NOVEL TECHNIQUE FOR THE EVALUATION OF AIRCRAFT HONEYCOMB SANDWICH STRUCTURES

Honeycomb sandwich structures can degrade in performance if the strength of the adhesive bonds within the structure is degraded due to the presence of moisture or if the honeycomb core itself corrodes. The HES is unique in its ability to perform accurate, reproducible and efficient tests to determine the integrity of honeycomb core and the strength of honeycomb cell node bonds in-situ. It is designed to complement other non-destructive inspection methods as the technique is applied to test a very localised area. The tool is uncomplicated and could be easily applied at a depot or even under field conditions with minimal operator training. The evaluation of honeycomb core node bonds using the HES gives greater confidence in the structural integrity of a component as node bond degradation can also indicate poor fillet bond strength and give an early warning of corrosion. The HES is also much less invasive compared to other techniques such as the adhesion pull-off test. The HES can also be used to proof cells to a given pressure level to help determine whether the honeycomb cells will withstand elevated temperature repair operations, where trapped water in the core can produce high steam pressures capable of causing core damage.