Assessment of cure residual strains through the thickness of carbon-epoxy laminates using FBGs, Part I: Elementary specimen

International audienceVariability of thereto-mechanical properties within a composite part is a well known issue. It is problematic at the early stage of structural design. This variability being generated during the processing phases, the characterisation of the initial state of a structure becomes a crucial operation. A first step to this objective is presented in this paper. It deals with the assessment of autoclave cure induced strains in carbon epoxy laminates. Distribution and amplitude are considered through the thickness of carbon/epoxy elementary and technological specimens thanks to a series of FBGs embedded at different levels of the ply stack. Part I of this work concerns the analysis of unidirectional reinforced specimens. It begins with all overview of the various phenomena that Cause the presence of residual stresses after cure and how they can be measured in experiments. Their development being closely related to the rheology of the matrix, an analysis of the M21 resin is given and assumptions are made to justify the following assessment procedures. A discussion leads to select the onset of gelation as the key point to start measuring residual cure stresses. The autoclave cure monitoring of the [O(8)] specimen is then carried out and analyzed. Depending on their location through the laminate thickness, the FBG sensors give different information highlighting the effects of interaction between the laminate and the tool/plat

Mechanical performance of composite structures with embedded silica sensors: concept of monitoring patch

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Mechanical performance of composite structures with embedded silica sensors: concept of monitoring patch

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Comportement d’une réparation en escalier obtenue par Jet d’Eau Abrasif

National audienceDes éprouvettes carbone/époxy pour évaluer la qualité d’une réparation en escalier sont usinées, réparées puis testées mécaniquement. L’usinage préalable à la phase de réparation est effectué par Jet d’Eau abrasif, sous forme de marches régulières de ratio 1/30, et dont la profondeur correspond à l’épaisseur d’un pli. Le relâchement des contraintes résiduelles observé pendant la phase d’usinage est quantifié grâce à la technique de mesure de champs par stéréovision, et simulé par EF. La plaque usinée est ensuite reconstruite par remplacement des plis usinés, et cocuit en autoclave. Le schéma de stratification de la partie réparée est décalé d’un pli par rapport à la zone initiale, de manière à restituer le transfert de charges. Des éprouvettes sont découpées dans les plaques réparées, et sollicitées en traction. Les résultats montrent que les charges à rupture obtenues atteignent 70 % des charges à rupture d’éprouvettes «vierges». L’analyse des fragments des éprouvettes démontre que la rupture de la zone de collage dans les interfaces 0/0 est à l’origine de la rupture finale de toutes les éprouvettes. Le croisement essais/calcul conduit à l’évaluation d’un critère de rupture en contrainte de cisaillement admissible pour l’interface zone parent/patch

Assessment of cure-residual strains through the thickness of carbon-epoxy laminates using FBGs Part II: Technological specimen

International audienceThis paper is a continuation of our previous study [Mulle M, Collombet F, Olivier P, Grunevald Y-H. Assessment of cure residual strains through the thickness of carbon-epoxy laminates using FBGs, part I: elementary specimen. Compos Part A 2008. doi:10.1016/j.compositesa.2008.10.008] pertaining to the assessment of autoclave cure-induced strains through the thickness of carbon-epoxy laminates. In this first part, postulates and measurement procedures were established for cure of elementary specimens. Based on these, this study undertakes investigation on what are called technological specimens. These specimens are of the beam type and contain geometrical specificities which represent typical structural issues. In-plane process-induced strains were studied through the thickness of a thick reinforced zone using several optical fibre Bragg gratings (FBGs) sensors embedded at different levels of the ply stack. A non-uniform distribution of residual strains was detected. Once cured, the technological specimen was subjected to a heating test whose cycle was comparable to the cure cycle. Thermally induced strains were measured with the embedded FBGs. The values recorded were compared with those of cure-induced residual strains and FEM simulation. Discrepancies were observed that strongly suggest the possible influence of environmental effects and the need for the calculation to take into account the through-the-thickness variability of thermal properties

Compressive behaviour of concrete elements confined with GFRP-prefabricated bonded shells

International audienceIn this paper, a new technique is proposed to confine concrete columns using GFRP-prefabricated bonded shells and a shrinkage-compensating cement mortar. The confinement is performed with three identical shells, each of which contains two stepped lap joints at their ends. The main advantage of this technique is that the shells can be directly assembled on site by structural bonding to cover any column shape. The gap between the shells and the column is filled with shrinkage-compensating cement mortar. To evaluate the efficiency of this technique, several concrete specimens were confined, instrumented and tested under monotonic compression. To simulate the actual strengthening conditions, the load was directly applied on the concrete cross-section. The results show clearly the benefits of an efficient confinement in terms of a noticeable increase in the axial strength and ductility where the stress\textendashstrain curves are characterised by a third softening phase and the failure mode which spread over the whole length of the shells

Study of the parameters variability of monitoring patch used in composites instrumentation

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Benefit from embedded sensors to study polymeric composite structures

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Large repair for aeronautics’ primary principal composite structures

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Large repair for aeronautics’ primary principal composite structures

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