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• Evaluation of impact resistant composites for aircraft cockpit

  R. Rocha, L. Pina, M. Gomes, J. Sousa

  Materiales Compuestos (2022). Vol. 04 - Comunicaciones Matcomp19 (2020), (Núm. 1 - Avances en Materiales Compuestos. Nuevos Campos de Aplicación.), 58

  
  

  Abstract

  Several impact events are known to affect the aircrafts airworthiness, namely, bird or hail strike and impacts from uncontained engine rotor failure or other metal debris. Therefore, improvement of impact protection solutions for the cockpit, front and lateral panels is required, capable of endure such events without weight penalty. Several manufacturing technologies were implemented and tested up to 200 m/s with a compressed air gas cannon assembled a smooth bore barrel of 4 meters. Steel and hail spheres were used as projectiles and driven with a sabot. A digital chronograph and two high-speed cameras provide the impact velocities. Ultrasonic phase-array and x-ray inspection were performed to assess the damage. Evaluation was performed by comparison with the provided baselines. Among the tested solutions, carbon fibers impregnated with an epoxy resin doped with carbon nanotubes presented the best energy absorption performance for hail impacts. On the other hand, for metal sphere impacts, a fiber metal laminate solution made of aluminium and Dyneema® present the best behaviour.

  Abstract
  Several impact events are known to affect the aircrafts airworthiness, namely, bird or hail strike and impacts from uncontained engine rotor failure or other metal debris. [...]

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• Comparative study on methods for obtaining voids, fibre and resin percentages in composite materials

  M. Jiménez, P. Morón, D. Alfaro, J. Sánchez, . K.Muñoz, F. Simón, L. Vicente

  Materiales Compuestos (2022). Vol. 04 - Comunicaciones Matcomp19 (2020), (Núm. 1 - Avances en Materiales Compuestos. Nuevos Campos de Aplicación.), 59

  
  

  Abstract

  Manufacturing quality in composite laminates is one of the key aspects to have in consideration when producing aerostructures. For composite structures quality evaluation, an iterative process of qualification of the first items manufactured is often followed. Thus, the manufacturing process parameters can be tuned until achieving an incremented maturity level that ensures the structure mechanical properties present values within the defined quality standards. Volume fraction of voids (pores), resin and fibre is part of the set of properties that must be verified, especially in novel and/or low cost manufacturing processess that can affect the structural behaviour. The ability to obtain results depending on the technique used for testing becomes very important at this point. This study proposes a comparative analysis of the measurement of voids, fibre and resin percentage on carbon fibre reinforced polymers by automated image analysis technique and acid digestion method, varying parameters of the test procedure with the purpose of evaluating their influence in the correct determination of volume fractions. The use of different methods and parameters allows to analyze comparatively the different results obtained and shows advantages and disadvantages of both methods as well as provides valuable information on the best practices for correct test execution following each procedure.

  Abstract
  Manufacturing quality in composite laminates is one of the key aspects to have in consideration when producing aerostructures. For composite structures quality evaluation, [...]

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• Composite materials for the railway sector

  M. Ordóñez, X. Valor, . C.Eraso, M. Seco, I. Echevarria, E. Bellvert, R. Villoria

  Materiales Compuestos (2022). Vol. 04 - Comunicaciones Matcomp19 (2020), (Núm. 1 - Avances en Materiales Compuestos. Nuevos Campos de Aplicación.), 77

  
  

  Abstract

  The intrinsic properties of composite materials make their use especially attractive for different industries, especially in the transport sector, where the reduction of weight and the consequent reduction of energy consumption are key factors. The main problem to implement composite materials within the railway sector is that each component and assembly in the complete train needs to fulfil the Fire, Smoke and Toxicity (FST) requirements described in standard EN 45545-2. At present, there are very few resins that comply with this regulation, due to the recent incorporation of this normative which was approved in 2013 and the resins that manage to comply with it are highly doped that it is difficult to obtain good manufacturing results with them. A preliminary selection of the materials validated by the railway industry will be carried out. Moreover, it will be necessary to develop a study and characterization of the different options in order to find the best possible choice according to the different applications. This way, materials will be evaluated in terms of processability, physical-chemical and mechanical properties. For preimpregnated materials, the properties obtained with different curing processes will be analyzed: Oven Cure and Autoclave (only as a comparative reference). The objective is to get a preliminary evaluation and compare the different materials between each other.

