The purpose of this paper is to present the scientific and technical issues related to the repair of aeronautical structures, made of multilayer monolithic long fibre composites, for which there is an increased need due to the entry into service of hundreds of B787 or A350 aircrafts per year. The first stage of this study corresponds to a machining phase using an abrasive water jet removal technique. This phase is carried out using a mobile machine (designed by the innovative small company Bayab Industries) and which is the only machine certified by Airbus for the repair of primary structures of the A350 [1]. This technique, unlike those by cutting tools, allows an offset machining "layer by layer" as a stepping, in order to carry out the repair via a patch covering plies [2]. The operational nature of the machining is absolutely fundamental to take into account the inherently variabilistic character of the composite which presents variations of ply thickness according to the considered position [3]. In the repair process, one of the issues is to limit the influence of this area of removal of material and reducing the prohibitive time of immobilization of the aircraft (which costs 100 to 200 kUS dollars by day). To illustrate our point, the studied plate consists of 20 plies of UD M21 T700 and presents a stacking sequence [+45, -45,+45, -45,+45, -45,+45, -45,+45, -45]s. An innovative multi-scale model is developed in which only the adhesive zone consists of volume finite elements. It is a question of avoiding the use of a F.E. calculation, too heavy, and which would penalize the design of repaired structures of greater dimension and would make the crossing tests computation very tedious. This method allows to describe and model the minimum volume of material to be removed while ensuring a nominal transfer of efficient stress flows between the parent composite part and the repair patch. It integrates a 3D approach of the glue joint by arranging all the stresses as well as deformations in all points, hence minimizing the number of degrees of freedom of the numerical model. Different overlapping lengths are considered to allow the cross-over of computational tests with specimens taken from the repaired motherboard and subjected to an axial effort. It is shown that the joint patent held by the Clement Ader Institute, the SME Composites Expertise and Solutions and the TPE Bayab Industries operates because it is based on the simple idea that a nominal overlapping length is only necessary if strictly in the direction of the UD ply fibres. It is shown that this approach makes it possible to reduce the grip of repair patches by more than 70%, making the adhesive patch certifiable by aeronautical certification authorities [4]. Illustrations related to the work of the Repair workshop (since 2010) of GDR 3371 MIC (Composite Manufacturing and Induced Properties) will be proposed.


[1] Hanser, S., Ferrer, G., Dupouy, S. A350 XWB composite bonded repair, New technology for new aircraft, pp 11-18, Fast#61, 2018.

[2] Cénac, F., Collombet, F., Déléris, M., Zitoune, R. Chapter 4. Abrasive Water Jet Machining of Composites, p.167-180, Machining Composite Materials, Paulo Davim, J., ed., ISTE Ltd 2010.

[3] Davila, Y., Crouzeix, L., Douchin, B., Collombet F., Grunevald Y-H. Spatial Evolution of the Thickness Variations over a CFRP Laminated Structure. Applied Composite Materials, Springer Verlag (Germany), 1201 - 1215, 24.

[4] Collombet, F., Grunevald, Y.H., Crouzeix, L., Douchin, B., Zitoune, R., Davila, Y., Cerisier, A., Thévenin, R. Chapter 10 Repairing composites, In book Advances in Composites Manufacturing and Process Design, Chap. 10, p.197-227. Ed.© 2015 Elsevier Ltd. 2015 ISBN: 978-1-78242-307-2.