Microstructural and mechanical properties of filler-added coal-tar pitch-based C/C composites: the damage and fracture process in correlation with AE waveform parameters Original Research Article

The mechanical behaviour of undirectional and 2D-laminate coal-tar pitch-based carbon/carbon composites was investigated in tension and bending conditions (3 and 4-point loading tests) at room temperature. One of the major drawbacks of such highly anisotropic structures is their poor resistance to delamination (high sensitivity to local shear components). In order to improve their interlaminar shear strength, carbon blacks were introduced between the unidirectional plies of the 2D-C/C specimens prior to the pitch infiltration. The damage and the failure mechanisms were identified by microscope observations on both UD and 2D-C/C composites. Two families of damage modes were identified, involving limited interfibre cracks and inter-layer delamination cracks homogeneously distributed within the composite. The fracture process is assigned to the propagation of the macrocrack in the failure envelope through a large intra and inter-layer delamination process interrupted by fibres/bundles fracture. Acoustic emission analysis was performed during the tests. An approach using a combination of acoustic emission waveform parameters as indicators of the physical damage of the composite is discussed.