  Abstract
  The intrinsic properties of composite materials make their use especially attractive for different industries, especially in the transport sector, where the reduction of weight [...]

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• Manufacture of aluminum composite materials reinforced with carbon fibers

  J. Bedmar, B. Torres, M. Sanchez, P. Rodrigo, A. Ureña, J. Rams

  Materiales Compuestos (2022). Vol. 05 - Comunicaciones Matcomp19 (2021), (Núm. 3 - Procesos de Fabricación – Materiales Funcionales.), 79

  
  

  Abstract

  The aluminum and its alloys stand out thermal conductivity and good mechanical properties, which, combined with a low density, high environmental resistance and a reasonable cost, makes them very suitable for multiple applications. In spite of this, different applications, such as In the case of LED-based lighting systems, it is necessary to increase the thermal conductivity; while the transport sector demands to improve its mechanical properties, like rigidity and strength. To meet these requirements aluminum composite materials reinforced with unidirectional carbon fiber and woven have been developed, initially manufacturing pieces of simple geometry, but coming to manufacture complex elements, such as luminaires or clutch housings, with improved mechanical and thermal properties compared to those manufactured without reinforcement meeting the demands of this class of applications. The process used has been based on the injection of high pressure aluminum on the dry tissue giving rise to a very fast and efficient process in which the formation of fragile interfaces is avoided and there are no viscosity problems, such as those that occur in the manufacturing processes most commonly employed. In conclusion, through a process of high pressure injection of aluminum on carbon fibers, unidirectional or fabrics, pieces of metal matrix composite material that have superior thermal and mechanical properties with respect to uncoated aluminum alloys have been manufactured.

  Abstract
  The aluminum and its alloys stand out thermal conductivity and good mechanical properties, which, combined with a low density, high environmental resistance and a reasonable [...]

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• Modeling and analysis of hybrid energy absorption devices for aircraft structures

  J. Paz, J. Díaz, L. Romera

  Materiales Compuestos (2022). Vol. 04 - Comunicaciones Matcomp19 (2020), (Núm. 1 - Avances en Materiales Compuestos. Nuevos Campos de Aplicación.), 63

  
  

  Abstract

  The design of structures according to impact protection or crashworthiness criteria aims for maximum kinetic energy dissipation through progressive component collapse, with the ultimate goal of minimizing the acceleration peaks suffered by occupants. One of the common trends for reducing accelerations in aircraft structures is that of including collapsible absorbers within the main structural design. This communication focuses on the crushing analysis through numerical simulation of thin-walled hybrid energy absorbers. These absorbers combine a confining metallic tube with a core made from composite materials and high-density structural foam. The components are characterized with different crashworthiness metrics, including the energy absorbed by the device or the peak force during the crushing process. The usage of hybrid elements delivers a significant enhancement compared to the single-component counterparts, improving the structural behavior of the aircraft under impact loading and better protecting the occupants. Results show that, at the component level, the usage of inner reinforcements modifies the collapse mechanism of the specimen and increases the specific energy absorption of the device, mainly rooted in the interaction effect between the core and the confining tube. 

  Abstract
  The design of structures according to impact protection or crashworthiness criteria aims for maximum kinetic energy dissipation through progressive component collapse, with [...]

