Uso de diversos materiales en el Boeing 787 Dreamliner. [1]

Los materiales compuestosWson ampliamente utilizados en la industria aeronáutica y han permitido a los ingenieros superar los obstáculos que se han encontrado al usar los materiales individualmente. Los materiales constituyentes conservan sus identidades en los compuestos y no se disuelven ni se fusionan completamente entre sí. Juntos, los materiales crean un material "híbrido" que ha mejorado las propiedades estructurales.

El desarrollo de materiales compuestos ligeros y resistentes a altas temperaturas permitirá que se materialice la próxima generación de diseños de aeronaves económicas y de alto rendimiento. El uso de dichos materiales reducirá el consumo de combustible, mejorará la eficiencia y reducirá los costos operativos directos de las aeronaves.

Los materiales compuestos se pueden formar en varias formas y, si se desea, las fibras se pueden enrollar firmemente para aumentar la resistencia. Una característica útil de los compuestos es que se pueden estratificar, con las fibras en cada capa corriendo en una dirección diferente. Esto permite a un ingeniero diseñar estructuras con propiedades únicas. Por ejemplo, una estructura puede diseñarse para que se doble en una dirección, pero no en otra. [2]

Síntesis de composites básicos

Ejemplo de un material compuesto básico.

En un compuesto básico, un material actúa como una matriz de soporte, mientras que otro material se basa en este andamiaje base y refuerza todo el material. La formación del material puede ser un proceso costoso y complejo. En esencia, una matriz de material base se presenta en un molde a alta temperatura y presión. Luego se vierte unepoxioresinasobre el material base, creando un material fuerte cuando se enfría el material compuesto. El compuesto también se puede producir incrustando fibras de un material secundario en la matriz base.

Los compuestos tienen buena resistencia a la tracción y resistencia a la compresión, lo que los hace adecuados para su uso en la fabricación de piezas de aviones. La resistencia a la tracción del material proviene de su naturaleza fibrosa. Cuando se aplica una fuerza de tracción, las fibras dentro del compuesto se alinean con la dirección de la fuerza aplicada, dando su resistencia a la tracción. La buena resistencia a la compresión se puede atribuir a las propiedades adhesivas y de rigidez del sistema de matriz base. El papel de la resina es mantener las fibras como columnas rectas y evitar que se pandeen.

Aviación y compuestos

Los materiales compuestos son importantes para la industria de la aviación porque proporcionan una resistencia estructural comparable a las aleaciones metálicas, pero con un peso más ligero. Esto conduce a una mejor eficiencia de combustible y rendimiento de una aeronave. [3] [4]

El papel de los compuestos en la industria de la aviación

Uso de diversos materiales en el Boeing 787 Dreamliner. [1]

La fibra de vidrio es el material compuesto más común, y consiste en fibras de vidrio incrustadas en una matriz de resina. La fibra de vidrio se utilizó por primera vez ampliamente en la década de 1950 para barcos y automóviles. La fibra de vidrio se utilizó por primera vez en el avión de pasajerosBoeing707en la década de 1950, donde comprendía aproximadamente el dos por ciento de la estructura. Cada generación de nuevos aviones construidos por Boeing tuvo un mayor porcentaje de uso de materiales compuestos; el más alto es el 50% de uso compuesto en el787 Dreamliner.

ElBoeing 787 Dreamlinerserá el primer avión comercial en el que los principales elementos estructurales están hechos de materiales compuestos en lugar de aleaciones de aluminio. [1] Habrá un cambio de compuestos arcaicos de fibra de vidrio a compuestos de laminado de carbono y sándwich de carbono más avanzados en este avión. Se han encontrado problemas con la caja del ala del Dreamliner, que se han atribuido a la rigidez insuficiente en los materiales compuestos utilizados para construir la pieza.[1] Esto ha llevado a retrasos en las fechas iniciales de entrega de la aeronave. Para resolver estos problemas, Boeing está endureciendo las cajas de ala agregando nuevos soportes a las cajas de alas ya construidas, mientras modifica las cajas de alas que aún no se han construido. [1]

Ensayos de materiales compuestos

Se ha encontrado difícil modelar con precisión el rendimiento de una pieza compuesta por simulación por computadora debido a la naturaleza compleja del material. Los compuestos a menudo se superponen uno encima del otro para mayor resistencia, pero esto complica la fase de prueba previa a la fabricación, ya que las capas están orientadas en diferentes direcciones, lo que dificulta predecir cómo se comportarán cuando se prueben. [1]

También se pueden realizar pruebas de esfuerzo mecánico en las piezas. Estas pruebas comienzan con modelos a pequeña escala, luego pasan a partes progresivamente más grandes de la estructura y finalmente a la estructura completa. Las piezas estructurales se colocan en máquinas hidráulicas que las doblan y tuercen para imitar tensiones que van mucho más allá de las peores condiciones esperadas en vuelos reales.

