Abstract

One of the main problems associated with the manufacture of composite materials by liquid moulding (injection, infusion, etc.) is the generation of porosity. The optimization of the properties of the composites passes through a better understanding of the mechanisms of pore formation and transport. This pore formation is associated with a non-homogeneity of resin flow during the manufacturing process as a consequence of the double-scale porosity present in textile preforms. In the channels between bundles of fibers, the resin flows controlled by the pressure gradient and its viscosity. However, within the fiber bundles, the resin flows as a result of the capillary pressure. As a consequence, if the viscous and capillary forces are not balanced, non-homogeneous local flow occurs and the formation of pores, either between the fiber bundles, or internally to the bundles is produced.In this work a systematic study of the spontaneous wetting process of an E glass fiber bundle through wicking tests, using several fluids with different properties, viscosity, surface tension and contact angle is presented. The visualization of the front position of the resin flow at microscopic scale, as well as the formation of the menisci between fibers has been performed using X-ray tomography techniques using synchrotron radiation. The reconstructed volumes have made it possible to obtain detailed quantitative information on the geometry of the menisci which occur as a consequence of the surface tension operating at such scale. These characterization techniques constitute a fundamental tool for the optimization of the processing of composite materials buy liquid moulding.

Abstract

Carbon fibre reinforced polymer composite material structures continue to be, despite the tremendous technological maturity achieved in recent decades, one of the most promising options to address the challenges of the aeronautical industry with respect to behaviour in the face of efforts such as improvements, regarding weight or costs.

Ongoing demands to address major societal challenges, promote industrial leadership in Europe, and address aviation decarbonisation for the purpose of protecting the environment drive the demand for more optimal materials designed to improve these aspects.

The previous tasks carried out to complete the test campaign will be described, showing its plan and design, details of preparation, assembly of the specimens and the execution of the tests. The philosophy proposed by Airbus (ADS) is presented with the consolidation of admissible design against alterations of the material that could realize its evolution or arise in the manufacturer's batches.

Observing changes in the material, leading to the improvement of its mechanical and handling characteristics, a comparison has been made by Airbus with the one used previously for the determination of admissible design. It is intended to incorporate assessments of effects associated with the process of its industrialization. Once the results and analyzes are available, the normalized results of the conclusions would be presented.

The activity carried out is included within the CERES project (Advanced Rear End Structural test program), belonging to the Clean Sky 2 Joint Undertaking European research aeronautical program.

Abstract

The aim of this project had been the infusion specimens manufacturing to support design, analysis and qualification for the “Outcome Lower Skin” pyramid structural tests inside the Clean Sky 2 programm. It is the reinforcement lower skin structural tests pyramid for the C295 military aircraft from Airbus Defence & Space.

Along the project UD dry fiber manufacturing process had been developed until to obtain an automatic, robust and efficiency process in order to be able to manufacture a lower skin with stringers and spars integrated and that will be able to compete with the typical prepreg process with regard to fabricability, ratio, performance and cost.

The manufacturing process includes the dry fiber pre-forms automatic lay-up by AFP (Automated Fiber Placement), a hot-forming process for the stringers and finally a process infusion by VAP (Vacuum Assisted Process). To achive this goal, the AFP has been set up to optimize the laying parameters for the processing of the material to be used (½” Hexcel Hi-Tape fiber) and RTM6 resin. On the other hand, several tests of hot forming had been carried out modifying process variables, and several infusion bags configurations had been used to stringers and skin integration by infusion (VAP) until to find the key process parameters to obtain valid parts for the structural test pyramid.

Abstract

Airbus Defence and Space está desarrollando una sección del cajón de torsión del ala en fibra de carbono e infusión de resina epoxi para el protipo FTB#2 del Programa de I+D europeo Clean Sky 2. Se integran, en una sola parte de infusión, el revestimiento inferior con larguerillos, y los largueros anterior y posterior. Se emplea laminado automático de fibra seca y conformado en caliente los largueros, larguerillos y rigidizadores previo a la infusión.

Este artículo muestra el concepto de diseño, pasos y logros alcanzados, de cara al objetivo final de conseguir el TRL6 en el prototipo del Clean Sky 2.

Las pruebas de fabricabilidad han crecido gradualmente en completjidad hasta llegar a producir subcomponentes representativos de una sección altamente integrada para un cajón de ala.

Se ha caracterizado el material seleccionado, y se esstá completando la piramide de ensayos estructurales; desde los cupones (ensayos ya terminados), pasando por los subcomponentes (también finalizados) a falta del ensayo “full scale” a carga última de una sección completa del ala exterior.

Abstract

Conventional continuous fiber reinforced polymer composites (FRP) have extensively been used as structural elements in a myriad of sectors, such as civil, transport, energy and marine, among other, due to their superior mechanical properties, low weight and ease of processing. However, the relatively weak compression and interlaminar properties of these composites limit their application field. Interest is, therefore, growing in the development of hierarchical or multiscale composites, in which, a nanoscale filler reinforcement is utilized to alleviate the existing limitations associated with the matrix dominated properties. The majority of the work has focused on carbon nanotubes, CNTs due to their extraordinary intrinsic properties. In addition to their outstanding mechanical properties, CNTs possess excellent electrical and mechanical properties, making them attractive materials as reinforcement for polymer matrices. CNTs provide both intralaminar and interlaminar reinforcement, thus improving delamination resistance and through thickness properties, without compromising in-plane performance. In recent years, there has been an increasing interest in the use of graphene as reinforcement of polymer nanocomposites. Compared to CNTs, graphene has advantages such as lower cost, higher surface area and a greater ease of processing. Graphene is more easily dispersed in the resin and causes a lower viscosity increase, which can facilitate the impregnation of the fibers. In this work, the fabrication and characterization of hierarchical composites are analyzed through the inclusion of graphene to conventional continuous carbon fiber reinforced epoxy composites by vacuum-assisted resin transfer molding.

Abstract

The current work has been performed in the context of FUSINBUL, an European project framed within CleanSky2 research programme funded by the EU’s Horizon 2020 (Grant Agreement nº 831946). The scope of this project is to accomplish the full barrel demonstrator tests, needed to certify the new conception of fuselage created and manufactured in the Green Regional Aircraft context. Two advanced manufacturing processes for composites materials (prepreg cobonding process in autoclave and LRI infusion process out of autoclave) are developed and validated to achieve full scale innovative pressure bulkheads for Regional Aircraft Fuselage barrel on-ground demonstrators. The design of the tooling has taken into account the main needs of both manufacturing processes to carry out the bulkheads and the industrial requests. In addition to this, innovative tool technologies have been developed and applied, such as cast aluminium by lost foam casting, precise but robust indexing system split and seal system of tool too large to be fabricated one shot, then precisely assembled with no gap or step. For both manufacturing processes, the most advanced techniques of lay-up are used to reduce labor costs and increase the level of industrialization in serial production to achieve bulkheads with a diameter of 3.5m and the required standards in aeronautical industry.