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• FEM simulation of stiffened structures with pultruded carbon fibre profiles

  R. Páez, M. Vázquez, . P.Astola

  Materiales Compuestos (2022). Vol. 04 - Comunicaciones Matcomp19 (2020), (Núm. 1 - Avances en Materiales Compuestos. Nuevos Campos de Aplicación.), 64

  
  

  Abstract

  Simulation of composite structures through Finite Elements Method (FEM) is widely used in the aeronautics sector to reliably predict its performance. The incorporation of new materials with enhanced properties, and also new manufacturing processes usually require the use of such tools for validation. This work has been focussed on studying an emerging technology such as Pultrusion for stiffeners manufacturing. For this, it has been used a demonstrator based on a common airframe structure, panels stiffened with profiles. This time, the classic stiffener manufactured using prepreg and autoclave cured has been replaced by stiffeners manufactured by Pultrusion. For that purpose, it was manufactured flat panels using prepegs and autoclave curing, for subsequently bond L shaped high resistance carbon fibre profiles manufactured by Pultrusion. Furthermore, FEM simulations were conducted over these coupons for three different mechanical testing conditions, tensile, compression and shear, aiming to determine the capability of these methods for simulating reliably the mechanical performance of pultruded materials on such above-mentioned structures. The results obtained in this work have been used for model parameter adjustments to obtain reasonable correlation levels, enabling the future usage of Pultrusion technology in the stiffener profiles manufacturing.

  Abstract
  Simulation of composite structures through Finite Elements Method (FEM) is widely used in the aeronautics sector to reliably predict its performance. The incorporation of [...]

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• Enhanced interlaminar fracture toughness of woven carbon fabric/epoxy composites by interleaving fluffy CNT veils

  Y. Ou, C. González, J. Vilatela

  Materiales Compuestos (2022). Vol. 04 - Comunicaciones Matcomp19 (2020), (Núm. 1 - Avances en Materiales Compuestos. Nuevos Campos de Aplicación.), 65

  
  

  Abstract

  While fiber reinforced polymer (FRP) composites are widely utilized in structural components due to their favorable mechanical properties, delamination between reinforcing plies remains a major problem, weakening the composite structure and limiting more widespread applications of FRPs. Carbon nanotubes (CNTs) carry the promise of enhancing this poor out-of-plane mechanical performance, although their integration has been challenging. In this work, macroscopic CNT veils with controlled nano-meso structure were drawn from the gas-phase using a semi-industrial process and then integrated into woven carbon fiber/epoxy matrix composites utilizing a facile and scalable approach. Interlaminar fracture toughness (ILFT) of the resulting composites was determined in Mode-I (opening mode) test. Additionally, crack propagation and interlaminar toughening mechanisms were systematically analyzed by means of optical microscope, SEM, and Raman analysis. The results showed that mode I ILFT was improved as much as 60% when interleaving as-received fluffy CNT veils and also revealed that interlaminar crossing between CNT veil/CF interfaces is of paramount importance in toughening mechanism.

  Abstract
  While fiber reinforced polymer (FRP) composites are widely utilized in structural components due to their favorable mechanical properties, delamination between reinforcing [...]

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• A new approach to attenuate low velocity impact damages on CFRP structures

  L. Amorim, A. Santos, J. Nunes, J. Viana

  Materiales Compuestos (2022). Vol. 04 - Comunicaciones Matcomp19 (2020), (Núm. 1 - Avances en Materiales Compuestos. Nuevos Campos de Aplicación.), 66

  
  

