Inspection Of Adhesively Bonded Aluminium Plates Using Air-coupled Ultrasonic Guided Waves

Nowadays,adhesively bonded joint plays a significant role in different applications such as aerospace structures,automobile assemblies and so on.As the development of this technology,a suitable detection method to find the defects inside the joint and maintain the quality of the component should be taken into account.Ultrasonic testing(UT)is widely applied in the industry for the bonded joint inspection.But there are some limitations while using the normal UT method,for example,procedures cannot be performed automatically and the coupling material applied to the specimen might be harmful for some special materials.During the inspection on the production lines,these limitations would slow down the inspection speed seriously during the production line inspection.In order to solve these limitations,Air-coupled ultrasonic testing is provided for the bonded joint inspection.It could be one of the most suitable detection method in such a case,because it's a real non-contact testing method in which the coupling material is not needed.But how to qualify bonded joints with air-coupled equipment is still a problem specially in the automobile industry.In the thesis,it is proved that air-coupled guided wave testing is a feasible method for the bonded joint inspection and some influent factors are also analyzed,which gives an idea how to find the proper detection conditions.The inspection of adhesively bonded joints by the air-coupled ultrasonic guided wave has been studied with both simulations using finite element method and experiments using the real air-coupled equipment.During the simulation part,four models are studied by COMSOL-Multiphysics and CIVA to analyze how the physical phenomenon happens during the inspection.The dispersion curves for different specimens are calculated by the CIVA in order to find the wave generation during the inspection firstly.Then these models are simulated in COMSOL aimed to explore the possibility of the inspection.During the COMSOL simulation,the first model is a benchmark study in order to build the right air-coupled inspection model and the other three models are used to explore the possibility of the inspection.Within simulation part,influent factors such as incident angle and air-gap between transducers and specimens are taken into account.As to the experiment part,a group of experiments are performed in order to validate the simulation results,while the set-up for the experiment is the same as simulation settings.As to the results for simulations and experiments,the dispersion curves generated by CIVA indicate which kinds of wave modes are generated in the specimen and the properties of different modes are also obtained from the calculation.During the COMSOL simulation,firstly the optimal detection conditions for different specific situations are found mainly by analyzing the changes caused by the incident angles and the air-gaps.While detecting under the optimal detection conditions,the received signal by the transducer can be clear and have the maximum amplitude.Besides,two defect inspections for two different models are also simulated in COMSOL,and the results prove the air-coupled ultrasonic guided wave inspection has the capability to detect the imperfect adhesively bonded joint.According to the experiments,the results obtained in the reality validate the simulation result successfully.And the optimal detection length is also determined by the experiments.