Evaluating impact damage in CFRP using fibre optic sensors

Damage in unidirectional carbon/fibre composite resulting from both low and high velocity/energy impacts was evaluated using embedded fibre Bragg grating (FBG) sensors, C-scan and microscopic analysis. It was found that the FBG sensors located 10 mm from the impact site could detect residual strains from a 0.33 J (1.3 m s−1) impact which was not detectable by C-scan or visual inspection. The measured residual strain increased with impact energy and damage changed from matrix cracking to severe delaminations. High velocity impacts (225 m s−1, 11 J) resulted in test panel perforation and delaminations. FBG sensors located within a distance of 2–3 the damage radius detected residual strain from the impact. With an array of embedded sensors it is believed that it will be possible to identify the site of both low and high velocity energy impacts and predict the damage from the response of the adjacent sensors providing the sensors are located sufficiently close to the impact site.