Electron microscopy and electron-energy-loss spectroscopy study of crack bridging in carbon–carbon composites

Crack bridging within pyrolytic carbon matrix of a carbon-fiber/carbon-matrix composite was studied by scanning electron microscopy and transmission electron microscopy combined with electron-energy-loss spectroscopy. An extensive propagation of concentric cracks around carbon fibers is observed in the matrix. The crack propagation is bridged by bent lamellae. The analysis of low-energy-electron losses in cracked regions shows that the bulk (π + σ) plasmon of planar lamellae lies close to those of graphite while the bulk (π + σ) plasmon in bent areas is shifted towards lower energy positions and is comparable with the plasmon resonance of a polymer film. The morphology of bridging areas is discussed by considering the degradation of the atomic structure of planar graphite by the presence of lattice defects and hydrogen atoms.