Application of fiber-optic distributed sensors to health monitoring for full-scale composite structures

The purpose of structural health monitoring (SHM) is to lead a structure to be safer at lower cost. SHM systems capable of assessing structural integrity during manufacture and in-service operation would allow timely maintenance actions to increase safety and lifetime of structures. In such systems, it is important to evaluate the actual state of a structure. Recently, fiber-optic sensors have been actively developed, and one can measure many kinds of the physical measurands by them. Since they also have excellent characteristic, such as immunity of electromagnetic interference, durability and capability to realize distributed sensing, they are supposed to be suitable sensors for SHM systems. We installed fiber-optic sensors into full-scale composite structures to monitor strain or temperature during manufacture or to monitor in-service structural performance, i.e., stiffness. The structures applied with the sensors are International America's Cup Class (IACC) yachts and a Japanese experimental reentry vehicle, namely, HOPE-X, that are made of carbon fiber reinforced plastic. The fiber-optic sensors used in this study are two kinds of distributed sensors using Brillouin scattering and Raman scattering, respectively. The former can measure strain or temperature and the latter can measure temperature at an arbitrary region along an optical fiber. We could successfully measure strain or temperature of the full-scale composite structures in field and access the structural state. The results of this study demonstrate the great potential of fiber-optic distributed sensors for practical applications to large composite structures.