Evaluation des propriétés microélastiques de l'os par microscopie acoustique (influence des phases minérale et organique)

PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

Modelling of weld inspection by using a paraxial ray-tracing

International audienceThe controllability of welded joints is a major industrial challenge to meet the requirements of safety and service life of structures. Nevertheless, in most of austenitic welds, ultrasonic detection performances decrease due to unfavourable wave interactions with microstructure. The understanding of such phenomena requires the use of accurate numerical models. In particular, the ray-based model implemented in CIVA can simulate weld inspections considering heterogeneous and anisotropic materials where the microstructure is described using several homogeneous domains. However, according to the size of the domains and the impedance contrast between neighbouring domains, such weld descriptions may lead to discrepancies between simulations and experimental results. To overcome this difficulty, the extension to smoothly inhomogeneous anisotropic media may be performed by using paraxial ray tracing. In this paper, simulation results obtained with this method are presented and compared to finite elements and experimental data on a well-documented sample representative of a weld located in the primary circuit of nuclear power plants.This work is a part of the MOSAICS project, supported by the ANR (French National Research Agency) which aims at significantly improving the understanding of the influence of the weld structure on the performance of ultrasonic NDT inspections

Adaptive Remodeling of Trabecular Bone Core Cultured in 3-D Bioreactor Providing Cyclic Loading: An Acoustic Microscopy Study

International audienceScanning acoustic microscopy (SAM) provides high-resolution mapping of acoustic impedance related to tissue stiffness. This study investigates changes in tissue acoustic impedance resulting from mechanical loading in trabecular bone cores cultured in 3-D bioreactor. Trabecular bone cores were extracted from bovine sternum (n = 15) and ulna metaphysis (n = 15). From each bone, the samples were divided in three groups. The basal control (BC) group was fixed post-extraction, the control (C) and loaded (L) groups were maintained as viable in a controlled culture-loading cell over three weeks. Samples of L group underwent a dynamic compressive strain, whereas C samples were left free from loading. After three weeks, L and C samples were embedded in polymethylmethacrylate and all samples were explored with a 200-MHz SAM. For each specimen, the acoustic impedance distribution was obtained over flat and polished section of bone blocks prepared parallel to the loading axis. Our results showed that in basal controls, the acoustic impedance varied with bone anatomical location and was 15% higher in weight-bearing ulna compared with nonweight-bearing sternum. The comparison between loaded and nonloaded groups showed that sternum-only exhibited significant change in acoustic impedance (L vs. C sternum: +9%). This result suggests that when the applied load is comparable with the stress naturally experienced by a weight-bearing bone (ulna), the tissue material properties (manifested by acoustic impedance) remained unchanged. In conclusion, SAM is a potentially relevant tool for the assessment of subtle changes in intrinsic microelastic properties of bone induced by adaptive remodeling process in response to mechanical loadin

Assessment of Microelastic Properties of Bone Using Scanning Acoustic Microscopy: A Face-to-Face Comparison with Nanoindentation

International audienceThe current work aimed at comparing, on site-matched cortical bone tissue, the micron-level elastic modulus Ea derived from 200 MHz-scanning acoustic microscopy (SAM) acoustic impedance (Z) combined with bone mineral density (assessed by synchrotron radiation microcomputed tomography, SR-µCT) to nanoindentation modulus En. A good correlation was observed between En and Z (R2=0.67, p<0.0001, root mean square error RMSE=1.9 GPa). The acoustical elastic modulus Ea derived from Z showed higher values of E compared to nanoindentation moduli. We assumed that the discrepancy between Ea and En values may likely be due to the fixed assumed value of Poisson's ratio while values comprised between 0.15 and 0.45 have been reported in the literature. Despite these differences, a highly significant correlation between Ea and En was found (R2=0.66, p<0.001, RMSE=1.8 GPa) suggesting that SAM can reliably be used as a modality to quantitatively map the local variations of tissue-level bone elasticity

SAM image (amplitude of the reflected ultrasound beam coded in gray levels).

<p>The data analysis was performed on an identical site-matched area on each one of the two investigated osteons (namely <i>ost1</i> and <i>ost2</i>).</p

Minima and maxima of acoustic impedance (<i>Z</i>) and mineral orientation (<i>I_SAXS</i>) show a positive correlation (linear regression for the pooled data from <i>ost1</i> (▾) and <i>ost2</i> (•).

<p>Minima and maxima of acoustic impedance (<i>Z</i>) and mineral orientation (<i>I_SAXS</i>) show a positive correlation (linear regression for the pooled data from <i>ost1</i> (▾) and <i>ost2</i> (•).</p

SAXS calibration of the mineral nanoparticle orientation.

<p><b>A</b> Composite image showing the 2D SAXS pattern as a function of scan position along the radial direction of the osteon and tilt angle ω; <b>B</b> zoom in the innermost part of the scan (close to the Haversian canal); <b>C</b> map of the intensity <i>I_SAXS</i> along the direction of the scan across the osteon as a function of the tilt angle, with the result of the fit overlaid in the form of white dots indicating a maximum. The position of the maximum was calculated by fitting the tilt profiles (from −60° to 60°) at each scan point by a sine function; <b>D</b> correlation between <i>I_SAXS</i> and the angular position of the maximum <i>I_SAXS</i> measured when tilting the sample between –60° and +60°.</p

Site matched images on <i>ost1</i>: <i>DMB</i> map (left), <i>Z</i>-map (right, background) and <i>I_SAXS</i> map (right, foreground).

<p>Site matched images on <i>ost1</i>: <i>DMB</i> map (left), <i>Z</i>-map (right, background) and <i>I_SAXS</i> map (right, foreground).</p

Comparison between local elastic properties and mineral ultrastructural characteristics.

<p>From top to bottom: <b>A</b> acoustic impedance (<i>Z</i>), <b>B</b> degree of mineralization of bone (<i>DMB</i>), <b>C </b><i>T</i>-parameter linked to the mineral thickness, <b>D </b><i>I_SAXS</i> related to changes in the lamellar orientation (the results are illustrated for <i>ost1</i>). For each investigated parameter, the solid line represents its variations along a radial profile going from the Haversian canal to the outer lamellae. The dashed line represents the corresponding smoothed profile after averaging the values between adjacent peaks. The coefficient of variation of the root-mean-square error CV(RMSE) provides a measure of the relative amplitude fluctuations of the measured values around the averaged profile curves.</p