University of Twente Student Theses


Durability of co-bonded stiffened CFRP panels subjected to post-buckling fatigue

Akker, B.P.H. van den (2018) Durability of co-bonded stiffened CFRP panels subjected to post-buckling fatigue.

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Abstract:Although bonded CFRP panel-like components are frequently used in the aircraft industry, they are not yet used to their full potential due to a lack of knowledge on the behavior of the adhesive joints throughout an aircraft's lifetime. To increase this knowledge, fatigue disbond growth under varying environmental conditions was studied. Co-bonded CFRP panels with a stiffener were subjected to cyclic post-buckling under pure compression. To promote local skin buckling all panels contained an artificial disbond between the skin and stiffener. The environmental conditions of these panels were room temperature ambient and room temperature wet, with the former stored in a clean room until the moment of testing and the latter hygrothermally aged at 80°C and 90% humidity for 290-396 days. The disbond of all panels grew throughout the cyclic loading as a consequence of the local skin-stiffener detachment during buckling. The disbond of the hygrothermally aged panels grew less than the disbond of the non-aged panels. Likely, this was partially caused by a combination of stress relaxation and crack blunting due to the moisture absorption. After the cyclic loading all panels were subjected to quasi-static compression until failure to determine their residual strength. The post-buckling fatigue and corresponding disbond growth did not influence the stiffness or strength of the panels when compared to non-fatigue loaded reference panels. Similarly, the hygrothermal aging did not alter the stiffness or strength of the panels. These factors indicate that bonded panel-like components in aircraft can repeatedly be taken into the post-buckling regime safely. To aid the implementation of these results in the industry a numerical simulation of the cyclic post-buckling loading was performed. The numerical model underestimated the disbond growth by 25% and overestimated the residual strength by 14%. Although these differences are quite significant, it was considered reasonably well given the fact that fatigue related material properties of the correct material combination were not available and therefore had to be taken from a different material.
Item Type:Essay (Master)
ITA, Sao Jose dos Campos, Brazil
Faculty:ET: Engineering Technology
Subject:52 mechanical engineering
Programme:Mechanical Engineering MSc (60439)
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