3 research outputs found
Generation and propagation of Lamb waves in multiplate structures : contribution of time reversal for ultrasonic non-destructive testing of generation IV reactor vessels
Les travaux de cette thĂšse sâinscrivent dans le contexte dâune inspection non destructive des structures internes de la cuve primaire dâun rĂ©acteur de gĂ©nĂ©ration IV, en utilisant des ondes de Lamb fuyantes gĂ©nĂ©rĂ©es Ă la surface de la cuve primaire. Le but est dâutiliser le retournement temporel afin de localiser des dĂ©fauts dans deux plaques en acier inoxydable immergĂ©es et parallĂšles entre elles. La gĂ©nĂ©ration et de la propagation des ondes de Lamb fuyantes dans une plaque libre immergĂ©e sont dâabord Ă©tudiĂ©es, ainsi que diffĂ©rents outils permettant leur analyse. Dans un second temps, plusieurs mĂ©thodes dâimagerie ultrasonore sont Ă©tudiĂ©es et plus spĂ©cifiquement celles employant le retournement temporel, dont lâĂ©nergie topologique qui est ensuite appliquĂ©e sur des signaux acquis expĂ©rimentalement. Deux types de dĂ©fauts (une fissure traversante reprĂ©sentĂ©e par le bord de la plaque et une entaille) sont dĂ©tectĂ©s et localisĂ©s dans une unique plaque immergĂ©e grĂące Ă lâĂ©nergie topologique dans le domaine temporel. Le cas de deux plaques parallĂšles immergĂ©es est finalement expĂ©rimentĂ©. LâĂ©nergie topologique frĂ©quentielle, moins coĂ»teuse en temps de calcul permet alors de dĂ©tecter le bord dâune des deux plaques selon le mode considĂ©rĂ©The work of this thesis is in the context of a non-destructive inspection of the internal structures of the primary vessel of a generation IV reactor, using leaky Lamb waves generated on the surface of the primary vessel. The goal is to use time reversal to locate defects in two immersed stainless steel plates parallel to each other. The generation and propagation of leaky Lamb waves in a free immersed plate are first studied, as well as different tools allowing their analysis. In a second step, several ultrasonic imaging methods are studied, and more specifically those employing time reversal, including topological energy which is then applied on experimentally acquired signals. Two types of defect (a through crack represented by the edge of the plate, and a notch) are detected and localized in a single immersed plate thanks to topological energy in the time domain. The case of two parallel immersed plates is finally experimented. The topological frequency energy, less expensive in term of computation time, allows to detect the edge of one of the two plates according to the considered mod
Sorbic Acid as a Renewable Resource for Atom-Economic and Selective Production of <i>p</i>âToluic Acid and Alkylâ<i>p</i>âToluates: Intermediates to Bioterephthalic Acid and Esters
A new pathway for the production
of <i>p</i>-toluic acid
and alkyl-<i>p</i>-toluates is described here, starting
from industrially relevant but underexploited renewable sorbic acid.
A simple optimized DielsâAlder reaction between sorbic acid
esters and ethylene, followed by aromatization, afford a full selectivity
to <i>para</i>-substituted toluates. <i>p</i>-Toluates
and hydrolyzed <i>p</i>-toluic acid are industrial terephthalic
and terephthalates precursors, which are major commodity chemicals
in the packaging and fiber industries after copolymerization with
diols