{"id":50847,"date":"2022-03-04T13:44:18","date_gmt":"2022-03-04T11:44:18","guid":{"rendered":"https:\/\/www.iemn.fr\/?p=50847"},"modified":"2022-03-21T18:09:23","modified_gmt":"2022-03-21T16:09:23","slug":"50847","status":"publish","type":"post","link":"https:\/\/www.iemn.fr\/en\/actualites\/50847.html","title":{"rendered":"Th\u00e8se de Marina Terzi \u2013 \u00ab\u00a0Ultrasonic imaging of contact defects under low frequency loading: application for SHM of elastic plates\u00a0\u00bb"},"content":{"rendered":"<style type=\"text\/css\" data-created_by=\"avia_inline_auto\" id=\"style-css-av-2g9j33-7c8b57050ac2355c6c660522d7754ba5\">\n.flex_column.av-2g9j33-7c8b57050ac2355c6c660522d7754ba5{\nborder-radius:0px 0px 0px 0px;\npadding:0px 0px 0px 0px;\n}\n<\/style>\n<div  class='flex_column av-2g9j33-7c8b57050ac2355c6c660522d7754ba5 av_one_full  avia-builder-el-0  avia-builder-el-no-sibling  first flex_column_div av-zero-column-padding'     ><section  class='av_textblock_section av-l0ccb5ih-a176b669e10f2aa1049649f296c3155d'   itemscope=\"itemscope\" itemtype=\"https:\/\/schema.org\/BlogPosting\" itemprop=\"blogPost\" ><div class='avia_textblock'  itemprop=\"text\" ><h3 style=\"text-align: center;\">Th\u00e8se de Marina Terzi<br \/>\n\u00ab\u00a0Ultrasonic imaging of contact defects under low frequency loading:<br \/>\napplication for SHM of elastic plates\u00a0\u00bb<\/h3>\n<blockquote><p>\n<style type=\"text\/css\" data-created_by=\"avia_inline_auto\" id=\"style-css-av-ikveov-92c0e1e8a70f730b34d6ee48b092e96b\">\n.av_font_icon.av-ikveov-92c0e1e8a70f730b34d6ee48b092e96b .av-icon-char{\nfont-size:30px;\nline-height:30px;\n}\n<\/style>\n<span  class='av_font_icon av-ikveov-92c0e1e8a70f730b34d6ee48b092e96b avia_animate_when_visible av-icon-style- avia-icon-pos-left av-no-color avia-icon-animate'><span class='av-icon-char' aria-hidden='true' data-av_icon='\ue8c9' data-av_iconfont='entypo-fontello' ><\/span><\/span>Soutenance le lundi 14 mars \u00e0 13h, en pr\u00e9sentiel<br \/>\nAmphith\u00e9\u00e2tre de l&rsquo;IEMN DOAE \u2013 Universit\u00e9 polytechnique Hauts-de-France<\/p>\n<\/blockquote>\n<h4>Jury :<\/h4>\n<p>C\u00e9dric Payan, Ma\u00eetre de conf\u00e9rences, LMA, Marseille<br \/>\nAnissa Meziane, Professeur, I2M, Bordeaux<br \/>\nDaniela Dragomirescu, Professeur, INSA, Toulouse<br \/>\nJulien de Rosny, DR CNRS, Institut Langevin, Paris<br \/>\nBastien Chapuis, Docteur, Ing\u00e9nieur, CEA LIST, Saclay<br \/>\nLynda Chehami, Ma\u00eetre de conf\u00e9rences UPHF, Valenciennes, Encadrante<br \/>\nEmmanuel Moulin, Professeur INSA HdF Valenciennes, Directeur de th\u00e8se<br \/>\nVladislav Aleshin, CR CNRS, IEMN, Co-Directeur<\/p>\n<h4>Summary:<\/h4>\n<p>Le contr\u00f4le-qualit\u00e9 de mat\u00e9riaux par m\u00e9thodes acoustiques sans r\u00e9f\u00e9rence suscite aujourd\u2019hui un grand int\u00e9r\u00eat en contr\u00f4le sant\u00e9 int\u00e9gr\u00e9 (CSI) au vu de la variabilit\u00e9 des conditions environnementales et op\u00e9rationnelles. Dans ce manuscrit, nous proposons une m\u00e9thode de d\u00e9tection synchrone\/non synchrone de d\u00e9faut soumis \u00e0 des sollicitations basses fr\u00e9quences, permettant une localisation sans \u00e9tat hypoth\u00e9tique \u00ab\u00a0sans d\u00e9faut\u00a0\u00bb. Une s\u00e9rie de tests \u00ab\u00a0pompe-sonde\u00a0\u00bb a \u00e9t\u00e9 men\u00e9e sur une plaque d&rsquo;aluminium. Un pot vibrant est fix\u00e9 sur cette derni\u00e8re afin de la mettre en vibration \u00e0 une fr\u00e9quence de quelques Hz. Une bille solidaire d&rsquo;une lame en acier est press\u00e9e contre la plaque (contact Hertzien) et joue le r\u00f4le d&rsquo;un d\u00e9faut (reproduisant ainsi un contact tel qu&rsquo;on peut le rencontrer par exemple entre deux fronts d&rsquo;une fissure). Un r\u00e9seau de transducteurs pi\u00e9zo\u00e9lectriques est utilis\u00e9 pour faire l&rsquo;imagerie ultrasonore. Le principe de la d\u00e9tection repose sur la modulation du contact entre la plaque et la bille par la vibration pompe basse fr\u00e9quence. Des mesures ultrasonores r\u00e9p\u00e9t\u00e9es (onde sonde) permettent ainsi d&rsquo;interroger le d\u00e9faut dans