Structural health monitoring in adhesively bonded CFRP joints with fibre optic sensors

In nature, many biological structures exhibit integrated sensors. These sensors fulfill avital function as they continuously monitor the organism to detect and minimize overload and irregular conditions before they evolve into serious damage [1]. In order to transfer this function principle from nature to technology, adequate sensors systems and their integration into materials need to be investigated. The application of sensored materials has the potential to save time and money by reducing preventive maintenance activities and prolonging replacement intervals of components and assemblies [2].Especially in the aeronautic industry, it is a mandatory prerequisite for the certification of adhesively bonded primary structures by the airworthiness authorities that the condition of the bond is diagnosable [3]. Through the use of sensored materials, Structural Health Monitoring (SHM) can provide such a function for the field of adhesive bonding. Besides the advantage of receiving information about the condition of the adhesive joint, the integration of such a sensor system represents an interference factor. This can influence the bond strength negatively. In this work, the influences of different interference factors caused by the integration of fibre optic sensors in adhesive joints are investigated. Fibres with various diameters and coatings are included in the study. Since the research focusses on bonding of CFRP structures in the aeronautic industry, the fibre-coating combinations are tested with film adhesives commonly used in this field. Furthermore, it is investigated how the integration into the joint influences the sensor as the usage of high temperature curing epoxy film adhesives presents challenges for the system.