Characterization of dynamic strain induced by drilling carbon fiber reinforced polymers using optical frequency-domain reflectometry

The use of a distributed optical fiber sensor based on optical frequency-domain reflectometry (OFDR) is proposed for drilling monitoring of carbon fiber reinforced polymer (CFRP) plates. The OFDR sensor response provides information of the drilling-induced temperature and strain over the CFRP plate within a 2D area closely located to the drilled hole. The different stages of the drilling process can be easily identified over time. In addition, a time-frequency analysis based on short-time Fourier transform allows the monitoring of the dynamic strain spectral content generated over the CFRP plate during drilling. Besides the spectral components resulting from the spindle rotation speed of the drill, this analysis allows for the detection of eventual microcracks and delamination of the CFRP plate, as experimentally verified.