Real-time detection of impact load on composite laminates with embedded small-diameter optical fiber

It is well known that the compression after impact (CAI) strength of carbon fiber reinforced plastic (CFRP) laminates decreases by impact damage, especially delamination. The impact damage has a close relation to impact energy, which can be derived from the time history of impact load. Thus, it is important to detect the impact load applied to the composites. In this study, single-mode or multi-mode small-diameter optical fibers embedded in CFRP laminates were used as a sensor for detecting the impact load. Diameters of the cladding and the polyimide coating are 40 mu m and 52 mu m, respectively. Such optical fibers embedded inside laminas cause no serious effect on the mechanical properties of composites. The optical fiber sensors were able to detect the impact by bending loss in the vicinity of impact point. The optical fibers were embedded parallel to reinforcing fibers in CFRP composites. Charpy impact tests were performed for the CFRP specimens. The strain on the surface of the specimens, the optical loss and the impact load were measured as a function of time. Then, the relationship between the optical loss and the impact load was discussed experimentally and theoretically.