Carbonaceous materials for their use as aircraft lightning strike protection
- Autores: Guillermo Mokry López
- Directores de la Tesis: Juan Baselga Llido (dir. tes.), Zulima Martin Moreno (codir. tes.), Javier Pozuelo de Diego (codir. tes.)
- Lectura: En la Universidad Carlos III de Madrid ( España ) en 2020
- Idioma: español
- Tribunal Calificador de la Tesis: Mauricio Terrones (presid.), Francisco Velasco López (secret.), José Sánchez Gómez (voc.)
- Programa de doctorado: Programa de Doctorado en Ciencia e Ingeniería de Materiales por la Universidad Carlos III de Madrid
- Materias:
- Enlaces
- Tesis en acceso abierto en: e-Archivo
- Resumen
The main motivation behind this work, was to substitute the current technology used as lightning strike protection in the aircraft industry. This protection is composed of metallic meshes of foils, normally bronze, copper, and in some exceptional cases, for example in some fairings, aluminum in which cases, Glass Fiber Reinforced Polymer (GFRP) material will be added to avoid corrosion that direct contact between the Carbon Fiber (from the structural Carbon Fiber Reinforced Polymer material (CFRP)) and the Al might cause. The bronze mesh adapts better to parts with complex geometries and is cheaper than cooper materials, however, its electrical conductivity is lower than the ones exhibited by copper meshes or foils. For those areas that need, not only Lightning Strike Protection (LSP), but also electromagnetic shielding, copper mesh or foils will be used such as Expanded Copper Foils (ECF), which is an epoxy pre-impregnated expanded copper foil that allows automated placement on the CFRP part.
ECF weights vary from 73 gm-2 to 815 gm-2. The selection of the ECF weigh will depend on the substrate (type of CFRP with which the part is manufactured), the presence of other materials in the part (e.g. insulating GRFP), the thickness of the part, the zoning of the aircraft (components are classified into different zones according to the probability of receiving a lightning strike and to the current flow allowed by the component design), and on the function of the part in the aircraft. The weight will be chosen in order to reach the best electrical requirements with the minimum weight.
However, copper being such a dense element (8.9 gm-3) makes this technology relatively heavy. Being one of the main goals in the aerospace structures design, the reduction of weight and thus, the lower fuel consumption, a new material lighter than those currently in use for lightning strike protection appears as a great and interesting opportunity for the aircraft industry.
The material to replace the current solutions shall meet the following criteria: The overall density had to be smaller than the one of copper. If aircraft industry searched for an alternative, it would be to improve on the existing materials. A lower density material would reduce the overall weight of the protection system and would therefore reduce fuel consumption. Other metals with a lower density have been tried in the past, such as aluminum. However, it has been found that this metal in contact with the carbon fibers in the airframe structure, causes a severe galvanic corrosion which makes its use not recommended for lightning strike protection.
Conductivity had to be the same as copper: Copper being one of the best conductors, with a conductivity close to 6·107 Sm-1 [4], is the perfect material for lightning strike protection. When lightning strikes, this mesh or foil is able to conduct the current away from the striking point towards electrostatic dischargers and diversion traps. If a new material was to be found, it would have to be at least as conductive as pure copper.
The maximum current density of the material had to be at least the one of copper: when a lightning pass through a conductor, this conductor is subjected to a big current density across a small cross section area. If the maximum current density this material could withstand (ampacity) was to be higher, it would allow a reduction of the cross section of the conductor, reducing like this the overall weight and space required for the lightning strike protection system.
During the course of this project, several limitations have oriented this work in very concise directions; scalability, being this an important factor when deciding which techniques to use for the synthesis of the new material, as it had to be possible to produce the material for industrial use; cost, as any expense increase in the production step, would make the main motivation of reducing costs in the final airplane implementation step futile; manageability, being very important for the material to be easily handled and resistant, to allow and easy, and as much as possible automated, integration in the airframe structure. Finally, the choice of materials was also a very important factor to take into account during this project. As it has been stated, aluminum exhibited lower densities, but caused galvanic corrosion when they are in contact with carbon fibers. Using carbon fibers on their own might prove light and cheap, but the conductivity values are below the requirement to withstand lightning strikes, especially since carbon fibers in the aircraft structure are impregnated with polymeric resins. These factors suggested that using copper as a part of a hybrid material, could be the best alternative to the problem at hand. This thesis presents the work of how a hybrid material consisting of copper and carbon was synthesized, and the many combinations and techniques that were tried.
