DEFECT DENSITY AND STRENGTH ESTIMATION OF ADHESIVELY BONDED COUPLINGS BY APPLYING THE ACOUSTIC EMISSION TECHNIQUE

It is widely demonstrated in literature that the presence and the density of adhesive bonding defects are difficult to estimate with conventional non-destructive testing techniques once the parts are assembled together. For this reason it is very important to set up a method capable of estimating the adhesive bonding defects and the final releasing moment of the assembled parts. The aim of this work is to study the use of Acoustic Emissions, as a non-destructive testing technique, applied to shaft-hub interference fitted and adhesively bonded joints. Five defect densities of the adhesive, 0%, 25%, 50%, 75% and 100%, were investigated. The first part of the chapter is dedicated to the calculation of the joint releasing moments depending on the effects due to the adhesive defect density and to the interference level. The second part is dedicated to verify the strong correlation between the adhesive defect density and the cumulative counts of the Acoustic Emissions. Finally, the last part is dedicated to improve and develop the non-destructive method based on the Acoustic Emissions applied to shaft-hub couplings, which can be capable of estimating both the adhesive bonding defect and the final releasing moment of the assembled joints accurately. Releasing tests were performed in accordance with the Design of Experiment methodology: a full factorial experiment was designed with two variables (interference and adhesive defect density) on different levels, in order to evaluate the significance of the main and of the interaction effects and to determine the mathematical model (response surface) of the failure load by applying the Analysis of Variance and the Fisher’s test to the results.