Acoustic emission in carbon fibre-reinforced plastic materials

Abstract

The mechanical behaviour of unidirectional (UD) and 2D-laminate Carbon Fibre-Reinforced Plastic composites was investigated under 4-point bending and tensile loads at room temperature. The mechanical behaviour of UD composites was first studied. The mechanical behaviour of a quasi-isotropic laminate was subsequently investigated under the same loading conditions and correlated to that of the UD plies. The damage and the failure mechanisms were identified by microscope observations on both UD and laminate composites. Two families of damage mode were identified, involving 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 measurement was performed during the tests. An approach using a combination of acoustic waveform parameters as indicators of the physical damage is discussed.