Composite honeycomb cores
Jegorova, Ksenia (2015)
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This thesis demonstrates how a certain type of a sandwich core - honeycomb is manufactured and post-processed, in case if it was made from composite material itself. Any sandwich structure consists of three essential elements: two faces, core and joints. The core represents good ability to carry shear loads. That part of the sandwich is incredibly significant, since it assures that sandwich is not just light but also stiff enough. Honeycomb core is one of the most structurally efficient core constructions, especially in stiffness-critical applications, which is provided with minimal density and high out-of-plane compression and shear properties. As it follows from its name, honeycomb core consists of hexagon-shaped cells, which are completely identical to each other. That core structure is an anisotropic one, which means it is anisotropically loaded inside the sandwich. That follows that honeycomb core could be made of an anisotropic material performing a maximum strength to mass ratio. Traditional honeycomb constructing methods include corrugation and expansion manufacturing processes as well as expansion combined with dipping into phenolic resin. Corrugation was chosen as a basis manufacturing process used to create honeycomb cores in the experimental part of this work. The process consisted of the following steps: prepreg glass fibre and carbon fibre sheets were shaped with a use of aluminium mould, heat and pressure and then sliced and glued together in order to create a composite honeycomb core. Post-processing by milling did not result in shear overload and delaminating of skins or delaminating of layers from each other. As a result some composite honeycomb cores and composite honeycomb sandwich panels were made. Macroscopic density (approx. 0.4 g/cm3) and price (at least 160.04 euro/kg) of the made products were competitive with Ultracor samples (approx. 0.3 g/cm3 and 16000 euro/kg). However these made products would have more performance if bonding between layers inside the honeycomb core would be stronger with less adhesive used.