FIB-SEM investigation and uniaxial compression of flexible graphite

Flexible graphite (FG) with ρ = 1 g/cm³ density is a type of highly porous and anisotropic graphite, mainly used for gaskets and sealing applications, but also suitable for energy absorption, such as in the beam dumping devices of the Large Hadron Collider (see Heredia 2021 [1]). Knowledge of its microstructure and mechanical properties needs to be developed for the selection of an adequate material model able accurately predict stresses and failure in FG components. Here, the FG microstructure properties available in literature are reviewed, followed by Focused Ion Beam - Scanning Electron Microscopy investigation and compression tests. Specifically, a single 100 μm × 150 μm cross section was obtained, and the 2D pore sizes and shapes were quantified using image segmentation. Monotonic and cyclic out-of-plane compression tests were performed in single and stacked configuration. Stress-strain curves showed three domains: the initial toe, the transition and the densification domain. The cyclic tangent modulus was also calculated from the cyclic tests. Many observations suggested that FG behaves similarly to crushable foams, crumpled materials and compacted powders, and that both crystalline microstructure and crumpled mesostructure play a predominant role in the deformation mechanism.