چكيده به لاتين
Given the widespread use of composite patches in the repair and reinforcement of structures, especially aerospace structures, proposing an effective quality control method for the assessment of composite patches seems necessary. Common defects in these patches are delamination between the composite layers and debonding between the patch and the main structure. The latter defect may occur during or after connecting the patch to the main frame, depending on loading and environmental conditions. To identify the debonding defect in composite patches, various nondestructive testing methods may be used. This project studies the feasibility of using vibrothermography in order to identify the debonding defect in composite patches. In order to do so, a sample containing an aluminum plate with an eight-layer anisotropic carbon/epoxy composite patch connected to it is tested as part of this thesis. Three debonding defects are created between the aluminum plate and the composite patch. To produce the required vibration, high-frequency piezoelectric vibrators have been employed. In order to determine the most appropriate juxtaposition of the vibrators so as to create uniform vibration in the test-piece, wave modelling has been performed in Abaqus™. The vibrothermography modelling has been carried out in COMSOL Multiphysics® to determine the viscoelastic heat generated due to the vibration. The modelling results confirm the fact that one will be able to distinguish the debonding defect providing one accurately obtains the vibrational frequency, the excitation location and the excitation amplitude via modelling. In the end, an vibrothermography test is conducted experimentally. The images obtained from the thermographic camera are analyzed and interpreted using the thermographic signal reconstruction method (the algorithm of which is written in MATLAB™). Unfortunately, due to difficulties in creating the debonding defect in the test-pieces and the existence of Teflon instead of air at the debonding location, the trials to identify these defects through vibro thermography did not produce desirable results. It was concluded that experimental tests to determine the debonding defect using the vibrothermography method requires further research.
Keywords: vibrothermography, fault detection, carbon/epoxy, debonding, piezoelectric vibrator