plusieurs \u00e9tats de sollicitation. Un algorithme d&rsquo;imagerie diff\u00e9rentielle permet alors de mettre en \u00e9vidence et localiser le d\u00e9faut. Deux modes de d\u00e9tection ont \u00e9t\u00e9 test\u00e9s : 1) mode synchrone entre la pompe et les signaux ultrasonores et 2) mode non synchrone. Dans ce dernier cas, une correction par des coefficients de pond\u00e9ration ad-hoc permet d\u2019am\u00e9liorer la d\u00e9tection. Une \u00e9tude param\u00e9trique a \u00e9t\u00e9 \u00e9galement r\u00e9alis\u00e9e en reliant le contraste des images en fonction de la section de diffusion de d\u00e9faut. Ceci a permis de d\u00e9finir un seuil minimal de d\u00e9tection d\u2019un d\u00e9faut de type contact variable.<br \/>\nL&rsquo;application de cette m\u00e9thode \u00e0 l&rsquo;imagerie passive par corr\u00e9lation de bruit a donn\u00e9 des r\u00e9sultats encourageants, \u00e0 condition d&rsquo;augmenter la densit\u00e9 du r\u00e9seau de capteurs ultrasonores. Enfin, des simulations num\u00e9riques en 2D, mod\u00e9lisant l&rsquo;interaction d&rsquo;une onde ultrasonore avec un contact de frottement type \u00ab\u00a0Hertz-Mindlin\u00a0\u00bb ont \u00e9t\u00e9 r\u00e9alis\u00e9es afin de comparer le d\u00e9faut actuel (bille press\u00e9e sur la<br \/>\nplaque) avec un d\u00e9faut r\u00e9aliste (une fissure).<\/p>\n<h4>Abstract:<\/h4>\n<p>In structural health monitoring, acoustic methods without use of a reference intact sample are nowadays of great interest due to variability of environmental and operational conditions. This thesis presents an acoustic reference-free method for detecting and localizing defects in thin plates. The proposed approach is based on pump-probe measurements and a differential signal processing algorithm. The pump-probe scheme here means the simultaneous excitation of low-frequency vibrations and high-frequency acoustic pulses generated by a piezoelectric transducer and recorded by an array of transducers of the same kind. The role of pumping vibrations is in imposing changes to loading conditions for a defect (here a model Hertzian contact i.e. a small ball pressed against the tested plate) while the ultrasonic Lamb wave pulses probe the defect in various loading states. Then a differential signal processing algorithm based on backpropagation of AO Lamb mode is used to detect and locate<br \/>\nthe defect. Two detection modes have been studied: the mode requiring the synchronization between the pump and probe signais, and the non-synchronous mode. In the latter case, a correction with the use of ad hoc weight coefficients improves the detection. Further, a parametric study was performed by computing the image contrast as a function of the defect scattering cross-section that allowed us to determine a minimum detection threshold.<br \/>\nThe application of the method to passive imaging (i.e. using white noise instead of probe pulses) produced encouraging<br \/>\nresults for the price of increasing the number of receivers. Finally, numerical modeling for the interaction of an ultrasonic wave with a Hertz-Mindlin frictional contact was performed in 2D to compare the model defect (ball pressed against the plate) with a more realistic one (crack).<\/p>\n<\/div><\/section><\/div>","protected":false},"excerpt":{"rendered":"","protected":false},"author":2,"featured_media":50850,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[8],"tags":[],"class_list":["post-50847","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-actualites"],"_links":{"self":[{"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/posts\/50847","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/comments?post=50847"}],"version-history":[{"count":0,"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/posts\/50847\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/media\/50850"}],"wp:attachment":[{"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/media?parent=50847"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/categories?post=50847"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/tags?post=50847"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}