning non-irradiated UO2 are presented. This paper mainly deals with the investigation of a relevant acoustic parameter: the attenuation. Indeed, the ultrasonic attenuation in UO2 as a function of the operating ultrasonic frequency has been measured on samples with various microstructures: variable fraction volume porosity (1–6%) and grain size (10– 90 μm ). Using a 15 MHz operating frequency, no attenuation has been observed. With frequencies around 40 MHz, we show that the measured ultrasonic attenuation is only sensitive to grain size (no effect of porosity has been observed). On the contrary, the ultrasonic velocities (which are very sensitive to porosity) are not affected by the sizes of the grains. These reversed and non-correlated effects constitute an interesting tool for UO2 study because two aspects of the microstructure can be studied separately with ultrasonic waves.

Non-destructive testing by acoustic signature of damage level in 304L steel samples submitted to rolling, tensile test and thermal annealing treatments

Abstract Acoustic signatures are used to detect in a non-destructive way the damage of rolled and drawn plates of 304L stainless steel from measurements of the propagation velocity VR of ultrasonic Rayleigh waves. This parameter is compared with the relative thickness decrease ‘e’ of the sample. Upon rolling, VR decreases gradually for e exceeding 5%. The corresponding evolution of wave attenuation and standard deviation of velocity indicate the damage of the sample structure as e increases. Dynamic Young’s moduli calculated from acoustic velocity measurements show a small evolution. Under tensile tests, VR reduces more rapidly as a function of e than for rolled samples. A tempering process of 2 h at 250°C applied to a sample with e=48% produces no detectable variations of the Rayleigh velocity, while annealing for 30 min at 850°C induces large changes.

Effect of Gas Adsorption on Acoustic Wave Propagation in MFI Zeolite Membrane Materials: Experiment and Molecular Simulation

The present study reports on the development of a characterization method of porous membrane materials which consists of considering their acoustic properties upon gas adsorption. Using acoustic microscopy experiments and atomistic molecular simulations for helium adsorbed in a silicalite-1 zeolite membrane layer, we showed that acoustic wave propagation could be used, in principle, for controlling the membranes operando. Molecular simulations, which were found to fit experimental data, showed that the compressional modulus of the composite system consisting of silicalite-1 with adsorbed He increases linearly with the He adsorbed amount while its shear modulus remains constant in a large range of applied pressures. These results suggest that the longitudinal and Rayleigh wave velocities (VL and VR) depend on the He adsorbed amount whereas the transverse wave velocity VT remains constant.

Emulsion characterisation by focused ultrasonic waves

Abstract A measurement method has been developed which can be used to measure the ultrasonic velocity of one liquid phase of an emulsion. The principle of this method is the reflection of a focused ultrasonic wave on the droplets of the other liquid phase. This technique allows analysing in line the evolution of acoustic properties of one phase of the emulsion, principally during liquid–liquid extraction processes.

Characterization of the chemical bond in novel materials by the study of the acoustic signature

Abstract Acoustic signature is processed by using focalized high frequency acoustic sensors. Through the knowledge of surface wave velocities, very sensitive to the material features, it provides local quantitative information on the elastic properties. This information was related to the chemical bonds in a-SiC:H thin films, in SiC/SiC minicomposites, in cross-linked photopolymers and at an aluminum/poly(ethylene terephtalate) (PET) interface.

New Developments in Scanning Acoustic Microscopy

The Scanning Acoustic Microscope (SAM) has become a useful new instrument for non destructive testing applications by its ability to penetrate optically opaque materials on a microscopy scale. Quantitative measurements has been added to the imaging capability known as acoustic material signature A. M. S. also called V(z).