STRUCTURAL HEALTH MONITORING OF FATIGUE TESTED CFRP-CFRP BONDED JOINTS USING OPTICAL BACKSCATTER REFLECTOMETRY AND X-RAY MICRO COMPUTED TOMOGRAPHY

Nowadays, adhesive bonded joints find large application in modern structures, especially for their lighter weight, lower stress concentration and better fatigue properties. Anyway, issues might arise from a multitude of different factors, like manufacturing defects and operational condition, which lead to local debonding and final unpredictable failure. Consequently, structural health monitoring techniques, able to evaluate damage development in real time, and non-destructive testing are needed to assess the in-service state of the joints, particularly in the case of fatigue load conditions. In the present paper, a fatigue test is performed on a Carbon Fibre Reinforced Polymer single lap adhesive bonded joint, and its damage initiation and propagation are investigated using X-ray micro-Computed Tomography and the Back-Face strain technique performed applying a distributed optical fibre sensor implementing Optical Backscatter Reflectometry. A good linear correlation is found between crack depth measured by X-ray micro-Computed Tomography and the position of strain peaks recorded by Optical Backscatter Reflectometry.