Factors of composite material usage

Weight reduction is the greatest advantage of composite material usage and is one of the key factors in decisions regarding its selection. Other advantages include its high corrosion resistance and its resistance to damage from fatigue. These factors play a role in reducing operating costs of the aircraft in the long run, further improving its efficiency. Composites have the advantage that they can be formed into almost any shape using the moulding process, but this compounds the already difficult modelling problem.

A major disadvantage about use of composites is that they are a relatively new material, and as such have a high cost. The high cost is also attributed to the labour intensive and often complex fabrication process. Composites are hard to inspect for flaws, while some of them absorb moisture.

Even though it is heavier, aluminum, by contrast, is easy to manufacture and repair. It can be dented or punctured and still hold together. Composites are not like this; if they are damaged, they require immediate repair, which is difficult and expensive.

Fuel savings with reduced weight

Fuel consumption depends on several variables, including: dry aircraft weight, payload weight, age of aircraft, quality of fuel, air speed, weather, among other things. The weight of aircraft components made of composite materials are reduced by approximately 20%, such as in the case of the 787 Dreamliner.[4]

A sample calculation of total fuel savings with a 20% empty weight reduction will be done below for an Airbus A340-300 aircraft.

Initial sample values for this case study were obtained from an external source.[5]

Given:

  • Operating Empty Weight (OEW): 129,300kg
  • Maximum Zero Fuel Weight (MZFW): 178,000kg
  • Maximum Take-Off Weight (MTOW): 275,000kg
  • Max. Range @ Max. Weight: 10,458km

Other quantities can be calculated from the above given figures:

  • Maximum Cargo Weight = MZFW - OEW = 48,700kg
  • Maximum Fuel Weight = MTOW - MZFW = 97,000kg

So, we can further calculate the fuel consumption in kg/km based on maximum fuel weight and maximum range = 97,000kg/10,458km = 9.275kg/km

Following is the calculation for anticipated fuel savings with a 20% weight reduction, which will only reduce the OEW value by 20%:

  • OEW(new) = 129,300kg * 0.8 = 103,440kg, which equates to a 25,860kg weight saving.

Assuming that cargo and fuel weight remain constant:

  • MZFW(new) = MZFW - 25,680kg = 152,320kg
  • MTOW(new) = MTOW - 25,680kg = 249,320kg

The 97,000kg mass of fuel has a reduced MTOW to deal with, and thus will have increased range because maximum weight and maximum range are inversely proportional quantities.

Using simples ratios to calculate the new range:

249,320kg275,000kg=10,458kmXkm{\displaystyle {\frac {249,320kg}{275,000kg}}={\frac {10,458km}{Xkm}}}{\displaystyle {\frac {249,320kg}{275,000kg}}={\frac {10,458km}{Xkm}}}

Solving for X gives a new range of:

  • X = 11,535.18km

This gives a new value for fuel consumption with reduced weight = 97,000kg/11,535.18km = 8.409kg/km

To put this in perspective, over a 10,000km journey, there will be an approximate fuel saving of 8,660kg with a 20% reduction of empty weight.

Environmental impact

Recycling of parts from decommissioned aircrafts is possible.[6]

There is a shift developing more prominently towards Green Engineering. Our environment is given increased thought and attention by today's society. This is true for composite material manufacture as well.

As mentioned previously, composites have a lighter weight and similar strength values as heavier materials. When the lighter composite is transported, or is used in a transport application, there is a lower environmental load compared to the heavier alternatives. Composites are also more corrosion-resistant than metallic based materials, which means that parts will last longer.[7] These factors combine to make composites good alternate materials from an environmental perspective.

Conventionally produced composite materials are made from petroleum based fibres and resins, and are non-biodegradable by nature.[8] This presents a significant problem as most composites end up in a landfill once the life cycle of a composite comes to an end.[8] There is significant research being conducted in biodegradable composites which are made from natural fibres.[9] The discovery of biodegradable composite materials that can be easily manufactured on a large-scale and have properties similar to conventional composites will revolutionize several industries, including the aviation industry.

An alternative option to aid environmental efforts would be to recycle used parts from decommissioned aircraft. The 'unengineering' of an aircraft is a complex and expensive process, but may save companies money due to the high cost of purchasing first-hand parts.[6]

Future composite materials

Ceramic matrix composites

Major efforts are underway to develop light-weight, high-temperature composite materials at National Aeronautics and Space Administration (NASA) for use in aircraft parts. Temperatures as high as 1650°C are anticipated for the turbine inlets of a conceptual engine based on preliminary calculations.[3] In order for materials to withstand such temperatures, the use of Ceramic Matrix Composites (CMCs) is required. The use of CMCs in advanced engines will also allow an increase in the temperature at which the engine can be operated, leading to increased yield.[10] Although CMCs are promising structural materials, their applications are limited due to lack of suitable reinforcement materials, processing difficulties, lifetime and cost.

