Carbon nanotube-based health monitoring of mechanically fastened composite joints

The onset of local damage in joints, such as delamination, cracking and fastener loosening can often be difficult to detect and has long-term implications on the performance of the structure. As the use of advanced fiber composites expands in large-scale structural applications, where joining of large structural members using adhesives and/or mechanical fasteners are employed, these connections represent a potential weakness in the structure where catastrophic failure could occur. As a result, it is crucial to develop innovative techniques to monitor the state of damage in composite structures. In this research we report the unique capability of carbon nanotube networks as in situ sensors for sensing local composite damage and bolt loosening in mechanically fastened glass/epoxy composite joints. Through careful design of the specimen it is possible to detect the onset and progression of damage in the joint.