Design and structural testing of 3D printed honeycomb cores with optimised integrated blended inserts

The integration of inserts into sandwich panel constructions is a complex multi-step process with significant human intervention that also limits the geometrical freedom of the insert design. In a standard sandwich construction, the panel core is made up of multiple materials across its main components: insert, potting and core. This multi-material assembly is not only difficult to manufacture, but it also promotes stress jumps at the insert-core interface, leading to a sub-optimal load distribution from the bolt to the panel core. Additive manufacturing (AM) can lead to a single-part core and insert assembly with more optimised insert geometries that can better transmit the loads applied to the panel. Previous work by the authors has explored the manufacturing limits and the failure modes of AM inserts integrated in cores printed out of sintered AlSi10Mg. The conclusions were that the core walls and insert elements should have a minimum design thickness of 0.5 mm to survive the tapping process without facesheets attached and it was found that the main failure mode of the geometries tested in pull-out was buckling of the insert walls. Based on these results, the paper proposes a novel insert design philosophy that can delay the buckling of 3D printed inserts and move the failure point of the insert away from the bolt. A set of inserts that follow this design direction is manufactured and tested under normal pull-out loads and the optimised designs outperform standard printed insert geometries by a factor of three. The design philosophy can be further developed to offer a suitable alternative to the current insert standard.