Effect of Core Crush on Honeycomb Sandwich Panels

Nomex honeycomb is used as the predominate core material in aerospace standard sandwich structure. To provide aerospace standard composite face sheets it is necessary to cure the sandwich structure in an autoclave at elevated pressure. The honeycomb material is capable of withstanding the forces experienced through its thickness, but the lateral forces applied by the elevated pressure cause a crushing effect on the cells of the material. To prevent this crushing a ‘core stabilisation’ technique is applied to the core, prior to the lay-up of the sandwich panel, which increases the rigidity of the material and protects the cells. The core stabilisation process is time consuming and therefore costly. The current work investigates the effect of core crush on the mechanical properties of sandwich beams, along with the success of eight core treatments to reduce core crush. Without stabilisation, the core crushed by almost 12%, and had a large detrimental effect on the mechanical properties of the beam. However, by curing in a conventional oven at vacuum pressure crushing was prevented and similar mechanical properties to the fully stabilised core were achieved. Finally, the effect of core crush on actual sandwich components is investigated by loaded representative panels on a specialist rig capable of applying representative pressure loads and measuring the stress distribution using full-field thermoelastic stress analysis (TSA).