Abstract

Abstract

Thermoplastic composite materials present advantages over thermoset materials since they can be re-shaped, which is a benefit in terms of recyclability and sustainability for the aeronautical industry.

It is possible to achieve a high level of integration in thermoplastic structures by developing new joining techniques such as welding processes, since the use of traditional methods to join thermoplastic composites is technically complex and results in high costs.

Welding is defined as the process of obtaining a new consolidation of the material by integrating differentiated surfaces resulting in the ability of transferring loads through the interface, due to the cross-linking of the polymer chains in the welded area. The quality of welded parts is comparable to the quality of parts consolidated in press or oven processes.

There are different welding technologies for thermoplastic composite materials depending on the heat transfer method along the welding interface. 

FIDAMC, together with Aciturri, has worked on the development of a conduction welding method on thermoplastic composite material, LMPAEK, within the framework of the NEOTAIL project "New Optimized Empennage with Advanced Technologies for Laminarity Integration". The welding process has been set-up on flat panels that represent the integration of the stringer foot on a skin, supported by numerical results of a simplified model made in Abaqus. The welded specimens have been tested obtaining mechanical properties above 80% with respect to the reference value considered. Finally, an omega stringer and a C-section spar have been welded on a skin, as an example of aeronautical application. This demonstrates FIDAMC capability to manufacture parts in thermoplastic composite material with a high level of integration

Abstract

The awareness for developing an eco-friendly industry based on green materials, sustainable technologies and optimum process with less environmental impact are a general societal consciousness, but it is still a considerable challenge to achieve. The biodegradable structural materials can contribute to reduce the CO2 emissions, the carbon footprint and increase the concept of recyclability for structural applications. In terms of performances, the natural fiber reinforced composite material could become in worthy alternative to E-Glass composite, wood reinforced materials and aluminum alloys because of their good ratio between mechanical properties, density and cost. However, the structural engineering applications are still very limited mainly because the lack of a robust manufacturing process. For that purpose, it has been developed an innovative mechanical extraction methodology based on the morphology of two species of bamboo, along with the optimization of the melting parameters to manufacture a fully biodegradable Bamboo-PLA composite. Furthermore, in order to define the future applications, the mechanical properties have been analyzed under different thermal cycling conditions.

Abstract

During the last years, the benefits of using carbon reinforced thermoplastic composite materials (CRTP) have been questioned and defended (higher fatigue resistance, greater toughness, better durability, reprocesability, recyclability and so on), they are considered as a future innovative technology allowing  highly integrated structures, impacting in weight reduction and reducing energetic costs by using out of autoclave processes. Therefore, (CRTP) could be considered as a future substitute of metallic materials and composite materials with thermoset matrices for aerospace applications, automotive and other industries.

Under the frame of the OUTCOME project (Clean Sky II), the design and analysis of the Upper Skin (upper coverage of a stiffened wing) for the militar aircraft C295 is developed, a medium tactical transport aircraft of ADS.

The selected material for the work is the unidirectional composite material APC2/AS4, supplied by Solvay, with PEEK as the thermoplastic matrix and carbon fibre as the reinforcement. Flat panels, detailed elementals and subelementals have been manufactured, all of them have been widely characterized attempting to obtain the required design allowables. 

Moreover, with the goal of cost reduction, productivity increases and environmental impact control, the manufacturing selected processes have been: a)  Hot-forming in oven and/or self heated toolings for stringers manufacturing and b) Automatic lamination in one step for the co-consolidation (full-integration) of the skin with the stringers.

The main goal of this review is showing the different steps in the manufacturing of a detailed element for a later structural test. 

Abstract

Fiber bridging is a mechanism that may significantly alter the fracture behavior of composite laminates, adhesively bonded laminates, welded laminates, and co-consolidated laminates. It is therefore quite important for the finite element to take that mechanism into consideration. Such models have been developed for thermosetting laminates; however, this is not the case for thermoplastic laminates and thermoplastic joints. In the present work, a numerical model based on the cohesive zone modelling (CZM) approach has been developed to simulate mixed-mode fracture of co-consolidated thermoplastic laminates by considering fiber bridging. A modified traction separation law of tri-linear form has been developed by superimposing the bi-linear behaviors of the matrix and fibers. Initially, the data from mode I (DCB) and mode II (ENF) fracture toughness tests were used to construct the R-curves of the joints in the opening and sliding directions. The aforementioned curves were embedded into the numerical models through a user-defined material subroutine developed in the LS-Dyna FE code, in order to extract the fiber bridging law directly from the simulation results. The model was used to simulate fracture of a Single-Lap-Shear (SLS) specimen in which a considerable amount of fiber bridging was observed on the fracture area. The numerical results show that the developed model presented improved accuracy in comparison to the CZM employing the bilinear traction-separation law.

Abstract

Rib-AM project aims to contribute to the development of novel in-situ manufacturing technologies applied to large size components of primary structure of aircrafts. Framed in Clean Sky 2, the activities within Rib-AM are set out to develop a leading-edge (LE) concept based on reinforced thermoplastic materials avoiding mechanical joints between the skin and the ribs. Induction Welding (IW) process has been selected for the integration of the ribs into the leading-edge structure. The development of an appropriate IW process methodology, including the introduction of magnetic flux concentrators and new coil designs, are key to assure the quality and structural integrity of the produced joints.

In this research, the mechanical strength of induction welded thermoplastic composites have been evaluated at sample level. Characterization specimens have been obtained by welding: (i) short carbon fiber reinforced polyether ether ketone (SCFR/PEEK), with 10 % carbon content, processed by additive manufacturing – fused deposition modeling; and (ii) multidirectional carbon fiber reinforced polyether ether ketone (CFR/PEEK) laminates processed by oven consolidation. The mechanical characterization of the strength has been carried out by means of the block shear test method. In addition, light optical microscopy has been performed to analyse the SCFR/PEEK - CFR/PEEK interface. Infrared thermography (IRT) has been considered for the non-destructive characterization of the welded joints to evaluate the feasibility of being applied as an inspection method for induction welded structures. IRT results have been validated by X-ray computed tomography.

Abstract

The OUTCOME Thermoplastic Upper Skin consortium is a European project framed within the Airframe ITD research platform of CleanSky2, funded by the EU's Horizon 2020 program. It is focused on developing, manufacturing, and validating a thermoplastic composite upper wing skin for future application in Airbus Defence and Space transport aircraft.

The upper skin consists of a stiffened panel of approximately 4 meters in length, with six integrated stringers. These elements were joined through a co-consolidation process, where they were welded simultaneously with the tape layup of the skin using In-Situ Consolidation (ISC). The integrated stringers were manufactured in a previous stage using an oven consolidation process. The skin lamination was carried out through ISC using an automated tape laying equipment such as AFP MTorres, assisted by a laser and utilizing PEEK APC-2/AS4 material with a ¼" tow width.

Throughout the project, a campaign of structural tests was conducted to obtain the mechanical properties and allowable values for the design of the outer wing box's upper skin. Detailed and subcomponent specimens (stiffened panels) were also designed, manufactured, and tested with the aim of validating the design, analysis methodology, manufacturing method, and quality control procedure. The activity will conclude at the end of the year with the ground structural testing of the wing box, of which the element is a part, completing the testing pyramid.