Residual Stress Analysis of Laser-Drilled Thermal Barrier Coatings Involving Various Bond Coats

The gas turbine combustion chamber of aero-engines requires a thermal barrier coating (TBC) by thermal spraying. Further heat protection is achieved by laser drilling of cooling holes. The residual stresses play an important role in the mechanical behaviour of TBC. It could also affect the TBC response to delamination during laser drilling. In this work, studies of the cracking behaviour after laser drilling and residual stress distribution have been achieved for different bond coats by plasma spray or cold spray. From interface crack length measured pulse-by-pulse after laser percussion drilling at 20° angle, the role of the various bond coats on crack initiation and propagation are investigated. It is shown that the bond coat drastically influences the cracking behaviour. The residual stresses profiles were also determined by the incremental hole-drilling method involving speckle interferometry. An original method was also developed to measure the residual stress profiles around a pre-drilled zone with a laser beam at 90°. The results are discussed to highlight the influence of TBCs interfaces on the resulting residual stresses distribution before laser drilling, and also to investigate the modification around the hole after laser drilling. It is shown that laser drilling could affect the residual stress state

LEPTINE ET TROUBLES DU METABOLISME GLUCIDIQUE AU COURS DE LA GROSSESSE

LILLE2-BU Santé-Recherche (593502101) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

Le système neurosécréteur caudal, l’autre système « neurohypophysaire » des poissons

Le système neurosécréteur caudal (SNSC) est un complexe neuroendocrinien propre aux poissons. Sur le plan structural, il présente de nombreuses similitudes avec le complexe hypothalamo-neurohypophysaire d’autres vertébrés. Il s’en distingue toutefois par sa position, à l’extrémité caudale de la moelle épinière, et par la nature des hormones qu’il sécrète, les plus importantes étant les urotensines. Le SNSC a été décrit pour la première fois il y a plus de 60 ans, mais son origine embryologique est totalement inconnue et son rôle reste mal compris. Paradoxalement, il n’est presque plus étudié aujourd’hui. Les développements récents en imagerie et en génie génétique pourraient justifier la reprise d’investigations sur le SNSC afin de lever les mystères qui continuent de l’entourer

Study of the residual stress distribution of thermally sprayed TBCs involving various interfaces and laser drilling

International audienc

Valorization of Invasive Plant Extracts against the Bispecies Biofilm <i>Staphylococcus aureus</i>–<i>Candida albicans</i> by a Bioguided Molecular Networking Screening

Invasive plants efficiently colonize non-native territories, suggesting a great production of bioactive metabolites which could be effective antibiofilm weapons. Our study aimed to look for original molecules able to inhibit bispecies biofilm formed by S. aureus and C. albicans. Extracts from five invasive macrophytes (Ludwigia peploides, Ludwigia grandiflora, Myriophyllum aquaticum, Lagarosiphon major and Egeria densa) were prepared and tested in vitro against 24 h old bispecies biofilms using a crystal violet staining (CVS) assay. The activities of the extracts reducing the biofilm total biomass by 50% or more were comparatively analyzed against each microbial species forming the biofilm by flow cytometry (FCM) and scanning electron microscopy. Extracts active against both species were fractionated. Obtained fractions were analyzed by UHPLC-MS/MS and evaluated by the CVS assay. Chemical and biological data were combined into a bioactivity-based molecular networking (BBMN) to identify active compounds. The aerial stem extract of L. grandiflora showed the highest antibiofilm activity (>50% inhibition at 50 µg∙mL−1). The biological, chemical and BBMN investigations of its fractions highlighted nine ions correlated with the antibiofilm activity. The most correlated compound, identified as betulinic acid (BA), inhibited bispecies biofilms regardless of the three tested couples of strains (ATCC strains: >40% inhibition, clinical isolates: ≈27% inhibition), confirming its antibiofilm interest

Le parallélogramme au fil des cycles.: Des ressources pour les enseignants et les formateurs

National audienc

Le parallélogramme au fil des cycles.: Des ressources pour les enseignants et les formateurs

National audienc

Study of delamination induced by laser drilling of thermally sprayed TBC interfaces

International audienceThe efficiency of the aero-engines combustion chambers with thermal barrier coating (TBC) is improved when highly numerous cooling holes are laser drilled with inclined angles. However, during the laser drilling process, especially in the percussion mode, a detrimental crack can be generated at the TBC interface. Thus, each hole could be edged with a nonvisible delaminated area underneath the ceramic top-coat. The present work is focused on the thorough study of the delamination induced by laser percussion drilling when interrupted drilling conditions are achieved. Shallow angles were applied on hole each having one different and increasing number of laser pulses (from 1 to 4). Crack length was assessed by conventional metallographic preparation. A special experimental method was carried out in order to inspect the delaminated interface and the lateral edge of a semi-hole. This non-destructive assessment of the delamination of laser drilled TBC was complemented by a 3D imaging of a semi-hole using X-Ray microtomography. Results are presented paying attention on both crack initiation and propagation during the laser percussion drilling of plasmasprayed TBC

Study of delamination induced by laser drilling of thermally sprayed TBC interfaces

International audienceThe efficiency of the aero-engines combustion chambers with thermal barrier coating (TBC) is improved when highly numerous cooling holes are laser drilled with inclined angles. However, during the laser drilling process, especially in the percussion mode, a detrimental crack can be generated at the TBC interface. Thus, each hole could be edged with a nonvisible delaminated area underneath the ceramic top-coat. The present work is focused on the thorough study of the delamination induced by laser percussion drilling when interrupted drilling conditions are achieved. Shallow angles were applied on hole each having one different and increasing number of laser pulses (from 1 to 4). Crack length was assessed by conventional metallographic preparation. A special experimental method was carried out in order to inspect the delaminated interface and the lateral edge of a semi-hole. This non-destructive assessment of the delamination of laser drilled TBC was complemented by a 3D imaging of a semi-hole using X-Ray microtomography. Results are presented paying attention on both crack initiation and propagation during the laser percussion drilling of plasmasprayed TBC