Characterisation of composite damage based on acoustic emission using optical fibre sensor at cryogenic temperature

The characterisation of composite damage at cryogenic temperature (CT) can be evaluated using the acoustic emission (AE) technique if the sensor can withstand CT and the correlation between the AE signal and composite micro-damage can be clarified. In this study, a new cantilevered phase-shifted fibre Bragg grating was used to detect AE signals from carbon fibre reinforced plastic laminates subjected to a three-point-bending test at CT. The sensor captured all low-energy and high-frequency AE hits at CT. The energy and peak frequency of the signals were statistically analysed and were correlated to the deflection – load curves and microscopic observations. The AE hits at CT had higher energies and covered a wider peak frequency range than those at room temperature. The first AE hit appeared earlier at a small deflection at CT than at RT. In addition, the signals at RT caused by the matrix cracks were concentrated in one cluster and those at CT were separated into two clusters, corresponding to matrix cracks and delamination. These phenomena are caused by the greater brittleness and modulus of the resin at CT and the mismatch of thermal expansion between the carbon fibre and resin and between the two adjacent cross-ply laminae.