A method of monitoring structural damage in a composite structure manufactured by co-curing, co-bonding or secondary bonding of several sub-components (7, 8), using fibre optic Bragg grating sensors attached or embedded to or between (in the bonding line) said sub-components, comprising a first step of measuring the wavelength spectra (31, 33, 40) of said Bragg grating sensors at the end of the manufacturing of the part, and in a known load condition, considered as reference and a second step of identifying the occurrence of a failure of the structure and the progress of said failure detecting the release of the residual stresses/strains stored during the curing process by measuring changes (31 to 32, 33 to 34, 40 to 41) with respect to said reference wavelength spectra.