Gilles Peres

Experimental and Numerical Methods to Characterize Electrical Behaviour of Carbon Fiber Composites Used in Aeronautic Industry

Carbon Fiber Reinforced Plastic materials are widely used in aeronautic industry because of their high strength to weight ratio, to replace metallic parts. As these materials are not as conductive as metal, there is an increasing need to characterize their electromagnetic properties in order to understand and anticipate direct or indirect effects of lightning and functional current return. Multilayer composite materials present a strong anisotropy due to the different type of material properties and fibers orientation. This has for consequence to create privileged paths for current circulation and possible voltage drops inside the material. The level of accuracy needed on electrical property of a CFRP part strongly depends on the way the CFRP material is electrically solicited (direct current injection, induced effects, illumination...) and consequently on its location and its function inside the aircraft structure. In addition, this level of accuracy depends also increasingly of the development stage of the aircraft: foreground project, mature design, certification, maintenance. For the above reasons, the importance of having adapted and flexible means of characterization becomes crucial. This chapter is divided in two main sections. The first section presents a general review of the main experimental techniques allowing electrical characterization of CFRP materials. The second starts by reporting existing numerical models of CFRP materials. Then, we present an original approach to simulate current distribution within the composite layup.

Numerical modeling support for the understanding of current distribution in carbon fibers composites

Composite materials have benefited from a strong increase of utilization in aeronautic industry. The replacement of metallic elements by CFRP ones involves to better control the current distributions into composite structures as their electrical conductivity is significantly lower than the those of metals. Numerical modeling appears to be of great interest when facing on high costs for lightning tests or impossibility to manufacture large composite mockups. The object of this paper is to present an original wired approach for modeling current distribution in a composite structure, in a frequency range comprised between the continuous up to few tens of MHz.

Effect of an upstream charge on flow electrification mechanisms of dielectric liquids

When the electric charge induced at the electrical double layer of a solid/liquid interface is transported by a liquid flow, a phenomenon known as flow electrification occurs and creates new charge to balance the interfaces electrical neutrality. In the context of an aircraft fuel tank being filled, this phenomenon is a generation source of electric charge on the tank wall. This charge is likely to accumulate if it is generated more efficiently at the walls than it relaxes to an electrical ground via an electrical path. In metallic fuel tanks, the charge relaxation is favored over the accumulation. However, the introduction of composite materials with different dielectric multilayers in the construction of future aircraft fuel tanks tends to reduce the relaxation of the charge and amplify the generation. Furthermore, the passage of the fuel through the upstream complex hydraulic and filtering circuits electrically charges the fuel before it enters the tank. This paper consists in analyzing the effects of an upstream charged liquid on the mechanisms of charge generation occurring at a downstream solid/liquid interface. This analysis is based on recent experimental observations for several solid/liquid couples within both cylindrical and rectangular laminar flow conditions.

From a single approach for A380 transfer functions determination to in-flight lightning measurements

This document presents the test method settled and applied for A380 lightning and low frequency HIRF transfer functions determination, deals with method evolutions necessary for composite aircrafts and is completed by in-flight lightning measurements system now available thanks to ILDAS project and its future application to A380.

In-strike dynamical measurements of contact resistances

Assemblies representative of aircraft junctions made of two materials and a fastener have been subjected to lightning current waveforms in laboratory. Current distributions on the different parts of the assemblies have been measured. An electrical equivalent circuit of the assemblies has been built. An inverse method has been designed to extract the dynamical in-strike electrical parameters (resistances, inductances, generators) of the circuit from the measured current distributions. It is shown in particular that the in-strike contact resistances between the different parts are systematically very small, even when the pre- or post-strike values are large. This effect is related to the appearance of internal discharges in the gaps of the assembly.

Electromagnetic modeling of multilayer carbon fibers composites

The increased use of carbon fibers composites in aeronautic industry has led to the development of new numerical methods to understand the electromagnetic behavior of these materials. In this paper, we present a numerical model of multilayer anisotropic composites with finite element method in frequency domain. Several applications can be addressed; shielding effectiveness, HIRF, indirect effects of lightning, functional current return in low frequencies.

Modeling strategy for functional current return in large CFRP structures for aircraft applications

The strong increase of utilization of CFRP materials in industry has deeply modified the methods of analysis and challenged the numerical tools. In electromagnetism, many issues arise from the replacement of metallic elements by CFRP ones, the main being the protection against direct and indirect effects of lightning. An other important issue is the sizing and optimization of functional current return path on a large structure as an aircraft fuselage. The object of this paper is to present an original approach for studying the current return in a partially metallic fuselage structure covered with CFRP panels in a frequency range comprised between the continuous current up to few tens of kHz.

BEM/MoM fast direct computation for antenna sitting and antenna coupling on large aeronautic plateforms

A long term objective for aircraft manufacturer is the complete integration of antennas in fuselage in order to reduce the aerodynamic drag of aeronautic platforms. Performances of typical BEM/MLFMM solvers may be affected by local mesh refinements needed to connect conformal antenna models on aircraft. BEM fast direct solvers based on H-matrix are a promising solution to overcome these difficulties. We propose in this paper a performance comparison between MLFMM and H-matrix on a realistic case; a GPS system mounted on a typical Single Aisle (SA) fuselage.

A unified approach for lightning and low frequencies HIRF transfer functions measurements on A380

In this paper the studies conducted at AIRBUS with the aim of using a unified method to assess the internal induced threats on aircraft in case of lightning and low frequencies High Intensity Radiated Fields (HIRF) are presented. The approach is presented as well as some results obtained during A380 certification.

A thin conducting sheet (TCS) model in 3D FDTD : Implementation and validation

We present in this article the extension to the 3D case of an original thin conducting sheet (TCS) model developed in for 1D FDTD simulations. This method is based on the use of time domain admittance operator as a sub-cell model of the conducting layer. We present the 3D scheme and report on validations that have been conducted and that demonstrate the ability of the model to deal with noticeable skin effect.