Abstract
In comparison to bolted joints, structural bonds are the desirable joining method for light-weight composite structures. To achieve a broad implementation of this technology in safety critical structures, the issues of structural bonds due to their complex and often unpredictable failure mechanisms have to be overcome. The proposed multifunctional bondline approach aims at solving this by adding two safety mechanisms to structural bondlines. These are a design feature for limiting damages to a certain size and a structural health monitoring system for damage detection. The key question is whether or not the implementation of both safety features without deteriorating the strength in comparison to a healthy conventional bondline is possible. In previous studies on the hybrid bondline, a design feature for damage limitations in bondlines by means of disbond stopping features was already developed. Thus, the approach to evolve the hybrid bondline to a multifunctional one is followed. A thorough analysis of the shear stress and tensile strain distribution within the hybrid bondline demonstrates the feasibility to access the status of the bondline by monitoring either of these quantities. Moreover, the results indicate that it is sufficient to place sensors within the disbond stopping feature only and not throughout the entire bondline. Based on these findings, the three main working principles of the multifunctional are stated. Finally, two initial concepts for a novel multifunctional disbond arrest feature are derived for testing the fundamental hypothesis that the integration of micro sensors into the disbond stopping feature only enables the crack arrest and the health monitoring functions, while reaching the mechanical strength of a conventional healthy epoxy bondline. This work therefore provides the fundamentals for future investigations in the scope of the multifunctional bondline.
Highlights
This region was first modeled with C3D8R, but the results showed a large scatter due to hourglass effects
disbond stopping feature (DSF) illustrate a significant change in the stress and the strain distribution within the DSF of the hybrid bondline for different crack lengths
A peak is present at the beginning of the DSF, which decreases until the level of the plateau is reached
Summary
Mechanical-wise structural bonds, i.e., bonded joints carrying high loads, are a very desirable method for joining lightweight composite structures. In comparison to bolted joints, structural bonds show better load transmission, and due to the absence of metallic fasteners, they are lighter, while the adherends are not locally damaged [1,2]. The quality of structural bonds is affected by many factors, and there is still a lack of methods to access their performance reliably [2]. The consequences of these uncertainties come into view when looking at the aviation industry for example. Both the European Union Aviation Safety Agency [3] and the U.S Federal Aviation
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