  Abstract

  Carbon Fibre Reinforced Polymers (CFRP) have been widely used in advanced markets, such as, the aeronautic, aerospace and military ones. Despite their extraordinary mechanical properties and low density, advanced composites, due to their intrinsic brittleness and layer-by-layer nature, present some vulnerability when submitted to impact, dynamic and flexural loading. Low velocity impacts (LVI) are one of the most dangerous events that composite laminate can face in their life time. These solicitations may develop imperceptible internal laminate damages, namely delaminations, that tend of propagate in service, compromising part performance. In order to improve interlaminar crack propagation, some works were already carried out using interleaved thin veils between laminate layers to enhance the interlaminar Mode I and II fracture toughness. In this work, a study was carried out on the distribution of stresses across the thickness of a carbon/epoxide laminate typically used in structural aircraft components, to define between which specific layers would be better to interleave thin veils made from four different materials (glass, carbon, aramid and polyester) to achieve better LVI damage tolerance. Samples made from the selected structural carbon/epoxy laminate were then produced by vacuum bag infusion with those thin veils located between their most appropriated layers to be submitted experimental testing and compare their mechanical and LVI performances with those without using interleaved veils. All studied laminates were observed under scanning electron microscopes (SEM) for assessing their processing quality and submitted to interlaminar shear strength (ILSS) and LVI tests to evaluate their delamination resistance and impact response, respectively.

  Abstract
  Carbon Fibre Reinforced Polymers (CFRP) have been widely used in advanced markets, such as, the aeronautic, aerospace and military ones. Despite their extraordinary mechanical [...]

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• Interlaminar fracture toughness of 3D printed continuous carbon fibre- reinforced polyamide

  M. Iragi, C. Pascual-Gonzalez, A. Esnaola, J. Aurrekoetxea, C. Lopes, L. Aretxabaleta

  Materiales Compuestos (2022). Vol. 04 - Comunicaciones Matcomp19 (2020), (Núm. 1 - Avances en Materiales Compuestos. Nuevos Campos de Aplicación.), 67

  
  

  Abstract

  In this study, the interlaminar fracture toughness of 3D printed continuous carbon fibre-reinforced polyamide was characterized under Mode I and II loadings. 3D printing of fracture test samples presents difficulties, mainly shrinkage and excessive warping. To minimize these effects, two solutions were developed. The results show that the Mode I interlaminar fracture behaviour of the printed samples is similar to that obtained by hot compression moulding. In mode II, however, propagation is not effective due to the type of microstructure of the 3D printed material. The hot pressing of the printed material reduces the fracture toughness under Mode I, but significantly improves the fracture toughness under Mode II. The causes of these behaviours are discussed in the paper.

  Abstract
  In this study, the interlaminar fracture toughness of 3D printed continuous carbon fibre-reinforced polyamide was characterized under Mode I and II loadings. 3D printing of [...]

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• Large Lifting surface optimized in cost and weight, for high rate production

  A. Pérez, V. García, M. Motilva, P. Nogueroles

  Materiales Compuestos (2022). Vol. 04 - Comunicaciones Matcomp19 (2020), (Núm. 1 - Avances en Materiales Compuestos. Nuevos Campos de Aplicación.), 68

  
  

  Abstract

  Commercial aviation is evolving towards high production rates in an increasingly competitive environment. The structures of composite materials offer the best performance in weight but, in this scenario, they have to do it with robust industrial processes and competitive costs. With this objective and thanks to the contribution of the Spanish goverment trough CDTI, a very effective collaboration was organized between Airbus, pushed by the initiative of the spanish comercial part, FIDAMC, the Technology center linked to Airbus in Spain, MTorres, a recognized supplier of composite industrial equipment and Hexcel, one of the lead suppliers of high performance composite materials. The Project, known as HDPREG, has allowed, trough a complete test pyramid, the development of a material, a new automatic lamination head and a manufacturing process, all adapted for the production of large lifting surface parts for aircraft use and compatible with the mentioned requirements. As a final exercise, beyond the scope of the project, FIDAMC, MTORRES and HEXCEL, funded the manufacture of an 18 m real-scale component, demonstrating the very high lamination productivity, as well as the feasibility of the application of the new material and the innovative manufacturing processes to meet the demands in terms of cost, weight, and industrial robustness.

  Abstract
  Commercial aviation is evolving towards high production rates in an increasingly competitive environment. The structures of composite materials offer the best performance [...]

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