Composite Bonded Repair Technology
Research Project
- Start Date:
- 2 March, 2009
- Project Status:
- Active
In 1972 DSTO invented, and now leads the world in the use of, composite bonded repairs to reinforce and repair aircraft structures. Originally developed to prolong the life of RAAF fighter aircraft, this invention has been applied to US Air Force aircraft as well as the civilian 727 and the 767.
-
- Composite bonded repair to F-111 wing
The technology has many advantages over traditional mechanical repair methods, such as bolting or riveting, and involves adhesively bonding “patches” or reinforcements of advanced fibre composite materials to damaged metal structures.
Relative to conventional fastened repairs, composite bonded repairs are lighter in weight, offer more uniform load transfer, seal interfaces to reduce corrosion and leakage, create minimal damage to the parent structure and facilitate non-destructive inspection.
Adhesive bonding is notoriously difficult to perform in the absence of a clean factory environment. Any contamination will prevent a good bond and if untreated absorption of atmospheric moisture will degrade the bond. DSTO invented the grit blast silane surface treatment, a key step in the bonding process. When performed in accordance with the procedure it allows the ADF to reliably produce durable bonds that do not degrade in the aircraft environments.
Australian-owned private company, Helitech Industries Pty Ltd, was licensed to market and develop DSTO composite bonded repair technology. Helitech has been highly successful in marketing the technology world wide.
Case Study: Acoustic Fatigue cracking in the F/A-18
Several years ago acoustic fatigue cracking was occurring increasingly in aluminium skin panels on the aft fuselage of the F/A-18.
The cracking was caused by aerodynamic effects and to a high intensity excitation from the engine.
DSTO developed a composite bonded repair with the objective of damping out the acoustically induced vibration as well as reinforcing already cracked skin panels.
The composite patch repairs were modelled extensively using new analytical tools developed by DSTO staff to allow the full potential of constrained layer damping to be achieved.
The repairs were also tested on specimens in the laboratory and showed excellent damping of the vibration.
In the final phase of this task, a repair was installed on the aft fuselage of ARDU aircraft F/A-18 A21-32, and was test flown in normal service from November 2002 to April 2003.
A Dosimeter on loan from the USAF was used to assess the vibration, and found the highly damped repair to be very effective.
During the summer the repair was subjected to temperatures up to 50-80oC in flight and speeds up to supersonic.
After 5 months, involving 50 hours flying, the repair was removed and an examination of the bond showed no disbonds or failure of the damping material.