Non-destructive Inspection of Weak Bonds in Composite Joints

Many advances in the design of composites adhesive bonded joints have been made in the last years. Since this kind of bondings are often use in lightweight structures such as aircraft, it is crucial to ensure that the bonded joints do not cause an effectively reduction in the stiffness of the entire system. The purpose of this thesis is to provide an innovative technique of inspection of joints. This strategy is based on the evaluation of the dispersion relations. The goal is to compare the dispersion diagrams obtained from the examined joint with the diagram resulting from the evaluation of the pristine specimen that acts like a reference case. In this way it is possible to monitor the status of the bonding, then with the help of some numerical techniques a quantification of the level of the damage will be feasible. The dispersion relations connected to the specimens will be evaluated experimentally using the Scanning Laser Doppler Vibrometer (SLDV) and mostly, the numerical dispersion diagrams will be extracted using the Finite Elements technique. The first results have been obtained matching manually the experimental and numerical results. However, in the last chapter an automatic approach will be presented in order the evaluate the residual strength of the bonding.