Towards a reliable fatigue life prediction in metallic crack patching

• Ansätze für die zuverlässige Abschätzung der Lebensdauer geklebter Pflaster aus Faserkunststoffverbunden zur Reparatur von Ermüdungsrissen in metallischen Bauteilen

Martens, Ulrike Silke; Schröder, Kai-Uwe (Thesis advisor); Widemann, Martin (Thesis advisor)

Düren : Shaker Verlag (2022)
Book, Dissertation / PhD Thesis

In: Aachener Berichte aus dem Leichtbau 4/2021
Page(s)/Article-Nr.: 1 Online-Ressource : Illustrationen, Diagramme

Dissertation, RWTH Aachen University, 2021

Abstract

The topic of "Ageing Aircraft" is one of the big issues in today's operational aircraft. Fatigue cracks for instance are of great concern when looking at old metallic aircraft structures. [1, 2] Increasing the aircraft's operational service life in terms of flight hours and flight cycles is of great interest not inly from a financial point of view. Contemporary demands for sustainability are of great concern in aviation industry. The aim to the delay the replacement of cracked components and to reduce inspection times and effort results in the need for effective and lasting repair methods. Adhesively bonded repair patches made of fibre reinforced polymers (FRP) can restore the component's structural integrity without structural degradation. Research into metallic crack patching goes back to the 1980s. Since then, effective design methods have been developed and improved to a very high level of accuracy. The majority of today's research still focuses on the general verification of patch efficiency and the improvement of the preliminary patch design methods. But, the actual difficulty is the reliable service life prediction. Cyclic mechanical loading combined with continuously changing environmental influences can significantly detract the repair's functionality over time. Hence, fatigue life assessments using the initial repair properties is limited due to their degrading characteristics. However, a full exploitation of the potential on the other hand can only act up with a reliable fatigue life prediction. In a comprehensive analysis of the design process the present study reveals effective starting points for prospective research. It shows why additional studies on patch effectiveness cannot lead to improve the reliability of bonded patches. With a coupon test series the theory is supported that the effect of even more precise preliminary patch design methods is insignificant concerning service life extension and that the focus of future studies has to be set on the assessment of service loads and their impact on the structural integrity. To this, a concluding test series shows how the method of infrared thermography enables significant improvements in the comprehension of the fatigue behaviour of a crack patched metallic structure.

Institutions

• Chair and Institute of Structural Mechanics and Lightweight Design [415610]