Engineers develop novel adhesive bonding and nondestructive testing techniques to combat the damaging effects of vibration.

AFRL materials engineers resolved a potentially serious problem that affects the operational life of F-15E vertical stabilizers. Working with engineers from Warner Robins Air Logistics Center (WR-ALC), Georgia, they successfully developed, demonstrated, and transitioned an adhesive bonding process and nondestructive inspection (NDI) technique that ensure the stiffening doublers attached to both sides of the aircraft's two vertical stabilizers remain adequately secured (see figure on next page). Successful transition of these innovative methods restores the operational life of the vertical stabilizers.

Several F-15E aircraft have lost doublers during takeoff and/or while in flight. To remedy this situation, AFRL adhesives experts created a new bonding process and nondestructive evaluation specialists developed and finetuned a thermography-based NDI procedure. Their combined efforts ensure the stiffening doublers remain a reliable and cost-effective structural reinforcement solution.

AFRL personnel install a composite stiffening doubler on an F-15E vertical stabilizer using the new bonding technique.
The F-15E's vertical stabilizers require composite stiffening doublers to reduce in-flight vibrations, which can decrease the stabilizers' life span up to 25%, by preventing crack growth in underlying substructure. WR-ALC engineers found the bonding process currently used for securing the doublers to the stabilizers was inadequate and resulted in extensive rework to replace damaged or detached panels. After receiving multiple reports of incidents where the stiffening doublers separated or partially debonded from the aircraft during takeoff or flight, they made the decision to cease further modifications until a more reliable bonding process could be implemented.