This study focuses on a non-destructive methodology for the elastic characterization of fiber-reinforced composites. The methodology uses the surface skimming longitudinal wave (SSLW) generated by an ultrasonic probe and detected via laser interferometry. Conventional mechanical and ultrasonic techniques frequently necessitate the use of multiple samples and intricate configurations to estimate the complete elasticity matrix, particularly in the case of anisotropic materials. To address these limitations, we propose a laser-based approach that enables precise measurement of group velocities across a 180° angular sector of a single specimen. The method was validated on isotropic PMMA and applied to two transversely isotropic composites: a unidirectional glass fiber-reinforced epoxy and a short-fiber bone-mimetic composite. A polar scanning scheme illustrated in B-scan, in conjunction with high-resolution time-of-flight analysis, enabled the extraction of SSLW velocities with a high degree of accuracy. These experimental velocities were then used in an inverse optimization algorithm based on Christoffel equations to retrieve four out of five independent elastic constants. The results showed strong agreement with contact-mode ultrasonic measurements and theoretical models. Furthermore, the method enabled the estimation of the principal anisotropy direction in a composite with unknown fiber orientation, thereby demonstrating the robustness and versatility of laser interferometry for comprehensive elastic characterization of composite materials.

In Pressurized Water Reactor (PWR) cores, turbulent flows can induce vibrations leading to grid-to-rod fretting. A nuclear reactor core being an opaque medium, displacements induced by vibration measurement are not easy with classical approaches, optics for instance. In this framework, ultrasonic methods could constitute an interesting way of investigation. Nevertheless, ultrasonic displacement measurement in turbulent flows remains scarcely documented. This study investigates ultrasonic wave propagation in a test section generating vortices at various Reynolds numbers, replicating conditions in a PWR cores. Measurements were conducted in both transmission and reflection modes, and local fluctuations in acoustic velocity caused by vortices were interpreted as errors in the measured distance. Results indicate that under frozen flow conditions, vortices do not affect reflection measurements, whereas in transmission, measurement dispersion increases with Reynolds number. These findings validate the use of ultrasonic reflection measurements for displacement monitoring in turbulent PWR flows and suggest further investigation into the limits of the frozen flow assumption.

In this work, we have investigated the estimation of particles size, to prove the feasibility of a simplified acoustic system for continuous characterization of turbid water during underwater cave exploration with autonomous vehicles. Because of the nature and concentration level of sediments in natural water networks, we have identified the most suitable models for suspended sediments. They were proposed by Urick [1] and Sheng & Hay [2] assuming that particles are movable, rigid and at low concentration. These models have the advantage to provide a simple analytical expression with a limited number of input parameters. In order to test a very simplified prediction tool, these models are used to calculate attenuation only for monodisperse particle size distributions Experimentally, we used clay powder sifted to 40 μm, to create turbid water similar to cave water. This mixture characterised using laser diffraction spectroscopy shows a large and non-uniform particle distribution. From the measurement of the echo amplitude in reflexion mode, we deduce the attenuation coefficient in a frequency range from 1.5 MHz to 16 MHz. We used several transducers for different travel distances (3.5 cm to 7.5 cm) and different clay concentrations in volume (0.3 to 1.7 %). We obtained a linear dependence between attenuation coefficient and concentration for any tested frequency in total agreement with the selected model. Fitting experimental attenuation data with this model, the best agreement was obtained with a particle diameter of 70 μm. This value is in agreement with the standard Dv90 parameter provided by laser diffraction analysis. This is an encouraging result to validate our minimalist experimental setup and the selected model for a simplified implementable system for in situ characterization of turbid water.

