Modeling Lightning Impact Thermo-Mechanical Damage on Composite Materials
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Modeling Lightning Impact Thermo-Mechanical Damage on Composite Materials Raúl Muñoz & Sofía Delgado & Carlos González & Bernardo López-Romano & De-Yi Wang & Javier LLorca
Received: 15 November 2013 / Accepted: 12 December 2013 # Springer Science+Business Media Dordrecht 2014
Abstract Carbon fiber-reinforced polymers, used in primary structures for aircraft due to an excellent strength-to-weight ratio when compared with conventional aluminium alloy counterparts, may nowadays be considered as mature structural materials. Their use has been extended in recent decades, with several aircraft manufacturers delivering fuselages entirely manufactured with carbon composites and using advanced processing technologies. However, one of the main drawbacks of using such composites entails their poor electrical conductivity when compared with aluminium alloy competitors that leads to lightning strikes being considered a significant threat during the service life of the aircraft. Traditionally, this problem was overcome with the use of a protective copper/bronze mesh that added additional weight and reduced the effectiveness of use of the material. Moreover, this traditional sizing method is based on vast experimental campaigns carried out by subjecting composite panels to simulated lightning strike events. While this method has proven its validity, and is necessary for certification of the structure, it may be optimized with the aid provided by physically based numerical models. This paper presents a model based on the finite element method that includes the sources of damage observed in a lightning strike, such as thermal damage caused by Joule overheating and electromagnetic/acoustic pressures induced by the arc around the attachment points. The results of the model are compared with lightning strike experiments carried out in a carbon woven composite. Keywords Carbon fiber laminates . Lightning impact . Damage modeling . Finite element method
R. Muñoz : C. González : D. > < 0 2 2 r < Rc 4π Rc ð8Þ pðr; tÞ ¼ 2 > μ > : 0 I ðtÞ r > Rc 4π2 r2 where r is the radial distance to the attachment point of the lightning, μ0 =4π×10−7 N/A the magnetic permeability and t the time [6, 15], Fig. 6a. It should be noted that the magnetic pressure was assumed to be constant within the arc radius, following standard approximation [15]. For instance, a typical A waveform peak amplitude of 200 kA injected with an arc radius of Rc =5 mm yields a maximum pressure at the arc root of the order of ≈50 MPa. This maximum pressure is approximately constant within the arc radius and decays with the inverse of the square of the radial distance to the arc attachment. Another possible source of mechanical damage during lightning strikes is acoustic overpressure. Lightning releases large amounts of energy (of the order of ≈104 to 105 J/m) in a short period (1 to 10 μs) and into a relatively small volume of air. Therefore, the air in the ionized channel is heated almost instantaneously to extremely high temperatures, creating high pressures of the expanding p
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