Dynamics and criteria of CFRP destruction by lightning currents

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The article discusses a promising conductive composite material such as carbon-plastic. This material has significant strength, not inferior to metal, has a low specific weight and has interesting electrophysical characteristics. For a wider use of the material in various structural products, it is necessary to consider its unique characteristics. The work is devoted to the study of the conductive properties of carbon fiber under the influence of lightning currents and the development of criteria for its destruction. Based on two models of destruction of CFRP by lightning currents, a theoretical analysis of its destruction has been carried out. The first model considered the composite material as a continuous medium with anisotropic-conducting properties. The solution of the Laplace equation with the Neumann boundary conditions made it possible to find the distribution of current densities over the material and theoretically determine the radius and depth of damage. The second model, the layered structure model, took into account the structure of real CFRP. The dynamics of layer-by-layer destruction is considered on the basis of the equivalent circuit of carbon fiber reinforced plastic, which takes into account the longitudinal and transverse resistivity of the composite. The distributions of the radial current density along the radius and depth of the material are constructed and the analysis of the spreading of currents at various degrees of material anisotropy is carried out. Strong anisotropy, leading to the release of total energy in the first layer. Destruction of the upper layer changes the distribution of currents in the rest of the layers. The results of numerical modeling of layer-by-layer destruction of CFRP for five layers are presented. The process of destruction under the action of large current pulses is considered. The fracture criteria for various degrees of material anisotropy are obtained and refined. The resulting formulas contain values that are reproduced in the experiment. The calculation results are in good agreement with experiment. In conclusion, it is concluded that the criteria are applied to predict the effects of lightning and optimize lightning protection at the design stage of an aircraft.