Specialized in non destructive characterisation by ultrasounds, we developed specific devices for operation in nuclear environment for EDF and CEA. For this purpose, the piezoelectric elements constituting the active part of our systems have been characterized for Gamma ray and neutron irradiation (BR1 SCH-CEN reactor. For their operations in hot labs, the specific electric problems induced by long distance transmission lines and nuclearized connectors have been solved. Thus, we have succeeded in introducing recently an Acoustic Microscope as an easy handling measurement system of the mechanical properties of fuel pellets in the hot lab of TUI (Germany). This implantation is the result of a collaboration with EDF to assess the Young’s modulus variation for nuclear materials submitted to high burn up rate (NFIR). Secondly, for investigation of fission gas release in very harsh environment, we have designed a new sensor to measure the internal pressure and the composition of HeliumXenon in a specifically instrumented fuel rod in pile or above the plenum of fuel rods for hot labs. This non destructive device is a safe and real-time measurement system. It is planned to operate in hot labs (CEA Cadarache) and first validation experiments have shown good agreement versus puncture validation measurement. Its design and performances have been successfully validated in November 2012 at the Osiris experimental reactor (CEA Saclay) providing the first kinetics of the fission gaz mixture evolution for an instrumented fuel rod during a real irradiation cycle. In conclusion, our skills for ultrasonic propagation, mechanical coupling, impedance matching and Electronics enable us to assess numerous applications for research activity in hot labs. Introduction Ultrasonic waves are widely used to provide non destructive evaluation means for Industry. At the University of Montpellier, two specific applications are developed: the local characterisation of surface elastic properties by high frequency Acoustic microscopy and the thermo physic characterisation of gas in sealed cavities to measure for instance the fission products release inside fuel rods plenum. Studies of surface acoustic wave propagation may give access to the elastic constants on very small areas using the acoustic signature method. Indeed, by using high frequency focused sensors around 500 MHz, the investigated volume may be limited to a diameter of 100 μm and a thickness of few microns. As these two dimensions are inversely dependent on frequency, this last parameter is chosen to fit with the sample size. For example, this local characterisation tool has been successfully applied for research on thin ion implanted layers for nuclear glasses used to trap high activity wastes for very long term storage. As acoustic sensors have a good resistance to radiation, we have designed a specific acoustic microscope for its introduction and operation inside hot cells. With this specific research device, the effects of long activity inside civil reactors on the fuel pellets mechanical properties have been investigated for numerous fuel rod samples with different high burn-up levels (NFIR program). In specific conditions, high frequency ultrasonic waves can be also used to enable gas characterization within small cavities. Despite the very high echo attenuation induced by acoustic impedance mismatch between solid and gas, we have succeeded in the development of acoustic sensors adapted to measure the inner pressure and the He/Xe mixture ratio of fission products contained in the plenum volume of fuel rods in a non destructive way. Used

Experimental data are presented here to highlight the performances of ultrasounds for the control or the better understanding of the quality of the mechanical contact between tightened plates. Thus, variations of the mechanical load as small as those induced by creep or stress relaxation are potentially detectable by simply monitoring the amplitude of the reflected acoustic plane wave reflected at this interface.To illustrate this, two 3 cm thick aluminium plates are firstly tightened with a given torque and next, the amplitude of the acoustic wave is monitored for several days. All long this test, the temperature of the sample is controlled as well as the compression load applied to the plates using a thermocouple and a bolt gauge sensor. The reflected amplitude decreases quickly during first hours and then stabilises after a week approximately. The total variation reaches -28% of the initial value of the reflected amplitude. During this test, temperature is remained almost constant and its fluctuation around the ambient temperature is not correlated with the reflected amplitude. As expected from classic stress relaxation tests, the compression load has slowly decreased by an amount of only -1% but this should have logically increased the reflected amplitude. Further investigations have shown that instrumentation drift were negligible. Consequently, this large decrease of the reflected amplitude has been interpreted as the indication of the increase of the contact area between the two tightened plates. This test attests the high sensitivity of ultrasonic reflection measurement to investigate quality of mechanical contacts for non destructive testing. (C) 2015 The Authors. Published by Elsevier B.V.

An ultrasonic reflectometry method has been used successfully to detect elasticity changes following the curing of 100 \(\upmu \)m thick epoxy films (DGEBA-PAA) coated onto 1.5 mm thick steel plates. The method employs a goniometric apparatus to measure the reflection coefficient amplitude around 5 MHz followed by a standard FFT analysis of the reflected signal. A specific ultrasonic wave mode was identified which was dependent on, and correlated with, the presence of the coating layer. The goniometer angle associated with this mode was different from that associated with Lamb modes of the plate, enabling the new mode to be detected reliably. The sensitivity of the new mode to variations in the paint mass density, longitudinal and transverse velocities and thickness has been quantified numerically by using Brekhovskikh’s model with due account taken of the finite width of the ultrasonic fields of the transducers. The method was tested for the detection of the evolution of the coating elasticity during curing at 80 \(^{\circ }\)C for 400 h. Compensation was applied to correct for the effect of the natural swelling of the paint layer on the angular position of the tracked mode, and this was validated experimentally. The evolution of the angular position was found to offer a reliable means to detect elasticity changes during the cure of the coating. The mass density variation in the coating during cure only weakly affected the angular position. This method will provide a promising tool for the non destructive evaluation of paint coatings, particularly in service for the detection of ageing effects in the longer term.

