Abstract
To realize future transport such as SST (HSCT), HST and space plane, we have to develop drastic technologies for lightening weight and assuring reliability of composite structures. In this connection, authors have studied damage monitoring techniques for composite structures by using fiber optic methods. In this paper, we investigated a possibility of bearing failure monitoring of the bolted joints of C/C composites by detecting the breaking of an attached optical fiber. Results obtained are summarized as follows: (1) Damage cannot be detected unless the plastic coating of optical fibers is stripped. (2) When attaching the stripped optical fiber longitudinally to the loading direction, bearing and net tension failure can be detected though shear-out failure cannot be detected. (3) When attaching the stripped optical fiber transversely to the loading direction, both bearing and shear-out failure can be always detected. There is a proportional correlation between the distance from the optical fiber to hole edge and the pin displacement at optical fiber breaking. This attached type fiber optics is effective to apply to the practical structure monitoring, i.e., not only high temperature composite structures but also some kinds of infrastructures.
