Application of smart bolt to early stage damage monitoring of composite shear fastener joint

Joints must be the most common source of failure in any structures. Especially, aircraft structures are strongly demanded to reduce their weight keeping structural reliability in higher level. In recent years, as composite materials became applied more and more in aircraft structures, there exist many composite/metal mechanical joints. So, it is important to make clear the damage behavior of composite/metal mechanical joint. Authors proposed the method to monitor the mechanical behaviors using the fastener bolt embedded an optical fiber sensor, i. e. Smart bolt. In this paper, we try to apply this method to detect the early stage of bearing damage around fastener holes of composites. The results are summarized as follows; (1) we can detect the damage by the change of inclination in the relationship between load and axial strain measured by Smart bolt, and (2) it was shown that the early stage of damage of composites around the fastener hole can be detected by using Smart bolt.