In this article we propose a new method able to determine the fission gas composition using in situ ultrasonic waves measurements. To do so an acoustic resonator was connected to a fuel rodlet, in order to perform speed of sound measurements of gas mixture (Helium and fission gases) inside the plenum. By using a dedicated signal processing the peaks due to resonant frequencies inside the gas mixture were successfully extracted from the output signal. From these data, the variations of helium and fission gas molar fraction were calculated using an adapted virial state equation. It will be proved that these data provide important information about the kinetics of gas release and about the effects of high neutron and gamma irradiation on piezoceramic sensors.

The aim of this experimental work is to provide a non destructive evaluation tool for quality control on paint films used for industrial purpose after deposition and in operation. The most sensitive conditions have to be found for ultrasonic inspection and the measured acoustic parameters have also to be linked to the state of the complex chemical structure of polymers. Ultrasonic reflectometry is tested to investigate the thermal ageing of epoxy coatings. As function of frequency and incident angle, the most sensitive modes have been identified from simulation and validated by experiments using an ultrasonic reflection goniometer system working around 5 MHz. Scanning Acoustic Microscopy has been complementary used to check the bonding quality and the layer homogeneity. The effect of local variations of the coating thickness on the sensitivity of this acoustic reflection method is presented as well as acoustic beam diffraction limitation. Next, these 100µm thick paint films on steel plates have been submitted to thermal ageing tests up to 110°C for several weeks. Evolutions of the acoustic angular reflection coefficient versus exposure time are presented with the corresponding IR spectra variations to compare the chemical coating oxidation kinetics with the sensitivity of ultrasounds to elastic properties.

Innovative in-pile instrumentation is crucial for advanced experimental programs in research reactors.

A fuel rod has been instrumented with a new design of an acoustic resonator used to measure in a non destructive way the internal rod plenum gas mixture composition. This ultrasonic sensor has demonstrated its ability to operate in pile during REMORA 3 irradiation experiment carried out in the OSIRIS Material Testing Reactor (CEA Saclay, France). Due to very severe experimental conditions such as temperature rising up to 150°C and especially, high thermal fluence level up to 3.5 10 19 n.cm 2 , the initial sensor gas speed of sound efficiency measurement was strongly reduced due to the irradiation effects on the piezoceramic properties. Nevertheless, by adding a differential signal processing method to the initial data analysis procedure validated before irradiation, the gas resonance peaks were successfully extracted from the output signal. From these data, the molar fractions variations of helium and fission gas were measured from an adapted Virial state equation. Thus, with this sensor, the kinetics of gas release inside fuel rods could be deduced from the in-pile measurements and specific calculations. These data will also give information about nuclear reaction effect on piezoceramics sensor under high neutron and gamma flux.

This experimental work presents reproducible measurement conditions to allow amplification of the mechanical vibration generated by photo-thermo-acoustics (PTA) effect using the resonance of circular silicon membranes clamped by nitrile o-rings on a diameter of 30 mm (D(i)). We use wafers with various thickness (h) between 250 and 1000 mu m and with carrier lifetime between 3 and 30 mu s. Under the condition to have a resolution of few picometers for the measurement, it is possible to characterize the resonance mechanism obtained without contact by conventional laser vibrometry using a modulated laser diode of only a few milliwatts of power. Compared to perfect clamped membranes, the first Eigen frequency presents a downward shift of some hundreds Hertz due to the circular clamping by o-ring as predicted by our simplified model. The resonance frequency depends linearly on the thickness as long as D(i)/h > 80. The quality factor (Q) does not exceed ten in agreement with our model for spring loaded membrane in air. The low value of quality factor and its variation according to thickness follow our predictions. Moreover, Q is independent of carrier lifetime whereas first resonance amplitude increases with it but less than prediction for bulks.

Although the characteristic time constant for viscous relaxation of glass is so large at room temperature that viscous flow would be hardly detectable, a permanent deformation can be easily achieved at ambient temperature by applying a sharp contact loading—a Vickers indenter for instance—for few seconds only. We provide direct evidence for densification and volume conservative shear flow by means of atomic force microscopy topological analysis of the indentation profile and volume on as-quenched and densified specimens (pressure up to 25 GPa). We show that both possible mechanisms contribute to different extents depending on the glass composition. A major finding is that densification predominates in glasses with relatively low atomic packing density but that shear flow relays on once densification is achieved.

