Electrothermics

5.5. Identifying the physical properties of composite materials by experimental methods

The electrical conductivity of composite materials is the most difficult parameter to measure. Indeed, the carbon fibers are numerous, with small diameters, oriented differently from one fold to the next and often inaccessible from the outside. Consequently, classical resistance measurement methods are not adapted to correctly evaluate the resistance of composite samples. To overcome these difficulties, different measurement techniques are introduced and analyzed in this section to determine the method most suited to identify the conductivity of composite materials.

Identifying the thermal properties, important data for the mastery of the process, is not discussed here. Indeed, this identification, outside of some difficulties linked to the inhomogeneous nature of the composite materials, is fairly classical. Nevertheless, we have given the values of these properties at the end of this section.

5.5.1. Influence of the geometry

The reinforce’s filling rate is generally under 70%. The composite material’s equivalent electrical conductivity therefore cannot be greater than two-thirds of the conductivity of the carbon fiber in this material. Furthermore, the support’s architecture can decrease the equivalent electrical conductivity by half. Figure 5.12 shows an example of the architecture of the support and fold orientation of a composite material.

Figure 5.12. Spotting the components of the properties ...