Ultrasonic NDT of dissimilar metal to composite joints with complex geometry

• Main Authors: Jasiūnienė, Elena, Samaitis, Vykintas, Mažeika, Liudas, Mattsson, David
• Format: Conference Object
• Language: English
• Published: 2014
• Subjects: ultrasonic NDT; global warming; material substitution; Ocean acidification
• Online Access: http://ktu.lvb.lt/KTU:ELABAPDB24490496&prefLang=en_US

The transport sector is continuously growing, which leads to huge emission of CO2 and other gasses which continually drive the global warming and ocean acidification. Using material substitution, the weight of airplanes and other vehicles can be reduced by 20-30% leading to huge reductions in CO2 emission. To meet the strict requirements the concept of hybrid structures where two or more lightweight materials, such as metals and composites are joined, was introduced. By joining those materials an optimized structure can be obtained with superial properties. However, inspection of such joints is a challenging task for any of the present techniques due to the presence of materials with essentially different properties. Therefore the objective of the work presented in this study is to investigate ultrasonic inspection techniques which would enable to determine the quality of the dissimilar joints. There are several techniques suitable for inspection of the joints, however, none of them is universal enough for inspection of any type of joint, for detection of a big variety of defects and for determination of the quality of the joint. For such structures one of the most promising techniques is ultrasonic inspection because it is based on direct measurement of elastic properties of the materials. However, different acoustic impedances, propagation velocities and levels of the attenuation of the joined materials in combination with complex geometries complicate the inspection and require improvements in current techniques. The hybrid joints studied in this work consist of a titanium adherend joined to a carbon fiber reinforced plastic laminate forming a single-lap joint. The titanium part contains of protruding pins that are entangled within the dry carbon fabric in a subsequently step prior to resin infusion ensuring both mechanical and chemical adhesion between the adherends. In the last manufacturing step the resin infusion creates both the joint and the composite adherend simultaneously. The different samples with innovative titanium/CFRP composite joint with artificial delamination defects in different layers of the sample have been investigated using ultrasonic techniques. The results have demonstrated that in general the 3D structure of the dissimilar composite to metal joint with complex geometry can be reconstructed and most of the defects in different layers and in different positions of the complex structure can be indicated.