We studied the tribological properties of a structural series of 11 silicate materials to identify the main physical parameters that control the brittle wear of these materials. First, for each material we characterized Young's modulus E by ultrasonic microscopy, roughness sigma by atomic force microscopy and crack pressure P-c by Hertzian indentation testing. Second, we measured the static and dynamic friction coefficients mu(S) and mu(D), respectively, with a ball probe tribometer for each material and for three hardnesses of the ball probe. The experiments showed that crack density, which quantified the brittle wear of the materials, was controlled by an adimensional number, C-r = P-c/mu E-S. We show in this paper how this number takes into account the combined effects of the mechanical properties, the lubricating coating layer and the residual internal stresses of these materials.

Edge connectors are very commonly used in instrumentation and control (I&C). Failures are difficult to explain and to predict. As a consequence the long-term reliability is difficult to demonstrate. We present in this paper the results of studies we carried out on the influence of the organic pollution in the reliability of HE9 connectors that have been used for more than 25 years. We demonstrate that organic pollution is one of the main important factor that influences the reliability and give an analysis method to evaluate its impact.

The development of a molecular dynamics method simulating the propagation of acoustic waves allowed their propagation velocities to be measured in borosilicate glasses. The qualitative results obtained in glass irradiated by heavy ions correctly reproduces the experimental results, i.e. a reduction in the acoustic wave propagation velocity in irradiated glass. These changes in the mechanical properties were correlated with structural changes, in particular increased disorder in the glass. The greater disorder results in broadening of the characteristic distributions of the glass: distances, angles, and ring sizes. Similarities were clearly observed between the effects of irradiation and the effects of higher quenching rates on the acoustic wave propagation velocities. An additional study of glass artificially expanded by homothetic volume transformation shows that a reduction in acoustic velocity is not necessarily associated with swelling. The artificial volume change combined with increased stresses in the glass results in higher acoustic velocities.

A pulse-echo ultrasonic method is presented to measure elastic parameter variations during thermal loading with high accuracy. Using a dry coupling configuration dedicated to high temperature investigation, this technique has been applied on 6061-T6 aluminium samples up to 220°C. Experimental settings are described to assess the measurement reproducibility estimated at a value of 0.2%. Consequently, the anisotropy of this aluminium between the rolling direction and two orthogonal axes has been clearly detected and also measured versus temperature. As regards the temperature dependence of these elastic parameters, these results are compared with the estimations of the Young’s modulus obtained during mechanical tests in conditions of low cycle fatigue (LCF). The same linear variation versus temperature is found but with a shift of 7GPa. This difference has been classically attributed to systematic experimental error sources and to the distinction existing between dynamic and static elastic modulus.

Silicon oxycarbide glass with the composition Si1.0O1.6C0.8 was synthesized from a commercial polysiloxane by polymer pyrolysis. Dense SiOC samples were obtained by cross linking of the polysiloxane followed by warm pressing to form cylindrical samples and subsequent pyrolysis of the shaped polymer at 1100°C in Ar. Hardness (H), Young's modulus (E) and Poisson's ratio (ν) of the as-prepared SiOC glass were evaluated from indentation studies and from acoustic microscopy. Indentation studies showed that E depends on the applied load and amounts to 90GPa for low load and to 180GPa for high load. Average values of 6.4 and 101GPa were obtained for H and E, respectively, by the Vickers indentation method. Acoustic microscopy analysis yielded values of 96GPa and 0.11 for E and ν, respectively. Compared to vitreous silica, the Young's modulus of the SiOC glass is about 1.3–1.5 times higher. To the knowledge of the present authors, the measured Poisson's ratio (ν=0.11) is the lowest reported so far for glasses and polycrystalline ceramics.

In 2001 we have published a paper [1] in which an ultrasonic method using a large bandwidth transducer with a spherical lens and based on acoustic waves separation near the focal region was presented. We have shown that compared to traditional acoustic microscopy (acoustic signature) the size of the zone analysed on bulk samples was highly reduced. This method is now extended to thin films on bulk substrates. Experimental dispersion curves for thin DLC (Diamond Like Carbon) films on steel are presented. The ultrasonic velocity of leaky Sezawa mode is assessed on a large bandwidth even in zones where the transducer is not very efficient. We show that the signal processing used enlarges the frequency domain explored. Such an element is essential for inverse problem treatment and coating elastic modulus calculation. Once again we show that the length of defocusing can by highly reduced. Hence, the zone analysed on the sample is smaller.