Thèse Développement d'Un Modèle de Jumeau Numérique pour l'Usinage à Non Débouchant de Matériaux Composites Destinés à des Applications Aérospatiales H/F Doctorat.Gouv.Fr

Établissement : Université de Toulouse École doctorale : MEGEP - Mécanique, Energétique, Génie civil, Procédés Laboratoire de recherche : ICA - Institut Clément Ader Direction de la thèse : Redouane ZITOUNE ORCID 0000000343750998 Début de la thèse : 2027-10-01 Date limite de candidature : 2026-11-23T23:59:59 Composite materials are widely used in the aeronautical industry due to their high strength to weight ratios and potential for structural weight reduction. However, material selection is increasingly shifting towards sustainable circularity, requiring improved repair and remanufacturing strategies. In this context, carbon fibre reinforced thermoplastic (CFRT) requires further investigation, particularly for precision shaping and surface texturing to enhance bonding during remanufacturing.
Surface preparation is currently performed mainly using conventional mechanical tools. While effective, these processes can cause fibre breakage, delamination, matrix degradation, and other defects that may reduce bonding performance. They can also generate fine and potentially hazardous dust. These issues are further amplified during manual repair of large aircraft structures, where process variability can affect surface quality and repeatability. As an alternative, abrasive water jet (AWJ) processing offers a promising solution for precise and controlled material removal, potentially reducing mechanical damage and dust emissions while improving process consistency.

This project focuses on a digital twin-enabled abrasive water jet (AWJ) machining process to achieve precision blind machining (e.g., milling) and texturing of carbon/thermoplastic materials. To achieve this, an in-depth study on the AWJ machining process of composite carbon/PEEK will be conducted to obtain the relationships between process parameters (e.g., water pressure, scan speed...) and the machining outcome (e.g., cutting depth, cutting width and straightness...). The fundamentals relating water particle energy with micro-scale material removal mechanics will be derived in WP 1, which will be material-specific to carbon/thermoplastics. Further refinement in AWJ machining parameters will also be explored to obtain varying levels of surface textures on the composites, which will be followed by an investigation on the influence of surface textures on structural mechanical strength and adhesion quality tests to achieve optimal composite adhesion for remanufacturing works in WP 2. Detailed interfacial characterization of the two texturized surfaces and cured epoxy adhesives in WP 2 will build a scientific understanding of the interfacial contact zones (adhesive/substrate) and their correlation with mechanical bonding strength. A digital twin (DT) framework will also be developed in WP 3 to integrate the fundamental understanding of AWJ machining process parameters on the machining of CFRT. The DT will deliver graphical representations of resultant geometrical features based on tool path and process parameter inputs. The importance of a DT for AWJ is found in the uncertainties relating material specific removal energy, the Gaussian profile of a water jet, and the resultant geometrical features. This is unlike traditional machining processes where geometrical accuracy is subject to other factors, such as machine tool tolerance, cutting tool wear, and workpiece damage mechanisms. WP 4 will apply the integration of the scientific material mechanisms and digitalization in demonstrators where AWJ will be employed to machine out various geometric features (e.g., multi-step elliptical patches) and surface textures on a parent body and an adhering repair patch. The demonstrators will confirm the feasibility of the research findings and affirm the academic significance of the project.
The aeronautical industry has a massive share in global transportation systems with its primary sustainability goals focused on reducing its direct carbon footprint (i.e., fuel consumption). In the context of sustainable aviation, the transformation from linear manufacturing paradigms into the closed models of a circular economy remains rudimentary [1] especially for aircraft structures made of fiber reinforced polymers (FRP), which forms a substantial portion of material used in aircraft manufacturing. Therefore, this project targets the aspect of creating and validating a digital twin model enabling repair as part of the 3R (Reduce, Reuse, and Recycle) circular manufacturing strategies for the next generation of aircraft composite materials. The proposed solution involves innovative digital twins model to enhance repair efficiencies and reduce material waste. In the context of economic and environmental sustainability, the objectives of repair are to increase the lifespan of the part by avoiding cases for scrapping and/or replacement during manufacturing and maintenance. The repair of aircraft composites must consider the aspects of: (a) patch manufacturing while taking into account manufacturing variabilities, (b) processing and surface preparation of the joining surfaces, and (c) the structural integrity of the repair. These aspects are addressed in our project through the optimization of the streamlined digital twin, providing user guidance through the process, to achieve the final desired repair quality.

