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Moisture absorption is known to alter many of the mechanical properties of polymer-based composites. This study presents ultrasonic characterization of moisture content based on the transmission of acoustic waves through composite plates. The elastic constants of 14 plates with different controlled water contents are obtained. The redundancy of the results allows to validate the characterization process and the assumption made on the sample symmetry. The sensitivity of the process to moisture content is then discussed. [ABSTRACT FROM AUTHOR]

Reflection of Lamb waves when the fundamental mode A0 is incident at the free end of a plate is studied, in order to identify the extent to which the generation of nonpropagating modes influences the field local to the end of the plate. Semi-analytical predictions, finite element simulations, and experimental measurements are presented for frequencies below the A2 cutoff. First it is shown, for frequencies below the A1 cutoff, that reflection of the A0 mode is accompanied by a delay in phase, and that there is significant additional motion due to nonpropagating modes within about five plate thicknesses of the end. The extend of this additional motion in the vicinity of the end of the plate is demonstrated by subtracting the contribution of the propagating modes from the displacement field. The wave field at frequencies above the A1 cutoff is more complex because the A1 as well as the A0 propagating modes are present at the end of the plate. Nevertheless, it has still been possible, using semi-analytical predictions and finite element simulations, to demonstrate the additional motion due to the nonpropagating modes. [ABSTRACT FROM AUTHOR]

Tissue temperature control during cardiac surgery is crucial for myocardial protection. To preserve the tissue, a hypothermic cardioplegia is applied in order to decrease the heart temperature down to around 10°C. The monitoring of the thermal evolution of the myocardium is then of importance to minimize deleterious effects on the heart. The present work aims at evaluating the potential of an ultrasonic velocimetric thermometry on the monitoring of in vitro tissues heating. An indentation process is first proposed to identify the experimental linear relationship linking, in myocardia, the speed of the ultrasonic longitudinal wave to the tissue temperature. An extension of this method based on the echo-tracking principle is then proposed to approach surgical conditions. Temperature changes are measured by monitoring the induced time delays of backscattered ultrasonic echoes. These results are compared to T-type thermocouple reference measurements. They are then discussed in terms of measurement precision and in situ applications., (Copyright © 2018 Elsevier B.V. All rights reserved.)

This paper presents a new method to compute the piezoelastic properties of multidomain single crystals from the single-domain constants. Based on a quasi static assumption, a PMN-chiPT multidomain is defined as a periodic medium with a lattice composed of layers of two domains in a twin structure. Such a structure is assumed to have charged domain walls that imply specific lattice media and boundary conditions. A numerical computation has been performed for a PMN-33PT single crystal in the rhombohedral phase. The effective elastic, piezoelectric, and dielectric constants of the macroscopic structure have been calculated, as well as the wave velocities in different configurations of domain patterns.

This article presents the interaction of the first symmetric Lamb mode S0 with vertical cracks in an aluminium plate placed in vacuum. The cracks are symmetrical regarding to the median plane of the plate and their heights are increasing from 0% to 100% of the plate thickness, by steps of 25%. The frequency-thickness product is chosen to be lower than the S1 frequency cut-off. A modal decomposition method is used to solve the diffraction problem. The variation with the height of the crack of the reflection and transmission coefficients of modes propagating in the far field is predicted. The displacement fields at both sides of the cracks are also calculated, so that it is possible to quantify the crack-opening displacement. These results are compared to numerical predictions obtained using a finite element software. Measurements are also conducted and compared to the predictions.