Spider silk fibres

Scientists have as of yet been unable to perfectly re-synthesize spider silk.

Spider silk is another promising material for composite material usage. Spider silk exhibits high ductility, allowing stretching of a fibre up to 140% of its normal length.[11] Spider silk also holds its strength at temperatures as low as -40°C.[11] These properties make spider silk ideal for use as a fibre material in the production of ductile composite materials that will retain their strength even at abnormal temperatures. Ductile composite materials will be beneficial to an aircraft in parts that will be subject to variable stresses, such as the joining of a wing with the main fuselage. The increased strength, toughness and ductility of such a composite will allow greater stresses to be applied to the part or joining before catastrophic failure occurs. Synthetic spider silk based composites will also have the advantage that their fibres will be biodegradable.

Many unsuccessful attempts have been made at reproducing spider silk in a laboratory, but perfect re-synthesis has not yet been achieved.[12]

Hybrid composite steel sheets

Another promising material can be stainless steel constructed with inspiration from composites and nanontech-fibres and plywood. The sheets of steel is made of same material and is able to handle and tool exactly the same way as conventional steel. But is some percent lighter for the same strengths. This is especially valuable for vehicle manufacturing. Patent pending, swedish company Lamera is a spinoff from research within Volvo Industries.

Conclusion

Due to their higher strength-to-weight ratios, composite materials have an advantage over conventional metallic materials; although, currently it is expensive to fabricate composites. Until techniques are introduced to reduce initial implementation costs and address the issue of non-biodegradability of current composites, this relatively new material will not be able to completely replace traditional metallic alloys.

References

  1. Saltar a: 1.0 1.1 1.2 1.3 1.4 1.5 Surface Modelling for Composite Materials - SIAG GD - Retrieved at http://www.ifi.uio.no/siag/problems/grandine/
  2. A to Z of Materials - Composites: A Basic Introduction - Retrieved at http://web.archive.org/web/20080806113558/http://www.azom.com/details.asp?ArticleID=962
  3. Saltar a: 3.0 3.1 INI International - Key to Metals - Retrieved at http://www.keytometals.com/Article103.htm
  4. Saltar a: 4.0 4.1 Boeing's 787 Dreamliner Has a Composite Problem - Zimbio - Retrieved at http://web.archive.org/web/20101002101128/http://www.zimbio.com:80/Boeing+787+Dreamliner/articles/18/Boeing+787+Dreamliner+composite+problem
  5. Peeters, P.M. et al. - Fuel efficiency of commercial aircraft (pg. 16) - Retrieved at http://www.transportenvironment.org/docs/Publications/2005pubs/2005-12_nlr_aviation_fuel_efficiency.pdf
  6. Saltar a: 6.0 6.1 National Geographic Channel - Man Made: Plane - Retrieved from http://channel.nationalgeographic.com/series/man-made/3319/Photos#tab-Videos/05301 00
  7. A study of the environmental impact of composites - Retrieved at http://web.archive.org/web/20060923103650/http://www.plastkemiforetagen.se/Publikationer/PDF/Composite_materials_in_an_environmental_perspective.pdf
  8. Saltar a: 8.0 8.1 Textile Insight - Green Textile Composites - Retrieved at http://www.textileinsight.com/articles.php?id=453
  9. A to Z of Materials - High Performance Composite Materials Produced from Biodegradable Natural Fibre Reinforced Plastics - Retrieved at http://www.azom.com/news.asp?newsID=13735
  10. R. Naslain - Universite Bordeaux - Ceramic Matrix Composites - Retrieved at http://web.archive.org/web/20101122114453/http://www.mpg.de/pdf/europeanWhiteBook/wb_materials_213_216.pdf
  11. Saltar a: 11.0 11.1 Department of Chemistry - University of Bristol - Retrieved at http://www.chm.bris.ac.uk/motm/spider/page2.htm
  12. Wired Science - Spiders Make Golden Silk - Retrieved at http://www.wired.com/wiredscience/2009/09/spider-silk/
Page data
Part of MECH370
Keywords aircraft, materials, materials processing
Authors B.S.Kukreja, Johan Löfström
Published 2009
License CC-BY-SA-4.0
Affiliations Queen's University
Derivatives Composites dans l'industrie aéronautique, Verbundwerkstoffe in der Flugzeugindustrie
Impact Number of views to this page and its redirects. Updated once a month. Views by admins and bots are not counted. Multiple views during the same session are counted as one.123,499
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