Abstract
The project “Multi-Layer Inserts” (MLI) proposes a new design for inserts used in thin-walled CFRP structures. The proposed inserts consist of multiple thin metal sheets and is build up simultaneously with the laminate in an intrinsic hybridization process, eliminating time-consuming post-processing steps. Furthermore, at equal weight, such inserts greatly increase the bonding area between metal and CFRP in comparison to conventional inserts. This results in a significant increase of the loads that can be transmitted into the CFRP. The present work discusses how the shape of the metal sheets which the proposed inserts consist of influences the mechanical properties of the surrounding laminate. This influence is investigated by measuring the strain distribution during tensile tests by means of digital image correlation. The strain distributions around the following three different MLI design approaches are compared: An elliptical metal sheet, which is expected to be ideal in terms of mechanical performance of the overall structure; a cross-shape metal sheet representing a production-driven simplification which only requires the ability to perform cuts in individual tows perpendicular to the laying direction and can be performed by state-of-the-art AFP systems; and lastly, a compromise between manufacturability and achieved mechanical performance, a decagonal metal sheet design, which requires angled cuts of the fiber tows. It is shown, that the decagon is able to evenly spread the strain over a larger area and is therefore able to significantly reduce the maximum strain values compared to a cross-shape metal sheet, while still being automatable.
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Notes
The strain computation of one facet within the digital image correlation is based on the change of distance to the surrounding facets. To be independent of axis misalignments, e.g. of the camera and specimen axes, the strain tensor is computed. The direction of maximal strain is defined as major strain.
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Acknowledgements
This paper is based on investigations of the subproject 1—‘Multilayer Inserts—intrinsic hybrid compounds for load introduction into thin walled high-performance CFRP-Structures’ (DE-447/123-1) of the priority program 1712 ‘Intrinsic hybrid composites for lightweight load-bearings’, which is kindly supported by the German Research Foundation (DFG).
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Groß, L., Herwig, A., Berg, D.C. et al. Production-based design of a hybrid load introduction element for thin-walled CFRP Structures. Prod. Eng. Res. Devel. 12, 113–120 (2018). https://doi.org/10.1007/s11740-018-0821-4
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DOI: https://doi.org/10.1007/s11740-018-0821-4