Keeping in mind the global sustainability goals, this project uses Carbon/thermoplastic composites. Traditionally, commercial aircrafts employ carbon/epoxy composites for aircraft structures, because they were predominantly perceived as cheaper and more resistant over thermoplastics during their incorporation. However, advancements in thermoplastics have positioned the material as the sustainable alternative following significant improvements in the properties of high-performance thermoplastics [2]. Carbon/thermoplastics (e.g., CF/PEEK) displayed superior impact resistance in comparison to carbon/epoxy composites [3], which offers a better proposition for aircraft structures. Moreover, thermoplastics offer greater viability for recycling and ease in recovery of carbon fibers as compared to thermosets. The acceleration of the adoption of thermoplastic repairs through, streamlined digital twin guidance, will inevitably advance the aeronautic industry towards achieving the global sustainability goals.
On the other hand, the topic on composite joining is not new, but it is rarely discussed in the context of repair for aircraft structures due to the inherent difficulties faced with traditional carbon/epoxy materials. However, there is transferable knowledge from laminated composite patches that may be applied to repair, such as techniques for damaged area removal and preparation of appropriate surfaces that can enhance the repair patch connections [4]. In the context of repair, it is important to further discuss the state-of-the-art in damage area removal with surface preparation, patch fabrication, and assembly methodologies.
Current aircraft maintenance involves manual machining, which presents several inconveniences such as, mechanical and thermal degradation of the matrix, harmful dust particle emissions [5], fiber pull-outs/damages, and inconsistent material removal control due to the variations in ply thickness [6]. Moreover, the smooth machined surfaces are unfavorable for bonding [7], and further sanding or grit blasting are often required, which increases the repair cost, reduces repair efficiency and increases dust emissions. While there are alternatively cleaner post-processes (e.g., corona, plasma, or laser texturing), polymers tend to degrade over time after processing. Therefore, an ideal case would be to involve single processes capable of material removal and surface preparation, such as the abrasive water jet process (AWJ). In fact, this process is a proven solution to remove damaged areas on carbon/epoxy composites while simultaneously preparing the surfaces for bonding of repair patches. It induces little forces and heat on the workpiece while ensuring precise machining and texturing [8]. The process has been jointly patented by UPS with SAFRAN, BAYAB Industries and AIRBUS and successfully applied for two material removal operations [9]. The two patents were filed in the context of using AWJ for surface machining of laminated composites and multi-materials for repair [10, 11]. AWJ has also been certified by AIRBUS for the repair of fuselage panels on the A350 commercial aircraft made of carbon/thermoset, and the repair of blade fans (made of carbon/epoxy/titanium) in the engine LEAP by SAFRAN. Selected combinations of AWJ parameters can generate different surface morphologies (e.g., broken fibers, crater sizes and shapes) [9], which had significant influence on bond strengths (e.g., Mode I energy restitution at the interface of 3D woven CMOs on Safran Aircraft Engines [12]. Meanwhile, AWJ processing of carbon/thermoplastic for repair surface preparations have not yet been studied, but we have begun preliminary testing on the feasibility of machining CF/PEEK by AWJ. The proposed project will be a first to investigate the effect of the AWJ process parameters on the final part quality. The hybrid digital twin of the depth of cut, the patch preparation and assembly method will leverage scientific knowledge and experimental measurements, to help choose the optimal process parameters as a function of the required repair. Moreover, We successfully demonstrated (1) ply-by-ply machining with low sensitivity to the initial contour/distortion of the part, (2) reduced dust emissions during machining, (3) lower damages to the fibers while maintaining fiber group integrity and the local fiber level heterogeneity, (4) surface texturing capabilities, (5) relatively low machining temperatures, and (6) machine mobility for machining on the tarmac.
When it comes to the patch assembly, the considered repairs focus on the non-bolted/non-riveted assemblies of composite materials, which include adhesive film bonding. However, to the best of our knowledge, the assembly quality of carbon/thermoplastics under the influence of surface topography for adhesive bonding has not been investigated, particularly in the context of repair. In this context, an accurate original numerical simulation, coupled to experimental augmentation, will allow us to understand and optimize the details and surface roughness and will qualify the nature of the flow during the crushing phase.

Considering the repair patch fabrication, patches are traditionally prepared by one of two means: pre-cured hard patches or in-situ wet layup with prepreg layers. The latter is preferable since, currently, prepreg laminates are manually cut according to the desired scarf geometry, manually positioned into the scarf cavities, and cured with adhesive bonding to ensure effective load distribution with the parent structure. This is currently the adopted procedure for commercial aircrafts Boeing 787 and Airbus 350 engine nacelles [13]. However, the process is dependent on the manual expertise of the workers, to ensure accurate geometrical tolerances during cutting and fiber orientations of each layer.
Therefore, we propose the development of a digital twin of the abrasive water jet machining for built-to-order patch geometries and surface topography. Despite multiple investigations on the influence of abrasive water jet rocess parameters on build quality [13, 14], the last has never been applied for the repair of carbon/thermoplastics (i.e., repair patch fabrication and structural evaluation of the repair). Therefore, a reliable hybrid twin of the process is required to democratize its use in the aircraft industry. Closed repair geometries are governed by the size of the initial damage and geometry, which can lead to a variety of patch shapes, such as circular, elliptical, or rectangular with rounded corners. In these cases, AFP will require dedicated tape placement strategies to limit discrepancies between the designed and actual patch peripherals, which are the most sensitive zones for defining repair quality as they represent the interface zone between the parent part and the repair patch.

The novelties of this research proposal can be found in (1) the target work material that offers greater sustainability potential and involves different mechanical properties due to different material properties and manufacturing processes (by automated fibre placement) that will react differently to AWJ processing and (2) the integration of the AWJ manufacturing process with a DT framework that will unlock beneficial visuals and tool path planning for processing CFRPs with AWJ. While DTs for manufacturing processes are widely available for various processes involving complex geometries, particularly seen in additive manufacturing, the DT has not been implemented for AWJ machining that involves a unique combination of process parameters like the water jet flow profile and the Gaussian-like particle interaction. The prospect of the project delivering a demonstrator is highly probable given the added precision and control of our proposed methodology as compared to traditional manual machining.