Fracture mechanism of flexible graphite sheets Original Research Article

The fracture behavior of flexible graphite sheets (FGSs) was investigated by loading along and perpendicular to the sheet surface. The vertical strength is lower than the tensile strength by two orders of magnitude, at only 0.03 MPa. The fracture processes of a notched specimen of FGS and compressed graphite worms were also studied directly and by in-situ observation by SEM. From observations of the fractured surfaces, structural units for the fracture of FGS are assumed to be interlocked micro-discs composed of orientated graphite layers, which originate from the worm-like particles of the original exfoliated graphite. During the formation of FGS by compression and rolling, micro-discs in the different worms interlock and become structural units. When a static tensile load was applied to FGS, some structural units rotated, cleaved and produced microcracks. When the load was increased, slip between the structural units of FGS started and the structural units slipped away from each other and the FGS was broken. Therefore, The tensile strength of FGS originates from the frictional force between the structural units.