Abstract
This paper presents the seamless monitoring of internal strains, consisting of process-induced strain and machining-induced strain, in a carbon fiber-reinforced plastic (CFRP) cross-ply laminate. The strains during processing and drilling were calculated from the Bragg wavelength shift and the temperature change measured using an embedded FBG (Fiber Bragg Grating) sensor and a thermocouple, respectively. The absolute internal strain was consistently monitored through processing (curing) to machining (drilling) by defining the strain at the gel point to zero. As a result, the drilling-induced strain is separated from the process-induced strain. The exact location of the FBG sensor and the delamination size around a drilled hole were identified using soft X-ray radiography. It was found that the internal strain detected by the FBG sensor was correlated with not only damage size, or a delamination factor, but also its relative position.
