Complex structures such as aircraft airframes are constructed from different components at part and assembly levels. A recent trend is the joining of metallic structures possessing high load bearing capability with composites that possess superior fatigue life performance, thus providing the opportunity for manufacturing lighter structures with enhanced service capabilities. These advanced structures which are made of dissimilar materials with different mechanical properties are known as hybrid structures. Since mechanical fasteners introduce damage to the fibrous structure of composites, the ideal method of joining hybrid structures is to bond them together using adhesives. It is vital that the reliability and integrity of such adhesive bonds be examined on a regular schedule and in a nondestructive manner. Traditional inspection methods are cumbersome and sometimes suffer from a lack of accessibility to the entire length of the joint. Such nondestructive testing methods are also not fully capable of quantifying the integrity of adhesive bonded joints.
In this research, a reliable and repeatable method for inspection of hybrid bonded joints is proposed. This method involves the use of ultrasonic interface guided waves for characterization of hybrid bonded structures. Unlike bulk waves and Lamb waves which propagate through the thickness of media, interface and surface guided waves, such as Stoneley and Rayleigh waves, propagate along the boundaries and interfaces of structures. Interface guided waves are potentially ideal for interfacial damage detection at the bondline of hybrid joints. Interface waves can interact with defects in bondline in a variety of ways. Similarly surface acoustic waves are ideal for inspection of surface roughness and also curved structures and bend sections where typical ultrasonic inspection methods are unable to perform damage detection. Through several case studies, it is shown that surface and interface waves are extremely sensitive to the condition and health of the bondline and the characteristics of guided waves can be used for investigating interfacial damages at hybrid bonded structures. Finite element simulations are used to assess the possibility of using interface waves to locate and identify the various forms and size of damage in a hybrid bonded joint. The results of this study demonstrate that the time-of-flight (TOF) of interface waves increases when there is a disruption in the traveling path of the interface wave.
|Advisor:||Santhanam, Sridhar, Ihn, Jeong-Beom|
|Department:||Department of Mechanical Engineering|
|School Location:||United States -- Pennsylvania|
|Source:||DAI-B 82/3(E), Dissertation Abstracts International|
|Subjects:||Mechanical engineering, Aerospace engineering|
|Keywords:||Hybrid bonded joints, Model based development, Nondestructive evaluation, Structural health monitoring|
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