Alain Lhémery

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Speed of sound measurements are widely used clinically to assess bone strength. Trabecular bone is an attenuating composite material in which negative values of velocity dispersion have been measured, this behavior remaining poorly explained physically. The aim of this work is to describe the ultrasonic propagation in trabecular bone modeled by infinite(More)
In a structure that guides elastic waves, a discontinuity (defect, shape variation) causes scattering (reflection, partial extinction or mode conversion). Two modal formulations have been developed to link separate models dealing with the calculation of the modal decomposition, with the generation and reception of guided waves (GW), with their scattering.(More)
The wedge of a contact transducer is imperfectly coupled to a component of irregular surface. A volume between the wedge and the component (filled by water or oil used as a coupling) is created that fundamentally modifies transducer radiation behavior. As a result, phenomena like beam spreading, skewing and splitting, generation of unwanted contributions(More)
Nondestructive methods aim at detecting, locating and identifying defects. Inversion of ultrasonic measurements obtained by inspecting a steel component of regular geometry with an immersed transducer leads to accurate location of defects. When the component is cladded, the irregular geometry of the surface and the anisotropic nature of the cladding(More)
The UT simulation tools developed at the French Atomic Energy Commission (CEA) in the CIVA software platform were up to now limited to methods based on bulk ultrasonic waves. This study aims at extending the capabilities of the models to deal with testing configurations using surface acoustic waves (SAW). In such configurations, specific transducer(More)
An electromagnetic acoustic transducer (EMAT) or a laser used to generate elastic waves in a component is often described as a source of body force confined in a layer close to the surface. On the other hand, models for elastic wave radiation more efficiently handle sources described as distributions of surface stresses. Equivalent surface stresses can be(More)
Ultrasonic testing of austenitic stainless steel welds is often difficult because the ultrasonic beam is subjected to many perturbations : deviation, partition, distortions and sometimes ghost echoes. These perturbations are due to the anisotropic and heterogeneous metallurgical structure of the welds. We are carrying out a research program in order to(More)
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